1. The Function of Digestion and The Human Digestive System
Lesson 1

2. Nutrition

3. Obtaining and Processing Food
All organisms, regardless of their size or complexity, must have a way of obtaining essential nutrients
Essential nutrients: the basic raw materials they need to make their own structures, perform their life functions, and obtain energy for survival

4. Macromolecules
Organic molecules contain carbon bonded to hydrogen, as well as to other atoms, such as oxygen, sulfur, and nitrogen.
Macromolecules are larger, more complex assemblies of organic molecules, also known as nutrients.
These are the raw materials that our bodies need to provide energy, to regulate cellular activities, and to build and repair tissues.

5. Often grouped into four major categories:
Carbohydrates
Lipids
Proteins
Nucleic acids

6. Macromolecules
Energy released from these macromolecules, and matter supplied by them, is used to maintain the body’s metabolism (all of the chemical processes carried out by cells to maintain life)
Together, the four major categories of macromolecules are known as essential nutrients.

7. Carbohydrates
Are macromolecules that always contain carbon, hydrogen, and oxygen
Almost always in the same proportion: 2H : 1O : 1C.
Provide short-term or long-term energy storage for organisms.
There are two main types of carbohydrates: simple sugars and polysaccharides.

8. Monosaccharides (Simple Sugars)
Carbohydrate molecules with three to seven carbon atoms.
Examples: glucose (the sugar found in blood) and fructose (the sugar found in fruit).
Disaccharides
Made up of two simple sugars (di- = two).
Examples: sucrose (table sugar), and lactose (the sugar found in dairy products).
Polysaccharides
Complex carbohydrates that consist of many linked simple sugars (poly- = many).
Examples: Starch stores energy in plants, and glycogen stores energy in animals.

9. Carbohydrates

10. Lipids Are insoluble in water.
The basic structure of lipids is a molecule of glycerol
3 carbon atoms, each attached to a fatty acid chain
Store 2.25 times more energy per gram than other biological molecules; function as energy-storage molecules.

11. Lipids Phospholipids, form cell membranes.
Examples of lipids are fats, such as butter and lard, and oils, such as olive oil and safflower oil.

12. Proteins Assembled from small sub-units known as amino acids
Polypeptides are chains for hundreds of amino acids joined together by peptide bonds
Most enzymes are proteins, and so are antibodies, which combat disease.
Proteins help build and repair muscles and cell membranes

13. Nucleic Acids
Nucleic acids direct growth and development of all organisms using a chemical code.
The two types of nucleic acids are ribonucleic acid (RNA) and deoxyribonucleic acid (DNA)

14. Hydrolysis A water molecule (H2O) is added to the macromolecule.
This breaks the chemical bonds that hold together the smaller molecules from which the macromolecule is made.
Digestive enzymes help to speed up the process of hydrolysis.

15. Minerals and Vitamins
Inorganic and organic substances that enable chemical reactions to occur and aid in tissue development, growth, and immunity.
Needed by a healthy, functional human body.

16. Minerals Mineral Key function in the body Possible Sources Calcium
Forming bone, conducting nerve signals, contracting muscle, clotting blood
Dairy products
Iron
Producing hemoglobin
Red meat
Magnesium
Supporting enzyme functions, producing protein
Dark, leafy greens
Potassium
Conducting nerve signals, contracting muscle
Grains
Sodium
Conducting nerve signals, balancing body fluids
Salt

17. Vitamins Vitamin Key function in the body Possible Sources
A (carotene)
Good vision, healthy skin and bones
Fruits
B1 (thiamine)
Metabolizing carbohydrates, growth and muscle tone
Beans
C (ascorbic acid)
Boosting immune system, healthy bones, teeth, gums, and blood vessels
Fruit D
Absorbing calcium, forming bone
Fish E
Strengthening red blood cell membranes

18. Water
Needed for the proper functioning of all cells and organs. Makes up 2/3 of body mass.
Functions include:
Transporting dissolved nutrients into the cells that line the small intestine
Flushing toxins from cells
Lubricating tissues and joints
Forming essential body fluids, such as blood and mucus
Regulating body temperature (by sweating)
Eliminating waste materials (in urine and sweat)

