What is Stomach?
Stomach is the widest and most distensible part of the alimentary canal between the oesophagus and the duodenum.
The main function of stomach are-
1- it forms a reservoir food.
2- Mixes food with gastric secretion to form a semifluid substance called chyme.
3- Controls the rate of delivery of chyme into the small intestine to allow proper digestion and absorption in the small intestine.
4- Hydrochloric acid secreted by the gastric glands destroys bacteria present in the food and drink.
5- Castle's intrinsic factor present in the gastric juice helps in the absorption of vitamin B12 in the small intestine.
LOCATION OF STOMACH
Stomach is situated in the upper left part of the abdomen occupying left hypochondriac, umbilical and epigastric regions. It extends obliquely from the left hypochondriac region into the epigastric region.
Most of the stomach lies under cover of the left costal margin and lower ribs.
Shape of the Stomach
The stomach is mostly "J" shaped. Its long axis passes downward, forward and to the right and finally backward and slightly upward.
Size and Capacity of Stomach
Length: 10 inches
Capacity : the capacity of the stomach is variable as the stomach is highly distensible.
1- At birth the capacity is only 30ml
2- At puberty the capacity is 1000ml.
3- In adults the capacity is 1500 to 2000ml
EXTERNAL FEATURE OF STOMACH
The stomach presents the following external features:
1) Two ends: Cardiac and pyloric
2) Two curvature: Greater and lesser
ENDS OF THE STOMACH
Cardiac End(Upper End)
It joins the lower end of the oesophagus and presents an orifice called "cardiac orifice"
Pyloric End (Lower End)
It joins the proximal end of the duodenum and presents an orifice called "pyloric orifice".
CURVATURES OF THE STOMACH
The stomach presents two curvature- lesser and greater
Lesser curvature
It is concave and forms the shorter right border of the stomach. The most dependent part of this curvature - the angular notch, indicates the junction of the body and pyloric part. The lesser curvature provides attachment to the lesser omentum.
Greater curvature
It is convex and forms the longer left border of the stomach. At its upper end this curvature presents a cardiac notch which separates it form the left aspect of the oesophagus . The greater curvature provides attachment to the greater omentum, gastrosplenic , and gastrophrenic ligaments.
SURFACES OF THE STOMACH
Anterosuperior (Anterior) Surface
It faces forward and upward
Posteroinferior (Posterior) Surface
It faces backward and downward
PARTS OF THE STOMACH
The stomach has four parts-
1- Cardiac part
2- Fundus
3- Body
4- Pyloric part
Cardiac part
It is the part around the cardiac orifice.
Fundus
The fundus is the upper dome-shaped part of the stomach situated above the horizontal plane drown at the level of cardiac notch. Superiorly, the fundus usually reaches the level of the left 5th intercostal space just below the nipple, hence gastric pain sometimes imitates the pain of angina pectoris. The cardiac lies between the fundus and the oesophagus .
Body
The body is the major part of the stomach between the fundus and pyloric antrum. It can be distended enormously along the greater curvature.
Pyloric part
The pyloric part is the funnel-shaped outflow region of the stomach. It is divided into three parts:
1- Pyloric antrum- it is the proximal wide part which is separated from the pyloric canal by an inconstant sulcus, sulcus intermedius present on the greater curvature.
2- Pyloric canal - it is a distal narrow and tubular part measuring 1 inch in length.
3- pylorus - it is the distal most and sphincteric region of the pyloric canal.
Microscopic structure of the stomach
The wall of the stomach consists of four coats . From outside inward, these are serous, muscular, sub mucous and mucous coats.
1- The serous coat is formed by the peritoneum.
- The muscular coat consists of three layers of unstriped muscles- outer longitudinal, middle circular and inner oblique.
2- Circular muscle coat thickens at the pylorus to form a ring of muscle called "pyloric sphincter".
3- The sub mucous coat consists of loose areolar tissue.
4- The mucous membrane is thick, soft and velvety. It presents a number of temporary folds which disappear when the stomach is distended.
BLOOD SUPPLY OF THE STOMACH
ARTERIAL SUPPLY OF THE STOMACH
The stomach has rich arterial supply derived from coeliac trunk and its branches. The arteries supplying the stomach are-
1- Left gastric artery, a direct branch from the coeliac trunk.
2- Right gastric artery, a branch of the common hepatic artery
3- Left gastroepiploic artery, a branch of the splenic artery
4- Right gastroepiploic artery, a branch of the gastroduodenal artery.
5- Short gastric arteries, branches of the splenic artery.
VENOUS DRAINAGE OF THE STOMACH
The veins of the stomach correspond to the arteries and drain directly into the portal vein. The vein of the stomach are:
1- Left gastric vein
2- Right gastric vein
3- Left gastroepiploic vein
4- Right gastroepiploic vein
5- Short gastric veins
NERVE SUPPLY OF THE STOMACH
The stomach has both sympathetic and parasympathetic innervation.
Sympathetic innervation
The sympathetic fibres are derived from T6 to T10 spinal segments via greater splanchnic nerves and coeliac and hepatic plexuses.
Parasympathetic Innervation
The parasympathetic fibres are drived directly from the vagus nerves.
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