Epithelia

Question 1

What are the four categories of tissues?

Answer 1

Epithelia, CT, muscle, neural tissue

Question 2

What is hematoxylin and eosin (H&E)?

Answer 2

Light Microscopy staining technique. Hematoxylin (basic dye) staining basophilic molecules - DNA + RNA in blue. Eosin (acidic dye) staining acidophilic molecules - proteins in pink.

Question 3

Where does epithelia cover?

Answer 3

It covers all internal and external surfaces of the body.

Question 4

What is a cutaneous membrane (skin)?

Answer 4

Epidermis (epithelium covering the external body surface) + underlying CT= cutaneous membrane

Question 5

What is a mucous membrane?

Answer 5

Epithelia/epithelium (internal body surfaces: internal passage ways that opens to the exterior) + underlying CT = mucous membrane

Question 6

What is endothelium?

Answer 6

simple squamous epithelium lining vessels, including arteries, veins, heart chambers, lymphatic vessels

Question 7

How are covering epithelium classified?

Answer 7

1. Simple epithelia: 1 layer of cells (@ sites of molecular transfer)
2. Stratified epithelia: > 1 layer of cells (@ sites of protection)

Question 8

What is mesothelium?

Answer 8

simple squamous epithelium lining internal body cavities not opened to the exterior cavities

Question 9

What is a serous membrane?

Answer 9

Mesothelium + underlying CT = serous membrane @ following cavities
- pleural (lung)
- pericardial (heart)
- peritoneal (abdomen)

Question 10

Epithelial Characteristics

Answer 10

1. Cellularity: densely packed cell and little material in between
2. Polarity: apical, later, and basal surface
3. Specialized intercellular junctions (jxn): connects physically & functionally
4. attached to basement membrane + CT
5. Regeneration (mitosis)
6. Avascular (no blood supply; dependent only on diffusion of CT) and innervated (nerve supply)

Question 11

What a basement membrane?

Answer 11

Acellular layer between epithelium + CT; contains no cells itself

Function:
- physically supporting the epithelium structure
- along with CT, keeps epithelia attached
- semipermeable molecular filter
- epithelial repair + regeneration

Question 12

Epithelia Function

Answer 12

structurally and functionally specialized based on location:
1. physical protection
2. controls permeability - transcellular (through) / paracellular (between cells) molecular transport
3. sense (touch, temperature, pain, vision, hearing, balance, smell)
4. specialized secretion production @ glandular epithelia

Question 13

Epithelia Development

Answer 13

@ embryo in the form of simple sheets covering the surface and becomes:
a) remain as simple epithelium (respiratory - alveoli)

b) stratified epithelium (skin)

c) gland: specialized in secreting and producing cell products; either multi/uni cellular

Question 14

How do glandular epithelia develop?

Answer 14

Exocrine Glands: outward secretion to surface often via duct

Endocrine Glands: inward secretion to tissue fluid to deliver hormones to target tissue via cardiovascular system

Question 15

What do multicellular exocrine glands consist of?

Answer 15

1. Acinus - secretory portion with vesicles
2. Duct - conducts & modifies secretory products

Question 16

What is the functional classification of exocrine glands?

Answer 16

1. Secretion Type
   - mucous glands: mucinogens secretion
   - serous glands: protein-rich watery solution secretion
   - mix seromucous glands
2. Secretion Mode
   - merocrine: exocytosis
   - apocrine: shred a part of cytoplasm + products in vesicles via “pinching”
   - holocrine: entire cell releasing cytoplasmic content

Question 17

List all of the multicellular exocrine glands.

Answer 17

Simple tubular - @ intestinal glands

Simple coiled tubular - @merocine& sweat glands

Simple branched tubular - @ gastric glands

Simple alveolar (acinar; spherical) - not in adults

Simple branched alveolar - @sebaceous glands

Compound tubular - @mucous glands

Compound alveolar - @mammary glands

Compound tubuloacinar - @salivary glands

Question 18

What are goblet cells?

Answer 18

unicellular form in exocrine glands interspersed amongst epithelial cells; apically secretes mucus to protect the covering epithelia

@respiratory epithelium & digest tract

Question 19

What are multicellular endocrine glands?

Answer 19

ductless foldable epithelial tissue surrounded by BM & CT

secretes cell products into the interstitial fluid to taken yo by BVs (systemic distribution)

Question 20

What are unicellular endocrine glands?

