Digestive system consist of 1)mouth 2) pharynx 3)esophagus 4)stomach 5)small intestine 6)large intestine.it is one of the most important system of our body, that helps to digest food.it is very important to know how digestive system work.so lets study about digestive system.
DIGESTION– Food must be broken down into mole that are small enough to enter body cells, a process known as digestion.
DIGESTIVE SYSTEM– The organ involved in breakdown of food collectively called the digestive system.
GASTROENTEROLOGY- The medical speciality that deals with the structures,function,diagnosis and treatment of disease of stomach and intestine is called gastroenterology.
OVERVIEW OF DIGESTIVE SYSTEM
Two groups of organ composes the digestive system.
1. The gastrointestinal tract
2.accessory digestive organ.
1.GASTROINTESTINAL TRACT ALSO CALLED ALIMENTARY CANAL
GI is the continuous tube that extend from mouth to anus.through the thoracic and abdominopelvic activities.
ORGANS OF TH GASTROINTESTINAL TRACT
2)Most of pharynx
-The length of gi tract is about 5-7 m in living person.
THE ACCESSORY DIGESTIVE ORGAN.
The accessory digestive organ include,
THE DIGESTIVE SYSTEM PERFORMS SIX BASIC PROCESSES.
1.INGESTION;This process involves taking foods and liquids into mouth.
2.SECRETION; Each day,cells within the walls GI tract total of about 7 lit of water, acid, buffers and enzymes into the lumen (interior space) of the tract.
3.MIXING AND PROPULSION ; Alternating contraction and relaxation of smooth muscle in the wall of GI tract,mix food and secretions. and propel them towards the anus.
[This capability of GI tract to mix and move material along its length is called MOTILITY]
4.DIGESTION– Mechanical and chemical processes break down ingested food into small mole.
There is two types of digestion.
IN MECHANICAL DIGESTION;
- The teeth cut the food before it swalled.
- Then smooth muscle of the stomach and small intestine churn the food.
- As a result food mole dissolved. and throughly mix with digestive system.
IN CHEMICAL DIGESTION;
- Large carbohydrate, lipid,protein and nucleic acid mole in food are split into smaller molecule by hydrolysis.
- Digestive enzymes produced by salivary gland, tongue, stomach,pancrea and small intestine.
- Few substance in food can be absorbed without chemical digestion. eg; vitamin, cholesterol, water.
FUNCTION OF DIGESTIVE SYSTEM
- INGESTION ; Taking food into mouth.
- SECRETION ; Release of water, acid, buffer and enzyme into lumen of GI tract.
- MIXING AND PROPULSION ; Churning and propulsion of food through GI tract.
- DIGESTION ; Mechanical and chemical breakdown of food.
- ABSORPTION ; Passage of digested product from GI tract into blood and lymphatic vessel and then circulate into cells.the entrance of ingested and secreted fluid, ions and products of digestion into epithelial cell lining.the lumen of GI tract is called absorption
- DEFECTION ; Elimination of feces from GI tract. waste,indigested sub,bacterial cells remove from epithelial cells and leave the body through anus process called defection.
LAYERS OF GI TRACT
The wall of GI tract from lower esophagus to anal canal has same basic. four layer arrangement of tissue.
The 4 layers of tract from deep to superfacial are;
mucosa ; or mucus membrane
- Inner laye of GI tract.
- It is composed of 1) epithelial 2) connective tissue 3) smooth muscle.
- EPITHELIAL ;
- 1) A layer of epithelium in direct contact with contents of GI tract
. 2) Location-in mouth, pharynx, esophagus and anal canal.
3) These are mainly non keratinized stratified squamous epithelium that serves protection.
4)Simple columnar epithelium-which function in secretion and absorption lines the stomach and intestine.
5) Epithelial cells are exocrine cells that secret mucus and fluid into lumenof tract and endocrines cells;collectively called entero endocrine cells,which secret hormones.
2.LAYER OF CONNECTIVE TISSUE /LAMINA PROPRIA.
- Is aerolar connective tissue,containing many blood vessel and lymphatic vessel.
- Blood vessel and lymphatic vessel carry nutrients absorbed in GI tract reach the outer tissue of the body.
- Lamina propria also contain majority cells of mucosa associated lymphatic tissue(MALT)
- MALT contain immune system cell protect against cell.
- MALT mainly present in tonsils,small intestine,appendix,large intestine.
3.THIN LAYER OF SMOOTH MUSCLE.
- Thin layer of smooth muscle called muscular mucosae.
- Muscularis mucosae throus the mucus membrane of stomach,small intestine into many small folds which increase area of absorption and digestion.
- Submucosa consist of areolar connective tissue that bind mucosa to muscularis.
- This layer consist of many blood and lymphatic vessel that receive absorbed food molecule.
- submucosa contain network of neuron called SUBMUCOSAL PLEXUS.
- The submucosa may also contain gland and lymphatic tissue.
- The mascularis of mouth, pharynx and superior and middle part of esophagus contain skeletal muscle that produces volutary swallowing.
- muscularis also contain smooth muscle that generally found in 2 sheets
- INNER SHEET-of circular fiber and
- OUTER SHEET-longitudinal fiber.
- Involuntary contraction of smooth muscle help break down food, mix it with digestive secretion and propel it along the tract.
- Those portion of GI tract suspended in abdominopelvic cavity have a superfacial layer called serosa.
- This layer composed of areolar connective tissue and simple squamous epithelium.
- serosa also called visceral peritoneum.
- it forms portion of peritoneum.