renal lecture 5 potassiumm regulation and hydrogen ion regulation?

Question 1

What is the most abundant intracellular ion?

Answer 1

Potassium (K) is the most abundant intracellular ion.
98% Intracellular fluid
2% Extracellular fluid

Question 2

Why is concentarion of K concentration important in extracellular fluid?
What is the resting potential of membranes related to?

Answer 2

-The K concentration in the extracellular fluid is extremely important for the function of excitable tissues (nerve and muscle)
-the resting membrane potentials of these tissues are directly related to the relative intracellular and extracellular K concentrations

Question 3

What is hyper vs hypokalemia?
What do they both cause?

Answer 3

Hyperkalemia: high concentration of K in the extracellular fluid (>5 mEq/L)
Hypokalemia: low concentration of K in the extracellular fluid (<3.5 mEq/L)
-Both cause abnormal rhythms of the heart and abnormalities of skeletal muscle contraction.

Question 4

What are the effects of hyperkalemia on the electrocardiogram?

Answer 4

-it can cause the heart to stop if K is equal to 8 or larger

Question 5

How much potassium os excreted into urine vs feces and sweat?
When would we need to restrict sodium input?

Answer 5

-90% excreted into urine (adjusted via input)
-10% excreted into feces/sweat
-need to restrict the input if you have a kidney defiency?

Question 6

Where is K freely filtered?
What do the tubules reabsorb most of?

Answer 6

-freely filtered at glomerulus
-tubules reabsorb most of this filtered K so that very little of the filtered K appear in the urine

Question 7

What can K do unlike sodium or water?
What are changes in K excretion mainly due to?

Answer 7

-unlike sodium or water, K can be secreted at the cortical collecting ducts
- due mainly to changes in K secretion in the CCD (some in the
DCT)

Question 8

What is normally the net reabsorption for K?

Answer 8

normally 86%

Question 9

What is Na+ reabsorption coupled with?

Answer 9

-Na+ reabsorption coupled with K+ secretion

Question 10

What is potassium secretion regulated by?

Answer 10

1. Dietary intake of potassium
2. Aldosterone

Question 11

How is K+ regulated by dietary intake and aldosterone?
How does this affect pasma secretion and potassium excretion?

Answer 11

-high potassium increases aldosterone secretion

Question 12

How does K+ secretion occur when the renin-aldosterone system is actiavted by other causes?
What occurs to plasma volume and Ag2 levels?
How does this affect aldosterone secretion, Na+ reabsorption and K+ secretion?

Answer 12

-

Question 13

What is hyperaldosteronism?
What is its common cause?

Answer 13

-The conditions in which the adrenal hormone aldosterone is released in excess.
common cause: adenoma of the adrenal gland that produces aldosterone autonomously.

Question 14

What are the symptoms of hyper aldosteronism?

Answer 14

Increased fluid volume, hypertension, hypokalemia.
Renin is suppressed. Metabolic alkalosis is often seen.

Question 15

What are metabolic rxns highly sensitive to?
What concentration of extracellular fluid tightly regulated?
What is its pH?

Answer 15

-hydrogen ion concentration of the environment
-hydrogen ion concentraion
-pH: ~7.4 ([H+]: ~40 nmol/L

Question 16

What is the equivalent of a bicarbonate ion being lost from the body?
What is the equivalent when a body gains a bicarbonate ion?

Answer 16

When bicarbonate ion is lost from the body, it is the same as if the body had gained a hydrogen ion
-when the body gains a bicarbonate ion, it is the same as if the body had lost a hydrogen iron

Question 17

What are the sources of hydrogen ion gain and their equivalent loss?

Answer 17

1. generation of H ion from Co2=hyperventilation (loss of Co2)
   2.production of nonvolatile acids from the metabolism=using H ions in the metabolism
   3.gain of H ions due to bicarbonate loss in diarrhea or other nongastric GI fluids=loss of H ions in vomit
2. gain of H ions due to bicarbonate in the urine= loss of H+ in urine

Question 18

What are the 3 nonvolatile acids?
What is the average net production

Answer 18

Phosphoric acid (phosphate)
Sulfuric acid (sulfate)
Lactic acid (lactate)
-Average net production: 40-80 mmol of H+ per day

Question 19

What is the defintion of a buffer?
What are most H ions buffered by?
What is pH equal to (formula)?

Answer 19

-Any substance that can reversibly bind hydrogen ions is
called a buffer.
- Most hydrogen ions are buffered by extracellular and intracellular buffers.
-pH=-log(H+)

Question 20

What is normal ECF and what does it correspond to?
What happens to H+ concentrarion without buffering?

Answer 20

Normal ECF pH 7.4 corresponds to 40 nanomoles/L of H+
-Without buffering, hydrogen ion concentrations changes a
lot.

Question 21

What is major extracellular vs intracellular buffer?
What does buffering not eliminate?

Answer 21

-Major extracellular buffer is the CO2/HCO3-system.
-Major intracellular buffers are phosphates and proteins
-Buffering does not eliminate hydrogen ions from the body. It only keeps them “locked up”

Question 22

What is ultimate balance of H+ ion controlled by (what systems/part of body)?
What do the systems work together to do?

Answer 22

Respiratory system (by controlling CO2)
Kidneys (by controlling HCO3-)
-work together to minimize the change of hydrogen ion concentration (pH)

Question 23

What are the renal mechanisms for H+ control for low H+ conc. vs high H+ conc.

Answer 23

-Low H+ concentration (high pH: alkalosis)—-> Kidneys excrete HCO3 (same as adding H+ to system)
-High H+ concentration (low pH: acidosis)—-> Kidneys produce new HCO3- and add to the plasma

Question 24

What ratio gives you H+ concentration?

Answer 24

-ratio of bicarbonate and Co2 determines H+ conc.

Question 25

What does H3O- excretion formula?
What do kidneys normally do for filtered HCO3-, when is there an exception?
Where is the transporter for HCo3-?

Answer 25

HCO3-excretion =HCO3- filtered (+ HCO3- secreted) - HCO3 -reabsorbed)
Normally, the kidneys reabsorb all filtered HCO3-
Exception: alkalosis
-on basolateral side

Question 26

Where is the main HCO3- reabsorption?

Answer 26

80% in the proximal tubules

Question 27

How do we add new HCO3- to plasma?
What can both processes be viewed as?

Answer 27

1. by H+ secretion and excretion on nonbicarbonate buffers (such as phosphate).
2. by glutamine metabolism with NH4+ excretion.
   -Both processes could be viewed as H+ excretion by the kidney

Question 28

What do kidneys normally contribute enough new HCO3- to the plasma to compensate for?

Answer 28

-to compensate for the hydrogen ions from nonvolatile acids generated in the body (40-80 mmol/day)

Question 29

When does the first method of adding HCO3- to plasma only happen?

Answer 29

This happens only after all the HCO3- has been reabsorbedand is no longer available in the lumen

Question 30

What is the 2nd method of adding HCO- to the plasma mainly take place?
What is this process also called?

Answer 30

-mainly in proximal tubule
-process is also called H+ excretion bound to NH3