Stomach: function,parts, anatomy and physiology
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| Stomach: function,parts, anatomy and physiology |
STOMACH
The body is the largest and main part of the stomach. This is where food is mixed and start to break down. The antrum is the lower part of the stomach; it holds the break-down food until it is ready to move into the small intestine.
The stomach is an organ in the upper abdomen. it can be divided into the cardia and the non-cardia which includes the under the body, the antrum, and the pylorus. the stomach is part of the digestive system.
Stomach is the most dilated part of the alimentary tract. It extends from the cardiac end to the pyloric end. At its upper end, it is continuous with oesophagus and at the lower end, it is continuous with the duodenum.
Position
In the supine position, the stomach occupies parts of the epigastric, umbilical and left hypochondriac regions.
Shape-
It is j-shaped. Upper part is broader than the lower part. It has 2 ends - upper cardiac and lower pyloric; 2 surfaces anterior and posterior; 2 borders or curvatures the right border or lesser curvature and left border or greater curvature. The greater curvature is four to five times longer than the lesser curvature.
Capacity
A newborn infants' stomach can hold upto 30 ml of milk (It is about the size of a lemon). In adults, stomach is capable of considerable expansion. When empty, it is slightly larger than the large intestine; but it can hold upto 2 to 3 litres of food.
Functions of Stomach(पेट के कार्य)-
1. It acts as a reservoir of food.
2. By its peristaltic activity, it makes the food particles smaller and softer and mixes the food thoroughly with gastric juice.
3. The gastric enzymes, produced by gastric glands have important role in digestion.
4. The hydrochloric acid secreted by gastric glands destroy many organisms present in food and drink.
5. Stomach secretes the intrinsic factor necessary for the absorption of vitamin B₁2.
6. Some substances are absorbed in the stomach, e.g. some drugs, alcohol, glucose, etc.
Parts of Stomach-
For descriptive purposes, stomach can be divided into 5 parts
1. Cardiac part
2. Fundus
3. Body
4. Pyloric part
5. Pylorus.
Cardiac Part-
The cardiac part or cardia lies around the cardiac orifice, which receives the opening of the abdominal part of oesophagus (It was given this name because it lies near the diaphragm where the pericardial sac containing the heart rests)
Fundus-
The fundus of the stomach, is the dilated portion, to the left and superior to the cardiac orifice. This is the most superior part of the stomach, which is related to the left dome of diaphragm. It usually contains a bubble of gas which can be seen in X-rays.
Body of the Stomach
The body of the stomach is the major portion of the stomach. It lies between the fundus and pyloric antrum.
Pyloric Part of the Stomach
There is a sharp angulation of lesser curvature of stomach called incisura angularis (angular notch) which indicates the junction of the body and pyloric part of the stomach. It has 2 parts-a wide portion, the pyloric antrum and a narrow portion, the pyloric canal. The pyloric canal is continuous distally with the pylorus.
Pylorus
The pylorus is a sphincter, which guards the pyloric orifice. It has a thick wall because it contains extra smooth muscle fibres, which controls the rate of discharge of stomach contents into the duodenum. The pylorus normally remains closed except when letting the stomach contents into the duodenum.
Relations
The right, concave border or lesser curvature gives attachment to a double fold of peritoneum called the lesser omentum which stretches towards the liver.
The Left Border or Greater Curvature
The left border or greater curvature gives attachment to the following peritoneal folds from above downwards, as shown in gastrophrenic, gastrosplenic and greater omentum (See CP5 in Colour Plate 2).
Between the two layers of lesser omentum, at the lesser curvature, is the anastomosis between left gastric and right gastric vessels.
Between the two layers of greater omentum at the greater curvature are the right and left gastroepiploic vessels.
Relations of Anterior Surface
1. Left lobe of liver
2. Diaphragm
3. Anterior abdominal wall
Relations of Posterior Surface
"The stomach bed" structures related to the posterior surface form the "stomach bed" They are:
1. Anterior surface of pancreas
2. Transverse mesocolon and transverse colon 3. Anterior surface of upper part of left kidney
4. Left suprarenal
5. Splenic artery
6. Diaphragm
7. Gastric surface of spleen.
Blood Supply of Stomach
Arterial Supply
The stomach has a rich blood supply from thé branches of coeliac trunk.
The left gastric artery: It is a branch of the coeliac trunk, which descends along the lesser curvature between the layers of lesser omentum.
Right gastric artery, a branch of hepatic artery, runs along the lesser curvature; it anastomoses with the left gastric artery and supply the right half of the stomach.
Left gastroepiploic artery, a branch of splenic artery; it descends along the greater curvature between the layers of greater omentum.
Right gastroepiploic artery, a branch of gastroduodenal artery, which goes along the greater curvature between the two layers of greater omentum and anastomoses with the left gastroepiploic artery. Short gastric arteries are 5-6 in number; they arise
from the splenic artery and supply the fundus of stomach.
Venous Drainage
Right and left gastric veins end in the portal vein, short gastric and left gastroepiploic veins drains into the splenic vein; right gastroepiploic vein drains into superior mesenteric vein. The prepyloric vein of Mayo connects the right gastric and right gastroepiploic veins and crosses the anterior surface of pylorus. So, it forms an important landmark for surgeons in the identification of location of pylorus.
Lymphatic Drainage
The stomach is divided into 4 zones as shown in. All the nodes finally drain into coeliac nodes.
Nerve Supply
Nerve supply is by autonomic nervous system. Parasympathetic fibres come from the vagus. Sympathetic fibres arise from the coeliac plexus. Parasympathetic stimulation increases the motility of stomach and increases the secretion of gastric juice rich in pepsin and hydrochloric acid.
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