Digestion Introduction

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  • 1. Biology 30S Unit 2 DIGESTION & NUTRITION
  • 2. Biology 30S Unit 2 DIGESTION & NUTRITION
    • Did you know . . .
      • We eat about 500kg of food per year.
      • 1.7 liters of saliva is produced each day. 
      • An adults stomach can hold approximately 1.5 liters of material.
      • Every day 11.5 liters of digested food, liquids and digestive juices flow through the digestive system, but only 100mls is lost in faces. 
      • Most of us pass somewhere between 200 and 2,000 ml of gas per day (average, about 600 ml).
  • 3. Biology 30S Unit 2 DIGESTION & NUTRITION How long is your digestive system? Estimate the length of your entire digestive system – starting at your mouth and ending at your anus. Let’s find out!
  • 4. Biology 30S Unit 2 DIGESTION & NUTRITION
  • 5. Biology 30S Unit 2 DIGESTION & NUTRITION Introduction
  • 6. Biology 30S Unit 2 DIGESTION & NUTRITION Introduction Eating is something you likely spend a lot of time thinking about---what you will eat, when you will eat, who you will eat with. Have you ever considered why you need to eat? Do you know the meaning of the term “junk foods”?  When we eat such things as bread, meat, and vegetables, they are not in a form that the body can use as nourishment. Our food must be changed into smaller molecules before they can be absorbed into the blood and carried to cells throughout the body. Digestion is the process by which food is broken down into smaller parts so that the body can use them to provide energy and build and nourish cells.
  • 7. Biology 30S Unit 2 DIGESTION & NUTRITION In this unit, you will study the structure and function of the human digestive system as well as some of the disorders and diseases that affect this system. You will identify essential nutrients, their sources and the effects of not enough or too much intake of these nutrients to normal body function. You will also have the opportunity to analyze your own eating habits.
  • 8. Biology 30S Unit 2 DIGESTION & NUTRITION Human Digestion The main function of the digestive system is to break down large macromolecules (proteins, fats and starch) into smaller molecules (amino acids, fatty acids and glucose) that can be absorbed into the circulatory system for distribution around your body. The breakdown of food is accomplished through a combination of mechanical and chemical processes.
  • 9. Biology 30S Unit 2 DIGESTION & NUTRITION The Alimentary Canal The human digestive system is a coiled, muscular tube (6-9 meters long when fully extended) called the alimentary tract extending from the mouth to the anus. This tube is like a disassembly line, a well-run factory in which a large number of complex tasks are performed.
  • 10. Biology 30S Unit 2 DIGESTION & NUTRITION The Alimentary Canal Several specialized compartments occur along this length: mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus . Accessory digestive organs are connected to the main system by a series of ducts: salivary glands, parts of the pancreas, and the liver and gall bladder.
  • 11. Biology 30S Unit 2 DIGESTION & NUTRITION Suppose you eat an apple. What path does it take as it is digested and eliminated from our body? Mouth/ Throat Esoph- agus Stomach Small Intestine Large Intestine Rectum/ Anus
  • 12. Biology 30S Unit 2 DIGESTION & NUTRITION
    • 5 Stages of Digestion
    • 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/molecules.
    • absorption - passage of the molecules into the bloodstream
    • elimination - removal of undigested food and wastes
  • 13. Biology 30S Unit 2 DIGESTION & NUTRITION Mouth
  • 14. Biology 30S Unit 2 DIGESTION & NUTRITION
    • Mouth
      • Receives food
      • Tongue
        • Mixes food with saliva
        • Rough surface- aids in mechanical digestion
        • Positions food for chewing
        • Positions food (bolus) to initiate swallowing reflex
  • 15. Biology 30S Unit 2 DIGESTION & NUTRITION
    • Mouth
      • Roof of mouth (Palates)
      • Together the hard and soft palate separate the oral and nasal cavities)
        • Hard palate - composed of bone, w/ which teeth are rooted
          • ridges for mechanical digestion
        • Soft palate - composed of muscle
          • uvula
            • Closes off nares during swallowing
  • 16. Biology 30S Unit 2 DIGESTION & NUTRITION
    • Mouth
      • Salivary glands
        • 3 pairs; parotid, submaxillary, and sublingual glands
        • Collective secretions are called saliva
        • Contains amylase, an enzyme for starch digestion
    • - The water in saliva moistens and dissolves particles of food, thereby aiding chemical digestion, the ability to taste, and the chewing process. Mucous helps make chewed food smooth and easy to swallow.
  • 17. Biology 30S Unit 2 DIGESTION & NUTRITION
    • Mouth
      • Teeth
        • Mechanical digestion; increase the surface area so that chemical digestion may be more effective.
        • Types of teeth
          • Canines (Tear and shred food)
          • Incisors (biting and cutting food)
          • Premolars ( grinding and chewing food)
          • Molars ( grinding and chewing food)
  • 18. Biology 30S Unit 2 DIGESTION & NUTRITION
    • Mouth
      • Overall functions of mouth
        • Mechanical digestion
          • Chewing food
          • Mixing with saliva
          • Bolus formation
        • Chemical digestion
          • Begin digestion of starches to dissaccharides
  • 19. Mouth
  • 20. Biology 30S Unit 2 DIGESTION & NUTRITION
    • Pharynx
      • Lies behind your mouth, below the soft palate
      • Lower part of the pharynx connects to two tubes: the trachea , which carries air to the lungs; and the esophagus , which delivers food into the stomach.
