HUMAN MEDICAL BIOLOGY, ANATOMY, PHYSIOLOGY AND PATHOLOGY - Y.I. Fedonyuk 2010

ANATOMY, PHYSIOLOGY, PATHOLOGY

CHAPTER 7. THE NUTRITIONAL PROCESS AND ITS PATHOLOGY

ANATOMY AND PHYSIOLOGY OF THE DIGESTIVE ORGANS

SMALL INTESTINE

1. SECTIONS OF THE SMALL INTESTINE

The Small Intestine (intestinum tenue) begins at the pylorus of The Stomach at the level of the first lumbar vertebra and, forming a series of bends along its path, terminates in the right iliac fossa, where it transitions into the cecum (Fig. 7.23). In a cadaver, the length of the small intestine is 5-7 m, exceeding the body length by 4.1 times, whereas in a living person it is 2.7 m, depending on the individual's age, sex, and physical development.

The loops of the small intestine lie below the stomach and Liver, occupying the umbilical region and partially extending down into the lesser pelvic cavity.

The small intestine is divided into three sections: 1) the duodenum (25-30 cm in length); 2) the jejunum; and 3) the ileum. There is no clear anatomical boundary between the jejunum and the ileum. It is generally considered that approximately 2/5 of its length is the jejunum, and 3/5 is the ileum.

The duodenum (duodenum) is the initial section of the small intestine, which curves in a horseshoe shape around the HEAD of the Pancreas (Fig. 7.22 - see Appendix). It comprises four parts: superior, descending, inferior horizontal, and ascending. At the level of the I-II lumbar vertebrae on the left, it forms a sharp bend and transitions into the jejunum. The initial and terminal sections of the duodenum are covered by the Peritoneum on all sides, whereas the greater part of it lies extraperitoneally (covered by the peritoneum only anteriorly).

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Fig. 7.23. Arrangement of Organs in the Abdominal cavity (diagram)

The jejunum and the ileum are collectively referred to as the mesenteric part of the small intestine because they are entirely covered by the peritoneum and suspended by the mesentery, between the leaves of which Blood Vessels, nerves, and Lymph Nodes are located.

The mucous membrane of the small intestine has a velvety appearance due to the presence of numerous villi that increase the absorptive surface area. These are mucosal projections containing a lymphatic sinus in the center and blood capillaries along the periphery, interspersed with individual smooth Muscle Cells. In the upper sections of the small intestine, the mucous membrane is thicker, containing a greater number of villi and blood vessels. Throughout its extent, it forms circular folds. In the descending part of the duodenum, alongside circular folds, There is a single longitudinal fold that terminates in the major duodenal papilla (Vater's papilla). The common Bile duct and the pancreatic duct open onto this papilla. Occasionally, there is an accessory minor duodenal papilla, where the accessory pancreatic duct opens. The mucosa also contains glands that secrete intestinal juice, while the duodenum houses more complex duodenal (Brunner's) glands. The lymphoid tissue of the mucous membrane forms solitary and aggregated (Peyer's patches) follicles. The latter are found exclusively in the ileum in quantities of 20-30.

The muscular layer consists of an outer longitudinal and an inner circular layer of smooth muscle cells.

The jejunum and ileum are covered intraperitoneally (on all sides) by the serous membrane.