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Pierce College
Putman/Biol 241
Unit 04 notes: Tissues (Histology)
A tissue is an integrated association of cells of a particular type that perform the same, specific function.
Histology is the study of tissues.
CLASSES OF TISSUES
There are four classes of tissues: epithelial, connective, muscle and nerve.
EPITHELIAL TISSUES
There are two classifications of epithelial tissues, depending on their general locations and functions: Covering &
Lining Epithelia and Glandular Epithelia
COVERING AND LINING EPITHELIUM
General Functions of Covering & Lining Epithelium
a) Mechanical protection from abrasion, as seen in the integument (skin) and pharynx (back of throat)
b) Innate immunity, the inhibition of pathogens into the body—the integument especially does this, but the lining
of the gut helps.
c) Osmotic & chemical balance. Covering and lining epithelia play a major role in the control of the loss/gain of
water, ions and other chemicals.
d) Secretion, which is the production of useable products such as mucous and digestive enzymes.
e) Absorption. All digested nutrients, water, ions, etc. enter the body through gut epithelium.
Characteristics of Covering & Lining Epithelium
a) Cells packed very closely together in continuous sheets. Tight junctions (= cell junctions) hold adjacent cells
together. There is very little interstitial space between cells; thus, this markedly inhibits fluid flow from one side
of the tissue to the other.
b) Basement membrane. Epithelial tissues have basement membranes. These are acellular (not made of cells), thin,
two-layered sheets that the cells of the epithelium attach to by their basal surfaces. The basement membrane
consists of two layers, the basal lamina and the reticular lamina. The basal lamina is secreted by the epithelium
and is composed of proteins including collagen, laminin and glycoprotein. The reticular lamina is secreted by
the connective tissue under the epithelium and is made of fibrous proteins. The basement membrane supports
and serves as an attachment site for epithelial cells, directs/guides epithelial cells during tissue growth and
repair, inhibits the movement of large molecules between epithial and underlying tissues, and aids in filtration
in the glomerular apparatus of the kidney. Note that only epithelial tissue has basement membranes.
c) May occur as single cell or multiple cell layer.
d) Has an apical surface, a surface that is open to the internal or external environment.
e) Avascular—epithelial tissue does not have capillaries in it, so obtaining nutrients, getting rid of wastes, and gas
exchange must occur through diffusion to/from the capillaries in underlying connective tissue.
f) Highly mitotic—epithelial tissue cells divide rapidly, enabling rapid tissue growth & repair.
Classification of Covering & Lining Epithelium
a) By layering of cells. 1. Simple Epithelium is made of a single layer of cells, with all cells attached to the
basement membrane; nuclei are generally at the same level. 2. Pseudostratified Epithelium is also a single layer
of cells, with all cells attached to the basement membrane; however, the nuclei are not all at the same level, so
the tissue looks stratified. 3. Stratified Epithelium is a multiple layer of epithelial cells, with only the basal cells
attached to the basement membrane.
b) By cell morphology (shape). 1. Squamous Epithelium is made of flat cells—very thin tissue. This accomodates
simple diffusion and transcytotic diffusion. 2. Cuboidal Epithelium consists of box-shaped cells; if cuboidal
epithelium is involved in secretion or absorption, then the apical surface is evaginated into microvilli. 3.
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Columnar Epithelium cells are markedly taller than cuboidal epithelium; if these cells are involved in secretion
or absorption, they also have apical surfaces evaginated into microvilli. 4. Transitional Epithelium is epithelium
capable of changing shape from cuboidal to squamous—this accomodates stretching in places like the urinary
bladder.
Specific Covering & Lining Epithelium Tissues
a) Simple Squamous Epithelium.
-Flat & delicate, not found where there is abrasion
-Found where transcytotic diffusion, simple diffusion & filtration occur such as the podocytes of the glomeruli in the
kidney, alveolar cells in the lungs, descending loop of Henle cells in kidney, endothelium of the circulatory system
(lining of heart, blood & lymphatic vessels), mesothelium (epithelium of serous membranes).
b) Simple Cuboidal Epithelium
-Single layer, box-shaped cells.
-Secretory & absorptive.
-Located in glands, ducts & tubules such as the thyroid gland follicular cells, ducts from thyroid gland, ducts from
pancreas, kidney nephron tubules, etc.
c) Simple Columnar Epithelium
-Single layer, elongated cells
-Ciliated Simple Columnar Epithelium: Line fallopian tubes & uterus (where cilia move eggs), central canal of
spinal cord (cilia move cerebrospinal fluid).
