Generalised gut

What are the features of the generalised gut wall?

Serosa, longitudinal muscle, circular muscle, sub-mucosa, mucosa, epithelium, lumen

What is the serosa?

It is a layer of connective tissue protecting the inner layers from abrasion. It carries blood vessels, lymphatic vessels and nerves

What are the longitudinal and circular muscles?

These make up the muscularis layer. It is smooth muscle (except in the oesophagus) and helps to physically break down food, mixing it with secretions and propel food through the digestive tract by peristalsis

What is the submucosa?

This contains dense connective tissue and some adipose tissue which carries the main arterioles and venules, and may contain glands

What is mucosa?

This is covered by a layer of epithelial cells; some of these produce mucus and others are responsible for the final stages of digestion and the absorption of nutrients

What is the mysentery layer?

A double layer of tissue that attaches to the abdominal wall and also helps to store fat, allowing the blood and lymph vessels and the nerves to supply the intestines

What do villi do?

Found in the duodenum and the ileum, these increase the efficiency of digestion and absorption through the folds in the wall

What are microvilli?

The surface of the epithelium cells covering the villi sometimes has additional folds to further increase the surface area

How are the villi adapted?

The rich capillary network absorbs and removes products of digestion and maintains a concentration gradient, lacteals absorb the products of fat digestion and maintain a concentration gradient for lipids, villi are thin to reduce diffusion distance, microvilli are sometimes present to increase the surface area, epithelial cells contain many mitochondria to provide ATP for active transport

Features of villi

Rich capillary network, lacteals, thin, microvilli, mitochondria in epithelial cells

In which parts of the digestive system are villi absent?

In the stomach and colon - they are also longer in the ileum than the duodenum