University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

140

Pages:

4
Author:

Mariam A. A.

CNS control of the gut • ANS o o o o o • Parasympathetic ganglia lie close to or within the organs of tissues that their neurons innervate Sympathetic ganglia lie at a more distant site from their target organs ANS motor (efferent) ganglia can be divided into preganglionic and postganglionic Parasympathetic postganglionic neurons are located in gut wall Sympathetic fibres innervating the gut are adrenergic, postganglionic fibres within cell bodies in the prevertebral ganglia (not in gut) Vagus nerve and postganglionic neurons in stomach wall o • • • Vagotomy disrupts innervation to gut and used to be used more commonly to stop acid secretion Sensory output from gut to CNS o Neurons that carry sensory info to CNS are termed primary afferent neurons o Carried in vagal (parasympathetic outflow) and splanchnic nerves (sympathetic outflow) o Vagal primary afferent neurons have cell bodies in the nodose ganglia (aka inferior vagal ganglion and is outside gut) o Splanchnic primary afferent neurons have their endings in the gut wall and their cell bodies in the dorsal-root ganglia (outside the gut) SNS and PNS o Sympathetic inhibits most gastric functions → vasoconstriction, reduced secretion, muscle relaxation o Parasympathetic stimulates most gastric functions ▪ Vagus nerve innervates tract from oesophagus to transverse colon ▪ Pelvic nerve from descending colon to anus Clinician’s corner: barium swallow is a test used to determine the cause of painful swallowing e.g. bird’s beak oesophagus in achalasia (tightness at lower oesophageal sphincter as it can’t relax) due to failure of inhibition Neural control of swallowing • Motor centres are present in the brainstem → patients with a stroke involving brainstem usually have major difficulty with swallowing and protecting their airway as they do so • Oesophageal peristalsis o Act of swallowing triggers a peristaltic wave (via vagus) o Presence of a bolus of food (if it is not swept all the way to the stomach on the first contraction wave helped by gravity if erect) triggers the peristaltic reflex to move the bolus onwards Peristaltic reflex • Stomach • Capacity of 0.8‐ 1.5L and is divided into 2 sections: the body (upper 2/3) and the antrum (lower 1/3) • Food processed in the stomach is ultimately forced through the pylorus into the duodenum • The stomach performs 3 functions: o Storage of food o Mixing with gastric secretions to form a semifluid mixture called chyme o Emptying of chyme at suitable rate for digestion Mixing and propulsion in the stomach • When food is present, peristaltic constrictor waves or mixing waves begin in body and move toward antrum. • • • Constrictor waves dig deep into food contents of the antrum → mixes the food and exposes more food to digestive juices that are secreted by the walls of the stomach Chyme is transferred to the duodenum with the aid of the migrating myoelectric complex (MMC) o Characterised by 10‐20 minutes of intense antral contractions every 1‐2 hours during fasting – clear particles from the stomach At the pylorus, some of the processed food (chyme) is passed into the duodenum, however most is pushed back upstream by strong contractions (increasing the mixing)