-Non-ciliated Simple Columnar Epithelium—two types: 1. cells with microvilli, found where there is a lot of
secretion & absorption, such as lining the gut from stomach to anus, and 2. goblet cells, which secrete mucus and are
found scattered among cells with microvilli.
d) Pseudostratified Columnar Epithelium
-Looks stratified, but all cells contact the basement membrane.
-Goblet cells scattered about, secrete mucus.
-Cilia present, moves mucus
-Located in nasal cavity, trachea & bronchi (lungs), as well as in the epididymis & vas deferens—the major spermcarrying tubes of the male reproductive tract.
e) Stratified Squamous Epithelium
-Multiple layers of cells; basal cells cuboidal, apical cells squamous in morphology. Cells of apical layers usually
dead and constantly slough off; this allows this tissue to be protective, withstanding rubbing and mechanical
abrasion well.
-Includes keratinized tissue. Keratin is a waterproof protein found in the integument (skin)—it makes the skin
waterproof.
-Non-keratinized stratified squamous epithelium is found in moist tissues that can withstand wear, such as those
tissues that cover the tongue, line the oral cavity, line the oro- & laryngopharynx, esophagus and vagina.
f) Transitional Epithelium
-Strechable tissue, stretches from cuboidal to squamous morphology.
-Found lining the urinary bladder.
GLANDULAR EPITHELIUM
General Functions of Glandular Epithelium
a) Synthesis & secretion of specific products
b) Form glands
General Characteristics of Glandular Epithelium
a) May be single celled to multicellular structures
b) Located deep under surface of epithelial tissues as deep invaginations/extensions of epithelial tissues.
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Specific Glandular Epithelial Tissues
a) Exocrine Glands
-Secrete into internal or external environments via ducts (tubes)
-Examples include: salivary glands, exocrine portion of pancreas, male secondary sex glands, sebaceous glands,
sudoriferous (sweat) glands of skin.
b) Endocrine Glands
-Secrete products (hormones) directly into interstitial fluids surrounding cells; do not have ducts. Products then
diffuse into blood.
-Example include: hypothalamus, pituitary, thyroid, parathyroids, thymus, etc.
CONNECTIVE TISSUES
General Functions of Connective Tissues
a) Connects, covers, strengthens, supports other tissues
b) Stores nutrients (adipose tissue does this)
c) Hematopoiesis (produces blood cells)
d) Transports materials (blood tissue does this)
General Characteristics of Connective Tissues
a) Consists of blast cells that secrete & are separated by extracellular matrix.
b) Blast cells are not closely packed; in fact, they are generally widely dispersed.
c) When surrounded by matrix, blast cells stop dividing and stop secreting matrix.
d) Matrix made of protein fibers and/or ground substance
Specific Connective Tissues
A) Loose Connective Tissues:
-Have variable cell types
-Matrix of fibers that are loosely held together.
-Include: Areolar Connective Tissue, Adipose Tissue and Reticular Connective Tissue.
1. Areolar Connective Tissue.
-Cell types: Fibroblasts, which secrete matrix; macrophages, which eat pathogens and dead cells through
phagocytosis; and mast cells, which produce histamine & heparin when tissue is damaged.
-Matrix fibers include collagen (tough & flexable), reticular fibers (a type of collagen) and elastin (elastic).
-Ground substance is clear and jelly-like, made of glycoproteins such as hyaluronic acid. White blood cells secrete
hyaluronidase, which digests hyaluronic acid, allowing white blood cells to navigate through tissue to sites of injury
and infection. Sperm also secretes hyaluronidase, allowing it to enter the egg during fertilization.
-Location of Areolar Tissue. Areolar tissue is very common and is found in the hypodermis of the integument (layer
under skin), around blood vessels, and around organs.
-Function: Elastic support & tissue connections.
2. Adipose Connective Tissue
-Cell type: adipocytes. These cells function to store triglycerides in vesicles. Adipocytes do not secrete an
extracellular matrix; the cells are, in fact, close together.
-Location: adipose connective tissue is found in subcutaneous deposits on the waste, breasts, hips and other
locations, around the heart & kidneys, and in yellow bone marrow.
-Function: Energy storage, insulation & padding.
3. Reticular Connective Tissue
-Cell type: reticulocytes and macrophages.
-Matrix fibers: spiderweb-like protein network
-Location: lymph nodules & nodes, liver & spleen stroma.
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-Function: The spiderweb-like reticulations of reticular connective tissue trap old blood cells in the spleen and trap
pathogens in the lymph nodes and nodules; in both places, macrophages consume the trapped cells.
