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. A closer look at the chemistry
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

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: Chemical:
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
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 prosecretin to 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 amylase converts 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: From the pancreas:
Prosecretinsecretin
Secretin goes to the pancreas
Pancreas, liver and gall bladder release basic solutions which neutralize the small intestine
From the pancreas:
Enzyme
Conversion
trypsin
ProteinPeptides
erepsin
PeptidesAmino Acids
Pancreatic amylases
Starchmaltose
Lipase
Fatglycerol + fatty acids

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 colon removes most of this moisture
The descending colon stores faeces until their excretion

51. ....Must come out! The rectum The anus
Last 5 cm of the large intestine
BREIFLY stores faeces
The anus
A ring of muscles (sphincter) at the end of the digestive track, forming the external opening through which waste is expelled
Peristaltic contractions throughout the colon and contraction of abdominal muscles cause defecation

52. Test your knowledge
Starch

53. Test your knowledge
Villi

54. Test your knowledge
lipases

55. Test your knowledge

56. Test your knowledge
Pancreatic amylases

57. Fatglycerol + fatty acids
Test your knowledge
Fatglycerol fatty acids

58. Test your knowledge
Jejunum

59. Test your knowledge
Bile

60. Test your knowledge
Peristalsis

61. Test your knowledge
Mechanical Digestion

62. Test your knowledge
Descending Colon

63. Test your knowledge
Gall Bladder

64. Test your knowledge
Uvula

65. Test your knowledge
Amino Acids

66. Test your knowledge
Maltase

67. Test your knowledge
Secretin

68. Test your knowledge
Fats