DIGESTIVE SYSTEM

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.