Jejunum, Part of Intestine: Anatomy & Function Guide

The jejunum is a crucial part of the small intestine, playing a vital role in the digestion and absorption of nutrients from the food we consume. It is the middle segment of the small intestine, connecting the duodenum to the ileum, and represents the longest part of the small intestine in humans.

Anatomy of the Jejunum

The jejunum is a segment of the small intestine that typically measures around 2.5 meters (8 feet) in length in adults. It is a highly convoluted tube-like structure located in the abdominal cavity, beginning at the duodenojejunal junction and ending at the jejunoileal junction.

Function of the Jejunum

The primary function of the jejunum is the absorption of nutrients from the partially digested food that enters it from the duodenum. It plays a crucial role in the absorption of carbohydrates, proteins, lipids, vitamins, and minerals. The jejunum also secretes digestive enzymes and hormones that aid in the digestive process.

Histology of the Jejunum

The jejunum is lined with a specialized mucosal layer that consists of finger-like projections called villi and microscopic glands called crypts. The villi increase the surface area for absorption, while the crypts secrete enzymes and mucus that aid in digestion and protect the intestinal lining.

Differences Between the Jejunum and Other Parts of the Small Intestine

While the jejunum shares some similarities with the duodenum and ileum, it also has distinct features. The jejunum has a larger diameter than the duodenum, and its mucosa is more heavily folded, which increases the surface area for absorption. Unlike the ileum, the jejunum does not contain Peyer’s patches, which are important components of the immune system.

Physiology of Digestion in the Jejunum

The jejunum plays a crucial role in the digestion and absorption of nutrients. Enzymes secreted by the pancreas and bile from the liver aid in the breakdown of food molecules. The jejunum also produces hormones like cholecystokinin and secretin, which regulate digestive processes.

Blood Supply and Innervation

The jejunum receives its blood supply from branches of the superior mesenteric artery, and its venous drainage is through the superior mesenteric vein. The jejunum is innervated by the vagus nerve (parasympathetic) and the splanchnic nerves (sympathetic), which regulate its motility and secretory functions.

Clinical Significance

Disorders affecting the jejunum can have significant impacts on nutrient absorption and overall health. Conditions like Crohn’s disease, celiac disease, and intestinal obstruction can affect the function of the jejunum. Diagnostic procedures like endoscopy and imaging techniques are used to evaluate the jejunum, and surgical interventions may be necessary in severe cases.

Development and Embryology

The jejunum develops from the midgut during embryonic development. The midgut is initially a straight tube that undergoes several rotations and looping, ultimately forming the small intestine, including the jejunum. Congenital anomalies affecting the development of the jejunum can lead to various malformations and complications.

Comparative Anatomy

The jejunum is a common anatomical feature in vertebrates, including mammals, reptiles, and birds. While the overall structure and function are similar, there may be variations in length, diameter, and specific adaptations based on the dietary habits and evolutionary history of different species.

Historical Perspectives

The jejunum has been studied by anatomists and physicians throughout history. Early descriptions of the small intestine can be found in the works of renowned anatomists like Andreas Vesalius and William Harvey. Over time, our understanding of the jejunum and its role in digestion has evolved through scientific discoveries and advancements in medical technology.

Research and Advances

Research on the jejunum continues to uncover new insights into its structure, function, and role in various physiological processes. Areas of active investigation include the study of nutrient absorption mechanisms, the role of the gut microbiome, and the development of targeted therapies for diseases affecting the jejunum.