Midterm paper

MODULE 9 LO5 Digestive Tract: Stomach Dr. Lisa Brinn [email protected]

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5) Stomach • Regions:

v Cardia v Fundus v Body v Pylorus

o Pyloric sphincter • Major functions:

v Mixes and churns food v Begins chemical breakdown of proteins v Releases chyme into duodenum v Absorbs some fat-soluble substances v Possesses antimicrobial functions

• Other functions: v Stimulates protein-digesting enzymes v Secretes IF

Stomach Musculature • Muscularis mucosae • Oblique muscle

• Rugae v Longitudinal folds

o Gastric pits v Permit gastric lumen expansion

• Receptive relaxation v Storage

• Retropulsion v Type of peristalsis

Strengthen the stomach wall Perform mixing and churning

Gastric Pits Cells • Surface mucous cells

v Secrete alkaline mucus • Mucous neck cells

v Secrete thin, acidic mucus • G-cells

v Secrete gastrin • Chief cells

v Secrete pepsinogen • Parietal cells

v Secrete HCl v Secrete intrinsic factor (IF)

Stomach Digestive Properties • Gastrin

v Production site: G cells of stomach v Production stimulus:

o Presence of peptides and aa in stomach v Target organ:

o Stomach - ↑ secretion by gastric glands Promotes gastric emptying

o Small intestine – promotes muscle contraction o Ileocecal valve – relaxes valve o Large intestine – triggers mass movements

• Somatostatin v Production site: stomach and duodenum v Production stimulus: presence of food in stomach

Sympathetic stimulation v Target organ:

o Stomach – restricts all gastric secretions, gastric motility and emptying o Pancreas – restricts pancreatic secretions o small intestine – reduces intestinal absorption by reducing blood flow

Stomach Digestive Properties (cont.) • Histamine

v Production site: stomach v Production stimulus: presence of food in stomach v Target organ:

o Stomach – stimulate parietal cells to secrete HCl • Serotonin

v Production site: stomach v Production stimulus: presence of food in stomach v Target organ:

o Stomach – contracts stomach muscles • Ghrelin

v Production site: stomach v Production stimulus: fasting state v Target organ:

o Hypothalamus – regulates food intake

Gastric Secretion 1. Cephalic phase

• Smell • Taste • Sight • Thought

2. Gastric phase • Local neural and hormonal mechanisms • Triggered by entry of food into stomach

3. Intestinal phase • Excitatory

a) Gastrin is released when food enters the duodenum b) Excites gastric juice secretion

• Inhibitory a) Enterogastric reflex – inhibits gastric secretion b) Closes pyloric sphincter