Changes

**Enterocytes are 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 a generous blood supply of capillaries that transport amino acids, monosaccharides and other digestive products and lacteals that transport triacylglycerides. Lacteals drain into the lymphatic system.

*'''Crypts''' are present at the base of each villus in the mucosa. Cell types in mucosal crypts (from luminal to basal):

*'''Crypts''' are present at the base of each villus in the mucosa. Cell types in mucosal crypts (from luminal to basal):

**''goblet''  at the tip of the crypt. Produce mucous by exocytosis.

**''goblet''  at the tip of the crypt. Produce mucous by exocytosis.

**''entero-endocrine''  in the middle of the crypt. Secrete peptides and amines.

**''entero-endocrine''  in the middle of the crypt. Produce many important substances for the regulation of GIT motility. See Regulation & Control.

**''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.

**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.

**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.

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

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

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

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

**Secrete a protective mucous.

**Produce an alkaline secretion which neutralises stomach acid.

**Produce an alkaline secretion which neutralises stomach acid.

**Open into the crypts in the mucosa above.

**Open into the crypts in the mucosa above.