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The majority extend transversely around the cylinder of the small intestine, [2] for about one-half or two-thirds of its circumference. Some form complete circles. Others have a spiral direction. The latter usually extend a little more than once around the bowel, but occasionally two or three times.
The jejunum has many large circular folds in its submucosa called plicae circulares that increase the surface area for nutrient absorption. The plicae circulares are best developed in the jejunum. There is no line of demarcation between the jejunum and the ileum. However, there are subtle histological differences:
It is organised into plicae circulares and villi, and the enterocytes have microvilli. The microvilli create a brush border that increases the area for absorption. In the ileum there are occasionally Peyer's patches in the lamina propria. Brunner's glands are found in the duodenum but not in other parts of the small intestine. [1]
Approximately 20,000 protein coding genes are expressed in human cells and 75% of these genes are expressed in at least one of the different parts of the digestive organ system. [ 25 ] [ 26 ] Over 600 of these genes are more specifically expressed in one or more parts of the GI tract and the corresponding proteins have functions related to ...
The small intestine or small bowel is an organ in the gastrointestinal tract where most of the absorption of nutrients from food takes place. It lies between the stomach and large intestine, and receives bile and pancreatic juice through the pancreatic duct to aid in digestion.
The gastric folds consist of two layers: Mucosal layer – This layer releases stomach acid. It is the innermost layer of the stomach. [5] It is affected by the hormone histamine, which signals it to release hydrochloric acid (HCl). Sub-mucosal layer – This layer consists of different vessels and nerves, ganglion neurons, and adipose tissue ...
These folds are about 12 mm. in width and are composed of the circular muscle coat of the rectum. They are usually three in number; sometimes a fourth is found, and occasionally only two are present. One is situated near the commencement of the rectum, on the right side.
Teeth are complex structures made of materials specific to them. They are made of a bone-like material called dentin, which is covered by the hardest tissue in the body—enamel. [8] Teeth have different shapes to deal with different aspects of mastication employed in tearing and chewing pieces of food into smaller and smaller pieces. This ...