Why do we eat?

1. Why do we eat? Biology 11

2. Why do we eat? • Cellular Respiration (how we get energy) • This energy comes from the nutrients we get from eating • Including: • Proteins • Carbohydrates • Fats • Vitamins • Minerals

3. Proteins

4. Proteins Defined • Key “worker molecules” are required in nearly every function that your body completes. • Made up of amino acids in a chain (50 to 2000!)

6. Amino Acids • Contains Nitrogen (N) • Required for life

7. Amino Acids • There are 20 amino acids required by the human body • 10 essential amino acids • Our bodies cannot produce them. • We must get them from our foods. • 10 non-essential amino acids • Our bodies can produce them

8. Protein Structure • Proteins= chains of amino acids • Broken down by enzymes

9. Carbohydrates

10. Carbohydrates • Used by your body to generate glucose (sugar) to provide you with energy to do stuff • Two types: • Simple Sugars • no modifications needed • Complex Sugars: Starch and Dietary Fiber • Must be broken down before they can be used

11. Simple sugar structure =

12. Complex Sugars • Chains of simple sugars • Broken down by enzymes

13. Fats (Lipids)

14. Purpose of Fats (Lipids) • Heat insulation • Energy Storage • Provides production of reproductive organs in women

15. Types of lipids = Cis fats = good fats = Trans fats = bad fats

16. Types of lipids • Cholesterol and other steroids are also lipids

17. Breakdown of fats • Fats must first be broken down into smaller droplets • emulsification of fats • Due to their polar nature. • Not soluble in water • Secondly, digested by enzymes

19. Enzymes break down these componets

20. The Digestive System A closer look at the chemistry

21. What is the point of digestion? • To break down protein, carbohydrates, and fats such that they can pass through cell walls by diffusion, and be absorbed into the body.

22. The Digestive Track

23. Parts of the digestive system: The Mouth • d

24. Parts of the Mouth • Teeth – a variety of teeth for consuming different foods • Tongue- detects taste • Hard palette – the front of the roof of the mouth • Soft palette- the back of the roof of the mouth • Uvula- soft tissue that hangs from the soft palette; blocks of nose during ingestion • Salivary Glands- secrete saliva

25. Mouth Function • Two types of digestion: • Mechanical: • Requires chewing with your teeth • Chemical: • Requires the use of enzymes secreted by salivary glands

26. Mouth Function Continued • Two purposes of saliva: • To lubricate food, • Allowing it to be swallowed easily • Dissolving food particles = taste • To break down starches (complex carbohydrates) • Amylase enzymes

27. Mouth Function Continued • Preventative Measures... • Uvula: Attached to the soft palettes of your mouth roof. • Blocks food from entering the nasal cavity during swallowing • Epiglottis: • Covers the wind pipe during swallowing to prevent food from entering

28. The Pharynx • The “throat” area of the digestive tract • The esophagus and trachea both branch off of it • Receives food from the mouth • Directs the food down the esophagus

29. The Esophagus= Food Pipe • Pathway of food from mouth to stomach • Diameter of a quarter • Peristalsis • Waves of rhythmic contractions of smooth muscles caused by the stretching of the esophagus by bolus • Bolus=moistened lump of food • Involuntary (happens automatically)

30. Ingestion • Food is moved to the back of mouth by tongue • Involuntary reflex is triggered to close off wind pipe • Peristalsis quickly takes the food down the esophagus

31. Don’t let it come back up! • The esophagus contains two values: • The upper esophageal sphincter • Allows food to enter the digestive track • The lower esophageal sphincter • Prevents stomach contents from “coming back up”

32. Into the Pit :The Stomach • Bolus enters the stomach from the esophagus • Muscular walls contract • Churning and mixing the bolus with gastric fluids

33. The Stomach: Gastric Fluids • Gastric Fluids: • Mucus –protects stomach lining from its own acid • Hydrochloric Acid (HCl): (pH 1 – 3) • Kills bacteria and • Converts an enzyme called pepsinogen into pepsin • Pepsin digests proteins

