1. 2.2 The Digestive and Excretory Systems
Nutrients are substances the body requires for energy, growth, development, repair, or maintenance.
We get nutrients from what we eat and drink.
Four Food Groups
Grain products
Vegetables and fruit
Milk products
Meat and alternatives
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2. Types of Nutrients Carbohydrates Proteins
The bodies quickest source of energy
Examples include: rice, vegetables, cereal, and bread
Proteins
Used to build parts of your bodies muscles, skin, hair, and nails
Examples include: fish, meat, eggs, nuts, soy products
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3. Types of Nutrients Fats Minerals and Vitamins
Used to build cell membranes and can be stored for future energy.
Examples include: butter, vegetable oil, and meat
Minerals and Vitamins
Needed in small amounts to perform various body functions
Two common minerals and vitamins are calcium and vitamin D
Water is not a nutrient but is necessary for life!
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4. The Four Stages of Digestion
The process in which food is broken down, nutrients are absorbed, and wastes eliminated is called digestion and occurs in the digestive system.
The fours stages of digestion are:
Ingesting
Digesting
Absorbing
Eliminating
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5. Stage 1: Ingesting
Ingesting, or ingestion, means to bring food into the body. This is the starting point of the digestive process.
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6. Each small piece of food is called bolus.
Stage 2: Digesting
The Mouth
Mechanical digestion occurs when your teeth and tongue break food into small enough pieces to swallow.
Each small piece of food is called bolus.
Chemical digestion occurs when saliva begins to break down the bolus.
An enzyme in your saliva begins to break down simple and complex carbohydrates.
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7. When you swallow, your food enters the esophagus.
Stage 2: Digesting
The Esophagus
When you swallow, your food enters the esophagus.
The esophagus is a long muscular tube that carries food to your stomach.
The bolus is pushed through the esophagus in a process called peristalsis.
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8. Inside the stomach is gastric juice, which is very acidic.
Stage 2: Digesting
The Stomach
Inside the stomach is gastric juice, which is very acidic.
The stomach walls are lined with mucus to protect the tissue from being damaged by the acid.
An enzyme called pepsin, present in gastric juice, breaks down protein.
The bolus that enters your stomach breaks down into a liquid called chyme.
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9. The first metre of the small intestine is called the duodenum.
Stage 2: Digesting
The Small Intestine
The first metre of the small intestine is called the duodenum.
The pancreas adds enzymes that help break down the carbohydrates, protein, and fat in the chyme.
The liver produces bile which is stored in the gall bladder.
Bile breaks the globs of fat into smaller droplets.
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10. The Small and Large Intestine
Stage 3: Absorbing
The Small and Large Intestine
Absorption is the process in which nutrients and water are absorbed by the small and large intestine.
The small intestine is covered with villi to help increase the rate at which nutrients are absorbed.
The large intestine absorbs water and some minerals.
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11. Liquid and gas wastes are removed by your excretory system.
Stage 4: Eliminating
Any solid material, undigested by the end of the large intestine is called feces.
Feces are stored in the rectum until they are eliminated through the anus.
Liquid and gas wastes are removed by your excretory system.
The main organs in your excretory system are your kidneys and your bladder.
Two major wastes : Urea : Urea is the major waste resulting from protein metabolism, accounting for about half of total urinary wastes. Most of the urea is eliminated through urine, and thus the amount of urea in the urine is often used as a marker of protein intake.
Sodium : Sodium is an essential mineral, coming exclusively from food. It has a key role in maintaining body fluid volume. Sodium can also be eliminated through perspiration or bowel elimination, but the major part is through urination. The kidneys can adapt sodium elimination to a wide range of intakes, from virtually 0 to about 25g per day
›› In a modern diet comprising many processed foods sodium intake largely exceeds our daily requirements, and most dietary sodium must be excreted in urine. That’s why it is sometimes used as an indicator of excess sodium intake ! Other waste products are also excreted, but in a smaller proportion: Ammonia : comes mainly from protein metabolism.
Uric acid : comes from the breakdown of compounds such as proteins that are ingested through foods.
Oxalate : part of the oxalate comes directly from food but the major part is a by-product of other substances such as vitamin C.
Minerals : calcium, magnesium, potassium, phosphorous… Their excretion is regulated by kidneys, depending on the internal mineral balance.
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12. Eating Disorders
Anorexia nervosa is a disorder when a person severely restricts what they eat.
Bulimia nervosa is a disorder when a person eats large amounts of food and then vomits or takes laxatives to get rid of the food before it is completely digested.
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Take the Section 2.2 Quiz
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