NUTRITION IN MAN

NUTRITION IN MANProcess1. Ingestion (food enters body through the mouth)2. Digestion (process whereby large food molecules arebroken down into smaller, solublefood molecules that can be absorbed into the bodycells)- Physical digestion: Ripping, cutting, grinding, actionof teeth, churning action ofstomach- Chemical digestion: Breakdown of complex substancesinto simpler substances by theaction of enzymes3. Absorption (process whereby digested food substancesare absorbed into the body cells)4. Assimilation (process whereby some of the absorbedfood substances are converted tonew protoplasm or used to provide energy)5. Egestion (removal of undigested food out of the alimentarycanal via the anus) Alimentary canal and associated organsThe organs of the alimentary canal are the mouth,pharynx, esophagus, stomach, small intestine,and large intestine. The associated organs are pancreas,liver and gall bladder. Mouth: Digestion starts in the mouth (both physicaland chemical)- Food is broken down into smaller chewable pieces throughchewing(grinding of teeth)- Saliva, containing water, electrolytes, antibacterialcomponents and enzymes such assalivary amylase (converts starch to maltose), mixeswith food to begin breaking it down- Tongue+ Rolling action of thetonguecombined with secretionof saliva (from salivary glands)rolls food into a bolus – mixes food with saliva+ Taste buds on the tongue identify and select suitablefoods

Pharynxa) Nasopharynxb) Oropharynx: Prevents the food from entering the trachea(windpipe)- Connects buccal cavity to oesophagus and the larynx(voice-box)- When food enters the oesophagus, the larynx of thevoice box closes, resulting inepiglottis covering the entrance of trachea Oesophagus- Narrow, muscular tube. It passes through the thorax(chest) and the diaphragm to join thestomach+ Diaphragm: Sheet of muscle separating the thoraxfrom the abdomen- Swallowing pushes the food bolus through the pharynx(throat) and into the oesophagus- When food enters the oesophagus, the larynx of thevoice box closes- Peristalsis occurs to push food to the stomach Stomacha) Oesophageal sphincter: At the junction between theoesophagus and the stomach,there is a thick ring of circular-smooth muscle thatprevents the movement of foodfrom oesophagus into the stomachb) Pyloric sphincter: Ring of circular-smooth musclethat direct the passage of food fromstomachsmall intestinec) Function- A distensible muscular bag, with thick and well-developedmuscular walls- Stomach stores food (2-4 hours) until it is digested,kill microorganisms- Begins the digestion of proteins+ When the stomach is fully distended, it sends signalsto the brain that it is sated.Stomach wall has pits that lead to gastric glandsthat secrete gastric juice into the stomachcavity. Stomach secretes gastric juice, hydrochloricacid, water, mucus, pepsinogen andrenin+ Pepsinogen is secreted by chief cells (present inthe deep fold of stomach lining) in thegastric glands+ Low pH level (1-3) of acid helps to convert pepsinogento pepsin and is theright pHfor pepsin-enzymatic action+ Mucus secreted by stomach lines the wall of thestomach and protects them from beingdigested by HCL and pepsin- Contractions of the smooth muscles in the walls ofthe stomach roll around its contents,mixing partially digested food with enzymes and acid The acidic fluid mixture of gastric juice is calledchyme. Through peristalsis movementsof the stomach walls, chyme is push towards the endof the stomach

Gates of pyloric sphincter relax briefly, hence chyme enters the small intestine (gradualemptying of the stomach over 4 hours) Liver (bile) - Dark red, made up of five lobes (three on the right,two on the left)- Attached to lower surface of the liver are three bloodvessels, the hepatic portal vein andthe hepatic artery- The liver cells produce and secret bile – alkalinegreenish-yellow liquid containingbilesaltsandbile pigment(waste products and are removedwith faeces and undigestedmatter) Gall bladder- Greenish-yellow bag attached to the liver- Bile is stored temporarily in the gall bladder- When gall bladder contracts, the bile flows into duodenumvia bile duct Pancreas - Gland connected to duodenum bypancreatic duct(releasepancreatic juice)- The bile duct joins the pancreatic duct just beforepancreatic duct opens into duodenum- Secretes pancreatic juiceinto the duodenum, alsomakes thehormones insulin andglucagon– play important role in controlling theconcentration of glucose in the bloodand carbohydrate metabolism (refer CARBOHYDRATE METABOLSM)

Small intestine:The lining of the walls of the smallintestine contains glands which secretedigestive enzymes. Wall of small intestine is alsoadapted to absorb digested food products andwater. a) Duodenum: First part of the small intestine (U-shaped)- Receive pancreatic juice containing trypsin (a protease),lipase and amylase. The juicealso contains sodium hydrogencarbonate which neutralizesacid from the stomach.+ Trypsin: ProteinPolypeptides+ Pancreatic amylase: StarchMaltose+ Pancreatic lipase:Emulsified fatFatty acidsand glycerol- Receive intestinal juice from intestinal gland containingmaltase, sucrase, lactase,peptidase+ Maltase: MaltoseGlucose+ Sucrase: SucroseGlucose and fructose+ Lactase: LactoseGlucose and galactose+ Peptidase: PolypeptidesAmino acidsb) Jejunum: 2 nd part of small intestine. Its lining isspecialized for the absorption byenterocytes of small nutrients molecules which havebeen previously digested byenzymes in the duodenumc) Ileum: The last part of the small intestine (coiled).Enzymes in the epithelial digestlactose and peptides. Its surface area is increasedby the presence of villi which allowthe efficient absorption of digested food moleculeshttps://biology-igcse.weebly.com/human-alimentary-canal.html The large intestine – NO digestion occurs1. Colon- Function: Absorb mineral water and salts from theundigested food materials- Caecum and appendix are at the junction between colonand the small intestine (nospecific function)2. Rectum: Temporarily store faeces (undigested and unabsorbedmatters). When contract,faeces are expelled through the anus.3. Caecum: Sac-like structure4. Appendix: Tubular, attached to caecum- Can be inflamed causing appendicitisAnusMuscles to control when faeces is egested from thebodyEgestion/defecation AbsorptionDefinition: Process whereby digested food substancesare absorbed into the body cells

Adaptation of small intestine (for absorption)- Surface area of small intestine- Membrane that separates the food substances from bloodcapillariesGlucose and galactose are absorbed directly into theblood stream from the small intestine DigestionDefinition: Process whereby large good molecules arebroken down into smaller, solublemolecules that can be absorbed into the body cells- Physical: Mechanical break-up of food into small porticles+ Mouth: Chew food by the action of the teeth andtongue+ Stomach: Continual contracts and relaxations offood muscles in stomach wall(longitudinal and circular muscles)Churning actionBreaks up food particles andmixes them with digestive enzymes- Chemical digestion: Breaking down of large moleculesin food, such as proteins, starchand fats, into smaller soluble molecules which canbe absorbed such as hydrolyticreactions catalyzed by digestive enzymes+ Hydrolysis: Any chemical reaction in which a moleculeof water breaks one or morechemical bonds Peristalsisa) Definition: Rhythmic, wave-like muscular contractionsof the walls of the alimentarycanalb) Process- Point 1: Circular muscles contract, longitudinal musclesrelax, wall of gut constricts, foodbolus is pushed forward (diameter of lumen decreases)- Point 2: Longitudinal muscles contract, circular musclesrelax, gut dilates to allow foodbolus to enter lumen (diameter of lumen increases)c) Muscles- Longitudinal and circular muscles produce slow, longcontracts that move food along thegut via peristalsis and enables food to be mixed withdigestive juices- The circular muscles constri