The Digestive System and Nutrition

1. The Digestive System and Nutrition

2. photosynthesis Herbivores Carnivores Heterotroph Omnivores Nutrition Autotroph

3. Balanced diet includes all 7 components Nutrition Energy content of food measured in kilocalories The average teen-ager needs Approximately 2200 calories for girls 2800 calories for boys Carbohydrate- Protein – Fats- 4.5 calories/g 4.5 calories/g 9 calories/g Obesity New Food Pyramid 2005 - emphasise importance of controlling weight and physical activity - dietary fats – limit saturated fats 20-35% or less of energy shouldcome from fats, healthiest are monounsaturated and polyunsaturated -limit sugar intake -stress benefits of wholegrains

4. Mouth -mechanical digestion (mastication) = teeth, tongue -chemical digestion = saliva (amylase, lysozyme) Uvula– prevents food entering the nose Epiglottis– safety hatch. A flap of cartilage prevents food from entering the trachea Alimentary canal • 2 main functions: • Digesting and absorbing nutrients • Protecting from invasion Trachea- windpipe

5. Oesophagus -transfers food to stomach by peristalsis Cardiac sphincter -opens to allow food oesophagus stomach -heartburn –acid escapes stomach oesaphagus http://library.thinkquest.org/11226/main/c03txt.htm

6. chyme Cardiac sphincter Pyloric sphincter Stomach Short term storage reservoir (1L for up to 4h) Digestion = chemical (HCl and enzymes) - proteins = mechanical - liquefication of food Slowly releases food into intestine http://35.9.122.184/images/41-AnimalNutrition/41-16-Duodenum-L.gif

7. Activated to pepsin Converts proteins peptides Ulcers (stomach, duodenum) – peptic ulcers. Most commonly caused by H. pylori Stomach Epithelium Mucous – goblet cells Prevents self-digestion Enzymes (pepsinogen) – chief cells Acid (HCl) – parietal cells pH 1-2 Kills bacteria Loosens fibrous foods Activates pepsinogen Denatures salivary amylase Hormone (gastrin) – G cells Controls gastric motility and acid secretion Stomach epithelial cells are some of the fastest growing cells in the body, typically replacing themselves about every 3 days

8. Small Intestine Around 6m in an adult Food takes 1-6 h to pass through 2 main tasks = digestion, absorption 3 parts Duodenum Jejenum Ileum

9. Duodenum = digestion= 25cm long Pancreas –pancreatic juice= NaHCO3, enzymes (insulin, glucagon) pH of duodenum = 7-8 Amylase, lipase, trypsinogen, chymotrypsinogen Liver – bile made in liver, stored in gall bladder = Water, salts, bile salts Neutralise HCl Digestion and absorption of fats and fat soluble vitamins (emulsification) Waste products eliminated by secretion into bile and elimination in feces (e.g. bilirubin, biliverdin)

10. The liver performs over 500 jobs. Some of these are: • Makes bile (600mls/day) • Detoxifies body (alcohol, drugs etc) • Breaks down excess amino acids urea (deamination) kidney • Converts glucose glycogen for storage (source of quick energy) • Converts excess carbohydrates fat • Stores vitamins - A, D, E and K • Stores minerals – Fe, Cu, Zn • Makes plasma proteins e.g. fibrinogen – blood clotting • Makes cholesterol – needed to form many hormones • Produces heat to warm blood • Clears blood of particles, including bacteria • Fights infections –half the body’s macrophages -destroy bacteria • Produces hormones, including the sex hormones Liver Weighs about 1.5kg Holds about 13% of total blood Liver cell = hepatocyte Unique ability to regenerate – average life = 150 days Right lobe Left lobe Blood rich in food from ileum http://www.britishlivertrust.org.uk/content/liver/about.asp

11. Small Intestine cont. Jejenum – digestion/ absorption. 2.5m long Ileum – absorption. 4m long Walls only one cell thick Villi, microvilli – increase surface area for absorption Rich blood supply – capillaries absorb water and soluble nutrients (glucose, amino acids, vitamins, minerals) and the blood carries the nutrients to the liver, which stores nutrients and releases them as required Lacteal – contains lymph. Fatty acids and glycerol are absorbed by the epithelial cells where they reform into fats. They become coated in protein (chylomicrons) and pass into the lymph in the lacteals. It takes around 18h for lymph to rejoin the blood, the protein coat dissolves and fats are absorbed into cells

12. Function unknown – in herbivores they contain bacteria that help digest cellulose Caecum Appendix Large Intestine 1.5m long, 6cm diameter Food stays 10h to a few days Colon Reabsorbs water – so waste is converted to semi-solid = faeces – egested Diarrhoea, constipation (fibre helps stimulate peristalsis)