pages 469-470 and 480-484. from the stomach to the large intestine: duodenum ◦ attached to the...

Pages 469-470 and 480-484

From the stomach to the large intestine: Duodenum

◦ Attached to the stomach via the pyloric sphincter 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

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 sphincterAccessory pancreatic duct

Pancreas

Jejunum

Main pancreatic duct and sphincter

DuodenumHepatopancreaticampulla and sphincter

Duodenalpapilla

Gallbladder

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 vesselsserving the smallintestine

Musclelayers

Villi

Lumen

Circular folds(plicae circulares)

(a) Small intestine

Absorptivecells

Bloodcapillaries

Lymphoidtissue

Muscularismucosae

(b)Villi

Lymphatic vessel

Submucosa

Villus

Protein and some carbohydrate breakdown started in the stomach◦ Fats begin in the intestine

Enzymes are released by the microvilli◦ “brush-border enzymes”

Break down larger sugars into simple sugars finish protein digestion

Protective mucus is secreted Pancreatic juice and bile

Pancreatic Juice: pancreatic enzymes are essential and act specifically on organic molecules:◦ 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.

Bile: breaks down fats; aids in absorption of fats and fat-soluble vitamins (K, D, E, A)

Neural and hormonal regulation control:◦ Pace of digestion◦ Secretion of enzymes and hormones

The presences of chyme stimulates hormone release by the mucosa◦ These hormones stimulate the release of bile and

pancreatic juice

Water and most end products (except fats) are absorbed into the blood via active transport◦ from here they travel to the liver via the hepatic

portal vein Fats are absorbed through diffusion

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