Chapter 5 Nutrition in Humans

Chapter 5: Nutrition in HumansAlimentary CanalAssociated organs to the Digestive system: Liver, gallbladder, pancreas What is Nutrition?Nutrition is the process by which organisms obtain food and energy for growth, repair and maintenance of the body It consists of the following processes: Process What is it? Feeding or IngestionTaking in food into the body Digestion Large food molecules are broken down into smaller soluble moleculesfor absorption into body cells Absorption Nutrients move from the small intestine into the bloodstream Assimilation Nutrients are used by cells to provide energy or to make new cytoplasm for growth Egestion Removal of undigested food waste from the body The function of the human digestive system is to break down large complex food substances into smaller and simple food substances  Physical DigestionMechanical Breakdown of large pieces of foodinto smaller pieces of foodThe Identites of the food substances remain unchanged, as no new products are formed To increase the surfacearea-to-volume ratio Mouth→ chewing actionStomach→ churning actionSmall Intestine→ emulsification ChemicalDigestion It is the process by which large insoluble complex foodsubstances arebroken down into smaller soluble simple substances.The identities of the food substances changed, as newproductsare formed To allow food substances to beabsorbed into the bloodstream through the intestinalwall Mouth→ starchStomach→ proteinsSmall intestine→ carbs, proteins,lipids The Mouth and Buccal CavityFood enters the body through the mouth which leads to the Buccal Cavity Salivary glands produce saliva which consists of a mixture of salivary amylase and mucus.The salivary amylase breaks down starch into maltoseTeeth breaks large pieces of food into smaller pieces. Chewing helps to increase the surface area of the food so that enzymes can act on it moreeffectivelyThe tongue helps to mix the food with the saliva and pushes the food to the back of the mouth while swallowing. The tongue rolls food intosmall, slippery and round masses called boli.  The PharynxThe pharynx connects the buccal cavity to the oesophagus, the larynx and the trachea. The glottis is a slit located at the larynxBoth food and air passes through the pharynx when food enters the body.Air passes through the trachea while food passes through the oesophagus.The epiglottis closes over the glottis to prevent the food from reaching the larynx and trachea while swallowing Oesophagus (gullet → no digestion)It is a long narrow muscular tube that passes through the thorax (chest) and diaphragm. it connects the mouth and the stomach.The muscles of oesophagus consists of a layer of circular muscles (inner wall) and a layer of longitudinal muscles (outer wall) which areantagonistic muscles (one muscle relax and another muscle contract to create movement) Circular muscles and longitudinal muscles are present along the whole gut from the oesophagus to the rectum. Food travels to the stomach with the help of peristalsis.

PeristalsisIt refers to the rhythmic, wave-like muscular contradiction in the wall of the alimentary canalIt enables food to be mixed with digestive juices and helps to push and propel food along the gut.  To push the bolus forwardThe circular muscles contracts and the longitudinal muscles relax. The wall of the gut constricts and becomes longer and narrower to squeezethe food forward.  Near the other end of the bolusThe circular muscles relax and the longitudinal muscles contract. This causes the wall of the gut to dilate and become shorter and wider. thisallows the lumen to become wider and allow the bolus to move into a new position.  Stomach → muscular → act as a food storage which can hold food for a few hours→ lies beneath the diaphragm, to the left side of the abdomen and partially covered by the liver.→ Has numerous pits and gastric glands found in the stomach lining.has secrete gastric juices that plays an important part in digestion Gastric Glands consists of:Hydrochloric AcidPepsinMucus Hydrochloric Acid provides an acidic environment (pH 2) which is the optimum pH for pepsin to function efficientlyIt also helps to kill bacteriaStops the action of amylase by denaturing it Pepsin digest proteins into polypeptides (incomplete) Mucus forms a protective barrier that prevents pepsin from digesting the stomach wall.Moistens food so that food can move within the stomach easily.  Small IntestineContains the U-shaped duodenum and the much-coiled ileum.It carries out most of the digestion processEnzymes in the small intestine speed up the rate of digestionContains glands in the wall lining, that secretes digestive enzymesAbsorption of nutrients and water from food usually takes place in the ileum. Large intestineShorter and broader than the small intestineconsists of a colon, rectum and anusabsorbs the remaining water and mineral salts from the undigested foodtemporarily stores faeces in the rectum  Liverthe largest gland in the body, located below the diaphragmThree blood vessels are attached to the lower surface of the liver: the hepatic portal vein, the hepatic vein and the hepatic artery.  Liver cells produce and secrete bile that contains bile salts that aids in the emulsification of fats→ Bile does not contain enzymes Gall BladderThe gall bladder is attached to the liverIt stores bile produced by the liver temporarily.When the gall bladder contract, it releases bile into the duodenum via the bile duct. PancreasIt is connected to the duodenum via the pancreatic duct. The bile duct joins the pancreatic duct before the pancreatic duct opens into theduodenumIt produces pancreatic juices which contains pancreatic amylase, lipase and protease. It also secretes hormones insulin and glucagon which are essential in regulating blood sugar concentration in our body.

Process that takes place in the mouthSalivary glands produces and secretes saliva which contains a mixture of salivary amylase and mucusThe tongue helps to mix the food with saliva and saliva helps to soften the foodSalivary amylase digests starch into maltoseThe optimum pH for salivary amylase to act on it pH 7Food is broken down into smaller pieces by chewing, which increases surface area-to-volume ratio for salivary amylase to act on it moreefficientlyThe tongue helps to move the food to the back of the mouth during swallowing.The tongue rolls the food into small and slippery round masses called boli. The boli is swallowed and it travels from the mouth to theoesophagus via the pharynx Processes that takes place in the StomachGastric glands found in the stomach lining secrete gastric juicesPeristalsis churns and breaks down the food and mixes the food with gastric juicesGastric juices contains hydrochloric acid, protease (pepsin) and mucus. Hydrochloric Acid which helps to create an acidic environment for protease to act on, kills bacteria and stops the action of salivary amylase bydenaturing itMucus that helps form a protective barrier that protect the stomach wall by preventing protease on acting on itPepsin digest proteins into polypeptidesThe food remains in the stomach for 3-4 hours, becoming a partially digested substance called chyme chyme passes into the duodenum in small amounts Processes that takes place in the small intestineAs chyme enters the duodenum, it stimulates the pancreas to release pancreatic juices The pancreatic juices passes to the duodenum via the pancreatic ductPancreatic juices contains enzymes like amylase, lipase and proteaseGall baldder releases bile via the bile duct. The bile does not cotnain enzymes, it cannot digest food.Bile speeds up the rate of fat digestion by breaking down large fat molecules into smaller fat molecules. {Emulsification]The small intestine produces maltase, lipase and protease(intestinal juices secreted by glands in the intestinal walls contain...)The acidic chyme is neutralised  by alkaline fluids released by pancreas, small intestine and gall bladder, thus acheiving a pH of 8, wh