week 11 defeaction Flashcards
(27 cards)
- What is the function of defecation and what structures are involved?
Defecation eliminates feces using the rectum
- Describe the role of the rectum and anus in the defecation process.
The rectum stores feces and signals stretch; the anus regulates release via sphincters.
- What is the function of the internal and external anal sphincters and how are they controlled?
The internal sphincter is involuntary via autonomic control and the external sphincter is voluntary via the somatic pudendal nerve.
- What are the roles of the ureters and bladder in urination?
Ureters transport urine from kidneys to the bladder which stores and expels it.
- How does the structure of the bladder enable it to store urine?
The bladder’s detrusor muscle and transitional epithelium allow expansion with minimal pressure increase.
- Which parts of the nervous system control defecation and how do they interact?
Parasympathetic nerves stimulate rectal contraction sympathetic nerves inhibit and somatic nerves control the external sphincter.
- What role does Barrington’s nucleus play in defecation?
It integrates sensory signals and coordinates pelvic organ motor control.
- Describe the function of the intermediolateral (IML) column and Onuf’s nucleus in defecation.
IML controls autonomic output and Onuf’s nucleus controls the external sphincter via the pudendal nerve.
- What is the difference between the somatic and autonomic pathways in defecation?
Somatic pathways control voluntary muscle while autonomic pathways regulate involuntary smooth muscle and internal sphincter.
- How do IPANs contribute to the defecation reflex?
They detect stretch in the rectal wall and initiate local enteric reflexes to promote peristalsis and sphincter relaxation.
- What is the recto-anal inhibitory reflex (RAIR) and its function?
RAIR is triggered by rectal distension and causes internal sphincter relaxation to allow sensory sampling of rectal content.
- Explain the gastrocolic reflex and its physiological relevance.
It increases colonic motility after a meal preparing the lower gut for defecation.
- Describe the cough-anal reflex and why it may be considered anticipatory.
It contracts the external sphincter during a cough to maintain continence under pressure.
- What is micturition and what structures are involved?
Micturition is urination involving the detrusor muscle internal and external urethral sphincters and associated nerves.
- Describe the steps involved in bladder filling.
The bladder fills passively while the detrusor remains relaxed and sphincters stay closed under sympathetic and somatic control.
- Describe the steps involved in bladder emptying (voiding).
Stretch signals activate the PMC which triggers parasympathetic detrusor contraction internal sphincter relaxation and voluntary external sphincter release.
- What are the functions of the detrusor muscle and bladder sphincters during filling and voiding?
During filling the detrusor is relaxed and sphincters are closed and during voiding the detrusor contracts and sphincters relax.
- Which nerves are involved in urination and what branches of the nervous system do they belong to?
Pelvic nerves are parasympathetic hypogastric nerves are sympathetic and pudendal nerves are somatic.
- Describe the role of the pelvic pudendal and hypogastric nerves in bladder control.
Pelvic nerves contract the detrusor pudendal nerves control the external sphincter and hypogastric nerves relax the detrusor and contract the internal sphincter.
- What is the role of the pontine micturition center (PMC) and periaqueductal gray (PAG) in urination?
PAG processes bladder sensory input and PMC coordinates autonomic and somatic motor output for voiding.
- How does high-intensity bladder afferent activity trigger urination?
It activates the PMC which increases parasympathetic output and suppresses somatic input allowing urination.
- What neurotransmitters are used in sympathetic parasympathetic and somatic control of urination?
Sympathetic uses norepinephrine parasympathetic uses acetylcholine and somatic uses acetylcholine at nicotinic receptors.
- What are non-adrenergic non-cholinergic neurons and where are they found in urination?
They release ATP and nitric oxide and are found in pelvic pathways affecting detrusor contraction and sphincter relaxation.
- What are the necessary physiological conditions to maintain urinary continence?
Low detrusor pressure closed internal sphincter and active somatic control of the external sphincter.
