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==Introduction==

==Introduction==

The duodenum is the proximal part of the small intestine. It extends from the pylorus of the stomach to the jejunum. The pancreatic and bile ducts open into the duodenum.

The duodenum is the proximal part of the small intestine and extends from the '''pylorus''' of the [[Monogastric Stomach - Anatomy & Physiology|stomach]] to the '''[[Jejunum - Anatomy & Physiology|jejunum]]'''. It has descending and ascending portions and both portions have digestive and absorptive functions.

==Structure==

==Structure==

 

The descending duodenum passes out of the '''pylorus''' of the [[Monogastric Stomach - Anatomy & Physiology|stomach]] (on the right side of the abdomen) and has a sigmoid flexure. It passes towards the right abdominal wall and rises dorsally. In its passage, it is related dorsally to the right lobe of the [[Pancreas - Anatomy & Physiology|pancreas]], ventrally to the [[Jejunum - Anatomy & Physiology|jejunum]] and medially to the ascending [[Colon - Anatomy & Physiology|colon]] and [[Caecum - Anatomy & Physiology|caecum]].  

At a point between the right [[Renal Anatomy - Anatomy & Physiology#Common Anatomy|kidney]] and pelvic inlet, it turns medially and cranially around the root of the mesentery to become the ascending duodenum. The point of turn is called the ''caudal flexure'' of the duodenum.

**The descending duodenum passes out of the pylorus of the stomach (on the right side of the abdomen) and has a sigmoid flexure. It passes towards the right abdominal wall and rises dorsally. In its passage it is related dorsally to the right lobe of the pancreas, ventrally to the jejunum and medially to the ascending colon and caecum.  

The ascending duodenum is shorter and bends ventrally to enter the mesentery and becomes the [[Jejunum - Anatomy & Physiology|jejunum]]. The '''mesoduodenum''' attaches the duodenum to the dorsal abdominal wall. Within the mesoduodenum is the right lobe of the [[Pancreas - Anatomy & Physiology|pancreas]]. The pancreatic and bile ducts open into the duodenum. The bile duct and one of the pancreatic ducts discharge into the proximal part of the duodenum by separate ''major duodenal papillae''. The second pancreatic duct discharges a little more distally on a smaller papilla. The cranial part of the descending duodenum is attached to the [[Liver - Anatomy & Physiology|liver]] by the '''hepatoduodenal ligament'''. This is a remnant of the [[Monogastric Stomach - Anatomy & Physiology|ventral mesogastrium]] in the embryo. The bile duct runs within the '''hepatoduodenal ligament'''.

**At a point between the right kidney and pelvic inlet it turns medially and cranially around the root of the mesentry to become the ascending duodenum. The point of turn is called the ''caudal flexure'' of the duodenum.

**The ascending duodenum is shorter and bends ventrally to enter the mesentery and becomes the jejunum.

*Mesoduodenum attaches the duodenum to the dorsal abdominal wall. This is relatively short in the horse and ruminant and longer in the carnivore and pig.

==Vasculature==

==Vasculature==

*The duodenum recieves blood from:

The duodenum receives blood from the '''coeliac artery''' and the '''cranial mesenteric artery'''. Both are branches of the aorta. The '''cranial mesenteric vein''' drains blood from the duodenum into the '''portal vein'''. This blood, carrying the products of digestion, enters the [[Liver - Anatomy & Physiology|liver]].

**Coeliac artery

**Cranial mesenteric artery

*Both are branches of the aorta.

*The cranial mesenteric vein drains blood from the duodenum into the portal vein.

**This blood, carrying the products of digestion, enters the liver.

==Histology==

==Species Differences==

The duodenum is about 25cm long in canine species. The mesoduodenum is relatively long.

*The mucosa is arranged into '''villi''' that provide a large surface area for absorption.

*Epithelium is simple columnar - ideal for absorption.

*'''Crypts''' are present at the base of each villus in the mucosa. Cell types in mucosal crypts (from luminal to basal):

*Lamina muscularis is smooth muscle.

**Contraction of smooth muscle shortens the villus. This helps to pump out absorbed products of digestion. Relaxation of smooth muscle lengthens the villus which increases surface area, facilitating absorption.

==Species Differences==

===Ruminant===

==Links==

==Links==