Mcp Lect 23: Epithelium And Glands

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Four basic tissue types:

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1. Epithelium
2. Connective
3. Muscle
4. Nervous

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Origin of epithelia:

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ectoderm, mesoderm, or endoderm

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Function of epithelia

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-primary function is to provide a boundary layer through which movement of substances can be regulated
-covers or lines all body surfaces, except for the join cavities
-Lines all passages that connect directly or indirectly to the exterior of the body
-Diverse functions including protection, absorption and secretion

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Maintainence of epithelia

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-Epithelia self renew!!
Intestine: 2-3 days
Epidermis: 28 days

-Contain STEM CELLS, pluripotent cells with the capacity to divide asymmetrically, producing copies of itself and more differentiated daughter cells

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Morphological characteristics of epithelia:

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1. Continuous sheets, solid organs, or glands held together by specialized junction with little to no intercellular material (*closely apposed)
-Junctions include: zonula occludens (barrier); zonula adherens (intermediate junctions -- adhesion), desmosomes (adhesions), and gap junctions (communication)

2. Avascular
-All nutrients must pass from blood vessels through underlying connective tissue, or lamina propria

3. Basal surface sits on basal lamina

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Basal lamina -- general description and FUNCTION

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-The basal surface of epithelial cells sits on the basal lamina
-The basal lamina is an extracellular structure that underlies epithelial and is visible only by EM (20-100 nm thick)
-proteins that make up the include type IV collagen, laminin, entactin, and proteoglycans. They are secreted by epithelial cells
-basement membrane is a light microscopic term for the periodic acid-schiff (PAS)-positive layer laminae: in most cases, it refers to the fused basal lamina and reticular lamina, the latter of which contains type III collagen secreted by connective tissue cells
-basal laminae attach to the reticular lamina via anchoring fibrils

FUNCTION:
1. Structural support
2. Filter for molecules and cells
3. Required for cells to maintain polarity; organize membranes

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Proteins making up the basal lamina

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-secreted by epithelial cells
-include type IV collagen, laminin, entactin, and proteoglycans

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T/F: Epithelial cells are polarized.

Explain and describe.

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True! Epithelial cells ARE polarized!

-they have apical and basolateral surfaces
-apical surface can be absorptive, containing numerous extensions of the plasma membrane (microvilli) to increase absorptive capactiy
-basolateral surface functions:
1. receive signals from chemical messengers (eg. hormones)
2. ATP-dependent Na+ export/K+ import (Na/K aTPase); histologically see highly infolded basal plasma membrane with LOTS of mitochondria

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Name the modifications on the apical plasma membrane of epithelial cells

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1. Microvilli
-1 um high, 0.08 um diameter
-actin filaments support microvilli
-can be anchored in terminal web
-microvillus brush border (striated border) found in small intestines, proximal renal tubule
-microvilli + glycocalyx = BRUSH BORDER

2. Stereocilia
-misnomer -- NOT cilia, they are not motile
-elongated, sometimes branching microvilli
-increase surface area and facilitate absorption
-found in the epididymis, ductus deferens, choclea of inner ear

3. Cilia
-5-10 um high, 0.2 um diameter
-motile; control fluid and particulate flow
-found in trachea, bronchi, oviduct
-contain microtubules arranged in 9+2 pattern (9 doublets surrounding 2 singlets)
-contain dynein arms with ATPase activity; energy from ATP allows motion
-cilia anchored into basal bodies, which are also composed of microtubules, but in a 9+0 (9 triplets) arrangement analogous to centrioles. Visible as electron dense structures just below the membrane

4. Flagella
-essentially a long cilium
-one per cell
-only on spermatozoa

5. Microplicae
-small ridge-like elevations of plasma membrane
-may help to hold layer of protective mucin
-found on "wet" epithelia such as in oral cavity and esophagus

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Brush border

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-microvilli + glycocalyx = BRUSH BORDER

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Microvilli

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Microvilli
-1 um high, 0.08 um diameter
-actin filaments support microvilli
-can be anchored in terminal web
-microvillus brush border (striated border) found in small intestines, proximal renal tubule
-microvilli + glycocalyx = BRUSH BORDER

Front 12

Stereocilia

Back 12

Stereocilia
-misnomer -- NOT cilia, they are not motile
-elongated, sometimes branching microvilli
-increase surface area and facilitate absorption
-found in the epididymis, ductus deferens, choclea of inner ear

Front 13

Cilia

Back 13

Cilia
-5-10 um high, 0.2 um diameter
-motile; control fluid and particulate flow
-found in trachea, bronchi, oviduct
-contain microtubules arranged in 9+2 pattern (9 doublets surrounding 2 singlets)
-contain dynein arms with ATPase activity; energy from ATP allows motion
-cilia anchored into basal bodies, which are also composed of microtubules, but in a 9+0 (9 triplets) arrangement analogous to centrioles. Visible as electron dense structures just below the membrane

