Histology of Small and Large Intestines Flashcards
4 basic histological layers of small intestine wall
Mucosa
Submucosa
Muscularis
Serosa
Describe epithelium of mucosa layer of small intestine
Simple columnar epithelium
Lamina propria
Muscularis mucosa
What histological structures are found in the mucosal layer of the small intestine and what is their purpose?
Intestinal glands/crypts of Lieberkuhn = invaginations of mucosa that increase intestinal surface area
[note that glands/crypts are also often found in submucosa]
Describe submucosa layer of small intestine
Dense irregular CT with neurovasculature and lymphatics, glands may be present
Describe muscularis layer of small intestine
Inner circular + outer longitudinal smooth muscle
Describe serosa of small intestine
Loose CT covered by visceral peritoneum
______ = folds of mucosa projecting into the lumen of the small intestine, increasing their surface area for absorption
Villi
_____ = folds of mucosa and some submucosa that differ from rugae in that they cannot lay flat if distended
Plicae circulares
Where in the small intestine would you find the most plicae circularis?
Jejunum
They are absent in the duodenum and less prominent in the ileum
____ = folding within the apical domain of enterocytes found in small intestine only
Microvilli
In the small intestine:
The first degree of folding = ______, which is evagination of the mucosa and part of the submucosa
The second degree of folding = ______, which is evagination of the mucosa only
The third degree of folding = ______, which are invaginations of the mucosa
The fourth degree of folding = ______, which are evaginations of the apical domain of the enterocyte
Plicae
Villus
Glands/crypts
Microvilli
Which histological layer of the small intestine holds the main distribution of blood and lymphatics?
The submucosa
[branches supply capillaries to the mucosa and muscularis layers]
Arterioles enter the mucosa of the SI and give rise to what 2 plexuses forming the microvascular system of the villus? What do they supply?
Villus capillary plexus - supplies intestinal villus and upper portion of the crypts of Leiberkuhn
Pericryptal capillary plexus - supplies lower half of crypts of Lieberkuhn
[both plexuses drain into the submucosal venule]
____ = single blind-ending central lymphatic capillary found in lamina propria of a SI villus. These structures will form a plexus that branches around a lymphoid nodule, forming the _____. They anastomose with efferent lymphatic vessels and leave the SI.
Lacteal; GALT
Motility of the SI is controlled by the ANS. Intrinsic innervation consists of what 2 plexuses? Histologically, where are they located?
Submucosal plexus of Meissner - controls glandular secretions from submucosal and mucosal layer
Myenteric plexus of Aurbach - sits between circular and longitudinal layers of muscularis layer
Neurons of the submucosal plexus of Meissner and the myenteric plexus of Aurbach receive intrinsic and extrinsic input from what sources?
Intrinsic input from the mucosa and muscle wall of SI
Extrinsic input from the parasympathetic (vagus n.) and sympathetic nerve trunks
What type of glands are found in the duodenum? Which layer are they found in?
Brunner’s glands in submucosa
Describe the Brunner’s glands found in the submucosa of the duodenum
Tubuloacinar mucous glands
Produce an alkaline secretion that neutralizes acidic chyme
The duodenum collects bile and pancreatic secretions via the ________ ______. The base of the crypts of lieberkuhn may contain ____ cells
Hepatopancreatic ampulla; paneth
What is unique about the histology at the gastroduodenal junction?
The pylorus of the stomach has simple columnar epithelium like that in the duodenum, but you will notice a massive bed of muscularis muscle at the pyloric sphincter, as will as abundant Brunner’s glands DEEP to the muscularis mucosae of the duodenum. Will also note secretory mucosa with villi, but the distinguishing featuer is usually the presence of glands at the beginning of the SI that were not present in the stomach
Describe the jejunum including its villi, lacteals, brunner’s glands, lamina propria, and paneth cells
Long finger-like villi and well-developed lacteal (villus core)
Lacks brunner’s glands
Lymphoid nodules/follicles in the LP
Paneth cells in the base of the crypts
What is the function of paneth cells found in the SI?
