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
