Animal Physiology Mammalian Nutrition Mr G R Davidson

Composition of Food Humans are adapted for feeding and digestion so that food molecules can reach the body cells. The main groups of food we eat are: Carbohydrates Fats Proteins Vitamins Minerals Sunday, September 23, 2018 Mr G Davidson

Composition of Food Carbohydrates contain the elements carbon, hydrogen & oxygen Fats contain the elements carbon, hydrogen & oxygen Proteins contain the elements carbon, hydrogen, oxygen & nitrogen Sunday, September 23, 2018 Mr G Davidson

Carbohydrates Carbohydrates provide us with energy for our normal activities. They consist of long chains of glucose molecules. Glucose Sunday, September 23, 2018 Mr G Davidson

Fats Fats release some energy for our use if required while the rest is stored in adipose tissue beneath the skin. This is used as insulation. Each fat is made up of a glycerol molecule joined to 3 fatty acid molecules. Glycerol Fatty acid Sunday, September 23, 2018 Mr G Davidson

Proteins Our body requires protein to build it up and for growth and repairing damaged tissue. Proteins are built up from long chains of amino acids. There are only about 20 different amino acids. Amino acid Sunday, September 23, 2018 Mr G Davidson

Vitamins Vitamins are required for good health. They do not provide energy. They act as coenzymes which are required in the various biochemical activities within cells. Some examples of vitamins, their source and the deficiency disease are given in the table. Sunday, September 23, 2018 Mr G Davidson

Reproductive Disorders Vitamins Vitamin Source Deficiency Disease A Milk, fresh veg. Night Blindness B1 (Thiamine) Cereal grains Beri beri B3 (Niacin) Cereal, lean meat Pellagra C (Ascorbic acid) Citrus fruits Scurvy D Liver, fish, milk Rickets E Wheat germ Reproductive Disorders K Green veg. Blood doesn’t clot Sunday, September 23, 2018 Mr G Davidson

Minerals Minerals are chemical elements which are required in very small quantities. They have a whole variety of functions, some of which are shown in the following table. Sunday, September 23, 2018 Mr G Davidson

Haemoglobin in Red Blood Cells Contraction of muscles Minerals Mineral Required For: Iron Haemoglobin in Red Blood Cells Iodine Thyroxine Sodium All cells Calcium Healthy teeth & bones Potassium Contraction of muscles Sunday, September 23, 2018 Mr G Davidson

Alimentary Canal The food we eat passes from the mouth to the anus through the “alimentary canal” or gut. As food passes through this canal it is processed in a number of ways and by a number of organs. Other organs, such as the salivary glands, liver and gall bladder are attached to the alimentary canal by ducts, and these are called associated organs. Sunday, September 23, 2018 Mr G Davidson

Alimentary Canal Mouth Salivary gland Oesophagus Stomach Liver Gall bladder Pancreas Large intestine Small intestine Rectum Anus Sunday, September 23, 2018 Mr G Davidson

The Mouth The food is physically broken down into manageable sizes by the teeth. It is mixed with a fluid called saliva, which contains the enzyme salivary amylase, to digest starch. Sunday, September 23, 2018 Mr G Davidson

The Mouth Saliva also contains mucus which makes the food easier to swallow. The food is then moved through the gullet (oesophagus) to the stomach by a process called peristalsis. Sunday, September 23, 2018 Mr G Davidson

Peristalsis Muscles contract here Food moves this way Muscles relax here Sunday, September 23, 2018 Mr G Davidson

Stomach The stomach is a muscular bag with a valve at either end. The CARDIAC sphincter at the top allows food in. The PYLORIC sphincter at the bottom allows food to leave. Sunday, September 23, 2018 Mr G Davidson

Stomach The stomach wall produces digestive juices from gastric glands which secrete mucus, acid and enzymes. For digestion to work properly the food must be well mixed with these juices. The stomach muscles contract and relax to mix up the juices and food. Sunday, September 23, 2018 Mr G Davidson

Gastric Gland Mucus-secreting cell Acid-secreting cell Mucus and gastric juices secreted into the stomach Mucus-secreting cell Acid-secreting cell Enzyme-secreting cell Sunday, September 23, 2018 Mr G Davidson

Gastric Glands The mucus-secreting cells release a slimy mucus which sticks to the wall of the stomach and protects it from damage by the strong digestive enzymes. Sunday, September 23, 2018 Mr G Davidson

Gastric Glands The acid-secreting cells release hydrochloric acid which has 2 functions: It creates conditions needed to produce active pepsin. It provides the optimum pH for the enzymes to work. Sunday, September 23, 2018 Mr G Davidson

Gastric Glands The enzyme-secreting cells release an inactive enzyme called pepsinogen. Once the pepsinogen comes in contact with the acid, it is converted to an active enzyme called pepsin. The pepsin can now break down proteins in the stomach to peptides, which will later be broken down further into amino acids. Sunday, September 23, 2018 Mr G Davidson

Stomach The longitudinal muscles contract to make the stomach shorter and fatter. The circular muscles contract to squeeze the stomach. Once the food has been in the stomach for a while, it is released slowly, small drops at a time into the small intestine. Sunday, September 23, 2018 Mr G Davidson

Small Intestine The food enters the small intestine from the stomach and is moved along by peristalsis. A number of digestive enzymes break down the large insoluble food molecules to small soluble food molecules before they are absorbed out of the intestine. Sunday, September 23, 2018 Mr G Davidson

Small Intestine The small intestine’s function is to absorb soluble food molecules and it is well suited to this job in a number of ways. It is very long (About 6m). The inner surface is folded into thousands of finger-like villi. The lining of each villus is very thin. (Only one cell thick) Each villus has a network of vessels for absorbing the food, both blood capillaries and lymphatic vessels. (Lacteals) Sunday, September 23, 2018 Mr G Davidson

A Villus Thin wall Blood capillary Lacteal Sunday, September 23, 2018 Mr G Davidson

Absorption The glucose and the amino acids are absorbed into the blood capillaries. These tiny blood capillaries all join up to form the hepatic portal vein and transport the absorbed food to the liver. Sunday, September 23, 2018 Mr G Davidson

Absorption The liver stores most of the glucose as glycogen until it is required, but some glucose remains in the blood. The amino acids are used in the body for growth and repair, but if there are any excess amino acids, these are broken down by the liver into urea. Sunday, September 23, 2018 Mr G Davidson

Absorption This is later removed by the kidneys and released in the urine. Vitamins and minerals are transported to cells where they have special functions which help to keep the body healthy. Any excess vitamins and minerals are either stored or excreted. Sunday, September 23, 2018 Mr G Davidson

Absorption Fats and fatty acids are absorbed by the lacteals which contain a fluid called lymph. This lymph is transported in the lymph vessels which will eventually drain into the blood system. The products of fat digestion can be used for energy, as insulation or simply stored until required. Sunday, September 23, 2018 Mr G Davidson

Large Intestine When the food eventually reaches the large intestine (Colon), it is mainly water and indigestible waste materials. The function of the large intestine is to absorb water back into the bloodstream leaving a semi-solid called faeces. The faeces is passed into the rectum (bowel) where it is stored until it is eventually eliminated through the anus. Sunday, September 23, 2018 Mr G Davidson