1.7 - Tissues & Organs

This is a region of the small intestine following the duodenum. It is very long with a small lumen. There are four different layers of tissue. 

The innermost layer of the ileum.

The lining is folded with numerous finger-like villi

At the base of the villi are Crypts of Liebekuhn

The cells at the bottom of the crypt are continually dividing by mitosis to produce new cells that continually move up the surface of the villi before being sloughed off and replaced.

Paneth cells lining the base of the crypts have an antimicrobial function (killing microbes).

Further digestion takes place as a result of disaccharidase (and peptidase) enzymes on the epithelial cell surface membrane 

The epithelium is columnar.

The epithelium contains goblet cells that produce mucus which protects/lubricate the lining of the gut.

The epithelial surface possesses microvilli/brush border. These greatly increase the surface area of the ilium.

Thus, the ilium is the major area of absorption.

Each villus possesses a network of blood capillaries that absorb products of digestion/sugars etc. and a lacteal which absorbs the majority of fats. 

The muscularis mucosa is a layer of involuntary muscle in the mucosa, which allows movement of the villi to enhance diffusion gradients for absorption 

The submucosa layer contains a rich supply of blood and lymph vessels which carry absorbed nutrients away from the intestine to the liver by the hepatic portal vein 

This muscle layer has two layers of involuntary/smooth/unstriated muscle.

The outer longitudinal layer has its muscle fibres arranged along the gut. Its contraction causes the gut to widen and shorten.

The inner circular layer has its muscle fibres arranged around the gut. Its contraction causes the gap to become longer and thinner.

Circular and longitudinal muscles work antagonistically to each other. Wave-like contractions of the muscle layers cause food to be moved along they got/peristalsis 

This is the most layer of the Ileum containing connective tissue which protects the rest of the gut