Epithelium Lab

STUDY – FOCUSING QUESTIONS: 1. Compare and contrast the following by tabulating the following information: a. Simple, stratified and specialized types of epithelia in terms of : their distinguishing features, location, function. Type of Epithelium

Distinguishing Features

Location - Endothelium: lines walls of blood and lymph vessels and cavities of the heart.

1) Simple Squamous

2) Simple Columnar

3) Stratified Squamos

> Consists of thin platelike cells arranged in a single layer. > Cells adhere closely to one another by their edges, which may be serrated or wavy.

> Consists of very tall and slender cells, which may appear like standing uprightlike columns > All oval nuclei approximately at the same level. > Ciliated columnar cells have projections known as cilia on their distal ends.

> Composed of more than 1 layer of cells, ranging from 5-30 or more. > Innermost layer of cells next to the basement membrane consist of a single row of tall columnar cells; above the columnar layer lie polyhedral cells; the superficial layers are

- Mesothelium: lines serous cavities (pleura, pericardium, peritoneum); tunica vaginalis; testis.

Function

- reduce friction between the blood and the walls of the blood vessels.

- Mesenchymal: lines the anterior chamber of the eye; perilymph spaces of the internal ear; subdural and subarachnoid spaces. - Flattened Cells: lines the pulmonary alveoli and kidney’s Bowman’s capsule. - Plain Tall Columnar: mucosa of the stomach; small and large intestines; gall bladder; bigger ducts of glands. - Ciliated Columnar: uterus and oviducts/ fallopian tubes; ductuli efferentes in patches. - Cuboidal: thyroid follicles; choroid plexus; pigmented epithelium of retina; smaller ducts of glands; germinal ephithelium of ovary; inner surface of lens capsule. - Keratinizing: Epidermis of skin. - Non-Keratinizing: mouth, esophagus, vagina, anal canal, vocal folds.

- Secrete mucus or slime, a lubricating substance to keep the surface smooth. - propel ovum to the uterus; cilia movement causes mucus, secreted by the goblet cells, to move towards target organ.

- Protect underlying tissue from mechanical injury, harmful chemicals, invading bacteria, and from excessive loss of water.

composed of thin squamos cells. > Gradual transition in shape from polyhedral to the flat shape

4) Pseudo-stratified Columnar Epithelium

> Only appears to be composed of several layers of cell, when there is only 1 cell layer. > All cells rest on the basement membrane.

- With motile cilia: nasal cavities, larynx, trachea, bronchi, bigger bronchioles, oviducts. -With motile cilia and goblet cells: respiratory system - With non-motile cilia or stereocilia: epididymis

- assists in removing dust particles and foreign bodies which have entered the passageways. - promotes the diffusion of gases, liquids, and nutrients.

- Non-ciliated epithelium: ductus deferens

5) Stratified Columnar Epithelium

6) Transitional Epithelium

7) Neuro-eptihelium

> Superficial cells are prismatic and cuboidal or columnar in shape, while the deeper layer consists of small irregularly polyhedral cells that do not reach the surface. > A transition form between stratified squamos and columnar epithelium. > When bladder is empty, surface cells are cuboidal in shape. When bladder is full, surface cells stretch and flatten to become squamos epithelium. > Composed of a chief sensory cell (for reception of stimulus) and supporting or sustantecular cells. > Supporting cells maybe tall columnar cells lying side by side with the chief cells, or basal cells.

- formices of the conjuctiva, vagina, middle portion of the urethra, big ducts before their opening on the skin.

- lines the ureter, urinary bladder, and urethra.

- Excrete waste products from the body and reabsorbs needed materials from the urine.

- tastebuds of tongue, organ of Corti in inner ear, retina of eyeball, olfactory epithelium of nasal cavity.

- Sensation

8) Pigment Epithelium

> Consist of a twocell thick layer of cuboidal cells. > Both layers are jet black due to the numerous large melanosomes which pack the cytoplasm of each cell.

- retina, pars ciliaris, pars iridica, retinae of eye

9) Pyramidal or glandualar epithelium

> Cells are pyramidal in shape > Cells are arranged

- lining secretory portions of the acini of glands

- Helps to optimixe visual contrast by reducing internal reflected light. - Has the ability to metabolise retinol and to engulf photoreceptor outer segments. - secrete specific substances such as enzymes,

10) Myoepithelial cells

in a single row around a circular lumen of varying size, where the proximal portion is broader and attached to the basement membrane while the distal end borders the lumen of the cavity. > Contractile epithelial cells > Located between the basal lamina and the bases of secretory acini and their ducts

hormones, and lubricating fluids.

