Download epithelial tissue

EPITHELIAL TISSUE
EPITHELIAL TISSUE
Objectives:
To grasp the structure of simple squamous
epithelium, simple cuboidal epithelium, simple
columnar epithelium, stratified squamous epithelium.
To understand the structure of transitional
epithelium.
Slide 58 Simple Squamous Epithelium ( Mesothelium ) AgNO3
This is a surface view of a frog’s mesentery. Choose thinner
place to observe, the cell limits are stained black with AgNO 3.
The individual cell has hexagonal or irregular wavy outlines, and
each contains a nucleus which is not shown in this slide.
Slide 32 Simple Squamous Epithelium ( Mesothelium )
H.E.
This is the cross section of colon. In the outmost layer,
mesothelium which likes a line is present. The mesothelial cells
are fusiform with deep-stained ovoid nuclei in centre. The
outlines of the cells are not clear.
Slide 42 Simple Cuboidal Epithelium ( Thyroid )
H.E.
In this section, there are many follicles in various sizes,
which are composed of simple cuboidal epithelium. In the lumen
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EPITHELIAL TISSUE
of the follicle contains red colored homogenous colloid. The
epithelial cells appear as a row of square profiles with round
nuclei in centre.
Slide 29 Simple Columnar Epithelium ( duodenum )
H.E.
This is a section of the duodenum. There are many intestinal
villi which are finger-like projections of mucosa.
The surface of villi are covered by the simple columnar
epithelium. The epithelial cells are mainly composed of columnar
cells which are the tall rectangle cells with elongated nuclei
occupying the base of these cells. Among the columnar cells
you can find some Goblet cells with a deep-stained and
triangle-shaped nucleus.
Slide 5 Pseudostratified Ciliated Columnar Epithelium
（Trachea）
H.E.
This is a ring of transversally sectioned treachea with large
central lumen. The thin bluish-purple colored layer lining the
luminal surface is pseudostratified ciliated columnar epithelium.
This epithelium appears as multilayered because of the
presence of nuclei at two levels. However all cells rest on a pink
basement membrane which is located between epithelium and
connective tissue, but some of them do not extend to the luminal
surface.The epithelium consists of 4 type cells:
Columnar cells are tall with ovoid nuclei at high level. Their
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EPITHELIAL TISSUE
free surface possesses regular cilia.
Basal cells are smallest and arranged in basal portion of this
epithelium. They are pyramidal in shape，but their apices do not
reach the free surface of the epithelium, their nuclei are round and
situate in the basal portion of the cells.
Fusiform cells are spindle in shape with oval nuclei at the
mid portion of the cells.
Goblet cells can be seen among the columnar cells. Their
apical portion enlarges like a pale round vacuole due to
dissolution of secretory granules during section preparation. Their
narrow basal portion contains deep blue-stained nucleus which is
compressed by apical secretion and become triangular in form.
Slide 4 Stratified Squamous Epithelium ( Esophagus )
H.E.
On the lumen side of the esophagus, you will be able to find
nonkeratinized stratified squamous epithelium.
The epithelium sheet is thick, which consists of many layers
of epithelial cells of different sizes and shapes but these epithelial
cells change their shape gradually from the basal layer to the
superficial layer. At the basal surface, connective tissue projects
toward the epithelium, forms many pyramidal papillae. A layer of
dark stained cells surrounding the papillae is the basal layer of
epithelium.
Basal layer contains one layers of small, cuboid or low
columnar epithelial cells which rest on the basement membrane.
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EPITHELIAL TISSUE
Mid layer is composed of several layers of large polyhedral
cells with clear boundary and ovoid nuclei.
Superficial layer is made of several layers of flat cells. The
cells closely overlap each other. Both the cells and their nuclei are
very flat.
Slide 66 Transitional Epithelium ( Bladder )
H.E.
This is a section of a contracted bladder. This special
stratified epithelium typifies the lining of urinary tract. Unlike the
previous stratified epithelia, however, the surface layer of cells
characteristically project into the lumen, giving them the name
“dome cells”. Cell outlines are less distinct in this epithelium, and
the cells are variably flattened, depending on the state
ofdistension. It is a layer of large, dome-shape cuboidal or
rectangular cells with deep-acidophilic cytoplasm. Occasionally
contains two nuclei.
The intermediate layer is composed of one to several layers
of irregular polyhedral cells and pear-shaped cells located above
the polyhedral cells.Pear-shaped cells are inverted-pear in shape
with its broad base upward toward the domes. The deepest layer
of cells consists of one layer of cuboid cells.
The full and distended bladder shows less layers of cells, and
the cells are more flattened.
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CONNECTIVE TISSUE PROPER
CONNECTIVE
TISSUE
PROPER
Objectives:
To grasp the spread and section of loose
connective tissue (fundus of stomach).
To understand reticular connective tissue (lymph
node), dense connective tissue and adipose tissue.
Slide 6 Loose Connective ( Areolar ) Tissue
Mesenterium in Spread Preparation.
Orcein or Aldehyde Fuchsin Stain.
This preparation was made by ripping off a small portion of
the mesentery spread with previous injection of trypan blue and
spreading it out gently on a slide before fixation.
Choose a thin and distinct area of the tissue for observation.
Two types of fibers can be distinguished:
Collagen fibers: --wavy stranded bundles of fiber of varied
thickness run in all directions. They are reddish in color. These
bundles of fiber branch by subdivision of the strands (i.e. by
separation of small collagen fibers from one another).
Elastic fibers: --stain in purple or dark red. These normally
appear straight but where breakage has occured may appear wavy
due to elastic recoil. Note unlike collagen fibers, it forms single
structures which branch directly at acute angles.
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CONNECTIVE TISSUE PROPER
Among these fibers at least two types of cells, macrophages
and mast cells can be seen:
Macrophages are irregularly shaped cells with small rounded
nuclei and engulf a lot of foreign particular matter such as trypan
blue granules in the cytoplasm.
Mast cells often lie along the course of the blood vessels,
and run in groups. They are round or ovoid with small rounded
nuclei, their cytoplasm contains a large amount of blue colour
granules.
Slide 3 Loose Connective Tissue ( Stomach )
H.E.
The portion of gastric fundus stained lightly is loose
connective tissue. It occupies the bluish-purple gastric mucosa
above and red muscular layer below.
Find and locate the loose connective tissue area in which
fibers are loosely arranged and variously sectioned, the
collagenous fibers are numerous, pinkish, while elastic fibers are
scant and in brilliant red but hardly distinguished. Among fibers,
many cells containing bluish-purple ovoid or fusiform nuclei are
fibroblasts. Ground substance is lost during preparation and only
empty spaces left between fibers and cells.
Within the loose connective tissue, many vessels can be
seen.
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CONNECTIVE TISSUE PROPER
Slide 8 Dense Connective Tissue ( Lymph node )
H.E.
Lymph node is surrounded by a capsule of dense connective
tissue.The pink-staining collagen fibers are in tightly packed
bundles parallel to the longitudinal axis of the node and the cells
between them are flattened to a fusiform with little cytoplasm.
Slide 19 Adipose Tissue ( Skin )
H.E.
This is the section of skin. Skin is composed of two parts, the
outer epidermis and inner dermis. Beneath the dermis is the
hypodermis, containing many fat cells. Fat cells are arranged in
groups and appear vacuolated cytoplasm due to the drops of lipid
being dissolved during section preparation. The nuclei are small
flattened in periphery.
Slide 7 Reticular Tissue ( Lymph node )
AgNO3
This is the section of lymph node. The reticular fibers are
stained black with AgNO3 ,showing short branches and network.
The reticular cells are lightly yellow with some processes.
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CARTILAGE
CARTILAGE
Objective:
To grasp the morphological feature of hyaline
cartilage (Trachea).
To understand the morphological feature of
elastic cartilage and fibrocartilage.
Slide 5 Hyaline Cartilage ( Trachea )
H.E.
This slide is a cross-section through the trache. Locate the
tracheal lumen and look at the blue-stained hyaline cartilage deep
to the epithelium.
The cartilage is covered by a layer of dense connective tissue
named perichondrium. The inner layer of the perichondrium is
rich in cells which can differentiate directly into chondroblasts,
while the outer layer of the perichondrium is rich in fibers.
The hyaline cartilage consists of a rather dense amorphous
ground matrix in which are embedded groups of prominent
rounded cartilage cells (chondrocytes). The cells are surrounded
by a cartilagious capsule. At the periphery of hyaline cartilage,
the chondrocytes have elliptic shape, with their long axis parallel
to the surface. They are round and may appear in groups . The
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CARTILAGE
matrix immediately around each group is rich in chondroitin
sulfate and may be stained more deeply than the remainder, in
living tissue, the chondrocytes fill the lacunae completely, the
cavities (lacunae) sometime appear empty since the cytoplasm of
chondrocyte tends to collapse after fixation. Note that the
cartilage is devoid of blood vessels.
Slide 9 Elastic Cartilage ( External Ear )
Orcein
The ear pinna is covered by skin , elastic cartilage located in
the center of the pinna. The cells are quite similar to those of
hyaline cartilage. Note the dense network of blue staining elastic
fibers which fill the matrix between lacunae containing the
chondrocytes. The fibers are thick and rich in number in the
center of cartilage, while the fibers settled peripherally are fine,
sparse and continuous with those of perichondrium.
Slide 10 Fibrocartilage ( Intervertebral Disc )
Mallory
Collagen fibers are the major constituent of this matrix. They
reveal as thick and compact collegenous bundles with blue colour,
paralleling or interweaving with one another. The red-stained
chondrocytes are ovoid in shape, small in size and arranged in
column. Small amount of matrix can be seen between the
collagenous bundles.
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BONE
BONE
Objective:
To grasp the structure of Haversian system.
Slide 11 Compact Bone ( Ground Bone )
Dialia Violet
Calcified bone is too hard to be sectioned on a microtome.
This section was prepared by cutting thin slices in transverse
section with a saw and grinding these down to the required
thickness with abrasives. The preparation is stained and the
organic material is not preserved . Such sections show the layered
calcified intercellular matrix but not the cellular structure or
other organic material.
Harversian system: You should be able to see the outlines of
irregular Harversian Systems. They consist of:
1) A centrally located Harversian canal in which vessels,
lymphatics, nerves and connective tissue are located at living
period, the empty space, which are filled with debris and dye stain
appear purple.
2) A series of concentrically arranged lamellae are the
Harversian lamellae. The bone lamellae are arranged in
concentric layers around a central Harversian canal. The lamellae
represent an alternation of dark and bright lamellae because the
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BONE
fibers in different lamellae are different in orientation. The bone
lamellae fluctuate from several layers to more than 10 layers.
Interstitial lamellae: They are irregular lamellae which
occupy the intervals between the Harversian system.
Circumferential lamellae: At the external surface of the bone,
there are the outer circumferential lamellae. These consist of
several lamellae that run about the circumference of the shaft of
bone. A similar but less well developed system of lamellae is
present on the inner surface of the bone, the inner circumferential
lamellae.
There are a lot of black ovoid lacunae between the lamellae
where the osteocytes are placed. Many delicate channels
radiated from the lacunae are canaliculi where the cytoplasmic
processes of the osteocytes project into. The canaliculi in the
adjacent lamellae are connecting with each other.
Slide 60 Compact Bone ( Ground Bone )
Dialia Violet
This section was prepared by cutting thin slices in
longitudinal section with a saw and grinding these down to the
required thickness with abrasives.
Slide 12 Decalcified Bone ( Compact Bone )
H.E.
In order to obtain sections thin enough for studying the
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BONE
organic constituents of bone, the tissue has to be “decalcified” by
seaking it for a long period in a dilute acid solution which dissolve
the bone salts. A bone treated in this manner retains its riginal
appearance and microscopic structure but is soft, flexible and can
be easily cut with a microtome knife after embedding in wax.
This is a transverse section of bone. The bone tissue
appears red, because the matrix of the decalcified bone has high
content of collagen. Within the Harversian cannel, the vessels
connective tissue and nucleus of the osteocytes within the lacunae
can be seen.
Slide 59 Decalcified Bone ( Compact Bone )
This is a longitudinal section of decalcified bone.
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H.E.
DEVELOPMENT AND GROWTH OF BONE
DEVELOPMENT AND GROWTH OF BONE
Objective:
To understand the development of bone.
Slide 54 Endochondrial Ossification ( Finger )
H.E.
There are 2 or 3 phalangs inside the finger, the 2 blue large
ends of the phalange are epiphysis and the pinkish intermediate
portion is diaphysis of long bone.
Select a typical phalange and study from epiphysis to
diaphysis. Recognize the 4 zones starting from the articulate
cartilage.
