Abdominal Veins and Arteries

Veins usually carry blood straight to the atria of the heart, but those of the abdominal tissues are exceptions. These come from networks in the stomach, intestines, pancreas, and spleen, and carry blood from these organs through a "portal vein" to the liver. There, the blood enters capillarylike "hepatic sinusoids," called the "hepatic portal system." The tributaries of the portal vein include (1) the right and left "gastric veins" from the stomach; (2) the "superior mesenteric vein" from the small intestine, ascending colon, and transverse colon, and (3) the "splenic vein" from a number of merging veins from the spleen, pancreas, and part of the stomach. Its largest tributary is the "inferior mesenteric vein," which brings blood up from the descending colon, sigmoid colon, and the rectum. After passing through the portal veins of the liver, blood is carried through a series of merging vessels into the "hepatic veins." These empty into the "inferior vena cava," and return the blood into circulation. The corresponding arteries of the same names are taking oxygenated blood to these sites in paths parallel to those of the veins.

Anus

The anus is a canal at the end of the digestive tract through which feces is expelled. It is about five inches long and is an extension of the rectum. It is only open during the expulsion of feces, because it is usually kept closed by sphincter muscles, which can be relaxed at will.

Transverse Colon

The transverse colon is the large part of the colon that attaches the ascending colon to the descending colon by crossing the abdominal cavitry.

Mesentery and Mesocolon

The intestines are supported by a thin, web-like structure called the mesentery which allows for changes in their size and position and still provides support. A specialized portion of the dorsal mesentery supports the large intestine and is called the mesocolon, and contains the blood vessels supplying the large intestine.

Submucosa

The submucosa is the layer of loose connective tissue directly under a mucous membrane.

Mucosa

The Mucosa is a membrane rich in mucus.

Intestines (An Overview)

The intestines are divided into two major segments - the small intestine and the large intestine, and like the entire gastrointestinal system, consists of five layers of tissue - the serosa or outer-most layer, the circular muscle and the longitudinal muscle which are the layers responsible for the wave-like muscular contraction of smooth muscle known as peristalsis, the submucosa, and the mucosa which contains roughly four million microscopic finger-like projections called intestinal villi which because of their shape, can increase surface area for digestion and absorption of nutrients.

Small Intestine

If the small intestine were not looped back and forth upon itself, it could not fit into the abdominal space it occupies. It is held in place by tissues which are attached to the abdominal wall and measures eighteen to twenty-three feet in the average adult, which makes it about four times longer than the person is tall. It is a three-part tube of about one and one-half to two inches in diameter and is divided into three sections: (1) the duodenum, a receiving area for chemicals and partially digested food from the stomach; (2) the jejunum, where most of the nutrients are absorbed into the blood and (3) the ileum, where the remaining nutrients are absorbed before moving into the large intestine. The intestines process about 2.5 gallons of food, liquids and bodily waste every day. In order for enough nutrients to be absorbed into the body, it must come in contact with large numbers of intestinal cells which are folded like gathered skirts. Each of these cells contain thousands of tiny finger-like projections called "villi," and each villus contains microscopic "microvilli". In one square inch of small intestine, there are about 20,000 villi and ten billion microvilli. Each villus brings in fresh, oxygenated blood and sends out nutrient-enriched blood. The villi sway constantly to stir up liquefied food and remove the nutrients which can be absorbed and then passed through the membranes of the villi into the blood and lymph vessels. The fatty nutrients go to the lymph vessels, and glucose and amino acids go to the blood and on to the liver. The muscles which encircle this tube constrict about seven to twelve times a minute to move the food back and forth, to churn it, knead it, and to mix it with gastric juices. The small intestine also makes waves which move the food forward, but these are usually weak and infrequent to allow the food to stay in one place until the nutrients can be absorbed. If a toxic substance enters the small intestine, these movements may be strong and rapid to expel the poisons quickly.

Splenic Flexure

The splenic flexure is the sharp bend of the colon where the transverse colon joins the descending colon. It is located under the spleen.

Rectum

The rectum is a short, muscular tube that forms the lowest portion of the large intestine and connects it to the anus. Feces collects here until pressure on the rectal walls cause nerve impulses to pass to the brain, which then sends messages to the voluntary muscles in the anus to relax, permitting expulsion.

Hepatic Flexure

The hepatic flexture is on the right side of the body near the liver. It is the right-angle bend in the colon that marks the connection of the ascending colon and the transverse colon.

Longitudinal Muscle

There are two longitudinal muscles in the tongue; superior and inferior. The superior longitudinal muscle is a thin stratum of oblique and longitudinal fibers that are underlying the mucous membrane on the dorsum of the tongue. The inferior longitudinal muscle is a narrow band situated on the inferior surface of the tongue.

Cecum

The cecum is the pouch where the large intestine begins. It is where ileum opens from one side and continues with the colon.

Sigmoid Colon

The the sigmoid colon is the part of the colon that forms an angle medially from the pelvis to form an S-shaped curve.

Decending Colon

The descending colon traverses inferiorly along the left abdominal wall to the pelvic region.

Appendix

Digestion takes place almost continuously in a watery, slushy environment. The large intestine absorbs water from its inner contents and stores the rest until it is convenient to dispose of it. Attached to the first portion of the large intestine is a troublesome pouch called the (veriform) appendix. The appendix has no function in modern humans, however it is believed to have been part of the digestive system in our primitive ancestors.