Renal Physiology Lecture 1: Micturition

Question 1

How much urine can the bladder hold?

Answer 1

~500mL

Question 2

What is the bladder held closed by?

Answer 2

• internal spinchter
• external spinchter

Question 3

internal sphincter

Answer 3

• Smooth muscle
• Part of the bladder wall
• Contracted at rest

Question 4

external sphincter

Answer 4

• Skeletal muscle
• Controlled by somatic motor neurons
• CNS stimulation maintains contraction unless urination occurring

Question 5

Process if micturition

Answer 5

Involves a spinal reflex. When bladder fills with urine activate stretch receptors that really sensory info to spinal chord and bladder activates parasympathetic neurons innnervating the bladder smooth muscle and triggers contraction of muscle and increase internal pressure of bladder. At the the same time somatic motor neurons innervation the external sphincter are inhibited which relaxes this sphincter and bladder cotnraction pushes urine down to urethra which forces the internal sphincter open at same time external sphincter relaxes and flows out which can be consciously controlled. Regions and brain stem and cerebral cortex receive sensory input regarding bladder fullness which can override the mixture Tati on reflex by blocking parasympathetic input to the bladder and also by maintaining closure of external sphincter.