8 - Micturition And Incontinence

Question 1

What does micturition mean?

Answer 1

To want to pass urine.

Question 2

What are the two phases the bladder can be in?

Answer 2

Storage phase,

Bladder voiding phase.

Question 3

What stimulates the storage phase of urine?

Answer 3

The sympathetic nervous system.

Question 4

What stimulates the bladder voiding phase?

Answer 4

The parasympathetic nervous system.

Question 5

What other nervous supply stimulates the bladder (apart from para/sympathetic)?

Answer 5

The somatic nervous system.

Question 6

What are the three main structures of the bladder?

Answer 6

Body, Trigone and Neck.

Question 7

Why is the trigone of the bladder named in this way?

Answer 7

The two ureteric and the internal urethral orifices are at the angles of a triangle.

Question 8

What is the basic function of the body?

Answer 8

To temporarily store urine before voiding.

Question 9

What is the basic function of the neck?

Answer 9

To connect the bladder to the urethra.

Question 10

What are the three main muscles of the urinary bladder?

Answer 10

Detrusor urinae muscle (detrusor = to push down; found in the lesser pelvis),
Internal urethral sphincter (physiological),
External urethral sphincter (anatomical).

Question 11

What is the embryonic origin of the bladder?

Answer 11

It is a hollow, smooth muscle organ derived from the hindgut.

Question 12

What is the arrangement of the detrusor urinae muscle’s fibres?

Answer 12

1. Layers of inner longitudinal muscle fibres,
2. Circular arrangement of fibres,
3. Layers of outer longitudinal muscle fibres.

Question 13

What is the benefit of the arrangement of the detrusor urinae muscle’s fibres?

Answer 13

It confers strength (inner longitudinal then circular then outer longitudinal) irrespective of which direction it is being stretched in. It cannot commit peristalsis.

Question 14

What type of epithelium is found in the bladder? Why is this advantageous to it?

Answer 14

Transitional - a specific type called urothelium, found extensively throughout the urinary tract. It confers the ability to the bladder, and other structures of the urinary tract, to distend.

Question 15

What is the primary muscle of continence?

Answer 15

The internal urethral sphincter. It is a direct continuation of the detrusor urinae muscle (smooth muscle).

Question 16

What do we mean when we say, physiological sphincter?

Answer 16

The internal urethral sphincter is an example. It functions as a valve, allowing urine to pass through passively. There is no muscle thickening, its action is solely due to its structure.

Question 17

What are anatomical sphincters?

Answer 17

The external urethral sphincter is an example. Functions as a valve which can be opened and closed at will. This is due to the circular muscle thickening can contract and relax depending on nervous stimulation).

Question 18

What is the external urethral sphincter formed from?

Answer 18

The pelvic floor muscles (levator ani etc.).

Question 19

What nervous systems control the external urethral sphincter?

Answer 19

The somatic nervous system (voluntary control). It is made up of skeletal muscle fibres that when contracted, constrict the urethra, preventing unwanted voiding.

Question 20

What are the boundaries of the lesser (or true) pelvis?

Answer 20

Roof: pelvic brim
Anterior: pubic symphysis
Posterior: sacrum, coccyx
Lateral: obtutaror internus
Floor: pelvic floor

The detrusor urinae muscle is within this structure.

Question 21

What is the nerve supply to the detrusor urinae muscle?

Answer 21

Sympathetic: Relaxation via B3 (Hypogastric Nerve - L10-T2).
Parasympathetic: Contraction via M3 (Pelvic Nerve - S2-S4).

Question 22

What is the nerve supply to the internal urethral sphincter?

Answer 22

Sympathetic: Contraction(!) via a1 (Hypogastric Nerve - L10-T2).

Question 23

What is the nerve supply to the external urethral sphincter?

Answer 23

Somatic: Contraction via Nicotinic Receptors (ACh-mediated; Pudendal Nerve - S2-S4).

Question 24

What is the storage (or continence phase) controlled by?

Answer 24

Continence neurones. Damage to which leads to reduced bladder capacity, urgency, urinary incontinence (failure to store urine).