1. Digestion and Nutrition
UNIT 2
Digestion and Nutrition

2. Human Digestive System Function
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.
This breakdown occurs because of a various mechanical and chemical processes. We need to digest food in order for us to get the energy (ATP) that is in it, into a useful form.

3. Introduction to Digestion
The pathway that food takes as it moves through the body during digestion is known as the digestive tract or the alimentary canal.

5. Five Stages of the Digestive Process
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.
Absorption – passage of the molecules into the bloodstream.
Elimination – removal of undigested food and waste.

6. Structures in the Human Digestive System
Food enters the alimentary canal through the mouth opening; the chamber that it enters is called the oral cavity.

7. *Often referred to as mastication*
The tongue helps to move the food around in the oral cavity, pushing the food between the teeth, which chew the food. The tearing and biting of food breaks it into smaller bits before it is swallowed. This is a very important step in human digestion, known as mechanical digestion.
*Often referred to as mastication*

8. The food is also lubricated in the mouth by the saliva, which is produced by three sets of salivary glands. These glands send their secretion, saliva, through small ducts into the oral cavity. Not only does saliva lubricate the food, it also begins to chemically digest carbohydrates in the food you have eaten.

9. There are 3 pairs of salivary glands that secrete their fluids into the mouth:
The Parotid Gland is located just in front of and slightly below the level of the opening of the ear. This is the largest of the glands which secretes salts, an enzyme (salivary amylase) and a watery serous fluid into the mouth through the parotid duct.
The Submaxillary Gland is located below the parotid gland near the angle of the lower jaw. It produces some serous fluid and some mucous and delivers them to the mouth through the submaxillary duct.

10. The Sublingual Gland is located under the tongue and secretes mostly thick stringy mucus, salts and salivary amylase. These substances are emptied into the mouth through the submaxillary duct.
Since the salivary glands deliver their secretions through ducts, they are called exocrine glands.
Saliva flows from the salivary glands at all times, keeping your mouth moist. However, the sight or smell of good food may cause your mouth to "water". Of the approximate 1L of saliva produced every day, 99% of that is water, with the remainder being mucus and enzymes. This water moistens and dissolves particles of food while mucous helps make chewed food smooth and easy to swallow.

12. Submaxillary

13. The Pharynx
The pharynx opens to two tubes that descend down into the neck.
Trachea, or windpipe, connects the pharynx to the lungs and is found in front of the esophagus.
Esophagus is the digestive tube that connects the pharynx to the stomach.

14. Uvula
a small mass of tissue that hangs down in the back of the mouth, and moves up to close off the openings to the nasal cavity when food is swallowed into the esophagus.

15. Soft Palate the roof of the pharynx in the back of the mouth
this soft tissue functions in closing off the openings to the nose and ears as food is swallowed.

16. Epiglottis
a thin, flaplike piece of cartilage that closes over the trachea opening, preventing food that is swallowed from entering the trachea
lies above the esophagus and diverts food into that tube
part of the larynx or voicebox

17. The Esophagus
Food that has been chewed and lubricated is ready to be swallowed. The bolus (ball of food) is swallowed and enters the esophagus or food tube, which lies behind the trachea and runs down the centre of your neck. The esophagus ends when it joins the stomach.

19. Food moves down your esophagus, pushed through by the rings of smooth muscle found in the walls of the esophagus. These muscles involuntarily contract and relax in waves as they push the food along. This rhythmic contraction is called peristalsis and it continues through the entire length of the digestive tract.
*involuntary - controlled subconsciously
- will happen without you having to think about it.

21. Peristalsis Videos Review of Swallowing
Peristalsis Throughout the Body
NOT FOR THE FAINT OF HEART
Review of Swallowing

22. The Stomach
Cardiac
sphincter

23. Cardiac sphincter muscle
Close off the opening to the stomach and serve to control the movement of swallowed material into the stomach.
Keeps partially digested food and stomach acid from working their way back up the esophagus, called reflux or better known as heartburn.

24. What Happens in the Stomach?
Three layers of muscle in the wall of the stomach contract and relax to mechanically break down the stomach's contents.
The bolus is churned and mixed with stomach secretions.
These secretions and the stomach's mechanical churning of the food act to further soften it and break it up into smaller pieces, taking on a soup-like consistency.

