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Tissues
-four primary tissue types:
1. Epithelial
2. Connective
3. Muscle
4. Neural
Epithelial Tissue
= lining epithelium & glands
•multiple functions of epithelial tissues:
1. protection - from dehydration, pathogens
2. synthesis – e.g. vitamin D
3. regulation - e.g. body temperature
4. excretion - e.g. waste
5. immune response
6. control of permeability – every substance must cross an
epithelial membrane first
7. sensitivity – epithelial membranes are well-innervated
• lining epithelium = line body surfaces and cavities
• glandular epithelium = secretion
Epithelial characteristics
1. Cellularity
2. Polarity
3. Attachment
1. to each other
2. to connective tissue
4. Avascularity
5. Regeneration
Epithelial characteristics
1. Cellularity: composed almost entirely of cells held together by cell junctions
-very little extracellular matrix
2. Polarity: possesses an exposed surface the faces the exterior
of the body - apical face
-also has an attached base which is anchored to other tissues -
basal face
-the organelles are not uniformly
distributed
Epithelial characteristics
3. Attachment: attached to underlying tissues via the basement membrane
-BM is produced by the basal surface of the cells
& connective tissue
-the BM is comprised of two layers
a. closest to epithelial cell = basal lamina
(glycoproteins, laminin and actin)
-acts as a barrier to transport
b. furthest from the epithelial
cell = reticular lamina
-collagen IV bundles produced
by the underlying connective
tissue cells
-provides strength
Epithelial characteristics
characteristics
Epithelial
1. Tight junctions: lipid portions of PMs are bound
together by interlocking membrane proteins
-very tight union - prevents passage of water and
solutes between the two cells
3. Attachment: also form extensive connections between each other
2. Desmosomes: comprised of
a. plaque of proteins inside the plasma membrane
-the plaque attaches to the intermediate filaments of
the cytoskeleton (keratin)
b. cellular adhesion proteins/CAMs called
cadherins
Epithelial characteristics
characteristics
Epithelial
3. Gap junctions: two cells held together
by proteins called connexons
-connexons are channel proteins
-materials can freely move between the two
cells
-passage of materials helps to coordinate
the activities of the adjacent cells
e. g beating rhythm of cilia
Epithelial characteristics
4. Avascularity: do not contain blood vessels
-must obtain nutrients via diffusion or absorption
5. Regeneration: damaged cells are replaced through differentiation of stem cells
located deep within the tissue
-rate of renewal depends on rate of cell death
-stem cells = germinative cells
-these cells are found closest to the basement membrane
-migrate towards the surface and differentiate into epithelial cells
Classification of Epithelia
• catagorizing epithelial tissue types
A. # of layers
simple = 1 layer
stratified = multiple
**pseudo = 1 layer
B. Cell shape
columnar
cuboidal
squamous
Classification of Epithelia
Simple Squamous Epithelium
-tile-like cells - cells are thin, flat and
irregular in shape = squamous
-simple squamous - most delicate tissue
in the body
-found in protected regions where
absorption occurs
-many types:
e.g. mesothelium - lines the
abdomen
e.g. endothelium - lines
heart chambers and vessels
Stratified Squamous Epithelium
-stratified squamous - where
mechanical stresses are severe
-cells on exposed surfaces may contain
keratin – a protein that reduces water
loss and provides strength =
keratinized epithelium
-non-keratinized epithelium is tough but
must be kept moist = e.g. oral mucosa
Stratified Squamous Epithelium – the Epidermis
-four types of cells:
1. keratinocytes – make up the majority of the epidermis
-epithelial cells that synthesize the protein keratin
2. melanocytes – cells for the synthesis of the light absorbing pigment melanin
3. Merkel cells – neurons that detect pressure
4. Langerhans cells – immune responses
Stratified Squamous Epithelium – the Epidermis
5 layers maximum
1.
2.
3.
4.
5.