19. Learning Check
Pg 406, Q 1-6

20. Types of Digestion Intracellular digestion: Extracellular digestion:
Digestion inside the cell
Phagocytosis - cell engulfs the food
Ex: single-celled organisms (paramecium, amoeba)‏
Extracellular digestion:
Digestion outside the cells
Food enters a tube and exits from the other end
Ex: most animals, human digestive tract

21. Mechanical Digestion
The physical breakdown of large food particles into smaller ones.
Achieved through chewing, mashing, chopping, breaking food into smaller pieces.
This increases the surface area of the food, allowing more enzymes to come into contact with the food.

22. Chemical Digestion
The chemical breakdown of large molecules into smaller ones:
Carbohydrates: polysaccharides (starch) are broken into monosaccharides (simple sugars)‏
Proteins: are broken down into amino acids
Lipids: (mainly triglycerides) are broken down into fatty acids and glycerol
Note: Food particles are broken down by enzymes. Each enzyme has a pH at which it performs best.

23. Types of Feeders Autotrophs:
Can feed themselves from inorganic molecules
Ex: plants use sun + H2O + CO2 to form organic compounds
Self-sufficient
Heterotrophs:
Depend on organic compounds made by other living things
Ex: animals, fungi, bacteria, etc.
Not self-sufficient

24. Filter Feeders
Aquatic animals that use a body structure similar to a filter basket to gather small organisms suspended in the water.
Siphons water into its mouth and then filters it to obtain small organisms to digest.
Examples include flamingoes, tube worms, clams, barnacles, and baleen whales.

25. Fluid Feeders
Obtain food by sucking or licking nutrient-rich fluids from live plants or animals.
Mouth parts are adapted to pierce or rip skin or leaf tissue and are used to suck or lick the blood or sap that is their food.
Examples: mosquitoes, ticks, aphids, spiders, bees, butterflies, vampire bats, and hummingbirds.

26. Substrate Feeders
Live in or on their food source and eat their way through it.
Examples: caterpillars and earthworms.
Caterpillars eat their way through the green tissues of leaves.

27. Bulk Feeders
Include many animals and most vertebrates (including humans).
Bulk feeders ingest fairly large pieces of food and some, like the great blue heron, swallow their food whole.
Use tentacles, pincers, claws, fangs, or jaws and teeth to kill prey, to tear off pieces of meat or vegetation, or to take in mouthfuls of animal or plant food.

28. The Digestive System

29. Introduction
The digestive system is used for breaking down food into nutrients which then pass into the circulatory system and are taken to where they are needed in the body.

30. Introduction There are four stages to food processing:
Ingestion: taking in food
Digestion: breaking down food into nutrients
Absorption: taking in nutrients by cells
Egestion: removing any leftover wastes

31. Human Digestive System
Begins when food enters the mouth (oral cavity).
It is physically broken down by the teeth (mechanical).
It is chemically broken down by enzymes released from the salivary glands.

32. Human Digestive System
The tongue moves the food around until it forms a ball called a bolus.
The bolus is passed to the pharynx (throat) and the epiglottis makes sure the bolus passes into the esophagus and not down the trachea!

33. Human Digestive System
The bolus passes down the esophagus by peristalsis.
Peristalsis is a wave of muscular contractions that push the bolus down towards the stomach.

34. Human Digestive System
To enter the stomach, the bolus must pass through the lower esophageal sphincter, a tight muscle that keeps stomach acid out of the esophagus.

35. Human Digestive System
The stomach has folds called rugae and is a big muscular pouch which churns the bolus (physical digestion).
The bolus is mixed with gastric juice, a mixture of stomach acid and enzymes (chemical digestion).

36. Human Digestive System
The stomach does do some absorption too.
Some medicines (i.e. aspirin), water and alcohol are all absorbed through the stomach.
The digested bolus is now called chyme and it leaves the stomach by passing through the pyloric sphincter.

