L2: Ureters, Urinary Bladder & Micturition

Question 1

What is Urinary Excretion equal to?

Answer 1

Urinary Excretion= Glomerular Filtration + Tubular Secretion – Tubular Reabsorption

Question 2

What lines the renal pelvis, ureters, and urinary bladder?

Answer 2

Urothelium

Question 3

Layers of the Ureter?

Answer 3

Question 4

Layers of the Bladder?

Answer 4

Question 5

What coats the lining of the urinary outflow system?

Answer 5

An organized array of uroplakin molecules coat the Urothelium forming a robust permeability layer

Question 6

Layers of the Urothelium?

Answer 6

Basal layers: cuboidal -10mm, single layer

Intermediate layers: columnar -10-25mm, several layers

Surface cells (aka. Umbrella/Dome cells): larger and rounded (25-250mm)

Umbrella cells are interconnected by tight junctions and their apical membrane contains impermeable plaques of uroplakin proteins

Question 7

________ of the Urothelium are interconnected by tight junctions and their apical membrane contain impermeable plaques of ___________

Answer 7

Umbrella cells of the Urothelium are interconnected by tight junctions and their apical membrane contain impermeable plaques of uroplakin proteins (80 90% of the surface)

Question 8

Path of urine to Bladder?

Answer 8

Urine flows from the nephron collecting ducts => the renal pelvis => ureters => bladder

Question 9

Process of Ureteral Contraction

When renal calyxes and upper regions of the ureters become distended due to urine accumulation, _______________ occur in the ureters that propel the urine bolus toward the bladder. These contractions originate from electrical pacemakers in the _______________ portion of the renal pelves.

Answer 9

When renal calyxes and upper regions of the ureters become distended due to urine accumulation, peristaltic contractions occur in the ureters that propel the urine bolus toward the bladder

Ureteral peristaltic waves originate from electrical pacemakers in the proximal portion of the renal pelves.

Question 10

Smooth triangular region of the internal urinary bladder formed by the two ureteral orifices and the internal urethral orifice?

Answer 10

Trigone

Question 11

Answer 11

1. Fundus: Expandable balloon-like chamber comprised of detrusor muscle
2. Internal Urethral Sphincter: Convergence of detrusor muscle fibers in neck of bladder
3. External Urethral Sphincter: ring of skeletal muscle

Question 12

Neural Control of Micturition?

Answer 12

Autonomic Nervous System (ANS): controls smooth (involuntary) muscles - detrusor muscle and internal urethral sphincter

Somatic Nervous System (SNS): controls skeletal (striated/voluntary) muscles- external urethral sphincter

Question 13

Sympathetic Innervation’s role in Micturition?

Pathway??

Answer 13

SNS promotes continence and relays information to the brain about the need to void

Sympathetic fibers originate in the T11–L2 segment, run through Hypogastric Nerve (HGN) and innervate detrusor and internal urethral sphincter releasing Noradrenaline

• Detrusor Muscle Relaxation (β-adrenergic inhibitory receptors)
• Internal Sphincter Contraction (α-adrenergic excitatory receptors)

Question 14

Parasympathetic Innervation’s role in Micturition?

Pathway??

Answer 14

Parasympathetic fibers arise from the S2-S4 sacral spinal segments => Pelvic Nerve to ganglia in pelvic plexus (PP) & bladder wall:

Detrusor Muscle Contraction:

• Acetylcholine (ACH) acts on M3 Muscarinic Receptors
• Adenosine Triphosphate (ATP) acts on P2X Purinergic Receptors (Internal urethral smooth muscle sphincter relaxation)

Internal urethral smooth muscle sphincter relaxation: Nitric oxide (NO)

Question 15

Somatic Innervation’s role in Micturition?

Pathway??

Answer 15

The somatic nervous system allows conscious control over micturition

Cholinergic motor nerve arise in S2–S4 motor neurons in Onuf’s nucleus and reach periphery through Pudendal Nerves:

• Release Ach activating Nicotinic Receptors in External Urethral Sphincter=> Contraction of EUS

Question 16

Nerves that INHIBIT Micturation?

Reflex Organization?

