RENAL PHYSIOLOGY III Flashcards
TRUE/FALSE: gain or loss of isosmotic fluid affects both the ICF and ECF
false
only affects ECF
what are the 3 important places where water is reabsorbed and what are the portion of the filtered load that those places reabsorbed?
- PCT: 67%
- DCT: 25%
- Collecting duct: 2-8%
—> <1-6% of filtered load is excreted
what are the 2 types of water reabsorption in the nephron?
- bulk (obligatory) water reabsorption
- regulated (facultative) water reabsorption
describe bulk water reabsorption?
- happens at PCT and descending limb of nephron loop
- accounts for 92% total water reabsorption
- automatic by leaky epithelia
- trans and paracellular water reabsorption
describe regulated water reabsorption?
- occurs at the collecting duct
- accounts for 2-8% of total water reabsorption
- regulated by anti-diuretic hormone (ADH)
- tight epithelia
- only transcellular reabsorption
what are the 4 important places where sodium is reabsorbed and what are the portion of the filtered load that those places reabsorbed?
- PCT: 67%
- ascending limb: 25%
- DCT: 5%
- collecting duct: 2-3%
describe the bulk Na+ reabsorption?
- occurs at the PCT and the ascending limb
- accounts for 92% of total Na+ reabsorption
describe the regulated Na+ reabsorption?
- accounts for 7-8% of total sodium reabsorption
- regulated by aldosterone (RAAS)
describe the reabsorption process at the PCT?
water
- reabsorption is driven by Na+ reabsorption
- water follows by the paracellular and transcellular pathways because leaky epithelia of PCT
Na+
- transporters such as sodium-glucose cotransport: use Na to reabsorb other solutes such as glucose
chloride (Cl-): follows via paracellular pathway because leaky epithelia of PCT
which part of the nephron loop is permeable to water?
descending
which part of the nephron loop is permeable to sodium?
ascending
describe the reabsorption process at the nephron loop
descending limb: leaky epithelium
- water reabsorbed into peritubular tube via aquaporins or across juntions between cells
ascending limb: reabsorption of Na+ into peritubular fluid
justamedullary nephrons: with the different permeabilities of the loop —> allows a hyper-osmotic medullary gradient (HOMG) to be generated
TRUE/FALSE: water reabsorption in the kidney is independent of sodium reabsorption
false
- where sodium moves, water wants to follow
BUT
water reabsorption in the kidney is facilitated by glucose reabsorption
what happens to osmolarity if TBW changes?
the plasma ECF osmolarity would be changed
in the ______1______ of ADH, there are no _______2______ in the apical membrane of epithelial cells in the _______3_______. This means that no water can be reabsorbed. Because of this, a _______4_______ volume of ______5______ urine is produced
in the _____6_____ of ADH, there are many _______2______ in the in the apical membrane of epithelial cells in the _______3_______. This means that lots of water can be reabsorbed. Because of this, a _____7______ of _______8______ urine is produced.
1: absence
2: aquaporins
3: collecting duct
4: large
5: diluted
6: presence
7: small
8: concentrated
how does ADH delivery work?
decrease in TBW –> increase in ECF osmolarity –> detected by osmoreceptors in hypothalamus –> increase in release of ADH in posterior pituitary –> insertion of aquaporins in apical membrane of CD cells –> increase water permeability –> increase in water reabsorption and decrease in urine volume –> ECF osmolarity returns to normal
where is ADH secreted?
posterior pituitary
what happens if our body is intoxicated/dehydrated?
intoxicated: hyposmotic in body fluid –> reduce ADH release to increase water excretion
dehydrated: opposite to above
what hormone related to sodium is secreted if ECF volume increase/decrease?
- increase: ANP
- decrease: aldosterone
how does RAAS work?
- decrease in blood volume/loss of isosmotic fluid (water + Na+)
- detected by pressure receptors in the kidney
- activation of RAAS from adrenal gland
- increased sodium channels in apical membrane of DCT or CD
- increase both sodium and water reabsorption
- return blood volume to normal
where is RAAS secreted from?
adrenal gland
what can you find in normal and pathological urine?
normal
- creatinine
- urea
- uric acid
- H+
- Na+
- medications and toxins
pathological
- glucose
- blood: haemoglobin, white blood cells, erythrocytes, RBCs
- protein especially albumin
- bacteria: infection
what does protein/glucose/blood presence in urine indicate?
- protein: damage to filtration barrier - glomerulonephitis
- glucose: uncontrolled diabetes
- blood: urinary infections
