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Flashcards in Epithelial transport Deck (24)
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1
Q

ECF composition

A
Ca= 1mM
H+ = 0.00004mM
K+ = 4mM
Cl- = 115 mM
2
Q

ICF composition

A
Ca or H+ = 0.0001mM
Na or K = 140 mM
pure water = 55000 mM
Bicarb (HCO3-) 24mM
Maximum urine osmolarity = 1200 mOSM
3
Q

Apical

A

Faces “sepcial fluid” like food in gut or urine..

Mucosal, luminal

4
Q

Basolateral

A

Exposed to interstitial fluid, often has generic transport properties like plasma mems of non-epithelial cells
Serosal, peritubular

5
Q

Endothelial cells

A

In lungs because do not need transporters for O2 and Co2, they are lipid soluble.
They separate blood from air.

6
Q

Pericellular shunt pathway

A

Tight junctions b/w epithelial cells are looser in some areas (movement of water and solutes).

7
Q

2 routes through epithelium

A

Through 2 membranes (apical and basolateral mem) or between cells in pericellular shunt pathway

8
Q

Na/K pump

A

ALWAYS on basolateral membrane.
Driving force for nearly all transport.
It keeps the intracell [Na] low (protons are universal exception because they have specific primary transporters… esp kidney and stomach).

9
Q

Basolateral mem ion permeability

A

Low Na permeability, high K permeability.
Also has some Cl channels.
Vm = -70mV

10
Q

Apical mem ion permeability

A

Relatively highly permeable to sodium not potassium
Depolarized compared to basolateral mem.
Vm= +10mV
Apical solution is negative compared to basolateral (makes sense b/c Na moves out of it that draws Cl- with it).

11
Q

Movement of ions

A

It is permeable across Na membrane so it crosses here and then is pumped out by basolateral, Cl- follows passively (drawn by electrical force) and H20 follows osmotic gradient into basolateral

12
Q

Replace Cl with SO4 (too large to cross)

A

Na/K pump would continue, but because no anion could follows the trans-epithelial voltage would increase.
The apical solution would become so negative the net transport would stop.

13
Q

TransPD

A

Transepithelial potential differenece = Vm (basolateral) - Vm (apical)

14
Q

Leaky epithelium

A

Moves larger amounts of material.

Also short out the transepithelial potential diff, so you measure a lower transepithelial voltage

15
Q

Apical Cl- channel

A

Typically closed at resting. When activated the cell will begin to secrete electrolytes and H20 into the lumen (open in digestion and cholera).
Cl- pumped across basolateral, leaks out apical, brings Na (electical draw) and water along. Intracell Cl high because of pump.
Net secretion of NaCl.
At rest absorption wins.

16
Q

Cystic fibrosis

A

Cl- channel type CFTCR. Channel is mutation and has decreased ability to secrete, get thick mucus secretions.

17
Q

Absorption of nutrients

A

AA’s and sugars in GI lumen are pumped into blood by GI epithelium. Glucose and Aa are reabsorbed by epithelial cells in kidney.
Na dependence.
Na/Cl leaks from blood to GI through the shunt pathway, and then it can provide drive for glucose uptake. Then nutrients go out basolateral mem by faciliated diffusion.

18
Q

ECF composition

A

This is regulated by chemical specificity not ECF composition. So we do NOT regulate ECF composition at the input end (kidneys at output end must regulate it).

19
Q

Impermeable to H20

A

Because H20 follows oslutes …
sweat glands. as fluid travels along sweat duct towards surface NaCl is resorbed by the epithelium lining the duct and returned to the blood.
Because ducts are impermeable to H20, water can’t follow salt, so fluid in lumen gets more dilute.

20
Q

Metabolic waste

A

Co2 is exhaled (majority of waste)
Most important fx. of kidney is to get rid of non-volatile metabolic waste (urea, protons)…. kind of like lungs in that blood is near tubules and it can move.

21
Q

Kidney and waste

A

It knows what it likes.
It takes everything and passes it through renal tubules (ultrafiltrate) and resorbs what it wants.
Very energetically expensive, need lots of ATP to drive reabsorbing pumps.

22
Q

Kidney and ECF

A

it regulates ECF composition by adjusting activity of transporters that do reabsorbing.

23
Q

Kidney and water

A

The epithelium can become impermeable.
The brain senses extra water as a drop in osmolarity, stops secreting anti-diuretic hormone (vasopressin), and kidney epithelial cells remove aquaporins from apical side.
Water is secreted.

24
Q

4 substances never pumped, always move passively?

A

Water, O2, Co2, urea