Small intestine histology

The small intestine is the longest portion of the gastrointestinal or GI tract.It’s approximately 6 meters long in adults and it’s the main site for both digestion and absorption of food in the body.Although the majority of the small intestine shares similar histological structures, it’s still divided into three main segments.The duodenum, jejunum, and ileum.The most proximal segment of the small intestine is the duodenum, and it’s also the shortest segment as well.The duodenum connects with the jejunum at the duodenojejunal junction.The jejunum is approximately 2.5 meters long and will gradually transition to the Ileum, which is the last segment of the small intestine.The ileum is usually about 3.5 meters long and leads to the cecum of the large intestine at the ileocecal junction.Similar to the rest of the GI tract, the wall of the small intestine has 4 main layers: the mucosa, submucosa, muscularis propria, and in the small intestine the outermost layer is a layer of connective tissue called the serosa.In these images, the serosa is only present in the image of the duodenum.Although each segment of the small intestine shares similar overall structures, there are still quite a few differences between each segment that can be seen with light microscopy.Even at low magnification, we can see that the finger-like projections or villi that extend into the lumen in both the duodenum and jejunum are very tall and slender when compared to the villi of the ileum are significantly shorter, broader, and their tips are flat in comparison to the duodenum and the jejunum.Let’s take a closer look at the mucosa of the duodenum.The villi of the entire small intestine are lined with enterocytes, which are simple columnar cells with microvilli.The microvilli increase the surface area available to the enterocytes for absorption.The pale cells within the villi are the goblet cells, which secrete mucus for lubrication and physical protection of the intestinal epithelium.The lamina propria is the loose connective tissue that supports the enterocytes and forms the middle or core of each villus.The crypts of Lieberkühn or intestinal crypts are glands found at the bases of the villi.The crypts contain stem cells that slowly differentiate into the cells that form the epithelial lining of the small intestine, which include both the enterocytes and goblet cells.The differentiated cells move up the villi as new cells are continually formed underneath them, and within a week, the cells will reach the tip of the villi where they’re shed into the lumen, similar to the separated epithelial cells seen at the top right of this image.Some of the crypts in the small intestine have cells with very eosinophilic or pink granules.These cells are called paneth cells, and they help provide an innate immune defence against intestinal pathogens.And finally, underneath the villi, crypts, and lamina propria, is a thin supporting layer of smooth muscle called the muscularis mucosa.If we look at a section of the jejunum, we can see that mucosa shares the same characteristics we saw in the duodenum’s mucosa.Including the crypts of Leiberkühn, paneth cells, enterocytes with their microvilli, goblet cells, lamina propria, muscularis mucosa, and the shedding of the epithelial lining.Now, if we look at a section taken from the ileum, it has the same characteristics as the duodenum and jejunum, but the mucosa of the ileum can be differentiated by its shorter, broader, villi, as well as Peyer’s patches.Peyer’s patches are masses of lymphoid tissue within the lamina propria that are only seen in the ileum.Also unique to the ileum are lacteals, which are the white spaces within the cores of some of the villi.These spaces actually represent lymphatic capillaries that absorb dietary fats from the intestinal lumen.The next layer of the small intestine underneath the mucosa is the submucosa.Portions of the mucosa can still be seen at the top of these images in green.The submucosa consists mostly of dense irregular connective tissue all throughout the small intestine, which is dark pink when the tissue is stained with Hematoxylin and eosin.The duodenum’s submucosa can be distinguished from other segments of the small intestine by unique glands called Brunner’s Glands, which are only seen in the duodenum and esophagus.They can be identified in images as a thick layer of coiled, tubular glands lying just beneath the muscularis mucosa.In the duodenum, they secrete alkaline mucus into the lumen of the small intestine in order to reduce the acidity of the gastric juices and partially digested food coming from the stomach.Near the top of this image, we can see that the glands will occasionally pass through the muscularis mucosa, in order to release their secretions into the crypts between the villi.If we go back and look at the images of the submucosa from the jejunum and ileum, we can see cross-sections of nerves that are part of a network of nerves called the submucosal plexus or Meissner’s Plexus.These nerves are responsible for innervating the mucosal goblet cells and the smooth muscle of the muscularis mucosa.We can also see a few large blood vessels within the submucosa that still have red blood cells within their lumens.All segments of the small intestine have a muscular layer that surrounds the submucosa called the muscularis externa or muscularis propria.This layer actually consists of two main layers of smooth muscle arranged in different directions.The inner layer has a circular or circumferential arrangement around the wall of the small intestine.The muscle cells of the outer layer have a rounder appearance compared to the inner layer because they have a longitudinal arrangement that runs parallel to the length of the small intestine; so in these images, we’re only seeing cross-sections of these muscle cells.Between the two layers of smooth muscle is another network of nerves, but these nerves are called the myenteric plexus or Auerbach’s Plexus.The myenteric plexus innervates the smooth muscle cells of the muscularis externa that surround the nerves.Looking at the same image, we can see a portion of the serosa, which is the fourth and outermost main layer of the small intestine.The serosa is a thin layer of loose connective tissue that allows the small intestine to move more freely within the abdomen and contains blood vessels,nerves, and lymphatic vessels as well.

also see a few large blood vessels within the submucosa that still have red blood cells within the lumens. All segments of the small intestine have a muscular layer that surrounds, the submucosa called the muscularis externa, or muscularis propria this layer actually consists of two main layers of smooth muscles arranged in different directions.

The inner layer has a circular or circumferentially Arrangement around the wall of the small intestine, the muscle cells of the outer layer have around her appearance, compared to the inner layer because they have a longitudinal Arrangement that runs parallel to the length of the small intestine.

So, in these images were only seen cross-sections of these muscle cells between the two layers. Of smooth muscle, is another network of nerves, but these nerves are called The Mind Teraflex us or our box plexus.

The Mind tarek plexus innervates, the smooth, muscle cells of the muscularis, externa that surround the nerves. Looking at the same image.

We can see a portion of the serosa, which is the fourth and outermost main layer of the small intestine. The serosa is a thin layer of loose, connective tissue that allows the small intestine to move more freely within the abdomen and contains blood vessels nerves and