Digestive System: –
A long muscular tube consisting of the following parts from above to downwards of the human digestive system is: the mouth, tongue, pharynx, oesophagus, stomach, small intestine, large intestine, rectum and anal canal. The ducts of the salivary glands open into the mouth.
Human Digestive System
The proximal end of the stomach is guarded by the cardiac sphincter and the distal end of the stomach is guarded by pyloric sphincter. After the pyloric sphincter the small intestine begins and consist successively the subdivisions are the duodenum, the jejunum and the ileum. From the stomach the duodenum receives food. Where the duodenum joints the jejunum, connective tissue and muscle fibres thicken the mesentery. The bile duct and the pancreatic duct jointly open in it through ampula of Vater. The small intestine in the human digestive system is very long and roughly more than 75 metres and the long length provides enough time and surface area, as a result digestion and absorption of foodstuff may be completed. The next part of the human digestive system is the large intestine where the small intestine opens. The opening between the small intestine and the large intestine is guarded by ileocolic sphincter. The faeces are formed at large intestine after absorption of water. The large intestine opens into the last part i.e. the rectum and anal canal. The anal canal opens outside through the anal orifice. Peritoneum is a serious membrane, which lines the interior of the abdominal cavity. The lesser omentum of the stomach attaches to the liver and the greater omentum hangs from the greater curvature of the stomach over the intestine to the colon, just like an apron.
There are hundreds of millions of body cell at our body. The foods we eat cannot reach cells because it cannot pass through the intestinal walls to the bloodstream and it should be make useful in a chemical state. The digestive system modifies food physically and chemically and disposes of unusable matter in the food. Digestion means the physical and chemical modification of the food which depends on exocrine and endocrine secretions and a controlled movement of the food through the digestive tract.
Mouth: –
The food enters into the digestive system through the oral cavity which is called the mouth. The outer opening of the mouth is protected by the lip, cheeks guarded laterally as two walls, the anterior roof formed by the hard palate and the posterior by the soft 
palate. The seal cavity maintains it’s communication through the behind of the soft palate.The floor of the mouth is a muscular body namely the tongue. Tongue has a bony attachments and attached to floor of the mouth. The teeth start the process of digestion by cutting the food staff into pieces then retain in the closed mouth and masticated, which are aided by the saliva ducted by the salivary glands opens at the various points into mouth. So, in the human digestive system the digestive process begins in the mouth and the food is partly broken down by the process of chewing and by the chemical action of salivary enzymes.
After leaving the mouth the food must cross the respiratory tract by a quite complicated mechanism called deglutination ( I.e. Swallowing) which make the mouth empty and ensures that no food particle gets entry through the wind pipe. The coordinate activity of tongue, soft palate, the pharynx and the oesophagus results the activities of swelling. Firstly the food being forced into the pharynx by the tongue and after this as a reflux process the tongue blokes the mouth, soft palate closes the nose and the larynx rises so that the epiglottis closes off the trachea. In this process the food moves into the pharynx and then by peristalsis aided by gravity.
Oesophagus: –
It is a long tube between the mouth and the stomach. Rhythmic muscle movements to force food from throat into the stomach organized here in human digestive system. It is the first part of the digestive tract. The greater part of the oesophagus lies in the thorax. The orifice in the diaphragm through which the oesophagus enters the abdomen is located at the level of 10th thoracic vertebra, slightly to left of the median plane. From the orifice the oesophagus passes downwards and to the left to end by joining the cardiac end of the stomach.
Stomach :-
A sac like muscular body that is attached to the oesophagus, that serves as a reservoir of swallowed food, and parlays an important part in digestion. It has a capacity of about two litres. It is the most dilated part of the alimentary canal of the human digestive system. It’s shape varies considerably which depends on whether it is full or empty. 
Pressure is also a factor of influence of stomach shape. The cranial end of the stomach is continuos with the oesophagus. As this end is nearer to the heart it is called the cardiac end. The stomach’s caudal end is continuous with duodenum which is called the pyloric end or pylorus. The stomach has two surfaces, the anterosuperior and the posteroinferior.
These surfaces meet At a concave upper border, and at lower convex border, which are called the lesser curvature and the greater curvature respectively. The stomach is lined by peritoneum on both it’s surfaces. The stomach is divided in number of parts. At the junction of left margin of the oesophagus with the greater curvature of the stomach there is a deep cardiac notch. This part of the stomach is called the fundus. The upper part of the lesser curvature faces to the right, where the lower part faces upwards and the junction of these parts of the curvature is often marked by a notch called the angular incisure. The part of the stomach to the left of the incisure which is more or less round in shape is called the body. The part of the stomach to the right of the angular incisure is the pyloric part which consist of a relatively dilated left part called the pyloric Antrum and the narrower right part called the pyloric canal.
