| Intestinal gland | |
|---|---|
 Micrograph of thesmall intestinemucosa showing theintestinal glands - bottom 1/3 of image.H&E stain. | |
| Details | |
| Identifiers | |
| Latin | glandula intestinalis |
| TA98 | A05.6.01.012 A05.7.01.008 |
| TA2 | 2942,2969 |
| FMA | 15052 |
| Anatomical terminology | |
Inhistology, anintestinal gland (alsocrypt ofLieberkühn andintestinal crypt) is agland found in betweenvilli in theintestinal epithelial lining of thesmall intestine andlarge intestine (or colon). The glands and intestinal villi are covered byepithelium, which contains multiple types ofcells:enterocytes (absorbing water and electrolytes),goblet cells (secreting mucus),enteroendocrine cells (secreting hormones), cup cells,myofibroblast,tuft cells, and at the base of the gland,Paneth cells (secreting anti-microbial peptides) andstem cells.
Intestinal glands are found in theepithelia of thesmall intestine, namely theduodenum,jejunum, andileum, and in thelarge intestine (colon), where they are sometimes calledcolonic crypts. Intestinal glands of the small intestine contain a base of replicatingstem cells,Paneth cells of theinnate immune system, andgoblet cells, which produce mucus.[1] In the colon, crypts do not have Paneth cells.[2]
Theenterocytes in the small intestinalmucosa containdigestive enzymes that digest specific foods while they are being absorbed through the epithelium. These enzymes includepeptidase,sucrase,maltase,lactase and intestinallipase. This is in contrast to thegastric glands of thestomach wherechief cells secretepepsinogen.
Also, new epithelium is formed here, which is important because the cells at this site are continuously worn away by the passing food. The basal (further from theintestinal lumen) portion of the crypt contains multipotentstem cells. During eachmitosis, one of the two daughter cells remains in the crypt as a stem cell, while the other differentiates and migrates up the side of the crypt and eventually into thevillus. These stem cells can differentiate into either an absorptive (enterocytes) or secretory (Goblet cells,Paneth cells,enteroendocrine cells) lineages.[3] BothWnt andNotch signaling pathways play a large role in regulating cell proliferation and in intestinalmorphogenesis andhomeostasis.[4]
Loss of proliferation control in the crypts is thought to lead tocolorectal cancer.
Intestinal juice (also calledsuccus entericus[5]) refers to the clear to pale yellow watery secretions from the glands lining thesmall intestine walls. TheBrunner's glands secrete large amounts of alkaline mucus in response to (1) tactile or irritating stimuli on the duodenal mucosa; (2) vagal stimulation, which increases Brunner's glands secretion concurrently with increase in stomach secretion; and (3) gastrointestinal hormones, especiallysecretin.[6]
Its function is to complete the process begun bypancreatic juice; theenzymetrypsin exists in pancreatic juice in the inactive formtrypsinogen, it is activated by the intestinalenterokinase in intestinal juice. Trypsin can then activate other protease enzymes and catalyze the reaction pro-colipase → colipase.Colipase is necessary, along withbile salts, to enablelipase function.[citation needed]
Intestinal juice also containshormones,digestive enzymes,mucus, substances to neutralizehydrochloric acid coming from thestomach. Variousexopeptidase which further digestspolypeptides intoamino acids complete the digestion ofproteins.[citation needed]
The intestinal glands in the colon are often referred to as colonic crypts. Theepithelial inner surface of the colon is punctuated by invaginations, the colonic crypts. The colon crypts are shaped like microscopic thick-walled test tubes with a central hole down the length of the tube (the cryptlumen). Four tissue sections are shown here, two (A and B) cut across the long axes of the crypts and two (C and D) cut parallel to the long axes.
In these images the cells have beenstained to show a brown-orange color if the cells produce amitochondrial protein calledcytochrome c oxidase subunit I (CCOI or COX-1). Thenuclei of the cells (located at the outer edges of the cells lining the walls of the crypts) are stained blue-gray withhaematoxylin. As seen in panels C and D, crypts are about 75 to about 110 cells long. The average crypt circumference is 23 cells.[8] From the images, an average is shown to be about 1,725 to 2530 cells per colonic crypt. Another measure was attained giving a range of 1500 to 4900 cells per colonic crypt.[9] Cells are produced at the crypt base and migrate upward along the crypt axis before being shed into the coloniclumen days later.[8] There are 5 to 6 stem cells at the bases of the crypts.[8]
As estimated from the image in panel A, there are about 100 colonic crypts per square millimeter of the colonic epithelium.[10] The length of the human colon is, on average 160.5 cm (measured from the bottom of the cecum to the colorectal junction) with a range of 80 cm to 313 cm.[11] The average inner circumference of the colon is 6.2 cm.[10] Thus, the inner surface epithelial area of the human colon has an area, on average, of about 995 cm2, which includes 9,950,000 (close to 10 million) crypts.
In the four tissue sections shown here, many of the intestinal glands have cells with amitochondrial DNA mutation in the CCOI gene and appear mostly white, with their main color being the blue-gray staining of the nuclei. As seen in panel B, a portion of the stem cells of three crypts appear to have a mutation in CCOI, so that 40% to 50% of the cells arising from those stem cells form a white segment in the cross cut area.
Overall, the percentage of crypts deficient for CCOI is less than 1% before age 40, but then increases linearly with age.[7] Colonic crypts deficient for CCOI reaches, on average, 18% in women and 23% in men, by 80–84 years of age.[7]
Crypts of the colon can reproduce by fission, as seen in panel C, where a crypt is dividing to form two crypts, and in panel B where at least one crypt appears to be fissioning. Most crypts deficient in CCOI are in clusters of crypts (clones of crypts) with two or more CCOI-deficient crypts adjacent to each other (see panel D).[7]
Cryptinflammation is known ascryptitis and characterized by the presence ofneutrophils between theenterocytes. A severe cryptitis may lead to a cryptabscess.
Pathologic processes that lead to Crohn's disease, i.e. progressive intestinal crypt destruction, are associated with branching of the crypts.
Causes of crypt branching include:
Intestinal glands contain adult stem cells referred to asintestinal stem cells.[12] These cells have been used in the field of stem biology to further understandstem cell niches,[13] and to generate intestinalorganoids.[12]
The crypts of Lieberkühn are named after the eighteenth-century German anatomistJohann Nathanael Lieberkühn.
