Epithelium

Question 1

Cell junctions

Answer 1

• bind & adhere cells together to form tissues
• it attaches the plasma membrane of adjacent cells together to be able to form tissues

Question 2

The 5 types of cell junctions?

Answer 2

Tight, Adherins, Desmosomes, Hemidesmosomes, Gap

Question 3

Tight junctions function?

Answer 3

fuse adjacent plasma proteins together, very tightly to prevent the leakage of contents from the cells themselves, they maintain apical-basal polarity. If there was no tight junction, there would be no control of absorption → free diffusion of lipids & membrane proteins would occur

Question 4

Tight junctions structure?

Answer 4

found at the apical end of epithelial cells, web-like strands of transmembrane proteins (made of Claudin & occludin)

Question 5

Tight junctions location?

Answer 5

urinary bladder

Question 6

Adherins junction structure?

Answer 6

made of plaques (dense layer of proteins on the inside of the plasma membrane that attaches to microfilaments & membrane proteins of the cytoskeleton) joined by cadherins (transmembrane glycoproteins)

Question 7

Adherins junction function?

Answer 7

often form extensive zones called “adhesion belts” that encircle the cell → provide structural support in areas that undergo mechanical stress(helps epithelial cells resist separation during various contractile activities like when food moves through the intestines), adheres several cells together so they function as a unit

Question 8

Adherins junction location?

Answer 8

located immediately below tight junctions, found in cardiac muscle cells → allows movement of the heart to expand & contract

Question 9

Desmosomes structure?

Answer 9

transmembrane proteins (cadherin) attached to intracellular plaques form connecting bridges between adjacent cells. intermediate filaments(keratin) extend across the cytosol of cells, contributing to the tissues stability (this prevents epidermal cells from separating under tension & cardiac muscle cells from pulling apart under contraction

Question 10

Desmosomes function?

Answer 10

provides strong adhesion, links intracellularly to intermediate filaments of the cytoskeletons of those adjacent cells

Question 11

Desmosomes location?

Answer 11

epididymis, myocardium

Question 12

Hemidesmosomes function?

Answer 12

anchoring the basal domain of epithelial cell to basal lamina of the basement membrane & allow for signaling in & out of cell

Question 13

Hemidesmosomes location?

Answer 13

skin cells

Question 14

Gap junction function?

Answer 14

connects the cytoplasm of 2 cells allows for communication via ions that can carry electric current

Question 15

Gap junction structure?

Answer 15

formed by connexon (transmembrane protein channels that form gaps between adjacent cells) mainly IONS, glucose, amino acids, and other small solutes can pass directly from cytoplasm of one cell into the next through the channel (not for equalibrium)-NOT in skeletal muscle

Question 16

Gap junction location?

Answer 16

areas of electrical activity e.g neurons & cardiac cells

Question 17

Basic tissues

Answer 17

a group of similar cells & cell products that perform a special function
4 types: epithelial, nervous, muscle, connective

Question 18

Epithelial tissue

Answer 18

• Consists of an uninterrupted layer of tightly packed cells. Holes such as the
  pores of a gland are an invagination of epithelium.
• Polarised: has a free surface (the apical surface) exposed to the outside
  and the basal surface (opposite) which may be attached to the underlying
  connective tissue; lateral surface → there are 2 sides of the cell which exhibits different features
• One or several layers of cells: apical (free) and basal layers.
• Underlying the covering epithelial tissue that line the body cavities is a layer
  of connective tissue – lamina propria which is bound to the epithelium by
  the basement membrane.
• Epithelium is avascular(does not have a blood supply) – receives nutrients by diffusion from lamina propria.
• has the capacity to readily renew themselves

Question 19

Basement membrane

Answer 19

• hemidesmosomes bind epithelial cells to the basement membrane
• separates epithelium from connective tissue
• formed by secretion of both, epithelial cells and cells in connective tissue
• acts as a selectively permeable filter between epithelium and connective tissue → prevents very large molecules from passing though → allows the nutrients from the blood to flow through
• has 2 layers (basal lamina, reticular lamina)

Question 20

2 layers of BM

Answer 20

• basal lamina
• reticular lamina

Question 21

Basal lamina

Answer 21

• (20-100 nm thick)
• consists of protein filaments (laminin, collagen; glycoproteins; proteoglycans) embedded in an amorphous matrix, produced by the epithelial cells
• attaches to basal surface of the epithelial cells

Question 22

Reticular lamina

Answer 22

consists of reticular fibres embedded in ground substance, synthesised by cells of the connective tissue underlying the epithelium