Unit 2: Digestion and Nutrition

1. Unit 2: Digestion and Nutrition

2. WHAT YOU WILL LEARN IN THIS UNIT: • Identify major structures and functions of the human digestive system from a diagram, model, or specimen. • Describe the processes of mechanical digestion that take place at various sites along the alimentary canal • Identify functions of secretions along the digestive tract.

3. Identify sites of chemical digestion along the alimentary canal, as well as the type of nutrient being digested. • Explain the role of enzymes in the chemical digestion of nutrients and identify factors that influence their action. • Describe the processes of absorption that take place at various sites along the alimentary canal.

4. Describe the homeostatic role of the liver with respect to the regulation of nutrient levels in the blood and nutrient storage. • Describe the functions of each of the six basic types of nutrients — carbohydrates, lipids, proteins, vitamins, minerals, and water. • Identify dietary sources for each of the six basic types of nutrients — carbohydrates, lipids, proteins, vitamins, minerals, and water.

5. Evaluate personal food intake and related food decisions. • Investigate and describe conditions/disorders that affect the digestive process. • Use the decision-making process to investigate an issue related to digestion and nutrition.

6. Introduction to Digestion • The main function of the digestive system is to disassemble food you eat into molecules so it can be used by your body for energy. • The pathway that food takes as it moves through the body during digestion is known as the digestive tract or the alimentarycanal.

8. Five Stages of the Digestive Process • Motility – movement of food through the digestive system. • Secretion – release of digestive juices in response to a specific stimulus. • Digestion – the physical and chemical breakdown of food into small particles. • Absorption– passage of the molecules into the bloodstream. • Elimination – removal of undigested food and waste.

9. Structures Involved in Digestion Mouth • Food enters the alimentary canal through the mouth. • Inside the mouth there are two types of digestion: A) Mechanical (physical) Digestion • Teeth break up food into smaller pieces • Tongue guides food to the back of the mouth

10. B) Chemical Digestion • As food is chewed, salivary glands in mouth secrete saliva • 4 – 8 cups of saliva are produced by salivary glands each day • Salivais composed of water, mucous and amylase • Salivary Amylase (enzyme) breaks down starch into smaller molecules • Saliva provides lubrication for chewing and swallowing • Saliva helps maintain pH in the mouth and helps regulate plaque.

11. There are three glands: 1.Parotid gland • located just in front of and slightly below the earlargest of the glands • secretes salts, an enzyme (Salivary Amylase), and a watery fluid into the mouth

12. 2.Submaxillary gland • located below the parotid gland near the angle of the lower jaw • produces watery fluid and some mucous into the mouth 3.Sublingual gland • located under the tongue and secretes mostly thick, stringy mucus, salts, and salivary amylase

14. Pharnyx • Most commonly known as the throat • Serves two purposes: • moves the air into your lungs through trachea • moves food into your stomach through esophagus

15. Uvula • a small mass of tissue that hangs down in the back of the mouth, and moves up to close off the openings to the nasal cavitywhen food is swallowed into the esophagus.

16. Soft Palate • the roof of the pharynx in the back of the mouth • this soft tissue functions in closing off the openings to the nose and earsas food is swallowed.

17. Epiglottis • Small flap of cartilage located behind the tongue • Prevents food from entering the respiratory tract by closing over the air passage each time you swallow • When you talk or laugh as you swallow, the epiglottis may open, causing food to enter the upper portion of respiratory tract. Your response, a reflex, is to choke and cough, forcing the food out of the respiratory tract.

18. Esophagus • Carries food from mouth to stomach • Food is passed through the esophagus through: A. Secretions of mucus • Cells of inner lining secrete mucus B. Peristalsis • Muscle layers in the esophagus alternatively relax and contract to push food ahead (involuntary movement)

20. Peristalsis Along Esophagus

21. Peristalsis Video • NOT FOR THOSE WITH A WEAK STOMACH • PERISTALISIS, STORAGE AND EXCRETION

22. Review of Swallowing • Video Demos

23. Cardiac Sphincter • Separates the esophagus from the stomach • Opens and closes as food passes through • Prevents stomach acid from entering the esophagus

25. Stomach Stomach • Main function is food storage • It changes size and shape according to the position of the body and the amount of food inside • Holds about 2 litres of food • Enzymes, water, and hydrochloric acid combine to form gastric juice • pH of stomach is about 2 • Food remains in stomach for 2-4 hours and is the consistency of tomato soup when it is ready to leave • Chyme is a mixture of food and gastric juice

26. Both physical and chemical digestion take place in the stomach: Physical digestion • Peristalsis • Three layers of muscles located within the wall of the stomach contract to physically break down food into smaller pieces

27. Chemical digestion Inner lining is lined with a layer of cells • Three types of cells: • one type secretes pepsin (enzyme) • breaks down proteins in food • one type secretes hydrochloric acid and water • kills bacteria and parasites ingested in food • provides the optimal pH for pepsin to function • one type secretes mucous • protects cells from gastric juices by forming a mucous layer between the lining and contents of stomach • ulcers are a result of mucus lining wearing too thin and cells are attacked by gastric juice

30. Pyloric Sphincter • Two muscles keep food within stomach • Muscles relax to allow partially digested food move into the small intestine

31. Small Intestine • Small diameter (2-3 cm) but long length (about 6 m) • Digestion of food is completed in small intestine • Food is moved along by muscle contraction to further mechanical breakdown of food • Chemical digestion of carbohydrates and proteins occurs through enzymes produced and secreted by the pancreas and liver

32. Chemical Digestion • Occurs in duodenum (first 25 cm of small intestine) • Most of the enzymes and chemicals that function in the duodenum enter through ducts that collect secretions (juices) from pancreas, liver, and gallbladder

33. Secretions Found in Small Intestine (Duodenum) A) Secretions of Pancreas • secretes a mixture of enzymes that break down carbohydrates, proteins, and fats. B) Secretions of Liver • produces bile • bile is stored in gallbladder and is then passed to the duodenum • breaks down fats

34. Absorption of Food • As digested food moves through small intestine, it passes over thousands of tiny fingerlike structures called villi • Mainly occurs in next two sections of small intestine – jejunum and ileum • The function of villi is to absorb digested food • Food molecules diffuse or are actively transported through connective tissue cells into bloodstream • Blood travels to liver to remove any excess glucose or amino acids from blood

36. Large Intestine • Also called the colon • 1.5 m long, about 6.5 cm diameter • There are three portions of the large intestine. These three sections create an upside-down U-shape and surround the small intestine.

37. Direction of food

38. Two main functions: 1. Intestinal walls absorb water and salts 2. Vitamin B and Vitamin K synthesis, which the body absorbs as needed

39. Food stays in large intestine for 18 to 24 hours • Where the large and small intestine join, there is a small projection called the appendix • Bacteria may grow and secrete toxic waste in appendix, resulting in painful inflammation called appendicitis • More common in children than adults because the opening to the appendix is larger in children • The only residue of food at the end of the colon is solid, indigestible waste called feces which travels to the rectum

40. Rectum • Feces are eliminated through the rectum • Feces are 75% water and25% solid matter • 30% dead bacteria • 10-20% inorganic matter • 2-3% protein • 30% undigested fiber of the food • Overall journey of food through digestive tract lasts 24-33 hours

42. Animations • Digestion • For Lunch Part 1 • For Lunch Part 2