The position of the stomach relative to the surface of the body may be stated as follow. The cardiac end is situated to the left of the median plane, behind left seventh costal cartilage, one inch from the midline. This point lies at the level of the eleven thoracic vertebra. The pylorus lies about half inch (1.2 cm) to the right of the midline. The highest part of the stomach s the fundus which reaches the left fifth intercostal space, just Delos the breast nipple. The greater curvature cuts the costal margin at the level of the tenth costal cartilage. Stomach’s lowest part is formed by the pyloric antrum which may lie below the level of the umbilicus, when the stomach is full. Commonly the stomach is J-shaped which have a long vertical part and a shorter horizontal part.
Small Intestine: –
It is a tube about five meters long and is divided into three parts 1) Duodenum, 2) Jejunum, and 3) Ileum.
Duodenum : –
It is the first part of the long intestine and is 25 cm (10 inch) long, C-shaped.
Duodenum
It curves around head of pancreas and the entry of common bile duct. It is continuous at its cranial end with the stomach. The junction between the two is called the pyloroduodenal junction . At the caudal end the duodenum becomes continuous with a junction called duodenojejunal flexure . Like the rest of the small intestine the mucous membrane of the duodenum is marked by transverse fold. But in the posteriolateral portion of the descending part the mucous membrane also shows a prominent vertical fold, the lower part of this fold is marked by a projection called the major duodenal papilla. A short distance cranial to, and in front of the major duodenal papilla there is a smaller projection named minor duodenal papilla. The major papilla bears an opening of a common channel, the hepatopancreatic ampulla, into which the bile duct and the main pancreatic duct open, whereas the minor papilla has an opening for the accessory pancreatic duct.
Jejunum and Ileum : –
In the human digestive system the Jejunum and ileum are in the form of long coiled tube suspended from the posterior abdominal wall by the mesentery. The Jejunum s proximal to the ileum and is about two meters long. The ileum is about three meters long. But there is no specific demarcation between the Jejunum and ileum. They are distinguished mainly on the basis of the structure of their walls. Because of the mobility of the Jejunum and ileum, their relation are quite variable. The coils occupy the central and lower part of the abdominal cavity, in the interval between the ascending colon and the descending colon. The first coil of the Jejunum lies in front of the left kidney, behind the transverse mesocolon. The end part of the ileum lies in the true pelvis and it passes to the right across to join the caecum.
Large Intestine: –
The large intestine of human digestive system is about one and half meter long . The main sub division of the large intestine are the caecum , the ascending 
colon, the transverse colon, the sigmoid colon, the rectum and the anal canal. The last part of the ileum becomes continuous with the large intestine at the ileocaecal junction, near which the caecum is also joined by a short, narrow, blind tube called the vermiform appendix. The ascending colon meets the transverse colon at the right colic flexure and the junction of the transverse colon with the descending colon is called the left colic flexure.The part of the large intestine lying below the level of ileocaecal junction is called the caecum. The caecum is in a open communication with the ascending colon and it is about 6 cm in height and about 7.5 cm in width. The vermiform appendix looks very much like a round worm. It is a tube only a few millimetres wide and about 9 cm in length. At the end, the apex, the appendix is blind, and at the other end, at the base it opens into the caecum. The ascending colon lies vertically in the right lateral region of the abdomen. It is about 15 cm long. The lower end is continuous with the caecum at the level of the intertubercular plane and its upper end meets the transverse colon at the right colic flexure. The transverse colon is the longest subdivision of the large intestine. It begins at the right colic flexure, and ends at the left colic flexure. The descending colon begins at the left colic flexure and descends through the left lateral region, then the left inguinal region to reach the left side of the brim of the true pelvis. It ends here by becoming continuous with the sigmoid colon. The sigmoid (or, pelvic) colon is highly variable in length. Usually it is 40 cm long and is continuous at one end with the lower end of the descending colon and at the other end with the rectum. After the rectum the terminal part of the human digestive system is the anal canal.
Rectum: –
The rectum is a wide tube about 12 cm long. It lies in the true more or less in the middle line. The sigmoid colon is continuous with its upper end. The lower end lies a little below and in front of the Ito of the coccyx, and this end becomes continuous with the anal canal. The lower part of the rectum is wider then the upper part which is called the ampulla . In the male the peritoneum passes from the front of the rectum to the urinary bladder which formed the rectovesical pouch and in the female the peritoneum from the front of the rectum passes to the posterior wall of the vagina forming the pouch of Douglas .
Anal Canal: – In human digestive system the anal canal is the lowest part of the alimentary canal. Above it is continuous with the lower end of the rectum. Below it opens to the exterior at the anus. The anal canal is about 4 cm in length. The rectum lies above the diaphragm in the true pelvis, but the anal canal lies below the diaphragm in the perineum.