25. Chyme term used for food after the stomach has digested it.
Rhymes with time (the h is silent)
About 9L of chyme enters your small intestine every day.

26. Hydrochloric Acid
This powerful acid protects us from harmful bacteria-what we may ingest with foods is fried by this strong acid.
HCl also helps keep the three pounds of bacteria found in the colon from moving up into the small intestine.
If this happens, "bad" bacteria and yeast can establish a foothold in the intestine, resulting in less than optimum absorption of nutrients and inflamed intestines.

27. HCL is paramount in our digestive process
HCL is paramount in our digestive process. It begins the digestion of protein and stimulates the pancreas to produce digestive enzymes. When we don’t digest foods well, there may be three results:
We don't get the nutrition we need
Our food passes through our bodies and into our bloodstream too quickly and becomes seen as invaders (allergens) in our body.
Food lingers and becomes a form of "bad" bacteria, which can make us very sick.
Cheeseburger in HCl

28. Pepsin
It is not an enzyme but a forerunner of the enzyme pepsin. Once the pH level of the stomach reaches a level of 2 or lower, pepsinogen is converted into pepsin, an active enzyme which begins the breakdown of proteins.

29. Mucous
The stomach is lined with mucous that coats the cells lining the stomach and protects them from the digestive action of the enzyme pepsin.
Unfortunately these protective measures do not always work, and the stomach starts to digest itself. The result is a peptic ulcer.

30. The stomach is primarily an organ of digestion.
The stomach is NOT an organ of absorption.

31. The Small Intestine
The small intestine lies between the stomach and the large intestine.
In adult humans, the small intestine is 5-6 metres in length, has a surface area of a m long tube and takes up a significant portion of the abdominal cavity.
The main processes of digestion and absorption are accomplished by the small intestine.

33. Pyloric Sphincter Located between the stomach and the small intestine
Controls the movement of the chyme into the small intestine
The stomach pushes chyme into it by peristalsis.

34. Digestion in the Small Intestines
The digestion that occurs is primarily chemical, most of which occurs in the duodenum.
The enzymes that act chemically on food to digest it come from the small intestine and the pancreas.
The pancreatic duct connects the pancreas with the small intestine and effectively carries pancreatic juice

35. The small intestine also possesses intestine glands that produce its own secretions; intestinal juice.
Peristalsis continues in the small intestine, churning and pushing the partially digested food through until it reaches the large intestine.

36. The Importance of Bile
In the small intestine, large lipid molecules (fats) are physically broken down or emulsified by bile (this is a mechanical process).
Droplets of lipids are formed that are more easily digested.

37. Bile is a product of the liver and is stored temporarily in the gall bladder.
The bile duct carries bile into the duodenum of the small intestine where it acts to emulsify fats, breaking them up into tiny droplets.

39. Villi Facilitates the absorption that occurs in the small intestine
Tiny finger-like projections that line the walls of the small intestine.

40. Capillaries uptake those food molecules and they are transported to other structures in the body via the blood.
The primary types of food molecules that are absorbed at this point are derived from the digestion of carbohydrates, proteins, and lipids.

42. The Large Intestine
Once the digestion of food in the small intestine is essentially finished, the remaining material passes into the large intestine or colon.

43. It extends from the end of the small intestine to the anus and is 1
It extends from the end of the small intestine to the anus and is 1.5 metres long. The large intestine is shorter than the small intestine but is larger in diameter.
There are three portions of the large intestine. These three sections create an upside-down U-shape and surround the small intestine.

44. Direction of food

45. What is left of the food after digestion is moved through the large intestine with the help of peristalsis. In the large intestine, water and essential minerals are reabsorbed into the bloodstream. Fibre, bacteria and other undigested products are then excreted as feces through the anus by peristalsis.

46. Appendix
A small pouch located at the point where the small intestine meets the large intestine.
This organ apparently serves no function in humans unless it is infected.
An infected appendix could rupture and release the infection into the body cavity which can be fatal.

47. Rectum Located at the end of the large intestine.
Primarily acts to store the feces before it is excreted by muscular contractions.
The anus is the opening of the rectum to the outside of the body.
The movement of feces to the exterior is controlled voluntarily by the external anal sphincter.
Digestion

48. Chemical Digestion
As we have seen, the organs in the digestive system secrete many different substances that play a role in the chemical digestion of food.

