Physiology

1. Digestive System
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2. GI: Overview: Organ systems
 GIT and accessory structures
 Gastrointestinal (GI) tract [Alimentary canal] a
continuous muscular digestive tube
 Digests:
 breaks food into smaller fragments
 Absorbs:
 digested material is moved through mucosa into the blood
 Eliminates:
 unabsorbed & secreted wastes.
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3. Organ systems
 Includes:
 Mouth, pharynx &
esophagus
 Stomach
 Small intestine
 Large intestine
 Accessory digestive
organs: teeth, tongue,
gall bladder, salivary
glands, liver &
pancreas
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4. Processes
 Ingestion
 Propulsion
 Mechanical digestion
 Chemical digestion
 Absorption
 Defecation
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5. Processes
 Ingestion: obtaining food
 Propulsion: moves food along the GI tract by
peristalsis (wave-like muscular contraction)
 Mechanical digestion :
 chewing & mixing with saliva
 mixing in stomach
 segmentation (local constriction in intestine to mix food
& digestive juices)
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6. Processes
 Chemical digestion: breaks down food to
molecular fragments (monomers) (Hydrolysis).
 Begins in the mouth with saliva & continues into the
small intestine.
 Absorption: movement of nutrients across the
mucosal membrane into blood/lymph
 Defecation: eliminates unused/indigestible &
secreted substances from the body
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7. Peritoneum : serous membrane
 Visceral peritoneum: covers the external surfaces of
most digestive organs
 Parietal Peritoneum: lines the body wall
 Peritoneal Space: potential space containing fluid
that separates the visceral & parietal peritoneum
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8. Peritoneum
 Mesentery: double layer of peritoneum fused together
that extends to the organs from the posterior body
wall.
 Provides support for the organs
 Provides support for vessels & nerves supplying the organs
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9. Peritoneum
 Retroperitoneal organs
 Organs that adhere to the posterior abdominal wall &
lose their peritoneum by resorption
 Parts of the large & small intestine & most of the
pancreas; (also kidneys)
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10. GI blood supply
 Blood supply: about 25% of cardiac output
 Arterial: Abdominal aorta g celiac trunk
 Celiac trunk g Hepatic, splenic & gastric branches
which serve the liver, spleen & stomach
 Celiac trunk g superior & inferior mesenteric
branches serve small & large intestine,
respectively.
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11. Nerves
 Intrinsic (Local): Short reflex
 Submucosal nerve plexus:
regulates glands & mucosal muscle
 Myenteric plexus: controls GI wall & GI motility
 Extrinsic (CNS): Long reflex
 Parasympathetic NS: enhances gut motility &
secretion
 SNS: inhibits gut motility & secretion
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12. Nerves
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13. Functional Anatomy: Mouth
 Mouth: lips, palate, &
tongue
 Mouth cavity = Buccal
cavity
 Salivary glands
 Teeth
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14. Functional Anatomy: Mouth
 Lips: extend from inferior margin of the nose to
the superior margin of the chin.
 Red area = red margin, is poorly keratinized & lacks
sweat or sebaceous glands.
 Palate:
 Hard palate: rigid surface against which food is
forced in chewing
 Soft palate: muscular structure that rises &
blocks off the nasopharynx during swallowing
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15. Functional Anatomy: Mouth
 Tongue: muscular tentacle composed of
interlaced muscle fibers that grips & repositions
food, mixes food with saliva & compresses food
to form a food bolus, prior to swallowing.
 It contains taste sensing structures, taste
buds.
 It is organ of speech.
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16. Functional Anatomy: Mouth
 Filiform papillae: rough surface
 Fungiform papillae: house taste buds
 Circumvallate papillae: house taste buds,
 Foliate papillae: posterolateral; taste buds 16

17. Functional Anatomy: Mouth
 Salivary Glands: intrinsic & extrinsic
 Intrinsic glands: scattered throughout the buccal
cavity mucosa
 Extrinsic glands: supply most of the saliva; outside
buccal cavity & supply secretions via ducts:
 Parotid
 Submandibular
 Sublingual
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18. Functional Anatomy:
Mouth, Pharynx
 Teeth:
 Primary: 2I 1C 2M x 2 = 20
2I 1C 2M
 Permanent: 2I 1C 2PM 3M x 2 = 32
2I 1C 2PM 3M
 Structures
 Crown: exposed above gingiva (gum)
 Root: anchored by periodontal ligament to the bone by a
fibrous joint (gomphosis)
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19. Functional Anatomy:
Throat & Esophagus
 Pharynx: oropharynx & laryngopharynx;
muscular wall propels food to the esophagus
 Esophagus:
 Muscular 25cm tube from laryngopharynx to
stomach
 Passes through the diaphragm at the
esophageal hiatus
 Gastroesophageal (cardiac) sphincter: A
physiologic sphincter that helps keep
esophagus closed when empty
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20. Functional Anatomy: Stomach
 Cardiac region: narrow, receives food bolus
 Fundus: bulge that extends superio-laterally to the cardia,
reaches the diaphragm
 Body: mid-portion
 Pyloric antrum : funnel shaped portion narrows to form the;
 Pyloric canal
 Pylorous 
 Pyloric sphincter 
 small intestine
 Rugae
 longitudinal mucosal
folds
 volume about 4L
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21. Rugae
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22. Digestive Processes (Stomach)
 Acts as a holding vessel for ingested food
 Participates in mechanical & chemical digestion
 Propulsion: Delivers its product (chyme) to the small
intestine
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23. Digestive Processes (Stomach)
 Protein digestion: HCl denatures protein
 HCl activates pepsinogen to pepsin
 Pepsin breaks peptide bonds of proteins
 Rennin: an enzyme that breaks down casein
(milk protein) secreted in infants
 Intrinsic factor: required for Vit. B12 absorption
(needed to mature RBC);
 Absence of B12 results in pernicious anemia
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24. Regulation of Gastric Activity
Figure 23.16
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25. Small Intestine: Gross Anatomy
 6-7m (9ft to 34.4 ft) long: from pyloric
sphincter to the ileocecal valve
 3 subdivisions:
 Duodenum
 Jejunum
 Ileum
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26. 26

