Biology Week 27 - Digestion and Excretion

Day 1 | Day 2 | Day 3 | Lab | Weekly Quiz

  • Digestion
  • Physical digestion
  • Chemical digestion
  • Nutrients
  • Nutrition
  • Carbohydrates
  • Sugar
  • Starch
  • Proteins
  • Amino acids
  • Fats
  • Saturated
  • Unsaturated
  • Polyunsaturated
  • Vitamins
  • Minerals
  • Water
  • Dehydration
  • Supplements
  • Allergies
  • Calories
  • Food calorie
  • Alimentary canal
  • Mouth
  • Saliva
  • Salivary amylase
  • Esophagus
  • Peristalsis
  • Stomach
  • Gastric glands
  • Cardiac sphincter
  • Pyloric sphincter
  • Small intestine
  • Duodenum
  • Jejunum
  • Ileum
  • Large intestine
  • Colon
  • Liver
  • Bile
  • Gallbladder
  • Pancreas
  • Excretion
  • Urea
  • Kidneys
  • Lungs
  • skin

Digestion and Excretion

click to find the answer to today's question What food group provides most of the body's energy?

Digestion - the two-part process that changes food into a form usable by body cells. link to an Internet Website

The average human male will eat about
50 tons of food during his lifetime!

Physical digestion breaks large pieces into smaller ones.
Most physical digestion occurs in the mouth.
human tooth structure

Adult humans have 32 teeth. link to a local picture link to an Internet Website link to an Internet Website

Parts of a tooth:

Chemical digestion breaks complex chemicals into simple ones.
Chemical digestion begins in the mouth and continues in the stomach.

click for a career
All foods link to an Internet Website contain nutrient link to an Internet Website molecules that provide energy and material for growth.

Teenagers + junk food link to an Internet Website = good nutrition. link to an Internet Website

Is a vegetarian diet link to an Internet Websitea healthy diet? link to an Internet Website

Fast food restaurants link to an Internet Websiteand the food pyramid. link to an Internet Website

The chemical composition of your bodylink to a local webpage includes most elements found in the earth's crust.

The following are the basic food nutrient groups:

Dietary Supplements: link to an Internet Website The Food and Drug Administration defines a dietary supplement as "any product taken by mouth that contains a so-called "dietary ingredient" and its label clearly states that it is a dietary supplement". The "dietary ingredients" in dietary supplements may include vitamins, minerals, herbs, and amino acids as well as substances such as enzymes, organ tissues, metabolites, extracts or concentrates. Dietary supplements can be found in many forms such as pills, tablets, capsules, liquids or powders. They must be identified on the label as a dietary supplement.

Food Allergies: link to an Internet Website One estimate suggests that approximately 7.5% of the human population may be allergic or have other forms sensitivity to a particular food or component of a food. Some may have a mild reaction while the reaction in others may be severe and require medical attention.

The energy available in food is measured in calories, a unit of heat. In chemistry and physics, a calorie is defined as the amount of heat needed to raise the temperature of one gram of water by one Celsius degree.

the key points to useful information on this page
A food calorie link to an Internet Websiteis actually a kilocalorie - the amount of heat needed to raise the temperature of 1000 grams of water by one Celsius degree. Since the density of water is one gram per cubic centimeter, 1000 grams of water is equal to a volume of 1000 cubic centimeters, or one liter.

Day 1 Assignmnet - Digestion and Excretion (Test Your Concept Understanding)

  1. Which group of food nutrients is most easily broken down by digestion?
  2. Which type of vitamins are stored in the body?
  3. How much gold is found in the human body?
  4. How many teeth are normally found in the lower jaw of a human adult?
  5. What is your favorite food that would be considered a carbohydrate?
  6. What is your favorite food that would be considered a protein?

Day 2

click to find the answer to today's question How long does food stay in your stomach?

Digestion occurs in the gastrointestinal tract, also known as the alimentary canal. Food remains in this "tube" while it passes through the body.

While individual metabolism rates are different, food generally takes from 18 to 20 hours to pass through the alimentary canal.