Answer 16

Micturition inhibited by activity in the Hypogastric (sympathetic) nerves and Pudendal Nerves (somatic)

Organization: reflex mechanisms organized primarily in the Spinal Cord

Question 17

Nerves that FACILITATE Micturation?

Reflex Organization?

Answer 17

Micturition facilitated by activity in the Pelvic Nerves (Parasympathetic)

Organization: reflex mechanisms organized in the Brain

Question 18

Nerves that inhibit Micturation?

Reflex Organization?

Answer 18

Micturition is inhibited by activity in the hypogastric (sympathetic) nerves and pudendal nerves (somatic)

reflex mechanisms organized primarily in the spinal cord

Question 19

Neural Circuits that Control Continence (Storage Reflex)?

Answer 19

1. Progressive bladder distension stimulates afferent fibers of Pelvic Nerves
2. At low pressures, this activity activates Hypogastric Nerve (Sympathetic)

• Relaxes Detrusor (Noradrenaline binds b-adrenergic inhibitory receptors)
• Contracts IUS (Noradrenaline binds a-adrenergic excitatory receptors)

3. Input by somatic motor neurons via Pudendal Nerve => Contraction of EUS (ACh binds Nicotinic Receptors)
4. Rostral Pons (the pontine storage centre) increases striated urethral sphincter activity via Pudendal Nerve => Further Contraction of EUS

Question 20

Neural circuits that control voiding (Micturation Reflex)?

Answer 20

Voluntary initiation of voiding reflexes results in activation of the micturition center of the pons, which signals parasympathetic motor neurons that stimulate contraction of the detrusor muscle and relaxation of the urinary sphincters.

1. Urine accumulates, afferent impulses enter spinal cord:

• Stimulates parasympathetic outflow
• Activates the pontine micturition center =>conscious desire to urinate

2. Parasympathetic efferent fibers CONTRACT Detrusor Muscle (ACH/ATP) and RELAX internal urethral sphincter (NO)

• Sympathetic efferents inhibited (Destrusor Contracts)
• Somatic efferents inhibited (external urethral sphincter relaxes)

Question 21

The sympathetic nervous system communicates with the bladder via the _____________. It releases ____________ leading to relaxation of the __________ and contraction of the ____________. These functions promote ______________.

Answer 21

The sympathetic nervous system communicates with the bladder via the hypogastric nerve (T12 L2). It releases Noradrenaline leading to relaxation of the detrusor muscle (Beta-Adrenergic) and contraction of the internal urethral sphincter (Alpha-Adrenergic). These functions promote Urine Retention

Question 22

The parasympathetic nervous system communicates with the bladder via the ____________that innervates ganglia in the __________ & _________. Increased signals from this nerve lead to the contraction of the ___________ and relaxation of the ___________. This stimulates _________.

Answer 22

The parasympathetic nervous system communicates with the bladder via the pelvic nerve (S2 S4) that innervates ganglia in the pelvic plexus (PP) & bladder wall. Increased signals from this nerve lead to the contraction of the detrusor muscle (Ach- M3, ATP - P2X) and relaxation of the Internal urethral sphincter (NO). This stimulates Micturition.

Question 23

_______________________gives us voluntary control over micturition. Constricts the ___________, by releasing ACh from the _________ nerve which binds ________ receptors. It can cause it to constrict (_________) or relax (_____________).

Answer 23

Somatic Nerves give us voluntary control over micturition. Constricts the external urethral sphincter, by releasing Ach from the _pudendal nerve (S2- S4)_nwhich binds nicotinic receptors. It can cause it to constrict (storage phase) or relax (micturition).

Question 24

In addition to the efferent nerves supplying the bladder, there are
___________________ that report to the brain(_________+________). They are found in the bladder wall and signal the need to urinate when the bladder becomes full.

Answer 24

In addition to the efferent nerves supplying the bladder, there are
sensory (afferent) nerves that report to the brain (Pons/Pontine micturition center). They are found in the bladder wall and signal the need to urinate when the bladder becomes full.

Question 25

Sympathetic innervation of Micturition arises in the_____________, whereas parasympathetic and somatic innervation originates in _____________________

Answer 25

Sympathetic innervation of Micturition arises in the thoracolumbar outflow of the spinal cord (T11-L2), whereas parasympathetic and somatic innervation originates in sacral segments of the spinal cord (S2-S4)