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
- Mucous layer
- Sub mucosa layer
- Muscular layer
- .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.
