The intestinal glands lie in the wall of the small intestine.Intestinal glands are two types: Crypts of Lieberkuhn and Brunner’s gland.
Crypts of Lieberkuhn
The crypts of Lieberkuhn are simple tubular glands and occur throughout the small intestine between the villi. The term Crypts of Lieberkuhn is named after the German anatomist Johann Nathanael Lieberkühn. They inactivated pepsin, HCl, and mucus.
Crypts of Lieberkuhn secrets:
1. Inactivated Pepsin (secreted at the bottom of the crypt)
2. Hydrochloric acid (secreted at the top)
3. mucus (to protect epithelial cells)
The inactivated pepsin is activated by hydrochloric acid. This is to prevent the cells lining the crypt from being digested by the pepsin. The cells towards the top of the crypt are protected by a coating of mucus.
There are two types cells in Crypts of Lieberkuhn:
- Paneth cells
- Argentaffin cells
Paneth cells are present in the mucous membrane lining of the small intestine at the base of the intestinal crypts.They are named after Austrian physiologist Joseph Paneth.
They have a 20-day average lifespan.They are the key effectors of innate mucosal defense.
Paneth cells secrete granules that are rich in α-defensins and additional antimicrobial peptides like lysozymes(an antibacterial enzyme which controls the number of bacteria in the gut) and secretory phospholipase A2 (sPLA2) into the lumen of the crypt.
The α-defensins are homologs of peptides that function as mediators of nonoxidative microbial cell killing in phagocytic leukocytes
Argentaffin cells are located among epithelial cells lining the crypts of Lieberkuhn. They are identified with the production of a serotonin. Serotonin is a powerful stimulant of smooth muscle, resulting in contraction, and may play a role in stimulating the peristaltic activity of the intestine.
The Brunner’s glands are branched tubular glands and. They secrete alkaline watery fluid, a little enzyme, and mucus. They open into the crypts of Lieberkuhn. The mixture of secretions is called Intestinal juice, or succus entericus.