Resting zone: It consists of hyaline cartilage, the
chondrocytes are small without morphologic difference from the
ordinary hyaline cartilage.
Proliferative zone: Chondrocytes divide rapidly and form
paralleled raws of flattened cells along the long axis of bone.
Toward the diaphysis the chondrocytes become hypertrophy.
Calcified cartilage zone: It contains large chondrocytes,
some of them are vacuolated and the diminished matrix is
calcified that is stained in deep-blue.
Ossification zone: The chondrocytes undergo degeneration
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DEVELOPMENT AND GROWTH OF BONE
and the thin partitions of matrix between the lacunae with a raw
are dissolution.The blood capillaries and undifferentiated cells
origination from the periosteum invade the cavity left by the
chondrocytes. These gaps are primitive marrow cavity. Farther
towards the center of diaphysis the residual calcified cartilage
matrix is stained in pink or substituted by osseous matrix
completely. These are newly-formed osseous trabeculae.
The marrow cavity: The trabeculae are resorbed that the
primary marrow cavities are joined with each other forming a
large cavity which lies in the central of the diaphysis with red
marrow and blood sinuses in it.
The sequential processes of endochondrial ossification may
be summarized as: cartilage model formation → cartilage
proliferation → cartilage regression → cartilage destruction
→bone formation.
Observe the ossification zone in detail. There are osteocytes
embedded in the trabeculae. Pay special attention to the
morphological features of the osteoblasts and osteoclasts.
Osteoblasts: These cells frequently lie in single row on the
surface of new bone. They are cuboidal or irregular in shape with
basophilic bluish-purple stained cytoplasm and large round
eccentrically placed nuclei. The osteoblasts secret osseous matrix.
As soon as they are embedded in the matrix, they are no longer
osteoblasts but osteocyts.
Osteoclasts: They are large, irregular, multinucleated cells
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DEVELOPMENT AND GROWTH OF BONE
which usually present an acidophilic cytoplasm lying within the
depressions in the bone where the bone is being resorbed.
Slide 55 Intramembranous Ossification
( Skull of Embryo )
H.E.
This is a section through the center of ossification in the
skull. Move the slide and locate the parietal area, you will be able
to see bone deposition within mesenchyme as a result of the
transformation of mesenchymal cells into osteoblasts. Some of the
osteoblasts have already been entrapped in the bone as osteocytes,
the others still left on the surface of bone trabecula. Sometimes
osteoblasts can be seen.
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BLOOD
BLOOD
Objective:
To grasp the functions and morphological
feature of erythrocytes, neutrophils, eosinophils,
lymphocytes, monocytes.
To understand the function and morphology
of basophils, platelets.
Preparation and Staining of Blood Smear
(1) Method of Obtaining blood
Blood may be obtained from the free margin in lobe of an ear
or finger top. Because they are less sensitive to be punctured.
(2) Preparation of the Blood Smear
Take a small drop of blood on a chemically clean and
dust-free slide about 2 cm from the end, taking care that the slide
does not touch the skin. Place the slide on a table or flat surface.
With the thumb and forefinger of the right hand hold the end of a
second slide against the surface of the first at an angle of 30 to 40
degrees.
The drop will immediately run across the end, filling the
angle between the two slides. If the drop of blood was of appropriate
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BLOOD
size, the thin portion of the film is about 3 cm. The film should be
allowed to dry in the air.
(3) Blood Stains
Wright’s stains are compounds of eosin Y with methylene
blue altered by the action of alkalies so as to contain a variable
amount of azure B, azure A, and methylene violet.
Method
1. Lay thin smear face up on a horizontal staining rack.
2. Cover smear with Wright’s staining solution (about 15
drops).
3. Let sit for 1 minute and then add twice the volumn of
distilled water. You should see a metallic sheen on the
solution before proceeding with step 4. Allow the water and
dye mixture to remain on the slide at least 2 minutes.
4. Drain off and rinse with water until the thinner portions of
the blood film are pink.
5. Blot dry, and mount in synthetic mounting medium.
Slide 24 Blood Smear
Wright’s Stain
Select an area in which the cells are evenly distributed. The
fields you view consist of a preponderance of erythrocytes
interspersed with blood platelets and nucleated leucocytes.
Remember that there are 500 or more red blood cells to one white
cells. You may need to look around the slide for some while before
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BLOOD
typical and unmistakable example of the various white cells are
found.
The higher power objective will usually be necessary: Set
your microscope up to give maximum brightness without glare.
Wrong condenser setting will give false impressions of the colour
of intracellular granules.
Erythrocytes -- red blood corpuscles. They are most
numerous, they are anuclear, biconcave disk. Owing to their
richness in hemoglobin, a basic protein, erythr ocyte are
red-staining.
Leucocytes -- white blood corpuscles. These appear
scattered randomly in a blood film, identifiable by their basophilic
nuclei. In normal blood there are 5 types of leucocytes of two
categories:
Neutrophils: They are the most numerous of white blood
cells. These comprise 60-70% of the white blood cells. Their
cytoplasm is slightly acidophilic with fine, pale pink neutrophilic
granules. The nucleus is divided into 2-5 lobes (usually 3 lobes)
linked to each other by chromatin strands.
Eosinophils: They are characterized by an abundance of
coarse, uniform size red granules (acidophilic granules). The
nucleus often consists of two lobes connected by a strand of
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BLOOD
chromatin.
Basophils: They constitute about 0.5-1% of the total number
of leukocytes and are, therefore, difficult to find. The cytoplasm
contains numerous basophilic deep-blue granules which are
different in size. The pale-stained nucleus is irregular in shape
and always obscured by overlying granules.
Lymphocytes: Their number in normal adults varies from
20-30% of the total white blood cell count. The small lymphocyte
is the most commonly seen in blood smears, but medium-sized
lymphcytes and lymphocyte as large as 18 um in diameter are
occasionally present. The small lymphocyte has a round, often
with a slight indentation, deep-purple nucleus which is enclosed
by thin rim of sky-blue-stained cytoplasm. The large lymphocyte
has more cytoplasm which may contain a few coarse azurophilic
granules.
Monocytes: They are the largest leukocytes, the nucleus is
irregular, kidney or horse-shoe in shape, the chromatin apppears
in a looser arrangement than in the lymphocytes.
Platelets -- They are irregular fragments of cytoplasm with
fine purple granules, they appear in small clusters among the
blood cells.
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HEMATOPOIESIS
HEMATOPOIESIS
Objective:
To understand the morphology and structures
of developing blood cells in red bone marrow.
Slide 53
Bone Marrow Smear
Wright’s Stain
Before you begin this exercise, review the morphology and
nomenolature of the developing blood cells of both myeloid and
erythoid series.
Select an area in which the cells are evenly distributed.
Many cells are damaged in preparing the smears and will cause
some confusion. If in doubt, ask the instructor to verify that you
are studying a good example of the cell in question.
1. Myeloid Series:
Myeloblast: The most undifferentiated cell which can be
recognized is a large cell with basophilic cytoplasm, no granules
and a large round nucleus with lacy chromatin and prominent
nucleoli which appear as lightly staining spheres within the
nucleus.
Promyelocyte: Azurophilic granules begin to appear in the
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HEMATOPOIESIS
cytoplasm. The cytoplasm is less basophillic and the nucleus is
still round or oval. Mucleoli may still be seen in the nucleus.
Neutrophilic myelocyte: The cell contains both azurophilie
granules and neutrophilic granules. Neutrophilic granules are very
small, yellow to pink in color, and are not easily resolve in the
light microscope, but clusters of these granules give the
cytoplasm a pink to yellow cast. The nucleus of noutrophilic
myelocyte is typically ovoid or slightly indented and the
chromatin is more condensed.
Neutrophilic
metamyelocyte:
The
nuclear
indentation
becomes prominent and the nucleus becomes orectic.
Mature or polymorphonuclear neutrophils
2. Erythrioid series:
Erythroid cells are less abundant than myeloid elements,
since the ratio of myeloid to erythroid cells (M:E ratio) for normal
marrow is about 3:1 . Cells of the erythroid series never possess
cytoplasmic granules.
Erythroblasts with obviously basophilic (blue stained)
cytoplasm and increasingly smaller cells with purplish stained
cytoplasm and increasingly small and densely stained nuclei. The
changes in the cytoplasm are caused by the increasimg amount of
haemoglobin present which produces a gradual change of
sraining from blue ( basophilic erythroblast ) to purple or gray
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HEMATOPOIESIS AND MUSCLE TISSUE
(polychromatophilic erythroblast) and finally to pink (late
erythroblalst). The nucleus become dense and pyknotic and is
eventually ejected from the cell when the mature red cell is
formed.
The late erythroblalst is allso sometime termed “normoblast”
in order to distinguish it from the abnormally large erythroblast
“ megaloblast ” which is present in the marrow of patient
suffering from vitaminB12 deficiency (pernicious anaemia).
3. Notice the large megakaryocytes with multilobular nuclei.
Slide 61 Bone Marrow Section ( Rib )
H.E.
In this slide identify the large megakaryocytes with
multilobular nuclei. Notice the presence of many fat cells.
22
MUSCLE TISSUE
MUSCLE
TISSUE
Objectives:
To grasp the morphological features of skeletal
muscle , understand the morphological features of
cardiac muscle, smooth muscle.
Slide 14 Skeletal Muscle ( Longitudinal Section )
H.E.
The skeletal muscle is composed of long cylindrical
multinucleate cells — the muscle fibres. Each fibre has an
extensible sheath — the sarcolemma. A number of oval nuclei are
usually immediately under the sarcolemma.
The pink sarcoplasm contains large number of
myofibrils.Locate an area that shows the bandings, and identify
the dark A bands interspersed with pale I bands. Identify the
delicate, dark Z-line which transverses the I band. The portion of
a myofibril between two Z-lines is called a sacomere. In relaxed
muscle fibres you may be able to detect a somewhat paler H zone
in the center of each A band.
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MUSCLE TISSUE
Slide 14 Skeletal Muscle ( Cross Section )
H.E.
The muscle fibres may be angular in cross section. The nuclei
are located at the periphery of the muscle fibres. With high power
objective, it may be seen each fibre subdivided everywhere into
small angular fields—Cohnheim’s area, which are themselves
finely dotted. The dots represent sections of the myofibrils of
which the fibres are composed.
Between the fibres is a certain amount of connective tissue,
which serves to support the blood-vessels and to unite the fibres
into fascicule;known as the endomysium. A group of muscle
fibres are surrounded by small amount of connective tissue
perimysium. A number of bundles are aggregated into a muscle
and united with connective tissue epimysium.
Slide 13 Skeletal Muscle
Iron hematoxylin
High magnification of muscle fibers demonstrates the
cross-striations. The A bands are prominent, dark-staining bands;
a lighter middle region, the H bands, is not visible. The I bands
are equally prominent and are lightly stained bands. Crossing
each central portion of the I bands are distinct, narrow lines, the
Z lines.
Slide 23
Cardiac Muscle
( Heart )
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H.E.
MUSCLE TISSUE
In longitudinal section, the cardiac muscle fibres differ from
those of skeletal fibres in the following particularis.
(1) The fibres are clearly branched, and united by their
branches.
(2) Their nuclei often lie near center of the fibres and oval in
shape.
(3) The cross striations (with A band, I band, M line and Z
line) are identical to those of skeletal muscle, but their
striations are less marked.
(4) The fibres are interrupted by thin transverse lines—the
intercalated discs which look like lightly dark-stained short
lines.
Between the fibres is a certain amount of connective tissue
which serves to support the large amount of capillaries.
In cross section, the cardiac muscle fibres are round in shape
with numerous finely dotted in cytoplasm. The dots represent
sections of the myofibrils of which the fibres are composed,
sometimes they are disposed radially. Large, ovoid nuclei, usually
one per cell, occupy the central position.
Slide 3 Smooth Muscle (Stomach)
H.E.
The smooth muscle is mainly visceral in distribution . In the
stomach, the muscularis is formed by several layers of smooth
muscle fiber. Smooth muscle cells are stained deeper than the
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MUSCLE TISSUE
connective tissue, arranged in layers of different direction and so
cut in both longitudinal and cross sections.
In longitudinal section, the muscle cells are elongated
fusiform-shaped. The nucleus is rod-shaped, centrally located
with fine chromatin, commonly one or two nucleoli. The nucleus
is shortened or thrown into folds when the muscle cell contracts.
The cytoplasm of muscle cells is called sarcoplasm. Although
myofibrils are present in the cytoplasm they cannot be seen at the
light microscope level. Between smooth muscle fibres are
capillaries and fibroblasts. Compare the differences between the
nuclei of fibroblasts and smooth muscle cells.
