Digestive processes
1. ingestion |
2. secretion |
3. motility |
4. digestion |
5. absorption |
6. defecation |
visceral muscle contractions
oesophagus |
peristaltic |
stomach |
peristaltic |
small intestine |
segmental, MMC |
colon |
segmentation, mass movement |
GI control
ENS |
intrinsic set of nerves, neurons extending from esophagus to anus, 2 plexuses: myenteric (GI tract motility) & submucosal (controlling secretions) |
ANS |
extrinsic set of nerves; parasympathetic stimulation increases secretion & activity by stimulating ENS |
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sympathetic stimulation decreases secretions & activity by inhibiting ENS |
regulation of acid secretion
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atropine muscarinic antagonist
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NSAID'S & PG'S PGE2 acid, misoprostol = PGE2 analogue
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Proglumide gastrin receptor antagonist
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H2 receptor antagonists cimetidine, ranitidine, famotidine
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PPI'S - protein pump inhibitors omeprazole, pantoprazole, rabeprazole, esomeprazole
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accessory organs
salivary glands |
three sets: parotid, sublingual & submandibular |
pancreas |
endocrine - insulin & glucagon, exocrine - digestive enzymes & bicarbonate |
liver |
excretion of bile pigments (bilirubin & bilverdin), bile salts e.g. deoxychoilic acid emulsification of fats |
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major structures
oesophagus |
small intestine - duodenum, jejunum, ileum |
large intestine - ascending colon, transverse colon, descending colon, sigmoid colon, rectum, anus |
hormonal control
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gastrin promotes gastric juice secretion, increases gastric motility, promotes growth of gastric mucosa
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secretin stimulates secretion of pancreatic juice & bile that are rich in bicarbonate ions
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cholecystokinin stimulates secretion of pancreatic juice rich in digestive enzymes, causes bile ejection from gallbladder & opening of sphincter of hepatopancreatic ampulla (sphincter of Oddi), induces satiety
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saliva
mostly water (99.5%) |
0.5% solutes - ions, dissolved gases, urea, nitric acid, mucus, immunoglobulin A, lysozyme & salivary amylase (acts on starch) & muramidase (anti-bacterial) |
submandibular & sublingual glands produce mucin rich saliva |
paratoid glands produce salivary amylase |
salivated is controlled by ANS, parasympathetic stimulation promotes secretion of moderate amount of saliva, sympathetic stimulation decreases salivation |
small intestine
circular fols called the plicae circulares are permanent ridges of mucosa & submucosa that encourage turbulent flow of chyme |
two muscle layers, has serosa not adventitia |
absorptive cell - digests & absorbs nutrients |
goblet cell - secretes mucus |
enteroendocrine cell -secretes hormones secretine, cholecystokin or GIP |
paneth cell - secretes lysozyme & is capable of phagocytosis |
major valves - sphincters
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oesophagus - upper oesophageal sphincter pharynx & oesophagus
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oesophagus - lower oesophageal sphincter oesophagus & stomach
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stomach - cardiac sphincter (LOS) oesophagus & stomach
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stomach - pyloric sphincter stomach & duodenum
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small intestine sphincter of Oddi
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large intestine - illeocaecal sphincter ileum & caecum
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large intestine - internal anal sphincter involuntary smooth muscle
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large intestine - external anal sphincter voluntary skeletal muscle
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large intestine
approx. 5 feet in length |
starts with ileocecal valve & has four parts: the cecum, colon (ascending, descending, transverse, sigmoid), rectum & anal canal |
no circular folds/villi |
mucosa = mostly absorptive epithelium mainly for water |
microvilli are plentiful |
interspersed goblet cells produce mucous but no digestive enzymes secreted |
gastric glands & cell types
surface mucous cell |
secretes mucus |
mucous neck cell |
secretes mucus |
parietal cell |
secretes HCl & intrinsic factor |
chief cell |
secretes pepsinogen & gastric lipase |
G cell |
secretes gastrin hormone |
pancreas
lies posterior to greater curvature of stomach |
pancreatic juice secreted into pancreatic duct & accessory duct & to small intestine |
pancreatic duct joins common bile duct & enters duodenum ay hepatopancreatic ampulla |
pancreatic juice = 1200 -1500 ml daily, composed of mostly water, sodium bicarbonate (buffers acidic stomach chyme), enzymes (pancreatic amylase, proteolytic enzymes - trypsin secreted as trypsinogen, chymotrypsin, carboxypeptidase, elastase), pancreatic lipase, ribonuclease & deoxyribonuclease |
histology: 99% of cells are acini, exocrine, secrete pancreatic juice (fluid + digestive enzymes)
1% of cells are pancreatic islets (islets of Langerhans), endocrine, secrete hormones glucagon, insulin, somatostatin, & pancreatic polypeptide
GI histology notes
oesophagus |
collapsible, muscular tube that lies posterior to the trachea & connects pharynx to stomach, has adventitia |
stomach (internal anatomy) |
rugae of mucosa , oblique, circular & longitudinal layers of muscle |
GI tract functions
mouth |
bite, chew, swallow |
pharynx & oesophagus |
transport |
stomach |
mechanical disruption; absorption of water & alcohol |
small intestine |
chemical & mechanical digestion & absorption |
large intestine |
absorb electrolytes & vit B, K |
rectum & anus |
defecation |
digestion phases
cephalic phase - stimulates gastric secretion & motility |
gastric phase - neural & hormonal mechanisms |
intestinal phase - neural & hormonal mechanisms |
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