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Flagella

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Flagella
-essentially a long cilium
-one per cell
-only on spermatozoa

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Microplicae

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Microplicae
-small ridge-like elevations of plasma membrane
-may help to hold layer of protective mucin
-found on "wet" epithelia such as in oral cavity and esophagus

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Microvilli

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Microvilli
-1 um high, 0.08 um diameter
-actin filaments support microvilli
-can be anchored in terminal web
-microvillus brush border (striated border) found in small intestines, proximal renal tubule
-microvilli + glycocalyx = BRUSH BORDER

Front 17

Stereocilia

Back 17

Stereocilia
-misnomer -- NOT cilia, they are not motile
-elongated, sometimes branching microvilli
-increase surface area and facilitate absorption
-found in the epididymis, ductus deferens, choclea of inner ear

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Cilia

Back 18

Cilia
-5-10 um high, 0.2 um diameter
-motile; control fluid and particulate flow
-found in trachea, bronchi, oviduct
-contain microtubules arranged in 9+2 pattern (9 doublets surrounding 2 singlets)
-contain dynein arms with ATPase activity; energy from ATP allows motion
-cilia anchored into basal bodies, which are also composed of microtubules, but in a 9+0 (9 triplets) arrangement analogous to centrioles. Visible as electron dense structures just below the membrane

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Flagella

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Flagella
-essentially a long cilium
-one per cell
-only on spermatozoa

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Microplicae

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Microplicae
-small ridge-like elevations of plasma membrane
-may help to hold layer of protective mucin
-found on "wet" epithelia such as in oral cavity and esophagus

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How do you classify covering epithelia?

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Based on number of cell layers as well as cell shape in the mot superficial layer

Number of cell layers:
A. Simple
-one cell layer; all cells touch basal lamina/basement membrane
B. Stratified
-multiple cell layers, not all of which touch basal lamina/basement membrane
C. Psuedostratified
-cells are different heights and nuclei are at different levels, so epithelium appears multilayered. However, there is just a single layer of cells: all cells touch basal lamina/basement membrane. Some cells may not reach the surface of the epithelium

Cell shape:
A. Squamous:
-flattened, scale-like. So flat that nucleus bulges from cell, cytoplasm difficult or impossible to distinguish at LM level. Function in diffusion, filtration
B. Cubodial:
-cells are cube shaped, or as wide as they are all. Nucleus round and centrally located. Function in lining passageways, secretion, absorption
C. Columnar:
-Cells are rectangular, or taller than they are wide. Nuclei ovoid, centrally or basally located. Function in secretion and absorption.
D. Transitional:
-surface layer of cells dome shaped, occasionally binucleate. Unique epithelium suited to stretching. Number of cell layers varies, depending on distension of organ. Has DOME shaped top !

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Example of simple/stratified/psuedostratified squamous epithelia:

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simple:
endothelium
mesothelium
Endothelium, mesothelium, panetal layer of Bowman’s capsule, thin segment of loop of Henle, rete testis, pulmonary alveoli.

stratified:
skin (keratinized);
mouth
esophagus
vagina (nonkeratinized)

psuedostratified:
none

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Example of simple/stratified/psuedostratified cubodial epithelia:

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simple:
thyroid
ovary surface
Thyroid, choroid plexus, ducts of many glands, inner surface of the capsule of the lens, covering surface of ovary.


Stratified:
sweat gland ducts

psuedostratified:
none

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Example of simple/stratified/psuedostratified columna epithelia:

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simple:
stomach
intestines
uterus

stratified:
conjunctiva

psuedostratified:
trachea
bronchus
epididymis

Large excretory ducts of glands, portions of male urethra

Epididymis
Trachea, bronchi
Eustachian tube
Portions of tympanic cavity

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Example of simple/stratified/psuedostratified transitional:

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simple:
none

stratified:
ureter
bladder
urethra

*Urinary system: renal calyces to urethra
Seminiferous tubules of adult testis

psuedostratified:
none

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Stratified squamous epithelium
-cells flattened on the surface, but thicker in deep layers
-tough endothelium that can resist wear and tear and protect underlying tissues
-deep (basal) cells continuously dividing; this pushes older cells upward through the strata and cells are eventually sloughed off
-keratinized stratified squamous epithelia of skin: sufrace layer is dead; cells lose all organelles including nucleus, and become a bundle of keratin before being sloughed
-nonkeratinized stratified squamous epithelia cover wet surfaces, such as oral cavity, esophagus, vagina. Superficial layer is alive.