Examine the outer longitudinal layer of muscularis external in
the same slide, where the muscle is cut transversely. In
cross-section, the smooth fibers are usually round or angular.
Since smooth muscle cells are elongated cross sections cut
through them seldom pass through their nuclei. The nuclei are
found in largest profiles, which represent sections through the
central portions of the fibers.
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NERVE TISSUE
NERVE TISSUE
Objectives:
To grasp the morphological features of neuron;
To grasp the morphological features of nerve
fiber;
To understand the neuroglial cell;
To understand the morphological features of
nerve ending (tactile corpuscle, lamellar corpuscle,
end plate).
Neuron
Slide 15 Motor Neuron ( Spinal Cord )
H.E.
The large cells, scattered through the H-shaped gray matter
are nerve cells.
Examine the motor nerve cells in the ventral horn (ventral
horn are short and thick).The cell is polyhedral or irregular
in shape with some short processes. The cytoplasm is filled
with finely granular or clumps of basophilic material called
Nissl’s bodies. The nucleus is typically large spherical and centrally
located with finely dispersed chromatin(vesicular nucleus). The
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NERVE TISSUE
nucleolus is prominent, large, dense, and stains dark. Sometime
you can find the axon hillock, which contains no Nissl material,
marks the site of origin of the axon. On the other hand, the
neuroglial nuclei are only stained prominently, whereas their
cytoplasm remains unstained.
Slide 16 Motor Neuron ( Spinal Cord )
Nissl stain
The section is similar to the slide 15 in shape, but stain
method is not the same. Examine the motor nerve cells in the
ventral horn (ventral horn are short and thick).The cell is
polyhedral or irregular in shape with some short processes. The
cytoplasm is filled with Nissl’s bodies which are stained as blue
colour. The nucleus is large spherical and centrally located with a
large, prominent nucleolus.
Nerve Fibers
Slide 17 Myelinated Fibers ( Sciatic Nerve )
H.E.
Cerebropspinal nerves are composed chiefly of myelinate
fibres. The slender strip is longitudinal section of sciatic nerve
and the small round one is a cross section.
First you examine the longitudinal section.The nerve fibres
are gathered up into round bundles and these are again united to
form the nerves.
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NERVE TISSUE
A nerve fibre is made up of a central axis cylinder (a process
of a neuron), a sheath of myelin, a neurolemma or Schwann
sheath and a delicate connective tissue sheath—the
endoneurium. The nerve fibre is interrupted at regular intervals,
at these places the neurolemma appears to produce constrictions
which are called nodes of Ranvier.
A reticular appearance has been noticed in the myelin sheath
after fixation with alcohol, the neurokeratin network, but it varies
greatly in aspect and is certainly produced by the action of the
reagents employed to show it.
Schwann cells constitute the sheath of Schwann or
neurolemma sheath. The pale oval nuclei of the Schwann cells
can sometimes be seen.
In the cross section of sciatic nerve, we can see the nerve
fibres are gathered up into round bundles. The connective tissue
connected the bundles and invested the whole nerve is called
epineurium. That which sheathes the bundles is known as the
perineurium. The delicate connective tissue which lies between
the nerve fibres of the bundle is termed endoneurium.
Slide 18 Myelinated Fibers ( Sciatic Nerve )
Osmic Acid Stain
Examine this slide. Osmic Acid stains the lipid in the myelin
sheath black. So the myelin sheath appears as a thick, black band
surrounding a lighter, central axon. Node of Ranvier can be seen
where the myelin sheath exhibits discontinuity.
29
NERVE TISSUE
Slide 73 Unmyelinated Fibers ( Sympathetic Nerve )
H.E.
The non-myelinated fibers devoid of the distinct double
contour which is characteristic of the absence of a myelin sheath.
They are beset with numerous nuclei which have ususally been
regarded as belonging to a delicate sheath, although it must be
admitted that the nuclei often appear to lie in the substance of the
fibres rather than at their surface.
Neuroglia
Slide 15 Neuroglia ( Spinal Cord )
H.E.
With H.E. stain, neuroglia only the nuclei and a little of the
adjacent cytoplasm can be seen.
Astrocytes: Their nuclei are large, round and lightly stained.
Microglia cells: Their nuclei are small oval, rod-like or irregular
in shape and deeply stained.
Oligodendroglia cells: Their nuclei size are intermediate
between the astrocytes and microglia cells, they are round shape.
Ependymal Cells: They line the central canal of the spinal
cord. They are a layer of simple columnar ciliated epithelium cells.
Nerve Endings
Slide 19 Tactile Corpuscles ( Skin of Finger Tip )
H.E.
Tactile corpuscles (Messner’s Corpuscles) occur in some of
30
NERVE TISSUE
the dermal papillae of the skin. Tactile corpuscles are ovoid in
shape. The flattened cells of capsule are arranged in the form of
multiple-stacked lamellae. Unmyelinated nerve terminals enter
the corpuscle, where they branch and follow a spiral course
among the connective tissue.
Slide 19 Lamellar Corpuscles ( Skin of Finger Tip )
H.E.
Lamellar corpuscles ( Pacinian Corpuscles) are large and
have a more complex structure. They are located deep in the
dermis and subcutaneous tissue. They are composed of a number
of concentric lamellae resemble a sliced onion in the section.
Between the lamellae is a small amount of loose connective tissue
with flat fibroblasts. A thin, dense connective tissue encloses the
lamellar corpuscles.
Slide 20 Motor End Plate ( Intercostal Muscle )
AuCl
This slide is a small piece of gold impregnated muscle press
slide. Muscle fibres are purple in colour, myelinated fibres are
stained as black colour. A myelinated fibre will branch two or
three times before ending, and then each branch passes directly
about the middle of a muscle fibre.The axis-cylinder ends in a
close terminal ramification with various expansions upon its
branches.
31
NERVOUS SYSTEM
NERVOUS
SYSTEM
Objectives:
To grasp the structures of the cerebral cortex;
To grasp the structures of the cerebellar cortex.
Cerebrum
Slide 56 Cerebrum
H.E.
This is a part of cerebrum. Overlying and covering the
surface of cerebrum is the delicate connective tissue of brain, the
pia mater containing many small vesseles. Beneath the pia mater
cerebral cortex is present. Although there are variations in
arrangement of cells in different parts of the cerebral cortex, six
distinct layers are recognized from outside to inside.
Molecular layer is located in the outermost layer. Blood
vesseles are found.
External granular layer is rich in granule cells.
External layer of pyramidal cells is thicker than the external
granular layer. It is composed of the medium-sized pyramidal
cells.
Internal granular layer contains numerous stellate cells.
32
NERVOUS SYSTEM
Internal layer of pyramidal cells is mainly composed of
larger pyramidal cells.
Multiform layer is near to the white matter of brain. There
are fusiform cells, granule cells, stellate cells. All of these cells
vary in size.
Slide 71 Pyramidal Cell ( Cerebral Cortex )
Golgi’s Method
This is a thick celloidin section of Golgi Silver preparation
of dog brain. This method shows the complete contour of nerve
cells in the cortex.
The bodies of pyramidal cells are triangular in shape and
various in size. The typical large vesicular nucleous with its
prominent nucleolus is outlined. The most prominent cell process
is the apical dendrite, which is directed toward the surface of the
cortex. Several dendritic collaterals are given off along its course
through the cortex. Smaller dendrites arise from other parts of the
cell body. The axon arises from the base of the cell body and
passes into the white matter.
The intercellular area is occupied by nerve fibers of various
cells in the cortex, small astrocytes, and blood vessels.
Each pyramidal cell has several basal and one large
apical dendron. Each cell has a single slender axon, which is
usually directed towards the medullary center.
33
NERVOUS SYSTEM
Cerebellum
Slide 57 Cerebellum
H.E.
The section of cerebellum appears leave-like in shape. The
out cortex of cerebellum is gray matter, the inner is the white
matter which consists of myelinated nerve fibers or axons.The
grey matter can be distinguished into three cell layers from
outside to inside.
Molecular layer is thicker than other layers, near to the
superficial layer of the grey matter with few cells.
Purkinje cell layer is a thin layer with Purkinje cells, which
are large and pyriform in shape with ramified dendrites that
extend into the molecular layer.
Granular layer contains numerous small cells with intensely
stained nuclei.
Slide 72 Purkinje’s Cells (Cerebellum Cortex ) Golgi’s Method
The slide is also a thick celloidin section. In the cortex
Purkinje’s cell is a large flask-shaped cell. Each of these cells
gives off from its base a fine process, the axon, while from the
opposite pole of the cell large remified processes ( dendrites )
extend into the superficial layer of the grey matter.The dendrites
spread out in planes transverse to the direction of the lamellae.
34
NERVOUS SYSTEM
Ganglion
Slide 1 Spinal Ganglion
H.E.
Examine the slide of spinal ganglion with a capsule. The
neurons are pseudounipolar, the processes are unsectioned. The
cell body can be spherical, ovoid, or angular, they are very large
and arranged in groups separated by bundles of nerve fibers.
With the 40x objective, the nucleus is large spherical and
centrally located, with finely dispersed chromatin (vesicular
nucleus). The nucleolus is large and well developed. These
neurons usually show fine Nissl’s bodies and droplets with
fuchsin. Each nerve cell is surrounded by a layer of flat satellite
cells.Their nucleus is darker.
Slide 73 Sympathetic Ganglion
H.E.
Similar to the spinal ganglion cells. In contrast to spinal
ganglion cells, the cells are multipolar neurons and are smaller
and more uniform in size. As a result, the outlines and their
processes of the sympathetic ganglion cells appear often irregular
in the sections. Their nuclei are often eccentric and binucleated
cells are not uncommon. Most of these cells contain lipofuscin
pigment in their cytoplasm.
Satellite cells are usually less numerous than around the cells
in spinal ganglion. The capsule may not be well defined, more
unmyelinated nerve fibers are pressent in the intercellular area.
35
CIRCULATORY SYSTEM
CIRCULATORY
SYSTEM
Objectives:
To grasp the morphological features of three
type capilaries;
To grasp the morphological features of
medium-sized artery, large artery, small artery,
and heart wall;
To understand the morphological features
of medium-sized vein, large vein , small vein.
Slide 21 Medium-Sized Artery
H.E.
This is a section through both femoral artery, vein and
nerves. Locate the femoral artery which has a thick muscular
wall—muscular artery.
An artery is composed of three coats:
Tunica intima is lined by a thin layer of endothelium, the
cells of which are somewhat elongated in the direction of the axis
of the vessel, and form a smooth lining to the tube. Next to the
endothelium of the arteries is a subendothelial layer of
connective tissue, which is not distinct. However, a prominent ,
wavy internal elastic membrane ( elastica interna ) is well
36
CIRCULATORY SYSTEM
developed. The tunica intima appears sealloped because of
postmortem contraction of smooth muscle in the tunica media.
Tunica media is a thick layer, and consists mainly of
circularly arranged smooth muscle fibres. They have long
rod-shaped nuclei. The muscle cells are often very irregular.
Between muscle cells are fine collagenous fibres and elastic
fibres.
Tunica adventitia is conposed of external elastic membrane,
(elastica externa) which is split into several lamellae, and a layer
of loose connective tissue, consisting mainly of collagenous fibres,
and elastic fibres. Nevers are also present.
Slide 21 Medium-Sized Vein
H.E.
It has a relatively thinner wall and a larger lumen than the
accompanying medium-sized artery. The veins resemble the
arteries in general structure, but exhibit certain differences.
In the tunica intima the same layers are present, but the
elastic tissue is less developed, and may be quite inconspicuous; it
seldom take the form of a completed membrane.
The tunica media contains less elastic tissue and also much
less muscular tissue, being partly occupied by connective tissue
fibres.
The tunica adventitia is relatively well developed. It is about
twice as thick as the tunica media.
37
CIRCULATORY SYSTEM
Slide 3 Small Artery and Small Vein ( Stomach )
H.E.
In the stomach wall, there are small blood vessels. The
structure of small artery is similar to that of the larger ones, but
the tunica media is much thicker, and the collagenous fibres of
tunica adventitia merge with the surrounding tissue.
The small vein are frequently accompanied closely with
small artery. The small veins are much thinner-wall vessels. They
have a high proportion of lumen to total diameter. The tunica
consists of flattened endothelium and sparse connective tissue
elements. The veins are usually filled with blood. In fact, they
also can be seen in the adventitia of the muscular artery or vein.
Slide 22 Large Artery ( Aorta )
H.E.
This is an example of elestic artery. Similar to the wall of
other vessels. Three layers can be identified.
