Chapter 6.2 – The Digestive System

1. Chapter 6.2 – The Digestive System Pages 217 - 231

2. 6.1 Summary • - Carbohydrates, lipids, proteins, and nucleic acids are macromolecules that are 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 does not have double covalent bonds between its carbon atoms so it contains all the hydrogen atoms it can bond with. (solid at room temperature) • An unsaturated fatty acid has double bonds between some of the carbons leaving room for additional hydrogen atoms. (liquid at room temperature)

4. -carbohydrates and lipids are used to store energy. Monosaccharides contain 3-7 carbons, disaccharides are made up of two monosaccharides. • Macromolecules that always contain hydrogen, oxygen and carbon. Almost always contain 2 Hydrogens & 1 Oxygen for every atom of Carbon.

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

6. Enzymes • Very 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 protein to synthesize.

8. Organic vitamins and inorganic minerals are not macromolecules, but play a key role in the many metabolic cell processes. • Both are required in small quantities. • Vitamins serve as co-enzymes (needed to make enzymes function) and are involved in tissue development, tissue growth, resistance to disease. • Minerals enable certain chemical reactions to occur, are readily absorbed into the bloodstream and help build bones and cartilage.

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. The Digestive system is specialized to ingest food and break it down into smaller components. • Digestion includes physical/ mechanical breakdown, through chewing, churning, and segmenting, and chemical breakdown, through hydrolysis.

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

13. Solid wastes that cannot be broken down for use by the cells are eliminated to the external environment via the anus.

14. The Digestive Tract • The digestive system consists of a continuous tube that makes up the digestive tract (also called the gastrointestinal (GI) tract) as well as accessory organs that aid digestion. • An average sized digestive tract is approximately 8 meters long in an adult human

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

18. The Esophagus • Directs food from the mouth to the stomach. • Contractions of the smooth muscle lining the esophagus “pushes” food towards the stomach. • The “wave like” action is called peristalsis. • Food enters the stomach through the esophageal sphincter (a circular muscle that acts like a valve.

19. The Stomach • The stomach has 3 main functions: storage, digestion and pushing food into the small intestine. • An empty stomach hold approx 50mL of fluid, the “accordion like” walls of the stomach can expand to hold 2-4L of food. • The pyloric sphincter controls the exit of the stomach’s contents into the small intestine. Possibly the grossest/ most disturbing video you will see this semester…

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

21. The Stomach • About 40 million cells that line the interior of the stomach secrete 2-3L of gastric juices each day. • Gastric juices are made up of: water, mucus, salts, hydrochloric acid and enzymes. • The gastric juices have a pH of 1-3. • The acidic environment breaks down proteins into chyme and kills most of the bacteria that is ingested with the food we eat.

22. The Stomach • The stomach has three methods of protection to prevent the gastric juices from digesting the proteins of the cells that make up the lining of the stomach: • Little gastric juices are secreted until food enters the stomach • Some cells secrete mucus that protects the cells. • Pepsin (protein digesting enzyme) remains inactive until hydrochloric acid is produced.

23. The Stomach • Very few substances are absorbed from the chyme in the stomach because most molecules are too large to diffuse across membranes into the circulatory system. • Substances the stomach does absorb: • Water • Salts • Some medications • alcohol

24. The Small Intestine • The small intestine is named for its small diameter. • The small intestine is the longest part of the digestive tract. • Mechanical digestion via segmentation occurs in the SI. • During segmentation, chyme “sloshes” back and forth between segments of the SI. Peristalsis pushes the food along the intestine. • The SI completes the digestion of macromolecules and absorbs their smaller sub units.

25. The Small Intestine • The small intestine can be divided into 3 segments: Duodenum, Jejunum and Ileum • Ducts from the liver and pancreas empty into the duodenum. • The duodenum is an important place of chemical digestion where the chyme from the stomach is received.

26. The Small Intestine • The duodenum is characterized by large in-foldings of the small intestine help to increase the surface area for absorption. • Villi (finger-like projections) and microvilli (brush border)help to further increase the surface area of the organ.

27. The Small Intestine • The jejunum contains more folds and secretory glands than the duodenum and accounts for about 2.5 meters of the small intestine. • The jejunum continues to break down chyme so that the smaller components can be absorbed. • The ileum contains smaller and fewer villi. • The ileum functions to absorb nutrients and “push” the remaining undigested material into the large intestine.

