Changes

==Structure and Function==

==Structure and Function==

The primary functions of the kidneys are ''osmoregulation'' and filtration.  That is, the kidneys filter small molecules and ions from the blood and support organismal [[homeostasis]] by balancing the concentration of water and salts in the bloodstream.  The kidneys also secrete hormones which regulate things like thirst and blood pressure.

The primary functions of the kidneys are osmoregulation and filtration.  That is, the kidneys filter small molecules and ions from the blood and support organismal [[homeostasis]] by balancing the concentration of water and salts in the bloodstream.  The kidneys also secrete hormones which regulate things like thirst and blood pressure.

Each kidney is composed of ~1,000,000 functional filter structures called [[nephron|nephrons]].  Each nephron contains a filter head ([[glomerulus]]) with re-absorptive tubules draining into a collecting duct.

Each kidney is composed of ~1,000,000 functional filter structures called [[nephron|nephrons]].  Each nephron contains a filter head ([[glomerulus]]) with re-absorptive tubules draining into a collecting duct.

Blood passing through the capillaries in the glomerulus passes over a sieve formed by specialized cells called ''podocytes''.  The filtrate which passes through the sieve then travels through the tubules where water and salts still needed by the body are reabsorbed into the bloodstream, concentrating the urine.  The urine then passes into the collecting duct system where it is further concentrated.  Finally, the urine passes through a papillary duct into the renal calyces, then into the pyelum and out through the ureter.

Blood passing through the capillaries in the glomerulus passes over a sieve formed by specialized cells called ''podocytes''.  The filtrate which passes through the sieve then travels through the tubules where water and salts still needed by the body are reabsorbed into the bloodstream, concentrating the urine.  The urine then passes into the collecting duct system where it is further concentrated as more water is reabsorbed.  Finally, the urine passes through a papillary duct into the renal calyces, then into the pyelum and out through the ureter and into the bladder.

The re-absorptive machinery in the kidneys is so efficient that only 1 liter of urine is produced for every ~100 liters of primary filtrate produced in the glomerulus.

The re-absorptive machinery in the kidneys is so efficient that only 1 liter of urine is produced for every ~100 liters of primary filtrate produced in the glomerulus.  This efficiency is important physiologically because it allows the body to conserve water and salts.  [[Diabetes insipidus]] is a disease state in which the ability of the kidneys to reabsorb water is somehow compromised, usually due to a deficiency in the hormone [[vasopressin]] (AVP).

==References==

==References==