Tunica intima is lined by the usual endothelium; outside this
is a considerable thickness of subendothelial connective tissue,
with elastic tissue chiefly composed of fine fibres, it is not
especially marked off by a definite elastie layer from the tunica
media.
Tunica media: There is a great development of elastic tissue
in this tunica, where is forms membranous layers or lamellar
networks which alternate with the muscular layers. A good deal
of connective tissue also takes part in the formation of this layer.
38
CIRCULATORY SYSTEM
This tunia consititutes almost the entire thickness of the wall, the
tunica intima and tunica adventitia being thin.
Tunica adventitia: This layer is composed mainly of
collagenous fibres, and some elastic fibres extending out from the
outermost layer of elastic membrane. Also present in the tunica
adventitia are small blood vessels and small bundles of nerve
fibres.
Slide 23 Capillaries ( Heart )
H.E.
In the connective tissue between the cardiac muscle, there
are numerous capillaries. They are very small, and have an
average diameter of 7 to 9 um. The capillary is made up of one or
two endothelial cells in section. The nuclei of the endothelial cells
are usually bulging into the lumen of the capillary.
Slide 23 Heart
H.E.
The wall of the heart consists of three layers: The middle
myocardium, an outer epicardium and an inner endocardium.
The innermost layer of the heart wall is endocardium. The
outline is much less regular than the outer surface. The inner
surface is lined by a single layer of endothelial cells. Immediately
beneath the endothelial cells is the thin subendothelial layer,
containing mainly fibroblasts and fine collagenous fibres.
External to this is a thick layer of connective tissue, called
39
CIRCULATORY SYSTEM
subendocardial layer. It contains collagenous, elastic fibres and
also some isolated bundles of smooth muscle cells. In addition,
this consists of branches of specialized impulse conducting
cardiac muscle — Purkinje fibre.
The myocardium forms the main thickness of the heart. It is
composed of a network of cardiac muscle fibres. The muscle
fibres are bound by connective tissue which consists of network
of reticular and collagenous fibres. In the connective tissue run
numrous capillaries and various sizes blood vessels.
The myocardium is covered externally by a layer of serous
membrane — the epicardium. It is composed of a single layer of
mesothelial cell and a thin layer of loose connective tissue
containing both elastic and collagenous fibres. Fibroblasts, fat
cells and blood vessels are also present in the epicardium.
Slide 23 Impulse Conducting System ( Sheep Heart )
H.E.
The Purkinje fibres have a widespread distribution in the
endocardium. Their diameter is much larger than fibres in the
myocardium. The myofibrils are sparse, and peripherally
displaced. The sarcplasm stains paler due to the paucity of
myofibrils. The nuclei of the fibres are centrally located, and are
surrounded by an unusually large amount of sarcoplasm.
40
IMMUNE SYSTEM
IMMUNE
SYSTEM
Objectives:
To grasp the morphological features of lymph
nodes, spleen;
To understand the structures of the thymus.
Slide 8 Lymph Node
H.E.
Lymph node is an ovoid or kidney-shaped organ. It is
composed of two main parts: peripheral deeply stained cortex and
central palely stained medulla.
Lymph node is a discrete body surrounded by a capsule of
connective tissue, from which the connective tissue extends into
interior to form trabeculae. At the hilum, the capsule is thickened
and extends deeply into the node, in which many blood vessels
extend and 1-2 efferent lymthatic vessels with wider lumen can be
found. The afferent lymphatic vessels is located in the capsule.
They possess valves which open toward the node while the
efferent lymphatics have valves which open outward from the
node. The fine reticular fibres which form both the capsule and
the trabeculae to constitute the reticular framework of this organ.
41
IMMUNE SYSTEM
In cortex the main structures are:
lymph nodules: They are composed of large number of
densely aggregated lymphocytes. The central portion of the each
nodule is stained pale and is called germinal center, which is
mainly composed of B lymphocytes. A typical nodule with a cap,
a dark and light zone can be seen at times. The peripheral part of
nodule consists of closely aggregated small lymphocytes with
deeply stained round nuclei. It also contains reticular cells and
macrophages, the former contain pale staining nuclei and
boundaries of the cell are unclear, the latter are large in size and
their cytoplasm are stained in red.
Paracortical region is that portion of the diffuse lymphoid
tissue located in the deep region of the cortex and between the
adjacent lymph nodules. In paracortical region T lymphocytes are
located. Post capllary venules are situated in the paracortical
zona near the medulla, lined by a layer of 4-6 cuboidal endothelial
cells.
Lymph sinuses: Nodules are separated from the capsule and
trabeculae by channel like spaces—lymph sinuses, which are
divided into subcapsular and peritrabecular sinuses.
In medulla it consists of medullary cords and medullary
sinus.
Medullary cords are deeply stained strands of densely
aggregated lymphoid tissue which branch and connect each other.
42
IMMUNE SYSTEM
It is also composed of aggregated lymphocytes, reticular cells
and macrophages.
Medullary sinus: The relatively cell-free areas between the
medullary cords are medullary sinuses, bridged by reticular fibre
supporting endothelial cells. Medullary sinus contains several
types of cells of reticular tissue: reticular cells, macrophages
and lymphocytes. Reticular cells are stellate in shape with
several processes, pink cytoplasm, centrally placed pale round or
ovoid nucleus and prominent nucleolus. Marophages are round or
irregular in shape with deeply stained cytoplasm contain engulfed
granular particles or cell debris. Lymphocytes are mostly small
lymphocytes. They are round in shape with scanty cytoplasm and
large round nuclei.
Slide 25 Spleen
H.E.
The spleen consists of three parts— white pulp, red pulp and
marginal zone.
The capsule encloses the surface of spleen and is relatively
thick. It consists of dense connective tissue containing a few
smooth muscle cells in addition to fibrous elements and has
smooth outer surface covered by peritoneal mesothelium. It
extends into parenchyma and forms trabeculae,which froms a three
dimensional supporting network and carries inwards blood
43
IMMUNE SYSTEM
vessels, lymphatics and nerves from the hilus. Between them
reticular fibers form both coarse and fine networks upon which
various cells are supported.
White pulp scatters throughout the spleen and is deeply blue
stained round or ellipsoid bodies. White pulp is composed of
splenic nodules and periarterial lymphatic sheath.
Splenic nodules as lymphatic nodules are a corpuscle of
dense lymphoid tissue containing sometimes a germinal center
and central artery. Unlike the nodules in other situations they
form sheathes around small arteries
Periarterial lymphatic sheat is tube-like structure made of
dense lymphatic tissue cords around the central artery.
Red pulp contains splenic cords and sinusoid.
Splenic cords lie around the sinusoid and are composed of
lymphoid tissue with numerous blood cells.
Sinusoids are the large irregular lumens containing RBC. Its
endothelial cells are larger than that of blood vessels and bulge
into lumen with their round of rod nuclei.
As the arteries which course through the white pulp, they
enter the red pulp and give rise to groups of small branches called
penicili. They may be recognised, at the periphery of some areas
of the white pulp, as small irregular bundles of arterioles in
connective tissue. In the red pulp these again branch to form small
vessels called ellipsoids or sheathed arteries. The ellipsoids are
44
IMMUNE SYSTEM
either directly continuous with the venous sinusoids or may open
into the spaces of the red pulp, from there the blood will return to
vascular system through the walls of the venous sinusoid. The
veins into which the blood drains are found close to or
surrounded by trabecular tissue.
Slide 65 Thymus
H.E.
Thymus is surrounded by a thin connective tissue capsule,
from which trabeculae extend into parenchyma and separate it
into numerous incomplets lobules of various size and shape. The
periphery of each lobule stains deeply and is called cortex, while
the central portion stains pale, called medulla. Since the lobules
are incomplete, the medullae are continuous between adjacent
lobules.
Cortex is mainly composed of large number of closely
aggregated lymphocytes. There are numerous capillaries among
them.
Medulla is essentially the same in structure as that of cortex
but lymphocytes are not so densely aggregated. In the central
region of medulla, there also are a number of red-stained thymic
corpuscles. The thymic corpuscle is small round corpuscles of
various size, each lobule contains one or more in number. It is
composed of flattened epithelial reticular cells arranged
concentrically, these cells become degenerated with shrank nuclei.
45
IMMUNE SYSTEM
The cells of the corpuscle center are completely degenerated
becoming the red homogenous structure.
Slide Palatine Tonsil
H.E.
The deeply stained side of this section is epithelium which
invaginates in some areas to form crypts. The deep blue portion
underlying the epithelium is lymphoid tissue, out of which is the
pink stained capsule.
The epithelium of tonsil is nonkeratinized stratified
squamous epithelium, which may infold in some places to form
crypts. It may be infiltrated with small lymphocytes and if the
infiltration were severe, the epithelium would decrease in layer or
even lose its normal pattern leaving only surviving epithelial cells
or their nuclei.
Lymphatic tissue distributes in the lamina propria beneath
the epithelium and around the crypts. It forms many lymphatic
nodules arranged in rows and surrounded by diffuse lymphatic
tissue. Several isolated masses of epithelium and lymphatic tissue
would appear.
Capsule is made up of loose connective tissue outside the
lymphatic tissue. Sometimes connective tissue extends into the
tonsil to form trabeculae. A few mucous glands may be seen in
exterior of the capsule.
46
DIGESTIVE TRACT
DIGESTIVE
TRACT
Objectives:
To grasp the morphological features of
esophagus, stomach, small intestine(duodeum,
jejunum, ileum, and large intestine).
To understand the structures of the tongue.
Slide 62 Tongue ( Filiform Papillae )
H.E.
The purple-stained parts is epithelium, under which the pink
coloured narrow zone is lamina propria. The deeply red stained
lower thick parts is the zone of skeletal muscle. Filiform
papillae are elongated conical in shape and quite numerous, and
are present over the entire surface of the tongue. The surperficial
cells of the epithelium are frequently partially keratinized with
red staining cytoplasm and wrinkled nucleus. The underling
connective tissue projects toward the epithelium forming primary
papillae which again project deeply to the epithelium forming
secondary papillae.
47
DIGESTIVE TRACT
Slide 62 Tongue ( Fungiform Papillae )
H.E.
They have a mushroom-like outline and are less numerous
than the filiform papillae. The epithelium is thinner and
nonkeratinized. The connective tissue core bears several
secondary papillae. Within the epithelium, taste buds can be
found.
Slide 62 Tongue ( Circumvallate Papillae )
H.E.
This is a transverse section through the posterior 1/3 of the
tongue. Identify the circumvallate papillae in this section. The
circumvallate papillae are larger papillae with expanded and
flattened top, and surrounded by a deep grove. There are many
taste buds stained pale in the epithelium of their lateral wall.
Taste buds: The taste buds are seen as pale, oval bodies
embedded in the darker-stained epithelium. The cells of tast bud
are long spindle-shaped. Two types of cells can be distinguished:
The taste cells are stained deeper and on their free surface are
taste hairs which project into the taste pore. The supporting cells
are stained pale and have a large round or ovoid nucleus.
Slide 4 Esophagus
H.E.
Master the four principal layers of digestive tract and observe
48
DIGESTIVE TRACT
the characteristics of each layer carefully.
The outline of the lumen is irregular in this transverse
section. There are many longitudinal folds projecting into the
lumen.
Mucosa: Immediately surrounding the lumen is a thick,
stratified squamous epithelium. Lamina propria is composed
of loose connective tissue which protrudes to the epithelium and
forms papillae. Muscularis mucosa is a thin layer of longitudinal
smooth muscle.
Submucosa: It is composed of loose connective tissue with
plenty small blood vessels and the esophageal glands.
Muscle layer: Basically, the inner layer muscularis is circular
and the outer longitudianl, but the arrangement of muscle is less
regular. It will contains skeletal muscle if the section is taken
from upper half of the esophague.
Advantitia: It consists of loose connective tissue containing
blood vessels and nerves.
Slide 3 Gastric Fundus ( Stomach )
H.E.
The weavy bluish-purple stained side is mucosa and the
remainder pink portion contains the rest coats.
The surface of mucosa is lined by a simple columnar
mucous secreting cells. At intervals the epithelium dips
downward forming the gastric pits, under the epithelium is the
49
DIGESTIVE TRACT
lamina propria which contains the straight tubular glands (or
gastric glands) open into the base of the gastric pits. The glands
may be present as longitudinal, oblique or cross section, three
types of cells can be identified:
Chief or zymogen cells are located in the middle and lower
portion of glands. They are pyramidal in shape with deeply
stained basophilic cytoplasm and basally located round nuclei. In
some cases, fine secretory granules may be seen in the apical
region of chief cells..