28. The Accessory Organs • The small intestine secretes enzymes from the villi to aide in digestion. • The pancreas, liver and gall bladder provide assistance by secreting other enzymes to help with digestion. • These are referred to as accessory organs since they play a vital role, but are not physically part of the digestive tract.

29. The Pancreas • The pancreas delivers about 1L of pancreatic juices into the duodenum each day. • Pancreatic juices contain a variety of enzymes: • Trypsin and chymotrypsin – digest proteins • Pancreatic amylase – digests starch • Lipase – digests fat • Enzymes are released in an inactive form and are activated by other enzymes that are secreted by the microvilli (brush border) of the duodenum lining. • Bicarbonate in the pancreatic fluid neutralizes the hydrochloric acid from the stomach 2pH  8 pH.

30. The Liver • The liver secretes bile, a 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.

31. The Liver and Gall bladder • Bile salts work like detergent to disperse large fat drops into a fine suspension of smaller droplets in the chyme. • The emulsification of the fats creates a larger surface area for the lipase to act on the lipids  speeds digestion. • Bile produced by the liver is sent to the gall bladder for storage between meals. • Fats in the chyme stimulate the gall bladder to contract and release the bile into the duodenum.

32. Digestion and Absorption in the Small Intestine • Digestive enzymes from the brush border (microvilli) of the small intestine, and secretions from the liver and pancreas contributes mucus, bile, water and enzymes. • Most of the chemical digestion in the small intestine occurs in the duodenum. • Digestion acts on all four categories of macromolecules. • Carboydrases digest carbohydrates • Lipases digest lipids • Proteases digest proteins • Nucleases digest nucleic acids.

33. Carbohydrate Digestion and Absorption • Salivary amylase begins digesting starch while in the mouth. Digestion is minimal due to the short time period. • Digestion of carbohydrates by pancreatic amylase continues after the chyme enters the small intestine. • The polysaccharide (starch) is digested into a disaccharide. • The disaccharide is finally digested into a monosaccharide (glucose, galactose, fructose). • Polysaccharide  disaccharide  monosaccharide  absorption

34. Carbohydrate Digestion and Absorption • Monosaccharides are simple enough to diffuse across the cell membranes of the intestine to enter into the blood stream. • Glucose is circulated to body cells for cellular respiration. • Other monosaccharides (ie. Galactose, fructose) are converted into glucose by the liver. • The liver also converts excess glucose in the blood into glycogen to be temporarily stored. Glycogen is easily converted back into glucose when needed.

36. Protein Digestion and Absorption • Pepsin begins the chemical digestion of protein in the stomach. Protein  polypeptides • Trypsin and chymotripsincontinue digestion in the small intestine. Polypeptides  short peptide chains and individual 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.

37. Protein Digestion and Absorption • Amino acids are transported to the liver to be converted for use as energy or transported to body cells where they are used to synthesize proteins for a variety of functions. • Proteins  polypeptides short peptide chains  amino acids  absorption

39. 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). Fat digestion

40. Fat Digestion and Absorption • Lipase (secreted in the duodenum) breaks down lipids by hydrolysis. • The resulting glycerol and fatty acids are absorbed by diffusion into the lymphatic system. • Glycerol is converted into glucose by the liver for use by the cells • Lipids + bile  emulsification  lipids  glycerol and fatty acids  absorbed

42. Nucleic Acid Digestion and Absorption • Nucleases (enzymes) digest nucleic acid in the small intestine. • Nucleotides are hydrolyzed into the bases, sugars and phosphates that make them up. • Bases, sugars and phosphates are absorbed like glucose and amino acids into the blood stream. • Nucleic acid  nucleotides  bases, sugars, phosphates  absorption

43. Last Stop on the Digestion Train…Elimination – the Large Intestine • The material that left in the small intestine after nutrients have been processed is moved into the large intestine. • Digestion does not occur in the large intestine. • The main function of the large intestine is to concentrate and eliminate waste materials. • In the large intestine, water and salts are absorbed from any undigested food. • Bacteria in the colon breakdown the food further. • At the end of this process any remaining indigestible materials along with the colon bacteria form the feces.