DIGESTIVE SYSTEM

Sunday, November 28, 2010


Digestive system is the collective name used to describe the alimentary canal ,   accessory organs and variety of digestive process

The system contains
Different parts of digestive canal    +    Liver    +   pancreas   +  Gallbladder    +   Digestion   +    Absorption
Digestive process takes place at different levels in the canal
Alimentary canal begins at the mouth passes  through the thorax, abdomen,  pelvis cavities and ends at the anus.

Parts of GIT
Mouth -----Pharynx-------Esophagus-------Stomach--------mall intestine---------Large intestine---------Anus

Accessory digestive organ
 Teeth ---Tongue---Slivery glands—Liver---Gallbladder-----Pancreas
Teeth is directly involved in digestion of food by breakdown of food
Tongue--------Chewing and swallowing
The other accessory digestive organs never come into directs contact with food
They produces secretions that flow into the GIT through ducts
These secretions-----Chemicals break down of food materials

Processes of digestion

There six processes in the digestive system

1. Ingestion
      Taking of food into the mouth ,eating and drinking\
2.Propulsion
       Mixes and moves the contents along the GIT
                    Contractions  & relaxations of smooth muscles in the walls of the GIT
        mix food & secretion & propel them towards anus ---Motility
3. Digestion
       It done by 2 processes
      A. Mechanical digestion
        Ex – Mastication  (Chewing)
 B. Chemical digestion
        Food metabolized  into small particles by enzymes present in the
        secretion produced by glands and accessory organs of the digestive
        system
4. Secretion
       Cells within the walls of the GIT & accessory digestive organs
       secrete a total about 7 liters, acid ,buffer sand enzymes into tract
5. Absorption
       This is the process by which digested food substances pall through
       the walls of some organs of the canal into t he blood & lymph
       capillaries for circulation and use by body cells
6. Elimination
             Food substances that have been eaten but cannot be digested & 
               absorbed are excreted from the alimentary y cannot as faces by
               process of defecation
GASTRO NTESTINAL TRACT
Layer  -  4 layers
Start from esophagus to anus

Layers
  1. Mucous layer
  2. Sub mucosa layer
  3. Muscular layer
  4. .Adventitia or serosa
1 . Mucous layer
A.    Mucous membrane layer
B.     Lamina propria
C.      Muscularis mucosae

A. Mucous membrane layer
Innermost layer
Made-up of simple columnar epithelium
Renewal of GIT epithelial cells is rapid
Every 5-7 days they slough off and are replaced by the new cells
Function—Protection, secretion, and absorption
Mucous membrane contain goblet cells each secretes mucous
Mucous lubricates the walls of the tract and protect them from digestive enzymes
It also contains endocrine cells that secretes hormones into their blood stream

B. Lamina propria
It is made up of loose connective tissue containing many blood & lymphatic vessels
By this layer the nutrients absorbed into the GIT and reaches the other tissues of the body
It is between epithelial cells and muscularis mucosa
It also contain Majority of mucosa associated lymphatic tissue  (MALT)
These present all along the GIT tract.
It protect the against disease

C .Muscularis mucosae

A thin layer of smooth muscle fibers called the muscular is mucosa
It is outer layer of smooth muscle
It throws the mucous membrane of the stomach and small intestine into many small folds which increase the surface area for digestion and absorption
Movements of the muscular is mucosa ensure that all absorptive cells are fully exposed to the contents of the GIT

2.     Sub mucosa

This layer consists of loose connective tissue collagen and some elastic fibers
It contains plexuses of blood vessels, nerves, lymph vessels and varying amount of lymphoid tissue.     The blood vessels are arterioles, venules and capillaries
The nerve plexus is the sub mucosal or muissners plexus containing sympathetic and Para- sympathetic nerves that supply the mucosal lining

3. Muscular layer

It consists of two layers of smooth muscle –Involuntary muscles
The muscle fibers of the outer layer are arranged longitudinally and those of the inner layer encircle the wall of the tube
Between these two muscle layer , there are blood vessels, lymph vessels and a plexus (net work) of sympathetic and parasympathetic nerves called my enteric plexus
These nerves supply the adjacent smooth muscle and blood vessels


4. Adventitia  or  serosa

This is the outermost layer
The outermost layer of the wall of GI tract is either serous or fibrous in nature
In this thorax it consists of loose fibrous tissue and in  the abdomen the organs are covered by a serous membrane (serosa) called peritoneum.
The serous layer is formed by connective tissue and mesoepithelial cells
It also called serosa or serous membrane.
It covers stomach, small intestine and large intestine
The fibrous layer is otherwise called fibrous .
It is formed by connective tissue .
It cover pharynx and esophagus.

