Copyright 2010 Pearson Education, Inc. Pancreas Location Behind
the stomach Head is encircled by the duodenum; tail abuts the
spleen
Slide 2
Copyright 2010 Pearson Education, Inc. Pancreas Endocrine
function Pancreatic islets secrete insulin and glucagon Exocrine
function Acini (clusters of secretory cells) secrete pancreatic
juice Zymogen granules of secretory cells manufacture digestive
enzymes
Slide 3
Copyright 2010 Pearson Education, Inc. Figure 23.26a Small duct
Acinar cells Basement membrane Zymogen granules Rough endoplasmic
reticulum (a)
Slide 4
Copyright 2010 Pearson Education, Inc. Pancreatic Juice
Approximately 1200-1500 ml produced daily Watery alkaline solution
(pH 8) neutralizes chyme Electrolytes (primarily HCO 3 ) Enzymes
Amylase, lipases, nucleases are secreted in active form but require
ions or bile for optimal activity Proteases secreted in inactive
form prevents auto-digestion of pancreas
Slide 5
Copyright 2010 Pearson Education, Inc. Pancreatic Juice
Protease activation in duodenum Trypsinogen is activated to trypsin
by brush border enzyme enteropeptidase Procarboxypeptidase and
chymotrypsinogen are activated by trypsin
Copyright 2010 Pearson Education, Inc. Regulation of Bile
Secretion Gallbladder contraction is stimulated mainly by
Cholecystokinin (CCK) from intestinal cells exposed to proteins and
fat in chyme CKK also causes the hepatopancreatic sphincter to
relax
Slide 8
Copyright 2010 Pearson Education, Inc. Digestion in the Small
Intestine Chyme from stomach contains Partially digested
carbohydrates and proteins Undigested fats
Slide 9
Copyright 2010 Pearson Education, Inc. Requirements for
Digestion and Absorption in the Small Intestine Slow delivery of
chyme Chyme is hyperosmotic Low Ph must be buffered in the duodenum
Delivery of bile, enzymes, and bicarbonate from the liver and
pancreas Mixing
Slide 10
Copyright 2010 Pearson Education, Inc. Motility of the Small
Intestine Segmentation Initiated by intrinsic pacemaker cells Mixes
and moves contents slowly and steadily toward the ileocecal valve
Wanes in the late intestinal (fasting) phase
Slide 11
Copyright 2010 Pearson Education, Inc. Motility of the Small
Intestine Peristalsis Initiated by motilin secreted by duodenal
mucosa in the late intestinal phase Each wave starts distal to the
previous Meal remnants, bacteria, and debris are moved to the large
intestine As food enters the stomach again, peristalsis is replaced
by segmentation
Slide 12
Copyright 2010 Pearson Education, Inc. Figure 23.3a From mouth
(a) Peristalsis: Adjacent segments of alimentary tract organs
alternately contract and relax, which moves food along the tract
distally.
