NUTRITION IN MAN.docx

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