Animal Nutrition

All living organisms need food. Even after you are fully grown, your body, just like any other machine, needs to make constant repairs to injured areas and must replace cells that have died. To make sure that the structure of your body is correct and strong, you must provide it a regular supply of the right building materials. Foods are the building materials for the body.


Classes of food

  • Carbohydrates
    Carbohydrates are organic chemicals containing only the elements carbon, hydrogen and oxygen. Carbohydrates are sugars and starches. These substances are used by your body to create energy. Carbohydrates are broken down into glucose or sugars that are used as fuel. Although all foods provide us with energy, carbohydrates are the cheapest and most readily available source of energy.
  • Proteins

Proteins contain the elements carbon, hydrogen, nitrogen and oxygen. Proteins are a major component of most tissues including muscles, bodily organs, and cells. Body protein is made from building blocks of amino acids. The human body can make most amino acids and use them to build proteins. Animal protein usually contains a relatively high amount of fat and very little fiber.

  • Lipids

Lipids contain the elements carbon, hydrogen and oxygen. Fats are also necessary for health. Fat is a component of all cell membranes, and is an important source of stored energy in your body. When you can’t avoid skipping a meal, your body uses fat for energy.

  • Vitamins

Vitamins are important for the cellular machinery of your body. They are chemical substances that help the body use energy, build proteins, make cells, and repair injuries. Vitamins are divided into two general categories: fat soluble and water soluble. The fat soluble vitamins are A, D, and E. The water soluble vitamins are Vitamin C and the B vitamins. Fresh food, however, generally has higher vitamin content than already prepared food.

  • Minerals

Minerals are also essential building blocks for your body, but do not provide calories or energy. The foods containing essential minerals also contain other energy supplying material.

  • Water

Water is essential for life. It is the single largest component of your body. Each and every day, you use water to metabolize your food, lose heat through sweating, and remove toxins in the urine. On average, an adult uses about 2 to 3 quarts a day just for perspiration and mixed with water, but no calories or fat.

Balance diet and special dietary requirements

A diet which contains all the basic class of food in the correct amount and proportion is called a balance diet. A balance diet for any individual person depends on the age, sex and life style /activity.


 The effects of malnutrition in relation to starvation, coronary heart disease, constipation and obesity

  • Malnutrition is a condition where certain nutrients of a balanced diet are missing, in excess, or taken in the wrong proportions.

E.g. Overconsumption of fatty foods is an example of malnutrition.

Coronary heart disease is less seen in third world countries but more in MEDC’s where over abundance of food intake is the problem. Coronary heart disease, as you will learn in Unit 5, speaking in terms of diet, is caused by an over-abundance of intake of fatty foods, and what happens is that the cholesterol and “bad” things deposit and eventually form a clog in the arteries, hence preventing proper blood flow in the body (more of this in Unit 5).

              Constipation is result of insufficient fiber in the diet.
Common causes

  • Lack of fiber intake.
  • Lack of water intake

Obesity A person is considered obese if his/her body weight is 20%above the standard body weight. Again, this is a problem that is more often seen in MEDC (More Economically Developed Countries), where an over-abundance of food intake is the problem. An over-abundance of calorie intake, increased dependence on fast food and sugary foods has accelerated the number of obese people.


  • Starvation is a pretty common concept that we are all familiar with. This is a problem occurring in many third world countries, where starvation occurs when a person has a severe deficiency of energy, nutrient and vitamin intake. Prolonged starvation may cause organ damage, and if not treated properly, death. Approximately 6 million people a year die of hunger.

Human Alimentary Canal

Human nutrition involves 5 basic stages. They are:

  1. Ingestion: it is a process of feeding or the intake of food into the altimetry canal through mouth.
  2. Digestion: it is the process by which food substances are converted into small and soluble substances.
  3. Absorption: it is a process by which digested food are taken into the blood stream.
  4. Assimilation: it is a process of using absorbed food in metabolic process.
  5. Egestion: it is removal of undigested food from the alimentary canal.

Human Alimentary Canal

The functions of the main regions of the alimentary canal

  • Mouth: food is mechanically digested here by cutting, chewing and grinding of teeth. Saliva is added, this contains amylase to being the digestion of starch.
  • Salivary Glands: These secrete amylase, which breaks down starch into maltose, so the substance can more easily be digested.
  • Oesophagus: boluses of food pass through by peristalsis, from mouth to stomach.
  • Stomach: Gastric juice added- contains protease to digest protein and hydrochloric acid to maintain pH 2 and kill bacteria
  • Small intestines:  After 1-2 hours a resulting thick liquid called chyme is produced. The chyme enters the duodenum, and is mixed with digestive enzymes in the pancreas. Eventually, this is passed down the small intestines.
  • Pancreas: Secretes pancreatic juice into the duodenum, also makes the hormone insulin and glucagon.
  • Liver: Makes bile, which is stored in gall bladder; bile contains salts that emulsify fats; digested food is assimilated here, e.g. glucose is stored as glycogen.
  • Ileum: digestion of food completed with the help of intestinal juice and absorption of all digested food takes place
  • Rectum: stores faeces until it is egested.
  • Anus: Stored feces are eliminated from the body through the anus, via the process egestion.

