Notes: Renal Physiology
- Afferent arteriole: delivers blood to the nephron unit
- Glomerulus: a ball of capillaries fed by afferent arterioles; site of filtration; located in the renal cortex area of kidney
- Efferent arteriole: takes blood away from the glomerulus.
- Glomerular capsule: (Bowman’s capsule); surrounds the glomerulus like a cup; it is continuous with the nephron tubule.
- Proximal convoluted tubule: first part of the nephron tubule network; found in the renal cortex; has many twists in its structure
- Nephron loop (Loop of Henle); made of a descending limb which projects into the renal medulla and an ascending limb which leaves the renal medulla to project back to the renal cortex
- Descending limb (see above)
- Ascending limb (see above)
- Distal convoluted tubule: twisted final portion of the nephron tubule; feeds into collecting duct
- Peritubular capillaries: capillary system fed by the efferent arteriole that surrounds the nephron tubule
- Collecting duct: fed by several nephron tubules; concentrates urine and empties into pelvis of kidney
- Glomerular filtration: capillaries of glomerulus have fenestrae (holes) allowing passage of dissolved solutes but not proteins to leave glomerulus; filtrate flows into the capsule and is transferred to the nephron tubule.
- Regulation of filtration: controlling the blood flow to the glomerulus; constriction of the afferent arterioles will decrease blood flow to glomerulus; filtration↓
- Site of most reabsorption of solutes: proximal convoluted tubule
- Reabsorption of
- Sodium: diffuses into tubule cells because tubule cells have a low Na+ concentration; this is maintained by the Na+/K+ pump that moves Na+ out of the tubule cells and into the peritubular capillaries
- Glucose and amino acids: moved against a concentration gradient by co-transport with Na+; each time a Na+ diffused in a glucose or amino acid is pulled in with it .
- water: drawn into the tubule cells by osmosis as the Na+ diffuses into the tubule.
- Nephron loop: creates an increasing concentration of Na+ as the loop travels deeper into the renal medulla.
- Descending vs. ascending limbs (permeability):
-descending limb is impermeable to Na+; no Na+ will enter or leave the tubule here; water will be drawn out.
-ascending limb Na+ and Cl- are actively pumped form the lumen of the tubule and into the tissue of the renal medulla; the Na+ and Cl- cannot enter the descending limb or peritubular capillaries so they are trapped in the renal medulla; ascending limb is impermeable to water
12. Renal medulla: has a Na+ concentration that increases deeper into medulla
13.Distal convoluted tubule: Na+ and K+ can be secreted or absorbed to fine tune the Na+ concentration of the blood
Collecting duct: picks up the fluid from several nephron loops; plunges through renal medulla; impermeable to Na+ but will allow water to exit; as filtrate moves down the collecting duct, more water is drawn out generating a concentrated urine; urine then moves to renal pelvis.
14. Regulation of absorption:
a. Antidiuretic hormone: affects tubule cells of collecting duct making them more permeable to water; when ADH↑ collecting ducts lose less water; urine is more concentrated
b. Aldosterone: activates Na+/K+ pump in distal convoluted tubule and the cortical part of collecting duct; Na+ is reabsorbed, K+ excreted; water will follow the Na+ into the capillaries due to osmosis
c. Atrial natriuretic factor: stimulates excretion of Na+ into distal convoluted tubule; water follows Na+ into DCT due to osmosis
15. Regulation of acid and base levels: H+ ions actively secreted into filtrate across the wall of the PCT.
by PCT; it is a base
In the filtrate, the high concentration of H+ causes it to bind to HCO3- forming Carbonic acid;
16. Carbonic anhydrase: enzyme breaking carbonic acid down into water and CO2;
CO2 diffuses back into the blood; this combines with H2O → carbonic acid;
Carbonic acid→ H+ and HCO3-
H+ is then pumped back into filtrate of PTC.
17. Control of urine pH: excretion of H+ and reabsorbing HCO3- gives urine a pH between 7 and 5.
18. High acidic urine: it may be necessary to remove large amounts of H+ and form highly acidic urine, as in acidosis; nephron cannot produce urine with a pH below 4.5; to get rid of more H+, the H+ are buffered by ammonia or HPO4- and removed attached to these ions.