DSA: Micturition

Question 1

Micturition= urination.

Our urinary tract can be divided into what 2 segments?

Answer 1

1. Upper urinary tract–> kidney and ureter
2. Lower urinary tract–> bladder and urethra

Question 2

The ureter is lined by ___________, which controls ___________.

Answer 2

Ureter is lined by smooth muscle, which controls ureteral peristalsis, contractions that move urin from [kidney–> lower urinary tract] via autonomic stimulation.

Question 3

Why do kidney stones cause pain?

Answer 3

Ureter also has pain fibers, which is why kidney stones cause pain

Question 4

What part of the lower urinary tract are under involuntary control?

Voluntary control?

Answer 4

1. Detrusor muscle and the internal urethral sphincter are lined by smooth muscle, are involuntary controlled.
2. External urethral sphincter is voluntary controlled.

Question 5

What is the trigone?

Answer 5

Trigone is an area that senses the fulness of the bladder.

It is made up of 2 ureteral openings and the internal urethral sphincter, which form a triangle.

Question 6

What happens if there is a blockage of ureteral outflow (kidney stones located in the ureter)?

What happens if there is continued blockage?

Answer 6

1. Increase hydrostatic pressure d/t an increase in the amount of ureter and kidney
2. Uretal dilation occurs due to the increase in volume of urine
3. Continued blockage will cause an increase in pressure and cause hydronephrosis, swelling of the kidney, increasing the risk of ARF.

Question 7

What are the 4 anatomic constrictions- points where the ureter can be compressed?

Answer 7

1. Uretopelvic junction (UPJ)
2. Testicular/ovarian a and vein
3. External iliac a and v.
4. Bladder wall

Question 8

What is the vesicoureteral reflex?

Answer 8

1. Vesicoureteral reflex occurs when bladder is contracting to push urine out and the ureter openings do not fully close. As a result urine is also pushed up through the ureter, causing ureter dilation, and into the kidney. This increases the risk of pyelonephritis.

Question 9

Bladder signaling occurs via recipricol signaling.

For example, when the bladder is full, signals need to be sent to the brain, which then sends signals back to the bladder to contract.

[bladder–>brain–> bladder].

What does the afferent (sensory) innervation convey and how?

Answer 9

Afferent (sensory) innervation send information from the bladder–> brain to convey fullness and pain. Mechanism:

1. Intravesical pressure stretch signals fire
2. –> Sending signals via [sensory nerves fibers (which run with pelvic splanchnic n and hypogastric plexus] –> [S2-S4 (sacral micturition center).

Question 10

Bladder fullness and bladder pain is sent to the brain via afferent sensory fibers. What fibers are responsible for each?

Answer 10

• Bladder fullness: myelinated A(delta) fibers
• Bladder pain: unmyelinated C fibers

Question 11

What are the 3 efferent (motor) pathways that convey information from the [brain–> bladder]?

Answer 11

1. Parasympathetic pathway (involuntary)

2. Sympathetic pathway (involuntary)

3. Somatic pathway (voluntary)

Question 12

Bladder signaling occurs via recipricol signaling.

For example, when the bladder is full, signals need to be sent to the brain, which then sends signals back to the bladder to contract.

[bladder–>brain–> bladder].

How is motor information conveyed via the parasympathetic pathway?

Answer 12

1. [S2-S4–> pelvic splanchnic nerve] releases ACh onto M3 receptors
2. Detrusor muscle contracts
3. Internal sphincter relaxes
4. Urine is released

Question 13

Bladder signaling occurs via recipricol signaling.

For example, when the bladder is full, signals need to be sent to the brain, which then sends signals back to the bladder to contract.

[bladder–>brain–> bladder].

How is motor information conveyed via the sympathetic pathway?

Answer 13

1. [L2–> hypogastric nerve] releases NE onto A-1 R on the urethra or bladder neck; B-2/B3 R on detrusor m or bladder wall
2. Detrusor m. relaxes
3. Internal sphincter contracts
4. Bladder fills

Question 14

Bladder signaling occurs via recipricol signaling.

For example, when the bladder is full, signals need to be sent to the brain, which then sends signals back to the bladder to contract.

[bladder–>brain–> bladder].

How is motor information conveyed via the somatic pathway (voluntary)?

Answer 14

1. S2-S4–> pudendal n, which releases ACh onto nAChR
2. External urethral sphincter to contract
3. Urine is retained

Question 15

What are the 2 bladder reflexes?

Answer 15

1. Storage reflex

2. Voiding reflex

Question 16

What is the storage reflex?

Answer 16

Storage reflex allows the bladder to fill without releasing the urine and only involves the spinal cord.

• Activated by: bladder filling.
• Detrusor m. relaxes via sympathetic innervation
• External sphincter contracts via somatic NS

Question 17

What is the voiding reflex and how does it occur?

Answer 17

Voiding reflex allows the bladder to release the urine and involves the brain.

Activated by: a full bladder.

Afferent neurons send signal from SC–> brain

• Parasympathetic NS is stimulated
• Sympathetic and somatic NS is inhibited
  
  • Detrusor m. contracts
  • External sphincter relaxes

Question 18

What parts of the brain are involved in the micturition reflex (storage reflex and voiding reflex)?

Answer 18

1. Cerebral CTX

2. Midbrain (periaqueductal gray)

3. Pons (Pontine micturition center (PMC))

Question 19

What is the role of the cerebral CTX?

Answer 19

1. Interprets sensation
2. Can partially inhibit the micturition reflex
3. Can contract the external sphincter when we are voiding (voluntary stop peeing)

Question 20

What is the role of the midbrain (PAG)?

Answer 20

1. PAG receives afferent bladder signals and sends excitation info to the PMC.
2. Stimulation or inhibition of the PMC is controlled by the cerebral CTX.

Question 21

What is the role of the pons (pontine micturition center, PMC)?

Answer 21

PMC is also called Barrington’s nucleus.

It is the main activator of urination.

1. PMC receives signals from the [PAG & cerebral CTX].
2. External sphincter relaxes
3. Sacal parasympathetic outflow is activated, resulting in micturition.

Question 22

What part of the brain control and coordinates S2-S4?

Answer 22

Pons.

Question 23

Adults have voluntary abilities to start and stop urinating.

Detrustor m. and the external sphincter, work/do not work in coordination.

Answer 23

do work in coordination.

Detrusor m. contracts and the external sphincter will relax (pressure drops to 0).

As the bladder fills, sphincter is firing. As we try to void, sphincter stops firing, pressure drops to 0 and it relaxes.

Question 24

Infants have involuntary abilities to start and stop urinating.

Detrustor m. and the external sphincter, work/do not work in coordination.

Answer 24

Detrusor m. and external sphincter m. work in coordination: when detrusor m. contracts, pressure of the external spincter m. drops.

Question 25

Parapalegic patients have involuntary abilities to start and stop urinating.

Detrustor m. and the external sphincter, work/do not work in coordination.

Answer 25

Voiding occurs at lower bladder volumes and have involuntary abilities to start and stop urinating.

Detrusor m. and external sphincter m. do not work in coordination- detrusor spincter dysnergia.

As the bladder fills, sphincter is firing. However, as we are trying to void, sphincter is still firing.