The Digestive System and Nutrition

Autotroph photosynthesis Nutrition Herbivores Carnivores Omnivores Heterotroph

Nutrition Balenced diet includes all 7 components Carbohydrate- Protein – Fats- 17kJ/g 38kJ/g Obesity New Food Pyramid emphasise importance of controlling weight and physical activity -dietary fats –limit saturated fats 20-35% of energy should come from fats, especially monounsaturated and polyunsaturated fats Energy content of food measured in Joules (J) Amount of food required depends on..? Approx 9600kJ girls 12,600kJ boys -limit sugar intake -stress benefits of wholegrains

Mouth -mechanical digestion (mastication) = teeth, tongue -chemical digestion = saliva (amylase – breaks down starches) Trachea – windpipe – part of respiratory system= air passage Uvula – prevents food from entering the trachea Alimentary canal 2 main functions: Digesting and absorbing nutrients Protecting from invasion Three main salivary glands: 1.Parotid - behind the ear 2.Submandibular – down and in front of parotid 3.Sublingual – under tongue

Epiglottis – safety hatch. A flap of cartilage prevents food from entering the trachea

Esophagus - tube -transfers food to stomach by peristalsis Cardiac sphincter -opens to allow food into the stomach -heartburn –acid escapes stomach and goes into the esophagus

Stomach Short term storage reservoir (1L for up to 4h) Digestion = chemical (HCl and pepsin) – proteins are broken down = mechanical - liquefication of food by peristalsis Slowly releases food into small intestine Chyme = released food Cardiac sphincter Pyloric sphincter Rugae = wrinkles of tissue that line inside of stomach – cause increase in surface area to help with mechanical breakdown of food

Acid (HCl) – Mucus – prevents self digestions Pepsin – Stomach epithelial cells are some of the fastest growing cells in the body, typically replacing themselves about every 3 days Ulcers (stomach, duodenum) – peptic ulcers. Most commonly caused by excess acid, stress pH 1-2 Kills bacteria Loosens fibrous foods Activates pepsin Denatures salivary amylase Converts proteins to smaller peptides Chemicals found in stomach

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 Mesentery = tissue that hooks intestine to abdomen wall

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 to the cells Small Intestine cont. Duodenum = = 25cm long – where the majority of food and water absorption occurs

Large Intestine 1.5m long, 6cm diameter Food stays 10h to a few days Reabsorbs remaining water, vitamins and minerals – so waste is converted to semi-solid = feces Diarrhea, constipation- Excess orlack of water absorption Fiber helps stimulate peristalsis Appendix Function unknown – in herbivores they contain bacteria that help digest cellulose

Bacteria 1-2kg of bacteria in your gut = 4000 species Good – symbiotic bacteria. These live in close harmony with the body without causing harm, and have additional health benefits. Probiotics are live micro-organisms that, when consumed in adequate amounts, confer a health benefit to the host. e.g. bifidobacteria, lactobacillus Bad - bacteria that can cause illness e.g. H pylori (ulcers), Salmonella, E. coli, Listeria (food poisoning) Aid digestion Break down toxins Produce vitamins B12 and K Stimulate the immune system Help prevent growth of cancers Convert prodrugs to drugs

Pancreas –releases pancreatic juice= sodium bicarbonate (a base), enzymes (insulin, glucagon) to the duodenum = pH of duodenum = 7-8 Enzymes =Amylase, lipase, trypsin, chymotrypsin Enzymes act on starches, fats, and proteins Liver – Bile made in liver, stored in gall bladder = contains water, salts, bile salts Neutralizes HCl Digestion and absorption of fats and fat soluble vitamins (emulsification) Waste products eliminated by secretion into bile and elimination in feces Accessory Organs

Liver Right lobe Left lobe Blood rich in food from ileum The liver performs over 500 jobs. Some of these are: Makes bile (600mls/day) Detoxifies body (alcohol, drugs etc) Breaks down excess amino acids to urea Converts Converts glucose to glycogen for storage (source of quick energy) Converts excess carbohydrates to 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 –helps the body’s white blood cells -destroy bacteria Produces hormones, including the sex hormones

Gall Bladder Stores and concentrates bile