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RS-13
Renal System - 4 - Coggle Diagram
RS-13
Renal System - 4
General Considerations
- Secretion, refers to the transport of solutes (e.g. K+, H+) from the peritubular capillaries into the tubular lumen, i.e. it is the addition of a
substance to the filtrate.
- The highest attainable rate of secretion is called the maximum tubular secretory capacity and is designated Ts (or Tm).
Substances that are secreted by the kidneys and have a Tm include: penicillin, certain diuretics, salicylate, para-amino hippuric acid (PAH) and thiamine (Vitamin B1).
H+ Secretion
- H+ secretion is a process by which the filtered HCO3- is reabsorbed and the tubular fluid becomes acidic.
The process of H+ secretion, like the
HCO3- reabsorption, occurs throughout the nephron, except in the descending limb of the loop of Henle. H+ secretion permits conservation of HCO3-
- H+ secretion into the tubular lumen occurs by active transport and is coupled to Na+
reabsorption.
Therefore, for each mole of H+ secreted,
one mole Na+ and one mole of HCO3- are reabsorbed into the peritubular capillaries.
The renal epithelium secretes approx. 4300
mEq (mmol) of H+ daily.
- Approx. 85% of the total H+
secretion occurs in the PCT. PCT cells are
very rich in enzyme carbonic anhydrase (CA).
- Approx. 10% of the total H+
secretion occurs in DCT, and
- Approx. 5% of the total H+
secretion occurs in CT by the I-cells.
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