The Digestive System

1. The Digestive System

2. Food for Energy and Growth • The food animals eat provides both a source of energy and essential molecules that the animal body is not able to manufacture for itself • an optimal diet contains more carbohydrates than fats and also a significant amount of protein

3. Figure 31.1 The pyramid of nutrition

4. Food for Energy and Growth • Carbohydrates are obtained primarily from cereals, grains, and breads • on the average, carbohydrates contain 4.1 calories per gram • the body uses carbohydrates for energy • Dietary fats are obtained from oils, margarine, and butter and are abundant in fried foods, meats, and processed snack foods • fats contain 9.3 calories per gram • the body uses fats to construct cell membranes, to insulate nervous tissue, and to provide energy

5. Food for Energy and Growth • Proteins can be obtained from many foods, including poultry, fish, meat, and grains • proteins have 4.1 calories per gram • proteins are used for energy and as building materials for cell structures, enzymes, hemoglobin, hormones, and muscle and bone tissue

6. Animation: Energy for Activity

7. Food for Energy and Growth • In wealthy countries, being significantly overweight is common • this is due to habitual overeating and high-fat diets, in which fats constitute over 35% of the total caloric intake • the standard measure of appropriate body weight is the body mass index (BMI), estimated as your body weight in kg, divided by your height in meters squared

8. Figure 31.3 Are you overweight? 66% of Americans are overweight with a BMI of 25 or more

9. Animation: Body Mass Index

10. Food for Energy and Growth • One essential characteristic of food is its fiber content • fiber is the part of plant food that cannot be digested by humans • diets that are low in fiber result in a slower passage of food through the colon • low fiber is thought to be associated with incidences of colon cancer

11. Food for Energy and Growth • Over the course of evolution, many animals have lost their ability to manufacture certain substances they need • many vertebrates are unable to manufacture one or more of the 20 amino acids used to make proteins • humans are unable to synthesize eight amino acids, which must be obtained from proteins in food • these are called essential amino acids

12. Food for Energy and Growth • In addition to supplying energy, food must also supply essential minerals, such as calcium and phosphorous • some minerals are required in very small amounts and are called trace elements • Essential organic substances that are used in trace amounts are called vitamins • many vitamins are required cofactors for enzymes

13. Digestion • Processing of food • Types • Mechanical (physical) • Chew • Tear • Grind • Mash • Mix • Chemical • Catabolic reactions • Enzymatic hydrolysis • Carbohydrate • Protein • Lipid

14. Types of Digestive Systems • Heterotrophs are divided into three groups on the basis of their food sources • herbivores eat plants exclusively • carnivores are meat eaters • omnivores eat both plants and animals • Single-celled organisms, as well as sponges, digest their food intracellularly • All other animals digest their food extracellularly, within a digestive cavity

15. Digestion • Phases • Ingestion • Movement • Digestion • Absorption • Further digestion

16. Digestive System Organization • Gastrointestinal (Gl) tract (Alimentary canal) • Tube within a tube • Direct link/path between organs • Structures • Mouth • Oral Cavity • Pharynx • Esophagus • Stomach • Duedenum • Jejenum • kIleum • Cecum • Ascending colon • Transverse colon

17. Digestive System Organization • Descending colon • Sigmoid colon • Rectum • Anus • Accessory structures • Not in tube path • Organs • Teeth • Tongue • Salivary glands • Liver • Gall bladder • Pancreas

18. The Mouth and Teeth • Many vertebrates have teeth, and chewing (mastication) breaks up food into small particles and mixes it with fluid secretions • mammals have heterodont dentition, teeth of different specialized types • the general pattern of dentition is modified in different mammals depending on their diet • in carnivorous mammals, the canines are prominent, and other teeth are more bladelike and sharp • in herbivorous mammals, incisors are well-developed for snipping, canines are reduced or absent, and molars are large and flat, with complex ridges well suited to grinding

19. The Mouth and Teeth • Humans are omnivores and human teeth are specialized for eating both plant and animal material • humans are carnivores in the front of the mouth and herbivores in the back • children have only 20 teeth but these are lost during childhood and replaced by 32 adult teeth

20. Figure 31.9 Human teeth The tooth is a living organ.

21. Anatomy of the Mouth and Throat

22. Human Deciduous and Permanent Teeth

23. Dorsal Surface of the Tongue

24. The Major Salivary Glands

25. Deglutition (swallowing) • Sequence • Voluntary stage • Push food to back of mouth • Pharyngeal stage • Raise • Soft palate • Larynx + hyoid • Tongue to soft palate • Esophageal stage • Contract pharyngeal muscles • Open esophagus • Start peristalsis

26. Deglutition (swallowing) • Control • Nerves • Glossopharyngeal • Vagus • Accessory • Brain stem • Deglutition center • Medulla oblongata • Pons • Disorders • Dysphagia • Aphagia

27. The Esophagus and Stomach • The esophagus is a muscular tube that connects the pharynx to the stomach • the upper third is enveloped in skeletal muscle for voluntary control of swallowing • the lower two-thirds is surrounded by involuntary smooth muscle • rhythmic waves of contractions, called peristalsis, propel food towards the stomach

28. Esophagus • Usually collapsed (closed) • 3 constrictions • Aortic arch • Left primary bronchus • Diaphragm • Surrounded by • SNS plexus • Blood vessels • Functions • Secrete mucous • Transport food