49. Chemical Digestion Aids in preparing food particles for absorption.
Takes place through the action of enzymes.
Large food molecules are chemically changed into smaller molecules
The types of nutrients that are digested through mechanical and chemical action are carbohydrates, proteins, and lipids.

50. Carbohydrates Made up of carbon, hydrogen, and oxygen
Quick sources of energy and include both simple molecules (sugars) and complex molecules (starches)
Common food sources are breads, pasta, and fruit

51. Proteins
Large complex molecules that contain carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulphur.
Serve as the structural framework of most living tissue and also serve as enzymes, but are not usually used as an energy source.
Made up of smaller molecules called amino acids.
Common food sources include meat, eggs, and nuts.

52. Lipids Make up fats, oils, and waxes.
Contain carbon, hydrogen and oxygen.
Capable of storing great amounts of energy in their chemical bonds.
Common food sources include margarine, cooking oil, and animal fat found in meat.

53. Enzymes
Biological catalyst that can speed up chemical reactions without being altered in the process.
Allows for the reaction to occur at a faster rate.

54. Digestive Enzymes
Enzymes are very specific; they only act on certain molecules called a substrate. Each type of enzyme is very specific in terms of which substrate it will act on. The names for enzymes start with the name of the substrate involved and end in "-ase". For example, an enzyme that acts on a protein molecule is a protease. An enzyme that acts on a carbohydrate molecule is a carbohydrase. And an enzyme that acts on a lipid molecule is a lipase.

55. An analogy that is often used to understand enzyme action is the “lock and key" concept in which the substrate acts as the lock and the enzyme is the key.

56. The key is unchanged but the lock has been changed, “opened”.

57. Enzymes
Animation of an Enzyme

58. Chemical Digestion in the Human Digestive Tract
Location
Secretion
Type of Enzyme
Action
Mouth
Saliva
Amylase
Begins digestion of starch to simple sugars.
Stomach
Gastric Juice
Protease
Begins digestion of proteins.

59. Location
Secretion
Type of Enzyme
Action
Small Intestine
Pancreatic Juice
Amylase
Completes digestion of starch to simple sugars.
Protease
Continues digestion of proteins.
Lipase
Completes digestion of lipids to fatty acids and glycerol with the help of bile.
Intestinal Juice
Completes digestion of proteins to amino acids.
Carbohydrase
Completes digestion of carbohydrates to simple sugars.

60. In addition to carbohydrates, proteins, and lipids, nucleic acids are also nutrient molecules that are broken down in the digestive system. When nucleic acids are broken down chemically, the results are nucleotides, which contain nitrogen, phosphorus, and sugars.

61. Once nutrient molecules are broken down chemically and mechanically, they are absorbed into the circulatory system. Most absorption occurs in the small intestine except vitamins, minerals, and water are absorbed in the large intestine.

62. Factors that Affect Enzyme ActionpH
The pH of a solution refers to how acidic or basic it is.
An enzyme that is structurally changed as a result of pH is said to be denatured; which leads to a loss of enzymatic activity.

63. The protease in the stomach, pepsin, is activated by this acidic environment and becomes deactivated when it enters the basic environment of the small intestine
Less acidic environment of the small intestine allows the enzymes produced by the small intestine and pancreas to be more effective in digestion.

64. Surface Area
When a food particle is mechanically broken down by chewing it into a number of smaller particles, the total surface area of exposed particles increases.
An increased surface area allows more enzymes to act on the food particles.

65. Coenzymes
Small organic molecules that are not proteins that help to facilitate the enzyme-substrate connection and are often produced from various vitamins
They are located at the active site of the enzyme molecule and facilitate the "lock and key" action of the enzyme and substrate molecules.
They are not themselves affected by the action of the enzyme on the substrate molecule.

66. Inhibitors
Compete with substrate molecules for the active sites of the enzymes.
Binds to the enzyme, rendering the enzyme ineffective on the substrate molecule that it was designed to act on.

67. Temperature
Most reactions in the human body that involve enzyme activity occur within a fairly small temperature range — usually from about 30°C to 40°C .
Temperatures outside of this range can cause denaturation of the enzyme.

