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Human Digestive System(Part 1)
2013-02-14, 9:50 AM

Human Digestive System

Introduction

The  task of the digestive tract is the physical and chemical breakdown of food. Following ingestion food and fluids are processed by the digestive organs so that the nutrients can be absorbed from the intestine and circulated around the body. Any residue of food i.e., not digested is solidified and eliminated from the body in the form of faeces (excreta).

Digestive tract

                The process of digestion begins when food enters the mouth and is largely completed at the end of small intestine.

 

Digestive organs

                It is composed of mouth, pharynx, oesophagus, stomach, intestine, rectum and anus which is basically a food processing pipe about 9metres (30ft) long.

                Associated digestive structure includes three pairs of salivary glands,the pancreas,the liver and gall bladder each of which has an important role.The appendix – a short blind ended tube attached to large intestine has no known function.

 

Digestive Enzymes

                They are protein molecules that increase the speed of chemical reactions in the body. These are secreted by the gland cells present in the wall of digestive system along with other substances in the form of juice.

 

Role of Enzymes in digestive system

 

                They add a molecule of water and split the chemical bonds in complex molecules. This process of splitting a molecule with the addition of water molecule known as hydrolysis.

 

·         Enzymes containing hydrolytic reactions known as hydrolytic enzymes (or) hydrolases.

·         The complex molecule on which enzyme acts – Substrate.

·         The simple molecules formed from complex molecule – Products.

 

One type of enzyme acts only on one substrate but not on other substrate of another enzyme.

Example: LIPASE acts on LIPIDS but not on PROTEINS

 

                Enzymes will be active basing on the concentration of hydrogen ions, temperature and amount of substrate. Some will be inactive when they are secreted, they will be active in the lumen of digestive system.

 

http://www.healthegoods.com/media/catalog/product/o/p/optimal_chewable_enzyme_function_chart_2.jpg

 

Digestive Glands

·         Mouth : Salivary glands

§  Parotid

§  Sub-mandibular

§  Sub-lingual

·         Stomach: Liver (largest gland) and Pancreas (Second largest gland).

·         Intestine: Duodenum, Jejunum and Ileum.

Digestion

                The process of converting complex molecules (Carbohydrates) into simple molecules (sugars) known as digestion.

                The digestive process breaks down the food by chemical and mechanical action into substances that can pass into the bloodstream and be distributed to the body cells.


Types of digestion

 Intercellular Digestion

    ·         Digestion occurs in the food vacuoles within cells.

    ·         Lysosomal enzymes are secreted into the food vacuole.

    ·         Products of digestion diffuse into cytoplasm through vacuolar membrane.

    ·         Ingestion occurs through pinocytic vesicle,

    ·         E.g. protozoans, sponges and coelenterates.

 Extracellular Digestion

    ·         Digestion occurs outside of cells in the lumen of the alimentary canal.

    ·         Salivary, gastric pancreatic and intestinal enzymes are secreted into the digestive cavity.

    ·         Digested food materials are absorbed into blood through gut epithelia.

    ·         Ingestion occurs through mouth.

    ·          E.g. coelenterates to chordates.

Detailed Description

                The digestive system of human beings comprises of

·         Alimentary canal: Mouth, Buccal cavity, Pharynx, Oesophagus, Stomach, Intestine (small & large),    Rectum and Anus.

  ·         Digestive glands:Salivary glands, Gastric glands and Intestinal glands.

Ø  Mouth

                It is a transverse slit like opening covered with upper and lower lips which helps in taking the food  materials – Ingestion process.

  Ø  Buccal Cavity

               This is the space or cavity present inside the mouth bounded dorsally by pellate, ventrally by throat and laterally by jaws composed of

 o   Pellate

It acts as a roof and divisible into anterior hard pellate and posterior soft pellate behind this, UVULA is present.

o   Tongue 

         It is a thick muscular sensory organ present on the floor of buccal cavity consisting voluntary muscles, blood vessels and sensory nerves.The functions of tongue are it helps in ingestion, chewing swallowing, tasting, cleaning the teeth and mixing the food with saliva.

o   Teeth

          It is the hardest material of the body which helps in cutting, tearing, chewing and grinding the food.

The teeth present in the buccal cavity constitute dentition. In human beings teeth are thecodont (embedded in jaws), heterodont (different types) and diphyodont (two sets).

o   Types of teeth

According to their shape and function they are divided into 4 types as follows:

§  Incisors: Flat shaped with sharp edges,    

 helps in cutting

§  Canines: Pointed edges, helps in tearing.

§  Pre molars: Ridged shaped, helps in grinding.

§  Molars: Flat shaped, helps in crushing, grinding.

 

 o   Using the Jaws

The process of digestion starts as soon as food enters the mouth. Food is chewed, lubricated by saliva and processed by the tongue. The flexible temperomandibular joint attaches the jaw bone to the skull which allows moving in different directions. With the help of tongue food moves in the mouth and by the teeth until it is formed into soft lump as a bolus for swallowing.

o   Structure of Tooth

The teeth are enclosed in sockets in the jaw bone and held in place by ligaments and shock absorbent gums. At the centre of each tooth, a soft pulp is present with blood vessels and nerves surrounded by a layer of sensitive tissue known as dentine. Above the gum tooth has an outer covering of hard enamel and below the gum a bone like tissue is present known as cementum forms the tooth’s outer layer. The important parts of this are

§  Crown: Present above the gum.

§  Root: Embedded in the gum.

§  Neck: Narrow part of the gum line.

        Tooth Structure

  •    Dental Formula

It is represented by D.F = N/D

                                                Where N stands for no. and kind of teeth in the upper part.

                                                                D stands for no. and kind of teeth in the lower part.

 

§  Dental formula in adults :  I 2/2, C 1/1, P 2/2, M 3/3 (x2= 32) 

The format will be 2:1:2:3/2:1:2:3

Where the numbers correspond to I: C: P: M          (upper)/I: C: P: M (lower).

 

§  Dental formula in children’:  2/2, C 1/1, P 2/2, M 3/3 (x2= 32)

                                                The format will be 2:1:2:0/2:1:2:0

Where the numbers correspond to I: C: P: M (upper)/I: C: P: M (lower).

`               The primary set of teeth developed during childhood known as Milk or Deciduos teeth and is replaced as a permanent teeth in adults.

                                The total set of teeth in the buccal cavity constitutes Dentition.

o   Salivary glands

                   The saliva contains an enzyme amylase and is carried by the ducts into the mouth. It is composed three pairs of salivary glands:

o   Parotid glands – Stenson’s gland

These are located in front of the ear and the duct opens inside the cheek opposite to the second upper molar tooth.

o   Sub-mandibular glands – Wharton’s gland

These are located deep into the mouth on each side of the jaw bone and the duct opens into small swelling on the underside of the tongue.

o   Sub-lingual glands – Rivinus gland

These are located under the tongue and the duct open into the floor of the mouth.

                            Salivary Glands

                                                           Continuation......... Next file

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