Each nephron has a different Tm therefore the substance can appear in the urine before the Tm for the kidney is reached. When substance first appears in urine is called the renal threshold. Also causes peripheral vasoconstriction. During formation of urine the tubular fluid flows through the tubules because of hydrostatic pressure difference between Bowmans capsule and kidney pelvis. Urine is transported from the renal pelvis to the urinary bladder by peristalsis in the ureters.
Micturition is the physiologic term for emptying the bladder.
Relexes controlling the emptying of the bladder are in the sacral spinal cord and brain stem Parasympathetics are the sole motor nerve supply to the detrusor muscle of the bladder. During transport to the lungs, CO2 diffuses into the erythrocytes and is hydrated under the influence of carbonic anhydrase. Chemical Buffer Systems First line of defense in maintaining constant pH of the extracellular fluids. Protein system positive and negative charges on proteins act as buffering agents.