Flashcards in The Oesophagus, Stomach and Their Functions Deck (56)
what is the oesophagus?
is a muscular tube that begins at the pharynx and ends at the stomach
what is the function of the oesophagus?
carries food and liquid from the mouth to the stomach propelled by peristalsis
what is the structure of the oesophagus?
has walls with general organisation of that of the intestine and is bounded by the upper and lower oesophageal sphincters
what lines the oesophagus?
stratified squamous epithelium
what is the musculature of the oesophagus?
striated in the upper third, smooth in the remainder, both organised as outer longitudinal and inner circular layers
what nerve innervates the oesophagus and supplies the muscle directly ?
what indirectly supplies the oesophagus?
the myenteric and submucous plexus
what does the swallowing centre do?
-found in pons and medulla
- triggers closure of the upper oesophageal sphincter (once food has entered the oesophagus) and also a primary peristaltic wave via vagus
how is the primary peristaltic wave mediated?
by skeletal muscle proximally and smooth muscle distally regions
What occurs during peristalsis?
Circular fibres behind bolus contract to squeeze it down towards stomach
Longitudinal fibres in front of bolus contract to shorten distance of travel
Lower oesophageal sphincter opens within 2-3 s of the initiation of a swallow (closes after passage of bolus to prevent reflux)
what happens if sticky food becomes lodged?
stimulating local pressure receptors that cause:
-secondary peristaltic wave - more forceful than primary – locally triggered
-increased saliva production
what are the functions of the stomach?
-relaxes receptively (driven by vagus) to accommodate food from oesophagus
-Starting point for digestion of proteins (by pepsin and HCl), continues carbohydrate digestion
- mixes food with gastric secretions to produce semi-liquid chyme
-limited amount of absorption
-stores food before passing it into small intestine as chyme for further digestion and absorption
-Secretes approximately 2 litre/day of gastric juice from gastric glands in the gastric mucosa
what is the fundus?
-Next to oesophagus
-Thin smooth muscle layer
-Receives food but little mixing
-Little food stored there – usually a pocket of gas
what is the body?
-Thin smooth muscle layer
-Food stored here
What is the Antrum?
-Next to duodenum
-Thicker smooth muscle layer
-Much mixing of c 30mL at a time with gastric secretions
what happens during gastric mixing and emptying?
-Food mixed by the churning action of gastric smooth muscle against a closed pyloric sphincter
- Peristaltic contraction driven by supra-threshold gastric slow-wave (3 min-1)
-The pylorus opens only intermittently to allow the movement of chyme into the duodenum
what determines the escape of chyme through pyloric sphincter?
The strength of the antral wave
what effects the strength of the astral wave?
Describe the gastric factor.
Rate of emptying proportional to volume of chyme in stomach :
Distention increase motility due to stretch of smooth muscle, stimulation of intrinsic nerve plexuses and increased vagus nerve activity and gastrin release
Consistency of chyme - emptying facilitated by thick liquid chyme
Describe the duodenal factor.
Duodenum must be ready to receive chyme: delays emptying by:
-neuronal response -the enterogastric reflex – decreases antral activity by signals from intrinsic nerve plexuses and the ANS
-Hormonal response – release of enterogastrones [e.g. secretin and cholecystokinin CCK)] from duodenum inhibits stomach contraction
what stimulis within the duodenum drive the neuronal and hormone response?
-Fat -particulary potent-delay in gastric emptying required for digestion and absorption in small intestine
- Acid – time is required for neutralization of gastric acid by bicarbonate-rich juice secreted from the pancreas (important for optimal function of pancreatic digestive enzymes)
- Hypertonicity – products of carbohydrate and protein digestion are osmotically active and draw water into the small intestine – danger of reduced plasma volume and circulatory disturbances (e.g. ‘dumping syndrome
what cells are responsible for synthesis and release of gastrin?
what helps with secretion of gastrin and what secrets it?
Somatostatin released from D cells
what do parietal cells do?
responsible for synthesis and release of hydrochloric acid and the release of intrinsic factor and gastroferrin which are important in synthesis of vitamin B12 and the movement of iron
what do chief cells do?
secrete pepsinogen in the pit of the stomach
what does enterochromaffin do?
releases histamine which acts as a local hormone regulating release of gastric acid
what is the function of HCL secretion?
-Activates pepsinogen to pepsin
-Kills most (not all) micro-organisms ingested with food
what is the function of pepsinogen secretion?
Inactive precursor of the peptidase, pepsin. Note: pepsin once formed activates pepsinogen (autocatalytic)
what is the function of intrinsic factor and gastroferrin secretion?
Bind vitamin B12 and Fe2+ respectively, facilitating subsequent absorption