1. Overview Flashcards
What are the functions of digestion?
To process food into a sterile, neutral, and isotonic solution of small sugars, amino acids and small peptides, small particles of lipids, and other small molecules.
What are the functions of saliva?
Protect mouth as wet, bacteriostatic, alkaline and high calcium. Lubricate food for mastication and swallowing as it is wet and has mucus. Starts digestion of sugars.
What are the functions of the oesophagus?
Swallowing of the bolus, rapid oesophageal transport to the stomach.
What are the functions of the stomach?
Storage, initial disruption of food, delivers chyme slowly into the duodenum.
How does the stomach initially disrupt food?
It contracts rhythmically to mix and disrupt, secretes acid and proteolytic enzymes to break down tissues and disinfect. The endpoint is chyme.
What are the functions of the duodenum?
Dilution and neutralisation of chyme.
How does the duodenum dilute and neutralise chyme?
Water drawn in from extracellular fluid, the duodenum is permeable to water. Alkali bile is added from liver to pancreas. Enzymes added from pancreas and intestine.
What are the functions of the small intestine?
Absorption of nutrients and electrolytes, and absorbs the majority of water.
How does the small intestine absorb nutrients and electrolytes?
Fluid passes very slowly through the small intestine and it has a very large surface area. Epithelial cells absorb molecules, actively or passively and often coupled to Na+ movement. Then passes into hepatic portal circulation.
What are the functions of the large intestine?
Final absorption of water during its very slow transit. Faeces forms and accumulates in the descending and sigmoid colon.
What are the functions of the rectum?
Controlled relaxation of sphincters and expulsion of faeces as it is propelled periodically into rectum and there is an urge to defecate.
What are the four layers of the alimentary canal?
Mucosa, submucosa, muscularis externa, serosa/ adventitia.
What is the mucus layer of the alimentary canal?
Epithelial lining and thin layer of smooth muscle.
What is the submucosa layer of the alimentary canal?
Fibroelastic tissue with vessels, nerves, leucocytes and fat cells.
What si the muscularis externa of the alimentary canal?
Inner circular and outer longitudinal layer of smooth muscle with the myenteric plexus lying in between the layers.
What is the serosa/ adventitia of the alimentary canal?
Thin outer covering of connective tissue.
How much food and liquid do we ingest in an average day?
1kg of food, and about a litre of liquids.
What is food mixed with to form chyme?
1.5L of saliva, and about 2.5L of gastric secretions.
What is added to chyme when it is released from the stomach?
About 9L of water from the extracellular fluid via osmosis.
Where is fluid absorbed along the alimentary canal?
12.5L of fluid absorbed in the small intestine, 1.35L absorbed by the large intestine.
What is the enteric nervous system made of?
Two nerve plexuses in the wall of the gut that may act independently of the CNS.
How is the GI system controlled nervously?
Both branches of the ANS. Parasympathetic control is most significant as it coordinated secretion and motility using a range of neurotransmitters.
What are the two structure groups of hormones in the gut?
Gastrin and secretin groups.
What is dysphagia?
Difficulty in swallowing. From problems with oesophagus - musculature, obstruction by tumour, neurological.
