Happy Thursday!!

1. Happy Thursday!! • Quickwrite 10/6 • Draw and label the organs in the digestive system!!

2. Digestive System Topic 6.1

3. 6.1 • Basics of Digestion • Ingestion: you eat the food • Digestion: a series of chemical reactions that convert ingested food to smaller and smaller molecular forms • Absorption: small molecular forms are absorbed through cells of digestive system, pass into nearby blood or lymphatic vessels • Transport: circulatory system delivers the small molecular nutrients to your body cells.

4. 6.1 • Digestion of macromolecules • Most food molecules are large polymers and insoluble • Too large to pass through cell membranes of the intestines and the capillaries • They must first be digested to smaller soluble molecules (hydrolysis) before they can be absorbed into the blood

5. 6.1.1 • Molecular type of some food categories

6. 6.1 • Digestion of macromolecules • Different organisms have different characteristic molecules that they create. • Digestion allows organisms to disassemble macromolecules from their food sources and use the ‘building blocks’ to create their own macromolecules.

7. 6.1 • Digestive Enzymes • Are specific for a specific food type. • Secreted into the lumen of the gut • Increase the rate of reaction of the hydrolysis of insoluble food molecules to soluble end products • Function at body temperature (which is why it is so important for your body to maintain a stable temperature)

8. 6.1 • General types of digestive enzymes • Amylases • break down complex sugars into monosaccharides • Proteases • break down proteins into amino acids • Lipases • break down lipids into fatty acids

9. 6.1 • Examples of digestive enzymes • Pancreatic amylase • Source: Pancreas cells • Optimal pH: 7.5-7.8 • Substrate: starch (amylose) • End product: disaccharide maltose • Action: hydrolysis of 1-4 glycosidic bonds

10. 6.1

11. 6.1 • Pepsin (a Protease: enzyme that digests proteins) • Source: stomach cells • Optimal pH: is 2 • Substrate: polypeptide chains (proteins) • End product: amino acids • Action: hydrolysis of peptide bonds within the polypeptide chain

12. 6.1

13. 6.1 • Pancreatic lipase • Source: pancreas cells • Optimal pH: 7.2 • Substrate: triglyceride lipid • The product: glycerol and fatty acid chains • Action: hydrolysis of ester bonds between the glycerol molecules and the fatty acid chains.

14. 6.1 • The action of pancreatic lipases also requires the presence of bile salts that emulsify the lipid. This emulsification has two effects: • Increases the surface area of the lipid for the digestion of fat • Exposes the glycerol 'head' structure to the enzyme

15. 6.1

16. 6.1 • Organs of the Digestive System • Food passes through the digestive tract in the following sequence: • Mouth, pharynx (throat), esophagus, stomach, small intestine, large intestine, rectum, anus • The liver, pancreas, and gallbladder are accessory digestive organs that produce digestive enzymes for secretion into the digestive tract

17. 6.1

18. 6.1 • Digestion • Mouth • specialized for ingestion and the beginning of the digestion process • Mechanicaldigestion begins as you bite, grind, and chew the meat and bun with your teeth • While food is being mechanically disassembled by the teeth, it is also moistened by saliva • Three pairs of salivary glands secrete about a liter of saliva into the mouth cavity each day • Saliva contains an enzyme, salivary amylase, which initiates the chemical digestion of starch into sugar

19. 6.1 • Throat • After a bite of food has been chewed and fashioned into a lump called a bolus, it is swallowed and moved through the pharynx and into the esophagus • The pharynx, or throat, is a muscular tube that serves as a hallway of the respiratory system as well as the digestive system • During swallowing, the opening to the airway is closed by a small flap of tissue called the epiglottis

20. 6.1 • Waves of peristalsis (muscle contraction) sweep the bolus through the pharynx and esophagus to the stomach • Circular muscle fibers in the wall of the esophagus contract around the top of the bolus, pushing it downward • Almost at the same time, longitudinal muscles around the bottom of the bolus and below it contract, shortening the tube

21. 6.1 • Stomach • The entrance to the large, muscular stomach is normally closed by a ring of muscle at the lower end of the esophagus • When a peristaltic wave passes down the esophagus, the muscle relaxes, permitting the bolus to enter the stomach • When empty, the stomach is collapsed and shaped almost like a hot dog

22. 6.1 • Folds of the stomach wall, called rugae, give the inner lining a wrinkled appearance • As food enters, the rugae gradually smooth out, expanding the capacity of the stomach to more than a liter • The stomach is lined with an epithelium that secretes large amounts of gastric juice, composed of • Tiny pits mark the entrances to the millions of gastric glands, which extend deep into the stomach wall

23. 6.1 • Parietal cells in the gastric glands secrete hydrochloric acid and a substance known as an intrinsic factor,needed for adequate absorption of vitamin B12 • Chief cells in the gastric glands secrete pepsinogen, an inactive enzyme precursor • When pepsinogen comes in contact with the acidic gastric juice in the stomach, it is converted to pepsin, the main digestive enzyme of the stomach • Pepsin hydrolyzes proteins, converting them into small polypeptides