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1 cell layer thick, shaped like cubes, nuclei are roundish

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bumps = nuclei in the simple squamous

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cells are more or less shaped in hexagonal or pentagonal ways

oblong nuclei

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surface cedlls DOMED shape, some are binucleated (another characteristic of transitional epithelium)depending on degree of extension, can be thicker or thinner. 10 layers thick to 4-6 layers thick as the tissue stretches

**bladder!!!

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Glandular epithelia

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this type of epithelium is comprised of groups of cells whose specialized function is secretion. The secretory cells of the gland are referred to as the PARENCHYMA. The connective tissue within the gland, which supports the secretory cells, is called the STROMA.

may be unicellula (eg. goblet cells within the small intestines and respiratory tract) or multicellular (classical glands, eg. salivary glands, pancrease)

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Parenchyma

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The secretory cells of the gland (glandular epithelia) are referred to as the PARENCHYMA.

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Stroma

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The connective tissue within the gland (glanduar epithelia), which supports the secretory cells, is called the STROMA.

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Two main types of glandular epithelia:

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1. Endocrine
– secrete product directly into blood
-closely appose capillaries and take one of two forms:
a.secretory cells arranged in cords (eg. pacreatic islets)
b. secretory cells arranged in follicles or hollow balls in which secretory product is stored (eg. thyroid)
eg. pancreatic islets, thyroid

2. Exocrine
-- possess ducts that convey the secretory product to the surface of the body or into the cavity of a hollow organ ie. outside the covering epithelium
eg. sweat glands, salivary glands, sebaceious glands

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Methods of secretion of glandular epithelia

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1. Merocrine:
-secretory granules extruded by exocytosis with no loss of cellular material
eg. parotid salivary gland, pancreas

2. Holocrine
-secretory extruded along with entire cell contents
eg. sebaceous gland

3. Apocrine:
-secretion discharged with small amount of apical cytoplasm
eg. mammary gland

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How do you classify the types of exocrine glands?

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3 ways:
1. ductal structure
A.simple: single unbranched duct
B. Compound: duct ramifies, branches repeatedly

2. secretory unit structure
A. Tubular (simple or compound)
B. Coiled tubular (simple only)
C. Branched tubular (simple only)
D. Acinar (aka alveolar; simple or compound)
E. Tubuloacinar (compound only)

3. type of secretion
A. Serous: water secretion contains low level of hydrophilic carbohydrates
eg. pancreatic acinar cells, parotid salivary gland. Histologically, nucleus is round; abundance of basal RER; apical secretory granules
B. Mucous: viscous secretion contains high level of hydrophilic carbohydrates (mucins);
eg. goblet cells of intestines. Histologically, nucleus flattened and basal; cytoplasm is light-staining and appears foamy
C. Mixed: both serous and mucus cells
eg. sublingual and submandibular salivary glands

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Stratified cubodial epithelium

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-rare; usually just two layers
-lines ducts of sweat glands

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Stratified columnar

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-rare
-deep cells are cubodial or polyhedral
eg. salivary gland duct

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Serous secretion

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A. Serous: water secretion contains low level of hydrophilic carbohydrates
eg. pancreatic acinar cells, parotid salivary gland. Histologically, nucleus is round; abundance of basal RER; apical secretory granules

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Mucus secretion

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B. Mucous: viscous secretion contains high level of hydrophilic carbohydrates (mucins);
eg. goblet cells of intestines. Histologically, nucleus flattened and basal; cytoplasm is light-staining and appears foamy

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Mixed secretion

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C. Mixed: both serous and mucus cells
eg. sublingual and submandibular salivary glands

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Secretory product can be serous (liquidy) or thicker mucousserous v. mucous have unique histological characteristicsmuscous secreting glands. Products more often that not product is extracted from cell, nothing left to stain. Usually kind of flattened nuclei vserous component – product is usually retained during histological processing. Picks up a lot of stain. Nuclei rounded can have both types in same gland. Eg. salivarywhen this happens serous can cap mucous regions – called SEROUS DEMILUNE (looks like half moon)serious units appear in grape like clusters acinear mucuous more tube structure

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**Be sure to review the junctions from Rosen's lecture **

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But seriously.

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**ABSOLUTELY POSITIVELY MUST GO THROUGH PPT 23 AND STUDY THE IMAGES. MUST MUST MUST DON'T IGNORE THIS CARD.**

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**ABSOLUTELY POSITIVELY MUST GO THROUGH PPT 23 AND STUDY THE IMAGES. MUST MUST MUST DON'T IGNORE THIS CARD.**

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How often would you expect to see twins, triplets, quads, and quints?

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Some general facts
1 in ~90 births
Triplets 1 in ~902
Quads 1 in ~903
Quints 1 in ~904
IVF increase these estimates due to exogenous gonadotropins

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The decidua secretes proteins such as __ to maintain the implanted embryo.

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Prolactin


(fyi: decidua = endometrium of preggers uterus)

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