Physiology of Micturition

Question 1

What is the pathway of urine from the kidneys

Answer 1

urine flows from the kidneys to the ureters via peristaltic contraction of the smooth muscle from the ureters, they enter the bladder at an oblique angle to prevent reflux of urine, the urine then passes from the bladder into the urethra

Question 2

What is the sphincters of urethra

Answer 2

The internal urethra spinchter

The external urethral spinchter

Question 3

why isn’t the internal spinchter a true spinchter

Answer 3

Is located where the smooth muscle at the start of the urethra and acts as a spinchter when the smooth muscle is relaxed, and therefore passive contracts

Question 4

Why is the external spinchter a true spinchter

Answer 4

is made up of skeletal muscle under voluntary somatic control

Question 5

What is the arrangement of the bladder

Answer 5

bag of smooth muscle called detrusor muscle, arranged in a spiral, longitudinal and circular bundles

Question 6

What is the characteristic shape of the preside -volume curve of the bladder

Answer 6

there is a long flat segment as the initial increments of urine enter the bladder and then suffer sharp rise as the micturition reflex is triggered

Question 7

What is a cytometrogram mesure

Answer 7

A plot of bladder (intravesical) pressure against the depressant of fluid in the bladder

Question 8

What is the normal daily urine production

Answer 8

varies between 750ml - 2500mls in temperate climates

Question 9

What is the difference between urethral and ureter obstructions

Answer 9

Urethral obstruction - bilateral renal problems

where ureter obstruction causes unilateral renal problems

Question 10

Overall how is mictruation controlled

Answer 10

By two controlling pathways learned to override spinal reflex urination

Question 11

What is the type of motor innervation is involved in the spinal reflex of mictruition

Answer 11

Rich parasympathetic supply (via pelvic nerves)

Spare sympathetic supply (via hypogastric nerves)

Somatic motor neurones (via pudendal nerves)

Question 12

What is the affect of parasympathetic innervation in motor control of mictrution

Answer 12

increase activity and contraction of detrusor muscle, causing an increase pressure within the bladder

Question 13

What is the affect of sympathetic innervation in motor control of mictrution

Answer 13

inhibit bladder contraction and closes the internal urethral spinchters

Question 14

How important is sympathetic supply to bladder function

Answer 14

not very important to bladder function (but cutting the hypogastric nerve causes frequency of micturition)

main function is to prevent the reflux of semen into the bladder during ejaculation

Question 15

What is the affect of somatic motor neurone innervation in motor control of mictrution

Answer 15

innervate the skeletal muscle that forms the external urethral spinchter, keep the spinchter closed even against strong bladder contractions, (gives a tonic discharge)

Question 16

What triggers sensory innervation in spinal reflex of mictrution

Answer 16

As the bladder fills, it becomes distended and the stretch receptors in the bladder wall are increasingly stimulated, until their output becomes great enough to cause bladder contraction

Question 17

How does the sensory innervation cause the bladder to contract

Answer 17

Causes:

Excitation of parasympathetic outflow

Inhibition of sympathetic outflow

Inhibition of motor neurones to external spinchter (so tonic discharge inhibited)

send pathway to sensory cortex to give sensation of fullness

Question 18

Why do babies wet themselves

Answer 18

the micturition reflex operates at this spinal reflex level because the higher brain connections have to be established to over ride it,

Thats why babies need to lean to potty train, to learn how to hold and delay their pee

Question 19

What are the two controlling pathway learned to overside spinal reflex

Answer 19

Delay of urination

Voluntary initaition of urination

Question 20

How is delay of urination achieved

Answer 20

Via the pontine storage area in the brain stem sending descending pathways that inhibit urination :

Inhibit parasympathetic

stimulate the somatic nerves to the eternal spinchters, thus over-ridding the input from the bladder stretch receptors

Question 21

How is voluntary initiation of urination achieved

Answer 21

Via the pontine mictruition pathway that involves descending pathway, that stimulate urination:

stimulate parasympathetic

inhibit the somatic motor neurones thus summating with the stretch receptor effects

Question 22

When does pontine mictruition area over ride pontine storage area

Answer 22

Happens when the bladder is full up the stretch receptors trigger the pontine centre as the need to pee is to much so over rides pontine storage area

Question 23

What happens when individual is consciously ready to urinate

Answer 23

consciously initiates voiding
causing the bladder to contract and the outlet to relax

(the relaxation of the muscles of the pelvic floor may cause a sufficient downward tug on the detrusor muscle to initiate its contraction)

Question 24

What can control the process of urination once initiated

Answer 24

perineal muscles and external spinchter can be contracted voluntarily, preventing urine flowing down the urethra or interrupting the flow once urination begins

Question 25

What occurs after urination in males and females

Answer 25

female urethra empties by gravity

urine remaining in the male urethra is expelled by contraction of bulbocavernousus muslce

Question 26

What are the abnormalities of mictrution due to neural lesion

Answer 26

interuption of afferent nerves

interuption of both afferent and efferent nerves

interruption of facilitatory and inhibitory descending pathways from the brain

Question 27

What affect does neural lesions have on mictrution

Answer 27

the bladder contracts but the contractions are generally insufficient to empty the bladder completely

Question 28

How do some paraplegic patients train themselves to initiate void

Answer 28

pinching or stroking their things causing a mild mass reflex

as after spinal section, afferent stimuli irradiate from one reflex to centre to another

so when a relatively minor noxious stimulus is applied to the skin, it may irradiate the autonomic centres to evoke bladder or rectal voiding

basically returning some measure of voluntary control by allowing them to induce an intentional mass reflex

Question 29

What is the adult volume of urine needed to overside voluntary control and initiate spinal reflex

Answer 29

300-350mls