Renal 5 Flashcards
Where is potassium abundant? And where is it important?
In the intracellular spaces. Extracellular concentration remains essential for the function of excitable tissue
Hypokalemia
Low concentration of K in the EXTRACELLULAR fluid
Hyperkalemia
High concentration of K in the EXTRACELLULAR fluid
What can be symptoms of both hyper- and hypokalemia?
Abnormal rhythms of the heart and abnormalities in skeletal muscle contraction
How is potassium balance maintained through EXCRETION? (2) Which can be regulated and how?
Excreted in feces/ sweat (not regulated)
Excreted into urine (regulated by hormones to change secretion in the CCD)
What are the renal processes of potassium? (filtration, secretion, reabsorption)
K is freely filtered
Most is reabsorbed, so very little FILTERED K is in the urine
K can be secreted at the cortical collecting ducts
T or F
Net reabsorption of K is very variable.
T
Net reabsorption can be between 15-99% depending on intake. Usually, around 86%
Explain the secretion mechanism of K.
Active transport of Na/K with the pump and a channel bringing K into the tubule (secretion of K in the CCD is coupled with Na reabsorption)
How is K SECRETION regulated?
- Dietary intake
- Aldosterone
What are the effects of increased dietary intake in K?
Plasma K increases
1. Increases secretion at the CCD
2. Increases aldosterone secretion, which increases K secretion at the CCD
What are the stimulis and effects of increased aldosterone for K?
- When plasma volume decreases, it increases angiotensin 2 which stimulates aldosterone secretion
- Increases plasma K will directly stimulate aldosterone secretion
Aldosterone will increase K secretion and Na reabsorption
What is Hyperaldosteronism? What are the symptoms?
Condition in which aldosterone is released in excess, generally due to an adrenal gland adenoma
Increases in fluid volume will lead to hypertension, and there can be hypokalemia. Renin is suppressed and metabolic alkalosis is often seen
Why is hydrogen ion concentration of the extracellular fluid tightly regulated?
Because metabolic reactions are highly sensitive to hydrogen ion concentration (pH of the environment)
How is hydrogen formed in the body?
CO2 + H2O <-carbonic anhydrase->H2CO3 <-> HCO3 +H
When bicarbonate is lost from the body, it is the same as if the body had _______ a hydrogen ion
gained
What are the sources of hydrogen gain and loss?
GAIN
1. Generation of ions from CO2
2. Production of nonvolatile acids from metabolism
3. Due to the loss of bicarbonate in diarrhea or other fluid
4. Due to loss of bicarbonate in urine
LOSS
1. Hyperventilation (loss of CO2)
2. Utilization of hydrogen in metabolism
3. Loss in vomitus
4. Loss in hydrogen
What are the three important nonvolatile acids?
Phosphoric acid
Sulfuric acid
Lactic acid
How are buffers useful in hydrogen balance?
It keeps hydrogen “locked up” to avoid changes in pH
What is the major extracellular buffer?
What is the major intracellular buffer?
CO2/HCO3 system
phosphates and proteins
Once Buffer + H <–> HBuffer, what important step is necessary?
H needs to be excreted or the buffer needs to be regenerated too keep the same amount available.
What is the CO2/HCO3 system (hydrogen regulation)?
Respiratory system (controlling CO2)
Kidneys (control HCO3)
What is the general hydrogen regulation by the kidneys (if H increases/decreased what happens)?
Low H concentration -> excrete HCO3
(high pH -> ALKALOSIS)
High H concentration -> produce new HCO3 into plasma
(low pH -> ACIDOSIS)
pH is calculated as follows:
pH = 6.1 + log10(HCO3/CO2)
What is important to understand from that equation?
If the body wants to maintain pH, the movement of either HCO3 or CO2 will need the other molecule to move in the same direction
Explain HCO3 reabsorption (H secretion)
In the epithelial cell of the proximal tubule
H2O+CO2 = H + HCO3
- H is actively transported into the lumen and reacts with HCO3 to make H2O (urine) and CO2 (circulation)
- HCO3 is transported into the capillaries
Altogether, one HCO3 less in the lumen and one into capillaries = equivalent of reabsorption
Where does HCO3 reabsorption mainly occurs?
In the proximal tubule (more than water and Na)
If there is a great amount of acid in the body, how is that regulated?
With the addition of a new HCO3 into the plasma by
1. H secretion and excretion on NONBICARBONATE buffers
2. glutamine metabolism (most efficient)
Explain the secretion and excretion on NONBICARBONATE buffers. Why does it occur in the CCD?
CCD:
H2O+CO2 = H + HCO3
- H into the lumen with another buffer and excreted
-HCO3 into capillary
Overall, HCO3 into blood without reabsorption
In the CCD/ distal tubule bc it happens when there is no more HCO3 needed to reabsorb
Explain the glutamine metabolism
Glutamine (from the lumen or interstitial fluid) makes NH4 and HCO3
- NH4 counterport of Na to be excreted
- HCO3 into capillary (new with no reabsorption)
