BIOL 2050U Lecture Notes - Duodenum, Gastrin, Medulla Oblongata

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Published on 29 Jan 2013
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Control Of Digestive Secretions
Nervous And Hormonal Control Of Salivary, Gastric And Pancreatic Secretions
Mammal has 2 communication systems → nervous and endocrine system
Nervous system is based on electrical impulses passing along nerve cells
o Short-lasting effects, can be switched on or off rapidly
o Secretes salvia when food enters mouth
Endocrine system is based on hormones
o Travel in blood to target organ
o Produce long-lasting effects
o Trigger secretion of bile and pancreatic juice
Endocrine system is only activated with large amounts of food intake
o Food takes a long time to reach small intestine
o Food stays there for a long time
o Digestive juice can be secreted as large amounts of food are present
o Digestive juice contains trypsin and pepsin → both enzymes are peptidases which
damage proteins → they would damage epithelial cells if only small amounts of
food would be present
Importance Of Simple And Conditioned Reflexes And The
Hormones
Nervous reflexes
Nerve pathway involving small number of nerve cells (2/3) → rapid response
Automatic response → particular stimulus has same effect
Condition reflex
Salvia and gastric juice are secreted
By various stimuli associated with food (smell/sight/sound)
By contact of substances in food with taste buds on tongue
Hormones
Secreted in response to presence of food in particular region of gut
Hormones travel in blood to glands / in glands, stimulate secretion of digestive juices
GASTRIN stimulates exocrine glands in stomach to release gastric juice
Acids (chyme) from stomach, fatty acids in duodenum stimulate release of SECRETIN
o Stimulates secretion of alkali (bicarbonate ions) from pancreas
Neutralises acidity from intestinal contents
When pH reaches neutrality, secretion of secretin is inhibited
o Inhibits gastric gland secretion
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