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 relationship between intrinsic and extrinsic innnervations of the enteric tract

Answer 6

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 7

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

Answer 7

• 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 8

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

Answer 8

• 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