27. Small Intestine: Gross
Anatomy
 Duodenum :
 Curves around the pancreatic head (~25cm long)
 Contains the hepato-pancreatic ampulla : formed
by the merger of the bile duct & the pancreatic
duct.
 Hepato-pancreatic sphincter controls admission of
bile & pancreatic enzymes to the duodenum
 Duodenum is retroperitoneal
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28. Small Intestine; Regulatory Function
 Duodenal regulation of gastric emptying:
Feedback mechanisms monitor the contents
being delivered from the stomach
 High fat content
 Low pH (high acidity)
 Hypertonicity (high osmolality)
 All result in decreased stomach emptying.
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29. Regulation of Gastric Emptying
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30. Small Intestine: Gross Anatomy
 Jejunum: extends from duodenum
to ileum (~2.5m long)
 Ileum: from jejunum to ileocecal
valve (~3.6m long)
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31. Small Intestine: Gross Anatomy
 Jejunum & Ileum function in absorption;
 Intraperitoneal
 Suspended from mesentery whose veins &
lymph vessels carry nutrients away from small
intestine
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32. Small intestine Wall
 Intestinal crypts with cells that secrete intestinal
juice
 contain Paneth cells that secrete protective
lysozyme (antibacterial)
 Peyer’s Patches: lymphoid follicle in submucosa
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33. Small intestine Wall
 Brunners glands (duodenum) secrete HCO3
- rich
mucous to increase the pH of chyme
 Villus epithelium is replaced every 3-6 days
 Intestinal Juice : isotonic with blood plasma,
slightly alkaline, low enzyme content
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34. Large Intestine:
Gross Anatomy
 Ileocecal valve to anus (~1.5m)
 Teniae coli: 3 ribbons of
longitudinal smooth muscle
 Haustra: pocket-like segments
of large intestine
 Epiploic appendages: fat filled
pouches of visceral peritoneum
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35. Large Intestine:
Gross Anatomy
 Cecum: blind pouch (below ileocecal valve)
 Appendix: attached to cecum (lymphoid)
 Colon: ascending, transverse, descending, sigmoid
 Transverse colon & sigmoid colon are intraperitoneal;
anchored by mesentery. The rest of the colon is
retroperitoneal
 Rectum
 Anal canal
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36. Large Intestine: Digestive Processes
 Propulsion:
 Haustra contractions: stretch stimulate haustra to
contract moving (& mixing) contents to next haustra
 Mass peristalsis: long, slow contractile waves moving
contents toward rectum (3-4 per day)
 Gastrocolic reflex: food intake causes mass peristalsis
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37. Structure of the Anal Canal
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38. Liver & Gall Bladder
 Liver produces bile (fat emulsifier) that is stored
in & concentrated by the gall bladder.
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39. Liver: Gross Anatomy
 Largest gland
 4 Lobes:
 Right, left,
quadrate, caudate
 Falciform ligament
 mesentery
supports liver
from diaphragm &
anterior body wall
 separates R & L
lobes
 Round ligament
fibrous remnant of
umbilical vein
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40.  Blood supply
 hepatic artery & hepatic
portal vein
 Bile
 drains from biliary ducts to
common hepatic duct
which fuses with cystic
duct from gallbladder to
form the bile duct
Liver: Gross Anatomy
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41. Liver: Microscopic Anatomy
 Liver lobule: hexagonal
 Central vein: drains the lobule
 Hepatocytes form plates that radiate from the
central vein
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42. Microanatomy of the Liver
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45. Liver & Gall Bladder
 Composition of bile: Alkaline solution (Bile salts,
bile pigments, cholesterol, fats & phospholipids)
 Bile salts & phospholipids participate in fat
digestion and absorption
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46. Liver & Gall Bladder
 Bile salts are conserved by enterohepatic
circulation
 Reabsorbed in the ileum
 Return to Liver in hepatic portal blood
 Re-secreted by the Liver
 Bile pigments & bilirubin break down to urobilin
then stercobilin
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47. Gall Bladder
 Gall Bladder = a muscular pouch that stores bile & expels bile
when needed via the cystic duct & the bile duct.
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48. Pancreas: Gross Anatomy
 Head encircled by duodenum
 Tail abuts the spleen
 Mostly retroperitoneal
 The pancreas is an elongated, tapered organ
located across the back of the belly, behind the
stomach.
 The right side of the organ—called the head—is
the widest part of the organ and lies in the curve
of the duodenum, the first division of the small
intestine.
 The tapered left side extends slightly upward—
called the body of the pancreas—and ends near
the spleen—called the tail.
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49.  The pancreas is made up of 2 types of glands:
 Exocrine. The exocrine gland secretes digestive enzymes.
These enzymes are secreted into a network of ducts that
join the main pancreatic duct. This runs the length of the
pancreas.
 Endocrine. The endocrine gland, which consists of the
islets of Langerhans, secretes hormones into the
bloodstream.
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