Parietal cells are present mainly in the neck and the body of
the glands. The cells are easily recognized by their triangular
shape and acidophilic cytoplasm. The nucleus is round and
situated in the center of the cell. Double nuclei may be seen in
these cells.
Mucous neck cells are present mainly in the neck region
interspersed with parietal cells. The cells are columnar-shaped.
The apical cytoplasm is full of mucus that makes the cells staining
faintly. The nucleus is oblate in form and is squeezed to the base
of the cell. (Argentaffin cells occur in the deepest parts of the
gland, but are not usually recognized).
Underneath the base of the glands, find the muscularis mucosa,
usually it consists of an inner circular, outer longitudinal muscle
layers.
The submucosa consists of connective tissue, in which larger
50
DIGESTIVE TRACT
blood vessels and lymph vessels are located.
The muscularis is rather thick and consists of three layers:
outer longitudinal middle circulalr, and inner oblique.
The serosa is composed of a thin layer of loose connective
tissue and mesothelial lining.
Slide 27 Esophagus-Stomach Junction
H.E.
A section through the junction of esophagus and the stomach.
Note the epithelial transition at the junction.
Slide 28 Pylorus-Duodenal Junction
H.E.
A section through through the junction of pylorus and
duodenum. Note epithelial transition. In pylorus the gastric pits
are deeper than that fundus. Pyloric glands columnar with striated
border. The goblet cells are interspersed.
Slide 29 Duodenum ( Small Intestine )
H.E.
Identify the four layers of the wall of the small intestine
under low power, then concentrate on the mucosa.
Mucosa: The villi with which the whole of the inner
surface of the small intestine is closely beset are projections of
the mucous membrane and are composed of connective tissue
covered with simple columnar epithelium. Between and at the
51
DIGESTIVE TRACT
base of the epithelial cells many leucocytes occur. Further, oval
spaces at intervals represent the positions of goblet cells with
their content (mucigen), dissolved during preparation. The
remaining cells are absorptive cells. Each villus has a central
connective tissue core, the lamina propria. In the middle of the
villus is a lymphatic vessel, known as the central lacteal.
Surrounding the lacteal are fine bundles of longitudinal smooth
muscle fibres.
Note that the free surface of the absorptive cell is specialized
to form a definite striated border.
The mucous membrane proper is provided with simple
tubular glands—the crypts of Lieberkuhn(intestinal glands)
which are lined throughout by columnar epithelium; with
scattered goblet cells. At the fundus of each crypt are a few cells
containing well-marked oxyphil granules known as the Paneth
cells.
Muscularis mucosa: The mucosa is bounded next to the
submucosa by a double (outer longitudinal and inner circular)
layer of smooth muscle fibres.
Submucosa: It is composed of loose connective tissue
containing blood vessels and a nerve plexus—Meissner’s plexus,
in which some gangilion cells may be found. The glands of
Brunner (Duodenal glands) occur in the duodenum.
Muscularis externa: It is composed of two layers of muscular
52
DIGESTIVE TRACT
tissue, an outer thinner longitudinal and an inner thicker circular.
Between them lies a nerve plexus— the plexus of Auerbach.
Serosa: It is composed of a thin layer of loose connective
tissue with mesothelium.
Slide 30 Jejunum ( Small Intestine )
H.E.
The wall of the jejunum also consists of four layers. The villi
are well developed. The intestinal glands are similar to those of
the duodenum. Goblet cells are interspersed with absorptive cells.
In the lamina propria connective tissue, lymphatic tissues
sometime are aggregated here and there into an isolate nodule.
Slide 31 Ileum ( Small Intestine )
H.E
The wall of the ileum also consists of four layers. Goblet
cells are plentiful. But in the lamina propria connective tissue,
lymphatic tissues are aggregated here and there into nodules. The
nodules constitute, when they occur agglomerated, known as
Peyer’s patches. They occur more often in the antimesenteric
region (away from the mesentery) of the intestine.
Slide 32 Colon ( Large Intestine )
H.E.
The large intestine has usual four coats, except near its termination
53
DIGESTIVE TRACT
where the serosa is absent. But it absence of any villi.
The mucosa of colon is lined by simple columnar
epithelium, but containing more goblet cells, abundant crypts of
Lieberkuhn and a cellular lamina propria. Lymphatic nodules
may be found in the lamina propria. The external border of the
mucosa is marked by a thin muscularis mucosa.
The submucosa is composed of connective tissue, blood
vessels and Meissner’s plexus.
The muscularis externa consists of an inner circular and
outer longitudinar layers. The inner circular layer is thick and
well developed, while the outer longitudinal muscular fibres are
gathered up into three thickened bands—taenia coli. Between
these bundles the muscle coat spreads to form a thin layer.
Slide 33 Appendix (Large Intestine)
H.E.
The lumen of the appendix usually contains masses of dead
cell debris. Absence of any cilli. The glands are fewer. The lining
cells are simple columnar, containing only few goblet cells. The
lamina propria is heavily infiltrated with leucocytes which have
the appearance of lymphatic nodules. Lymphoid tissue highly
developed in submucosa. The muscularis externa consists of the
usual inner circular and outer longitudinal layers. Muscular coats
thick. A serosa is present.
54
DIGESTIVE GLAND
DIGESTIVE
GLANDS
Objectives:
To understand the structural features of
salivary gland.
To grasp the morphological features of
liver, pancreas.
Slide 35 Parotid Gland ( Salivary Gland )
H.E.
The parotid gland is surrounded by a capsule of connective
tissue, which extend into the parenchyma and divides it into lobes
and lobules. Each small lobule is formed of a group of irregularly
saccular or tubular alveoli from which a small duct passes, and
this unites with other to form larger ducts. The parotid glands are
composed of serous only. Note that the acinar cells have
spherical nuclei situated toward the base of the cells. The
intercalated ducts, and striated ducts are present in the lobules
also called intralobular ducts. The ducts in the septa are called
excretory ducts or extralobular ducts. The intercalated ducts
are lined by simple squamous epitheliun. The lining epithelium of
striated ducts and excretory ducts range from simple columnar
55
DIGESTIVE GLAND
to pseudostratified.
Slide 36 Submandibular Gland ( Saliary Gland )
H.E.
The submandibular gland is a mixed gland; both serous and
mucous alveoli (the latter have crescents) are present, although
serous alveoli predomonant. The structure of the gland is similar
to the parotid gland except for the presence of mucous secreting
cells and demilunes. Identify also the intercalated and striated
ducts.
Slide 37 Sublingual Gland ( Saliary Gland )
H.E.
The sublingual gland is a mixed gland, but mucous alveoli
are more numerous. Many of these show crecsents at their
margins. Pure serous acini are rare. The mucous alveoli being
larger, more uniform in shape. There is no capsule surrounding
the sublingual gland. The intercalated duct is short, therefore it is
difficult to find in this gland.
Slide 34 Pancreas
H.E.
The pancreas consists of lobules separated by loose
connective tissue, which contain blood vessels, lymphatics, nerves
56
DIGESTIVE GLAND
and also branches of duct system. The pancreatic lobules are
made up of large number of serous acini, separated by a minimal
amount of connective tissue.
Within the lobules there occur scattered throughout the gland
small irregular masses of paler stain cells. These are the islets of
Langerhans.
The cells which line the alveoli are columnar or polyhedral
in shape. The lumen of the acinus is small, and is difficult to see
in many cases. Myoepithelial cells are not present. The basal
cytoplalsm of the acinar cells is strongly basophilic. The apical
cytoplasm is acidophilic due to the present of zymogen granules.
In the centre of each acinus there may generally be seen a
few nuclei. These are nuclei of centroacinar cells. They apear to
be continued from the cells which line the smallest ducts.
Examine the duct system. The smallest branches of the duct
are centroacinar cells. The intercalated ducts are small ducts,
lined by three or four low cuboidal cells in section. Compare the
intercalated ducts with the capillaries.
The intralobular ducts are more numerous in section. It is
to be found within the lobules of the pancreas. The lumen is wide
and lined by cuboidal or low columnar cells.
The interlobular ducts ocour in the septa between lobules.The
lumen is lined by columnar epithelium in which goblet cells may be
found. The duct is surrounded by a thin layer of connective tissue.
57
DIGESTIVE GLAND
Islets of Langerhans are the endocrine portion of the
pancreas. The islets contain four kinds of cells—A, B,D and PP
cells. These cell type can only be distinguished by special stain
such as Mallory-azan and under the electron microseope. You
won’t be able to distinguish them apart from your H.E.
preparation. The islets is rich in blood supply.
Slide 2 Liver
H.E.
Under low power, note there is a layer of connective tissue
underneath the serosa covering of the liver, forming an external
capsule to the organ. The connective tissue extends into and
divide mass of hepatic parenchymal cells into many roughly
hexagonal shaped units called hepatic lobules. The centre of the
lobule is marked by the central vein. Each central vein appears as
a single empty space in the section although it is fillled with
blood in life.
The connective tissue between the liver lobules is called the
interlobular septum. The region where interlobular septa of adjacent
lobules meet, is called the portal area. Each portal area consists
of branches of the hepatic artery; portal vein, a lymphatic vessel
and a bile duct. Identify these structures in the portal area.
Locate the central vein of the hepatic lobules; then search a
shordistance from the central vein for the portal areas surrounding
58
DIGESTIVE GLAND
the central vein; the area marked off by the portal areas is the
hepatic lobule.
Now examine the hepatic lobule in more detail. Note that
hepatic lobule is made up of hepatic cords arranged as
anastomosing plates radiating out from the central vein. The
cytoplasm the hepatocytes is homogenous or vacuolated and
eosinophilic. The nucleus is large, spherical, vesicular and with a
well developed nucleolus. Most cells have a single nucleus but
binucleate cells occur frequently.
Between the cords or plates of hepatocytes are the sinusoids.
Note that the walls of the sinusoids are lined partly by endothelial
and partly by Kupffer cells. The nuclei of the endothelial cells are
elongated and rather densely stained while those of the Kupffer
cells are more oval and paler stained.
Slide 38 Liver （Pig’s Liver）
Mallory
You will immediately notice that the hepatic lobules in the
pig’s liver are well demarcated. The interlobular septa with blue
color in the pig’s liver is well developed. In the portal areas, there
are interlobular artery, interlobular vein and interlobular bile duct.
The interlobular vessels and bile ducts exhibit numerous branches
in the liver parenchyma. Thus, in a cross section of the liver
lobule, it is possible to see more than one section of each of these
59
DIGESTIVE GLAND
structures whin a portal area.
Slide74 Kupffer Cells ( Rabbit’s Liver )
H.E.
Kupffer cells can be readily identified in this section of
liver which was previously injected with trypan blue (or India
ink). The Kupffer cells have phagocytosed the trypan blue (or
carbon particles) which can be seen in the cytoplasm of the
Kupffer cells in the sinusoids. The phagocytic Kupffer cells are
large with several processes, and exhibit an irregular or stellate
outline.
Slide 64 Glycogen ( Liver )
Bestcarmine
The glycogen of liver can be examined on this section. The
glycogen granules are showed as red granules and an irregular
distribution within the cytoplasm.
Slide 39 Bile Canaliculi ( Liver )
Silver
Examine this section. The bile canaliculi are showed with a
special silver techniques. The bile canaliculi appear delicate
filaments with brown-black colour between individual cells in the
hepatic plates.
Slide 67 Gall Bladder
H.E.
The mucosa exhibits temporary folds, which disappear when
60
DIGESTIVE GLAND
the gallbladder is distended with bile. So the lumen of it in this
section is irregular due to the folds. The crypts or diverticula
between the folds ofen form deep indentations in the mucosa.
They reaemble tubular glands in the lamina propria; however,
there are no glands in the gallbladder proper (escept in the neck
region). The mucosa is composed of the simple columnar
epithelium without goblet cells, and lamina propria containing
loose connective tissue and some diffuse lymphatic tissue.
The muscularis is a thin layer with loose connective tissue
that are rich in elastic fibers.
The serosa is the outermost layer and covers all of these
structures except the hepatic, where an adventitia attaches it to
the liver.
Slide 63 Human Soft Palate
H.E.
This is the sagittal section of the soft palate. The central
support of the soft palate is a sheet of skeletal muscle. On the oral
surface, the palate is covered by typical oral mucosa lined by
stratified squmous nonkeratinized epithelium. The submucosa is
characterized by the presence of mucous gland. On the nasal side,
the soft palate is covered by the pseudostratified ciliated
columnar epithelium of the nasal cavity. The lamina propria of
the epithelium also contains a few glands.