B) Dense Connective Tissues
-Have one cell type: fibroblasts
-Matrix fibers densely held together
-Include: Dense Regular Connective Tissue, Dense Irregular Connective Tissue and Elastic Connective Tissue.
1) Dense Regular Connective Tissue
-Matrix fibers tightly-packed, wavy, uniform rows of tough collagen.
-Location: tendons (muscle to bone connections), ligaments (bone to bone connection), aponeuroses (muscle to
muscle connections)
-Function: tough, durable connections
2) Dense Irregular Connective Tissue
-Matrix fibers tightly packed, irregular, collagen.
-Location: Dermis of integument (layer under skin), membrane capsules around organs (pericardium of heart,
around liver, kidneys, lymph nodes), bone periosteum (covering of bone), cartilage perichondrium (covering of
cartilage), joint capsules.
-Function: covers, protects, strengthens in a tough capsular structure.
3) Elastic Connective Tissue
-Matrix fibers of elastin.
-Location: respiratory system (trachea, lungs, bronchial tree), some arterial walls, ligaments of vertebrae, penis
suspensory ligaments.
-Function: elastic support.
C) Cartilage
-Cell type: chondrocytes located in spaces called lacunae.
-Matrix fibers of densely-packed collagen (provides strength)
-Ground substance of chondroitin sulfate which provides resilience—the ability to return to normal shape after being
stretched.
-Avascular: cartilage does not host any capillaries, thus it is very slow to heal. All other connective tissues have
capillaries!
-No nerve endings in cartilage.
-Perichondrium is a dense, irregular connective tissue membrane that covers cartilage.
-Types of cartilage include: hyaline cartilage, fibrocartilage and elastic cartilage.
1) Hyaline cartilage
-Most common type of cartilage
-Structure notes: chondrocytes numerous, single or double in lacunae; ground substance clear, bluish-white because
collagen fibers in ground substance are very fine and cannot be seen.
-Locations: nose cartilage, larynx cartilage structures, rings of trachea & bronchi, ends of long bones & ribs,
embryonic & fetal skeletons are made of hyaline cartilage.
-Function: support with flexability; smooth, very tough joint articulation surfaces, matrix for embryo/fetal skeleton
ossification.
2) Fibrocartilage
-Structure notes: chondrocytes single, in lacunae; collagen fibers irregular & thick (visible)
-Locations: interverebral discs, pubic symphysis, knee menisci.
-Functions: connect bones with resilient, tough shock absorbers.
3) Elastic Cartilage
-Structural notes: chondrocytes single, in lacunae; elastin fibers irregular, threadlike & visible.
-Locations: auricle of ear (external part of ear), epiglottis.
-Function: elastic support
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D) Osseus Tissue (Bone)
-Notes: develops from ossification of hyaline cartilage of fetus.
-Cell types: osteocytes in lacunae spaces.
-Matrix fibers made of collagen protein, provide some flexibility to bone.
-Ground substance made of hydroxyapetite (calcium phosphate-calcium carbonate salts), arranged as either compact
bone (distinct, concentric rings) or spongy bone (sponge-like); provides strength.
-Locations: forms skeleton and middle-ear ossicles.
-Function of osseus tissue: 1) organ support & protection, 2) attachment for muscles so body can move, 3) calcium
storage, 4) hematopoiesis (the synthesis of blood cells in myeloid & lymphoid tissues of the red bone marrow), and
5) hearing (middle-ear ossicles).
E) Blood
-Cell types: formed elements, which include: erythrocytes (red blood cells, RBCs), leucocytes (white blood cells,
WBCs), thrombocytes (platelets).
-Matrix is plasma, a water-based liquid rich in proteins, salts, etc.
-Location: cardiovascular system.
-Function: 1. Transportation of materials throughout body. These materials include anything that needs
transportation: the formed elements, water, proteins, respiratory gases (erythrocytes), nutrients, wastes, hormones,
salts, etc. 2. Immunity—leucocytes involved in this. 3. Blood clotting (thrombocyes).
F) Lymph
-Cell types: leucocytes
-Matrix: Lymphatic fluid—like plasma but with less protein and more lipid.
-Location: lymphatic system
-Function: transports water, lipids; immunity.
MUSCLE TISSUES
General Functions of Muscle Tissues
a) Movement of body
b) Posture maintenance
c) Heat generation
Characteristics of Muscle Tissue
a) Contractile
b) Uses ATP & calcium (Ca++) for contraction
Types of Muscle Tissue
1) Skeletal Muscle
-Location: attached to bones by way of tendons; attached to each other by aponeuroses.
