[OS 206] E03-T09-Micturition_compressed

• Micturition is under both autonomic and voluntary control and involves the lower urinary tract.
• It is the process where the urinary bladder empties when filled.

Anatomy of the Lower Urinary Tract

• Bladder: Includes the detrusor muscle, trigone, and ureterovesical junction.
• Urethra: Features the bladder neck/proximal urethra and external sphincter.
• Other components: Prostate (in males), pelvic floor, and the nervous system (peripheral nerves, spinal cord, pons, and cerebral cortex).

Physiology of the Lower Urinary Tract

• Functions: Urine storage and periodic elimination.
• Two phases: Filling/storage phase and voiding phase.

Urodynamics

• Definition: A test to study and assess the integrity of a patient’s micturition cycle.
• Purpose: Study of hydrodynamics of urine storage and voiding and the physiological relationship between the bladder, urethra, and pelvic floor.
• Measures: Records pressure and flow during micturition cycle, assessing lower urinary tract function and dysfunction.
• Procedure: Involves inserting catheters into the bladder and rectum/vagina, attached to a transducer.
• Measurements taken as: bladder is filled with fluid, and the patient voids into a flowmeter.

Filling/Storage Phase

• Occurs as urine enters the bladder from the kidneys via the ureters.
• Characteristics: Low pressure is generated by the urine in the bladder, allowing continuous urine flow from the ureter to the bladder without leakage or discomfort.

Detrusor Muscle During Filling/Storage

• Properties: Compliant, relaxes, and accommodates urine.
• Compliance: Ability to maintain low pressure despite increases in volume, allowing a normal capacity of 400-450 mL without significant pressure increase.
• Control: Kept under control to prevent abnormal, uncontrolled contractions.

Urethra and Sphincter During Filling/Storage

• Function: Competent to prevent leakage.
• Mechanism: Sphincter remains closed due to muscle contraction, contracts as needed.

Anatomy of Closure/Competence

• Bladder neck factors: Intrinsic (smooth muscle and elastic connective tissue) and extrinsic (pubourethral and puboprostatic ligaments).
• Urethral smooth muscle: Inner longitudinal layer (role uncertain) and outer circular layer (provides closure at rest).
• External urethral sphincter (rhabdosphincter): Slow-twitch fibers exert major resting pressure, reflex contraction during stress.
• Inner urethral factor: Richly folded epithelium and spongy tissues within the submucosa, dependent on hormonal status in females.

Pelvic Floor Role

• Function: Contracts to help control leakage during filling, contracts more as needed.
• Composition: Pubovisceralis muscle group (pubourethralis, pubovaginalis, puborectalis, pubococcygeus).
• Connective Tissue (Endopelvic Fascia): Maintains proper position of the proximal urethra through interdigitation of collagen and elastin fibers.
• Damage to endopelvic fascia: Can compromise urethral support and closure during abdominal straining.
• Composition: pubocervical fascia, pubourethral fascia, cardinal fascia, uterosacral fascia, and rectal pillar.

Normal Urodynamic Study Details

• Pressure display: Shows the bladder's ability to maintain low pressures despite increasing volume.
• Compliance is aided by:
  • Viscoelastic property of smooth muscles.
  • Collagen and elastin content of the submucosal layer.
  • Slow conduction of nervous impulses through gap junctions.

Voiding Phase

• Normal voiding is characterized by adequate pressure, good and continuous urine flow, and absence of discomfort.
• In a urodynamic study: the pressure line rises, and the urine flow line shows an increasing rate.

Detrusor Muscle During Storage/Filling

• Properties: Contractile, requires sustained stimulation to contract until empty.

Detrusor Muscle Anatomy and Physiology for Contraction

• Syncytium enables sustained and complete emptying.
• Trigonal muscles prevent urine backflow to the kidneys during voiding.

Urethra and Sphincter Roles

• Relaxes and opens during voiding
• Pelvic Floor:
  • Relaxes and opens during voiding
  • Control: inherent contraction is inhibited

Neurophysiologic Control of Lower Urinary Tract

• Ensures proper control and coordination of the detrusor/bladder, sphincter, and pelvic floor musculature.

Micturition Switches

• Involves on-off switches in the nervous system: cortical center, rostral pons, suprasacral spinal cord, sacral spinal cord, peripheral nerves (hypogastric, pelvic, pudendal).