68. Enzymes are very important in the human digestive system
Enzymes are very important in the human digestive system. Their production and accumulation in the body are carefully controlled so that homeostasis is maintained.

69. The Liver
Almost all the blood circulating from the intestines to the heart passes through the liver.
Everything you eat that gets into the bloodstream passes through your liver.
The liver then either stores nutrients or breaks them down even more.
The liver transforms nutrients into proteins, fats, and cholesterol and stores vitamins (A, D, K, and B12), minerals, and carbohydrates.

70. The liver also plays the role of a filtering system
The liver also plays the role of a filtering system. Toxic substances, including alcohol, are transformed into less harmful substances.

72. The Role of the Liver in Homeostasis
Recall: Glucose is necessary for cells to produce ATP, the molecule that stores energy. The amount of ATP that the body needs at any one time changes; therefore, the body needs to be able to store glucose when it is not needed, but release glucose when it is needed.

73. Two hormones responsible for controlling the concentration of glucose in the blood are insulin and glucagon, which are produced in the pancreas.
The liver also plays an important role in blood glucose control. It is here that excess glucose is stored in the form of glycogen.

74. When you eat a meal, blood glucose levels start to rise
When you eat a meal, blood glucose levels start to rise. When they reach a certain concentration, receptors in the pancreas stimulate the production of insulin. This hormone reaches the liver, which then converts blood glucose into glycogen. Blood glucose levels drop and return to a normal level.

75. If blood glucose levels drop below a certain level, receptors in the pancreas stimulate the production of glucagon. This hormone reaches the liver, which then converts glycogen into glucose. Glucose is released into the bloodstream and blood glucose levels rise until they return to a normal level.

76. Nutrients
There are six basic types of nutrients used by the human body.
carbohydrates, lipids, proteins, vitamins, minerals, and water
Some of the uses that your body makes of nutrients are functional and others are structural in nature.

77. Carbohydrates Used by the cells of the body to produce energy.
The human body cannot produce its own carbohydrates and must rely on eating other organisms to acquire them.
Primary source of energy for humans, supplying 50 to 80% of the total energy required.
Provide short-term energy to cells through the process of cellular respiration.

78. Monosaccharides Simple single sugars
Most common is glucose which provides energy for cellular respiration and the production of ATP and fructose which is found in fruit

79. Glucose

80. Disaccharides Double sugars
Made by joining together simple sugars with chemical bonds.
Most common is sucrose (white table sugar), lactose (dairy products)

81. Sucrose

82. Polysaccharides
Complex sugars made of many simple sugars joined by chemical bonds.
Several hundred glucose molecules join together to form starches which are the primary form of storage carbohydrate used by plants.
Cellulose, which is found in the cell wall of plants, is the fibre we need in our diets; which our digestive system requires to function correctly.

83. Simple Carbohydrates
Usually sweet-tasting like cookies, candy, pop, pastries, fruits, and juices.
Good sources of carbohydrates, but do not always contain vitamins or minerals.
Considered “empty-carbs”

84. Complex Carbohydrates
Starchy carbohydrates take longer to be digested than simple carbohydrates and therefore provide a more long-term source of energy for the body.
Complex carbs, are found in breads, pasta, rice, and potatoes and most vegetables like corn, tomatoes, carrots, and lettuce

85. Lipids (Fats)
are only used for energy when the supply of carbohydrates in the bloodstream is low
difficult to break down
stored source of excess energy for the body
about twice as energetic as one gram of carbohydrate

86. important in helping the body absorb vitamins effectively
key structural components of cell membranes, a form of insulation for the body and serve as protection for delicate vital organs
the raw material from which hormones are produced
an important component in the transmission of nerve impulses in the nervous system

87. Cholesterol Fat molecule that occurs naturally in the body
Produced by the liver and is transported by the blood to cells
Found in all animal products
Very important component of cell membranes.
The body processes cholesterol in the diet in different ways, depending on what type of food contained the cholesterol that was ingested.

