Water and Electrolyte Balance Flashcards
Give some examples of ECF
Interstitial fluid
Lymph
Plasma
Transcellular fluids
What is the main cation in the ECF and ICF
ECF = Na+ ICF = K+
What is the function of the kidneys
Maintain the composition, osmolality and volume of the ECF
Control acid-base balance
Roughly what % of water and Na+ reabsorption happens in the LOH
20%
Roughly what % of water and Na+ reabsorption is fine tuned by hormones in the DCT and CD
15%
What hormones are involved in the regulation of reabsorption in the nephron
ADH
Aldosterone - affects sodium reabsorption and K+ excretion
Renin-angiotensin-aldosterone system
How does ADH affect water reabsorption
Acts by increasing the permeability of the CD and DCT to water, allowing it to achieve equilibrium with the surrounding interstitial fluid in the medulla
Where is ADH released from
posterior pituitary
Where are the receptors for ADH found
On the membranes of tubular (principal) cells in the collecting ducts
What does activation of ADH receptors cause
Synthesis of several proteins including aquaporin-2 that facilitates passage of water through the membrane
What causes ADH secretion
Increases in plasma osmolality are detected by osmoreceptors in the hypothalamus and this stimulates ADH release from the posterior pituitary
What is diabetes inspidus and what are some symptoms
Inadequate secretion or action of ADH/vasopressin
Collecting ducts aren’t very permeable to water and so a large volume of dilute urine is produced
Dehydration and intense thirst
What is diabetes mellitus, what are some symptoms and how does it affect urine production
Inadequate secretion or action of insulin causes hyperglycaemia and glycosuria.
A large volume of iso-osmotic urine is produced as the excreted glucose carries water with it and so the osmotic pressure increases in the tubules
Where is most of the filtered potassium reabsorbed
PCT
Where in the nephron does the majority of potassium secrete into
DCT
Where are most Hydrogen ions secreted into in the nephron
DCT
What controls reabsorption of sodium ions in the DCT
Aldosterone
What secretes aldosterone
the zone glomerulosa in the adrenal cortex
In the DCT what is sodium reabsorbed in exchange for
Potassium and hydrogen ions
What effects does aldosterone have on ions absorption and excretion
Increases renal sodium absorption
Increases potassium excretion
What in the blood stimulates the secretion of aldosterone from the adrenal cortex
Increased K+
Decreased Na+ (aldosterone secretion is an indirect effect of renin-angiotensin
How does decreased Na+ affect blood volume
causes a fall
What is renin released in response to
- Sympathetic stimulation
- a fall in renal perfusion pressure at the afferent arteriole (ie a fall in systemic arterial pressure)
- hyponatraemia (low Na)
What does renin do
Cleaves angiotensinogen into AT1 and is then converted into AT2 by ACE
What is the main role of angtiotensin
Restore volume after blood loss
What does angiotensin act on and what does that cause
Acts on vascular smooth muscle, causes vasoconstriction in the systemic circulation as a whole and increases arterial blood pressure and reduces renal blood flow and GFR
What does angiotensin stimulate in the PCT
Sodium reabsorption
What hormones does angiotensin stimulate to release
Aldosterone and ADH
How does a decrease in blood volume effect renin secretion, AT2 production and aldosterone secretion
renin - increased
AT2 - increased
Aldosterone - increased
How does an increase in blood volume effect renin secretion, AT2 production and aldosterone secretion
Renin - decreased
AT2 - decreased
Aldosterone - decreased
How does an increase in K+ volume effect renin secretion, AT2 production and aldosterone secretion
Renin - none
AT2 - none
Aldosterone - increased
How does an increase in sympathetic activity volume effect renin secretion, AT2 production and aldosterone secretion
Renin - increased
AT2 - increased
Aldosterone - increased
How does a decreased blood volume cause its affect on renin, AT2 and aldosterone
Fall in renal perfusion at the afferent arteriole. Granular cells from JG apparatus release renin
How does an increased blood volume cause its affect on renin
Increased Na+ in DCT acts via macula dense to inhibit renin release
How does an increased K+ cause its affect on aldosterone
Direct stimulation of adrenal cortex
How does an increase in sympathetic activity cause its affect on renin, AT2 and aldosterone
Beta-adrenergic effect stimulates renin directly
