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This is a diagram which shows the villi of the small intestine, as shown by the arrows in the chart above, at greater magnification.

You are watching: Circular folds and intestinal villi


The main features of the little intestine room digestion, absorb of food and production of gastrointestinal hormones. The small intestine is 4-6 metres lengthy in humans.

To help in digestion and also absorption:

the small intestine secretes enzymes and has mucous creating glands. The pancreas and liver also deliver your exocrine secretions into the duodenum. The mucosa is highly folded. big circular folds dubbed plicae circulares (shown in the diagram to the right), most many in the upper part of the little intestine smaller folds called villi, which are finger choose mucosal projections, around 1mm long. the lining columnar epithelial cells have fine projections on their apical surfaces called microvilli.

Together, these folds provide a huge surface area for absorption. Between the villi there space crypts, referred to as crypts the Lieberkuhn, which expand down to the muscularis mucosae. This crypts are quick glands.

The lamina propria which underlies the epithelium has actually a affluent vascular and also lymphatic network, i beg your pardon absorbs the digestive products, and also there is a muscularis mucosae layer immediately at the basic of the crypts. The lymphatic capillaries are dubbed lacteals, and also absorb lipids. The vascular capillaries are fenestrated to help absorption.

The muscularis externa layer has two class of smooth muscle, an inner circular and outer longitudinal, for continuous peristaltic activity of the little intestine. There are around 200 or so lymphoid aggregations dubbed Peyer"s patches in the mucosa.


Look in ~ this photograph of a section through the small intestine, and also make sure you can identify the mucosa, submucosa, muscularis mucosae, muscularis externa, and villi.

Sometimes the villi are cut in cross-section, and also sometimes longitudinally - and also you have the right to see this mixture of part here.

You can additionally see part of the wrinkles - plica circulares.

Lymphoid aggregations are typically found in the sub-mucosa of the tiny intestine, one you deserve to see one here. The bigger aggregations the lymphoid organization are recognized as Peyer"s Patches.

These spot are much more likely come be found in the ileum than in the duodenum.


Mucosa


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The epithelium of the villi is consisted of of tall columnar absorptive cells referred to as enterocytes, and goblet cells, i m sorry secrete mucin, for lubrication that the minister contents, and also protection that the epithelium.

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This shows the epithelium of component of a villus at high magnification. Girlfriend should have the ability to identify goblet cells, and enterocytes, and notification the "brush border" ~ above the apical surface of the enterocytes, i m sorry is as result of the microvilli.

(Click right here to compare the epithelia of the oesophagus, stomach, duodenum, tiny and huge intestines)


Crypts

The crypts furthermore contain

Paneth cells (at the basic of the crypts) - they have actually a defensive function, and stain intensely eosinophilic, as result of secretory granules the antimicrobial peptides referred to as defensins, as well as lysozyme and also phospholipase A. This cells critical for number of weeks. Endocrine cells, (also eosinophilic) which develop secretin, somatostatin, enteroglucagon and serotonin. One type of endocrine cell because that each type of hormone. Stem cells, found at the basic of the crypts, i beg your pardon divide consistently to replace enterocytes (every 2-3 days), goblet cells, paneth cells and also neuroendocrine cells. Intraepithelial lymphocytes (mostly T-cells).

Duodenum


The very first part the the little intestine is the duodenum, and its framework is similar to the seen elsewhere in the small intestine, with some differences. The villi are broader, Peyers patches are much less common, and also it has one distinct feature: Brunner"s glands, i beg your pardon are discovered in the sub-mucosa.

The duodenum is regularly mistaken for the tiny intestine, so take it a minute to to compare this ar to the of the tiny intestine in the snapshot above. Make sure you can differentiate correctly in between the two, and identify Brunner"s glands correctly.

Both Brunner"s glands, and also the goblet cell in the duodenum secrete mucus. The rubber secreted by Brunner"s glands is alkaline, and also helps come neutralise the acid chyme developed by the stomach, to create chyme v a pH suitable for the digestive enzyme of the small intestine.

See more: Dreaming Of Wetting The Bed, Nocturnal Enuresis (Bed Wetting)


Digestion:

The chyme is mixed with pancreatic enzymes, and also molecules are soaked up by the enterocytes. Proteins space denatured and also chopped up by pepsin native gastric glands, and then further broken down through trypsin, chymotrypsin, elastase and carboxypeptidases in the lumen the the small intestine. Further enzymes in the plasma membrane that the enterocytes complete malfunction into amino acids, and each amino acid is proactively transported right into the enterocyte. Carbohydrates room hydrolysed by amylases, and membrane bound enzymes convert sugars to monosaccharides i beg your pardon are soaked up by helped with diffusion. Lipids space converted right into an outlet emulsion in the stomach, and into a good emulsion in the duodenum by pancreatic lipases. Little lipid molecules are took in by the enterocytes.