37. Learning Check
Pg 414, Q 7-12

38. Human Digestive System
Food is now in the small intestine.
The majority of absorption occurs here.
The liver and pancreas help the small intestine to maximize absorption.
The small intestine is broken down into three parts:

39. Human Digestive System
Duodenum
Bile enters through the bile duct. It breaks down fats.
The pancreas secretes pancreatic juice to reduce the acidity of the chyme.

40. Human Digestive System
Jejunum
The jejunum is where the majority of absorption takes place.
It has tiny finger-like projections called villi lining it, which increase the surface area for absorbing nutrients.

41. Human Digestive System
Each villi itself has tiny fingerlike projections called microvilli, which further increase the surface area for absorption.

42. Human Digestive System
Ileum
The last portion of the small intestine is the ileum, which has fewer villi and basically compacts the leftovers to pass through the caecum into the large intestine.

43. Human Digestive System
The large intestine (or colon) is used to absorb water from the waste material leftover and to produce vitamin K and some B vitamins using the helpful bacteria that live here.

44. Human Digestive System
All leftover waste is compacted and stored at the end of the large intestine called the rectum.
When full, the anal sphincter loosens and the waste, called feces, passes out of the body through the anus.

45. Chemical Digestion

46. Introduction
Food cannot be broken down into small enough nutrients by physical digestion alone.
Special enzymes in our body help chemically break down food into small nutrients.

47. Magic School Bus – “For Lunch”

48. Enzymes Enzymes are special proteins made at ribosomes.
There are different classes of enzymes:
Carbohydrases break down carbs
Proteinases break down proteins
Lipases break down lipids.

49. Enzymes
These enzymes are secreted into the digestive system by special groups of secretory cells called glands.
Glands are usually connected to the digestive system through special tubes called ducts.

50. Enzymes
The item that an enzyme breaks down is called a substrate. The enzyme is not changed at all during this process.
Every enzyme performs best under its own optimal conditions.
This depends on temperature, pH and the presence/absence of certain ions or vitamins and minerals.

51. The Mouth Three salivary glands produce saliva which contains:
Water and mucous: lubricates the food
Sodium bicarbonate: reduces the acidity of the bolus
Salivary amylase: enzyme that begins to break down carbohydrates

52. The Stomach
Hydrochloric acid (HCl) kills off any invading bacteria or viruses.
The enzyme pepsin breaks down proteins.
The enzyme lipase breaks down lipids.
Mucus protects the lining of the stomach from being eaten away by the acid.

53. The Pancreas Produces and releases into the small intestine:
Enzymes that act on proteins, carbohydrates, and fats.
Bicarbonate solution to raise the pH of the chyme.
Produces and releases into the blood stream:
Insulin that converts glucose to glycogen, which gets stored in the body cells for later use.

54. The Liver Makes bile, which aids in fat digestion
Most of the glycogen is stored here
Vitamins A, D, E, K are stored here
Detoxifies poisons that are ingested (including ethanol)‏
Cirrhosis: breakdown of liver cells due to high levels of poisons.

55. The Gall Bladder Stores the bile produced in the liver.
Releases bile into the small intestine.
Illnesses of the gall bladder include
Gall stones: crystals of bile salts around cholesterol.
Jaundice: collection of bile pigment in blood.

56. Digestion and Homeostasis
A large meal activates receptors that churn the stomach and empty it faster.
If the meal was high in fat, digestion is slowed, allowing time for the fat to be broken down.
Hence why we feel fuller after eating a high fat meal.

57. Digestion and Homeostasis
The endocrine, nervous, digestive and circulatory systems all work together to control digestion.
Before we eat, smelling food releases saliva in our mouths and gastrin in our stomachs which prepares the body for a snack.
The Hormone Gastrin

58. Hormones
Hormones are chemical regulators, they also help control digestive enzymes.
The hormone gastrin stimulates the digestive glands around the stomach.
The hormone secretin stimulates the pancreas to release its enzymes which help neutralize the stomach contents as they enter the small intestine.

59. Learning Check Pg