1. Part I The Chemistry of Life
The Digestive System
Part I
The Chemistry of Life

2. Questions for Consideration
The Chemistry of Life
Questions for Consideration
List the 5 nutrients required to maintain good health;
List two ways the body uses:
Lipids
Proteins
Carbohydrates
Vitamins
Minerals
List some foods that are mainly carbohydrates.
List some foods that are mainly fats.
Are fats good or bad for you? Justify your answer.

3. Why do we eat?
Biology 11

4. Cellular Respiration (how we get energy) &
Why do we eat?
Cellular Respiration (how we get energy) &
The building blocks for cell production & chemical processes
This energy comes from the nutrients we get from eating
Including:
Proteins
Carbohydrates
Fats
Vitamins
Minerals

5. Chemistry of Life Vitamins and Minerals Proteins Fats (Lipids)
Chemicals of Life
Carbohydrates
Are the primary energy source for all cells.
Proteins
Structural and functional components of the cell (e.g. Building blocks of muscles).
Composed of amino acids.
Fats (Lipids)
Energy storage compound.
Structural component of cell membranes.
Vitamins and Minerals
Help in chemical reactions
Found in complex chemicals (such as hormones and enzymes).

6. The Chemistry of Life
In order to fully understand the digestive system you must have a good understanding of both biology (anatomy) and chemistry.
Biochemistry

7. Called macromolecules
Chemistry of Life
Food can be classified into 3 nutrient types:
Carbohydrates
Proteins
Fats (also called lipids)
Called macromolecules

8. Protein Sources

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

11. Amino Acids
Contains Nitrogen (N)
Required for life

12. 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

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

14. Carbohydrate Sources

15. Carbohydrates
Used by your body as a source of glucose (sugar) to provide you with energy to do stuff (ATP)
Two types of carbs:
Simple Sugars
minimal to no modifications needed
Complex carbohydrates: Starch & Dietary Fiber
Must be broken down before they can be used

16. Simple sugar structure
chain or ring

17. Complex Carbohydrates
Chains of simple sugars
glucose molecules long
Broken down by enzymes

18. Fats (Lipids)

19. Purpose of Fats (Lipids)
Heat (insulation)
Energy Storage
Provides protection of reproductive organs in women

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

21. Cholesterol and other steroids are also lipids
Types of lipids
Cholesterol and other steroids are also lipids

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

24. Enzymes break down these components

25. A closer look at the chemistry
The Digestive System
A closer look at the chemistry

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

27. The Digestive Track

28. Parts of the digestive system: The Mouth

29. 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

30. Two types of digestion:
Mouth Function
Two types of digestion:
Mechanical:
Requires chewing with your teeth, mashing with the tongue (& later the stomach muscles)
Chemical:
Requires the use of enzymes secreted by salivary glands

31. 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)
Salivary amylase enzymes

32. 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

33. The “throat” area of the digestive tract
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

34. 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)

35. Ingestion Food is moved to the back of mouth by tongue
Involuntary reflex triggers epiglottis to close off trachea (windpipe)
Peristalsis quickly takes the food down the esophagus

36. Don’t let it come back up!
The esophagus contains a gate:
The lower esophageal sphincter is also called the Cardiac Sphincter
Prevents stomach contents from “coming back up”

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

38. 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

39. Mechanical Digestion in the stomach
As the stomach churns, it mechanically breaks apart chunks of food separating molecules of
Proteins
Carbohydrates
& fats
Into more easily digested molecules.
Fats require mostly mechanical digestion at this stage

40. Exiting the Stomach
Chyme = mixture of food and gastric fluids
After 2 to 3 hours:
foods are now more soluble
The pyloric sphincter opens and chyme is released into the small intestine

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

42. 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 the only compound digested in the stomach?
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

43. Enter the Small Intestine

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

45. 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 pancreas to release pancreatic enzymes &
The gallbladder and liver to release bile

46. 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 (neutralizes) the stomach acids
H+ + OH- H2O

47. 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!)

48. 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)

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

50. Upon entry of acidic juices:
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:
Enzyme
Conversion
trypsin
ProteinPeptides
erepsin
PeptidesAmino Acids
Pancreatic amylases
Starchmaltose
Lipase
Fatglycerol + fatty acids

51. 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.

52. The Small Intestine Continued
Three Sections:
Duodenum
Enzymatic 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

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

54. Into the large intestine

55. 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

56. ....Must come out! The rectum 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

57. Test your knowledge
Starch

58. Test your knowledge
Villi

59. Test your knowledge
lipases

60. Test your knowledge

61. Test your knowledge
Pancreatic amylases

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

63. Test your knowledge
Jejunum

64. Test your knowledge
Bile

65. Test your knowledge
Peristalsis

66. Test your knowledge
Mechanical Digestion

67. Test your knowledge
Descending Colon

68. Test your knowledge
Gall Bladder

69. Test your knowledge
Uvula

70. Test your knowledge
Amino Acids

71. Test your knowledge
Maltase

72. Test your knowledge
Secretin

73. Test your knowledge
Fats