Stratum Basale/Germinativum
Stratum Spinosum
Stratum Granulosum
Stratum Lucidum
Stratum Corneum
Epidermis: layers
-stratum basal/germinativum:
-inner most/deepest layer of the epidermis - attached firmly to the
basement membrane between epidermis & dermis underneath
- contain germinative stem cells that differentiate into the keratinocytes
and melanocytes of the epidermis
-Merkel cells are found in hairless regions- pressure and touch receptors
- stratum spinosum: several layers of keratinocytes
-keratinocytes of the stratum basale migrate into this layer
-keratinocytes are interconnected by desmosome for strength
-keratinocytes can divide to increase thickness of this layer
-melanocytes are common
-Langerhans cells of the immune system also found in the more superficial
layers
Epidermis: layers
-stratum granulosum:
-made up of keratinocytes migrating up from the stratum spinosum
-cells synthesize large quantities of proteins (including keratin) – cytoplasm
appears granular
-as more and more keratin is made – keratinocytes become thinner and flatter
-the cells then die and dehydrate
Epidermis: layers
-stratum lucidum:
-flattened, densely packed cells filled with keratin
-have a glassy appearance because they do not stain well
-present only in the skin of fingertips, palms & soles
A. stratum
corneum
C. stratum
D.
spinosum
granulosum
B. stratum
lucidum
C.
D. stratum
stratum
spinosum
granulosum
Epidermis: layers
- stratum corneum: cornu = horn
-15-30 layers of flattened, dead, interlocking cells
-if large amounts of keratin are present – the tissue is said to be “cornified”
- keratin makes this layer water-resistant - very dry to prevent growth of bacteria
-kept moist by oily secretions from sebaceous glands
-penetration is promoted by attachment to a lipid or dissolution in a lipid-based
solutions
-transdermal drug patches – drugs are in oils or lipid-soluble carriers
- moisturizing lotions – only penetrate few first layers of corneum
-takes 15-30 days to move from
germinativum to corneum
-cells will remain in corneum for an
additional 2 weeks before being shed
Transitional Epithelium
-stratified squamous epithelium that permits stretching
-located in walls of the bladder, renal pelvis and the ureters
e.g. bladder wall - when empty the epi. looks as if it has several layers
-actual number of layers can be seen upon stretching
Transitional Epithelium
Simple Cuboidal Epithelium
-cells are cubes
-big, round nucleus found in the center of the cell
-found in regions of secretion and absorption
e.g. kidney tubules
pancreas & salivary glands - buffers & enzymes
thyroid follicles - thyroid hormones
Simple Cuboidal Epithelium
Simple Columnar Epithelium
-height is greater than their width
-oval shaped nuclei found close to the BM & aligned with each other
-simple columnar: found in areas of absorption and secretion
-located in the gallbladder, larger ducts of exocrine glands, gastric pits of
stomach
-frequently the apical face is modified with microvilli
e.g. intestinal lining = brush border
-short-lived cells – replaced every 4 to 5 days
-frequently found with Goblet cells (intestine and stomach)
Simple Columnar Epithelium
microvilli
wandering lymphocytes
Pseudostratified Columnar Epithelium
-pseudostratified columnar: only a single layer despite looking like many
-nuclei are at varying levels - appearance of multiple layers
-BUT basal face of every cell contacts the BM
-exposed apical surface typically bears cilia
e.g. respiratory epithelium
Pseudostratified Columnar Epithelium
-these tissues are generally ciliated
Type:
Description:
Function:
Location:
Simple squamous
single layer, flattened cells
filtration, diffusion, osmosis
lungs, linings of blood
vessels
single layer, cube-shaped
cells
secretion, absorption
ovaries, kidneys, certain
glands
single layer, elongated
cells
protection, secretion, absorption linings of uterus, stomach
and intestines
protection, secretion, movement
of mucus
linings of respiratory
passages and reproductive
protection
outer layer of skin, oral
cavity, throat
Simple cuboidal
Simple columnar
Pseudostratified
columnar
single layer, elongated
cells
Stratified squamous
multiple layers, flattened
cells
Glandular Epithelium
• epithelial cells specialized to produce and secrete substances
•gland = single epithelial cell OR multiple cells
•two types of glands: 1) exocrine = secrete into ducts
e.g. sweat glands
2) endocrine = secrete directly into bloodstream
e.g. thyroid, pituitary
** one gland is mixed - e.g. pancreas
•exocrine gland structure:
• Unicellular: single-celled glands
e.g. goblet cells
SIMPLE COLUMNAR with GOBLET CELLS
-goblet cells = unicellular exocrine glands that secrete mucus
