histology: epithelium & glands

lecture 2

three types of epithelia:

1. simple

2. stratified

3. pseudostratified

and they can be:

• squamous

• cuboidal

• columnar

• cuboidal

• transitional

• pseudostraified

• keratinized

types of glands

1. unicellular

2. multicellular

3. simple

4. compound

5. exocrine

6. endocrine

types of secretions

serous and mucous

mechanisms of secretion

1. merocrine

2. apocrine

3. holocrine

characteristics of epithelia

• form continuous sheet lining all free surfaces

• one cell thick of multilayered

• polarized: free apical surface vs basal surface attached to basal lamina

• express keratin intermediate filaments

• avascular

• lining or glandular

external surface is

ectoderm-derived eg: epidermis

internal surface is

endoderm derived eg: GI, respiratory tract

internal surface is

mesoderm derived (mesothelium) eg: pericardial cavity

epithelial functions

1. protection: water proofing, insulation, stomach lining)

2. surface transport (cilia movement respiratory up; oviduct cilia move the ovum)

3. absorption (intestinal epithelium in microvilli and kidney tubules absorb nutrients)

4. secretion (unicellular and multicellular glands)

5. trans-epithelial transport

   1. apical to basal: kidney tubules transport nutrients rom lumen to basal connective

   2. basal to apical: lymph resorption into lymphatics

6. reproductive (seminiferous tubule generates sperm)

7. special sensory (taste buds, hair cells in cochlea)

8. contraction (myoepithelium)

keratinization

stratum corneum dead layer of skin

underneath is the granulosum which is dark because keratohyaline granules (- proteins)

no nuclei

VS

para-keratinization: no stratum granulosum and the surface cells are living

developed with eating harder foods

*all epithelial are avascular: blood is below the basement membrane

basal lamina

• physical support

• development: morphogenesis and differentiation

• cell migration after injury

• may be discontinuous

• composed mainly of type IV collagen and laminin

external lamina

the equivalent of basal lamina bit these cells are non-polarized so they don’t have basal lamina

glands

epithelial gland types

modes of secretion

merocrine

secretion by exocytosis only product is released

apocrine

aka decapitation

portion of apical membrane and cytoplasm is released along with the product

holocrine

entire cell and its contents (sebum) become the secretory product

ex: fordyce spots secrete this way

entire sebaceous gland cell ruptures and disintegrates to release its contents. The cell's cytoplasm is filled with sebum (a mixture of lipids), and when the cell reaches maturity, it bursts, releasing sebum into the gland's duct. Fordyce spots result from sebaceous glands that are misplaced or "ectopic," meaning they are located on mucosal surfaces (like the lips and inside of the cheeks) where sebaceous glands are not typically found.

the extra