Module 5: Renal III Flashcards
What factor complicates potassium balance?
The fact that K+ is both reabsorbed and secreted.
Where is K+ secreted in the nephron?
Distal tubule and cortical collecting duct.
Where is K+ reabsorbed in the nephron?
Proximal tubule and ascending limb of Loop of Henle.
Why is K+ regulation important?
Improper K+ levels can lead to hyperkalemia or hypokalemia.
Which hormone plays a critical role in K+ homeostasis? What does it do?
Aldosterone. Enhances secretion in P cells
What are the three behavioral mechanisms involved in salt and water balance? What part of the body signals these mechanisms?
- Thirst
- Salt craving (aldosterone and ANG II)
- Avoidance behaviors
These mechanisms are controlled by the hypothalamus.
Potassium balance is particularly important in _____ tissues. What are two examples?
Excitable, heart or skeletal muscles
_____ 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)
Hypokalemia
_____ 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.
Hyperkalemia
What 4 things can cause disturbances in K+ balance?
Disturbances in K+ balance may result from:
- Kidney dysfunction
- Eating disorders
- Loss of K+ in diarrhea
- Use of diuretics that prevent kidneys from properly reabsorbing K+
_____ are critical in restoring the normal state, particularly when ECF volume decreases or osmolarity deviates.
Behavioral responses
Can the kidneys add fluid?
No, they can only conserve.
_____ is normally the only way to replace lost water and _____ is the only way to raise the body’s Na+ content.
Drinking water, eating salt
Receptors in the _____ act as saline receptors, which stimulate a thirst response.
Hypothalamus
Does water need to be absorbed to relieve thirst? Why?
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.
A midday nap called a “siesta” is an example of a what?
An avoidance behavior.
Increased _____ or _____ increases the desire to take in salty food
Aldosterone, angiotensin II
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):
- Conserving fluid to prevent additional loss
- Trigger cardiovascular reflexes to increase blood pressure
- Stimulate thirst so normal fluid volume and osmolarity can be restored
Four compensatory mechanisms with redundant overlap overcome the symptoms of dehydration:
- Cardiovascular mechanisms
- Renin-angiotensin system
- Renal mechanisms
- Hypothalamic mechanisms
During severe dehydration, decreased ECF volume would signal to increase _____ release, but at the same time _____ inhibits the release.
Aldosterone, osmolarity
What is the largest source of acids in the body on a daily basis?
CO2 from aerobic metabolism
What are the 3 mechanisms to maintaining pH in the body?
- Buffers
- Ventilation (75%)
- Renal regulation
Decreases in plasma pH are sensed by what chemoreceptors?
Carotid and aortic
Increases in plasma PCO2 are sensed by what chemoreceptors?
Central chemoreceptors
What two mechanisms do the kidneys use to handle pH disturbances? Describe each briefly.
- Directly: altering the rates of excretion or reabsorption of H+
- Indirectly: by changing the rate at which HCO3- buffer is reabsorbed or excreted
In general, during acidosis excess H+ is buffered by _____ within tubule cells or enters lumen and is buffered by phosphate ions
Ammonia
H+ is not filtered, enters tubule via _____ only
Secretion
The proximal tubule secretes _____ and reabsorbs _____
H+, HCO3-
How is HCO3- transported apically?
Glutamine is metabolized to ammonium and bicarbonate (7)
The _____ controls acid excretion
Distal nephron
Initial portion of the _____ plays a significant role in the fine regulation of acid-base balance. What 2 ways is this done?
Collecting duct.
- Cells contain high amount of CA
- H+ transported via H+ ATPase or H-K ATPase, HCO3-/Cl- exchanger
During acidosis, _____ cells in the collecting duct begin to function. What happens, and what is this usually accompanied by?
Type A intercalated cells. They increase H+ secretion and HCO3- reabsorption. Usually accompanied by increased K+ reabsorption (hyperkalemia).
During alkalosis, _____ cells in the collecting duct begin to function. What happens and what usually accompanies this?
Type B intercalated cells. They increase H+ reabsorption and HCO3- secretion. Usually accompanied by increase K+ secretion (hypokalemia).
Respiratory induced changes in pH must be resolved via _____ mechanisms.
Renal
Occurs when alveolar hypoventilation results in CO2 retention and elevated plasma CO2
Respiratory acidosis
Occurs as a result of hyperventilation in the absence of increased metabolic CO2 production
Respiratory alkalosis
Occurs when dietary and/or metabolic input of H+ exceeds H+ excretion
Metabolic acidosis
Two common causes; excessive vomiting of acidic stomach contents or excessive ingestion of bicarbonate-containing antacids
Metabolic alkalosis
Metabolic alkalosis is usually rapidly resolved by a _____, but effectiveness is limited. Why?
Decrease in ventilation. Because it can cause hypoxia if breathing slows too much
