Digestion, Absorption and Transport

1. Digestion, Absorptionand Transport

2. Objectives for Chapter 3 • List the organs and accessory organs of the digestive tract. • Discuss the main roles of each of the organs of the digestive tract. • Identify how other body systems assist the digestive tract. • Name a digestive disorder that can occur for each of the following: mouth, esophagus, stomach, and intestines.

3. What Is Digestion? Digestion: a multi-step process of breaking down foods into absorbable components using mechanical and chemical means in the gastrointestinal (GI) tract • Gastrointestinal tract consists of: • Mouth • Esophagus • Stomach • Small and large intestines • Other organs

4. What is Digestion? • Anatomy of the GI • mouth  esophagus  stomach  small intestine  large intestine • GI tract is about 23 feet long with extensive surface area for nutrient absorption. • Cells lining GI tract are replaced every 3–5 days.

5. What Is Digestion? • Main roles of the GI tract are to: • Break down food into smallest components • Absorb nutrients • Prevent microorganism or other harmful compounds in food from entering tissues of the body • GI tract is highly efficient: 92-97% of nutrients from food are digested and absorbed.

6. Digestion Is Mechanical and Chemical Mechanical digestion: chewing, grinding food to aid swallowing • Peristalsis: the forward, rhythmic muscular contraction that moves food through GI tract Chemical digestion: digestive juices and enzymes break down food into absorbable nutrients

7. Digestion • The mouth • Saliva released: contains water, electrolytes, mucus and a few enzymes • Softens, lubricates, dissolves food particles • Bolus (food mass) moves into pharynx, is swallowed, and enters the esophagus. • Epiglottis closes off trachea during swallowing to prevent food from lodging in the windpipe. • involves mastication (chewing),

8. The epiglottis prevents food from entering the trachea when you swallow.

9. Digestion • The esophagus • Esophagus leads food into the stomach • Bolus is pushed down esophagus by peristalsis. • Lower Esophageal Sphincter (LES):at bottom of esophagus relaxes and allows food into stomach • LES then closes to prevent backflow of hydrochloric acid (HCl) from stomach • “Reflux” of stomach acid causes “heartburn” (irritation of esophagus lining).

10. Peristalsis: Muscles around organs of GI tract constrict in wavelike manner to move food along.

11. Digestion • The stomach • Stomach stores, mixes and prepares food for digestion • grinds the bolus to a semi-liquid mass called chyme. • Stomach produces powerful digestive secretions: • HCl: activates enzyme pepsin, enhances absorption of minerals, breaks down connective tissue of meat • Makes the stomach acidic with a pH of 1.5 – 1.7 • Mucus protects stomach lining from damage • Digestive enzymes, intrinsic factor (for vitamin B12 absorption), stomach hormone gastrin

12. Digestion The Stomach (cont’d) • The pyloric sphincter regulates the flow of partially digested food into the small intestine. Allows about 1 tsp of chyme to enter the small intestine every 30 seconds • Gastrin: stimulates digestive activities and secretion of HCl, increases gastric motility and emptying • Liquids, carbohydrates, low-fiber and low-calorie foods exit stomach faster • High fiber, fat and protein foods exit slower, keep you feeling full longer

15. Digestion • The small intestine • Most digestion and absorption occur in the small intestine • receives digestive juices from the gallbladder and the pancreas. • long, narrow, coiled, has three segments: • Duodenum (10 inches) • Jejunum (8 feet) • Ileum ((12 feet) • Interior surface area tremendously increased by villi, microvilli, circular folds

16. Surface Area in the Small Intestine

17. Digestion • Peristalsis moves chyme through intestine • Segmentation mixes chyme with chemical secretions • Pendular movement enhances nutrient absorption • Chyme moves at rate of 1 cm/minute • Total contact time 3–10 hours, depending on amount and type of food

18. Digestion • The large intestine • Large intestine absorbs water and some nutrients • Ileocecal sphincter: prevents backflow of fecal matter into ileum • Most of nutrients in chyme have been absorbed when it reaches large intestine • Large intestine has three sections: cecum, colon, rectum • About 5 feet long, 2.5 inches in diameter • Absorbs water and electrolytes • No digestive enzymes; chemical digestion done by bacteria

19. Digestion & Absorption • Intestinal matter passes through colon in 12-70 hours depending on age, health, diet, fiber intake • Bacteria in colon produce vitamin K and biotin and break down fiber and undigested carbohydrates • Stool stored in rectum

21. Secretions of Digestion • Enzymes – protein molecules which facilitates a chemical reaction • Saliva – made by salivary glands • Gastric Juice – made by the stomach, very acidic, HCL • Pancreatic Juice/intestinal Enzymes – Contains bicarbonate to neutralize acidic gastric juices as it enters the small intestine • Bile – secreted by the liver, stored in the gall bladder, emulsify fat. Only acts on fat

22. Accessory Organs Liver: largest gland in body • Produces bile needed for fat digestion • Metabolism of carbohydrates, fats and protein • Stores nutrients: vitamins A, D, B12, E, copper, iron, glycogen (glucose storage form) • Detoxifies alcohol Gallbladder: concentrates and stores bile • Released into GI tract when fat is ingested

23. Accessory Organs Pancreas: • Produces hormones: insulin and glucagon, regulate blood glucose • Sodium bicarbonate neutralizes acidic chyme, protects enzymes from inactivation by acid • Digestive enzymes: • Amylase: digests carbohydrate • Lipase: digests fats • Trypsin, chymotrypsin, and carboxypeptidase: digest protein

25. Other Body Systems • Nervous system stimulates your appetite. • Hormone ghrelinsignals brain to eat when stomach is empty. • Circulatory system transports nutrients, oxygen, waste products through your blood. • Lymphatic system distributes fat and fat-soluble nutrients through your lymph. • Excretory system eliminates wastes from circulatory system via the urine.

26. The Circulatory and Lymphatic Systems

27. The Excretory System

28. Common Digestive Disorders Disorders of the mouth and esophagus: • Gingivitis and periodontal disease – gum swelling, bleeding and oral pain • Swallowing problems: • Choking • Food becomes lodged in the trachea. • The larynx cannot make sounds. • The Heimlich maneuver may need to be used.

30. Common Digestive Disorders • Esophageal problems • Heartburn (acid reflux) may be caused by weak LES (lower esophageal sphincter) • Certain foods, • smoking, • drinking alcohol, • being overweight or obese, • tight-fitting clothes, • reclining after eating

31. Common Digestive Disorders Stomach Disorders: • Gastroenteritis – cause by bacteria or virus “stomach flu” • Peptic ulcers - a sore in the lining of the stomach (gastric ulcer) Gallbladder Disease: • Gallstones – cause by high cholesterol bile, may lead to obstruction of the bile duct

35. Common Digestive Disorders Disorders of the Small Intestine: • Nutrient malabsorption disorders • Celiac disease: inability to digest gluten protein • Duodenal ulcers - a sore in the lining of the duodenum of the small intestine (duodenal ulcer). • Intestinal enzyme deficiencies • Short bowel syndrome

36. Common Digestive Disorders Disorders of the Large Intestine: • Constipation may be due to insufficient fiber and water intake, inactivity, stress, illness. • Diarrhea is treated by fluid and electrolyte replacement. • Irritable bowel syndrome (IBS): alternating patterns of diarrhea, constipation, abdominal pain • Colon cancer often begins with polyps. • Curable when detected early and treated

37. Videos • Digestion 1 • Digestion 2 – Enzymes