Human Digestive System•Digestion is the process of breaking down largefood molecules into smaller soluble molecules thatcan be readily absorbed by the body.•Digestion occurs in an eight – metre long tubecalled the gut or alimentary canal.
The human digestive system includes the alimentarycanal and organs such as the salivary glands, liver,gall bladder and pancreas.
•The gut has an opening (mouth) into which food istaken and another (anus) from which undigestedmaterial is ejected.•Below is the flow of food particles in the alimentarycanal.Mouth Oesophagus StomachAnusLargeintestinesSmallintestinesDuodenum
•There are two types of digestion – physical digestion andchemical digestion.•Physical digestion is the mechanical breakdown offood by the chewing action of the teeth and thechurning action of the stomach.•Chemical digestion involves the use of enzymes to breakdown food substances.•Enzymes are protein substances which act as catalystsand generally speed up the chemical reactions in ourbody. Enzymes that break down food substances in thegut are called digestive enzymes.
There are three main types of digestive enzymes.a.Carbohydrates – break down carbohydratesb.Proteases – break down proteinsc.Lipases – break down fats and oils.
Process of Digestion•Digestion in the moutha.Food is broken down into smaller pieces by the teeth.b.At the same time, food is mixes with saliva from thesalivary glands.c.Saliva contains salivary amylase (a kind ofcarbohydrates) which catalyses the breaking down ofstarch into maltose ( a kind of sugar)
•Swallowing and peristalsisa.Our tongue shapes the food into a round lump calledbolus before it is swallowed.b.The bolus is swallowed down the oesophagusc.The bolus is pushed along the oesophagus to thestomach by a wave – like action called peristalsis.d.Peristalsis is caused by the contraction andrelaxation of muscles in the oesophagus.
•Digestion in the stomacha.The stomach is a muscular sac with a volume of 2 to4 litres.b.Functions of the stomach:Stores food for 2 to 6 hours.Assist in the mechanical breakdown of food(peristaltic and churning actions break apart the foodsubstances)Secretes gastric juices.c. Gastric juices contain proteases and hydrochloricacid.d. Proteases catalyse the breakdown of proteins intopolypeptides or peptones.
e. Functions of hydrochloric acids:Stops the action of salivary amylaseProvides an acidic medium suitable for the action ofproteases.Changes the inactive forms of proteases to theiractive formsKills most micro – organisms in food.f. Food is gradually converted to a semi – fluidsubstance called chyme.g. Mucus in the stomach protects the stomach wallfrom being destroyed by the acid and proteases.h. Chyme is pushed into the duodenum.
•The liver and the pancreasa.The main function of the liver in digestion is toproduce bile.b.Bile is a brownish – green liquid which contains bilesalts and bile pigments.c.Bile is stored in the gall bladder and released intothe duodenum through a tube called the bile duct.d.The pancreas produces pancreatic juice which isreleased into the duodenum through the pancreaticduct.
•Digestion in the duodenuma.The duodenum is the first part of the smallintestines.b.The duodenum receives bile from the liver andpancreatic juice from the pancreas.c.Functions of bile:Neutralizes acidic chymeDigests carbohydrate, lipids and proteins- pancreatic amylase breaks down starch intomaltose.- protease changes proteins to poliypeptides.- lipase turns fats and oil into fatty acids andglycerol.
•Digestion in the lower part of the small intestinea.Tiny glands in the small intestine produce intestinaljuice which contains several type of digestiveenzymes.b.Carbohydrate turns maltose into amino acids, andlipases convert fats to fatty acids and glycerolClass of food End productCarbohydrates GlucoseProteins Amino acidsFats Fatty acids and glycerolThe end products of digestion
Place ofdigestionGlands Secretion Enzyme Digestive actionStomach GastricglandsGastricjuiceProteases Starch to maltoseHydrochloricacid•Killsmicroorganisms•Provides acidicmedium for actionof proteases•Stops action ofsalivary amylase•Converts inactiveforms ofproteases toactive formsSummary of digestion
Duodenum Liver Bile Emulsifies fatsPancreasPancreatic juice•pancreaticamylase•Proteases•lipase•starch tomaltose•Protein topolypeptides•Fats to fattyacids andglycerolLowerparts ofsmallintestinesIntestinalglandsIntestinaljuice•Carbohydrate•Protease•lipase•Maltose toglucose•Polypeptides toamino acids•Fats to fattyacids andglycerol