Kidney function III Flashcards
what is oliguria
Low vol of urine produced - below 0.428L/day
What is osmolar clearance
volume of plasma cleared of osmotically active particles per unit time
How do you calculate osmolar clearance
C = UV/P where U = osmolarity of urine mosm/ml V = urine flow rate ml/min P = plasma osmolarity mosm/ml C = osmolar clearance ml/min
What is typical fasting osmolar clearance
2-3 ml/min
How do you calculate free water clearance
Renal clearance - osmolar clearance = free water clearance
What is the free water clearance of a patient producing hypotonic urine
> 0
What is the free water clearance of a patient producing hypertonic urine
<0
What is the free water clearance of a patient producing isotonic urine
0
Where are the osmoreceptors that are involved in the release of ADH
Organum vasculosum lamina terminalis
Medican preoptic nucleus
subformical organ
What do the osmoreceptors involved in the release of ADH signal to?
Magnocellular neurosecretory cells in paraventricular supraoptic nuclei in hypothalamus
Why is ADH effective in its role
It has a short life span = 20-30 mins allowing for fine control
It is released rapidly
What effect does angiotensin II have on ADH secretion
It increases it
What effect does natriuretic peptides have on ADH secretion
It decreases it
What effect does nicotine have on ADH
+
What effect does nausea have on ADH
+
What effect does pain have on ADH
+
What effect does stress have on ADH
+
What effect does alcohol have on ADH
-
What can promote/inhibit ADH other than osmoreceptor action?
Alcohol Stress Nausea Pain Nicotine
What are the two types of diabetes insipidus
Neurogenic; congenital or from brain injury, trauma, tumour
Nephrogenic; inherited (mutated V2, AQP2 gene), acquired from infection, drug
What mutations can cause nephrogenic diabetes insipidus
Mutated V2 or AQP2 gene
What are the characteristics of diabetes polyuria
Polyuria
Polydipsia
nocturia
Describe the physiology of the reabsorption of K+ in the PCT of the nephron
There is a K+ ion in the apical membrane which is used to move K+ from inside the cell into the lumen.
Then there is transcellular movt of K+ from lumen into the interstitial space.
The Na+:K+ ATPase in the basolateral membrane moves K+ into the cell and then another K+ channel allows K+ to flow into interstitial fluid from inside the cell.
Then a K+:CL- co-transporter also pumps K+ into interstitial fluid
There is paracellular movt of K+ too
Describe the physiology of the reabsorption of K+ in the thick ascending limb of the LOH of the nephron
In the apical membrane there is a Na+:K+:Cl- cotransporter moving ions inside the cell (NKCC2 transporter). There is also a K+ channel moving K+ ions back into the lumen.
There is a Na:K ATPase pump moving K+ in to the cell. There is a K+ channel in the basolateral membrane moving K+ from the cell into the interstitial space.
There is a K+:CL- cotransporter moving K+ out of the cell with Cl-
There is paracellular movt of K+
Describe the physiology of the reabsorption K+ in the collecting ducts
Occurs in the intercalated cells of the collecting duct.
There is a H+:K+ exchanger that moves K+ into the cells in favour of H+ from the lumen of the nephron.
Then there is a K+ channel in the basolateral membrane which removes K+ from the cell and allows it to travel into the interstitial space.
Describe the physiology of the secretion of K+ in the collecting ducts
Occurs in the principle cells of the collecting duct.
There is a Na:K ATPase pump in the basolateral membrane that moves K+ into the cells.
K+ channels in the apical membrane called ROMK = renal outer medullary K+ channels; and Ca2+ activated big conductance K+ channels that allow the flow of K from within the cell into the lumen of the nephron.
There is a Na channel in the apical membrane that allows Na to enter the cell from the lumen.
There is also a K:Cl cotransporter in the apical membrane which removes ions from the cell and places them in the lumen.
There is a K+ channel in the basolateral membrane which moves ions from inside the cell out.
What are the K+ channels found in the apical membrane of the principle cells of the collecting ducts of the nephron.
Renal outer medullary K+ channels (ROMK)
Ca2+ activated big conductance K+ channels
What effect does aldosterone have on K+ channels in the nephron?
It activates them
What effect does tubular flow rate have on K+ secretion and why?
It increases it as positive charges are washed away when tubular flow is higher meaning that an electrochemical gradient is maintained.
What effect does acidosis have on K+ secretion?
It inhibits it
What effect does alkalosis have on K+ secretion?
It stimulates it
What is hypokalaemia?
Plasma [K+] < 3.5 mM
What causes hypokalaemia?
Increased tubular flow rate (increased K+ secretion)
Hyperaldosteronism
Alkalosis
How would you treat a patient with hypokalaemia?
KCl administered via IV or orally
Feed w/ foods rich in K+
Treat alkalosis
What is hyperkalaemia?
Plasma [K+] > 5.5mM
How would you treat a patient with hyperkalaemia?
Short term -> give Ca2+ to antagonise effect of K+ on heart muscle
Intermediate term -> Give insulin to move K+ into cells, give glucose to prevent hypoglycaemia
Long term -> remove K+ from body giving diuretics
Possible C(H2O) range
-1.3 to 14.5 ml/min
How do osmoreceptors work
The OVLT, MPN and SFO signal to magnocellular neurosecretory cells in the paraventricular and supraoptic nuclei in the hypothalamus which then causes the release of ADH from the posterior pituitary gland
Normal range of plasma osmolality
285-295 mosm/kg
What are the characteristics of diabetes insipidus
nocturia
polyuria
polydipsia
Describe osmotic diuresis
Increased blood glucose more glomerular filtration of glucose, increased osmolarity of filtrate decreased water reabsorption polyuria
Where is the largest amount of potassium reabsorbed in the kidney
%65 absorbed passively in the proximal tubule
What type of co transporter is used to absorbed K in the asc LOH
NKCC2
What type of exchanger is used to absorbed K in the distal tubule
K+:H+ exchanger
What is the normal K plasma range
3.5-5 mM
