Transport Across Epithelium + Lipids Flashcards
What proteins are found in tight junctions?
- Occludins
- Claudins
— Claudin 2 and 16 = allow
— Claudin 4 + 8 = block
What are the types of Cell-Cell Junctions?
- adherens junctions (actin + cadherins)
- desmosomes (IF + cadherins)
- gap junctions (6 connexin = connexon)
What are the 4 layers of Epidermis?
Stratum corneum (dead cells with no nuclei)
Stratum granulosum (water impermeable barrier)
Stratum spinosum (increase in adhesions)
Stratum basale (replenish cells)
Epithelial vs Mesenchymal Cells
Epithelial = actin cortical and not motile
Mesenchymal = actin in stress fibres and migratory
What is EMT?
Epithelial Cells
- loss of tight junctions, adherens junctions, desmosomes
Mesenchymal Cells
- cadherin contact - assemble adherens junction, desmosome, tight junctions
EMT vs MET effectors?
EMT = cytokines and growth factors
MET = adhesion and cortical actin
What are the 4 types of membrane transport?
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)
What are the types of epithelial cells?
Simple squamous (endothelial)
Simple cuboidal (line exocrine glands)
Simple columnar (small intestine)
Stratified squamous (epidermis)
Stratified cuboidal (sweat glands)
Stratified columnar (uretha)
What are the properties of Absorptive Epithelia?
- polar
- barrier
- increase surface area
- avascular
Which types of transport are used to transport glucose?
- 2nd active transport (glucose against in, Na with in)
- Uniporter (transport glucose in/out)
- active transport (Na out, K in) - regenerate Na
What are the 4 glucose transporters?
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)
Pancreatic Beta Cell
- 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
What is simple rehydration therapy?
- 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
What are three examples of a symporter?
Amino Acid/Na+ Symporters
- Lysine exporters
- Alanine/Glycine symporter
- Branched chain amino acid symporter
What is an example of an antiporter?
Ca2+/Na+ Antiporter
- used in muscle contraction
- more Ca2+ = contraction
- 3:1 Na+/Ca2+
How does muscle contraction signalling work?
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)
How does iron transport work?
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
How does iron uptake work?
- 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)
What are some diseases related to iron?
Anemia - lack of hemoglobin/iron
Hemochromatosis - iron overload
How is iron absorbed?
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+
How is dietary lipid absorbed?
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
What are the components of lipoprotein?
- Apolipoprotein
- Cholesterol
- Triglyceride
- Phospholipids
How is lipid transported after absorption?
- 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
What are the types of Lipoproteins?
Chylomicron (triglyceride)
Very Low Density Lipoprotein (triglyceride + phospholipid)
Low Density Lipoprotein (cholesterol)
High Density Lipoprotein (protein)
How is Low Density Lipoprotein internalized?
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
What is a disease associated with LDL?
Familial Hypercholesterolemia
- mutation to LDL receptor
- too much internalization of LDL
