Biology Week 27 - Digestion and Excretion
Day 1 |
Day 2 |
Day 3 |
- Physical digestion
- Chemical digestion
- Amino acids
- Food calorie
- Alimentary canal
- Salivary amylase
- Gastric glands
- Cardiac sphincter
- Pyloric sphincter
- Small intestine
- Large intestine
Digestion and Excretion
||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.
||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.
Adult humans have 32 teeth.
- 8 Incisors - teeth with a single cutting edge.
- 4 Canines - round teeth for puncturing.
- 8 Premolars - teeth with several cutting edges for shredding.
- 12 Molars - teeth with a flat surface for grinding.
Parts of a tooth:
- Enamel - the smooth, hard covering.
- Dentine - the porous "bone" of the tooth.
- Pulp - the cavity containing blood vessels and nerves.
- Cementum - binds the enamel to the dentine.
Chemical digestion breaks complex chemicals into simple ones.
Chemical digestion begins in the mouth and continues in the stomach.
The following are the basic food nutrient groups:
- Carbohydrates - compounds composed of carbon, hydrogen, and oxygen. These substances are fairly easily broken down and provide most of the body's energy for cellular respiration.
- monosaccharides - simple sugars such as glucose (dextrose) that can be absorbed directly into the bloodstream.
- disaccharides - sucrose (cane sugar) and lactose (milk sugar) are two monosaccharieds combined.
- polysaccharides - most of the starch in food is a polysaccharide composed of long chains of glucose molecules.
- Proteins - composed of long chains of amino acids these compounds are the major structural materials for cell growth and repair.
- Fats - the body stores excess food as fats. Most of the fats found in foods are triglycerides - composed of three molecules of fatty acids and one molecule of glycerol.
- saturated fats - solids at room temperature, found primarily in animal products.
- unsaturated fats - liquids at room temperature, found primarily in vegetable products.
- Vitamins - complex organic molecules that assist many chemical reactions within the body. With the exception of vitamin D, the body does not synthesize vitamins and must obtain them from food.
- fat-soluble vitamins: A, D, E, and K
- As fats are stored in the body, fat-soluble vitamins are stored with them. This allows the body to build up a reserve of these vitamins.
- water-soluble vitamins: B and C
- As water is excreted from the body, excess water-soluble vitamins are lost. For this reason, the body cannot build up a reserve of these vitamins.
- Minerals - inorganic substances required for the body to function normally. Plants absorb minerals from the soil. Animals get the minerals they need from those stored in plants they eat.
- Water - over half of your body weight is water. Its importance to the body cannot be over-stated. The chemical reactions within the body take place in water. Dehydration is a term referring to a multitude of cellular problems that develop as the amount of water in the body begins to get too low.
To avoid dehydration:
- Drink at least 8 glasses of water a day.
- Drink water regularly throughout the day, not all at once.
- Drink before you feel thirsty. Thirst is a sign that your body is already partially dehydrated.
- Drink extra fluids 30 minutes to 1 hour before exercise, then every 20 minutes during exercise to stay fully hydrated.
- All caffeine-free fluids help hydrate the body, but plain water is the best.
- Your body also gets water from foods like fruits and vegetables.
Dietary Supplements: 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: 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.
A food calorie is 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.
Carbohydrates and proteins contain 4 calories per gram.
Fats contain 9 calories per gram.
Day 1 Assignmnet - Digestion and Excretion (Test Your Concept Understanding)
- Which group of food nutrients is most easily broken down by digestion?
- Which type of vitamins are stored in the body?
- How much gold is found in the human body?
- How many teeth are normally found in the lower jaw of a human adult?
- What is your favorite food that would be considered a carbohydrate?
- What is your favorite food that would be considered a protein?
||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
- 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:
- Liver - Thirty per cent of the blood pumped through the heart in one minute passes through the liver to be cleaned. The liver is the largest gland in the body, weighing 21/2 to 31/2 pounds. The liver produces bile to be stored in the gallbladder.
- Gallbladder - Food passing into the small intestine causes the gallbladder to secrete bile into the duodenum. Bile helps liquify fats to ease their digestion.
- Pancreas - Pancreatic fluid is secreted into the duodenum. This fluid contains several enzymes needed to complete the digestive process. Here are a few of them:
- Sodium bicarbonate which changes the pH of the partially digested food from acid to base.
- Pancreatic amylase which completes the digestion of carbohydrates.
- Pancreatic lipase which breaks down fats into fatty acids and glycerol.
- Trypsin which splits proteins into peptides.
Smoking and your digestive system.
Day 2 Assignmnet - Digestion and Excretion (Test Your Concept Understanding)
- 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?
- Approximately how long is the gastrointestinal tract of a human adult?
- What causes the condition known as "heartburn"?
- The bacteria E.coli is commonly found in the human intestines. What role does this bacteria play?
||What are the main organs of excretion in the body?
Excretion - the process of removing metabilic wastes from the body.
Organs of excretion:
The main waste products eliminated by the body are carbon dioxide, CO2 from cellular respiration, and nitrogenous compounds from the metabolic breakdown of proteins.
The most common mammalian metabolic waste is urea, CH4N2O.
- Nitrogenous wastes are brought to the liver as ammonia, NH3 a chemical so toxic that it could not remain long in the body without harming cells.
- The liver removes ammonia from the blood and converts it into the less harmful urea.
the primary organs excretion, the kidneys play a vital role in maintaining the homeostasis of body fluids. They control the amount of ammonia, salt, and water in the blood.
the primary site of CO2 excretion, the lungs also carry out detoxification, altering harmful substances so they are not poisonous.
through perspiration, water, salts, and small amounts of urea are excreted from the body.
Day 3 Assignmnet - Digestion and Excretion (Test Your Concept Understanding)
- Explain the difference between excretion and elimination.
- 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.
Most products of excretion and elimination can transmit disease organisms if proper hygene is not practiced.
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.