True or False?
Potassium secretion will occur in the distal tubule and collecting ducts of the nephron with or without aldosterone.
True.
Aldosterone just makes the process more efficient.
What is the result as Na+ is reabsorbed in the DT and collecting ducts, given the fact that no Cl- channels or transports exist here?
The outside of the cell membrane becomes more negative, while the cytoplasm becomes more positive.
What causes potassium to move out of the tubular epithelial cells of the DT and collecting ducts?
It is repelled by the intracellular positive charge and attracted to the extracellular negative charge. It also moves down its concentration gradient (caused by the Na+/K+ ATPase on the basolateral membrane of the cell).
True or False?
The exchange that occurs in the DT and collecting duct of the nephron involving Na+ and K+ is a coupled symport process.
False.
It is a loose exchange between the two solutes, but they experience independent permeabilities.
What two triggers initiate aldosterone secretion?
1.) Angiotensin II
2.) [K+]ECF
What allows for the secretion of potassium in the absence of aldosterone?
1.) Na+/K+ ATPase on the basolateral membrane of tubular epithelial cells
2.) Concentration gradient of K+ from interstitium to tubular cell
*In short, K+ can stimulate its own secretion by bulk flow/balance.
In the absence of aldosterone, which solute - sodium or potassium - can cause a more significant change in plasma concentration of that solute.
Sodium.
Since potassium can somewhat regulate its own secretion by bulk flow.
An increase in sodium delivery to the DT will cause a(n) (increase / decrease) in the amount of potassium secretion.
Increase.
K+ must be secreted in order to maintain an electrochemical gradient.
What might cause an increased delivery of sodium to the DT of the nephron?
High blood pressure, causing pressure diuresis and thus less proximal reabsorption.
Why doesn't increased MAP lead to hypokalemia?
Although increased BP can cause increased K+ secretion in response to increased Na+ reabsorption in the latter nephron, Aldosterone secretion shuts down in response to higher MAP in order to avoid hypokalemic conditions.
What is the optimal pH range for body fluids?
7.38-7.42
What are the body's three defenses against changes in pH, in order of response and how fast they work?
1.) Buffering systems (immediate results)
2.) Adjustment of respiratory rate (about 15 minutes)
3.) Excretion of acidic or alkaline urine (1-2 days)
Which buffering system exists in the ECF? What is its pKa?
1.) Bicarbonate - carbon dioxide system
2.) pKa = 6.1
What is the equation for the bicarb-CO2 buffering system?
H2O + CO2 <--> H2CO3 <--> H+ + HCO3-
What does it mean when pH = pKa of a molecule?
50% of the molecule exists in its acid form, 50% exists in its basic form.
If carbonic acid's pKa is 6.1 and the pH of the body is 7.4, does the molecule tend to dissociate or keep its proton?
At pH of 6.1 equation is at equilibrium. At a pH of 7.4 we have less H+ protons than at equilibrium. Therefore, the equation shifts right, producing more H+ protons and HCO3-.
What is Key Concept #5?
The Henderson-Hasselbach equation:
pH = 6.1 + log( [HCO3-] / [CO2] )
* Log (base/acid).
What are the two intracellular buffer systems?
1.) Phosphate system
2.) Protein system
The best buffer has a pKa close to the desired pH (body is 7.4).
Why isn't phosphate (pKa 6.8) the major buffer of the body as opposed to bicarb. (pKa 6.1)?
Our body's can't regulate phosphate because they have no way of producing it.
The bicarbonate system, however, can be regulated.
True or False?
Proteins do not usually provide a large amount of buffering capacity.
False.
Proteins have a "tremendous amount of buffering capacity."
Why must proteins act only as temporary buffers?
Protons must be removed soon after buffering, otherwise the proteins 3D structure (and therefore function) will be altered.
What is the body's source of CO2?
Normal intracellular metabolism (aerobic respiration).
True or False?
CO2 is not lipid soluble and therefore does not diffuse readily.
False.
CO2 is lipid soluble and diffuses freely.
If the normal concentration of HCO3- in the body is 24 mmol/L, what is the normal concentration of CO2?
