The digestive system and control of metabolism

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The digestive system and control of
metabolism Structure and function of the
digestive system Digestion of specific
nutrients Control of metabolism nutritional
requirements endocrine regulation the pancreas
and disorders
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Movement of food through the digestive
system chewing and swallowing peristalsis Secre
tions- exocrine (digestive enzymes and other
components) Digestion- catabolism (hydrolysis of
macromolecules) Absorption- into
blood Elimination of indigestible substances
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Mucosa- absorption and secretion Submucosa-
supports mucosa highly vascularized
(absorption) Muscularis-inner circular and outer
longitudinal layer innervation stimulated by
parasympathetic nerves also intrinsic
system Serosa- outer membrane
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Chewing and swallowing are voluntary the rest
of the process is not Peristalsis pushes food
through the esophagus to the stomach Esophageal
sphincter keeps food from regur- gitating to the
esophagus
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Secretions of the stomach Mucus- goblet
cells HCl- parietal cells Pepsinogen (pepsin)-
chief cells Gastrin- G cells Entrochromaffin-like-
histamine, serotonin Somatostatin- D
cells Intrinsic factor- parietal cells (necessary
for absorption of vitamin B12) These all
contribute to gastric juice
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Why is stomach so acidic? To digest proteins
(pepsin works optimally at low pH) Very little
is absorbed through the stomach Peptic ulcers
erosions of the mucous membranes most are caused
by bacteria (H. pylori) Treatment of
gastritis bicarbonate histamine
blockers avoidance of acid-stimulating foods
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Small intestine duodenum, jejunum, ileum Most
food molecules are absorbed in duodenum and
jejunum Bile salts, water, electrolytes in
ileum Villi and microvilli facilitate absorption
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Intestinal enzymes involved in digestion Various
enzynes convert disaccharides to glucose Peptida
ses produce amino acids Phosphatases facilitate
absorption of calcium remove phosphate
groups Peristalsis facilitates mixing
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Large intestine Consolidation of waste Absorbs
water , electrolytes and vitamins Bacterial
flora in intestine help ferment
molecules otherwise indigestible Diarrhea trans
port of salt into intestine, followed by
water inflammation lactose intolerance
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Secretory role of liver, gall bladder,
pancreas Liver secretes bile (via gall bladder)
which facilitates digestion of fat Pancreatic
juice helps with digestion in small intestine Li
ver performs a number of essential functions
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Detoxification of blood Kupffer
cells conversion of toxic molecules to
more innocuous ones Blood glucose to glycogen
and back Lipid metabolism- production and
excretion of cholesterol ketone
bodies Synthesis of plasma proteins Synthesis
and secretion of bile
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Gall bladder Stores and concentrates bile Gall
stones cholesterol has low solubility clusters
with lecithin and bile salts in micelles when
these calcify they form gall stones
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Pancreas Exocrine and endocrine gland Acini and
islets of Langerhans, respectively Pancreatic
juice- water, bicarbonate, amylase, lipase,
trypsin- among others Many are synthesized in
inactive form
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Regulation of the digestive system Gastric
secretion Cephalic phase- higher brain centers
stimulate gastric juice secretion via vagus
nerve (primes the stomach) Gastric phase-
gastrin is secreted by gastric mucosa. Controls
secretion of HCl and pepsin Intestinal phase-
neural reflexes and hormonal secretion from
duodenum inhibits stomach activity
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Enteric nervous system controls
intestinal function- smooth muscle
contraction Secretion of pancreatic juice and
bile controlled by secretin and cholecystokinin
(CCK) Other hormones maintain digestive tract
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How and where does digestion happen? Mouth-
salivary amylase starts to digest
starch completed in small intestine (brush
border) Protein digestion- begins in stomach,
completed with help of pancreatic
enzymes Lipids- emulsified by bile salts,
digested in small intestine eventually rebuilt
into triglycerides transported to blood via
lymph
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Control of metabolism Review energy
pathways Hormonal control mobilization of
energy molecules growth mobilization of
calcium