Module 5: Renal III

Question 1

What factor complicates potassium balance?

Answer 1

The fact that K+ is both reabsorbed and secreted.

Question 2

Where is K+ secreted in the nephron?

Answer 2

Distal tubule and cortical collecting duct.

Question 3

Where is K+ reabsorbed in the nephron?

Answer 3

Proximal tubule and ascending limb of Loop of Henle.

Question 4

Why is K+ regulation important?

Answer 4

Improper K+ levels can lead to hyperkalemia or hypokalemia.

Question 5

Which hormone plays a critical role in K+ homeostasis? What does it do?

Answer 5

Aldosterone. Enhances secretion in P cells

Question 6

What are the three behavioral mechanisms involved in salt and water balance? What part of the body signals these mechanisms?

Answer 6

1. Thirst
2. Salt craving (aldosterone and ANG II)
3. Avoidance behaviors

These mechanisms are controlled by the hypothalamus.

Question 7

Potassium balance is particularly important in _____ tissues. What are two examples?

Answer 7

Excitable, heart or skeletal muscles

Question 8

_____ causes muscle weakness because it’s more difficult for hyperpolarized motor neurons and muscles to fire AP’s (failure of respiratory and cardiac muscles is particularly worrisome)

Answer 8

Hypokalemia

Question 9

_____ is more dangerous, initially leads to hyperexcitability (depolarized resting membrane potential). Eventually cells are unable to repolarize and actually become less excitable. Can lead to life threatening arrhythmias in the heart.

Answer 9

Hyperkalemia

Question 10

What 4 things can cause disturbances in K+ balance?

Answer 10

Disturbances in K+ balance may result from:

1. Kidney dysfunction
2. Eating disorders
3. Loss of K+ in diarrhea
4. Use of diuretics that prevent kidneys from properly reabsorbing K+

Question 11

_____ are critical in restoring the normal state, particularly when ECF volume decreases or osmolarity deviates.

Answer 11

Behavioral responses

Question 12

Can the kidneys add fluid?

Answer 12

No, they can only conserve.

Question 13

_____ is normally the only way to replace lost water and _____ is the only way to raise the body’s Na+ content.

Answer 13

Drinking water, eating salt

Question 14

Receptors in the _____ act as saline receptors, which stimulate a thirst response.

Answer 14

Hypothalamus

Question 15

Does water need to be absorbed to relieve thirst? Why?

Answer 15

​The act of drinking relieves thirst, water does not actually have to be absorbed. Unknown receptors in the mouth/pharynx respond to water by decreasing thirst and decreasing AVP release.

Question 16

A midday nap called a “siesta” is an example of a what?

Answer 16

An avoidance behavior.

Question 17

Increased _____ or _____ increases the desire to take in salty food

Answer 17

Aldosterone, angiotensin II

Question 18

Severe dehydration results in a loss of ECF volume, decrease in blood pressure and an increase in osmolarity. The compensatory mechanisms aim to restore these three factors by (3):

Answer 18

1. Conserving fluid to prevent additional loss
2. Trigger cardiovascular reflexes to increase blood pressure
3. Stimulate thirst so normal fluid volume and osmolarity can be restored

Question 19

Four compensatory mechanisms with redundant overlap overcome the symptoms of dehydration:

Answer 19

1. Cardiovascular mechanisms
2. Renin-angiotensin system
3. Renal mechanisms
4. Hypothalamic mechanisms

Question 20

During severe dehydration, decreased ECF volume would signal to increase _____ release, but at the same time _____ inhibits the release.

Answer 20

Aldosterone, osmolarity

Question 21

What is the largest source of acids in the body on a daily basis?

Answer 21

CO₂ from aerobic metabolism

Question 22

What are the 3 mechanisms to maintaining pH in the body?

Answer 22

1. Buffers
2. Ventilation (75%)
3. Renal regulation

Question 23

Decreases in plasma pH are sensed by what chemoreceptors?

Answer 23

Carotid and aortic

Question 24

Increases in plasma P_CO2 are sensed by what chemoreceptors?

Answer 24

Central chemoreceptors

Question 25

What two mechanisms do the kidneys use to handle pH disturbances? Describe each briefly.

Answer 25

1. **Directly**: altering the rates of excretion or reabsorption of H+ 2. **Indirectly**: by changing the rate at which HCO3- buffer is reabsorbed or excreted

Question 26

In general, during acidosis excess H+ is buffered by _____ within tubule cells or enters lumen and is buffered by phosphate ions

Answer 26

Ammonia

Question 27

H+ is not filtered, enters tubule via _____ only

Answer 27

Secretion

Question 28

The proximal tubule secretes _____ and reabsorbs \_\_\_\_\_

Answer 28

H+, HCO₃-

Question 29

How is HCO₃^- transported apically?

Answer 29

Glutamine is metabolized to ammonium and bicarbonate (7)

Question 30

The _____ controls acid excretion

Answer 30

Distal nephron

Question 31

Initial portion of the _____ plays a significant role in the fine regulation of acid-base balance. What 2 ways is this done?

Answer 31

Collecting duct. 1. Cells contain high amount of CA 2. H+ transported via H+ ATPase or H-K ATPase, HCO₃-/Cl- exchanger

Question 32

During **acidosis**, _____ cells in the collecting duct begin to function. What happens, and what is this usually accompanied by?

Answer 32

Type A intercalated cells. They increase H+ secretion and HCO₃- reabsorption. Usually accompanied by increased K+ reabsorption (hyperkalemia).

Question 33

During **alkalosis**, _____ cells in the collecting duct begin to function. What happens and what usually accompanies this?

Answer 33

Type B intercalated cells. They increase H+ reabsorption and HCO₃- secretion. Usually accompanied by increase K+ secretion (hypokalemia).

Question 34

Respiratory induced changes in pH must be resolved via _____ mechanisms.

Answer 34

Renal

Question 35

Occurs when alveolar hypoventilation results in CO₂ retention and elevated plasma CO₂

Answer 35

Respiratory acidosis

Question 36

Occurs as a result of hyperventilation in the absence of increased metabolic CO₂ production

Answer 36

Respiratory alkalosis

Question 37

Occurs when dietary and/or metabolic input of H+ exceeds H+ excretion

Answer 37

Metabolic acidosis

Question 38

Two common causes; excessive vomiting of acidic stomach contents or excessive ingestion of bicarbonate-containing antacids

Answer 38

Metabolic alkalosis

Question 39

Metabolic alkalosis is usually rapidly resolved by a \_\_\_\_\_, but effectiveness is limited. Why?

Answer 39

Decrease in ventilation. Because it can cause hypoxia if breathing slows too much