Urinary L7.1

Question 1

Describe the anatomy of the bladder
1) Describe the position of the bladder
2) What are the 3 layers of the bladder wall?

Answer 1

1) Lower abdomen, posterior to pubic symphysis

2) Mucosa: Transitional epithelium, stretch, contract
Detrusor muscle: middle layer, smooth muscle for bladder contraction. Bladder contraction important for urinating
aDVENTITIA: outermost layer, connective tissue anchoring bladder

Question 2

1) Describe Neural control of micturition

2) How do we have voluntary control of urination?

3) What is the difference in the case of infants?

4) At what age does urinary control develop?

Answer 2

1) Primary controlled by spinal cord reflex
Reflex is automatic. Controls emptying of bladder

2) Reflex facilitated / inhibited by higher brain centres in brainstem + cerebral cortex. Therefore, we have voluntary control over urination

3) Simple reflex in infants: No voluntary control. Micturition is purely reflexive. Higher brain centers not fully developed. Urination occurs automatically when bladder is full.

4) Development of volunary control (ability to inhibit micturition reflex):
age 2-3.

Question 3

Micturition: Autonomic + Voluntary Functions

1. What is continence?
2. What is voiding urine?
   3) Describe the coordinaton of somatic + autonomic systems

Answer 3

1) Ability to store urine in bladder without involuntary leakage. Coordinated control of bladder + sphincter muscles to keep bladder closed + prevent urine flow

2) Microturition. Process of removing urine from bladder. Active process. Requires relaxation of sphincter muscles, contraction of bladder.

3) Somatic nervous system: Controls external urethral sphincter (voluntary)

Autonomic: sympathetic + parasympathetic: control of bladder muscle (detrusor) + internal sphincter

Systems work together to regulate continence + microturition.

Question 4

1) What initiates process of micturition?

Answer 4

Spinal cord reflex when bladder is full
Reflex facilitated / inhibited by higher brai centers.

Voluntary control over micturition allows consicous facilitation (starting urination) or inhibition (delaying urination)

Question 5

1) Explain the two phases of micturition

2) What happens when continence neurones are damaged? (symptoms)

3) What happens to damage to voiding neurones?

Answer 5

1. Continence phase (urine storage)
   -controlled by continence neurones
   -Keep bladder closed, prevent involuntary leakage, allow bladder to store neurones

2) Failure to store urine.
Symptoms: reduced bladder capacity, frequent urination, incontinence (involuntary leakage of urine)

Phase 2: voiding phase: microturition

Controlled by separate set of neurones
Acticates bladder contraction to void urine voluntarily

3) Failure to pass urine voluntarily
Urinary retention (inability to fully empty bladder). Bladder can overfill, then urine released involuntarily, leading to overflow incontinence.

Question 6

Which neurones detect continence?

Answer 6

2 sensory neurones
-Pelvic
-Hypogastric

Detect stretching as bladder fills

Signalling need to void urine

Question 7

1) Neural control of voiding

2) Describe trends in urinary flow rates

Answer 7

1) neural apparatus, voiding circuits
Voiding centres in brain initiate process by controlling voiding centres in SC

Parasympathetic nerves from spinal cord levels (S2-S4) play a critical role in voiding
-contract detrusor muscle, push urine out
-Relax interal urethral sphincter, allowing urine to flow from bladder

Voiding normally takes less than 30 seconds

2) Flow rate from full bladder varies, age, gender
-Young men: 24 seconds
-Pre-menopausal women, 22 seconds
Urinary flow rate decreases with age

Question 8

Function of
1) Body of bladder
2) Trigone
3) Neck of bladder

Answer 8

1) Temp store of urine until voding
2) Triangular area at vase of bladder formed by
-Uretic orifices (opening of ureters, bring urine from kidneys)
-internal urethral orifice (urine exits bladder into urethra)
3) Narrow region, connects bladder to urethra

Question 9

Three key muscle components
1. Detrusor muscle
2. Internal urethral sphincter
3. External urethral sphincter

Answer 9

1. Involuntary, smooth muscle
2. Involuntar, smooth muscle
3. Voluntary, striated muscle,FORMED BY PELVIC FLOOR MUSCLES

Question 10

The three nerves that directly innervate the bladder:

Answer 10

Hypogastric Nerve (Sympathetic): Controls the internal urethral sphincter (inhibition of urination).

Pelvic Nerve (Parasympathetic): Controls the detrusor muscle (facilitates urination).

Pudendal Nerve (Somatic): Controls the external urethral sphincter (voluntary control of urination

Question 11

1) State adaptations of detrusor muscle

2) Neural Supply of the Detrusor Muscle:

Answer 11

1) The muscle fibers are arranged in three directions:

Two longitudinal layers.
One circular layer.

fiber orientation provides the bladder with strength and flexibility

2) ANS -provides both, sympathetic, parasympathetic control

1. Sympathetic (T0-S2)
   Hypogastric nerve - relax detrusor muscle (during urine storage)
2. Parasympathetic (S2-S4):
   Pelvic nerve: contraction of detrusor mscle,initiate + sustain urine flow during microturiton

Question 12

Histology of Urinary Bladder
What type of epithelium lines urinary bladder?

What is the difference between urinary bladder and the ureters?

Answer 12

In the ureters, there is no smooth muscle but, there is peristaltic activity

In the bladder, there is no peristaltic activity

Question 13

1) Where do afferent nerves originate from in the bladder?

2) What nerve pathways do these afferent nerves take?

