Animal Physiology

1. Animal Physiology Mammalian Nutrition Mr G R Davidson

2. 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 Mr G Davidson

3. 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 Mr G Davidson

4. Glucose Carbohydrates • Carbohydrates provide us with energy for our normal activities. • They consist of long chains of glucose molecules. Mr G Davidson

5. Fatty acid Fatty acid Glycerol Fatty acid 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. Mr G Davidson

6. Amino acid 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. Mr G Davidson

7. 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. Mr G Davidson

8. Vitamins Mr G Davidson

9. 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. Mr G Davidson

10. Minerals Mr G Davidson

11. 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. Mr G Davidson

12. Mouth Salivary gland Oesophagus Stomach Liver Pancreas Gall bladder Large intestine Small intestine Rectum Anus Alimentary Canal Mr G Davidson

13. 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 salivaryamylase, to digest starch. Mr G Davidson

14. 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. Mr G Davidson

15. Muscles contract here Food moves this way Muscles relax here Peristalsis Mr G Davidson

16. 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. Mr G Davidson

17. 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. Mr G Davidson

18. Mucus and gastric juices secreted into the stomach Mucus-secreting cell Acid-secreting cell Enzyme-secreting cell Gastric Gland Mr G Davidson

19. 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. Mr G Davidson

20. 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. Mr G Davidson

21. 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. Mr G Davidson

22. 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. Mr G Davidson

23. 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. Mr G Davidson

24. 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) Mr G Davidson

25. Thin wall Blood capillary Lacteal A Villus Mr G Davidson

26. 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. Mr G Davidson

27. 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. Mr G Davidson

28. 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. Mr G Davidson

29. 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. Mr G Davidson

30. 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. Mr G Davidson