Chapter 6 – The Digestive System

1. Chapter 6 – The Digestive System Pages 217 - 231

2. 6.1 Summary • Carbohydrates, lipids, proteins, and nucleic acids are macromolecules made up of smaller identical units • The process of positioning and breaking chemical bonds is carried out in cells by proteins called enzymes.

3. Lipids • A saturated fatty acid: • Has single C-C bonds • No space for more hydrogen • Is solid at room temperature • An unsaturated fatty acid: • Has at least one double C=C bond • Can fit more hydrogen • Is liquid at room temperature

4. Carbohydrates • Carbohydrates are used as an energy source • Carbohydrates contain carbon, hydrogen and oxygen in a 1:2:1 ratio • Saccaride (sugar): • Monosaccaride (contains 3-7 carbons) ie. glucose • Disaccaride (made of 2 monosaccarides) ie. sucrose • Polysaccaride (made of many monosaccarides) ie. Starch, cellulose

5. Proteins • used in the many cellular and body processes • Complex 3D molecules • Enzymes are proteins that increase the rate of biochemical reactions • Proteins are composed of smaller subunits called amino acids

6. Enzymes • High temperatures can denature the enzyme (destroy it). • Enzymes operate at best at optimal temperature ranges • Most human enzymes work best between the range of pH 6 to 8

7. Nucleic acid is the building block of genetic material • The genetic code controls growth and structure by telling a cell which proteinto synthesize • Two types: • DNA • RNA

8. Vitamins and Minerals • Vitamins: • Organic • Co-enzymes (help enzymes function) • Important for growth and development • Minerals: • Inorganic • Necessary for many chemical reaction • Help build bones and cartilage • Both required in small quantities

9. Macromolecules are assembled by dehydration, the removal H+ and OH- to produce a water molecule. • Macromolecules are disassembled by hydrolysis, the addition a water molecule in the form H+ and OH-.

10. The Digestive System • Test your prior knowledge by labeling as many of the organs that aid the process of digestion.

11. Digestive system: • specialized to ingest food and break it down • physical/ mechanical breakdown, through chewing, churning, and segmenting • chemical breakdown, through hydrolysis.

12. Resulting substances are absorbed into the bloodstream and delivered to body cells by circulatory system.

13. The Digestive Tract • Continuous tube makes up the digestive tract (gastrointestinal (GI) tract) as well as accessory organs that aid digestion • Average sized GI tract is 8 meters long in adult

16. The Mouth • Chewing food is beginning of mechanical digestion • Saliva released by salivary glands in mouth • Salivary amylase, begins the chemical digestion of starch • Saliva lubricates the to assist with swallowing

17. The Esophagus • Directs food from mouth to stomach • Wave like contraction of smooth muscle (parastalsis) lining the esophagus “pushes” food towards the stomach • Food enters the stomach through the esophageal sphincter (circular muscle)

18. The Stomach • The stomach has 3 main functions: storage, digestion and pushing food into the small intestine • Empty stomach holds approx 50mL of fluid, wall of stomach can expand to hold 2-4L • Pyloric sphincter controls exit of stomach contents into small intestine

19. The Stomach • Peristalsis in stomach pushes food downward and churns it back upwards. • The mechanical digestion and chemical digestion produces a liquid called chyme.

20. The Stomach • Cells lining interior of stomach secrete 2-3L of gastric juices each day. • Gastric juices: • water, mucus, salts, hydrochloric acid and enzymes. • pH of 1-3 • breaks down proteins into chyme • killsmost pathogens ingested with food

21. The Stomach • 3 methods of protection: • Little gastric juices are secreted until food enters the stomach • Cells secrete mucus to protects the cells • Pepsin (protein digesting enzyme) remains inactive until hydrochloric acid is produced

22. The Stomach • Substances absorbed in stomach: • Water • Salts • Some medications • alcohol • Other substances are too large to pass across cell membrane

23. Small Intestine • Named for small diameter. • Longest part of the digestive tract. • Mechanical digestion via segmentation; chyme “sloshes” back and forth • Peristalsis pushes the food along • Digestion of macromolecules and absorbs their smaller sub units

24. The Small Intestine • Divided into 3 segments: • Duodenum • Jejunum • Ileum

25. Duodenum • Ducts from the liver and pancreas empty into the duodenum. • Where the chyme from the stomach is received. • In-foldings of the small intestine help to increase the surface area for absorption. • Villi (finger-like projections) and microvilli (brush border) further increase the surface area of the organ

26. Jejunum and Illeum • Jejunum: • more folds and secretory glands than the duodenum • 2.5 meters of the small intestine. • continues chyme breakdown and absorption • ileum: • smaller and fewer villi • absorbs nutrients • pushes undigested material into large intestine

27. Accessory Organs • Pancreas, liver and gall bladder assist digestion by secreting enzymes • Referred to as accessory organs since they are not physically part of the digestive tract.

