ECF Volume Regulation 1 Flashcards
What solutes account for the “major osmoles” (oncotic pressure) in the ICF and ECF?
ICF: K ions are the major osmoles
ECF: Na & Cl ions
How is water distributed between the ICF and ECF? What about between the components of the ECF?
Water - 1/3 ECF, 2/3 ICF
ICF:
- 3L plasma
- 11L ISF
When there is salt and water loss (vomiting / diarrhoea) what effects does this have on kidney function?
- Causes lower atrial pressure & BP, which results in increased ADH secretion and therefore water reabsorption at the kidneys
- Sympathetic response to low BP causes renal artery constriction and an increase in renin
What are the functions of Angiotensin II?
- Vasoconstriction
- CVS responses to increase BP (inc. HR / CF)
- Stimulate ADH release at hypothalamus
- Stimulate thirst & salt craving at hypothalamus
- Stimulate the release of aldosterone
What causes the increased reabsorption at the proximal tubule during times of hypovolaemia (dehydration)?
- Angiotensin II causes peritubular capillary constriction, lowers the pressure and hydrostatic force
- The loss of salt & water that leads to hypovolaemia results in a greater oncotic pressure at the proximal tubule, as [protein] is higher than usual
Does GFR change in times where plasma volume is reduced?
No, unless the volume decrease is extremely significant
- Sympathetic nerves and Angiotensin II keep the afferent arterioles constricted so the GFR remains constant (might actually be the efferent arterioles constricted, afferent dilated to keep GFR up? - check that)
Which hormone controls Na reabsorption at the distal tubule? What is the rate limiting step in the release of this hormone?
Aldosterone
- Production and release of renin is the rate limiting step, as this causes activation of the RAAS
What are the components of the juxtaglomerular apparatus? Where is the apparatus located?
Macula densa cells + juxtaglomerular cells
- Located at the articulation of the glomerulus and the distal convoluted tubule
What cells are responsible for the secretion of renin?
Juxtaglomerular cells
Describe the production of angiotensin II
- Angiotensinogen produced by the liver and secreted to the blood
- Renin produced by the juxtaglomerular cells of the kidney
- Renin cuts angiotensinogen to angiotensin I
- Blood vessel endothelium secretes ACE, ACE cuts angiotensin I to active angiotensin II
How does the vasoconstriction produced by angiotensin II lead to increased absorption at the distal tubule?
- Via constriction of the peritubular capillaries which lowers the hydrostatic pressure
This along with the increased osmolarity of blood during dehydration (increased oncotic pressure) causes salt and water reabsorption at the proximal tubule
What stimulates the release of renin?
- A decrease in pressure at the afferent arteriole
- Sympathetic nerve activity (Beta 1 effect)
- Reduced NaCl delivery (presence) at the macula densa of the distal tubule
How is the decrease in pressure at the afferent arteriole that triggers the release of renin detected?
- The juxtaglomerular cells act as baroreceptors, when they experience less distension (swelling) they release renin
(intrinsic property that occurs even if denervated)
Where does NaCl reabsorption in the distal tubule occur?
The macula densa
What inhibits the release of renin?
- Angiotensin II feeds back to inhibit renin
- ADH inhibits renin release