Filling Phase Events

• Empty bladder: Afferent receptors at detrusor submucosa are deactivated.
• Mechanism: Cerebral inhibitory impulses reactivate, micturition reflex from pons deactivates, and suprasacral reflex and hypogastric nerve stimulate.
• Results: Hypogastric nerve stimulation causes bladder neck closure, inhibiting detrusor and trigonal contractions.
• External Components: Pudendal nerve stimulation restores external sphincter and pelvic floor muscle contraction.

Full Bladder (Shouldn't Void)

• Receptors: Detrusor submucosa and detrusor activated.
• Signal: Receptors send signal to sacral micturition center via pudendal nerve.
• Pelvic actions: Pelvic nerve causes trigonal contraction and opens bladder neck.
• Cortex role: The cortex sends more inhibitory signals to pons micturition center, which sends stimulatory signal to pudendal nerve.
• Action: Causes pudendal nerve contracts external sphincter and the pelvic floor muscle further and inhibits pelvic nerve stimulation of detrusor.

Voiding When You Can Void

• Inhibitory: Inhibitory cortical impulses are stopped
• Reflex: Micturition reflex is activated
• Hypogastric Nerve: Hypogastric nerve inhibited with the bladder neck opening
• Contraction: Pelvic nerve stimulated with the trigone contracting, the bladder neck further opens and funnels
• Action: Pudendal nerve inhibited with the external urethral sphincter and pelvic floor muscles relaxing.

Organs Involved in Micturition

• Bladder: Urine Storage - detrusor muscle contracts during urination, and relaxes during filling.
• Urethra: Pathway of urine.

Male Urogenital Tract

• Good model for understanding micturition.
• Components: Internal and External Sphincters
• External sphincter: Located in the urogenital diaphragm.
• Prostate Gland (males only): Located between the internal and external sphincters with an important role in activating sperm.
• Prostate hyperplasia: Cause obstruction in the urethra and leads to problems with urinating.
• UrethraLies between sphincters and has a passage of urine from bladder to outside (environment).

Female Urogenital Tract

• Females have no prostate gland.
• Females only have an external sphincter.
• Female urethra is shorter than in males.

Cortex Actions

• Sends inhibitory signals to suprasacral cord and Sends stimulatory signals to sacral cord.

Micturition Center

• Located in the pons.

Nerves and Actions

• Hypogastric nerve: Stimulates α1 receptor, causing internal sphincter contraction (+).
• Stimulates β3 receptor causes relaxation of detrusor muscle (-).
• Pelvic efferent nerve: Micturition center stimulation leads to stimulation of pelvic efferent nerves and inhibition of the hypogastric nerve (sympathetic).
• Pudendal nerve contraction: Stimulating the nicotinic receptors and causing contraction of the external sphincter hold urine voluntarily

Efferent Nerve Fibers Involved

• A1 causes contraction of internal sphincter (+).
• Hypogastric or sympathetic nervous system responsible for urine retention.
• Parasympathetic nervous system responsible for voiding.

Filling: Nerve Role

• Trigger: Bladder barely contains urine (not much stretching will result in pelvic afferent nerve (sensory) will only send slow impulses to a sacral neuron which stimulates the hypogastric nerve

Empting Bladder Neurotransmission

• Pudendal nerve: Inhibitied to allow for the relaxation of external sphincter
• Sympathetic nerve: Allows to hold urine in the bladder

Full Bladder Signal

• Leads to inhibition of the hypogastric nerve (sympathetic):No relaxation of detrusor, No function of α1 receptor results in relaxation of the internal sphincter.

Micturition and Nerves:

• Neurotransmitters- Hypogastric - cause retention of the urine (sympathetic innervation)
• Bladder: stretch receptors- signal pontine micturition center
• pelvic: muscle contractions, M3, acetylcholine transmission
• pudendal: tonic control of external sphincter (nicotinic, somatic)

Mictutrion structures:

• kidney
• ureter
• bladder with dertrusor muscle
• Urethra- internal and external sphincters
• male: prostate, urogenital diphragm
• female- shorter urethra

Trigone

• Vital in the process of urination
• Contains the ureteric orifices and internal urethral orifice.
• Ureterovesical junction: oblique entry of the ureter into the bladder

Pelvic floor exercise: kegel

• contracts pelvic floor

Hormone in females

• estrogen helps with cushion- decreased menopause leads to stress incontinence
• DM-increased urinary incontinence - manage with medication

Normal urination factors

• no splitting
• strong stream
• no pain