•exocrine gland structure:
•Multicellular glands – multiple cells grouped together
•multicellular glands can be classified based on:
•1. Mode of secretion – used by physiologists
•Merocrine
•Apocrine
•Holocrine
•2. Consistency of secretion – used by histologists
•Serous
•Mucus
•Mixed
•3. Structure – used by histologists
•shape of the secretory portion
•branching pattern of the duct
• simplest multi-cellular gland is a secretory sheet
•e.g. gastric epithelium
Serous Glands
1. serous - watery fluid that contains
enzymes
e.g. saliva – parotid salivary gland
Mucus Glands
2. mucous - glycoproteins called mucins that absorb water to form a
slippery mucus
Mixed Glands
3. mixed - more than one type of gland cell
-produces different types of secretions - mucus and serous
e.g. submandibular or sublingual salivary gland
Connective Tissue
• provides support
• binds structures together
• fills cavities
• produces blood
• protects organs
Connective Tissue
•components: matrix + cells
-matrix: non-cellular support material
-comprised of extracellular protein fibers – mainly collagens
e.g. 1. collagen fibers (white) – collagen type I
2. elastic fibers (yellow)
3. reticular fibers – collagen type III
4. fibronectin
-plus a ground substance = water + hyaluronan (sugar),
proteoglycans and glycoproteins
-cells: secrete the matrix
-some have become very specialized and make a very
specialized matrix
The way I organize Connective
tissues
•
•
•
•
Loose – areolar CT, adipose & reticular
Dense – dense (regular, irregular), elastic
Supportive – bone & cartilage
Fluid – blood
Types:
1. Areolar
2. Dense –
regular and
irregular
3. Adipose
4. Cartilage
5. Bone
6. Blood
Type:
Description:
Function:
Areolar
Cells in fluid-gel matrix
Adipose
Cells in fluid-gel matrix
Dense
Cells in fluid-gel matrix
Binds organs together,
holds tissues, fluids
Protects, insulates and
stores
Binds organs together
Cartilage
Cells in solid-gel matrix
Bone
Cells in solid matrix
Blood
Cells in fluid matrix
Supports, protects,
provides framework
Supports, protects,
provides framework
Transports gases, defends
against disease, clotting
Loose connective tissues: Loose Areolar tissue
-cells are mainly fibroblasts, spaced far apart
-matrix: mostly ground substance + collagen fibers, elastic fibers
-cushions and can be distorted due to loose organization
e.g. found beneath the dermis connecting it to muscle and bone
Loose connective tissues: Adipose tissue
-cells = adipocytes (fat storing fibroblasts)
-cushions joints and organs
-stores energy
-insulates
-often found intermixed with areolar tissue
Dense connective tissues: types
-most of the tissue is densely packed extracellular matrix fibers of collagen type I
-cells are fibroblasts
-often called fibrous tissue
-two types: 1) dense regular – dense & elastic in nature
e.g. tendons, ligaments
2) dense irregular - interwoven meshwork or fibers
-e.g. dermis of skin, perichondrium of joints
and periosteum of bone
Dense connective tissues: Dense Regular Connective
-few fibroblasts
- multiple, closely packed collagen I fibers
- fine network of elastic fibers
e.g. tendons, ligaments
Dense connective tissues: Dense Irregular Connective
• found in the deepest layers of
the dermis = also called the
reticular layer (don’t
confuse it with reticular
tissue)
Connective Tissue: The Dermis
-two major components:
1. papillary layer
2. reticular layer
Papillary Layer
-about 1/5th thickness of dermis
-loose areolar connective tissue
-well vascularized and innervated
-dermal projections into the epidermis
= dermal papillae
-some papillae contain Meissner’s corpuscles
for touch
-also free nerve endings – project into the
epidermis - sensations of pain, warmth, itching
Reticular Layer (“little net”)
-dense irregular connective – interwoven
collagen bundles plus elastic fibers
-contains blood vessels, nerves,
hair follicles, sweat glands and
sebaceous/oil glands
-also contains lamellated corpuscles
(Pacinian corpuscles) that detect deep
touch and pressure
Connective Tissue: The
Subcutaneous layer
-also referred to as the
hypodermis or superficial fascia
-connects the skin to underlying muscles
or other organs
-made up of:
1. loose connective tissue
2. adipose tissue - “baby fat”
-also contains elastic fibers for flexibility
-fat content helps reduce heat loss
-fat distribution changes with age and gender:
-males – neck, upper arms,
abdomen and lower back
-females – breasts, abdomen,
buttocks, hips and thighs
-contains large arteries and veins – blood supply helps give skin its color
-the superficial layers of the hypodermis are the sites for drug injections – hypodermic
injections
Supportive Connective tissues: Bone & Cartilage
-cartilage & bone
