Digestive System

1. Digestive System

2. Nutrition • Nutrient: substance in food used to promote growth, maintenance, and repair • Major nutrients: • Carbohydrates – sugars & starches • Lipids – saturated/unsaturated fats • Proteins – eggs, milk, meat (complete – all AA); legumes, nuts, cereals (incomplete) • Vitamins – A, B, C, E, D, K • Minerals – Ca, P, K, S, Na, Cl, Mg, Fe

3. Functions • Ingestion - mouth • Digestion • Mechanical– fragment food into smaller particles (teeth, tongue, stomach, SI) • Chemical– enzymes (ends in –ase), water • Mouth = carbs • Stomach = proteins • SI = carbs, proteins, fats, nucleic acids • Absorption – transport from SI to blood • Defecation – eliminate indigestible residues (feces)

4. Anatomy • Alimentary canal • Gastrointestinal (GI) tract • Mouth  pharynx  esophagus  stomach  small intestine  large intestine  rectum anus • Accessory digestive organs • Teeth, tongue, salivary glands, liver, gall bladder, pancreas

6. Mouth • Oral cavity: mechanical, chemical digestion • Salivary glands: saliva lubricates food • Saliva = mucus, salivary amylase(starch breakdown) • Mastication:teeth chew food • Tongue mixes food + saliva

7. Pharynx: back of throat • Epiglottis: flap of cartilage, covers larynx when swallowing • Peristalsis (involuntary waves of muscle contraction) • Esophagus (gullet): passageway to stomach

8. Bolus: (forms in the mouth) is a ball of food that has been masticated and mixed with saliva.

9. Stomach • Stores food & breaks down food • Mechanical – churn, mix • Chemical – protein digestion • Gastric juice: converts meal to acidic chyme • HCl: pH 2, kills bacteria, denatures proteins • Pepsin: enzyme breaks down proteins into amino acids; optimum conditions = pH 2 • Rugae= large folds • Mucus= protects lining of stomach

10. DIFFERENT PARTS OF THE STOMACH • The stomach can be divided into four distinct parts. These are the cardia, fundus, body, and pylorus. • The cardia first portion: food passes from the esophagus into the stomach. Gastric juices are manufactured. • The fundus stores undigested food and gases released chemical digestion.

11. The body of the stomach or the corpus is the largest of the four parts; where the bulk of the partial digestion occurs. • The pylorus is connected to the duodenum or the beginning of the small intestine. The contents of the stomach through the pyloric canal to the SI.

12. THE STOMACH WALL • The walls of the stomach consist of four layers; starting from the innermost (closest to the lumen) layer: mucosa, sub-mucosa, muscularis, and the serosa. • The mucosa consists mainly of the gastric glands that secrete the digestive juices. It is covered by a layer of columnar epithelial tissue.

14. The sub-mucosa consists of dense connective tissue and has blood vessels, lymphatic vessels, and nerve. The sub-mucosa supports the mucosa and allows it to move in a flexible manner during peristalsis. The mucosa and the sub-mucosa are present as folds termed rugae. When the stomach is distended with food, the rugae are flattened out and appear smooth.

15. Peristalsis is the contraction and relaxation of the stomach muscles to physically breakdown food and propel it forward. These contractions are created by the muscular wall of the stomach which consists of inner circular and outer longitudinal smooth muscle.

16. The outermost layer of the stomach wall, the serosa consists of an epithelial layer and connective tissue which connects to the surrounding organs. • The serous membranes of the abdominal cavity are called peritoneum. • Visceral peritoneum lines the outer surface of the organs of the abdominal cavity • Parietal peritoneum lines the walls of the cavity • Mesentery is the double membrane in the abdominal cavity

17. CELL TYPES IN THE STOMACH • There are four main types of cells for stomach; secretions spread over the inner surface of the stomach: • Goblet cells secrete the alkaline mucous protects epithelium from hydrochloric acid. Found in the cardiac, fundic, and pyloric region.

18. Parietal cells, located in the cardiac, fundic, and pyloric region, secrete HCl; acid activates release of pepsin and kills micro-organisms. • Chief cells secrete pepsin. These cells are located in the fundic region. • G cells are found in the fundic and pyloric region. Secrete gastrin which stimulates the secretion of HCl.

20. Small Intestine • Digestion & absorption • Duodenum: (1st section) digestive juices, major chemical digestion, openings for pancreatic and common bile ducts • Jejunum (2nd): absorb nutrients • Ileum (3rd): absorb Vit. B12, bile salts, remaining nutrients

21. Folds, villiand microvilliincrease surface area for absorption

22. Digestive Glands • Secrete into SI (duodenum) • Pancreas: bicarbonate neutralizes acidic chyme, enzymes: pancreatic amylase = carbs, trypsin = proteins optimal pH 7.5 pancreatic lipase = fats • Bile salts: made in liver, stored in gallbladder • Emulsify fats (make smaller fat droplets)

23. Large Intestine (Colon) • Absorb water, eliminate food residue • Cecum: pouch where SI & LI meet, ferment plant material • Appendix = extension of cecum, role in immunity • Bacteria: make Vitamin K, produce gases • Rectum: feces stored until elimination

24. Homeostatic Imbalances of Digestive System

25. Gastric Ulcers • Lesions in the stomach lining • Caused mainly by bacterium Heliobacter pylori

26. Gall Stones • Crystallized cholesterol in gallbaldder • Bile stored too long or too much water removed

27. Appendicitis • Inflammation of appendix

28. Vomiting (emesis) • Caused by irritation of stomach; inner ear disturbance • Abdominal muscles & diaphragm contract • “reverse peristalsis”

29. Diverticulosis • When diet lacks bulk (low-fiber diet) • Diverticula: pouches form on colon wall • Diverticulitis: when diverticula become inflamed  feces gets trapped, bacteria grow in pouch

30. Hepatitis • Inflammation of liver • Viral infection from contaminated water, blood transfusions, needles Jaundice

31. Cirrhosis • Chronic inflammation of liver • Severe damage  hard and fibrous liver • Alcoholism

32. Microscopic study of the digestive system organs and glands

33. Observe and draw diagrams of the following slides: • Lingual (salivary) glands • Tongue • Esophagus • Stomach • Pancreas • Small Intestine • Liver

34. Label the types of cells and tissues that you observe in each drawing • Describe the function of the cells and tissues in each organ or gland

35. Salivary Glands • Salivary glands are made up of secretory acini (acini - means a rounded secretory unit) and ducts. There are two types of secretions - serous and mucous. • Serous and mucous cells, are glandularepithelial cells • Cells that line the salivary ducts are simple columnar epithelial cells

36. The acini can either be serous, mucous, or a mixture of serous and mucous. • A serous acinus secretes proteins in an isotonic watery fluid.A mucous acinus secretes secretes mucin - lubricant

42. Tongue – fungiform papillae with taste buds

43. Tongue – taste buds

44. Esophagus

45. Esophagus

46. Stomach

47. Stomach

48. Stomach

49. Pancreas