34. Mechanical Digestion in the stomach • As the stomach churns, it mechanically breaks down molecules of • Proteins • Carbohydrates • & fats • Into more easily digested molecules. • Fats require the most mechanical digestion at this stage

35. Exiting the Stomach • Chyme= mixture of food and gastric fluids • After 2 to 3 hours: • foods are at a highly soluble level • and a hydrogen ion concentration of a certain level is present. • The pyloric sphincter opens and chyme is released into the small intestine

36. What leaves when? • Fluids empty quicker then carbohydrates • Carbohydrates empty quicker then proteins • Proteins empty quicker then fats

37. Test your knowledge! • Food enters the mouth • What are the two types of digestion? • Mechanical digestion by teeth • Chemical digestion by salivary amylase (digests starches) • Once food is swallowed it is called: • Bolus • It travels down the esophagus due to involuntary muscular contractions known as: • peristalsis • Food enters the stomach and is mixed with gastric fluids for 2 to 3 hours. What is digested here? • Proteins • Other materials are made more _________ in the stomach: • Soluble • At this point, the digesting food is called: • Chyme • and exits to the small intestine via the ? • Pyloric sphincter

38. Enter the Small Intestine

39. Small Intestine • Long (7 meters) and narrow (2.5 cm diameter) • Villi increase its surface area • Most digestion occurs here • Most digestion occurs in the first 30 cm, called the duodenum, • Pancreas, liver, and gall bladder release secretions (juices/enzymes) into this area for digestion (chemical)

40. Signal to the accessory organs • Stomach acid entering the duodenum causes prosecretinto become the hormone: secretin • Secretin travels through the bloodstream and signals: • The pancreases to release pancreatic juices • The gallbladder and liver to release bile

41. Pancreatic Juices and Bile • Pancreatic juices and bile are both alkaline solutions (Bicarbonate) • The release of these basic solutions, cause the pH of the small intestine to rise from 2.0 to 9.0. • This inactivates the stomach acids • H+ + OH- H2O

42. Pancreatic Juices- Proteins • The pancreatic juices contain trypsinogen, an enzyme • In the small intestine enterokinase converts trypsinogen to trypsin. • Trypsin further breaks down proteins • The pancreas also releases erepsins • erepsins complete the digestion of proteins into amino acids (which the body can use!)

43. Pancreatic Juices -Carbohydrates • The pancreatic juices also contain amylase enzymes: • Pancreatic amylaseconverts starch into maltose (a type of sugar) • Maltase(an enzyme) is released from the intestinal cell walls. • Converts maltose into glucose (the smallest sugar)

44. Pancreatic Juices- Lipids • Finally, the pancreatic juices contain lipases (enzymes) • Lipases break down lipids (fats) into fatty acids and glycerol

45. Recap the duodenum • Upon entry of acidic juices: • Prosecretinsecretin • Secretin goes to the pancreas • Pancreas, liver and gall bladder release basic solutions which neutralize the small intestine • From the pancreas:

46. The liver and gall bladder • The liver has two main functions: • To filter and separate waste from nutrients • Store glucose and other nutirents • To produce bile • Bile=Water, bile salts, fats, cholesterol • Bile is stored and concentrated in the gall bladder. • Moved from the liver to gall bladder through bile ducts • Bile is released into the stomach to turn fats into fatty acids during digestion.

47. The Small Intestine Continued • Three Sections: • Duodenum • Digestion of foods • Jejunum • Absorption of carbohydrates and proteins by diffusion • Ileum • Absorption of fats, vitamins, minerals, and other nutrients by diffusion • Absorption of enzymes to be “recycled” by diffusion

48. Absorption in the small intestine =Villi • Small intestine covered in villi throughout • Coating of capillary beds allows for easy absorption & quick transport of nutrients to the liver

49. Into the large intestine

50. What goes into the large intestine.... • Waste contains lots of water. • Water needs to be absorbed back into the body • The ascending colon and transverse colonremoves most of this moisture • The descending colonstores faeces until their excretion