Peritoneum
The peritoneum I largest serous membrane of the body
It consists of a closed sac, containing a small amount of serous fluid within the abdominal cavity
It is richly supplied with blood and lymph vessels, and contains many lymph nodes,
It provides a physical barrier to local spread of infection and can isolate an infective focus such as appendicitis preventing involvement of other abdominal structures
It has two layers
Parietal layer   -  which lines the abdominal wall
Visceral layer   - which cover the organs(viscera) within the abdominal and pelvic cavities
The two layers of peritoneum are actually in contact
The friction between them is prevented by the presence of serous fluid secreted by the peritoneal cells
The peritoneal cavity is only a potential cavity
A similar arrangement is seen with the membranes covering the lungs, the pleura.
In  the male the peritoneal  cavity is completely closed  but in the female the uterine tubes open into it and the ovaries are the only structures  inside

Nerve supply
 
The GIT and its related accessory organs are supplied by nerves from both divisisions of the autonomic nervous system---Sympathetic and Para sympathetic parts

Their actions are antagonistic and one has a greater influence than the other, according to body needs, at any particular time.

When digestion is required this is normally the parasympathetic nervous system


Para sympathetic supply

One pair of cranial nerves, the vagus nerves, provides this supply to most of the alimentary tract and the accessory organs.

Sacral nerves supply the most distal part of the tract .

The effects  of parasympathetic stimulation are

Increased muscular activity especially peristalsis ,because there is less stimulation of the my enteric plexus

Increased glandular secretion , through activity of the sun mucosal plexus
  Sympathetic supply

Nerves from thorax and lumbar nerves
 These nerves forms plexuses in the thorax  abdomen and pelvis , from which nerves pass to the organs of the alimentary tract
  
The effects of sympathetic stimulation are
 Decrease muscular activity m especially peristalsis, because there is less stimulation of the my enteric plexus
Decrease glandular secretion , as stimulation of the sun mucosal plexus id reduced.

Digestion, Absorption and Metabolism of proteins



The dietary proteins are formed by long chains of amino acids bound together by peptide linkages

Diet containing protein are

Wheat        -      Glutenin, gliadin

Milk             -     Casein, albumin, lactalbumin and myosin

Egg              -      Albumin and vitelin

Meat            -      Collagen, albumin and myosin

Digestion of proteins

The enzymes responsible for digestion of proteins are called proteolytic enzymes

Mouth                     -  No digestion

Stomach                -  Pepsin is the only proteolytic enzymes in gastric juice
                                     Rennin is also present in gastric juice
                                     But rennin is absent in human

SI                             -  Most of the proteins are digested in SI  by photolytic enzymes

Pancreatic juice   - Trypsin, chymotrypsin and carboxy poptidases
                                     These break down the bonds of the protein molecules


Succus Entericus   -DI, tri and amino peptidases

Absorption of protein

The final products of protein digestion are the amino acids which are absorbed into blood from intestine

The levo amino acids are actively absorbed by means of sodium co- transport, whereas the dextro amino acids are absorbed by means of facilitated diffusion

It contains di, tri , amino peptidases
 
DIGESTION OF PROTEINS
                                                    
AREA

JUICE

ENZYME
SUBSTRATE
END POINT

MOUTH
SALIVA
NO
PROTEOLYTIC
ENZYME
STOMACH
GASTRIC JUICE
PEPSIN
PROTEINS
PROTEOSES
PEPTONES








SMALL INTESTINE





PANCREATIC JUICE















SUCCUS ENTERICUS



TRYPSIN


CHYMO
TRYPSIN





CARBOXY PEPTIDASES  A & B





DIPEPTIDASES


TRIPEPTIDASES


AMINO PEPTIDASES





PROTEOSES
PEPTONES






DIPEPTIDES
TRIPEPTIDES
POLYPEPTIDES





DIPEPTIDES


TRIPEPTIDES


LARGE POLYPEPTIDES




DI, TRI  &
POLYPEPTIDES






AMINO ACIDS










AMINO ACIDS