THE DIGESTIVE SYSTEM 3
The descending colon:
It is about 25 cm in length. It extends from the splenic flexure to end at the inlet of the pelvis where it joins the pelvic colon.
The pelvic colon
It is about 40 cm in length. It begins at the inlet of the pelvis and ends at the middle of the sacrum where it is connected with the rectum.
It forms a loop and it is surrounded by a peritoneal fold called pelvic mesocolon, so it is freely movable and hangs in the pelvic cavity.
It is about 12 cm in length. It begins at the middle of the sacrum and ends below the coccyx where it opens into the anal canal. In human, it is not straight as its name implies but it rather forms 3 flexures two convex to the right and one to the left.
The anal canal:
It is about 4 cm in length and ends below, in the perineum by the anal opening (anus). Interna) and externa! sphincters control the opening.
It is a serous membrane formed of two layers; i parietal layer lining the wall of the abdomen, and a viscera Saver covering the abdominal viscera. ~
In some regions it extends as a fold formed of ‘. layers to connect the internal organs with the abdomina
wall, e.g. the mesentery and the transverse mesocolon, so that it facilitates the movement of organs of alimentary canal.
The glands associated with the alimentary canal:
1. The Salivary glands: (Fig. 27)
There are three pairs of salivary glands, which secrete the saliva into the mouth.
1. The parotid glands: located one on each side in front and below the external ear. Each gland has a duct that opens in the vestibule of the mouth opposite the upper 2nd molar tooth.
2. The submandibular glands: located below the body of the mandible near its angle. Their ducts open under the tongue on the sublingual papillae.
3. The sublingual glands: located directly under the
tongue, covered by the mucous membrane of the floor of
the mouth, raising the two sublingual folds. They open by
numerous short ducts (8-20) in the floor of the mouth.
II. The pancreas:
The pancreas extends transversely on the posterior abdominal wall in front of the upper two lumbar vertebrae. It is 15 cm in length. Its expanded right part is called the head and it is surrounded by the duodenum. The head is followed by a constricted part called the neck, which lies in front of. the portal vein. The neck is followed by the main part called the body. .The left tapering end of the pancreas is the called the tail which rests on the spleen. The pancreas serves both exocrine and endocrine functions. It secretes the
pancreatic juice and the hormone, insulin. The duct of the pancreas, which transmits the pancreatic juice, opens with the common bile duct in the middle of the second pan of the duodenum.
III. The liver:
The. liver is a large gland weighing over 1.5 kg. It is wedge shaped with its base directed to the right and its apex directed to the left.
It lies principally in the right hypochondrium but stretches across the epigastrium to reach the left hypochondrium.
It is divided into two man lobes; a large right lobe and smaller left lobe. A smaller part; the quadrate lobe, is demarcated on the inferior surface of the right lobe and another circumscribed part on its posterior surface is called the caudate lobe.
The porta hepatis is an opening on its inferior surface behind the quadrate lobe through which the right and left hepatic ducts, the hepatic artery and the portal vein pass in that order from before backwards.
Blood supply of the liver:
The liver has a dual blood supply:
a) Oxygenated blood form the hepatic arterv which arises form the coaliac trunk: a branch from the aorta.
b) Portal venous blood from the portal vein.
The blood leaves the through the hepatic veins to the inferior vana cava. The liver is the site of very many vital metabolic processes. It also secretes bile.
The biliary apparatus:(Fig. 28)
It consists of the ducts through which the bile is transported and the gall bladder, which concentrates it.
Interlobular ducts discharge their contents into the tributaries of the right and left hepatic ducts, which leave
the liver through the porta hepatis and unite to form the common hepatic duct (3cm in length).
The common hepatic duct unites with the cystic duct from the gall bladder to form the common bile duct (7.5 cm in length).
The common bile duct opens together with the
pancreatic duct in the middle of the second part of the duodenum.
The gall bladder is a pear shaped organ 7 -10 cm in length having a capacity of about 30-50″ ml. it is attached to the inferior surface of the liver to the right side of the quadrate lobe.
It consists of a fundus; which project beyond the inferior margin of the liver, a body and the neck which is the narrow part following the body and continuous with the evstic duct. The cystic duct is 3-4 cm in length. It unites with the common hepatic duct at an acute angle to form the common bile duct.