for xii standard digestive system exit. an illustration from … t. madhavan, m.sc., m.l.i.s.,...

For XII standard

Digestive systemDigestive system

EXIT

An illustration from …T. MADHAVAN, M.Sc., M.L.I.S., M.Ed., M.Phil., P.G.D.C.A., Lecturer in Zoology..

Digestive system: AnatomyDigestive system: Anatomy

EXIT

Digestive system

comprises the alimentary

canal, associated glands and regions of

absorption of food.

Digestive systemDigestive system: Physiology.: Physiology.

An illustration from …T. MADHAVAN, M.Sc., M.L.I.S., M.Ed., M.Phil., P.G.D.C.A., Lecturer in Zoology..EXIT

Food provides us with fuel to live, energy to work and play, and the raw materials to build new cells.

All the different varieties of food we eat are broken down by our digestive system into simple components

and transported to every part of our body by our circulatory system.

Digestive system serves to transfer organic molecules, salts and water from the external environment to the body’s internal environment.

Digestion is accomplished by the enzymes produced from the glands associated with the digestive system.



Digestion in MouthDigestion in Mouth

In mouth digestion starts with chewing.

Chewing breaks up large pieces of food into smaller particles that can be swallowed without choking.

It is accompanied by teeth, tongue, jaws and saliva.

Chewing is controlled by the somatic nerves to the skeletal muscles of mouth and tongue.

Saliva is secreted by 3 pairs of salivary glands, namely

Parotid gland

Sub lingual gland

Sub mandibular gland



Salivary amylase or ptyalin is an enzyme which converts cooked starch into maltose.

Mucin is a glycoprotein helps in the lubrication of food.

The lubricated, swallowable form of food is called the bolus.

Salivary secretion is controlled by reflex activities.

Daily secretion of saliva ranges from 1000 ml to 1500 ml.

Saliva contains the salivary amylase and Mucin.



SwallowingSwallowing

It is a complex reflex process controlled by the medulla oblongata.

During swallowing;

the soft palate is elevated,

larynx gets raised,

tongue forces food back into the pharynx,

the epiglottis closes the glottis

and the food slowly passes into the osesophagus.

Oesophageal phaseOesophageal phase begins with relaxation of upper oesophageal sphincter.

In oesophagus the food is moved towards stomach by a progressive

wave of muscle contraction proceed downward to the stomach.

Such waves are known as Peristaltive waves. One peristaltive wave takes 9 seconds to reach the stomach.

Due to peristaltive waves, swallowing can occureven when a person is

upside down.



Digestion in StomachDigestion in Stomach

During feeding the volume of stomach may increase up to 1.5 litre.

Stomach’s contractile action will produce peristaltic waves proceed towards the pyloric region.

In the wall of stomach there are 40 million glands producing the gastric juice.

The parietal (Oxyntic) cells produce HClparietal (Oxyntic) cells produce HCl to create the acidic medium for enzymes.



Enzymes of stomach are pepsin pepsin and renin renin.

Pepsin is secreted as inactive pepsinogen, which is converted as active pepsin by the Hydrochloric acid.

Pepsin hydrolyses the proteins into short polypeptides chains and peptones.

Renin acts on soluble milk protein caesinogen and converts it into insoluble caesin.

In the presence of ca+ ions caesin is precipitated to insoluble calcium-caesin compound (curd).

Digestion in Stomach



(Inactive) pepsinogen + HCl → Pepsin (Active)

Proteins pepsin → polypeptides + peptones.

Caesiongen Renin → caesin.

caesin + ca+ → calcium-caesin

Repeated peristaltic waves in the stomach help to soften the food.

The food leaves the stomach in the form of chymechyme and enters the upper small intestine at periodic intervals

Digestion in StomachDigestion in Stomach



Digestion in Small intestineDigestion in Small intestine

The food in the small intestine is mixed with 3 juices namely

bile juice, pancreatic juice, intestinal juice.bile juice, pancreatic juice, intestinal juice.

Bile juice: Bile juice: It is a brownish green, alkaline secretion of the liver and stored in the gall bladder and pored into duodenum via the bile duct.

Bile salts emulsify fats and helps enzymes like lipase to act upon fats.

Bile salts convert bigger fat particles into smaller fat globules called chilomicrons.



pancreatic juice: pancreatic juice: It is an alkaline [pH 7-8] fluid transported to duodenum through the pancreatic duct.

It contains water, mineral salts and enzymes.

Important enzymes are trypsin, chymotrypsin, amylase, lipase, carboxypeptidase and nuclease.

Proteins + trypsin → polypeptides + peptones.

Proteins chymopepsin → large peptides.

polypeptides Carboxypeptidase → di peptides + tri peptides + fatty acids

Emulsified fat (Tri glycerides) lipase → fatty acids + monoglycerides

Starch Pancreatic Amylase → Maltose

Digestion in Small intestineDigestion in Small intestine



Changes take place in succus entericus

Erypsin converts poly peptide into aminoacids.

Maltase acts on maltose and converts into glucose.

Sucrase (Invertase) acts on sucrose and converts

into glucose and fructose.

Lactase acts on lactose and converts into glucose

and galactose.

Lipase acts on fats and converts into fatty acids and

glycerol.

Digestion in Small Digestion in Small intestineintestine



Absorption and AssimilationAbsorption and Assimilation

Fatty acids absorbed through the lymph vessels. Vitamins by diffusion process. Glucose by active transport.

Carbohydrates are broken into Glucose or fructose.

Lipids are broken into glycerol and fatty acids.

Proteins are broken into Amino acids.

Along with this simpler molecules minerals, vitamins, water etc. are absorbed through the intestinal villi.

From the lumens of the intestine absorbed food constituents are carried to the liver through the hepatic portal vein.

From the liver food materials are transported to all other regions of body for utilization.



Absorption and AssimilationAbsorption and Assimilation

From the lumens of the intestine absorbed food constituents are carried to the liver through the hepatic portal vein.

From the liver food materials are transported to all other regions of body for utilization.

This conversion of food into energy and cellular organization is called assimilation.



Any useful substances in the leftovers, such as spare water and body minerals, are absorbed through the walls of the large intestine.

The remains are formed into brown, semi-solid faeces, ready to be removed from the body.

Digestion in Large intestineDigestion in Large intestine

In Rectum and Anus

The end of the large intestine and the next part of the tract, the rectum, store the faeces.

These are finally squeezed through a ring of muscle, the anus, and out of the body.



The indigestible material is known as roughage.

The removal of faecal material is known as defecation (or) egestion.

Defaecation takes place through anus

Egestion



End

for xii standard digestive system exit. an illustration from … t. madhavan, m.sc., m.l.i.s.,...

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