Structure of human tooth

The tooth has two anatomical parts. The crown of a tooth is that part of the tooth which is covered with enamel and this is the part usually visible in the mouth.The root is the part embedded in the jaw. It anchors the tooth in its bony socket and is normally not visible.

Structure of human tooth

Enamel: The hard outer layer of the crown. Enamel is the hardest substance in the body.

Dentine: Not as hard as enamel, forms the bulk of the tooth and can be sensitive if the protection of the enamel is lost.

Pulp: Soft tissue containing the blood and nerve supply to the tooth. The pulp extends from the crown to the tip of the root.

Cementum: The layer of bone-like tissue covering the root. It is not as hard as enamel.

Different types of human teeth – structure and function of teeth

Different types of human teeth

Type of teeth Structure Function
Incisor (4 in each jaw)


Chisel-shaped(sharp edge) Biting off pieces of food
Canine (2 in each jaw) Slightly more pointed than incisors Similar function to incisors and also helps in tearing flesh in carnivores
Premolar (4 in each jaw) Have 2 pointed cusps; have 1-2  roots Chewing and Grinding food
Molar (6 in each jaw) Have 4-5 cusps; have 2-3 roots. Chewing and Grinding food


Tooth decay

Tooth decay happens when the hard outer enamel of the tooth is damaged. This can happen when bacteria in the mouth convert sugars into acids that react with the enamel. Bacteria can then enter the softer dentine inside.

Causes of dental decay

  • Bacteria are present on the surface of our teeth. Food deposits and bacteria form a layer called plaque. Bacteria on the plaque feed on sugars, producing acid. This acid dissolves enamel, forming a hole.
  • Dentine underneath the enamel is softer – it dissolves more rapidly.
  • If the hole reaches the pulp cavity, bacterial infection can get to the nerve. This results in toothache and possibly, an abscess (an infection in the jaw).

Tooth decay and gum disease can be prevented

  • Avoid sugary food, especially between meals, so bacteria cannot make acid
  • Clean teeth regularly to remove plaque.
  • Use dental floss or a toothpick to remove pieces of food and plaque trapped between teeth.
  • Visit a dentist regularly so any tooth decay is treated early and any stubborn plaque is removed.


  Absorption of food

Absorption: Movement of digested food molecules through the wall of the intestine into the blood.

The inside wall of the small intestine need to be thin, with really big surface are. This allows absorption to happen quickly and efficiently. If the small intestine had a tick wall and small surface areas, lot of digested food might pass out of the body before it had a chance to be absorbed.

To get a big surface areas, the inside wall of the small intestine is lined with tiny villi. These stick out and given big surface area. They also contain blood capillaries to carry away the absorbed food molecules.

Structure of a villus

Structure of a villus

  • Capillaries: The nutrients that are absorbed through the wall of the small intestine get absorbed by the capillary network within the villi and they will come together to form the hepatic portal vein that goes directly to the liver for processing.
  • Lacteal: This is also a capillary. What the lacteal does is that it absorbs fats in the villi of the small intestine.
  • Villi: Increase internal surface area of the intestinal walls.
    Larger surface area for absorption.
    This is particularly useful because digested nutrients pass into the villi.
    This increased surface basically means that the distance travelled by nutrient molecules is decreased, hence allowing for more efficient absorption of nutrients.

Function of villi is to absorb nutrients. Villi increase surface area to volume ratio for absorption. If the villi destroyed, the surface are to volume ratio for absorption will decrease, leading to decreased absorption of digested food into the blood stream. The absorb nutrients are distributed to the body cells to provide substrates for tissue respiration and new material for growth and repair. When the villi are destroyed, little or no nutrients will be taken in. body mass will decrease, body functions will become less effective, and energy levels will decrease. Hence a person with coeliac disease will lose weight, be easily fatigued and have insufficient energy and also shows dietary deficiency disease

Transport and Assimilation

Blood rich in simple sugar and amino acids flows from capillaries of  villi into blood vessels and then into hepatic portal vein. The hepatic portal vein transports the simple sugars and amino acids to the livers for metabolism. They are then distributed to the rest of the body cells by the circulatory system. Blood transports the digested food products round the body after they are being absorbed by the villi in the ileum. They are then taken up by cells. The uptake and use of the products of digestion is called Assimilation.

Assimilation is the process where some of the absorbed foods are converted to new protoplasm or used to provide energy.


Transported from small intestine to liver via hepatic portal vein. Glucose is used as fuel by all respiring cells. Energy is produced as a result of respiration and used in. When the body needs energy or when the blood sugar level decreases, the glycogen various cellular activities. Excess glucose is converted into glycogen with the help of insulin and stored in the liver cells and muscle tissues in the form of glycogen granules in the liver will be converted back to glucose and released into the blood circulatory system. If the stored glycogen is not used for more than 6hours, it may be converted to fats and stored in the adipose tissue.


Amino acids are transported to the liver from small intestine by the hepatic portal vein. They are essential substance to form new protoplasm, for growth and repair of the tissues and to form enzymes and hormones. The excess amino acids cannot be stored in the body. The excess amino acids are broken down in the liver through process called deamination. In this process, they are converted to urea which is then excreted in urine.