61
ENDOCRINE SYSTEM
ENDOCRINE
SYSTEM
Objectives:
To grasp the morphological features of thyroid
gland, adrenal gland, pituitary gland (hypophysis).
To understand parathyroid gland.
Slide 42 Thyroid
H.E.
The thyroid tissue is composed of follicles, which are
irregular, spherical structure, grouped together by connective
tissue septa. The follicles are variable in size. The wall of follicles
is made up of simple cuboidal epithelium and the lumen contains
red homogeneous colloid material. the There are many blood
capillaries and clusters of interfollicular cells between the
follicles.
The parafollicular cells are frequently polygonal in shape
and are large in size, the cytoplasm reveal pale with faintly
stained round nucleus. These cells are often scattered among the
follicular epithelial cells or gathered into groups between
follicles.
62
ENDOCRINE SYSTEM
Slide 43 Parathyroid
H.E.
The thin sheet of connective tissue encloses the gland and
separates the gland from thyroid.
The parenchyma glandular cells are arranged into cords or
clusters with blood vessels and connective tissue between them. It
is composed principally of chief cells. These cells are polygonal
in shape, the cell boundaries are indistinct. The cytoplasm is
faintly stained and only round nucleus can be seen easily. Many
capillaries can be seen between cell clusters and cords.
Slide 44 Adrenal Gland
H.E.
The peripheral red-stained portion of this specimen is
adrenal cortex and central pale stained portion is adrenal medulla.
Connective tissue capsule invests the whole gland. At lower
magnification, the adrenal glands is seen to be divided into an
outer cortex and inner medullar portions.
Cortex:
The cortex can be further divided into three zones according
to the arrangement of the cells.
Zona glomerulosa: A thinner layer lying beneath the
capsule, contains smaller cells which are arranged in irregular
ovoid clusters. The cytoplasm of these cells is often
deeply-stained with only a few lipid droplets in it.
63
ENDOCRINE SYSTEM
Zona fasciculata: A thicker layer occupies large part of the
cortex. It consists of paralell cords of cells, which are polyhedral
with a central nucleus. They are arranged in straight cords and
contain a great number of lipid droplets in their cytoplasm. After
the lipid contents in cytoplasm are dissolved out during specimen
preparation, the fasciculated cells appear highly vacuolated.
Zona reticularis: It is situated between zona fasciculata and
medulla. It consists of irregular cord forming anastomosing
network of closely packed clumps of cells. The cells are stained
deeply.
The 3 layers of the cortex are not demarcated clearly.
Connective tissue and abundant capillaries settle among cell
cords and cell clusters.
Medulla:
The cells are arranged in cords and clusters and have large
granular nuclei. When fixing the adrenal gland in a fixative
which contains chrome salts, the stored catecholamine granules in
the medullary cells are oxidized to brown color, refered to as the
chromaffin cells.
In medulla, the central vein and its attributive branches can
often be seen.
Sometimes a few dispersed sympathetic ganglion cells can
be identified.
64
ENDOCRINE SYSTEM
Slide 46 Pituitary Gland ( Hypophysis )
Mallory
This is sagittal section through the pituitary. The
deeply-stained portion is pars distalis and the small faintly-stained
portion is pars nervosa. The poorly narrow portion between them
is pars intermedia.
1. Pars distalis: The pars distalis is the largest part of the
gland, the cells are usually grouped in cords or clusteres which
are intimate contact with extensive sinusoidal capillary network.
On the basis of stainbility, it can be divided into 3 types, and cells
of same type are frequently gathered together.
Acidophils (alpha cells): They are large in size and coloured
red. Mostly are polyhedral or irregular in shape with round nuclei.
They can easily be distinguished from the remainder by virtue of
densely packed red granules in their cytoplasm.
Basophils (beta cells): They are lesser in number and tend
to be a little large than acidophils. The basophils are ovoid or
polyhedral cells. They have ronud nuclei. The cytoplasmic
granules are basophil and coloured bluish purple.
Chromophobes (c cells): They are the most numerous cells
in pars distalis. They are small, round or polygonal cells. Their
cytoplasm is stained pale so that the cell boundaries are not easily
visible. Round nuclei are seen in the central position of cells.
2. Pars nervosa: It consists primarily of nervosa tissue
represented by non-myelinated axons of the hypothalamohypophyseal
65
ENDOCRINE SYSTEM
tract. Distributed among these nerve fibres are specialized
neuroglial cells termed pituicyte. The nuclei of pituicytes are
round or ovoid in shap. Some pituicytes may contain brown
pigments in their cytoplasm. A few bluish gray homogenous
corpuscles i.e. Herring’s bodies disperse among the nerve fibers.
3. Pars intermedia: It is a narrow portion between pars
distalis and pars nervosa, which consists of small and pale
staining cells. Several follicles varies in size and are lined by
simple cuboidal epithelium.
Slide 45 Pituitary Gland ( Hypophysis )
H.E.
The pars distalis is the largest part of the hypophysis and
contains two main types of cells, chromphil cells and
chromphoble cells. Numerous capillaries are visible here.
The chromphil cells are subdivided into acidophils (alpha
cells) and basophils (beta cells). The cytoplasm of chromophils
stains red in acidophils and blue in basophils. The chromphoble
cells exhibit a light-staining, homogeneous cytoplasm. They are
normally smaller than the chromophils and are found in groups.
The pars nervousa is stained lightly and characterized by
unmyelinated nerve fibers and pituicytes. Oval nuclei of
pituicytes are seen, but not the scanty cytoplasm. Numerous
capillaries are presen.
The pars intermedia contains colloid-filled cysts or vesicles.
66
RESPIRATORY SYSTEM
RESPIRATORY
SYSTEM
Objectives:
To grasp the morphological features of lungs
and trachea
Slide 5 Trachea
H.E.
The cross section of trachea is circular in shape. C-shaped
blue colored tissue is tracheal cartilage. The wall of the tachea
and the bronchi system can generally be divided into three layers:
the mucosa which is the innermost layer; the middle layer or
submucosa which contains glands and the adventitia, including
the cartilage and the connective tissue outside the cartilage.
The mucosa of the trachea is lined by pseudostratified
ciliated epithelium with a red clear basement membrane. Beneath
the epithelium is the lamina propria composed of dense fine
connective tissue. It contains a large number of elastic fibers
which appear as red dots, and glandular ducts, blood vessels as
well as diffuse lymphatic tissue.
The external border of the lamina propria is continuous with
the submucosa. But there is no clear boundary between the
submucosa and lamina propria. The submucosa contains many
67
RESPIRATORY SYSTEM
mixed gland, small vessels, nerves, and loose connective tissue.
The adventitia is composed of loose connective tissue and
hyaline cartilage ring. In the membranous portion of the
posterior wall of the trachea, there is no cartilage in adventitia,
which is made up of connective tissue and circular smooth
muscles. The glands of the submucosa may be penetrated into
adventitia.
Slide 40 Lung
H.E.
In some samples, the pleura, which contains of mesothelium
and a thin layer of connective tissue, can be seen. Under the
pleura there is the pulmonary parenchyma, which contains
numerous alveoli and bronchi in various sizes. Around bronchi
there are some connective tissue in which blood vessels and
nerves can be encountered. The thin tissue between the alveoli is
called the alveolar septa.
Intrapulmonary bronchus also possesses 3 layers as in
trachea, but its dimension and wall become smaller and thinner.
Pseudostratified ciliated epithelium becomes relatively thin, but
bundles of smooth muscle outside lamina propria are prominent.
Glands in submucosa diminish. Cartilage in adverntitia changes
into several pieces of various size.
Bronchioles are canal with narrow and irregular folded
68
RESPIRATORY SYSTEM
lumen. Its epithelium is pseudostratified ciliated columnar
epithelium or simple ciliated columnar epithelium. Goblet cells
can occassionally be seen. Outside lamina propria, there is a
circular layer of smooth muscles. Cartilage pieces disappear.
Terminal bronchioles: The caliber is smaller. The wall is
thinner, and the lumen is irregular in starlike appearance. Their
epithelium is simple ciliated columnar in type, but in some cells,
the cilia are disappeared. In the wall of a terminal bronchiole,
goblet cell, cartilage and gland disappear, and outside lamina
propria a layer of circular smooth muscle can be seen.
Respiratory bronchioles: Respiratory bronchioles resembles
the terminal bronchioles in structure except that their walls are
interrupted by numerous alveoli or connected with the alveolar
ducts. The form of the epithelium is simple columnar or cuboidal
epithelium and transforms into simple squamous epithelium at
alveolar openings. It contains some smooth muscle and
connective tissue outside the epithelium.
Alveolar ducts: Alveolar ducts may be surrounded by several
alveoli or alveolar sacs. Their walls become discontinuous and
consist of a succession of alveoli, the mouths of which are outlined
by thin connective tissue and network of smooth muscle. They
appear as knobs between adjacent alveoli.
Alveolar Sac: It is the terminal portion of alveolar duct
with several alveoli opening into it , but the terminal portion of
69
RESPIRATORY SYSTEM
alveolalr septa has no knobs.
Alveoli: In the pulmonary parenchyma, numerous saclike
alveoli with irregular forms, varied in size, can be seen. Between
the alveoli there are alveolar septa. The surface of the alveoli is
lined with simple squamous cells (type I cells) and secretory
cells (type II cells).
The squamous cells are extremely thin and even not be
distinguished. The flattened alveolar type I cells form the main
lining of the alveolar wall. It has an elongate nucleus, and its
cytoplasm is not clearly visible in the light microscope.
The cuboidal alveolar type II cell with abundant vacuolated
cytoplasm, occurs either singly or in groups between alveolar
type I cells. Their nuclei are rounded and located in the center of
the cells.
Alveolar septa: It consists of two thin squamous epithelial
layers between which lie capillaries and few connective tissue
with some macrophages. The alveolar septa possese abundant
network of blood capillaries, which tightly attach to the alveolar
epithelium.
Macrophage (dust cells): This cells are ovoid or irregular in
shape. Their nucleus is round in the centre, but often masked by
the granules. Its cytoplasm is red stained and filled with numerous
engulfed dark brown granules.
70
URINARY SYSTEM
URINARY
SYSTEM
Objectives:
To grasp the morphological features of
kidney;
To understand the morphological features
of urinary bladder and ureter.
Slide 41 Kidney
H.E.
The red outer portion is cortex and the light inner portion is
medulla. Sometimes deeply stained renal column may be seen on
side of renal pyramid.
The cortex is covered by a renal capsule, composed of a very
thin dense connective tissue. Pay attention to distinguish the
cortical labyrinth and medullary rays in cortex: The cortical
labyrinth is the region where renal corpuscles and sections of
convoluted tubules are located, while the medullary rays are
straight tubules which arranged parallely and grouped into a
bundle. The medulla consists of straight tubules often oblique or
longitudinal sectioned. At the junction of cortex and medulla,
71
URINARY SYSTEM
sections of arcuate artery can be seen.
In the cortical labyrith the renal corpuscles are the most
distinctive components of the cortex. The center of each renal
corpuscle consists of a cluster of capillary loops (the renal
glomerulus). The wall of the corpuscle is lined with simple
squamous epithelium (parietal layer of Bowman’s capsule). The
glomerular basement membrane is interposed between the
capillary endothelium and the visceral layer of Bowman’s
capsule. These two layers are difficult to distinguish from one
another by light microscopy. Surrounding each corpuscle are
many convoluted tubules. These are of two types: proximal
convoluted and distal convoluted.
The proximal convoluted tubules are numerous, have a
relatively small, often uneven lumen and are composed of large
broad cuboidal cells whose granular cytoplasm stains deeply with
eosin. Brush borders are present but are not always well
preserved in sections.
The distal convoluted tubules are fewer in number, have a
large regular lumen, the cells are smaller and more distinctly
cuboidal, their cytoplasm stains less deeply and brush borders are
not present.
The medullary rays include three types of tubules. The
straight (descending) segments of proximal tubules are
generally similar in structure to the convoluted parts of
72
URINARY SYSTEM
proximal tubules. The straight (ascending) distal segments are
generally similar in structure of distal convoluted tubules.
Collecting tubules are distinct because of their lightly stained
cuboidal cells with visible cell boundary.
The parenchymal components of the medulla consists of
collecting tubules which empty at the apex of the pyramid and
ascending and descending thin limbs of Henle’s loop. The latter
have a thin squamous epithelial lining similar to the endothelium
of capillaries. Capillaries can be singled out by the erythrocytes in
their lumen. Near the corticomedullary border, the ascending
limbs of Henle’s loop are lined by taller, cuboidal epithelial cells.