Organs of Digestion
link to an Internet Website link to an Internet Website

  • Mouth (15cm) - both mechanical and chemical digestion begin in the mouth. While the teeth physically break down food into small particles, saliva begins to mix with the food. Saliva is a mixture of water, mucus, and the digestive enzyme called salivary amylase. The mucus in saliva softens and lubricates food and helps hold the food together. The salivary amylase begins the chemical digestion of carbohydrates by breaking down starch into the disaccharide maltose.
  • Esophagus (50cm) - this muscular tube connects the mouth with the stomach. Food passes through this tube by rhythmic muscular contractions and relaxations called peristalsis.
  • Stomach (30cm) - The average adult stomach stretches to hold from two to three pints and produces about the same amount of gastric juices every 24 hours. Both mechanical and chemical digestion occur in this J-shaped elastic bag located in the upper left side of the abdominal cavity, just below the diaphragm.

    The outer walls of the stomach are composed of three layers of muscle - a circular layer, a longitudinal layer, and a diagonal layer. Together, these muscles twist and turn the stomach.

    The inner lining of the stomach is a thick, wrinkled mucous membrane dotted with gastric pits. These pits are the open ends of gastric glands, some of which secrete mucus, while others secrete digestive enzymes or hydrochloric acid into the stomach.

    The stomach has a band of circular muscle at each end regulating the flow into and out of the stomach. When the cardiac sphincter is closed, food cannot reenter the esophagus. The pyloric sphincter, located at the lower end of the stomach, opens to release food a little at a time. Food usually remains in the stomach for three to four hours.

  • Small intestine (5.75m) - chemical digestion is completed and nutrients are absorbed into the blood stream in the small intestine. Secretions from the liver and pancreas, as well as enzymes from the intestine lining break down peptides into amino acids, disaccharides into monosaccharides, and fats into glycerol and fatty acids.

    The lining is highly folded to form microscopic finger-like projections called villi, pictured here, which increase the surface area to help with absorption. The process is so efficient that in a normal adult, over 95% of ingested carbohydrates and proteins are absorbed.

    There are three parts to the small intestine based on function:

    • Duodenum (25cm) - The receiving area for chemicals and food from the stomach.
    • Jejunum (2.5m) - Where most of the nutrients are absorbed into the blood.
    • Ileum (3m) - The remaining nutrients are absorbed before moving into the large intestine.
  • Large intestine, or Colon (165cm) - consists of three sections. Food enters the assending colon, then travels across the body in the transverse colon, then down the descending colon.

    About 9 liters of water enters the small intestine each day, but only 1.5 liters of water is present in the material that enters the large intestine. Minerals, vitamins, and the remainder of the water are absorbed into the blood stream from the large intestine. The first half of the colon absorbs fluids and recycles them into the blood stream. The second half compacts the wastes and secretes mucus which binds the wastes into feces.

  • The total length of the digestive system in an average adult is 8 1/2 meters.

Digestion is also aided by enzymes from these organs:

Smoking and your digestive system. link to an Internet Website


Day 2 Assignmnet - Digestion and Excretion (Test Your Concept Understanding)

  1. Although the liver, gallbladder, and pancreas are not part of the "food tube", they are important to the digestion of food. What purpose do each of these serve in digestion?
  2. Approximately how long is the gastrointestinal tract of a human adult?
  3. What causes the condition known as "heartburn"?
  4. The bacteria E.coli is commonly found in the human intestines. What role does this bacteria play?

Day 3

click to find the answer to today's question What are the main organs of excretion in the body?

Excretion - the process of removing metabilic wastes from the body.

Organs of excretion:

Day 3 Assignmnet - Digestion and Excretion (Test Your Concept Understanding)

  1. Explain the difference between excretion and elimination.
  2. The capillary bed of the kidneys filters about 125 milliliters of fluid from the blood each minute. Calculate how many liters of fluid the kidneys filter in twenty four hours.
Blood easily transmitts disease from one person to another Most products of excretion and elimination can transmit disease organisms if proper hygene is not practiced.

Research Links:

Biology Class










Carbohydrates provide most of your body's energy.










Food stays in the stomach three or four hours.










The kidneys are the main organs of excretion in the body.