Slide 13
Copyright 2010 Pearson Education, Inc. Large Intestine Regions
Cecum (pouch with attached vermiform appendix) Colon Ascending
Transverse Descending Sigmoid Rectum Anal canal
Slide 14
Copyright 2010 Pearson Education, Inc. Figure 23.29a Left colic
(splenic) flexure Transverse mesocolon Epiploic appendages
Descending colon Teniae coli Sigmoid colon Cut edge of mesentery
External anal sphincter Rectum Anal canal (a) Right colic (hepatic)
flexure Transverse colon Superior mesenteric artery Haustrum
Ascending colon IIeum IIeocecal valve Vermiform appendix Cecum
Slide 15
Copyright 2010 Pearson Education, Inc. Rectum and Anus Rectum
Three rectal valves stop feces from being passed with gas Anal
canal The last segment of the large intestine Sphincters Internal
anal sphinctersmooth muscle External anal sphincterskeletal
muscle
Slide 16
Copyright 2010 Pearson Education, Inc. Figure 23.29b (b) Rectal
valve Rectum Anal canal Levator ani muscle Anus Anal sinuses Anal
columns Internal anal sphincter External anal sphincter
Hemorrhoidal veins Pectinate line
Slide 17
Copyright 2010 Pearson Education, Inc. Bacterial Flora Enter
from the small intestine or anus Colonize the colon Ferment
indigestible carbohydrates Release irritating acids and gases
Synthesize B complex vitamins and vitamin K
Slide 18
Copyright 2010 Pearson Education, Inc. Functions of the Large
Intestine Vitamins, water, and electrolytes are reclaimed Major
function is propulsion of feces toward the anus Colon is not
essential for life
Slide 19
Copyright 2010 Pearson Education, Inc. Motility of the Large
Intestine Haustral contractions Slow segmenting movements Haustra
sequentially contract in response to distension Occur mostly in the
transverse and descending colon
Slide 20
Copyright 2010 Pearson Education, Inc. Motility of the Large
Intestine Gastrocolic reflex Initiated by presence of food in the
stomach Activates three to four slow powerful peristaltic waves per
day in the colon (mass movements)
Slide 21
Copyright 2010 Pearson Education, Inc. Defecation Mass
movements force feces into rectum Distension of rectal wall
initiates defecation reflex Stimulate contraction of the sigmoid
colon and rectum Relax the internal anal sphincter Conscious
control allows relaxation of external anal sphincter
Slide 22
Copyright 2010 Pearson Education, Inc. Chemical Digestion
Catabolic process (breaks down large molecules into smaller ones
(monomers)) Hydrolysis enzymatic breakdown of any type of food
molecule
Slide 23
Copyright 2010 Pearson Education, Inc. Chemical Digestion of
Carbohydrates Carbohydrates Monosaccharides Digestive enzymes
Salivary amylase, pancreatic amylase, and brush border enzymes
(dextrinase, glucoamylase, lactase, maltase, and sucrase)
Slide 24
Copyright 2010 Pearson Education, Inc. Chemical Digestion of
Proteins Proteins Amino Acids Enzymes: pepsin in the stomach
Pancreatic proteases Trypsin, chymotrypsin, and carboxypeptidase
Brush border enzymes Aminopeptidases, carboxypeptidases, and
dipeptidases
Slide 25
Copyright 2010 Pearson Education, Inc. Chemical Digestion of
Lipids Lipids Fatty Acids & Monoglycerides
Pre-treatmentemulsification by bile salts Enzymespancreatic lipase
Absorption of glycerol and short chain fatty acids
Slide 26
Copyright 2010 Pearson Education, Inc. Vitamin Absorption In
small intestine Fat-soluble vitamins (A, D, E, and K) are carried
by micelles (fatty clusters) and then diffuse into absorptive cells
Water-soluble vitamins (vitamin C and B vitamins) are absorbed by
diffusion or by passive or active transporters. Vitamin B 12 binds
with intrinsic factor, and is absorbed by endocytosis
Slide 27
Copyright 2010 Pearson Education, Inc. Vitamin Absorption In
large intestine Vitamin K and B vitamins from bacterial metabolism
are absorbed
Slide 28
Copyright 2010 Pearson Education, Inc. Malabsorption of
Nutrients Causes Anything that interferes with delivery of bile or
pancreatic juice Damaged intestinal mucosa (e.g., bacterial
infection)
Slide 29
Copyright 2010 Pearson Education, Inc. Malabsorption of
Nutrients Gluten-sensitive enteropathy (celiac disease) Gluten is
found in wheat, rye, and barley products Gluten damages the
intestinal villi and brush border Symptoms include: bloating,
diarrhea, pain, & malnutrition Treated by eliminating gluten
from the diet (all grains but rice and corn)
Slide 30
Copyright 2010 Pearson Education, Inc. Developmental Aspects
During old age GI tract activity declines, absorption is less
efficient, and peristalsis is slowed Diverticulosis, fecal
incontinence, constipation, and cancer of the GI tract
Slide 31
Copyright 2010 Pearson Education, Inc. Cancer Oral cancers are
detected during routine dental exams Stomach and colon cancers
rarely have early signs or symptoms Metastasized colon cancers
frequently cause secondary liver cancer Prevention Regular dental
and medical examination