Answer 20

@ covering epithelia

diffuse neuroendocrine cells (ex. enteroendocrine /EE cells from GI)

secretes cell products across BM and CT
- influence adjacent cells via paracrine signalling (EE cells -> secrete gastrin -> influence adjacent cells to secrete acid -> aid digestion)
- systemic distribution via endocrine signalling (EE cells -> CCK -> digestive hormones release from pancreas + bile to gall bladder)

EE cells from small intestine

Question 21

What is specialized at the apical surface of covering epithelia?

Answer 21

1. Microvilli: finger-like extensions with minimally motile which increase SA for more absorption and secretion; not viewable in LM

and size = rate of molecules moving through apical CM

focused on the small intestine (increased the rate of nutrient absorption) + kidney

2. finger-like extension with highly motile and synchronized which moves fluid along the luminal surface (>microvilli); viewable in light microscopy

core consists with microtubules and associated proteins (dynein)

focused on respiratory epithelia + uterine tubes

Question 22

What is simple squamous epithelia?

Answer 22

a thin epithelia with rapid and passive (usually) transport

@ alveoli (as “pneumocytes”), blood vessel (as endothelium), and mesothelia

Question 23

What is simple cuboidal epithelia?

Answer 23

height = width of the cell

active secretion and absorption

may have microvilli to increase SA of the apical membrane and rate of molecular transport

@kidney

Question 24

What is simple columnar epithelia?

Answer 24

height > width of the cell performing high rates of secretion and absorption

@small intestine
@gall bladder with microvilli
- paracellular mvt prevention via tight junction
- transports water out
- stores and concentrate bile

Question 25

What is pseudo-stratified epithelium?

Answer 25

fakes stratified, all cells contact BM - simple epithelium

often ciliated

@respiratory tract (ciliated pseudostratified epithelium + goblet cells = cleans air)

Question 26

What is stratified squamous non-keratinized epithelium?

Answer 26

internal surface protection that is kept moist in all time by glandular secretion

@mouth, throat, esophagus, rectum, anus, vagina, cervix epidermal cells joined by desmosomes

Question 27

What is stratified squamous keratinized epithelium?

Answer 27

external surface and dehydration (epidermal layer) protection

@palm of the hand

keratinization: a dead sheet of surface cells strongly connected by desmosomes to develop water-resistant properties

Question 28

What is transitional epithelium?

Answer 28

stratified epithelium allowing stretches and recoiling

no tension (empty organ) = domed surface cells

tension (filled organ) = flat cell

round apical nuclei

@urinary bladder and ureter

Question 29

What are the functional classes of intercellular junctions?

Answer 29

internally attached into a functional unit:

1. Anchoring junctions - mechanical strength by connecting each other by cytoskeleton and to BM
2. Occluding junctions - blocks the intercellular space; control paracellular (btw cells) molecular mvm
3. Communicating/gap junctions - ionic and molecular mvt control btw adjacent

Question 30

How do cells anchor each other?

Answer 30

1. Zonula adherens
   - belt: surround cells with an actin microfilament network to bind in all directions (@ small intestine, epithelial sheet) and distribute shear (parallel) forces
   -the intercellular space linked by cadherins; cadherins + proteinaceous plaque –> actin microfilaments
2. desmosomes
   - bolt: joining the laterally linking cytoskeletal intermediate filament network of adjacent (@skin, epithelial sheet) and distributing shear forces
   - the intercellular space linked by cadherins
   - more desmosomes = more cell-cell adhesion

Question 31

What are hemidesmosomes?

Answer 31

half desmosome linking cytoskeletal intermediate filament network on basal anchoring epithelium to BM (@ skin, epithelial sheet)

integrins (transmembrane protein) link BM across extracellular space

Question 32

What is the function of tight junctions and its implications?

Answer 32

prevents / controls paracellular movement and back diffusion of actively transported molecules

creates [gradient] and maintains

barrier can be:
tight - small bowel + blood-brain barrier
leaky - kidney

@ blood-brain barrier, blood-testis barrier, blood thymus barrier

claudins (integral transmembrane glycoproteins) branches and determines TJ permeability

zonula occludens arranged in a belt form interacting with signalling molecules

Question 33

What is a junctional complex?

Answer 33

Combination of tight junction, zonula adherens and desmosomes occurring together

@ small intestine

Question 34

What is the function and parts of gap junction?

Answer 34

intercellular communication (metabolically and electrically) via intercellular connection with adjacent cells to coordinate cellular function
- permits the passage of ion + small molecules from cell to cell
- open/close conformation change
-synchronous movement

connexin (the pore of the gap junction): complex of 6 transmembrane proteins in the lateral CM

@bone cells, cardiac myocytes, and SM cells to coordinate cellular function