Micturition

Question 1

1. What is the definition of micturition

Answer 1

the periodic discharge of urine from the bladder through the urethra

Question 2

2. what is micturition intiated by?

Answer 2

it is initiated by voluntary relaxation of the sphincter muscle below the bladder

Question 3

3. What maintains micturition

Answer 3

maintained by reflex contraction of the muscles of the bladder

Question 4

where does urine produced by the kidneys drain into

Answer 4

Drains into urinary bladder via ureters on both sides of body

Question 5

how much volume does the adult bladder hold?

Answer 5

500ml

Question 6

what does the internal urethral sphincter guard?

Answer 6

internal urethral sphincter guards outlet to urethra

Question 7

what is the external urethral sphincter responsible for?

Answer 7

External sphincter (aka external urethral sphincter) responsible for voluntary control

Question 8

why is female urethra shorter than male urethra

Answer 8

Male urethra travels through penile shaft therefore female urethra is shorter

Question 9

5. What type of organ is the Urinary bladder

Answer 9

hollow organ

Question 10

6. What forms the BODY of the urinary bladder

Answer 10

– formed by detrusor muscle

Question 11

7. What forms the NECK of the urinary bladder?

Answer 11

trigone in its posterior aspect

Question 12

8. What guards the emptying of the bladder?

Answer 12

internal and external sphincters

Question 13

9. What type of muscle is the internal sphincter made of

Answer 13

completely involuntary ( smooth muscle)

Question 14

10. What type of muscle is the external sphincter made of

Answer 14

voluntary. ( skeletal muscle)

Question 15

11. What muscle is responsible for emptying of the bladder

Answer 15

Detrusor muscle

Question 16

12. What is the advantage of the urinary tract being made up of stratified Squamous epithelium

Answer 16

It allows stretching of the bladder

Question 17

13. What nerve fibres supply the urinary bladder and the internal sphincter

Answer 17

supplied by sympathetic and
parasympathetic nerve fibres

Question 18

14. What vertebral levels is the sympathetic supply found and what is the nerve called

Answer 18

• L1/L2
• Hypogastric nerve

Question 19

15. What nerve fibres supply the external sphincter

Answer 19

supplied by somatic nerve fibres
called the Pudendal nerve

Question 20

what vertebral levels is the sympathetic supply found and what is the nerve called

Answer 20

• S2,S3,S4
• pelvic nerve

Question 21

16. What do sensory fibres in the pelvic nerve do?

Answer 21

carry impulse from the stretch receptors present on the wall of urinary bladder and urethra.

Question 22

17. What does the stimulation of the hypogastric nerve cause?

Answer 22

Relaxation of detrusor muscle and
Constriction of internal sphincter which causes filling of the bladder

Question 23

18. What is another name for the hypogastric nerve

Answer 23

nerve of filling.

Question 24

19. What does stimulation of the pelvic nerve cause

Answer 24

Contraction of detrusor muscle
And relaxation of internal sphincter resulting in the emptying of the bladder

Question 25

20. What is another name for the pelvic nerve

Answer 25

the nerve of micturition.

Question 26

21. What state does the pudendal nerve keep the external sphincter in?

Answer 26

constricted state.

Question 27

22. What happens when the pelvic nerve is blocked

Answer 27

When this nerve is blocked, external sphincter relaxes however can be controlled voluntarily

Question 28

23. What type of smooth muscle does the wall of the ureter contain

Answer 28

spiral, longitudinal and circular bundles of smooth muscle.

Question 29

24. How often do peristaltic contractions occur

Answer 29

occur 1 to 5 times per minute

Question 30

25. When does the first sense of filling occurs

Answer 30

When volume of urine reaches nearly 150ml

Question 31

26. At how many ml of urine does a marked sense of filling occur at?

Answer 31

400ml

Question 32

27. Where are spinal centres of micturition located

Answer 32

Located in sacral and lumbar segments

Question 33

28. What are spinal centres of micturition controlled by

Answer 33

higher centres of brain.

Question 34

29. Where is the facilitatory centre of the higher centres of micturition located

Answer 34

Pontine region, Posterior hypothalamus.

Question 35

where is the inhibitory centre of the higher centres of micturition located?

Answer 35

mid brain

Question 36

outline the 10 step process of the micturition reflex

Answer 36

1. volume of urine in the bladder reaches near 400ml and intra-vesical pressure increases 2. Bladder wall stretches and stretch receptors on the bladder wall are activated 3. Sensory signal is given to spinal centres through sensory fibres of parasympathetic (pelvic) nerve and a reflex arc is produced in spinal cord. 4. Motor signal is given to urinary bladder through motor fibres of parasympathetic nerve (pelvic nerve), causing detrusor muscle contracts and internal sphincter relaxed. 5. Urine passes down into proximal urethra and an afferent impulse is given to the spinal cord 6. Afferent impulse reaches the higher centres in brain via the spinethalamic tracts. If the signal from brain stem is to micturate, impulse created from spinal centre block pudendal nerve. 7. at the same time the sympathetic efferent are inhibited 8. external sphincter relaxes and micturition occurs 9. If the signal from brain stem is not to micturate, sympathetic efferents are stimulated and as a result, detrusor expands and internal sphincter constricts 10. External sphincter remains constricted. so, urine continues to accumulate in bladder.

Question 37

31. What are 3 types of bladder abnormalities

Answer 37

- Deafferentation - Denervation - Absence of regulation by higher centres

Question 38

32. How can deafferentation occur?

Answer 38

Due to injury to afferent sensory nerve fibres

Question 39

33. What are features of deafferentation

Answer 39

- Individual is unaware of distension of bladder - Voluntary micturition is possible - If such person fails to micturate at reg intervals, bladder overflows + causes dribbling of urine overflow incontinence.

Question 40

34. Why does bladder wall remain flaccid?

Answer 40

- Because no afferent supply

Question 41

35. What is automatic bladder?

Answer 41

bladder empties automatically and the sphincter relaxes passively by increased intra-vesical pressure seen in Tabes dorsalis ( syphilis)-degeneration of dorsal nerve roots (tabetic bladder).

Question 42

36. What is denervation?

Answer 42

injury to both afferent and efferent nerves.

Question 43

37. What are features of denervation

Answer 43

- Voluntary micturition is completely lost. - Nerve supply completely lost, so it’s called isolated bladder /decentralized bladder.

Question 44

38. What is denervation also called

Answer 44

called flaccid neurogenic bladder/ hypoactive neurogenic bladder.

Question 45

what are the 2 higher centres that can regulate micturition

Answer 45

1. Lesion of superior frontal gyrus 2. Lesion in midbrain

Question 46

what happens to micturition in there is a lesion of superior frontal gyrus

Answer 46

reduces desire to urinate and difficulty in stopping micturition once it has started

Question 47

how do paraplegia patients initiate micturition

Answer 47

they pinch or stroke their thighs which provokes a mild mass reflex

Question 48

what happens to micturition if there is a lesion in the midbrain

Answer 48

causes continuous excitation of spinal micturition centres, resulting in frequent and uncontrollable micturition