Anatomy of the Stomach

The stomach has many different compartments and is composed of many sections. It is derived from the foregut, located in the left hypochondrium, epigastrium, and umbilical regions. Its separated into the fundus, body, and pyloric regions. The pyloric region is split into three different areas: the pyloric antrum, canal, and sphincter. Finally, the stomach is located from T10-L1 vertebral columns.

The fundus usually contains gas and is located at the superior portion of the stomach. The body of the stomach lies between the fundus and angular notch of the stomach. The pyloric area is located at the level of the first lumbar vertebrae, and extends from the angular notch of the stomach to the gastro-duodenal junction.

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The pyloric region is the thickest part of the stomach, and its pyloric sphincter directs what gets into the doedenum and what doesn't. Two thirds of the time the pyloris remains in an open or relaxed state, allowing small quantities of food to pass into the duodenum. Because it is so narrow, it only allows food that is well emulsified to pass through into the first part of the small intestine.

The organ itself is completely covered in peritoneum, which then passes to the liver as the lesser omentum and also hangs down from the stomach, fuses with the transverse colon as the greater omentum. The upper and lower borders of the stomach are called the lesser and greater curvature, respectifully.

In order to preven gastric reflux, the cardio-oesophageal junction is the most fixed point. It is at this location that the right crux of the diaphragm, mucosal rosette, lower oesophageal sphincter and intra-abdominal part of the oesophagus contract and prevent contents of the stomach back up the oesophagus.

The stomach lies just under the left side of the diaphragm. At its posterior side there are a few structures that are important clinically. Its posterior wall is covered by peritoneum of the anterior wall of the omentum bursa (lesser sac), and the bed is covered by the posterior wall of the lesser sac.The bed consists of the dome of the diaphragm, left crus, the top part of the left kidney which is overlaid by a few structures, namely: the tail of the pancreas, the spleen and the suprarenal gland.

On the lower border of the stomach you will see part of the pancreas showing through, with the transverse mesocolon passing on the underside of the inferior border of the pancreas. While to the right of the lesser curvature, you will see the aorta, with the coeliac trunk diving into it's three branches, and coeliac ganglia on either side with coeliac lymph nodes.

The blood supply of the stomach comes from the embryological foregut, so it is supplied by the artery of the foregut: the coeliac trunk. Along the lesser curvature the left and right gastric arteries anastomose between the layers of the lesser omentum. The right gastric artery is a branch of the gastroduodenal or hepatic artery. The fundus and upper part of the greature curvature receive its blood supply from the short gastric arteries, which pass from the splenic artery in the gastrosplenic ligament. Lastly, the rest of the stomach is supplied by the right and left gastroomental arteries from the gastroduodenal artery and the splenic artery respectively. Branches of these arteries pass down the omentum, and are the largest arteries supplying the peritoneum. These arteries make sure that the mobile omentum receives all the phagocytes it needs to combat infection. Veins of the same names drain into the hepatic portal vein itself or its splenic or mesenteric tributaries.

Ultimately, all lymph drainage reaches the coeliac nodes. The greatest area of drainage in the stomach is along the left gastric artery and are called the superior gastric nodes. The second largest drainage area is found by the right gastroomental artery and are called the inferior gastric nodes. The most common gastric cancers are found in the nodes located along the pyloric region.

Nerve supply to the stomach are primarily through the vagal nerve with controls motility and secretion. The anterior and posterior vagal trunks, from the oesophageal plexus form the anterior and posterior nerves of Latarjet. These two nerves run down the lesser omentum, giving off branches to the anterior and posterior of the stomach.

Anatomy of the Stomach

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The Colon Anatomy - What it Does

Anatomy
The location of the parts of the colon are either in the abdominal cavity or behind it in the retroperitoneum. The colon in those areas is fixed in location.

Ascending colon
The ascending colon is on the right side of the abdomen, is about 12.5 cm long. It is the part of the colon from the cecum to the hepatic flexure (the turn of the colon by the liver). It is [retroperitoneal] in most humans. In grazing animals the cecum empties into the spiral colon. Anteriorly it is related to the coils of small intestine, the right edge of the greater omentum, and the anterior abdominal wall. Posteriorly, it is related to the iliacus, the iliolumbar ligament, the quadratus lumborum, the transverse abdominis, the diaphragm at the tip of the last rib; the lateral cutaneous, ilioinguinal, and iliohypogastric nerves; the iliac branches of the iliolumbar vessels, the fourth lumbar artery, and the right kidney.

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Transverse colon
The transverse colon is the part of the colon from the hepatic flexure (the turn of the colon by the liver) to the splenic flexure (the turn of the colon by the spleen). The transverse colon hangs off the stomach, attached to it by a wide band of tissue called the greater omentum. On the posterior side, the transverse colon is connected to the posterior abdominal wall by a mesentery known as the transverse mesocolon.

The transverse colon is encased in peritoneum, and is therefore mobile (unlike the parts of the colon immediately before and after it). More cancers form as the large intestine goes along and the contents become more solid (water is removed) in order to form feces. It is primarily supplied by the middle colic artery, a branch of superior mesenteric artery.

Descending colon
The descending colon is the part of the colon from the splenic flexure to the beginning of the sigmoid colon. It is retroperitoneal in two-thirds of humans. In the other third, it has a (usually short) mesentery.

Sigmoid colon
The sigmoid colon is the part of the large intestine after the descending colon and before the rectum. The name sigmoid means S-shaped (see sigmoid). The walls of the sigmoid colon are muscular, and contract to increase the pressure inside the colon, causing the stool to move into the rectum.

Due to the intermittent high pressure within it, the colon can develop pockets called diverticuli in its walls. The presence of diverticuli, whether harmful or not, is called diverticulosis. An infection of the diverticuli is called diverticulitis.

Sigmoidoscopy is a common diagnostic technique used to examine the sigmoid colon.

Function
The large intestine comes after the small intestine in the digestive tract and measures approximately 1.5 meters in length. Although there are differences in the large intestine between different organisms, the large intestine is mainly responsible for storing waste, reclaiming water, maintaining the water balance, and absorbing some vitamins, such as vitamin K. This is why a colon cleanse is very important to vibrant health.

By the time the chyme has reached this tube, almost all nutrients and 90% of the water have been absorbed by the body. At this point some electrolytes like sodium, magnesium, and chloride are left as well as indigestible carbohydrates known as dietary fiber. As the chyme moves through the large intestine, most of the remaining water is removed, while the chyme is mixed with mucus and bacteria known as gut flora, and becomes feces. The bacteria break down some of the fiber for their own nourishment and create acetate, propionate, and butyrate as waste products, which in turn are used by the cell lining of the colon for nourishment. This is an example of a symbiotic relationship and provides about 100 Calories a day to the body. The large intestine produces no digestive enzymes - chemical digestion is completed in the small intestine before the chyme reaches the large intestine. The pH in the colon varies between 5.5 and 7 (slightly acidic to neutral).

There are a number of diseases or disorders of the colon:

Angiodysplasia of the colon,
Chronic functional abdominal pain,
Colitis,
Colon cancer,
Constipation,
Crohn's disease,
Diarrhea,
Diverticulitis,
Diverticulosis,
Hirschsprung's disease (aganglionosis),
Irritable bowel syndrome,
Polyposis (see also Polyp),
Pseudomembranous colitis,
Ulcerative colitis and toxic megacolon.

The Colon Anatomy - What it Does

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