ECF Volume Regulation 1&2 Flashcards
Which ions are the major ECF osmoles?
Sodium and chlorine
Which ion is the major ICF osmole?
Potassium
How is ECF volume regulated?
Regulation of body sodium
How is the total body water (42L) regulated?
ECF = 14L (Plasma = 3L and interstitial = 11L) ICF = 28L
How is sodium regulated?
High and low P baroreceptors
What happens when there is salt and water loss
Plasma volume decreases leading to a decrease in blood pressure and a decrease in carotid sinus baroreceptor inhibition of sympathetic discharge
What happens when there is an increase in sympathetic discharge?
There is an increase in vasoconstriction which increases the blood pressure towards nornal
What effect does an increase in sympathetic discharge have on the kidneys?
it increases the renal VC nerve activity which increases renal arteriolar
What happens when there is an increase in renin?
It causes an increase in angiotensin Ii which decreases the peritubular capillary hydrostatic pressure and increases sodium reasbsorption
Why is there an increase in sodium reabsorption caused by angiotensin II
Because there is greater reabsorptiveforces in the peritubular capillaries
What is the reabsorptive range in the proximal tubule?
65% in volume excess to 75% in volume deficit
What affect does a change in reabsorption have on the GFR?
Very little: autoregulation maintains the GFR and VC of afferent and efferent means there is little effect unless it is large enough to cause a change in MBP
Which hormone regulates sodium reabsorption in the distal tubule?
Aldosterone
How is aldosterone secretion controlled?
Reflexes involving the kidneys themselves
What are juxtaglomerular cells?
Large epithelial cells with plentiful granules
What forms the juxtaglomerular apparatus?
Juxtaglomerular cells + macula densa
Which hormone is secreted by the juxtaglomerular cells?
Renin: proteolytic enzyme which acts on angiotensin 1
Which enzyme converts angiotensin I to angiotensin II?
Angiotensin converting enzyme (ACE)
Where are angiotensin converting enzymes found?
Vascular endothelium especially in the pulmonary circuit
What is the function of Angiotesin II?
It stimulates the aldosterone secreting cells in the zona glomerulosa of the adrenal cortex
Which step in the RAAS system is the rate limiting step?
Release of Renin
What causes an increase in renin release?
A decrease in pressure in the afferent arteriole at the juxtaglomerular cells
Sympathetic nerve activity (on beta 1 cells) and decreased NaCl delivery
What causes a decrease in renin release?
Angiotensin II feedback inhibits renin and ADH inhibits renin release
How does Angiotensin II respond to hypovolaemia?
It stimulates aldosterone, it is a potent vasoconstrictor, it stimulates ADH secretion and it stimulates the thirst mechanism and salt appetite
In the case of a person who has lost both salt and water, what takes priority: ECF volume or ECF osmolarity?
ECF volume: emergency mechanism to save perfusion to the brain
What is the management of large losses of salt and water?
Infuse/drink saline
DO NOT give pure water
Which hormone promotes sodium reabsorption?
Aldosterone
What is ANP and what does it do?
Atrial Natriuretic Peptide: promotes sodium excretion
What affect does aldosterone have on potassium secretion?
It increases the secretion
Which cells secrete ANP?
Atrial cells
Why does renal disruption in uncontrolled diabetes lead to a hyperglycaemic coma?
1) glucose remains in the tubule exerting an osmotic effect
2) Sodium conc. in the lumen is decreased and as sodium enters the proximal tubule sodium reabsorption will be decreased
3) As glucose shares a transporter with sodium, glucose reabsorption is decreased
4) Movement of water out of the tubule is reduced meaning fluid in the descending limb is not so concentrated: interstitial gradient is abolished
5) Large volumes of urine are produced and if ingestion is not adequate then the resulting hypotension may be severe enough to cause a hyperglycaemic coma (due to inadequate blood flow to the brain)