      • Connects the mouth and the esophagus
      • Swallowing reflex
        • Uvula closes off nares
        • Trachea moves upward under epiglottis
        • Airways close off
        • Bolus of food moves down esophagus
  • 21. Biology 30S Unit 2 DIGESTION & NUTRITION
    • Esophagus
    • Passes from pharynx to stomach ( 25 cm, flexible, muscular tube)
      • The inside of the tube is covered with a film of slippery mucous, which helps food to pass easily.
      • Layers of muscles: circular muscles, which encircle the esophagus; and longitudinal muscles, which run the length of the esophagus.
      • Peristalsis
        • Rhythmic wave of contraction throughout tract
        • Propels bolus down esophagus
      • Sole purpose is conduction of food
      • Esophageal Sphinctor (entrance to stomach)
        • Muscles that encircle tubes
        • Act like valves
  • 22. Biology 30S Unit 2 DIGESTION & NUTRITION Stomach
  • 23. Biology 30S Unit 2 DIGESTION & NUTRITION
    • Stomach
    • The stomach
      • Thick-walled J-shaped organ
      • Lies on left side of abdomen
      • Rugae -folds in wall
        • Mechanical digestion-friction
        • Allows expansion
      • 3 muscle layers
        • Longitudinal
        • Oblique
        • Circular
  • 24. Biology 30S Unit 2 DIGESTION & NUTRITION
    • Stomach
    • The stomach cont’d.
      • Gastric glands
        • Found in the bottom of the rugae folds
        • Produce gastric juice - which contain hydrochloric acid and digestive enzymes. Secretions of these glands are controlled by nervous signals such smells and thoughts and hormone (endocrine) signals.
          • Pepsinogen - Protein digestion
          • HCl - Activates pepsinogen to pepsin (protein digestion)
      • Mucous cells
        • Produce thick protective mucus layer
  • 25. Biology 30S Unit 2 DIGESTION & NUTRITION
    • Stomach
    • The stomach cont’d.
      • Mixture of gastric juice, mucous and food is called chyme, an acidic paste with a pH of about 2.
      • Moves into intestine through pyloric sphincter
  • 26. Biology 30S Unit 2 DIGESTION & NUTRITION
    • Stomach
      • Overall function of the stomach
        • Mechanical digestion
          • Mixing of food with gastric juice
          • Forms semi-liquid called chyme
        • Chemical digestion
          • Initiation of protein digestion
        • Storage of food
  • 27. Biology 30S Unit 2 DIGESTION & NUTRITION Small Intestine
  • 28. Biology 30S Unit 2 DIGESTION & NUTRITION
    • Small Intestine
      • An extremely important part of your digestive system. It is here that digestion is completed and the products of digestion are absorbed into the blood stream.
      • About 6-7 m in length and 3 cm in diameter
      • Coiled in abdomen and held together by mesentery, which serves to keep untangled and feeds the SI with many blood vessels.
  • 29. Biology 30S Unit 2 DIGESTION & NUTRITION
    • Small Intestine
    • Duodenum
        • First 25 cm of small intestine
        • Principal site of digestion of nutrients
        • Receives bile, a greenish-yellow liquid, from the liver (which was stored in the gallbladder)
          • Emulsification of fats
  • 30. Biology 30S Unit 2 DIGESTION & NUTRITION
    • Small Intestine
    • Duodenum (continued)
        • Receives pancreatic juice from pancreas
          • Many carbohydrate, lipid, and protein digesting enzymes for digestion of nutrients
          • Bicarbonate along with bile, neutralizes the acidic chyme coming from the stomach.
        • Receives intestinal juice
          • Secretes carbohydrate, lipid, and protein digesting enzymes
  • 31. Biology 30S Unit 2 DIGESTION & NUTRITION
    • Small Intestine
    • Small intestine cont’d.
      • Jejunum and ileum
        • Principal site of absorption of nutrients
        • Lining has villi
          • Increases surface area
          • Outer layer of villi have microvilli- more surface area
          • Villi contain lymph lacteals
            • Absorb fatty acids and glycerol
          • Villi contain blood capillaries
            • Absorb sugars and amino acids
  • 32. Biology 30S Unit 2 DIGESTION & NUTRITION
  • 33. Biology 30S Unit 2 DIGESTION & NUTRITION Small Intestine
  • 34. Biology 30S Unit 2 DIGESTION & NUTRITION Large Intestine
  • 35. Biology 30S Unit 2 DIGESTION & NUTRITION
    • Large Intestine
    • The large intestine or colon is about 1.5 m long and 8 cm in diameter. Its shape resembles an inverted "U".
    • Another sphincter, the ileocecal valve , occurs at the SI/LI junction. Its function is to control the rate at which the contents of the small intestine pass into the colon.
    • The main functions of the large intestine are to eliminate undigested food wastes and to reabsorb water.
  • 36. Biology 30S Unit 2 DIGESTION & NUTRITION
    • Large Intestine
      • Cecum
        • Blind end of the large intestine
        • Appendix
          • Projection of cecum
          • May play a role in fighting infections
          • Rupture may cause peritonitis
      • Colon
        • Ascending, transverse, and descending portions
        • Absorption of water, salts
        • Terminates at the rectum
  • 37. Biology 30S Unit 2 DIGESTION & NUTRITION
  • 38. Biology 30S Unit 2 DIGESTION & NUTRITION Rectum/Anus
  • 39. Biology 30S Unit 2 DIGESTION & NUTRITION
    • Rectum/Anus
    • As a result of the reabsorption of water, the remnants of digestion become drier and more solid. This material is called feces . It is stored in the rectum , the last 20 cm of the large intestine. A muscular valve, the anal sphincter , keeps the lower portion of the rectum closed.
    • When this valve opens, the waste materials from digestion are released from the body through the anus.
  • 40. Biology 30S Unit 2 DIGESTION & NUTRITION