-see your lecture on the skeletal system
Fluid Connective tissue: Blood
-cells suspended in a fluid matrix = plasma
-plasma ~ 55% blood volume
-inorganic salts
-organic substances - e.g. sugars, proteins
-cells: 1) RBCs - biconcave, disc-shaped
-contains hemoglobin - 4 globin proteins
+ heme group (iron)
2) WBCs - fight infection
= leukocytes
- many types: a. monocytes/macrophages
b. lymphocytes - T and B cells
c. basophils - histamine
d. neutrophils - 1st at infection
e. eosinophils - allergic response
3) platelets - blood clotting response
Membranes
-superficial epithelial
sheet + underlying
connective layer
(called a lamina
propria)
-cover & protect
-four types:
1. serous
2. mucous
3. cutaneous
4. synovial
1. Serous membranes
-line the subdivisions of the abdominopelvic cavity and thoracic cavity
-covers, protects and moistens/lubricates
-comprised of an epithelial layer (simple squamous epithelium) called a
mesothelium + underlying loose areolar connective tissue
-the mesothelium secretes a watery fluid = serous fluid (separates and
lubricates the movement of organs)
-divided into two separate layers: 1)outer parietal layer - lines the cavity
2) inner visceral layer - covers organs
-serous membrane lining the pleural cavity (lungs) = pleura
- serous membrane lining the pericardial cavity (heart) = pericardium
- serous membrane lining the peritoneal cavity (abdomen) = peritoneum
2. Mucous membranes
-line cavities that directly communicate with the exterior environment
e.g. respiratory, urinary, reproductive, digestive
-covers, protects and moistens/lubricates
-epithelial layer (simple squamous, simple cuboidal, simple columnar) is
kept moist through production of mucus by glands, other glandular
secretions or exposure to fluids (e.g. urine)
-in areas of physical stress = stratified epithelial tissue rather than simple
-connective tissue layer is loose areolar tissue = lamina propria
--supports embedded blood vessels and nerves
3. Synovial membranes
-lines & lubricates the synovial joint cavity - to permit easy movement of
bones over each other
-bones are covered by incomplete layers of simple squamous or cuboidal
epithelial cells
-some cells within the synovial membrane are phagocytic to remove
pathogens
-others are secretory - secrete a watery synovial fluid for lubrication
4. Cutaneous membrane (skin)
-covers the surface of the body
-22 sq. ft or 16% of body weight
-epithelial layer is keratinized stratified squamous = epidermis
-underlying tissue is areolar tissue reinforced with dense connective tissue = dermis
-skin is attached to underlying muscle and bone by areolar tissue + adipose
-skin turns in at the mouth, nasal cavity, anus and urethral and vaginal openings – meets
the mucous membranes lining these cavities
1. physical protection: protection from microbes, abrasion, heat
2. chemical protection – keratin - dryness of the epidermis; salt of sweat
3. regulation of water exchange: by sweating
4. regulation of body temperature: thermoregulation
-by sweating & adjusting blood flow through the dermis
5. excretion of wastes -by sweating
6. nutrition – synthesis of vitamin D precursor
-activated in skin, converted to calcitrol in liver
7. sensation: touch, pressure, vibration, pain & thermal
8. immune defense: Langerhans cells of the epidermis
Muscular Tissue
•specialized for contraction
•very distinct organelles within the cells
•3 types
•1. skeletal – voluntary muscle
•2. cardiac – involuntary muscle
•3. smooth – involuntary muscle
Skeletal Muscle: voluntary muscle
-voluntary nervous control
-repeating banding patterns of actin & myosin = striated appearance
-mature cells = multi-nucleated cells – made from fusion of myoblasts
-cells are very long – sometimes called muscle fibers
-cannot divide – but new cells form from differentiation of myogenic stem cells =
satellite cells
-attached to bones via tendons
Cardiac Muscle: involuntary muscle
-cells are striated but uni-nuclear = cardiomyocytes
-incapable of dividing – PLUS there are no satellite cells
-therefore damaged heart muscle cannot be regenerated
-identified by the presence of intercalated discs
-for cell-cell communication and force transmission
Smooth Muscle: involuntary muscle
-lines blood vessels, airways and organs
-non-striated
-spindle shaped cells - single nucleus (uni-nuclear)
-control their own rate of contraction through
action of pacemaker cells
-BUT nervous system can also control
contraction
-slow, sustained & strong contraction
Neural Tissue (Nervous Tissue)
•specialized for the conduction of electrical impulses from one body
region to another
•two types of neural cells: 1) neurons
2) glial cells – astrocytes, oligodendrocytes,
microglia