Functional Human Physiology for the Exercise and Sport Sciences The Gastrointestinal System

1. Functional Human Physiologyfor the Exercise and Sport Sciences The Gastrointestinal System Jennifer L. Doherty, MS, ATC Department of Health, Physical Education, and Recreation Florida International University

2. Overview of Gastrointestinal System Function • Digestion • Absorption • Secretion • Motility

4. Organs of the Gastrointestinal System The alimentary canal • Continuous hollow tube extending from the mouth to the anus • Called the gastrointestinal (GI) tract as is passes inferior to diaphragm • Functions: • Digestion • Absorption of digested fragments into blood

6. Accessory organs Assist in the chemical process of digestion by secreting saliva, enzymes, and bile Salivary glands Pancreas Liver Gallbladder Assist in the mechanical process of digestion Teeth Tongue Organs of the Gastrointestinal System

8. Digestion • The process mechanically breaking down food into particles small enough to be absorbed through cell membranes • Two methods of food breakdown • Chemical • Mechanical

9. Digestion: 5 Integrated Steps • (1) Ingestion • Foodstuff enters the GI tract via the mouth • (2) Propulsion • The process that moves foodstuff through the GI tract via coordinated reflexive contraction activity • (3) Digestion • The process of breaking down large food particles into smaller particles via chemical and mechanical action

10. Digestion: 5 Integrated Steps • (4) Absorption • The movement of digested end products through the intestinal wall and into the blood or lymph • End products include small organic molecules, electrolytes, & H2O • (5) Defecation • The process of discharging undigested and unabsorbed foodstuff

11. The GI Tract The Gastrointestinal Wall • 4 layers • (1) Muscosa • Lamina propria • Muscularis mucosa • (2) Submucosa • (3) Muscularis Externa • (4) Serosa

13. Mucosa • Inner most mucous membrane • Lines lumen • Composed of simple columnar epithelium • Contains many mucus secreting goblet cells

14. Mucosa • Lamina propria • Underlying loose CT • Contains blood vessels, sensory nerve endings, lymph vessels, and scattered lymph tissue • Muscularis mucosa • Layer of smooth muscle • Produces local movements that change the shape of the lumen

16. Mucosa Functions: • Protect underlying tissue • Absorb digested material • Secrete mucous or digestive juices • Increase surface area • Folds in the mucosa • Villi present in the small intestine

17. Submucosa • Composed of loose CT • Contains blood vessels and lymphatics • Function to circulate absorbed nutrients • Contains nerves from the ANS • Form the submucosal plexus • A component of the intrinsic nervous system of GI tract

19. Muscularis Externa • Composed of two layers of smooth muscle • Inner layer - circular fiber arrangement • Outer layer - longitudinal fiber arrangement

21. Muscularis Externa Inner layer - circular fiber arrangement • When fibers contract = ↓ lumen size • Forms sphincter muscles • Prevent backflow of materials Outer layer - longitudinal fiber arrangement • When fibers contract = mix and propel food along the alimentary canal

22. Muscularis Externa • Myenteric plexus • Extensive nerve network between the smooth muscle layers • Regulate motility • Movement/contraction of the GI tract walls • Regulate glandular secretions • Secretions into the lumen of the GI tract

24. Serosa • Outermost layer of the GI wall • Inner layer • Consists of fibrous CT • Provides structural support • Outer layer - Mesothelium • Consists of epitelium • Secretes a water lubricating fluid allowing organs to slide past one another

26. Peritoneal Cavity • The space between the visceral peritoneum and parietal peritoneum • Both visceral and parietal peritoneum secrete serous fluid into the peritoneal cavity • Lubricates and protects abdominal tissues as they slide past one another

27. GI Motility Patterns • Contractions of the muscularis externa • Two methods • Peristalsis • Segmentation

28. GI Motility Patterns Peristalsis • Propelling motion produced by alternate waves of contraction and relaxation of muscularis externa layer • Occurs due to contraction of one part of wall with simultaneous relaxation of the wall ahead • Propels food along tube

30. GI Motility Patterns Segmentation • Occurs due to rhythmic, local contractions of the smooth muscle in the muscularis externa layer • Mechanically grinds foodstuff in the stomach and intestines mixing it with digestive juices

32. Gastrointestinal Regulation • Intrinsic Control • Submucosal Plexus • Myenteric Plexus • Extrinsic Control • Parasympathetic nerve fibers • Sympathetic nerve fibers

33. Gastrointestinal Regulation: Intrinsic Control • Provided through the • Submucosal Plexus • Myenteric Plexus • Local stimulus = distension of submucosa or muscularis externa walls • Local response = activation of stretch receptors • ↑ glandular secretions • ↑ smooth muscle contractions in the immediate area

34. Gastrointestinal Regulation: Extrinsic Control • Includes Parasympathetic and Sympathetic input from the ANS • Fibers within the muscularis externa layer specifically assist in controlling the rate and strength of contractions

35. Gastrointestinal Regulation: Extrinsic Control Parasympathetic activity • Impulses carried by the vagus nerve • ↑ motility • ↑ glandular secretions

36. Gastrointestinal Regulation: Extrinsic Control Sympathetic activity • Opposes parasympathetic activity • ↓ motility • ↓ glandular secretions • Causes sphincters to contract thus slowing the movement of foodstuff through the GI tract

37. Digestion: 5 Integrated Steps • (1) Ingestion • (2) Propulsion • (3) Digestion • (4) Absorption • (5) Defecation

39. Digestive Function: Ingestion • The digestive process begins in the mouth • Includes… • Mechanical fragmentation of foodstuff • Foodstuff mixes with saliva

41. Digestive Function: Ingestion Organs and associated structures Tongue • Mixes foodstuff with saliva during chewing • Initiates swallowing • Contains taste buds • Sensitive to chemical differences among food molecules • Differentiate sweet, sour, salty, or bitter tastes

43. Digestive Function: Ingestion Organs and associated structures Teeth • Tear and grind food • Mastication • Mechanical breakdown of foodstuff into smaller fragments

45. Digestive Function: Ingestion Organs and associated structures Lips and Cheeks • Keep food in mouth • Involved in speech

46. Digestive Function: Ingestion Organs and associated structures Palate • Forms roof of mouth • 2 distinct parts • Hard Palate • Soft Palate

47. Digestive Function: Ingestion Organs and associated structures • Hard palate • Anterior region composed of bone • Forms a hard surface against which foodstuff is pushed during chewing • Soft palate • Posterior region composed of skeletal muscle • Rises reflexively to close off nasopharynx during swallowing

48. Digestive Function: Ingestion Organs and associated structures Salivary glands - 3 pairs • 1). Parotid glands • Largest salivary glands • Anterior to the ears • 2). Submandibular glands • Inferior to the jaw • 3). Sublingual glands • Inferior to the tongue

50. Digestive Function: Ingestion Organs and associated structures Saliva • Produce 1 - 1.5 L/day • Basic composition • Water (98 - 99%) • Salivary Amylase: a digestive enzyme • Mucins: mucous that lubricates the mouth and food • Ions, buffers, metabolites, antibodies, etc • Dissolves foodstuff