Digestive System:- 

"The Breakdown of large insoluble of food molecules into the Small soluble molecules to be absorbed into the body cells".

The digestive system includes the Gastrointestinal (GI) tract and the accessory digestive organs. this GI or Alimentary canal is connected from mouth to anus by a tube.Organ of GI tract includes the mouth,
esophagus tube
stomach
the small intestine
the large intestine
most of the pharynx.
The accessory digestive organs include:-
The Teeth
Tounge
Salivary Gland
Liver
Gallbladder and
Pancreas.

Functions of Digestive system:-

 1) Ingestion:- taking food into the mouth

2)Secretion:- Release of water, acid, buffers, enzymes into the lumen of the GI tract.
3)Mixing and Propulsion:- Churning and propulsion of food through the GI tract.
4)Digestion:- The Mechanical and chemical breakdown of food.
5)Absorption:-passage and assimilation of digested product from GI tract into the blood and lymph.
6)Defection:- The elimination of feces from the GI tract.

Digestive Activities in the GI tract

 In the mouth:- The mouth is formed by the cheeks, hard and soft palates, lips and tongue.

Function:-Secrete Saliva from Salivary glands that softens moistens, and dissolves food and cleanses mouth and teeth.Salivary amylase present in saliva splits starch into smaller fragments.

                :-secrete Lingual lipase from lingual glands.

In Pharynx:- Receives a bolus from the oral cavity and passes it into the Esophagus tube. 

In Esophagus:- Receives a bolus from the pharynx and moves it into the stomach. The requires relaxation of the upper esophagus sphincter and secretion of mucus.

In Stomach:- The stomach has main four regions:-

1) The Cardia :- the superior opening area of the stomach are called Cardia.

2) Fundus:- To the left of the Cardia and rounder portion is called Fundus.

3) Body:- Inferior area and the large central portion is called Body. 

4) pylorus:- The region of the stomach that connects with the duodenum is The Pylorus.

Function of Stomach

1):-Mixes saliva, food and gastric juice to form chyme.

2):- Secretes Gastric juice, which contains HCl ( Secretion of Parietal cells that kills bacteria and denatures protein).

Pepsin( secretion of Cheif cells that begins the digestion of proteins)

Intrinsic factor( secretion of Parietal cells and aids absorption of vitamin B12) 

Gastric lipase( aids digestion of Triglycerides)

3):-Secretes gastrin( from G cells ) into blood which stimulates parietal cells to secrete HCL and Cheif cells to secrete Pepsinogen; contracts lower esophagus sphincter increases motility of the stomach and relaxes Pyloric Sphincter. 

The small intestine:-

Length 2-3 meter and in diameter 1-1.5 inches.

Regions of the small intestine include:-

1) The Duodenum:-C shape 

2) The Jejunum:- coiled shape

3) The Ileum:- Coiled shape

 

Function of the Small intestine:-

1)- Segmentation mix chyme with digestive juices and bring food into contact with the mucous for absorption; peristalsis propels chime through the small intestine.

2)- Completes the digestion of carbohydrates; proteins; and lipids; begins and completes and digestion of nucleic acids. 

3)-Absorbs about 90% of nutrients and water that pass through the digestive system.

The large intestine:-

The large intestine length 1-2 

Regions of the large intestine are the cecum, colon, rectum and anal canal.

Function of the large intestine:-

1) Haustral churning, peristalsis, and mass peristalsis drive the contents of the colon into the rectum.

2) Bacteria in the large intestine convert proteins to amino acids, breakdown amino acids and produce some B vitamins and vitamin k.

3)Absorbing some water, ions, and vitamins.

4) Forming feces.

5)defecating( emptying the rectum)

 

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