Biology – Animal Nutrition

Biology – Animal Nutrition Ingestion ● food is taken into the alimentary canal through the mouth Digestion ● the breakdown of large insoluble molecules into small soluble molecules that can be absorbed and assimilated by the body 1. Mechanical Digestion ● digestive juice contains enzymes● increases the surface area fro the action of enzymes● breakdown food into smaller pieces● absence of chemical change● eg. chewing by teeth, churning and peristalsis, emulsifying by bile 2. Chemical Digestion ● breakdown food into smaller molecules by enzymatic reaction ○ to help absorbtion ● presence of chemical change Stage One : Mouth Cavity ● Salivary amylase ○ starch is broken down to maltose ● Water ○ dissolves soluble food ● Mucus ○ moistens food to help swallowing○ digested food is hence shaped into a bolus Stage Two : Swallowing ● Before swallowing ○ food is chewed by the teeth○ tongue shapes the food into a bolus ● During swallowing ○ tongue rises to push the bolus to the back○ bolus pushes the soft palate upwards – to prevent the food from going up to the nasal cavity ○ larynx rises, epiglottis covers the entrance to the trachea – to prevent the food from entering the trachea ○ bolus enters the oesophagus Stage Three : Peristalsis

● Behind the bolus ○ circular muscles contract○ longitudinal muscles relax○ lumen becomes smaller○ food is squeezed forward ● In front of the bolus ○ circular muscles relax○ longitudinal muscles contract○ food slides through the lumen Stage Four : Stomach ● muscles contract● food is churned up to form chyme (semi-solid) ○ a kind of mechanical digestion to increase surface area for enzyme activation ● gastric juice (gastric glands) ○ protease – catalyses the breakdown of proteins into peptides○ hydrochloric acid – kill germs, provide acidic medium for enzyme to work, stop the action of amylase ○ mucus – lubricates the food, prevents stomach wall from being digested by the proteases and damaged by hydrochloric acid Stage Five : Duodenum ● Bile ○ secreted by liver, temporarily stored in the gall bladder○ released through bile duct into the duodenum○ bile salts – emulsifying fats into oil droplets, increase surface area for lipase to act on ○ bile pigments – products of the breakdown of haemoglobins○ sodium hydrogencarbonate – provides an alkaline medium for pancreatic juice, neutralises the acidic chyme ● Pancreatic juice ○ pancreatic amylase – breaking down starch into maltose○ proteases – catalyse the breaking down of proteins into peptides and amino acids ○ lipase - catalyses the breaking down of emulsified fats into glycerol and fatty acids ○ sodium hydrogencarbonate - makes the juice alkaline, neutralises the acidic chyme from the stomch, provides the optimum pH for the enzymes to work at ● Intestinal juice ○ released by glands in the walls of duodenum and ileum○ carbohydrates – catalyse the breaking down of disaccharides into monosaccharides ○ protease – catalyse the breaking down of peptides into amino acids○ sodium hydrogencarbonate – neutralises the acidic chyme and provides the optimum pH for the enzymes to work at

Absorption ● movement of digested food molecules through the wall of the intestine into the blood or lymph by diffusion or active transport ● small intestine absorbs 90% of water● large intestine reabsorbs water and the remaining 10% of water Structural adaptations of the small intestine ● very long● greatly folded● has many villi to increase the surface area for absorption● thin epithelium (one cell thick) ○ shorten the distance for diffusion○ allows rapid absorption ● network of blood capillaries ○ absorbed food can be carried away rapidly○ maintain a steep concentration gradient to enhance the rate of diffusion ● movement of the villi ○ increases chance of contracting the food ● lacteal ○ transport fat molecules in food○ fatty acids and glycerol are combined together again Villus ● fatty acids and glycerol recombine to form oil droplets in the walls of villi● oil droplets enter the lacteal ○ pass to the main lymph vessels and eventually to the blood stream Assimilation ● the incorporation of digested substances from food into the tissues of an organism Egestion ● undigested and unabsorbed compounds are removed as feces through the anus Liver ● connected to three blood vessels● hepatic vein ○ carries deoxygenated blood away from the liver to the heart ● hepatic artery ○ supplies the liver with oxygenated blood from the heart ● hepatic portal vein ○ carried deoxygenated blood which is rich in nutrients from the villi to the liver Roles of the liver

● regulation of the blood glucose level ○ glucose is converted to glycogen when blood glucose level is high○ glyogen is converted to glucose when blood glucose level is low ● storage of glycogen, iron, fat soluble vitamins ○ stores glycogen○ stores iron from old red blood cells○ stores fat soluble vitamins (Vitamin A and Vitamin D) ● production of bile, vitamin A, heat ○ secretes bile○ changes carotene to vitamin A○ produces heat and helps to maintain body temperature ● deamination ○ deaminates excess amino acids○ amino groups (nitrogen containing part of amino acids) are converted into urea ○ remaining parts are converted into carbohydrates or fats for the release of energy ● detoxification ○ changes some toxins (eg. alcohol and drugs) into harmless substances Chewing ● breakdown food into smaller pieces by teeth to increase the surface area for enzymatic reaction (physical digestion) Teeth ● provide mechanical digestion of food by breaking, cutting and tearing up of food● 2123/2123 ○ milk teeth : without molar, 20 teeth○ permanent teeth : no replacements for most, 32 teeth (including wisdom teeth) Structure of teeth ● Crown● Enamel ○ contains 97% calcium salt, the hardest part○ would not grow down into the root region but replaced by cement ● Periadontal membrance ○ fibres from the cement pass into the jawbone to anchor the teeth forming it ● Dentine ○ occupies a large part of the tooth is hard like bone but softer than enamel○ living ● Pulp cavity ○ contains living cells which make dentine○ contains blood vessels which supply oxygen and food○ contains nerves which produce sensation of pain

Incisors ● chisel-shaped● sharp● one root● for biting and cutting of food Canine ● pointed and curve● well developed in carnivores eg. lion● one root● for tearing flesh Premolars ● broad top with cusps in humans● two roots● for chewing, crushing, grinding food Molars ● similar to premolars, but larger● three roots● for chewing, crushing, grinding food● last molars: wisdom teeth Tooth Decay ● oral bacteria, food debris and saliva form a plaque on tooth surface● oral bacteria digest the sugar in food debris to form acid● acid dissolves the enamel and makes small holes● bacteria reach the holes and digest the dentine and infect the tissue in pulp cavity● acid wil irritate the nerves and cause pain● if not too serious, the decayed area can be drilled out and replaced with a filling Prevention of Tooth Decay ● have a balanced diet (including calcium, phosphorus, vitamin D)● adding fluoride in water to strenfthen the enamel of our teeth ○ not chlorine as it is used for killing bacteria in water ● avoid sugary food and drinks between meals, so bacteria cannot make acid● use dental floss ○ to remove food that remains between teeth ● form a good tooth-cleaning habit by using dental disclosing agent● brush our teeth at least twice a day● replace your toothbrush when it wears out● do not bite hard materials● have a dental check up at least once year to make sure any tooth decay is treated early

Fluoride ● growing children can absorb fluoride in their diet ○ from toothpaste or fluoridated water ● becomes part of the enamel of their developing teeth and the enamel is then more resistant to tooth decay Argument of adding fluoride to public water supplies ● For ○ reduce the number of tooth decay (kids)○ cannot buy fluoridated toothpaste ● Against ○ a form of mass medication ■ people have no choice about whether or not they want the treatment fluoride can lead to flurosis (white patches) ○ only benefit to growing children ■ if children take proper care of their teeth, fluoridation is unnecessary