Summary of the Kidney

What is the hormone production in the kidney?

• Erythropoietin

• Production stimulated by decrease in PO2 (pressure)

• Produced in interstitial cells in the kidney (not in the nephron)

• Stimulates erythrocyte production through differentiation of CFU-E

into proerythroblast

• Calcitriol

• Active form of vitamin D

• Produced by hydrolysis from stored forms released from the Liver

• Essential in maintenance of calcium uptake from the GI tract

What is the filling and voiding cycle?

The filling and voiding cycle is complex and requires co-ordination

between contractile motions of the bladder and reciprocal motions of the bladder neck.

What is bladder nerve supply?

• Pudendal nerve fibres from sacral segments maintain closure of the

external sphincter (consist of skeletal muscles).

• Parasympathetic nerves from sacral segments to the bladder and

outflow tract are inactive

• Sympathetic nerves from lower thoracic and upper lumbar segments

are active and maintain relaxation of the bladder.

What is micturition?

There is a switch of function:

• Parasympathetic nerves are now active (Sympathetic nerves are now inactive)

• they release acetylcholine and the bladder contracts

• they relax the outflow tract

• Pudendal nerve fibres are less active and the external sphincter opens

• The filtrate does not change composition after leaving the collecting duct and

exits the body as urine

• Micturition involves voluntary and involuntary muscle contractions

• Stretch receptors trigger a spinal reflex, which we learn to control in childhood

• There are 2 sphincters between bladder and urethra

• Internal sphincter (smooth muscle)

• External sphincter (skeletal muscle)

• Centers in the brain stem and cerebral cortex override basic reflexes under

parasympathetic control