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what is the structure of the alimentary canal?

Series of hollow organs running from mouth to anus (oral to aboral) that are separated by sphincters, controlling movement


what is the purpose of the mouth and oropharynx?

chops and lubricates food, starts carbohydrate digestion, propels food to oesophagus


what is the purpose of the oesophagus?

muscular tube - propels food to the stomach


what is the purpose of the stomach?

stores/churns food, continues carbohydrate and initiates protein digestion, regulates delivery of chyme to duodenum


what is the purpose of the small intestine?

principal site of digestion and absorption of nutrients


what is the purpose of the large intestine?

Colon reabsorbs fluids and electrolytes, stores faecal matter before delivery to rectum


what is the purpose of the rectum and anus?

storage and regulated expulsion of faeces


what are the accessory structures of the alimentary canal?

(i) salivary glands,
(ii) the pancreas,
(iii) the liver and gall bladder (hepatobiliary system)


what is it called when food moves towards the anus?

aboral direction


what is it called when food moves towards the mouth?

oral direction


what is the modality?

Mechanical activity mostly involving smooth muscle (skeletal at mouth, pharynx, upper oesophagus and external anal sphincter)


what is secretion?

Into the lumen of the digestive tract occurs from itself and accessory structures in response to the presence of food, hormonal and neural signals


what is secretion required for?

(i) digestion,
(ii) protection
(iii) lubrication


what is digestion?

Chemical breakdown by enzymatic hydrolysis of complex foodstuffs to smaller, absorbable, units (note physical digestion in the mouth, stomach and small intestine contributes)


what is absorption?

Transfer of the absorbable products of digestion (with water, electrolytes and vitamins) from the digestive tract to the blood, or lymph – largely mediated by numerous transport mechanisms


what is the inner most layer of the generalised digestive tract wall?

Mucosa containing:
-epithelial cells
-exocrine cells
-endocrine gland cells
-lamina propria (capillaries, enteric neurones, immune cells)
-muscularis mucosae


what is the 2nd layer from the inside of the digestive tract?

Submucosa containing:
-connective tissue
-larger blood and lymph vessels
-nerve network
(submucous plexus)


what are the two layers of the 3rd layer from the inside of the tract wall :muscularis externa?

-circular muscle layer
-longitudinal muscle layer


what other structure is in the muscularis externa layer?

nerve netwrok


what is the outer layer of the digestive tract wall?

serosa containing:
connective tissue


what is gastrointestinal motility?

Mostly due to the activity of smooth muscle (circular, longitudinal layers and the muscularis mucosae), but skeletal muscle is important in the mouth, pharynx, upper oesophagus and external anal sphincter


what happens to the lumen when circular muscle contraction occurs?

lumen becomes narrower and longer


what happens to the intestine when longitudinal muscle contraction occurs?

intestine becomes shorter and fatter


what happens when muscarlis mucosae contraction occurs?

change in absorptive and secretory area of mucosa (folding), mixing activity


what are adjacent smooth muscle cells coupled by and what does this allow?

Gap junctions -allow spread of electrical currents from cell to cell forming a functional syncytium


what is a synchronous wave?

when hundreds of cells are depolarised and contract at the same time i.e single unit smooth muscle


what drives spontaneous activity across the syncytium ?

specialised pacemaker cells


what modulates the spontaneous activity produced by pacemaker cells?

-Intrinsic (enteric) and extrinsic (autonomic) nerves
-Numerous hormones


what spontaneous electrical activity occurs in the stomach, small intestine and large intestine?

occurs as slow waves - rhythmic patterns of membrane depolarization and repolarization that spread from cell to cell via gap junctions


what does the slow wave electrical activity determine?

max. frequency, direction and velocity of rhythmic contractions