Regulate the microbiome by secreting anti-microbial proteins
In which part of the SI would you find Peyer’s patches?
Ileum
Describe the ileum in terms of peyer’s patches, brunner’s glands, villi, and paneth cells
Peyer’s patches, lymphoid follicles (also called nodules) found in the mucosa and part of submucosa
Absence of Brunner’s glands
Shorter finger-like villi compared to jejunum
Paneth cells found at base of crypts
Intestinal mucosa and crypts of Lieberkuhn are simple tubular glands lined by what type of epithelium?
Simple columnar
What cell types are associated with intestinal mucosa and crypts of lieberkuhn?
Enterocytes (absorptive cells) Goblet cells Enteroendocrine cells Paneth cells Intestinal stem cells
[bottom 3 are within each gland/crypt, enterocytes and goblet cells found throughout]
How would you histologically distinguish goblet cells from enterocytes in terms of surface features?
Goblet cells lack microvilli at their surface
Each enterocyte has an apical domain with a prominent _____ (striated) border that contains about 3000 closely packed microvilli to increase SA. Each ends on the _______ ____, a zone with cytoskeletal filaments
Brush; terminal web
Microvilli are 0.5-1 micrometer with a core bundle of 20-40 cross-linked actin filaments.
Each actin bundle:
Projects into the apical portion of the cell as a ______ and is cross linked to its neighbors. The end of each rootlet attaches to _________ filaments. The cross-linking proteins form part of the terminal web, maintaining the _____ position and shape of microvillus
Rootlet; intermediate; upright
Columnar mucus-secreting cells scattered among enterocytes
Goblet cells
Describe the 2 domains associated with goblet cells
Apical = goblet-shapped, with large mucus granules released by exocytosis
Basal = houses RER, golgi, and nucleus (where the granules are made)
What is the overall purpose of the presence of goblet cells scattered among the enterocytes of the small intestine?
Their secretory product contains glycoprotein-based mucus that hydrates the intestine mucosa, forming a protective shield from abrasion and bacterial invasion
What 3 important hormones are secreted by eneteroendocrine cells of the small intestine?
Gastrin
Secretin
Cholecystokinin
What hormone, released by enteroendocrine cells of the SI, slows emptying of the stomach by acting on pyloric sphincter, stimulates bile release from gallbladder, and stimulates secretion of pancreatic enzymes?
Cholecystokinin
What hormone, released by enteroendocrine cells of the SI, stimulates bicarb secretion by the pancreatic duct as well as enhances insulin secretion by B cells of the islet of langerhans?
Secretin
What hormone, released by enteroendocrine cells of the SI, stimulates the secretion of HCl by parietal cells, stimulates insulin secretion by B cells of the iselt of langerhans, and stimulates gastric motility and growth of the mucosal cells?
Gastrin
The basal domain of paneth cells contains the ______. the apical region shows numerous protein granules of diverse AMPS - like what?
RER
Defensins, lysozyme, angiogenin 4 (ANG4)
Where would you find intestinal stem cells?
ISCs reside in niche at crypt base, near paneth cells
They repopulate the entire epithelial lining of the SI, and may differentiate as goblet cells, enterocytes, and enteroendocrine cells
Plicae circularis and intestinal villi are not found beyond which point in the GI tract?
Ileocecal valve
[So LI can be distinguished by lack of these things, as well as TONS of goblet cells]
The layers of the LI are the same as those in the SI: mucosa, submucosa, muscularis, serosa.
What is the main function of the mucosa in the LI?
Absorption of water, sodium, vitamins, and minerals
The absorptive capacity of the colon favors the uptake of substances such as sedatives, anesthetics, and steroids. Why might this be clinically important?
Medications can be administered there when they cannot be taken orally - due to things like vomiting
How are the tubular glands, or crypts of lieberkuhn, oriented differently in the LI vs. the SI?
In the LI, they are oriented perpendicular to the long axis of the colon, are much deeper than the SI, and have higher proportion of goblet cells
What 4 cell types are found in the mucosa (surface epithelium and tubular glands) of the LI?