Juxtaglomerular Cells
Look for renal corpuscle. At vascular pole, near the renal
corpuscle, the smooth muscle cells of the afferent arteriole
become hypertrophic and modified into epithelioid cells. The
nuclei are relatively large, and round or ovoid shape with fine
chromatin. There are a great number of purple stained granules in
cytoplasm.
Macula Densa
At the point that the distal convoluted tubule is in contacted
with the vascular pole of the renal corpuscle, the epithelial cells
of the tubule become narrower and taller and turn columnar. Their
73
URINARY SYSTEM
nuclei are closely packed together, forming the macula densa, the
cell boundaries are relatively distinct.
Slide 69 Ureter
H.E.
The undistended ureter has a small and irregular lumen, the
convolution being due to longitudinal mucosal folds.
The mucosa consists of transitional epithelium, and lamina
propria of connective tissue.
The muscle layer consists of an inner longitudinal layer and
an outer circular layer of smooth muscle.
The advantitia is made up of loose connective tissue and
continuous with surrounding connective tissue.
Slide 66 Urinary Bladder
H.E.
The mucosa is made of transitional epithelium and lamina
propria. The most characteristic feature of the transitional
epithelium is the presence of large bulging cells in the superficial
layer. In distendend bladder the superficial cells are flate and thin.
The muscularis is a thick coat. It is more or less in 3 layers:
The inner is longitudinal and middle is circular and the outer is
longitudinal. But these 3 layers often intermingled with each
other and are difficult to distinguish.
The advantitia is made of connective tissue.
74
MALE REPRODUCTIVE SYSTEM
MALE
REPRODUCTIVE
SYSTEM
Objectives:
To grasp the morphological features
of the Testis and Epididymis;
To understand the structures of the
prostate gland;
To understand the structures of the
ductus deferens.
Slide 47 Testis
H.E.
Under low power note the testis is enclosed by a strong
fibrous capsule, the tunica albuginea, containing sections through
large arteries and veins in its inner most layer. The tunica
albuginea is covered externally with a thin layer of serous
epithelium. From its inner surface there proceed fibrous processes
or trabeculae, which imperfectly subdivide the organ into lobules.
Posteriorly the capsule is prolonged into the interior of the
gland in the form of a mass of fibrous tissue, which is known as
the mediastinum testis. Each lobule contains numerous sections
75
MALE REPRODUCTIVE SYSTEM
of the highly convoluted seminiferous tubules.
Using high power, the tissue reveals a variety of planes of
section through the seminiferous tubules. The seminiferous
tubules are formed of a connective tissue membrane. In the adult,
the tubules contain several layers of epithelial cells. There are two
cell types that can be identified. The sustentacular or Sertoli
cells and the spermatogenic cells.
The Sertoli cells here and there between the spermatogenic
cells, they are enlarged, and project between the more internal
layers. The cells have their oval or irregular shaped nuclei
containing prominent nucleoli localized along the basement
membrane. These are relatively few in number.
The spermatogenic cells in various stages of development
or differentiation can be found.
The one next to the basement membrane is a stratum of clear
cubical cells—spermatogonia, the most of nuclei exhibits the
irregulalr network which is characteristic of the resting condition,
but in some tubules the nuclei show indication of division. There
are two main classes of spermatogonia: Type A have a spherical
or ovoid nucleus containing fine chromatin granules and a
nucleolus; Type B have a centrally located nucleus with heavily
stained chromatin masses.
Next to this lining epithelium is a zone of larger
cells—primary spermatocytes. They have large nuclei and large
76
MALE REPRODUCTIVE SYSTEM
cell volume. Their nuclei reveal variable appearance due to the
different states of activity of the chromatin usually at the
pachytene stage.
The secondary spermatocytes are not frequently encounted
and less readily identified.
Next to them, and most internal, are to be seen as the result
of this division a large number of small cells with simple
spherical nuclei—spermatid.
The spermatozoa lie in groups, their heads lie in the recesses
of the cytoplasm of Sertoli cells. Their tails project into the lumen
of the tubule.
Between the seminiferous tubules, the connective tissue
contains blood vessels, lymph vessels, nerve and the usual
connective elements. In addition, clusters of epithelioid cells, the
interstitial cells (Leydig cells) are also present. They are larger
and more rounded than other cells between the seminiferous
tubules with eosinophilic cytoplasm.
Slide 47 Epididymis
H.E.
The epididymis can be seen in the same section of the testis.
The epididymis is located on the posterior-superior surface of the
testis. The proximal part, or head of the epididymis is formed by
the ductuli efferentes which joins the rete testis. The epithelium
77
MALE REPRODUCTIVE SYSTEM
of the ductuli efferentes is simple, consisting of alternating groups
of high ciliated columnar cells and shorter nonciliated cells ,
which are believed to be absorptive. The basal surface of the
ductuli has a smooth contour. Locatde under the basement
membrane is a thin layer of connective tissue containing a thin
layer of circularly arranged smooth muscle fibers.
The body and tail of the epididymis is formed by the ductus
epididymis. The duct is a long, highly convoluted tubule, which is
lined by a pseudostratified epithelium of tall columnar cells with
long, nonmotile stereocilia and small basal cells. The epithelium
is surrounded by the basement membrane, connective tissue
containing circular smooth muscle and many blood vessels.
Spermatozoa can be seen in the lumina of some of the tubules.
Slide
Vas Deferens
H.E.
The vas deferens is a thick-walled tube. Note the extremely
well development of the muscular coat, having three layers: The
inner and outer layers are made up of longitudinal bundles of
smooth muscles, the wide middle layer of circular fibers. There is
a good deal of connective and elastic tissue between the muscle
bundles. The tube is lined by a mucous membrane, the inner
surface of which is covered by pseudostratified columnar
non-ciliated epithelium.
78
MALE REPRODUCTIVE SYSTEM
Slide 48 Prostate
H.E.
The prostate is a tubuloacinar gland. It is composed of many
glandular acini in a stroma of connective tissue and smooth
muscle. The acini vary in size. The larger-sized acini exhibit wide,
irregular lumina. The folded walls of acini are lined by simple
cuboidal or columnar cells. In older people, the acini often
contain colloid prostatic concretion, which may undergo
calcification.
79
FEMALE REPRODUCTIVE SYSTEM
FEMALE
REPRODUCTIVE
SYSTEM
Objectives:
To grasp the morphological features
of ovaries and uterus;
To understand the structures of the
oviduct;
To understand the structures of the
mammaty gland.
Slide 75 Ovary
H.E.
Under the low power examine the ovary is covered by a
single layer of flat epithelial cells. Beneath the epithelium there
is a layer of thick connective tissue—the tunica albuginea.
Identify the medullary region, containing several blood vessels
and a small amount of loose connective tissue. This is surrounded
by a thick cortex. There are no sharp limits between the cortex
and medulla.
The stroma of the cortex is composed of characteristic
80
FEMALE REPRODUCTIVE SYSTEM
spindle-shaped connective cells. Scattered throughout the stroma
are follicles of different sizes, the smallest being near the surface
to the organ, the larger ones placed more deeply in the stroma.
Two types of folliclels can be distinguished: primordial follicles
and growing follicles.
The primordial follicles are located in the periphery of the
cortex and under the tunic albuginea. They are the smallest and
simplest in structure. Each primordial follicle consists of a
primary oocyte enveloped by a single layer of flattened follicular
cells.
The growing follicles are subdivided into two stages—the
primary follicles and secondary follicles.. Find the various
stages of development of the follicles and look for the following
features:
1. Oocytes is a primary oocyte.
2. Zona pellucida is the noncellular glycoprotein layer
surrounding oocyte. It appears pink.
3. Follicular cells change to simple cuboidal or columnar,
even more layers which are called as granulosa cells.
4. Corona radiata are a single layer and more columnar
than the other granulosa cells. They are attached radially to the
zona pellucida.
Follicular antrum appears and is filled with follicular
fluid. (Larger follicles with antral cavities of various sizes are called
81
FEMALE REPRODUCTIVE SYSTEM
as secondary follicles).
Stratum granulosa refers to the cells which consist of the
wall of follicles.
Cumulus oophorus is located on one side of the follicle
and projects into the antrum with oocyte, zona pellucida, and
corona radiata.
5. Theca interna and theca externa differentiated by
stromal cells surround the follicles. The theca interna is an inner
layer of vascularized, secretory cells. The theca externa is an
outer layer of connective tissue cells.
Between the follicles there are some atretic follicles in
which degenerating oocytes can be seen.
Scattered between follicles, there are groups of round cells
with foamy of pink-stained cytoplasm. These are interstitial cells,
which are probably derived from theca of atretic follicles.
This section do not well show the structures of the corpus
luteum.
Slide 49 Ovary
H.E.
Examine the corpus luteum. They consist of the granulosa
lutein cells, which are the hypertrophied granulosa cells of the
follicle, and the theca lutein cells, fromed from the theca interna
cells of the follicle. The granulosa lutein cells constitute the
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FEMALE REPRODUCTIVE SYSTEM
mass of the corpus luteum. These cells are large, have large
vesicular nuclei, and stain lightly because of lipid inclusions. The
theca lutein cells are smaller than granulosa lutein cells, their
cytoplasm stains deeper and their nuclei are smaller and darker.
Numerous capillaries and fine connective tissue septa are
visible between the lutein cells. The stroma around the corpus
luteum is highly vascular.
Slide 50 Uterus ( Proliferative Phase )
H.E.
The body of the uterus is formed of the following three
layers:
1. Serosa ( perimetrium ): which covers the greater part of
the fundus.
2. Myometrium: which is of great thickness and is formed of
smooth muscle fibres disposed in three or four layers, which are
not well defined: the stratum submucosum, the stratum
vasculare, the stratum supravasculare, and the stratum
subserosum. The first and the forth are composed mainly of
fibres disposed longitucdinally. The stratum vasculare has many
large blood vessels. In this layer, has circular and obligue muscle
bundles.
3. The endometrium consists of epithelium and lamina
propria containing long, simple, tubular glands—uterine glands.
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FEMALE REPRODUCTIVE SYSTEM
The epithelial cells are simple columnar and are a mixture of
ciliated and secretory cells. The uterine glands is similar to the
superficial epithelium. The connective tissue of the lamina
propria contains a large number of spindle-shaped cells.
Connective tissue fibres are rare.
Pay special attention should be:
(1) thickness of the endometrium ;
(2) interlacing of the endometrium and myometriun at their
junction;
(3) height and character of the lining epithelium;
(4) number, length, diameter and shape of glands;
(5) the close packing of the stroma cells and the position and
shape of the blood vessels.
Slide 68 Oviduct
H.E.
The wall of the oviduct is composed of three layers:
The mucosa has long longitudinal folds. The epithelium
lining the mucosa is simple columnar and contains two types of
cells. One is provided with cilia and the other is devoid of cilia
and appears to be secretory. The lamina propria of the mucosa is
composed of loose connective tissue.
The muscular layer is composed of a thin longitudianl layer
of smooth muscle fibres and an outer thicker circular smooth muscle
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FEMALE REPRODUCTIVE SYSTEM
fibres.
Externally the tube is covered by a serosa—connective tissue
and mesothelium.
Slide
Mammary Gland ( Resting Breast )
H.E.
The resting gland consists mainly of connective tissue and
scattered groups of excretory ducts with branches which terminate
in collapsed alveoli or solid cell cords.
Slide
Mammary Gland ( Lactating Breast)
H.E.
In this section, the connective tissue is reduced to thin septa
which enclose large lobules of densely packed ducts and alveole
which are actively secreting. The alveolar epithelium is composed
of low columnar cells, secretory droplets accumulate in the apical
cytoplasm, while the nucleus is displaced basally.
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SKIN
SKIN
Objectives:
To grasp the five-layer structures of epidermis;
To grasp the hair, hair follicle and hair bulb;
To understand the structures of the sebaceous
gland, arrector pelli, sweet glands.
Slide 19 Skin ( Finger )
H.E.
Under low power, note the skin is composed of two parts, the
outer epithelial layer, the epidermis and inner dense connective
tissue layer, the dermis. Beneath the dermis is a loose connective
layer, the hypodermis, containing many fat cells, large bundles of
nerves and Pacinian corpuscles (lamellated corpusles).
The epidermis is keratinized stratified squamous epithelium.
It contains no blood vessels. The nourishment of the cells is
derived from vessels of the dermis through diffusion. The
epidermal-dermal junction is wavy, due to projections of the dermis
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(dermal papillae) into the under surface of the epidermis.
For descriptive purposes, the epidermis can be distinguished
into five layers.
