Descending colon
Encyclopedia
The descending colon of humans passes downward through the left hypochondrium
and lumbar regions, along the lateral border of the left kidney
.
At the lower end of the kidney it turns medialward toward the lateral border of the psoas
muscle, and then descends, in the angle between psoas and quadratus lumborum, to the crest of the ilium, where it ends in the sigmoid colon
.
The peritoneum covers its anterior surface and sides, and therefore the descending colon is described as retroperitoneal. (The transverse colon and sigmoid colon, which are immediately proximal and distal, are intraperitoneal). Its posterior surface is connected by areolar tissue with the lower and lateral part of the left kidney, the aponeurotic origin of the transversus abdominis, and the quadratus lumborum.
It is smaller in caliber and more deeply placed than the ascending colon
. It has a mesentery
in 33% of people, and is therefore more frequently covered with peritoneum
on its posterior surface than the ascending colon (which has a mesentery in 25% of people). However, it is less likely to undergo volvulus
than the ascending colon.
In front of it are some coils of small intestine
.
Hypochondrium
The hypochondrium is the upper part of the abdomen dorsal to the lowest ribs of the thorax. The word derives from the Greek term ὑποχονδρος hupochondros, meaning abdomen, or literally under cartilage.The liver is found in the right hypochondrium....
and lumbar regions, along the lateral border of the left kidney
Kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...
.
At the lower end of the kidney it turns medialward toward the lateral border of the psoas
Psoas major muscle
-External links: - "Posterior Abdominal Wall: Muscles of the Posterior Abdominal Wall"* *...
muscle, and then descends, in the angle between psoas and quadratus lumborum, to the crest of the ilium, where it ends in the sigmoid colon
Sigmoid colon
The sigmoid colon is the part of the large intestine that is closest to the rectum and anus. It forms a loop that averages about 40 cm...
.
The peritoneum covers its anterior surface and sides, and therefore the descending colon is described as retroperitoneal. (The transverse colon and sigmoid colon, which are immediately proximal and distal, are intraperitoneal). Its posterior surface is connected by areolar tissue with the lower and lateral part of the left kidney, the aponeurotic origin of the transversus abdominis, and the quadratus lumborum.
It is smaller in caliber and more deeply placed than the ascending colon
Ascending colon
The ascending colon is smaller in caliber than the cecum.It passes upward, from its commencement at the cecum, opposite the colic valve, to the under surface of the right lobe of the liver, on the right of the gall-bladder, where it is lodged in a shallow depression, the colic impression; here it...
. It has a mesentery
Mesentery
In anatomy, the mesentery is the double layer of peritoneum that suspends the jejunum and ileum from the posterior wall of the abdomen. Its meaning, however, is frequently extended to include double layers of peritoneum connecting various components of the abdominal cavity.-Mesentery :The...
in 33% of people, and is therefore more frequently covered with peritoneum
Peritoneum
The peritoneum is the serous membrane that forms the lining of the abdominal cavity or the coelom — it covers most of the intra-abdominal organs — in amniotes and some invertebrates...
on its posterior surface than the ascending colon (which has a mesentery in 25% of people). However, it is less likely to undergo volvulus
Volvulus
A volvulus is a bowel obstruction with a loop of bowel whose nose has abnormally twisted on itself.-Types:* Volvulus Neonatorum.* Volvulus Small Intestine.* Volvulus Caecum.* Volvulus Sigmoid Colon .* Gastric volvulus....
than the ascending colon.
In front of it are some coils of small intestine
Small intestine
The small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...
.