- 2 functions of the kidneys: get rid of waste material that are ingested or produced by metabolism and control volume and electrolyte composition of the body fluids
- what is the regulatory function of the kidneys: balance b/w intake (due to ingestion and metabolic production) and output (due to excretion and metabolic consumption) = maintains stable environment (homeostasis)
- filter plasma and filtrate by excreting them into the urine
- some products of metabolism that are eliminated as waste by the kidney: creatine, urea, uric acid, end products of hemoglobin breakdown and metabolites of various hormones
- also eliminate most toxins such as pesticides, drugs and food additives!
- excretion of water and electrolytes must match intake, intake depends on person's diet
- EX: response to daily rapid jump of sodium intake = kidneys have to later sodium excretion, in many people sodium intake can be increased 10x normal w/ relatively small changes in the ECF volume or plasma sodium concentration (otherwise sodium will accummulate and raise the ECF beyond normal causing hormonal changes and other responses to signal kidneys to increase sodium excretion)
- regulate arterial pressure, acid-base balance, erthroyte production, D3 production, and glucose synthesis
- blood flow to the 2 kidney is about 22% of cardiac output
- renal circulation has 2 capillary beds = glomerular and peritubular, arranged in series, separated by the efferent arterioles
- efferent arterioles lead from the glomerulus to the peritubular capillaries that surround the renal tubules (afferent arterioles lead to the the glomerulus)
- these arterioles help regulate the hydrostatic pressure in both sets of capillaries
- high hydrostatic pressure in the glomerular capillaries causes rapid fluid filtration
- a much lower hydrostatic in the peritubular capillaries permits rapid fluid reabsorption
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