Digestive System

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The Digestive System Components

Back 1

Mouth, Esophagus, Stomach, Small Intestine (duodenum, ileum, jejunum), large intestine (ascending colon, transverse colon, descending colon, sigmoid colon), rectum, anus).

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Mouth

Back 2

Chemical and Mechanical Digestion. Chemical: Carbohydrate breakdown with salivary amylase. Mechanical: Chewing - increases surface area of the foo, enables more enzymes to act upon it during the digestive process. Saliva - coats food for ease of swallowing. Chewed food = bolus. Pushed into esophagus via swallowing.

Front 3

Esophagus

Back 3

Food moves down via peristalsis. Involuntary muscle contractions of the lining. Occurs with a wave motion. The saliva has lubricated the food to make the passage down the esophagus. No digestion here.

Front 4

Stomach

Back 4

Mixes food. Stores food. Reduces it to chyme. Contains exocrine glands. Protein digestion via pepsin (pepsinogen +Hcl = pepsin). Low pH of the stomach also denatures the proteins assisting in the process.

Front 5

Major cell types of the stomach

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G cell: secretes gastrin. Large peptide hormone. Absorbed into the blood. Stimulates parietal cells to secrete HCl. Parietal cell: Exocrine gland of the stomach. Secrete Hcl, which diffuses to the lumen. Lowers the pH of the stomach, raises pH of blood. Secretes intrinsic factor: helps ileum to absorb B12. Chief (peptic) cells: Secrite pepsinogen - zymogen precursor to pepsin. Pepsin begins protein digestion. Mucous cells: secrete mucous. line the stomach wall. lubricate wall so food can slide along the the surface. Protects epithelial lining from acidic environment.

Front 6

Small Intestine

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90% of Digestion and Absorption. Duodenum - most digestion. Jejumum ileum: most absorption. Contains villi - increase surface area. Each villi has capillary network and lacteal - through which nutrients are absorbed and passed into. Microvilli - smaller projections - create brush border.

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Brush Border

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membrane bound digestive enzymes are contained here: dextrinase, maltase, sucrase, lactase, peptidase, nucleosidases.

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Goblet Cells

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of Small intestine - produce mucus to lubricate the intestine and protect the brush border.

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Pancreas

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Produces bicarbonate ion. Secreted into the small intestine and neutralizes the chyme. Releases major enzymes: trypsin, chymotrypsin, pancreatic amylase, lipase, ribonuclease, deoxyribonuclease as zymogens into the small intestine.

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Liver

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Produces bile, which is stored in the gall bladder and secreted into the small intestine. Bile emulsifies fat - breaking it apart so that it has better access to the lipase for breakdown.

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Large Intestine

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Functions in Absorption of water and electrolytes. Contains E. Col - produces vitamin K, B12, thiamin, riboflavin. Mutualistic symbiosis.

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Enterocytes

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Intestinal absorptive cells. That accept the nutrients from the small intestine. After whch the nutrients are processed and carried to the individual cells for use.

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Glycogenesis

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Formation of glycogen from glucose. Done in order to store glucose that is not needed.

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Glycogenolysis

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Takes place in the liver. Formation of glucose from glycogen when blood glucose level decreases.

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Fat cells

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Glucose is converted to fat in the liver and fat cells for storage in the fat cells.

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Protein absorption

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Amino acids are absorbed directly into the blood. Taken up by all cells of the body especially the liver. Transport into cells may be facilitated or active, but never passive. Amino acids are too large and polar for that. Cells create proteins from the amino acids so that th eintracellular amino acid concentration remains low. Most proteins are easily broken down and returned to the blood when needed. Protein storage upper limit reached? Amino acids - burned for energy or converted to fat for storage.

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Fat absorption

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Triglycerides = dietary fat. Broken down to monoglycerides and fatty acids before going to brush border via bile micelles. Diffuse through enterocyte membrane. Micelle is shuttled back to chyme after delivery. The fat components are turned back into triglycerides at smooth ER. AGGREGATE WITH SMOOTH ER LUMEN WITH CHOLESTEROL AND PHOSPHLIPIDS. VIA CHYLOMICRONS - LACTEALS. . major fat absorption in the liver and adipose tissue. fatty acids are transported as free fatty acids after leaving adipose tissue. with albumin. Lipoproteins carry lipids in between meals.

Front 18

Carbohydrate absorption

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By secondary active transport mechanism down the concentration gradient of sodium. Sodium - pumped out of enterocyte on basolateral side. Creates low sodium concentration inside enterocyte. That brings sodium into cell through transport protein after glucose has attached itself to the protein. Facilitated transport moves glucose out of enterocytes on the basolateral side. Absorbed into blood stream - carried b portal vein to liver. Absorbs it . stores it as glycogen via glycogenesis. Until blood glucose level drops, then glycogenolysis breaks glycogen down to return glucose to the blood. All other cells but eneterocytes glucose is transported via facilitated diffusion. high concentrationt o low concentration.

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Liver Functions (8 of them) K

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1. blood storage, 2. blood filtration, 3. carbohydrate metabolism, 4 fat metabolism, 5. protein metabolism, 6. detoxification, 7. erythrocyte destruction, 8. vitamin storage

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Ketone bodies

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when liver movilizes fat for energy - produces acids - ketone bodies. Results in ketosis or acidosis. Raising the blood acidity.