Download Ch 14 Small and Large Intestine- pgs. 469-472 and 483-487

Pages 469-472 and 483-487
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From the stomach to the large intestine:
Duodenum
◦ Attached to the stomach via the pyloric sphincter
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Jejunum
Ileum
◦ Meets the large intestine at the ileocecal valve
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Begins in the small intestine via enzymes from:
◦ Intestinal cells
◦ Pancreas
 Pancreatic ducts carry enzymes to the duodenum
◦ Bile, formed by the liver, enters the duodenum via the
bile duct
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The pancreatic and bile ducts come together
to form a joint duct that releases into the
duodenum – the hepatopancreatic ampulla
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Bile duct and sphincter
Accessory pancreatic duct
Pancreas
Gallbladder
Jejunum
Duodenal
papilla
Hepatopancreatic
ampulla and sphincter
Main pancreatic duct and sphincter
Duodenum
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Three structural modifications increase
surface area for food absorption:
1. Villi—fingerlike projections formed by the
mucosa

House a capillary bed and lacteal
2. Microvilli—tiny projections off of the villi (create a
brush border appearance)
3. Circular folds (plicae circulares)—deep folds of
mucosa and submucosa
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Blood vessels
serving the small
intestine
Muscle
layers
Villi
(a) Small intestine
Lumen
Circular folds
(plicae circulares)
Absorptive
cells
Villus
Blood
capillaries
Lymphoid
tissue
Muscularis
mucosae
Lymphatic vessel
Submucosa
(b) Villi
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Macromolecular breakdown
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brush-border enzymes : enzymes released by microvilli
of the small intestine
 Break down larger sugars into simple sugars
 Finish protein digestion
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Protective mucus is secreted
Pancreatic juice and bile
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Pancreatic Juice: pancreatic enzymes which are
specific to the organic molecules they target:
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◦
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Amylase : starch
A collection of protein enzymes including trypsin
Lipase: fats
Nucleases: nucleic acids
Bicarbonate keeps the pH slightly alkaline
 Neutralizes the chyme upon entry to the small int.
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Bile: breaks down fats; aids in absorption of fats
and fat-soluble vitamins (K, D, E, A)
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Neural and hormonal regulation control:
◦ Pace of digestion
◦ Secretion of enzymes and hormones
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The presences of chyme stimulates hormone
release by the mucosa
◦ These hormones stimulate the release of bile and
pancreatic juice
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Water and most end products (except fats) are
absorbed into the blood via active transport
Fats are absorbed through diffusion
◦
Then they all travel to the liver via the hepatic
portal vein
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What remains at the ileum: (the end)
◦ Water
◦ Undigestible foods
◦ Lots of bacteria (which cannot enter the blood)
 Peyer’s Patches (clusters of lymph tissue) help prevent this
…Of a senior
Pages 470-472 and
484-486
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Extends from the ileocecal valve to the anus
Subdivisions:
 Cecum
 Appendix
 Colon (has it’s own subdivisions)
 Rectum
 Anal canal
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Functions:
 Dry out food residue (absorb any remaining
water)
 elimination
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Transverse
mesocolon
Transverse
colon
Haustrum
Descending
colon
Ascending colon
Ileum (cut)
Ileocecal valve
Teniae coli
Sigmoid
colon
Cecum
Appendix
Rectum
Anal canal
External anal sphincter
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Cecum—first part of the large intestine
◦ Connects to the ileum via the ileocecal valve
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Appendix
◦ Cluter of lymphoid tissue
 can become inflamed (appendicitis)
 Its twisted arrangement allows bacteria to accumulate
◦ Appendage of the cecum
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Colon –
◦ first 3 subdivisions create an upside down “U”
 Ascending—travels up right side of abdomen
 Transverse—travels across the abdominal cavity
 Descending—travels down the left side
◦ Sigmoid—S-shaped region; enters the pelvis
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Rectum- connects sigmoid colon to anus
◦ Walls stretch to initiate the defecation reflex
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Anus—opening of the large intestine
◦ Internal anal sphincter—smooth muscle,
involuntary control
◦ Remains closed to prevent feces from leaking between
defecations
◦ External anal sphincter—skeletal muscle, voluntary
control
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Sphincters stay closed until neural signals tell
them to open
• Peristalsis initiates defecation
• Waves of reflexive contractions continue until defecation
takes place
• Defecation can be helped by use of diaphragm and
Transverse
mesocolon
Transverse
colon
Haustrum
Descending
colon
Ascending colon
Ileum (cut)
Ileocecal valve
Teniae coli
Sigmoid
colon
Cecum
Appendix
Rectum
Anal canal
External anal sphincter
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Goblet cells : line the interior surface
◦ produce alkaline mucus
◦ lubricates the passage of feces
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Muscularis externa : (the muscular tunic)
◦ three bands of muscle called teniae coli
◦ cause the wall to pucker into haustra (pocketlike sacs)
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Few nutrients remain in food
No digestive enzymes are produced
Bacterial flora within the large intestine metabolize
remaining waste:
 This creates gas! Yum (methane and hydrogen sulfide)
 Synthesize Vitamins K and some B vitamins
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Absorption is limited to:
◦ Vitamins produced
◦ Remaining water and ions
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Feces- includes undigested food, mucus, bacteria, and
any remaining water