28. The Pancreas • 1L of pancreatic juices into the duodenum each day • Pancreatic juices: • Trypsin and chymotrypsin – digests proteins • Pancreatic amylase – digests starch • Lipase – digests fat • Enzymes released in inactive form are activated by other enzymes secreted by microvilli of the duodenum • Bicarbonate neutralizesHCl from stomach 2pH  8 pH

29. The Liver • Secretes bile • Bile: • greenish – yellow fluid mixture of pigments and bile salts. • Bile pigments are waste products of from the liver’s destruction of red blood cells; eventually eliminated in the feces. Bile pigments do not take part in digestion • Bile salts help lipase (secreted by pancreas) to access fats. Bile salts are partly soluble in water and in fats

30. Liver and Gall bladder • Emulsification of the fats by bile salts creates larger surface area for the lipase to act on the lipids  speeds digestion. • Bile produced by the liver is stored in gall bladder • Fats in the chyme stimulate the gall bladder to contract and release the bile into the duodenum

31. Digestion and Absorption Small Intestine • Digestive enzymes from brush border and secretions from liver and pancreas contribute mucus, bile, water and enzymes • Most chemical digestion occurs in duodenum • Digestion acts on all four categories of macromolecules • Carbohydrases digest carbohydrates • Lipases digest lipids • Proteases digest proteins • Nucleases digest nucleic acids

32. Carbohydrate Digestion and Absorption • Mouth: • Salivary amylase: polysaccaride disaccaride • Small Intestine: • Pancreatic amylase: polysaccaride and disaccaride monosaccaride • Polysaccharide  disaccharide  monosaccharide  absorption

33. Carbohydrate Digestion and Absorption • Monosaccarides: • Small enough to diffuse across cell membrane • Glucose: circulated to body cells • Galactose and fructose: converted into glucose by liver • Liver converts excess glucose into glycogenfor short-term storage • Glycogen is easily converted back into glucose when needed

35. Protein Digestion and Absorption • Pepsin begins chemical digestion of protein in stomach; Protein  polypeptides • Trypsin and chymotripsincontinue digestion in the small intestine. Polypeptides  short peptide chains and amino acids • Peptidase digests short peptide chains into individual amino acids. • Amino acids diffuse across cell membranes of the small intestine into the blood stream.

36. Amino acids transported to body cells to synthesize proteins or to liver for energy source • Proteins  polypeptides short peptide chains  amino acids  absorption

37. Fat Digestion and Absorption • Infants have specialized lipases in their stomachs to increase lipid digestion (diet is high in fat) • Adults do not begin to digest lipids until the chyme enters the small intestine. • Fats in the duodenum stimulates the gall bladder to release bile. • Bile emulsifies the large fat globules into small fat droplets (increasing the surface area of the fat).

38. Fat Digestion and Absorption • Lipase breaks down lipids by hydrolysis • Glycerol and fatty acids absorbed into lymphatic system • Glycerol converted into glucose by liver for use by the cells • Lipids + bile  emulsification  lipids  glycerol and fatty acids  absorbed

40. Nucleic Acid Digestion and Absorption • Nucleases digest nucleic acid in small intestine • Nucleotides are broken into bases, sugars and phosphates • Bases, sugars and phosphates are absorbed into the blood stream • Nucleic acid  nucleotides  bases, sugars, phosphates  absorption

41. Last Stop on the Digestion Train…Elimination – the Large Intestine • Material left in small intestine is moved into the large intestine • No digestion occurs in large intestine • large intestine concentrates and eliminates waste • Water and salts are absorbed from undigested food • Bacteria feed on wastes and synthesis vitamins • Indigestible materials and colon bacteria form the feces

42. Summary Video: • National Geographic – The Digestive System