- Lacrimal, salivary, mammary, and sweat glands, seminiferous tubules.

- contraction helps expel products of exocrine glands

b) Exocrine, endocrine, and neuro-endocrine glands on the basis of: transport of secretions, structure/ cell number, embryonic origin, secretory products, mode of secretion, location.

Transport of Secretions

Structure/ Cell Number

Exocrine Gland

Endocrine Gland

Utilize a system of ducts that open into the surface

Secretions are released into blood or lymph for transport to target tissues.

Maybe unicellular or multicellular

Embryonic Origin

Secretory Products

Mode of Secretion

Location

Neuro-endocrine Gland Released into the blood in response to stimulation of the nervous system.

Multicellular glands

Multicellualr

Endoderm

Mesoderm

Mucous secretions, Serous secretions, and a mixture of mucous and serum. Merocrine, apocrine or holocrine secretion Pancreas, simple columnar epithelium of small and large intestines, stratified columnar epithelium of respiratory system, oral cavity, esophagus, duodenum, gastric and uterine mucosa, sweat glands.

Ectoderm

Polypeptide secretions (insuline, glucagons, growth hormone, TSH, GTH, ACTH, thyroglobulin)

Enteroendocrine hormones, Interleukins, Colony-stimulating factors (CSF).

Steroid secretions (ovary, testis, adrenals) Directly into the bloodstream

Pituitary gland, thyroid gland, thymus gland, adrenals

Brain, epithelia of intestinal and respiratory tracts.

c) Microvilli, stereocilia, cilia and flagella in terms of: their width and length, presence of plasma membrane covering, presence of microtubules or microfilaments, motility, presence of axonemes and basal bodies, function, location.

Width/ Length Presence of plasma membrane covering Presence of

Microvilli 80 – 90 nm in diameter and 1-2 µm long.

Stereociia

Cilia

Flagella 15-200 µm long

Yes Yes Yes. Parallel

Yes Yes

Presence of

Yes

microtubules/ microfilaments

bundles of actin microfilaments are present in cytoplasm.

microtubules (which make up axoneme)

Presence of axonemes and basal bodies

Axoneme and basal bodies are present. Moves with the help of ATPdependent and dynein-generated sliding of doublet microtubules.

Motility

Non-contractile

Non- motile

Function

For support; to enhance the surface area of membranes exposed to substances for absorption and digestion.

Absorptive epithelium may promote absorption by amplifying the cell surface.

To propel fluid or a coating of mucus towards the exterior.

Epithelium lining of the epididymis and hair cells of inner ear.

Lining of fallopian tubes, ductuli efferentes, respiratory system (nasal cavities, larynx, trachea, bronchi, bigger bronchioles, oviducts)

Location

Spermatozoon, epithelia of nephrons, rete testis, nonciliated cells of the uterine ephithelium, ducts of glands.

d) Merocrine, holocrine, and apocrine modes of secretion in terms of: portion of the cell that is released, example of gland. Merocrine Holocrine Apocrine Portion of the cell A portion of the apical Release of product Cytoplasm is released cytoplasm, containing along with cell discharged into the secretory granules, is membrane glandular excretory duct pinched off Example Pituitary gland, Spermatozoa, Mammary glands pancreas sebaceous glands e) Neurocrine, paracrine, and endocrine cells in terms of: distances their products must travel to reach their targets, example of gland. Neurocrine Paracrine Endocrine Distances products Released by neurons Secreted by one cell Secreted directly into must travel into the blood for action and diffuse to adjacent the bloodstream at distant targets cells Example Epinephrine released by histamine released by Insulin from pancreatic adrenal medulla injured cells causes beta cells local capillary walls to become more permeable, allowing more white blood cells and fluid to leak into injured area.

f) Serous and mucous cells in terms of: appearance and secretory products. Serous Cells Mucous Cells Appearance Smaller, darker staining and Occur as unicellular sheet or more basophilic than mucous solid glands; light staining, foamy cells appearance caused by the numerous large mucuscontaining vesicles concentrated near the cell apex.

Pancreatic enzymes, Parotid gland secretions

Secretory Products

Goblet cell secretions, sublingual salivary gland secretions.