Simple columnar absorptive cells - with apical microvilli
Goblet cells
Stem cells at base of glands
Enteroendocrine cells
Describe mucosal layer of LI
Simple columnar epithelium formed by enterocytes and goblet cells
Glandular epithelium with enterocytes, goblet cells, stem cells, and enteroendocrine cells (+paneth cells in cecum)
Lamina propria and muscularis mucosae present, isolated lymphoid follicle penetrate submucosa
Describe submucosa of LI
Dense irregular CT that lacks glands, vascularized
Describe muscularis layer of LI
Inner circular layer is typical (same as SI)
Bundles of the outer longitudinal layer fuse to form taenia coli
3 longitudinally oriented ribbon-like bands that draw the colon into sacculations (haustra)
What is unique about the serosa of the LI as compared to SI?
Epiploic appendices present (aggregates of adipocytes surrounded by serosa)
Describe histological layers of appendix
Similar to that of LI
Mucosa of simple columnar with goblet cells (no villi); lymphoid follicles and lymphocytes within LP that extend into submucosa
Submucosa contains adipocytes and dense irregular CT
Muscularis: inner circular layer is well developed, but outer longitudinal layer is NOT
Covered with serosa
Abnormal form of constipation caused by aganglionosis in the distal colon
Hirschprung’s Disease (congenital megacolon)
[Failure of NCC development (NCCs are what form the ganglion cells in plexuses of Meissner and Auerbach)]
What causes Hirschprung’s Disease?
Mutations of the RET gene encoding a RTK
RTK signaling required for formation of Peyer’s patches, migration of NCC into distal portions of large intestine, and differentiation of NCC into neurons of the enteric nervous system
In a patient with Hirschprung’s disease:
What would an intestinal biopsy show?
How is it treated?
Biopsy shows thick, irregular nerve bundles, a lack of ganglion cells, and abundant AChE staining
Treatment = surgical removal of affected colon segment
The rectum is divided into 2 parts. Describe them histologically
Upper part (rectum proper): similar to colon - simple columnar epithelium with tubular glands
Lower part (anal canal): 8-10 rectal/anal columns with mucosal folds forming anal valves
The lower part of the rectum (anal canal) contains columns that form anal valves. What 2 structures are contained within the valves?
Anal sinuses
Anal mucous glands
At the base of the columns of the lower part of the rectum (anal canal) is the _________, which represents the epithelial transformation zone.
What epithelial transformation occurs here? Why is this transformation functionally important?
Pectinate line
Epithelium goes from simple columnar to non-keratinized stratified squamous (so that continuous shedding of cells d/t defecation may occur without issue)
Describe histology of the rectum as it transitions to anus below the pectinate line
Below the pectinate line, at the level of the anus, the inner circular layer of muscularis thickens to form the internal anal sphincter. At this location, the mucosa consists of stratified squamous epithelium with circumanal glands in the submucosa. The external anal sphincter (skeletal m.) and levator ani m. also present. Epithelium of the anus is highly keratinized stratified squamous
IBD includes what 2 diseases? How do those 2 differ?
Ulcerative colitis and Crohn’s disease
Both are characterized by diarrhea, pain, and periodic relapses.
UC affects mucosa of LI
Crohn’s affects any segment of intestinal tract, usually terminal ileum and LI
Describe pathology of Crohn’s disease
Inflammatory cells produce cytokines that cause damage to the intestinal mucosa
Infiltration of neutrophils into crypts of Lieberkuhn —> destruction of intestinal glands d/t crypt abscesses —> progressive atrophy, ulceration of the mucosa
Major identifying feature of esophagus histo
Mucous glands in submucosa (only found here and in duodenum)
Major identifying feature of stomach histo
Inner oblique layer of muscularis externa (near border to submucosa)
Major identifying feature of duodenum histo
Glands in submucosa (Brunner’s)
Major identifying feature of jejunum histo
Long villi
Major identifying feature of ileum histo
Peyer’s patches
Major identifying feature of appendix histo
Abundant lymphoid tissue
Major identifying feature of colon histo
Tons of goblet cells
Major identifying feature of rectum histo
Anal columns in submucosa
