gastrointestinal motility intro

Question 1

describe the factors which regulate appetite in common domestic species

Answer 1

• neuroendocrine signals (hypothalamus and vagal/medulla) produce ghrelin, leptin and insulin
• nutrient sensors/receptors (glucose, amino acids and fatty acids)
• gut hormones (cholecystikinin, peptide YY and glucagon like peptide
• behavioural influences

Question 2

describe the major effects of the sympathetic and parasympathetic stimulation on GIT motility including sphincter tone

Answer 2

sympathetic: reduce motility, increase sphincter tone and decrease secretions (epinephrin acting on Beta-1, alpha-1 and alpha-2 receptos respecitvely)
parasympathetic: enhance GI motility, decrease sphincter tone and increase secretions (acetylcholin od muscarinic receptors)

Question 3

describe the layout of the divisions of the ANS within the abdomen and pelvis including the thoracic and pelvic splanchnic nerves

Answer 3

Sympathetic Division:
- Thoracic Splanchnic Nerves: These include the greater, lesser, and least splanchnic nerves, arising from the thoracic sympathetic trunk and innervating abdominal organs.
- Lumbar Splanchnic Nerves: Originate from the lumbar sympathetic trunk and innervate the pelvic organs.
- Collateral Ganglia: Include the celiac, superior mesenteric, and inferior mesenteric ganglia, which are key relay points for sympathetic fibers.

Parasympathetic Division:
- Vagus Nerve: Provides parasympathetic innervation to most of the abdominal organs up to the transverse colon.
- Pelvic Splanchnic Nerves: Arise from S2-S4 spinal nerves and supply the lower part of the GI tract and pelvic organs.

Question 4

recall the mechanism of the generation of an action potential

Answer 4

1. Resting Membrane Potential: Maintained by the differential distribution of ions, particularly Na⁺ and K⁺, across the cell membrane due to the Na⁺/K⁺ pump.
2. Depolarization: Triggered by a stimulus causing the opening of voltage-gated Na⁺ channels, allowing Na⁺ influx and raising the membrane potential.
3. Repolarization: K⁺ channels open, allowing K⁺ to exit the cell, restoring the negative membrane potential.
4. Hyperpolarization: Excess K⁺ exit causes a temporary more negative membrane potential than the resting state.
5. Return to Resting State: The Na⁺/K⁺ pump and leak channels restore the original ion distribution.

Question 5

identify the positions of the autonomic ganglia and plexuses within the abdomen and pelvis

Answer 5

• Celiac Plexus: Located around the celiac trunk, providing sympathetic and parasympathetic innervation to the stomach, liver, and spleen.
• Superior Mesenteric Plexus: Surrounds the superior mesenteric artery, innervating the small intestine and part of the large intestine.
• Inferior Mesenteric Plexus: Around the inferior mesenteric artery, innervating the distal colon and rectum.
• Hypogastric Plexus: Located in the pelvis, supplying pelvic organs, including the bladder and reproductive organs.

Question 6

describe the distribution and function of the enteric nervous system

Question 7

describe the relationship between intrinsic and extrinsic innnervations of the enteric tract

Answer 7

extrinsic: involves autonomic nerves that modulate the activity of the GI tract from the central nervous system
intrinsic: the ENS operates mostly independently to control local GI functions
integration: the extrinsic ANS modulates the ENS enhancing or inhibiting its activities in response to broader physiological needs

Question 8

explain what is meant by electrical coupling between smooth muscle cells and its importnce for generating waves of activity along the GIT

Question 9

describe the principl anatomical and biophysical characteristics of the GIT smooth muscle

Answer 9

• single unit smooth muscles common in the GIT where cells are connected by gap junctions allowing synchronous contraction
• multi unit smooth muscles are found in specific regions like the sphincters where individual cell control is necessary
• function is for spontaneous activity for slow waves and response to stretch and chemical stimuli

Question 10

understand the origin and physiological significance of slow wave development in GIT smooth muscle

Answer 10

• interstitial cells of Cajal = pacemaker cells that generate slow waves and are essential for the coordination of smooth muscle contractions in the GIT
• slow waves are rhythmic fluctuations in membrane potential that set the baseline rhythm for GI contractions although they dont always trigger contractions themselves

Question 11

understand the features of segmentation and propulsive peristalsis in the small intestine and outline the importance of the enteric nervous system in the development of intestinal problems including disease

Question 12

describe the mechanisms involved in the control of gastric motility and the factors influencing stomach emptying in monogastric animals and the enterogastric reflex

Question 13

describe how gastric emptying can be affected by osmotic pressure or chemical composition of the stomach contents

Question 14

describe the integrated reflexes that initiate vomiting

Question 15

describe the origin and activity of the major gastro-intestinal hormones and describe the physiological stimuli controlling their release

q

Question 16

recall the mechanism of ion transport across the membrane of cells and the mechanism of neuromediators release in the synaptic cleft and explain the importance of the kiss and run mechanism regarding the leak of neuromediators in the synaptic cleft