ECF Volume Regulation Flashcards
What are the two major ECF osmoles?
Na+ and Cl-
What is the major ICF osmole?
K+
What is the result of ECF volume regulation?
Regulation of body Na+
What occurs if there is a change in Na+ concentration in ECF?
ECF volume changes, the volume of blood perfusing tissues changes and thus,circulating volume and BP are affected
What is the renal response to a decrease in ECF volume?
Hypovolaemia
When is there an increase in salt and a loss of water?
Vomiting, diarrhoea or excess sweating
What is the effect of an increased salt concentration and a net loss of water?
Decrease in Plasma Volume, decrease in venous pressure, decrease in Venous Return, a decrease in atrial pressure, a decrease in End Diastolic Volume and stroke volume= Decreased Cardiac output and stroke volume which DECREASES CAROTID SINUS BARORECEPTOR INHIBITION OF SYMPATHETIC DISCHARGE
What affects do decreased atrial pressure and decreased carotid sinus discharge have on ADH?
Increases ADH concentration
What affect does an increase in sympathetic discharge have on renin concentration?
There is an increase in renal VC nerve activity which increases renal arteriolar constriction and thus there is an increased in renin
What affect does an increase in renin concentration have on peritubular capillary hydrostatic pressure?
Inc. Renin, inc. angiotensin II which decreases PC hydrostatic P = increase in Na reabsorption and a decrease in Na excretion
What affect does an increase in renin concentration have on aldosterone?
Increased renin, increased Angiotensin II = increased aldosterone = increase in Na reabsorption and decrease in Na excretion
What is Na+ reabsorbtion controlled by?
Aldosterone
What do Juxtoglomerular Cells produce?
Renin
What does renin act on?
The alpha 2 globulin fraction of angiotensinogen
What controls renin release ?
- Afferent arteriole pressure at level of JG cells decreases
2 Increases sympathetic nerve activity
- Decreased NaCl delivery at macula densa
- Angiotensin II feeds back to inhibit renin
- ADH inhibits renin release
Why is angiotensin II important in response to hypovolaemia?
It stimulates aldosterione = NaCl and H2O retention
Acts as a vasoconstrictor
Acts on hypothalamus to stimulate ADH secretion to increase H2O reabsorption
Stimulates thirst mechanism and salt appetite
What promotes Na+ Excretion?
ANP
Describe Aldosterone escape?
ANP can override aldosterone effects on Na+ reabsorption due to volume expansion
Why is renal function disrupted in uncontrolled diabetes?
Glucose remains in tubule and exerts an osmotic affect to retain water.
Results in a decreased [Na+] in the lumen bc Na+ is present in a larger volume = decreased concentration gradiet = decreased Na reabsorption = decreased ability to reabsorb glucose since it shares a symport with sodium
H2O movement out of descending limb of LoH into instestitium is reduced. Fluid in LoH is not so concentrated
Fluid delivered to ascending loop is less concentrated. Less NaCl and H2O are reabsorbed by loop of henle so a large volume of NaCl and H2O are delivered to the distal tubule and interstitial gradient is gradually abolished.
Macula Densa detects high rate of delivery of NaCl so renin secretion is suppressed thus Na reabsorption at d.tubule is decreased
What urine is secreted in uncontrolled diabetes?
Isotonic urine
What happens when there is an increase in blood volume?
Atrial baroreceptors stretch and cause myocardial cells to stretch and produce natriuretic peptides
What affect does natriuretic peptide have on the hypothalamus?
There is a decrease in ADH production
What affect does natriuretic peptide have on the kidney?
There is a DECREASE in Renin (which reduces BP)
and an increase in GFR
What affect does natriuretic peptide have on the adrenal cortex?
There is a decrease in aldosterone production
If you decrease ADH and Aldosterone levels yet increase GFR, what occurs?
NaCl and H2O excretion
What does ANP do?
Promote Na excretion in response to ECF and BP
When is H+ secretion upregulated ?
During hypokalaemia