2. List the structural and functional characteristics of epithelial tissues that distinguish them from other tissue types. Consider the following: a. Cell polarity Polarity is characteristic of most epithelial cells. It is best seen in simple epithelia, where each cell has three types of surfaces: an apical (Free) surface, lateral surfaces that adjoin neighboring cells, and a basal surface attached to the basal lamina. b. Specializations of apical, lateral and basal surfaces The cell's apical surface is on the organ's external or internal (lumen) surface. It is specialized to carry out functions that occur at these interfaces, including secretion, absorption, and movement of luminal contents. Such modifications include cilia, flagella, microvilli, and stereocilia. Epithelial cells attach tightly to one another by specialized intercellular junctions. Zonulae are bandlike junctions are similar in shape to maculae but differ in composition and function. A junctional complex is any combination of ntercellular junctions close to the cell apex that looks dark in the light microscope. The basal surface contacts the basal lamina. Because it is the surface closest to the underlying blood supply, it often contains receptors for blood borne factors such as hormones. such structures include basal lamina and tunica propia. c.

Nutrition

d. Innervation e. Mitotic Rate f.

Vascularity Blood vessels in the subjacent connective tissue rarely penetrate the basal lamina to invade epithelia.

3. Which intercellular junction(s) is/are associated with the following? a. a disklike structure Gap junction- A gap junction (nexus) is a disk- or patch-shaped structure, best appreciated by viewing both freeze-fracture and transverse thin EM sections. b. a bandlike structure Zonulae - Zonulae are bandlike junctions are similar in shape to maculae but differ in composition and function. c.

areas of fusion of outer leaflets of the plasma membrane of adjacent cells Zonula occludens - Zonula occludend (tight junctions, occluding junctions) are located near the cell apex and seal off the intercellular space, allowing the epithelium to isolate certain body compartments. Their structure results from the fusion of 2 trilaminar plasma membranes of adjacent cells to form a pentalaminar; this fusion may require specific "tight-junction proteins."

d. a sealing effect are allowing the

Zonula occludens - Zonula occludens (tight junctions, occluding junctions) located near the cell apex and seal off the intercellular space, epithelium to isolate certain body compartments.

e. cell-to-cell communication Gap junction- As sites of electrotonic coupling (reduced resistance to ion flow), gap junctions are important in intercellular communication and coordination. They are found in most tissues. f.

cytokeratin

Macula adherens - A macula adherens, or desmosome, consists of 2 dense, granular attachment plaques composed of several proteins and borne on the cytoplasmic surfaces of the opposing cell membranes. Cytokeratin intermediate filaments insert into the plaques or make hairpin turns and return to the cytoplasm. The gap between the attached membranes is often over 30 nm. g. dense attachment plaques Macula adherens - A macula adherens, or desmosome, consists of 2 dense, granular attachment plaques composed of several proteins and borne on the cytoplasmic surfaces of the opposing cell membranes. h. connexons Nexus or Gap junction- The intercellular gap is 2 nm, and the membrane on each side contains a circular patch of connexons, Each connexon Is a protein hexamer with a central 1.5-nm hydrophilic pore. The connexons in one mem brane link with those in the other to form continuouspores that bridge the intercellular gap, allowing passage of ions and small molecules (<800 daltons). 4. Name the structural modifications and staining properties of epithelial cell types specialized for the following and give examples of each type: a. transport of ions and water Structural modifications: Ion-transporting cells typically have highly infolded basal plasma membranes that interdigitate with numerous mitochondria. Sheets of such cells form active barriers that control ion and water concentrations in body compartments. Tight junctions are often found between the cells and appear to restrict backflow. Epithelial cells specialized for pinocytosis have tight junctions and abundant pinocytotic vesicles. The vesicles transport substances across the cell from the luminal surface to the basal surface or vice versa. The best example is the endothelial cells lining the blood vessels, where transcellular transport is rapid. b. synthesis and secretion of proteins Structural modifications: Epithelial cells that synthesize proteins from segregation and secretion have abundant basophilic RER, a well-developed Golgi complex, and frequently, an accumulation of secretory granules in the cell apex. Examples: Pancreatic acinar cells and the chief cells of the stomach, liver hepatocytes, chief cells of the parathyroid gland c.

synthesis and secretion of mucus Structural modifications: Mucous cells occur as unicellular or solid glands. Staining properties: PAS-positive staining from an abundance of oligosaccharide resi dues, predominantly acidophilic staining with H&E Lining epithelium of the esophagus, mouth and vagina

d. synthesis and secretion of steroids Structural modifications: Endocrine cells specialized to secrete steroid hormones are polygo nal or rounded, with a central nucleus and pale-staining, acidophilic cytoplasm that often contains numerous lipid droplets. Their abundant SER contains enzymes for cholesterol synthesis and for converting steroid hormone precursors (eg, progesterone) into specific hormones leg, androgens, estrogens, and progesterone). Their mitochondria typically have tubular rather than shelflike cristae and contain enzymes that convert cholesterol to progesterone. Examples: interstitial cells of the testes, follicle cells of the ovaries, granulosa lutein cells of the corpus iuteum, and cells of the adrenal cortex