Changes

*The mucosa is arranged into '''villi''' that provide a large surface area for absorption.

*The mucosa is arranged into '''villi''' that provide a large surface area for absorption.

*Epithelium is simple columnar - ideal for absorption.

*Epithelium is simple columnar - ideal for absorption.

**Epithelial cells are known as enterocytes.

**Epithelial cells are known as '''enterocytes'''.

**A single layer of enterocytes overlies the lamina propria.

**A single layer of enterocytes overlies the lamina propria.

**Enterocytes originate from progenitor cells that migrate from mucosal crypts. They differentiate as they migrate up the villus.

**Enterocytes originate from progenitor cells that migrate from mucosal crypts. They differentiate as they migrate up the villus.

**Enterocytes ane absorptive and posses microvilli.

**Enterocytes are absorptive and posses microvilli.

*Membrane bound enzymes and transport proteins are also within the epithelium.

*Membrane bound enzymes and transport proteins are also within the epithelium.

*Each villus houses capillaries that transport amino acids, monosaccharides and other digestive products and lacteals that transport triacylglycerides. Lacteals drain into the lymphatic system.

*Each villus houses capillaries that transport amino acids, monosaccharides and other digestive products and lacteals that transport triacylglycerides. Lacteals drain into the lymphatic system.

**''paneth''  at the base of the crypt. Function unknown. Contain eosinophilic granules.

**''paneth''  at the base of the crypt. Function unknown. Contain eosinophilic granules.

*Lamina muscularis is smooth muscle.

*Lamina muscularis is smooth muscle.

*'''Brunner's glands''' are present in the submucosa.

*'''Brunner's glands''' are present in the submucosa.

**Produce an alkaline secretion which neutralises stomach acid.

**Produce an alkaline secretion which neutralises stomach acid.

**Open into the crypts above in the mucosa.

**Open into the crypts in the mucosa above.

***Submucosa is loose connective tissue containing blood vessels and nerve fibres.

*Tunica muscularis is smooth muscle.

 

**It consists of two muscle layers (see regulation & control).

 

**Contraction of smooth muscle shortens the villus. This helps to pump out absorbed products of digestion. Relaxation of smooth muscle lengthens the villus which increases surface area, facilitating absorption.

*Serosa is loose connective tissue.

==Species Differences==

==Species Differences==