unit i: metabolism digestive system part ii chapter 21
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Tissue Table
Digestive Organ Epithelial Tissue Muscle Type pH
Oral Cavity
Pharynx
Esophagus
Stomach
Small Intestine
Large Intestine
Anal Canal
Small Intestine
• Nearly all chemical digestion and nutrient absorption occurs in small intestine
SegmentsDuodenum
Jejunum
Ileum
Transversecolon (cut)
Ascendingcolon
Descendingcolon
Sigmoidcolon
Cecum Rectum
Ileum
Duodenum
JejunumSerosaMuscularisexternaSubmucosa
Mucosa
Muscularismucosae
Circular folds
Villi
Peyer Patches
Small Intestine
• Duodenum -10 in.
– neutralizes stomach acids, emulsifies fats, pepsin inactivated by pH increase, pancreatic enzymes
• Jejunum - next 8 ft.
– Simple columnar
– Smooth muscle
• Ileum - last 12 ft.
– lymphatic nodules
– ileocecal junction
Lacteal
Columnar epithelial cell
Mucous cell
Nerve
Capillary network
ArterioleLymphatic vesselVenule
Muscularis mucosae
Lamina propria
• Circular folds - up to 10 mm tall
– chyme flows in spiral path
• Villi - 1 mm tall– contain blood vessels and
lymphatics (lacteal)• nutrient absorption
• Microvilli 1 micron tall– brush border enzymes
– Dextrinase– Glucoamylase– Maltase– Sucrase, lactase
Circular folds
Villi
Small Intestine - Surface Area
Intestinal Crypts• absorptive cells, goblet cells and at
base, rapidly dividing cells
• Brunner’s glands
• Secrete 1-2 L of intestinal juice/day
• pH 7.4-7.8Brunner’s Glands
Gross Anatomy of Large Intestine
• 500 ml of indigestible food residue/day
• 5 ft long and 2.5 inches in diameter in cadaver
• Appendix – columnar epithelium, goblet cells, WBC, and lymphocytes
Aggregatedlymphoid
nodule
Simple columnarepithelium
Intestinal gland
Mucous cells
Muscularis mucosae
Submucosa
Muscularis Externa
Circular layer
Longitudinallayer
Microscopic Anatomy of Large Intestine
• Mucosa - simple columnar epithelium – anal canal: non-keratinized stratified squamous
• Muscularis Externa – smooth muscle− anal canal: skeletal
• No circular folds or villi
Anatomy of Anal Canal
• 3 cm total length• Anal columns • Anal sinuses• Internal & External anal sphincters
Bacterial Flora and Intestinal Gas
• Bacterial flora populate large intestine
– ferment cellulose and other undigested carbohydrates;
– synthesize vitamins B and K
• Flatus (gas)
– average person produces 500 mL per day
– most is swallowed air
– hydrogen sulfide, indole and skatole produce odor
Accessory Organs:Liver, Gallbladder and Pancreas
• All release important secretions into small intestine to continue digestion
Gross Anatomy of Liver
• 3 lb. organ located inferior to the diaphragm• Simple cuboidal epithelium• 4 lobes -
– falciform ligament– round ligament
Hepatocytes
Hepatic sinusoids
Bileduct
Hepatic Portal vein
HepaticArtery
Hepatic Triad
Microscopic Anatomy of Liver
• Hepatic lobules (2mm by 1mm)
• Sinusoids lined with fenestrated endothelium
Bileduct
Branch of hepaticportal vein
Branch ofhepatic artery
Blood enters the hepatic sinusoids from hepatic portal vein and hepatic artery.
Hepatocytes regulate solute and nutrient levels and absorb or secrete molecules.
Kupffer, phagocytic cells, engulf pathogens, cell debris, and damaged blood cells. Also responsible for storing iron, some lipids, and heavy metals (such as tin or mercury).
Central vein hepatic veins inferior vena cava.
Hepatocytes secrete bile into bile canaliculiBile ductules hepatic bile ducts in the nearest Triad
Start
Liver Function: Overview
Right and left hepatic ducts
Round ligament Commonhepatic duct
Hepatic portal vein and hepatic artery
Common bile duct
Gallbladder
Cystic duct
Liver Duodenum
Stomach
Pancreas
Pancreas
Common bile ductPancreatic duct
HepatopancreaticsphincterDuodenal
papilla
Intestinallumen
Ducts of Liver, Gallbladder, and Pancreas
Duodenum
CCK
Lipiddroplet
Bile salt
The liversecretes bilecontinuously—roughly 1 literper day.
Between meals, bile becomes moreconcentrated.
CCK triggers dilation ofthe hepatopancreatic sphincterand contraction of the gallbladder.
Liver
Start
Gallbladder and Bile
• Gallbladder: 10 cm long• Bile: minerals, bile acids, cholesterol, bile
pigments, fats and phospholipids– bilirubin
• intestinal bacteria convert to urobilinogen = brown color
– bile acid (salts)• enterohepatic circulation –
hepatocytes liver small intestine
Head ofpancreas
Body ofpancreas
Pancreatic lobules
Pancreatic duct
Common bile duct
Accessory pancreatic duct(present in 3–10 percent
of individuals)
Duodenal papilla
Duodenum
Tail ofpancreas
Gross Anatomy of Pancreas
• Endocrine and exocrine gland
– secretes insulin and glucagon
– secretes 1500 mL pancreatic juice/day
• Pancreatic juice:
– Water, zymogens, enzymes, and sodium bicarbonate
Pancreatic Acinar Cells
• Zymogens proteases
– Trypsinogen trypsin
– Chymotrypsinogen chymotrypsin
– Procarboxypeptidase carboxypeptidase
• Other enzymes
– Amylase (starch)
– Lipase (fat)
– Ribonuclease (RNA) and deoxyribonuclease (DNA)
Pancreaticduct
Endocrine cells inpancreatic islet
Cells of pancreatic acinus
The exocrine pancreatic acini