Tubular function 2 Flashcards
What is the permeability of the descending thin limb
Highly permeable to water
Much less to urea and NaCl (movement largely passive)
What is the permeability of the ascending limb
Impermeable to water
Some Na+ reabsorbed
Cl- and K+ reabsorbed
What are symporter proteins and which drugs inhibit these proteins
Loop diuretics inhibit Transport these across the apical membrane into the epithelial membrane: 2x Cl- K+ Na+
How are Cl- moved across the basolateral membrane
Diffuse through chloride channels
How are Na+ moved across the base;ateral membrane
Na+ pump
Where do K+ go once inside epithelial cells
some diffuse through K+ channels into peritubular fluid but some go back into the tubular lumen which creates a positive charge within tubular fluid. This is driving force for paracellular transport (ions move between cells. This is how 50% of these get reabsorbed)
How does the distal tubule further decrease osmolality
IT is impermeable to water and continues active dilution using the sodium potassium pump which creates the gradient for other ions to continue to move.
Where do thiazide like diuretics act on
Symporter proteins on the early distal tubule
What are the two different types of epithelial cells in late distal tubule and collecting duct
Principal cells- reabsorb sodium ad water and secrete potassium
Intercalated cells- Important role in regulation of acid base balance by secreting new bicarbonate ions. Secrete H+ into tubular fluid which can be excreted in urine as free H+ or can be buffered with hydrogen phosphate to form dihydrogen phosphate or can be buffered with ammonia to form ammonium
How does aldosterone affect Na+ reabsorption in principal cells
Enhances Na+ reabsorption
- Increases number and activity of apical Na+ channels
- Increases activity of basolateral Na+ pump
How does aldosterone affect K+ secretion in principal cells
Enhances K+
- INcreases number and activity of apical K+ channels
- Increases activity of basolateral Na+ pump
- Na+ reabsorption
HOw does aldosterone affect H+ secretion in intercalated cells
Stimulates H+- ATpase pump
How does excess aldosterone affect the body
Causes metabolic alkalosis, hypokalaemia, hypertension and oedema (due to Na+ and water retention)
How does hypoaldosteronism affect the body
Hyperkalaemia
What does ADH have an effect on
Late distal tubule and collecting duct
What does ADH do
Facilitates the reabsorption of water. Increases water permeability in the late distal tubule and collecting duct through stimulation of insertion of aquaporins into apical membrane because of principal cells.
What is antidiuresis
When ADH is present and causes concentrated urine
What is diuresis
Increased urine volume
How does ADH affect permeability
Increases aquaporins on the surface of the membrane
Increases permeability of inner medullary collecting duct (IMCD) to urea
How does ADH increase permeability of IMCD to urea
IN absence of ADH, urea permeability of nephron is restricted to proximal tubule and inner medulla
UT1 on apical membrane in IMCD. In presence of ADH, water reabsorption concentrates urea which diffuses out of tubule lumen into medullary interstitial
Urea reabsorption helps to maintain osmotic gradient between interstitial and collecting duct lumen
Urea diffuses into ascending and descending limbs of loop of hence
What is diabetes insipidus
Inadequate secretion or response to ADH so a large volume of dilute urine is excreted
What is SIADH (syndrome of inappropriate secretion of ADH)
Usually at night, ADH secretion increases so we don’t have to urinate at night. However, in this disorder, there is increased secretion of ADH and so this leads to bed wetting
What is urea recycling and what is its effect
ADH increases the urea channels in DCT and so it goes to the ascending limb of loop of henle. This increases the concentration of the fluid inside the tubule which helps increase water reabsorption into the body.
What does ADH increase permeability of
Late distal tubule and collecting duct
