Essential Nutrients and Digestion: Understanding Mammalian Dietary Requirements

1. Mammalian Nutrition Chapter 11

2. Requirement for food • A balanced diet must contain: • - Fats • - Proteins • - Carbohydrates • - Vitamins & Minerals • All foods contain the elements Carbon (C), Hydrogen (H) & Oxygen (O). • Protein also contains Nitrogen (N) • Age, gender, body size, occupation - all affect food requirements

3. Fats • Energy-rich (twice as much as energy as carbohydrates) • Made up of 2 components • - glycerol & 3 fatty acid molecules • Fat is insoluble • Stored around the organs to provide a layer of padding & insulation

4. carbohydrates • Glucose (C6H12O6) is the most common simple sugar • Glucose molecules (soluble) can join to form larger carbohydrates (insoluble) • In animals • – glucose stored as glycogen (in liver) • In plants • – stored as starch • - converted to cellulose (in cell walls) • - indigestible (forms roughage in diet)

5. protein • Made up of amino acids • Protein is used for tissue growth & repair • Human body cannot store excess protein • - (minimum daily intake 80g) • Excess protein is used for energy • Structural proteins are only ever used for energy in an emergency (starvation)

6. vitamins • 2 types : • Fat soluble (e.g. A & D) • Water soluble (e.g. B & C) • Work as coenzymes to promote chemical reactions • Are constantly re-used, so only required in small quantities

7. minerals • Chemical components of food required for many functions in the body • Calcium (dairy foods): • - hardening bones & teeth • Iron (meat & eggs): • - structural component of haemoglobin • Sodium/Potassium (in most foods): • - for muscle contraction and nerve impulses

8. Food tests • Starch • - will turn iodine solution blue/black • Protein • - will turn Biuret reagent lilac • Simple Sugar • - will turn heated Benedicts solution orange • Fat • - produces a translucent stain on white paper • - OR red layer with Sudan III

9. Need For Digestion • Food is needed for cells: • Give fuel for energy • Provide building materials for • - growth • - repair • - fighting infection (antibody production) • Digestion breaks down large insoluble molecules • - into small soluble molecules • These molecules can then be absorbed into the bloodstream

10. Alimentary Canal • A long tube running from mouth to anus • Has several associated organs connected to it • e.g. liver, pancreas, salivary glands • These organs are connected by tubes or ducts Pharynx (throat) Oesophagus

11. Mouth & Salivary Glands • In the mouth food is broken down in 2 ways: • mechanically • - by chewing and grinding of teeth • chemically • - by amylase, from the salivary glands (starch into maltose) • saliva also contains mucus • - keeps the mouth & food lubricated

12. Oesophagus & Peristalsis • Oesophagus is a muscular tube • - connects the mouth to the stomach • It’s wall is lined with circular muscle • Contraction & relaxation of this muscle pushes food along • This is known as Peristalsis

13. Stomach • A muscular sac, lined with 2 types of muscle • - longtitudinal & circular muscle • Muscles contract & relax • - helps churn & mix food with digestive juices • 2 sphincters at either end • - hold the contents inside

14. Gastric Glands • Found in the inner lining of the stomach • - Mucus-secreting cells • mucus sticks to the stomach lining • - protects it from acid and digestive enzymes • - Acid-secreting and enzyme-secreting glands • Acid lowers pH • - converts inactive pepsinogen into pepsin • Pepsin can then converts protein into peptides (amino acids)

15. Associated Organs • Liver: • - produces bile • - processes products of digestion • Gall Bladder: • - stores bile • -passes it into small intestine via bile duct • - bile helps emulsify fat • Pancreas: • - produces amylase, trypsin, & lipase

16. Small Intestine • Where the majority of digestion (& all absorption) takes place • Food moved along by peristalsis • Food broken down by digestive enzymes • - e.g. amylase, lipase, trypsin • Digestion products absorbed into the bloodstream

17. Small Intestine - Structure • Very long • Folded inner lining • -covered in finger-like villi • The epithelial cells lining the villi are folded into microvilli • Provides a very large surface area for food absorption • Lining is only 1 cell thick

18. Small intestine - absorption • Has a very dense network of blood vessels • Each villus has a blood capillary and lacteal • Glucose & amino acids pass into the capillary • Fat digestion products pass into the lacteal • Vitamins & minerals also pass across

19. Fate of absorbed materials • Amino acids & glucose: • - passed to the liver through the hepatic portal vein • Glucose : • - converted into glycogen & stored • - released into circulation as an energy source • Amino Acids : • Some used for growth & repair • Excess broken down into urea (deamination) • - removed by kidneys • Fat • - passed via the lymphatic system into the blood • - some used as an immediate energy source • - excess fatty acids & glycerol are converted into fat and stored in the tissues • Vitamins & minerals • - carried by the blood to the cells that need them

20. Large Intestine • Undigested material, bacteria & dead cells pass into the large intestine • Any excess water is reabsorbed • The remaining faeces are eliminated • - by passing to the rectum • Faeces are finally expelled through the anus