24. 6.1 • Several protective mechanisms prevent the gastric juice from digesting the wall of the stomach: • Cells of the gastric mucosa secrete an alkaline mucus that coats the stomach wall and neutralizes the acidity of the gastric juice along the lining • Epithelial cells of the lining fit tightly together, preventing gastric juice from leaking between them and into the tissue beneath • These mechanisms sometimes malfunction, and part of the stomach lining is digested, leaving an open sore, or ulcer • The bacterium heliobactor pylori has been implicated as a causative factor in ulcers because it causes a reduction in the amount of mucus secreted

25. 6.1 • The actual process of digestion in the stomach is as follows: • The stomach churns and chemically degrades the food so that it assumes the consistancy of thick soup; this partially digested food is called chyme • Protein digestion then begins, and any proteins are degraded into polypeptides • Digestion of starch to small polysaccharides continues until salivary amylase is inactivated by the acidic pH of the stomach • Over a period of several hours, peristaltic waves release the chyme in spurts through the stomach exit, the pylorous, and into the small intestine

26. 6.1 • Small Intestine • Digestion of food is completed in the small intestine, and nutrients are absorbed through its wall • The small intestine, which is 5-6 m (about 17 ft) in length, has three regions: • Duodenum • Jejunum • Illium

27. 6.1 • Most chemical digestion takes place in the duodenum, not in the stomach • Bile from the liver and enzymes from the pancreas are released into the duodenum and act on the chyme • Enzymes produced by the epithelial cells lining the duodenum catalyze the final steps in the digestion of major types of nutrients

28. 6.1 • The lining of the small intestine appears wrinkly because of its millions of tiny finger-like projections called villi • The villi increase surface area for digestion and absorption of nutrients • The intestinal surface is further expanded by thousands of microvilli, folds of cytoplasm on the exposed surface of the epithelial cells of the villi

29. 6.1 • Absorption of nutrients is primarily the job of the intestinal villi • The wall of a villus consists of a single layer of epithelial cells • Inside each villus is a network of capillaries and a central lymph vessel, called a lacteal • To reach the blood (or lymph), a nutrient molecule must pass through an epithelial cell of the intestinal lining and through a cell of the blood or lymph vessel lining

30. 6.1 • Absorption occurs by a combination of simple diffusion, facilitated diffusion, and active transport • Fructose is absorbed by facilitated diffusion • Amino acids and glucose are absorbed by active transport and then transported directly to the liver by the hepatic portal veins

31. Intestinal Villi

32. 6.1.7

33. Digestive Muscles • Contraction of circular and longitudinal muscles of the small intestine mix food with enzymes and move the mixture through the gut. • Epithelium, mucosa, longitudinal and circular muscles.

36. 6.1.5 • Liver • The liver, the largest internal organ as well as one of the most complex, lies in the upper right part of the abdomen just under the diaphragm • The liver’s food processing functions include the following: • Secretes bile, which is important in the mechanical digestion of fats • Helps maintain homeostasis by removing or adding nutrients to the blood • Converts excess glucose to glycogen and stores it • Converts excess amino acids to fatty acids and urea • Detoxifies alcohol and other drugs and poisons

37. 6.1.5 • Gallbladder • Bile is stored in the pear shaped gallbladder, which concentrates the bile and releases it into the duodenum as needed • Bile consists of water, bile salts, bile pigments, cholesterol, salts, and lecithin (a phospholipid). • Bile mechanically digests fats by a detergent like action • Because it contains no digestive enzymes, bile does not enzymatically digest food

38. 6.1.5 • Pancreas • The pancreas is an elongated gland that secretes both digestive enzymes and hormones that help regulate the level of glucose in the blood • Among its enzymes are: • trypsin and chymotrypsin, which digest polypeptides to dipeptides; • pancreatic lipase, which degrades fats • pancreatic amylase, which breaks down almost all types of carbohydrates except cellulose to disaccharides • ribonuclease and deoxyribonucleas which split the nucleic acids to free nucleotides

39. 6.1.5 • Large Intestine • Undigested material, such as the cellulose of plant foods, along with unabsorbed chyme, passes into the large intestine • The small intestine joins the large intestine, forming a blind pouch called the cecum • From the cecum to the rectum, the large intestine is known as the colon

40. 6.1.5 • The regions of the large intestine are the cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, and anus – the opening for elimination of wastes • As the chyme passes slowly through the large intestine, water and sodium are absorbed from it, and it gradually assumes the consistancy of normal feces • Bacteria inhabiting the large intestine are nourished by the last remnants of the meal and benefit their host by producing vitamin K and certain B vitamins that can be absorbed and used

41. 6.1.5 • Absorption vs. Assimilation • Insoluble food molecules are digested to soluble products in the lumen of the gut. • Absorption: • The soluble products are first taken up by various mechanisms into the epithelial cells that line the gut. • These epithelial cells then load the various absorbed molecules into the blood stream. • Assimilation: • The soluble products of digestion are then transported to the various tissues by the circulatory system. • The cells of the tissues then absorb the molecules for use within this tissues