DIGESTION DIGESTION DIGESTION DIGESTION

What is digestion?• Digestion is the process of breaking down

large complex food molecules into small molecules which can diffuse into our body cells

• Digestion of food is helped by enzymes present in digestive juices secreted to the digestive system...

THE DIGESTIVE THE DIGESTIVE SYSTEMSYSTEM

MOUTHMOUTH

OESOPHAGUSOESOPHAGUS

LIVERLIVER

SMALL INTESTINESSMALL INTESTINESPANCREASPANCREAS

STOMACHSTOMACH

mouth esophagus stomach

duodenumsmall intestinelarge intestine

rectum anus

The alimentary canal consists of all the organs through which food passes:

IN THE MOUTHIN THE MOUTHfood is masticulated and food is masticulated and mixed with saliva which mixed with saliva which contains ptyalin which breakscontains ptyalin which breaksdown starch to maltose.Food down starch to maltose.Food passes down the oesophaguspasses down the oesophagus

IN THE STOMACHIN THE STOMACH food is mixed with gastric juicesfood is mixed with gastric juices which contain HCl and enyzmeswhich contain HCl and enyzmes proteins are digested here. Pepsin actsproteins are digested here. Pepsin acts on proteins and rennin acts on casein on proteins and rennin acts on casein

IN THE SMALL INTESTINEIN THE SMALL INTESTINE digestion is completed with the help digestion is completed with the help of enzymes from the pancreas and of enzymes from the pancreas and those in the ileumthose in the ileum

• Food is cut/chewed into smaller pieces • this gives a larger surface area for

enzymes to act on• food is mixed with saliva• starch maltose by ptyalin or

salivary amylase• partly digested food is rolled into soft

balls by tongue• swallowed into oesophagus by peristalsis

• food is mixed with gastric juice produced by stomach

• gastric juice contains hydrochloric acid(HCl) and enzymes

• hydrochloric acid provides an acidic environment for the enzyme, pepsin, to work in

• hydrochloric acid also kills bacteria in the food to stop decay...

• Enzyme renin coagulates the milk present so that it is easier to digest

• another enzyme, pepsin, digests the protein

• finally, food in semi-liquid form is released to the duodenum in small quantities...

• food here is mixed here by bile and pancreatic juice

• bile is made by the liver, stored in the gall bladder

• fats and oil in food are emulsified by bile to give a larger surface area for digestive juices to work on

• pancreatic juice, produced by the pancreas contains enzymes(amylase, lipase, protease) ...

• Any undigested food is digested into small intestine:proteases

amylase

lipase

• digested food in small molecules are absorbed through wall of small intestine into bloodstream by diffusion...

proteins and peptides

peptides and amino acidsStarch Maltose

FatsFatty acid and glycerol

Digestion in the ileum

• Fats are acted upon by lipase and broken down to fatty acids and glycerol which are absorbed by the lacteal of the villi of the ileum.

• Peptones are broken down by peptidases to amino acids.

• Double sugars like maltose, lactose and sucrose are acted upon by maltase, lactase and sucrase respectively and changed to simple sugars.

Digestion of sugars in the ileum

• Maltose is broken down by maltase to glucose

• Sucrose is broken down by sucrase to glucose and fructose

• Lactose is broken down by lactase to glucose and galactose.

• All these simple sugars are absorbed in the bloodstream through the villi of the ileum

• Bloodstream carries the digested food to body cells

• mineral salts and vitamins which need not be digested are also absorbed in the small intestine and carried by blood to the body cells...

Absorption..Absorption is the process of passage of the

products of digestion through the walls of the digestive tract. This takes place in the ileum

• Villi of the small intestine are fingerlike projections supplied with numerous blood capillaries for

• the absorption of water-soluble nutrients, amino acids, monosaccharides Vitamins B and C and other elements

It also contains a tiny tube called the lacteal for the absorption of fatty acids and glycerol

• Undigested or unabsorbed food moves on to large intestineIt is a semi solid waste known as faecesThis moves on into the rectum and are later discharged through the anus...

