THE DIGESTIVE SYSTEM 2

Posted by DAM on February 10, 2012 in The Digestive System | Short Link
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THE DIGESTIVE SYSTEM 2

 

The stomach: (Fig. 26)

It is the most distensible part of the alimentary tract It transmits food from the oesophagus to the duodenum, li lies in the upper left part of the abdominal ca\iiy below the diaphragm.

It has two openings: the cardiac orifice lying ai the junction with the oesophagus and the pyloric orifice a! the junction of the stomach with the duodenum.

It has two surfaces; anterior and posterior, and r»< borders called the lesser and the greater curvatures. The

 

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lesser curvature is the concave right border while the greater curvature is the larger (4 times larger) convex left border. The stomach is divided into two portions:

a)     Cardiac portion: It includes, the cardiac orifice, the fundus (which is the part above the cardiac orifice) and the body (which follows the fundus and it is the largest part of the stomach).

b)     Pyloric portion: It includes the pyloric antrum that follow the body of the stomach, the pyloric canal which is the cylindrical part the follows the pyloric antrum and the pylorus which is the part corresponding to pyloric orifice, it contains the thick pyloric sphincter.

The position and shape of the stomach vary in different people and in the same individual depending on its content and the person’s position.

The stomach is capable of holding up to 3 liters of material in the adult. In the newborn, the stomach is about the size of the hen’s egg, and it can hold about 30 ml of fluid. The stomach functions as a reservoir for food and it secretes the digestive juice which contains hydrochloric acid and certain enzymes.

The small intestine:

The small intestine extends from the pylorus of the stomach to the ileocaecal junction where it joins the large intestine. It is about 6 meters (20 feet) long and it is divided into three parts; the duodenum, the jejunum, and the ileum. The jejunum and ileum are connected to the posterior abdominal wall by a peritoneal fold called the mesentery.

  

 

a)           The duodenum:

It is 25 cm (10 inches) long. It lies on the posterior abdominal wall behind the peritoneum. It is C-shaped and it surrounds the head of the pancreas.

The bile duct and the pancreatic duct unite and open by a common opening in the posteromedial part about the middle of the duodenum. For descriptive purposes, the duodenum consists of 4 parts: 1* part above the head of the pancreas, 2nd part on its right side, 3rd part below it, and 41h part on its left side.

b)          The jejunum:

It is called so because it contains no food after death. It comprises the upper 2/5 of the small intestine distal to the duodenum.

c)          The ileum:

It is called so because it is the most coiled part of the small intestine. It comprises the following 3/5 of the small intestine.

 

Differences between the jejunum and ileum:

1 No.

Jejunum

Ileum

1 5

Larger in diameter

Smaller in diameter

2.

The mesentrv contains small amount of fat so the blood vessels can be seen

The mesentry contains much fat obscuring its blood vessels

3.

The circular folds of the mucosa and the villi are larger and more numerous

The circular folds and villi of the mucosa are smaller and less numerous

 

Function of the small intestine:

The upper part of small intestine is mainly digestive, while its lower part is mainly absorptive.

 

The large-Intestine:

The large intestine extends from the ileocaecal junction to the anus; it is about 1.5 m long. It consists of the caecum and vermiform appendix, the ascending colon, the right colic flexure (hepatic flexure), the transverse colon, the left colic flexure (splenic flexure), the pelvic colon, the rectum and anal canal.

 

Differences between the large and small intestines:

No.

Large intestine

Small intestine

1

It has a greater calibre.

It has a lesser calibre

2.

It is 1.5 m in length

It is 6m in length

3.     The external surface

i

j contains sacs full of fat i called

! appendices epiplociae.

The external surface does not contain

appendices epiplociae.

4.

The longitudinal muscle ; layer forms 3 longitudinal | bands called taeniae col! ! which are shorter in length ! than the true length of the S large intestine so that the ! wall presents ilia titrations ! (sacculations).

The longitudinal muscle layer does not form bands 2nd the wall of the small intestine is smooth without haustrations.

  

The caecum

The caecum is present in the right iliac fossa. It is 6cm long. It is a blind pouch which- is continuous above with the ascending colon.

The ileum opens into the large intesine at the junction between the caecum and ascending colon. The vermiform appendix opens into the posteromedial aspect of the caecum about one inch (2.5cm) below the ileocaecal junction.

 

The vermiform appendix:

A very narrow worm-like tube which opens into the posteromedial aspect of the caecum about one inch (2.5 cm) below the ieocaecal junction.

Its average length is 9cm. It usually lies behind the caecum (retrocaecal) or extending into the pelvis (pelvic).

The ascending: colon: It is about 15 cm in length.

It begins at the upper end of the caecum and extends to the inferior surface of the liver, where it bends to the left to

form the right flexure (hepatic flexure) which connects it with the transverse colon.

 

The transverse colon:

It is about 50 cm in length. It extends transversely across the abdomen from the hepatic flexure to the left splenic flexure where it continues as the descending colon. A peritoneal fold called the transverse mesocolon surrounds it, so it is freely movable.

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