Answer 13

1) Bladdder wall, conveying sensory information to CNS - stretch receptors, send signals when bladder fills, signal to void.
Also signal pain (inflammation of bladder lining), temp

2) Parasympathetic nerves (especially pelvic nerve)

Question 14

State the role of Aδ (A-delta) Fibers

and

C Fibers

In bladder sensory function

Answer 14

1. Aδ (A-delta) Fibers:
   fast transmission of sensory signals.
   sense bladder fullness and respond to stretching as the bladder fills.
   Neurotransmitter: Glutamate is released by Aδ fibers
2. C Fibers:
   slow transmission and respond to pain or irritation.
   Neurotransmitters: C fibers release Glutamate, Substance P (SP), and CGRP (Calcitonin Gene-Related Peptide)

Question 15

Describe Spinal Motor Control of Bladder

Answer 15

1. SYMPATHETIC PATHWAY
   Origin: T11-L2
   Pathway:
   Travel via the inferior mesenteric ganglia.
   Through the hypogastric nerve to the pelvic nerves.
   Inhibits bladder contraction and promotes urine storage.
   Neurotransmitter: Noradrenaline (NA).
   β3-adrenergic receptors: Causes bladder smooth muscle dilation (relaxation).
   α1-adrenergic receptors: Causes urethral smooth muscle contraction (to retain urine).
2. PARASYMPATHETIC PATHWAY
   Origin: S2-S4
   Pathway: Travel via sacral roots and pelvic nerves to the ganglia in the pelvic plexus and bladder wall.
   Function: Stimulates bladder contraction for urination.
   Neurotransmitters: ACh (acts on muscarinic ACh receptors)
   ATP induces bladder smooth muscle excitation.
   Nitric oxide (NO) causes urethral smooth muscle relaxation for urine flow.
3. Somatic Motor Pathways
   Origin: S2–S4 motor neurons
   Pathway: Through the pudendal nerves.
   Function: voluntary control over the external urethral sphincter, allowing conscious control of urination.
   Neurotransmitter: Acetylcholine (ACh) acts on nicotinic ACh receptors (nAChR) to cause contraction of the external sphincter skeletal muscle, which prevents urination until voluntary relaxation.

Question 16

Preliminary summary

Answer 16

Question 17

What controls the urinary bladder above the spinal cord?

What is the function of the lateral region and medial region?

Answer 17

Pontine centres controlling the urinary bladder

Question 18

State two disorders with pontine micturition centres

Answer 18

1. Biltaerl lesions in pontine storage centre (lateral)
   -inability to store urine
   -reduction in bladder capacity
2. Dorsomedial Pontine Tegmentum (medial)
   -reduced voiding

Question 19

How does lateral pontine micturition centre work?

Answer 19

Located in pons (brainstem). Regulation of urinary continence

Bilateral outputs - signals come from both sides of brainstem

Descending outputs do not secussate.

Key Functions:

1. Silecning of detrusor muscle activity
2. Relaxation of detrusor muscle (β3-
   receptors in the fundus and body of the
   bladder)
3. Increase in urethral sphincter pressure (α-adrenoceptors population in neck)

Question 20

Go through the mechanical events that take place during urinary continence (storage)

What is the stretch-relaxation phenomenon?

Answer 20

1. Walls of bladder highly folded,makes them distensible
2. Folds in bladder = rugae
3. As bladder fills with urine, internal urethral sphincter tightens, closes
4. As bladder fills with urine, rugae flatten
5. This causes capacity of bladder to increase (from 400ml to 700ml)
6. As bladder fills with urine, intravesical pressure (pressure in bladder) hardly changes due to stretching + flattening of rugae (stress, relaxation phenomenon)

Muscle initially stretches to increase volume, then relaxes to prevent signigicant rise in pressure

Question 21

Go through mechanical events that take place through voiding

Answer 21

Threshold for feelings suggestive of a full bladder is around 400ml

When the bladder is full

Urge to void the bladder arises

The brain informs the spinal cord
to void the bladder

Urine is expelled from the body

What actually happens?
1. Strong contraction of Detrusor muscle
2. Increase in intravesical pressure (PS-
S2-S4- Pelvic nerve)
3. Relaxation of the Internal Urethral
Sphincter (sympathetic T10-L2
Hypogastric nerve
4. Voluntary relaxation of the External
urethral sphincter (Somatic- S2-S4
Pudendal nerve)
5. Expulsion of Urine

Question 22

What is the threshold for feeling full bladder?

When is voiding inevitible?

Answer 22

Threshold for feelings suggestive of a full bladder is around 400ml

700 mL

Question 23

Summary of Micturition and Bladder Control - Very Important

Answer 23

1. Bladder fills, stretch receptors activate. Receptors sense increase in vol and pressure
2. Stretch receptors send signals through afferent fibres to spinal cord (SACRAL REGION). Initiating micturition reflex
3. Two responses:
   Sensory Signal Transmission to the Brain - sensation of bladder fulness to thlamaus. Then to cerebral cortex, so you are consciously aware bladder is full and you need to urinate
   Activation of Parasympathetic Motor Neurons
   -Afferent signals stimulate parasympathetic motor neurones (S2-S4). These neurones send efferent signals back to bladder, cause detrusor muscle to contract, interal urethral to relax, initiate process of urination

Question 24

1) What happens if the external urethral sphincter does not relax during urge to urinate?

2) When does internal sphincter open forcefully?

3) Residual urine after micturition

4) Infant bladder control

Answer 24

1) External urethral sphincter is under voluntary control. If does not relax during urge to urinate, bladder relaxes to accomodate increase vol of urine.

When more urin fills, micrturition reflex re-initiate, you feel need to urinate again

2) Bladder fills > 500 ml
Pressure forces it open. External urethral sphincter then relaxes too. Leads to involuuntary release of urine

3) less than 10 ml of urine remains in the bladder.

4) Lack voluntary control over urination. cortico-spinal connections (nerve pathways between the brain’s cortex and spinal cord) necessary for voluntary control of the external sphincter are not fully developed.