-Characteristics of muscle cells: 1) Very long, as long as individual muscles. 2) Cylindrical. 3) Striated. 4) Multinucleated. 5) Voluntary. 6) Quick to act, quick to tire.
-Functions: voluntary movement of body, posture maintenance, heat generation.
2) Smooth Muscle
-Location: walls of gut (esophagus, stomach, intestine), walls of hollow organs (urinary bladder, gall bladder;
myometrium of uterus), sphincters (muscular valves that regulate the flow of materials through ducts and tubes), iris
of eye, walls of arteries & veins, respiratory passages (trachea & respiratory tree).
-Characteristics of cells: 1) Tapered. 2) Not striated. 3) Uninucleate. 4) Involuntary. 5) Slow to act, slow to tire.
3) Cardiac Muscle
-Location: myocardium of heart
-Characteristics of cells: 1) Short. 2) Cylindrical & branched. 3) With intercalated discs. These are structures that
attach cardiac muscle cells end-to-end and are thickenings of the cell membrane containing lots of tight junctions
through which electrical conduction can occur during the cardiac cycle of the heart. 4) Striated. 5) Uninucleated. 6)
Involuntary. 7) Rhythmic, doesn’t tire.
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NERVE TISSUES
General Functions of Nerve Tissue
a) Conduction of nerve impulses (action potentials)
b) Secretion of neurotransmitters & some hormones.
c) Support of nervous system.
Locations of Nerve Tissue
a) Cranium (brain)
b) Vertebral canal (spinal cord)
c) Throughout body (peripheral nervous system)
Cell Types
a) Neurons
-Conduct nerve impulses (action potentials) allowing for communication between organs and the coordination &
control of the body.
-Dendrites have receptors that receive neurotransmitters, thus receive signals; dendrites can’t send signals.
-Nerve cell body is where the nucleus is found.
-Axons convey nerve impulses to axon endings.
-Axon endings have vesicles that secrete neurotransmitters, thus axon endings send signals; axon endings can’t
receive signals.
b) Neuroglia
-Don’t convey nerve impulses! Instead, neuroglia 1) facilitate nerve impulses (speed nerve impulses up), provide
nutrients for neurons, protect, support & maintain the integrity of the nervous system.
-Specific examples of neuroglia:
1) Schwann Cells: wrap around peripheral nervous system axons and act to speed up nerve impulses.
2) Ependymal Cells: Line the ventricles of the brain & central canal of the spinal cord where they secrete and
circulate cerebrospinal fluid.
3) Astrocytes: star-like neuroglia that provide nutrients to the brain.
MEMBRANES
General Characteristics of Membranes
a) Composite structures made of epithelium (usually) + connective tissue.
b) Function to line body cavities, cover surfaces and secrete fluids such as lubricants and enzymes.
Types of Membranes
a) Cutaneous Membranes
-Location: epidermis & dermis of skin
-Function: protection of the body and the secretion of sebum (anti-bacterial oil) and sweat (lubricant and used in
temperature homeostasis to regulate your temperature).
b) Mucous Membranes
-Location & characteristics: Mucous membranes line moist body cavities that open directly into the external
environment. These include 1) entire gut—mouth, pharynx, esophagus, stomach, intestines, rectum & anus, 2) entire
respiratory tract—nasal cavity, trachea, respiratory tree, 3) reproductive tracts, and 4) urinary tracts.
-Have goblet cells that secrete mucus.
-Some mucous membrane cells secrete digestive enzymes.
-The epithelium component of mucous membranes attaches, by way of its basement membrane, to the lamina
propria, an underlying areolar connective tissue layer.
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c) Serous Membranes
-Location & characteristics: Serous membranes line body cavities not directly open to the external environment.
These include 1) visceral serosa covering organs, 2) parietal serosa lining cavities. Serous membranes also cover
blood vessels as the tunica serosa. Serous membranes consist of mesothelium (simple squamous epithelium) +
areolar connective tissue.
-Functions: 1) Mesothelium secretes serous fluid into body cavities. Serous fluid is a watery lubricant. 2) Serous
membranes also serve to bind structures together and protect them.
d) Synovial Membranes
-Locations & characteristics: Synovial membranes line the synovial cavities of joints. They consist of areolar
connective tissue only and don’t have an epithelium component.
-Functions: 1) Secretion of synovial fluid into joint capsules (lubricates joints) and 2) nourishes hyaline cartilage of
articular regions of bones in joints.
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