Mictruition

Question 1

What happens there is a blockade of ureteral outflow (kidney stone)?

Answer 1

• Increased hydrostatic pressure (due to fluid retention)
• Ureteral dilation (to accommodate fluid retention)
• If stone is not removed, pressure will continue to increase and Hydronephrosis (kidney swelling) will occur and potentially cause Acute Renal Failure
• Painful stimuli will cause sympathetic constriction of ureter, blocking urine movement through blocked ureter

Question 2

What are the 4 locations of potential Anatomic constrictions of the ureter?

Answer 2

1. Uretopelvic junction
2. Testicular/Ovarian Artery and Vein (top third of ureter)
3. External Iliac Artery and Vein (2/3 down the ureter)
4. Bladder Wall

Question 3

What is the Vesicoureteral Reflex?

Answer 3

The ureteral openings in the bladder do not fully close, thus when the bladder contracts, some urine is ejected back up the ureters

Pylonephritis (kidney infection) can occur if any bacteria invade the urine in the bladder and are ejected back up to the kidney

Question 4

How are afferent signals in the bladder initiated?

Answer 4

Intravesical Pressure Stretch signal

Question 5

Where do the afferent sensory signals synapse?

Answer 5

S2-S4 (sacral mictruition center)

Question 6

What do the afferent sensory signals convey, which nerve fibers do they travel through, and are they myelinated or unmyelinated?

Answer 6

Bladder fullness (normal) - Alpha-Delta nerve fibers, myelinated

Bladder Pain (abnormal; infection) - “C” nerve fibers, unmyelinated

Question 7

For efferent motor parasympathetic signaling:
Where does the signal start in the spine?
What nerve does it travel through?
What is its action?
What neurotransmitter does it use?
What is the receptor?
Is this voluntary or involuntary?

Answer 7

• S2-S4
• Pelvic Splanchnic Nerve
• Contraction of the Detrusor Muscle & Relaxation of the internal urethral sphincter
• ACh
• mACh; M3
• Involuntary

Question 8

For efferent motor sympathetic signaling:
Where does the signal start in the spine?
What nerve does it travel through?
What is its action?
What neurotransmitter does it use?
What is the receptor?
Is this voluntary or involuntary?

Answer 8

• L2
• Hypogastric Nerve
• Relaxation of the Detrusor Muscle & Contraction of the internal urethral sphincter
• Norepinephrine
• Adrenergic: Alpha-1 (urethra); Beta-2 & Beta-3 (detrusor muscle)
• Involuntary

Question 9

For efferent motor somatic signaling: 
Where does the signal start in the spine?
What nerve does it travel through?
What is its action?
What neurotransmitter does it use?
What is the receptor?
Is this voluntary or involuntary?

Answer 9

• S2-S4
• Pudendal Nerve
• Contraction of the external urethral sphincter
• ACh
• nAChR
• Voluntary

Question 10

What is the storage reflex?

Answer 10

Reflex that prevents voiding (bladder is filling, but not full)

Activated by bladder filling

Occurs in the spinal cord (no brain involvement)

Sympathetic and Somatic outflow occurs, causing detrusor muscles to contract and EXTERNAL urethral sphincter to relax

Question 11

What is the Voiding Reflex?

Answer 11

Causes voiding to occur when the bladder is full

Activated by full bladder

Afferent nerves transmit signal to spinal cord, then to the brain

Stimulates Parasympathetic outflow and inhibits sympathetic/somatic outflow.

Caused Contraction of Detrusor Muscle and relaxation of the EXTERNAL urethral sphincter

Question 12

What is the role of the cerebral cortex in bladder control?

Answer 12

1. Interprets fullness and emptiness of the bladder
2. Can partially inhibit the Voiding reflex
3. Can contract external sphincter even while in the process of voiding

Question 13

What is the role of the Midbrain in bladder control?

Answer 13

The Periaqueductal Gray (PAG) of the Midbrain is responsible for:

1. Receiving afferent bladder signals
2. Is the Primary Excitation Input for the Pontine Micturation Center (PMC)
3. Higher brain centers (cerebral cortex) can stimulate/inhibit PAG signaling to the PMC

Question 14

What is the role of the Pons in bladder control?

Answer 14

The Pontine Micturation Center (PMC) (AKA Barrington’s Nucleus) of the Pons is responsible for:

1. Receives signaling from the Periaqueductal Gray (PAG) of the Midbrain and from higher brain centers (cerebral cortex)
2. Activates the sacral parasympathetic outflow (causing detrusor muscle contraction and internal sphincter relaxation) and causes external urethral sphincter to relax
3. Controls/coordinates S2-S4 (Sacral Micturation Center)

Question 15

What are the important characteristics of adult urination pattern?

Answer 15

• Voluntary ability to start/stop
• Detrusor muscle and External urethral sphincter work in coordination
• Sphincter pressure increases as volume increases, then plummets as detrusor muscles contract

Question 16

What are the important characteristics of infant urination pattern?

Answer 16

• Infants void at lower bladder volume
• Involuntary start/stop
• Detrusor muscle and external urethral sphincter work in coordination

Question 17

What are the important characteristics of paraplegic patient urination pattern?

Answer 17

• Voiding occurs at lower bladder volume
• Involuntary start/stop of urination
• Uncoordinated action of the detrusor muscle and external urethral sphincter