88. LDL (“bad” cholesterol)
Low-density lipoprotein
Can accumulate on artery walls and restrict blood flow.
Liver maintains a "normal" level of cholesterol by removing excess LDL from the blood

89. HDL (“good” cholesterol)
High-density lipoprotein
Lowers blood cholesterol by carrying LDLs back to the liver which can break down the LDL molecule
The level of HDL in the blood can be increased if you decrease the amount of saturated fat in your diet and if you increase your physical activity.
HDL can reduce the risk of heart attack and stroke

90. Comparison between Unsaturated and Saturated Fats
Unsaturated Fats
liquid at room temperature
usually come from plants
oils
Example:
olive oil
sunflower oil
corn oil

91. Saturated Fats solid at room temperature come from animals
linked to heart disease
more difficult for the body to break down
can accumulate on the inside of blood vessels, causing circulatory problems.
Example: fat found in beef, pork, chicken, and dairy products made from milk, such as butter

92. It is recommended that no more than 30% of your total energy intake should be in the form of lipids, since lipid molecules store about twice as much chemical energy as carbohydrate molecules.

93. Proteins Primary structural component of all cells
Broken down by your digestive system into amino acid molecules which are then rebuilt into other proteins.
Muscle, cartilage, ligaments, skin, and hair are all examples of protein molecules.

94. Smaller protein molecules also play vital roles as hormones, antibodies, enzymes, and hemoglobin.
Vary in size and shape which allows for incredible diversity of functions performed by proteins

95. Amino Acids 20 amino acids
9 of them cannot be made by the human body and are referred to as the essential amino acids because they must be eaten.
All 20 "building blocks" allow the synthesis of all of the many proteins that your body manufactures.

96. Glycine

97. Food Sources of Proteins
Complete Proteins
contain all of the essential amino acids
beef, chicken, fish, eggs, milk, and many animal products

98. Incomplete Proteins do not have all of the essential amino acids
vegetables, fruits, grains, seeds, and nuts

99. It is recommended that you consume 0. 8 - 1
It is recommended that you consume grams of protein per kilogram of body weight. People who are on a vegetarian diet need to pay special attention to the foods they eat to make sure that they acquire adequate amounts of all amino acids.

100. Vitamins
Organic substances (must contain a carbon chain) that are needed in very small amounts
Part of the structure of many enzymes
If your diet is deficient in a certain vitamin, the result could be an enzyme deficiency that can in turn cause serious health problems

101. Are chemicals that are necessary for normal growth and metabolism.
Some vitamins are required for the chemical reactions that result in the release of energy from carbohydrates, fats, and proteins.

103. Fat-soluble vitamins (A, D, E, and K)
are not as readily excreted from the body
stored in the liver
Water-soluble vitamins (C, and the B vitamins)
can become depleted more quickly leading to a deficiency
must be included regularly in your diet

105. Minerals
Unlike vitamins, minerals are inorganic — that is, they are not based on a carbon chain. Most minerals are molecules of a single element. Minerals do not provide energy for the body, but they do play very important roles in many cellular reactions. For example, minerals are vital in maintaining nervous system functions, water balance, and skeletal health.

106. 16 Essential Minerals
Sodium is found in table salt and helps maintain proper blood pressure.
Potassium is found in bananas and keeps nerves and muscles working properly.
Calcium is found in dairy products and is needed to build strong bones.
Iron is found in red meats and wholegrain vegetables; it is very important in the production of red blood cells.

107. Water
Water is an essential component of cytoplasm — the intracellular fluid that makes up all cells.
Water is an important solvent because most chemical reactions in the body occur between molecules that are dissolved in it.
Water is also an important lubricant and bathes body cells.

108. *without water, many life functions would not occur*
Water is a primary component of blood and transports vital nutrients and unneeded wastes throughout the body.
Water also serves an important role in temperature regulation.
*without water, many life functions would not occur*

109. Water is acquired in many ways
Water is acquired in many ways. Drinking water is the most obvious way that you obtain water. However, many foods have a high water content, such as fruit and vegetables. Also, many cellular processes involve the production of water. For these reasons, it is suggested that you drink about 8 cups of water or other non- caffeinated fluids per day to maintain adequate hydration.

110. Dietary Decisions

111. Guidelines for Healthy Eating
Enjoy a variety of foods.
Emphasize whole grain cereals, breads, other whole grain products, vegetables, and fruit.
Choose lower-fat dairy products, leaner meats, and foods prepared with little or no fat.
Achieve and maintain a healthy body weight by enjoying regular physical activity and healthy eating.
Limit salt, alcohol, and caffeine.