Transcript Large Intestine

The Large
Intestine
Pages 470-472 and
484-486
…Of a senior
Large Intestine
• Extends from the ileocecal valve to the anus
• Subdivisions:
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
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Cecum
Appendix
Colon (has it’s own subdivisions)
Rectum
Anal canal
• Functions:
 Dry out food residue (absorb any remaining water)
 elimination
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Figure 14.8 The large intestine.
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
Large Intestine Anatomy
• Cecum—first part of the large intestine
– Connects to the ileum via the ileocecal valve
• Appendix
– Cluter of lymphoid tissue
• can become inflamed (appendicitis)
– Its twisted arrangement allows bacteria to accumulate
– Appendage of the cecum
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Large Intestine Anatomy
• 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
• 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
• 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 abdominal muscles
Figure 14.8 The large intestine.
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
Additional anatomical features
• Goblet cells : line the interior surface
– produce alkaline mucus
– lubricates the passage of feces
• Muscularis externa : (the muscular tunic)
– three bands of muscle called teniae coli
– cause the wall to pucker into haustra (pocketlike
sacs)
© 2015 Pearson Education, Inc.
Activities of the large intestine
• Few nutrients remain in food
• No digestive enzymes are produced
• Bacterial flora within:
– metabolize what’s left
• This creates gas! Yum (methane and hydrogen sulfide)
– Synthesize Vitamins K and some B vitamins
• Absorption is limited to:
– Vitamins produced
– Remaining water and ions
• Feces- includes undigested food, mucus, bacteria,
and any remaining water