1. Stratum basale (S. germinativus). This is a single layer of
cells, the deepest cells of the epithelium, which are set on the
surface of the dermis, are columnar, cuboidal, even squamous in
shape. The cytoplasm is stained brownish, exhibited pigment
(melanin) granules in these cells (especially in the darker parts of
the skin). Many of the cells show mitosis, an indication that the
epidermis is regenerated from these cells.
2. Stratum spinosum or prickle cell layer. Immediately
above the basal layer is stratum spinosum. This layer is three to
four cells thick. The cells of stratum spinosum are closely packed,
polyhedral form. Between the cells there are fine intercellular
clefts separating the cells from one another. All the cells bear
short cytoplasmic process which called intercellular bridges. The
cells of this layer are basophilic, contain various amount of
cytoplasmic fibrils or keratin. Cell divisions occur in this layer,
and occasional mitotic figures can be seen.
3. Stratum granulosum. This layer is formed of 2～5 layers
somewhat flattened cells filled with granules or droplets of
material (eleidin) staining deeply with carmine and hematoxylin.
These cells form an irregular layer.
4. Stratum lucidum. Superficial to the stratum grenulosum
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is a layer in which the cell-outlines are indistinct and the cells
contain flakes or larger droplets of a hyaline material,
kerato-hyalin, staining less intensely than the granules in the last
layer, and tending to run together. This layer has a clear
appearance in section, but is absent in thinner skin.
5. Stratum corneum. Immediately superficial to the stratum
lucidum is the cornified cells of the epidermis. It is composed of a
number of layers of flattened, dead cells, the nuclei of which are
no longer visible, the cytoplasm js packed with keratin.
The stratum basale and spinosum are often grouped together
collectively as the stratum Malpighi
The dermis is composed of dense connective tissue. It can be
subdivided into:
1. Superficial or papillary layer is connective tissue that
consitutes dermal papillae; these project into the epidermis, which
is moulded over and attached to them. The papillary layer consists
mainly of fine collagenous fibres, reticular fibres and elastic
fibres interweaving with blood vessels. Some papillae may
contain special sensory terminations—Meissner’s corpuscle
(tactil corpucles)
2. The reticular layer consists mainly of bundles of coarse
collagenous fibres running in various directions but mainly
parallel to the surface. It also contains extensive network of blood
vessels, nerves and lymphatics.
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Below the dermis and likewise not sharply differentiated
from it is the subcutaneous connective tissue (superficial fascia)
which serves to bind the integument to the underling organs. This
layer contains connective tissue, often heavily infiltrated with
adipose tissue.
Slide 26 Scalp ( Human Scalp )
H.E.
The hair follicles can be seen in black-purple stain, hair
shafts are exposed near the surface of the skin or may be cut off.
The fundamental structure of the scalp is similar to that of
palmar skin, but the epidermis is especially thinner.
The stratum cornum consists merely of several layers of
keratinized cells. The stratum basale contains more brown
pigments. The dermis is thicker and hairs, arrector pelli muscle,
sebaceous glands and sweet glands are located in it.
The hair and its follicle: Each hair consists of a hair shaft
which projects above the surface and a root which is embeded
within its distal deep portion and a hair follicle. The hair is
composed of keratinized cells stained in red, pigment granules are
found in and between the cells. The hair follicle is made up of
epithelium and connective tissue. The epithelial sheath is divided
into an internal root sheath and outer root sheath.The internal root
sheath is stained in red. Their cells are corresponding to the
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89
stratum corneum of the epidermis. The outer root sheath is
corresponding to the stratum spinosum and basale of the
epidermis. The connective tissue sheath is similar to the dermis.
In some longitudinal section of the hair, the terminal dilatation
callled the hair bulb, which the connective papillar projects in,
can be seen.
The arrector pili consist of smooth muscle cells gathered
into a bundle, which bunds to the connective tissue sheath of the
hair follicle and connects it to the papillary layer of the dermis.
The sebaceous glands are attached to the upper of the hair
follicle. The cells comprising the sebaceous secretory unit are
characterized by a centrally located nucleus and a pale staining,
vaculated cytoplasm. The excretory ducts are lined by stratified
squamous epithelium continuous with the epidermis.
SENSORT ORGAN
SENSORY
ORGAN
90
Objectives:
To understand the structures of eye ball;
To grasp the morphological features of cornea;
To understand the morphological features of
lens, retina, eyelid;
To understand the structures of the inner ear;
To grasp the morphology and structure of
spiral organ (Organ of Corti).
Slide 51 Eye Ball
H.E.
The eye ball consists of the wall of the eye ball and refractive
media.
The wall of eye ball is composed of 3 tunics, from outside to
inward are: tunica fibrosa, tunica vasculosa and retina. The
refractive media includes vitreous body, lens and aqueous humor.
Tunica fibrosa is the outermost red stained layer and is
divided into 2 parts: the cornea and the sclera.
Cornea is the slightly bulged anterior part. It is composed of
five layers. From anterior to posterior:
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91
Cornea is the slightly bulged anterior part. It is composed of
five layers. From anterior to posterior:
1. the cornea epithelium is a thin layer of nonkeratinized
stratified squamous epithelium, and consists of 5 to 6 layers of
cells.
2. Bowman’s membrane (anterior limiting membrane) is a
homogeneous layer beneath the epithilium.
3. the substantia propria is the thickest layer and formed by
several sheets of regularly arranged collagenous fibers, the
fibroblasts lie between collagenous fibre sheets, no blood vessel
is there.
4. Descemet’s membrane (posterior limiting membrane) is
also a homogeneous layer, and lies internal to the substantia
propria.
5. Endothelium is simple squamous epithelium on the
posterior surface of cornea.
Sclera is the posterior five sixth of the external layer of the
eye. It consists of dense fibrous connective tissue made up mainly
of flat collagenous bundles. Few fibroblasts and pigment cells
scatter between fibre bundles.
Tunica vasculosa is the brownish colored tunic inside tunica
fibrosa, and this tunic is divided into 3 parts again: choroid,
ciliary body and iris.
Choroid is the posterior part of this tunic, closely applied to
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92
the interior of sclera. It is composed of loose connecrtive tissue
and contains many blood vesseels and pigment cells.
Ciliary body is an anterior thickened portion of tunica
vasculosa, triangulalr in shape in section and situated just behind
the cornea scleral junction. In the inner side of anterior portion of
ciliary body, there are many folds or processes, which is ciliary
processes. The main part of ciliary body is composed of loose
connective tissue with blood vessels, pigment cells and
well-developed ciliary muscle. This muscle is composed of 3
bundles of smooth muscle fibers in defferent directions. Two
layers of cuboidal cells extending from the retina line the inner
surface of the ciliary body, the outer layer is pigmented cells and
the inner layer is free of pigment.
Iris is a membranous extension of the ciliary body and
partially covers the lens, its central aperture, the pupil. The iris is
consists of a pigment, highly vascular connective tissue. The
anterior surface is lined with endothelium. Its posterior surface is
covered with a double layer of heavily pigment cuboidal
epithelium. In the anterior layer of the epithelium, two groups of
smooth muscle—the circular sphincter of the pupil and the
radially arranged dilatator of the pupil can be seen.
Retina lies close to the inner surface of the vascular layer.
In cross section, from external to internal, the layers of the
retina are as follows:
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93
1. Pigment epithelium
2. Layer of rods and cones
3. External limiting membrane
4. Outer nuclear layer
5. Outer plexiform layer
6. Inner nuclear layer
7. Inner plexiform layer
8. Ganglion cell layer
9. Optic nerve fiber layer
10. Internal limiting membrane
Lens: It lies behind the iris. It is ovoid in shape and is
enveloped by a thin lens capsule. Under the anterior surface of the
capsule there is a simple cuboidal epithelium named subcapsular
epithelium. At the equatorial region of the lens, the epithelial cells
elongate to form the lens fibers with an elongated nucleus in their
center. The lens fibers arrange in a concentric fashion. In the
central part of the lens, the nuclei of the lens fibers undergo
degeneration and disappear at last.
Vitreous body: It fills the space between the lens and retina.
Anterior and posterior chambers: The space lies between
the cornea and the lens is anterior chamber and that lies between
vitreous and lens, iris as well as ciliary body is posterior chamber.
The angle formed by the cornea with the basal part of the iris is
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94
the iris angle or angle of the anterior chamber.
Near ora serrata, the visual portion of retina become thin
suddenly, and the layer of it also reduced in numbers, only 2 layer
cells remain, and changes to the blind portion of retina.
Optic papilla is the region all the nerve fibers of ganglion
cells dissappear. The margin of the pupilla bulges inward and
with its central part depressed. The area where optic nerve fibers
cross the sclera is the area cribrosa. The nerve fibers gether into
bundles and enveloped with comparatively dense connective
tissue which is continous with sclera, and thus optic nerve is
formed.
Slide 70 Eyelid
H.E.
The outer surface of the eyelid is skin. It is thin with hair,
sebaceous glands and sweat glands in the dermis. The sebaceous
glands located near the palpebral maigin are small that is glands
of Zeis. There are also composed of special sweat glands with
large lumen—the glands of Moll as well as thick eyelashes
without arrector pili muscle. The subcutaneous layer is a thin
layer of loose conective tissue and is almost completely avoid of
fat.
The muscle layer consists of skeletal muscle—the
orbicularis oculi muscle and the levator palpebrae muscle.
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95
The tarsus is a plate of dense connective tissue which is the
skeleton of the lid. In which the Meibomian glands are embeded.
The Meibomian glands are sebaceous glands, the ducts of which
open at the palpabral margin.
The deep inner surface of tarsal plate is palpabral
conjuctiva, which is composed of stratified columnar epithelium
and contains some goblet cells occasionally. Its lamina propria is
composed of connective tissue with numerous lymphocytes.
Slide 52 Cochlea ( Inner Ear )
H.E.
The pyramidal structure in the center of this section is the
cochlea. The deeply stained area in the centre of cochlea is
modiolus. On the both sides of modiolus, there are 3～4 small
canals respectively, these are cross-section of osseous cochlea
around the modiolus. The lumen of each osseous cochlea is
devided into three cavities: an upper cavity—the vestibuli; lower
cavity—the seala tympani; and an intermediate cavity—the
cochlear duct.
The modiolus is composed of spongy bone, and contains
blood vessels and spiral ganglion. Form the modiolus a shelf of
bone projects toward the lumen of the osseous canal of the
cochlea. That is the osseous spiral lamina. Blood vessels and
spiral ganglion are located in its basal portion.
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The cochlear duct: The osseous spiral lamina is continous
outward with a membranous spiral lamina. The cochlear
periosteum become thickened at its outer attachmentas the spiral
ligament to form complete transverse septum. A thin membrane,
which extends obliquely from the osseous spiral lamina to the
upper part of the spiral ligment, is the vestibular membrane.
Thus the cochlear duct has 3 walls: The upper
wall—vestibular membrane; the outer wall—the spiral ligament;
and the lower wall—basilar membrane.
The vestibular membrane is composed of very thin layer of
connective tissue and covered by simple squamous epithelium on
both sides. The spiral ligament is in contact with lateral bony
wall and is composed of thickened connective tissue covered by
pseudostratified columnar epithelium. This epithelium is rich in
blood vessels and is called stria vascularis. The lower wall is
higher and irregular limbus, from which derives a glycoprotein
structures—the tectorial membrane. Spiral organ (Organ of
Corti) lies on upper side of basilar membrane.
Spiral organ (Organ of Corti). The membranous spiral
lamina is composed of 3 layers: a central basilar membrane in
which contains auditory strings is covered by epithelium in both
of its superior and inferior surfaces. The inferior epithelium is a
thin layer of squamuous epithelium continuous with that lining
the scale tympani. The superior epithelium becomes thickened
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and differentiates into the spiral organ which contain several
types of cells. Two main cell types is divided — the supporting
cells and the hair cells.
The supporting cells: According to their morphology.
Inner and outer pillar cells: They are tall and the basal
portions of the cells are border which situated on the basal
membrane. Apical end and basal portion of these cells interlock
and form a triangular space —inner tunnel. Nuclei of these cells
are round, and situated in basal portion of cells,deeply stained.
Inner and outer phalangeal cells: The inner phalangeal
cells are arranged in a row along the inner surface of the inner
pillar cells. The inner hair cells are situated on them. The outer
phalangeal cells are arranged along the outer surface of the outer
pillar cells. Their number varies in different regions of the
cochlear duct. It is 3 rows in the base of the cochlear duct and 5
rows in apex. The 3～5 rows of outer hair cells are rested on
them.
The inner and outer hair cells are supported by the inner
and outer phalangeal cells, respectively. They are sensory cells.
On the top of some hair cells, cilia can be seen.
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