• Water in food is absorbed in the large intestine

• Digestive enzymes are chemical substances set free by digestive organs to help in the digestion of food

• enzymes speed up process of digestion but they themselves remain unchanged when food is digested

• each enzyme only work on one type of food

• enzymes work best in 37ºC. they are destroyed at high temperatures

• enzymes function in either acidic medium or alkaline medium...

Enzymes in digestion

StarchStarch• in the mouth - salivary in the mouth - salivary

amylase (ptyalin)amylase (ptyalin)

• pancreas- pancreatic amylasepancreas- pancreatic amylase

• small intestines- maltase, small intestines- maltase, lactase, sucraselactase, sucrase

StarchStarch• in the mouth - salivary in the mouth - salivary

amylase (ptyalin)amylase (ptyalin)

• pancreas- pancreatic amylasepancreas- pancreatic amylase

• small intestines- maltase, small intestines- maltase, lactase, sucraselactase, sucrase

Enzymes in digestion

Protein• stomachrennin and

pepsin • duodenumtrypsin• small intestineerepsin

FatsFats•stomachstomachLipaseLipase

•pancreas pancreas lipaselipase((liver- bile salts stored in the liver- bile salts stored in the gall bladder gall bladder emulsifies the fatsemulsifies the fats))•duodenum and small intestineduodenum and small intestinelipaselipase

In the mouth, In the mouth, No digestion of fatsNo digestion of fats

FoodFood moves along the oesophagus moves along the oesophagus

In the stomachIn the stomach, food is mixed with gastric juice., food is mixed with gastric juice.No digestionNo digestion but fats are melted. but fats are melted. Food stays in the stomach for 2-4 hours Food stays in the stomach for 2-4 hours

In the duodenum , In the duodenum , melted fats are emulsified by the bile melted fats are emulsified by the bile from the liver and the chyme is made alkalinefrom the liver and the chyme is made alkaline.. The enzyme lipase The enzyme lipase from the pancreatice juices splits fats into fatty acids and from the pancreatice juices splits fats into fatty acids and glycerol. glycerol.

In the small intestineIn the small intestine the the enyzme lipase splits the remaining fatsenyzme lipase splits the remaining fatsinto fatty acids and glycerolinto fatty acids and glycerol which are absorbed by the lacteal which are absorbed by the lacteal of the villi . of the villi .

In the mouthIn the mouthfood is chewed and mixed with salivafood is chewed and mixed with saliva.Ptyalin.Ptyalinacts on starches & change them to maltose. acts on starches & change them to maltose.

Food moves down oesophagusFood moves down oesophagus

In the stomachIn the stomachfood is mixed with gastric juices.No digestion of CHO

In the pancreas, amylase is produced.In the duodenum, this amylase acts on any starch left and changes it to maltose

In the small intestineIntestinal glands produce enzymes –maltase which acts on maltose, sucrase on sucrose and lactase on lactose. These are changed to simple sugars which are absorbed into the blood vessels of the villi.)

MOUTHMOUTHNo chemical No chemical digestiondigestionSTOMACHSTOMACHGastric juices create an acid medium for enzymes to act efficiently.Rennin coagulates milk proteinPepsin break down proteins into smaller parts.

DOUDENUMDOUDENUMPancreas produces pancreatic juice containing trypsin which breaks down protein further.SMALL INTESTINESMALL INTESTINEintestinal juices containing erepsin acts on the peptones and converts them into amino acids. These are absorbed into the capillaries of the villi

Metabolism and storage of nutrient

Once nutrients are absorbed in the capillaries they unite to form one large vein known as the hepatic portal vein. This vein carries the absorbed nutrients from intestine to the liver

The liver

• Level of glucose is regulated• Some glucose is removed from the blood and

converted to glycogen• Fat is formed when the limit is reached for the

amount of glycogen that can be stored.• Level of amino acids controlled-excess is

deanimated in the liver. The nitrogen is excreted as urea.

• Reserves of nutrients stored-the liver stores Vitamin A, D, B12, Iron Potassium and copper

Metabolism

• This modified blood has the correct nutrients and most living cells are able to absorb.

• Amino acids-built into structural proteins• Fats broken down by enzymes in a series of

chemical reactions to form carbon dioxide and water. Energy is released

• Glucose is broken down by the cells to form carbon dioxide and water. Energy is released. Process is known as cellular respiration