Epithelial tissue

Question 1

Types of epithelial tissue with example

Answer 1

1. Simple squamous: flat cells single layer
   a. Mesothelium (serosal) - provides cover to pericardium, pleural and peritoneum cavity
   b. endothelium - found in blood vessels where quick exchange of substances required between blood and tissue
2. Simple cuboidal: cuboidal cells (equal size) in single layer
   Eg: collecting ducts of kidne y - absorption and transport of substances; Thyroid - secretion of substances
3. Simple columnar: contains microvilli for food absorption, goblet cells for mucous secretion
4. Stratified squamous:
   a. contains moderate keratin: found in oesophagus
   b. contains high keratin: found in skin epidermis
5. Pseudostratified
   a. ciliated columnar epithelium: found in trachea
   b. columnar epithelium with stereoclilia: epididymis
6. Transitional (urothelium): found in urinary bladder contains columnar, intermediate and basal cells
7. Stratified cuboidal: found in ovarian follicle

Question 2

Three domains of epithelial cell

Answer 2

1. apical domain: uppermost portion facing lumen or external environment
2. Lateral domain: cell facing other cells on the side and they joined by cell adhesion molecules and junctional complexes
3. Basal domain: attaches cell to basal lamina that separate epithelium from underlying connective tissue

Question 3

Cilia and axoneme

Answer 3

Originate from basal body anchored by rootlet to the cytoplasm.
multiple motile cilia:
Cilia contains concentric arrangement of 9 microtubule doublets + 2 central microtubules.
Basal body contains helicoid arrangement of 9 microtubule triplets with no central microtubule.
Eg: presence in trachea for protection from environment and fellopian tube for movement of egg

Single non-motile cilia
Function as
- sensory unit to send signals to cell about external environment
- Early fetus development - in organogenesis
- Participate in hadgehog signalling
- kinocilium in ear canal for maintenance of body balance and hearing

Axoneme: Plasma membrane structure surrounding microtubule

Question 4

Microvilli and Stereocilli

Answer 4

Microvilli: consisting core of actin microfilament and other proteins. Finger like projection from the apical portion of the cell. Eg: present in intestine and kidney for absorptive purpose
Stereocilia: same composition but contains branched finger like projections Eg; stereocilia found in epididymis lining

Question 5

Cell adhesion molecule

Answer 5

1. Calcium dependant
   a. Cadherin-catenin complex: cadherin linked to actin microfilament via catenin complex and other proteins
   b. Selectins: unlike cadherin selectin bound to carbohydrate molecule and they are c type lectin family receptor importance in immune reaction
2. Calcium independent
   Ig-cell adhesion molecule (Ig-CAM) family
   Integrins: bound to actin microfilament via connecting protein

Question 6

Cell junction

Answer 6

1. Tight junction: determines polarity of epithelia cell by separating apical domain and basolateral domain. belt like desmosomes and connected to actin microfilaments
2. zonula adherens (belt desmosomes) - belt like desmosomes and linked to actin microfilament
3. Macula adherens - spot like desmosomes attached to intermediate fillaments
4. Hemidesmosomes: connection of basal lamina with basal domain of epithelia cell and attached via intermediate filaments

Question 7

Gap junction

Answer 7

symmetrical communicating junctions produced by the protein connexin. 6 connexin monomer produces connexon - joined end to end to create pore between adjacent cells - important in chemical and electrical coupling between adjacent cells Eg: cardiac muscle cells

Question 8

Basement membrane

Answer 8

Basal Lamina: Close to epithelia cell formed by type IV collagen, proteoglycan and laminin molecule
Reticular lamina: contains reticular fiber and type III collagen, close to connective tissue.

BL and RL collectively called basement membrane

Question 9

Exocrine and Endocrine glands

Answer 9

Exocrine glands - their secretions released on the surface of the epithelial cells
Endocrine glands - their secretions released into the blood

Question 10

Types of exocrine glands and location

Answer 10

Exocrine gland: contains tubular exocrine duct and secretory portion
1. simple tubular: small and large intestine
2. simple tubular coiled: sweat gland
3. simple tubular branched: gastric mucosa
4. simple tubular acinar/alveolar: sebaceous gland
5. Branched tubular: oral cavity
6. branched acinar/alveolar: exocrine pancreas
7. branched tubularalveolar: mammary gland

Question 11

Mechanism of secretion of exocrine glands

Answer 11

Merocrine: secretion is brought to plasma membrane by secretory vesicle and released by exocytosis. Eg; zymogen from exocrine pancreas, milk proteins of mammary gland

Apocrine: secretion of substance involves pinching off and loss of plasma membrane. Eg: milk lipids of mammary gland

Holocrine: cell synthesize and accumulate secretory substance in the cytoplasm and then disintegrate to release the secretion Eg: Sebum in sebaceous gland