Human Nutrition PDF

R. Gallagher www.theconicalflask.ie Human Nutrition Nutrition is the process by which an organism obtains and uses its food. Digestion: The breakdown of food It is necessary for solubility a...

R. Gallagher www.theconicalflask.ie Human Nutrition Nutrition is the process by which an organism obtains and uses its food. Digestion: The breakdown of food It is necessary for solubility and transport. The mouth Physical digestion: Teeth and tongue Chemical digestion: Saliva (amylase) Humans have four types of teeth each with a specific function Incisor Canine Premolar Molar Cutting & slicing Grip, stab & tear Crush and chew Crush and chew food food food Human dental formula for an adult is: 2 I 2 C1 PM 2 M3 = 32 teeth 2 1 2 3 Chemical digestion is carried out by the enzyme amylase in the mouth. The ideal pH of the mouth is 7. Optimum pH for amylase. The epiglottis closes over the trachea to ensure the bolus goes into the oesophagus and not into your wind pipe. Oesophagus A muscular tube which carries food to the stomach by peristalsis. Peristalsis description: The contraction and relaxation of muscles. It occurs in the small intestine and fallopian tube also. Benefits of Fibre Function: Stimulates peristalsis. Source: Wholemeal bread, cereals, fruit and vegetables 63 R. Gallagher www.theconicalflask.ie Stomach A muscular bag that stores and digests food. Physical digestion: Churning Chemical digestion: Hydrochloric acid, pepsinogen and mucous. Chemical digestion: HCl functions: Mucous functions: 1. Kill micro-organisms 1. Prevents self digestion of 2. Loosen fibrous foods stomach. 3. Activate pepsinogen (low pH) Mucous is made by the stomach lining. Pepsinogen: Activated by a low pH Forms pepsin when active Pepsin is a protease Physical digestion: Muscle contracts mixing the HCl, pepsinogen/pepsin and mucous with the dissolved food. The chemicals mixed together before mixing is called gastric juice. Once this liquid has been churned it is now called chyme. Chyme (acidic) is what enters the duodenum. 64 R. Gallagher www.theconicalflask.ie Small intestine Composed of: Duodenum: Enzyme digestion + Neutralisation Ileum – absorption of nutrients Duodenum The duodenum is a tube that connects the stomach to the ileum. The duodenum is where the chemicals of both the liver and pancreas act. Both the liver and pancreas are classified as glands. Liver Location: Under the diaphragm. Functions: Produce bile Deamination Stores glycogen Produces heat. Bile: Bile is produced by the liver. Bile is stored in the gall bladder. Bile acts in the duodenum. Bile functions: 1. Emulsifies lipids (maximises surface area). 2. Contains sodium hydrogen carbonate - a base which neutralises chyme. Pancreas A leaf shaped gland Function: Secretes pancreatic juice into the duodenum Pancreatic juice: 1. Contains sodium hydrogen carbonate - a base which neutralises chyme. 2. Contains the enzymes lipase and amylase. 65 R. Gallagher www.theconicalflask.ie Ileum Function: Absorbs nutrients by diffusion into the bloodstream e.g. glucose, amino acids, fatty acids & glycerol. Peristalsis pushes contents through the small intestine. The ileum has several adaptations to carry out absorption of nutrients: Lined with villi and microvilli. Rich blood supply (capillaries) Walls are one cell thick. Contain a lacteal, Villus (Villi): Food is pushed through the intestines by the process of peristalsis. Peristalsis description: The contraction and relaxation of muscles. The villi absorb nutrients by the process of diffusion. The lacteal absorbs fatty acids and glycerol and transports this to the lymphatic system. Capillaries absorb nutrients (glucose & amino acids) and carry away from the Ileum to the liver via the hepatic portal vein. Main function: To increase surface for absorption. Hepatic Portal System A portal system is a blood pathway that begins and ends in capillaries. The hepatic portal vein carries nutrients from small intestine to the liver. Nutrients in the liver are stored (glycogen) or used for metabolic processes. 66 R. Gallagher www.theconicalflask.ie Large intestine Consists of the caecum, appendix, colon and rectum Caecum & Appendix No known function in humans Now vestigial organs (Lost their use) Colon Function: 1. Reabsorb water. 2. Produce vitamins B & K (symbiotic bacteria). 3. Egestion: Removal of undigested waste Symbiotic bacteria in colon Symbiosis: Two organisms of different species living in close contact where at least one of them benefits. Bacteria live in large intestine and feed off undigested waste being passed through. Symbiotic bacteria functions: 1. Produce vitamins B & K 2. Compete with other bacteria that may be pathogenic. Heterotroph types A heterotroph is an “organism that cannot make its own food.” Herbivores: Only eat plants e.g. Sheep and cows. Carnivores: Only eat meat e.g. Dogs and cats Omnivores: Eat both meat and plants e.g. humans and bears. 67 R. Gallagher www.theconicalflask.ie Enzymes Only three enzymes in biology need to be known. They are all catabolic. Amylase: Produced in the salivary glands and acts in the mouth. Produced in the pancreas and acts in the duodenum. Lipase: Produced in the pancreas and acts in the duodenum. Pepsin: Called pepsinogen until activated by a low pH. Produced in the stomach and acts in the stomach. 68