29. Peristalsis and Segmentation

30. Esophagus • Sphincters • Upper • Lower • Abnormalities • Achalasia • Atresia • Hernia • Barret’s esophagus • Esophageal varices

31. The Esophagus and Stomach • The movement of food from the esophagus into the stomach is controlled by a ring of circular smooth muscle, called a sphincter • contraction of the sphincter prevents food in the stomach from moving back into the esophagus • in humans, stomach contents can be brought back out during vomiting • the relaxing of the sphincter may lead to acid reflux, which is when stomach acid moves into the esophagus • this produces a burning sensation known as heartburn

32. The Esophagus and Stomach • The stomach is a saclike portion of the digestive tract • the stomach contains an extra layer of smooth muscle for churning food • gastric juiceis released by gastric glands in the lining of the stomach • parietal cells secrete hydrochloric acid (HCl) • chief cells secrete pepsinogen • pepsinogen requires a low pH to be activated into pepsin, a protease that begins the digestion of proteins

33. Stomach • Usually “J” shaped • Left side, anterior to the spleen • Mucous membrane • G cells – make gastrin • Goblet cells – make mucous • Gastric pit – Oxyntic gland – Parietal cells – Make HCl • Chief cells – Zymogenic cells • Pepsin • Gastric lipase

34. Anatomy of the Stomach

35. Stomach • 3 muscle layers • Oblique • Circular • Longitudinal • Regions • Cardiac sphincter • Fundus • Antrum (pylorus) • Pyloric sphincter • Vascular • Inner surface thrown into folds – Rugae • Contains enzymes that work best at pH 1-2

36. Stomach • Functions • Mix food • Reservoir • Start digestion of • Protein • Nucleic acids • Fats • Activates some enzymes • Destroy some bacteria • Makes intrinsic factor – B 12 absorption • Destroys some bacteria • Absorbs • Alcohol • Water • Lipophilic acid • B 12

37. The Small and Large Intestines • The small intestine is the true digestive vat of the body • only relatively small portions of chyme are introduced into the small intestine at one time • this allows time for acid to be neutralized and enzymes to act • in the small intestine, carbohydrates, protein, and lipids are broken down and absorbed into the bloodstream

38. Small Intestine • Absorbs • 80% ingested water • Electrolytes • Vitamins • Minerals • Carbonates • Active/facilitated transport • Monosaccharides • Proteins • Di-/tripeptides • Amino acids • Lipids • Monoglycerides • Fatty acids • Micelles • Chylomicrons

39. 1.6 The Small and Large Intestines • While some enzymes necessary for digestion are secreted by the cells of the intestinal wall, most are made in the pancreas • the pancreas is an exocrine gland, meaning it secretes through ducts • the pancreas sends it products via a duct that empties into the first part of the small intestine, the duodenum

40. The Small and Large Intestines • Much of the food energy the vertebrate body harvests is obtained from fats • fat digestion involves bile salts that are secreted into the duodenum by the liver • bile salts act like detergents and combine with drops of fat to form microscopic droplets • this process is known as emulsification • this increases the surface area for the enzyme lipase to work on in order to breakdown the fat

41. Small Intestine • Secretes digestive enzymes • Peptidases • Amino- • Di- • Tri- • Sucrases • Maltase • Lactase • Saccharidases • Di- • Tri- • Lipase • Nucleases

42. Small Intestine • Control • Requires pancreatic enzymes & bile to complete digestion

43. Large Intestine • Extends from ileocecal valve to anus • Regions • Cecum – Appendix • Colon • Ascending • Transverse • Descending • Rectum • Anal canal

44. Anatomy of the Large Intestine

45. Large Intestine • Histology • No villi • No permanent circular folds • Smooth muscle • Taeniae coli • Haustra • Epiploic appendages • Otherwise like rest of Gl tract

46. Large Intestine • Functions • Mechanical digestion • Haustral churning • Peristalsis • Reflexes • Gastroileal • Gastrocolic • Chemical digestion – Bacterial digestion • Ferment carbohydrates • Protein/amino acid breakdown • Absorbs • More water • Vitamins • B • K • Concentrate/eliminate wastes

47. Feces Formation and Defecation • Chyme dehydrated to form feces • Feces composition • Water • Inorganic salts • Epithelial cells • Bacteria • Byproducts of digestion • Defecation • Peristalsis pushes feces into rectum • Rectal walls stretch • Control • Parasympathetic • Voluntary

48. Liver • Location • R. Hypochondrium • Epigastric region • 4 Lobes • Left • Quadrate • Caudate • Right • Each lobe has lobules – Contains hepatocytes – Surround sinusoids – Feed into central vein

49. Liver • Functions • Makes bile • Detergent – emulsifies fats • Release promoted by: • Vagus n. • CCK • Secretin • Contains • Water • Bile salts • Bile pigments • Electrolytes • Cholesterol • Lecithin

50. Liver • Detoxifies/removes • Drugs • Alcohol • Stores • Gycolgen • Vitamins (A, D, E, K) • Fe and other minerals • Cholesterol • Activates vitamin D • Fetal RBC production • Phagocytosis • Metabolizes absorbed food molecules • Carbohydrates • Proteins • Lipids