Transport Across Epithelium + Lipids

Question 1

What proteins are found in tight junctions?

Answer 1

• Occludins
• Claudins
  — Claudin 2 and 16 = allow
  — Claudin 4 + 8 = block

Question 2

What are the types of Cell-Cell Junctions?

Answer 2

• adherens junctions (actin + cadherins)
• desmosomes (IF + cadherins)
• gap junctions (6 connexin = connexon)

Question 3

What are the 4 layers of Epidermis?

Answer 3

Stratum corneum (dead cells with no nuclei)
Stratum granulosum (water impermeable barrier)
Stratum spinosum (increase in adhesions)
Stratum basale (replenish cells)

Question 4

Epithelial vs Mesenchymal Cells

Answer 4

Epithelial = actin cortical and not motile
Mesenchymal = actin in stress fibres and migratory

Question 5

What is EMT?

Answer 5

Epithelial Cells
- loss of tight junctions, adherens junctions, desmosomes
Mesenchymal Cells
- cadherin contact - assemble adherens junction, desmosome, tight junctions

Question 6

EMT vs MET effectors?

Answer 6

EMT = cytokines and growth factors
MET = adhesion and cortical actin

Question 7

What are the 4 types of membrane transport?

Answer 7

Diffusion (passive, small molecules)
Facilitated Diffusion (protein-mediated, specific)
Active Transport (against gradient, hydrolyze ATP)
2nd Active Transport (1 with and 1 against, hydrolyze ATP)

Question 8

What are the types of epithelial cells?

Answer 8

Simple squamous (endothelial)
Simple cuboidal (line exocrine glands)
Simple columnar (small intestine)

Stratified squamous (epidermis)
Stratified cuboidal (sweat glands)
Stratified columnar (uretha)

Question 9

What are the properties of Absorptive Epithelia?

Answer 9

• polar
• barrier
• increase surface area
• avascular

Question 10

Which types of transport are used to transport glucose?

Answer 10

• 2nd active transport (glucose against in, Na with in)
• Uniporter (transport glucose in/out)
• active transport (Na out, K in) - regenerate Na

Question 11

What are the 4 glucose transporters?

Answer 11

GLUT1 - RBC (independent of blood [glucose])
GLUT2 - liver + pancreas (glucose increase as blood [glucose] increases)
GLUT3 - neurons (independent of blood [glucose])
GLUT4 - fat + muscle (insulin dependent, relocate to PM)

Question 12

Pancreatic Beta Cell

Answer 12

• GLUT2 brings glucose in cell
• converts to ATP
• closes K+ channel = depolarization
• Ca2+ voltage-gated channel brings in Ca2+
• triggers insulin release
• GLUT4 brought to PM – glucose enters muscle cells

Question 13

What is simple rehydration therapy?

Answer 13

• glucose and Na+ create an osmotic gradient to bring water into cell
• when dehydrated – glucose and electrolytes needed to allow water to flow into cell

Question 14

What are three examples of a symporter?

Answer 14

Amino Acid/Na+ Symporters
- Lysine exporters
- Alanine/Glycine symporter
- Branched chain amino acid symporter

Question 15

What is an example of an antiporter?

Answer 15

Ca2+/Na+ Antiporter
- used in muscle contraction
- more Ca2+ = contraction
- 3:1 Na+/Ca2+

Question 16

How does muscle contraction signalling work?

Answer 16

1) action potential depolarizes membrane
2) Ca2+ enters cell and released from SR
3) Ca2+ binds to troponin = contract

• Ca2+ pump back into SR with ATP
• Ca2+ pumped out, 3 Na+ pumped in
• 3 Na+ pumped out, 2 K+ pumped in (concentration balance)

Question 17

How does iron transport work?

Answer 17

1) Fe3+ ingest – Fe2+ absorb by active transport
2) Fe3+ bind to transferrin
3) Bone marrow - Fe –> Heme –> Hb –> RBC synthesis
4) Spleen - destroys old RBC and convert Hb to bilirubin
5) Bilirubin excreted as urine or bile
6) Liver stores excess Fe3+ as ferritin

Question 18

How does iron uptake work?

Answer 18

• transferrin with Fe3+ = high affinity at pH=7 (initial bind)
• transferrin without Fe3+ = high affinity at pH=5 (in endosome)
• transferrin without Fe3+ = low affinity at pH=7 (dissociate)

Question 19

What are some diseases related to iron?

Answer 19

Anemia - lack of hemoglobin/iron
Hemochromatosis - iron overload

Question 20

How is iron absorbed?

Answer 20

1) Fe3+ –> Fe2+ by ferrireductase
2) Fe2+ enter cell via DMT1
3) Fe2+ transport across basolateral by ferroportin
5) Fe2+ –> Fe3+ by hephaestin and bind to transferrin

• Ferritin binds excess Fe2+ –> Fe3+

Question 21

How is dietary lipid absorbed?

Answer 21

1) Bile salts coat fat droplets = emulsion
2) Pancreatic lipase convert to micelles (fatty acids)
- Fatty acids enter cell by diffusion
- Cholesterol transport into cell

3) Fats and cholesterol form chylomicron
4) Chylomicron removed by lymphatic system

Question 22

What are the components of lipoprotein?

Answer 22

• Apolipoprotein
• Cholesterol
• Triglyceride
• Phospholipids

Question 23

How is lipid transported after absorption?

Answer 23

• lipid travels in chylomicrons, remnants to liver
• adipose cells extract lipids
• excess cholesterol stored by liver
• liver sends lipids to body
• adipose sends lipids to liver

Question 24

What are the types of Lipoproteins?

Answer 24

Chylomicron (triglyceride)
Very Low Density Lipoprotein (triglyceride + phospholipid)
Low Density Lipoprotein (cholesterol)
High Density Lipoprotein (protein)

Question 25

How is Low Density Lipoprotein internalized?

Answer 25

1) LDL bind to receptor –> clathrin-coated pit
2) Endocytosis
3) Vesicle lose clathrin coat
4) LDL dissociate from receptor at low pH
5) LDL goes to lysosome and receptor fuses to membrane
6) Exocytosis of receptor

Question 26

What is a disease associated with LDL?

Answer 26

Familial Hypercholesterolemia
- mutation to LDL receptor
- too much internalization of LDL