6. Small/Large Intestine Histo Flashcards
What is the principal site for digestion of food and absorption of digested products?
Small intestine: duodenum, jejunum and ileum
What is the main hallmark for the small intestine which is more visible in the jejunum rather than the ileum?
Plicae Circulares which are transverse folds with submucosal core with intestinal villi
Intestinal villi are in the mucosa and project into the lumen of the small intestine to increase absorptive area. The core contains loose CT with a lacteal. What other two things are important in the intestinal villi?
Enterocytes which produce enzymes for digestion/absorption
Goblet cells which provide mucus to sheild from abrasion
What is contained inside a lacteal in the intestinal villi?
Blood supply and a lacteal which helps absorb nutrients from the SI
Where are plicae circulares with intestinal villi absent?
duodenum
Enterocyte microvilli have striated border, increasing luminal surface. What does the terminal web allow?
Terminal web has actin/myosin allowing for contraction of microvilli
The mucosa of the SI is simple columnar epithelium with tubular intestinal glands, lamina propria and muscularis mucosae to release gland contents. What about the submucosa, muscularis externa and serosa layers?
all the same as esophagus.
Dense ireg CT
inner circular/outer longitudinal
serosa w loose CT and peritoneum
Motility of the SI and LI is controlled mainly by the ANS. What does the enteric (intrinsic) nervous system consist of? (2)
Submucosal plexus of meissner
myenteric plexus of auerbach (in muscularis externa between inner and outer)
The intestinal glands are simple tubular glands lined by simple columnar epithelium which is continuous with the epithelium that covers the intestinal villi. What are the 4 types of cells in the intestinal glands?
Enteroendocrine
Paneth
Intestinal Stem cells
M (microfold) cells
Enteroendocrine cells are found throughout the intestinal glands and secrete hormones to control gut motility, HCl, bile and other things. What are some of the main hormones they secrete? (5)
Gastrin Secretin Gastric Inhibitory polypeptide (GIP) Motilin Cholecystokinin (CCK)
What type of cells are at the base of intestinal glands mainly only in the SI, which function in innate immunity by secreting antimicrobial substances such as lysozymes?
Paneth cells
Paneth cells regulate normal bacterial flora. When these cells are found in the normal colon, what could it suggest?
Pathological conditions
Intestinal stem cells (ISCs) reside at the crypt base near paneth cells. They repopulate epithelial lining and can move out a crypts to differentiate into?
Goblet cells, enterocytes, and enterendocrine cells
What cell has a deep pocket like recess which houses dendritic, macrophages and T/B cells. It also has microfolds and glycocalyx and overlie PEYER’s patches?
M (microfold) Cells
The apical surfaces of M cells express receptors that bind macromolecules and bacteria to do what?
internalize and transfer to immune cells
M CELLS ARE HIGHLY SPECIALIZED ANTIGEN-TRANSPORTING CELLS
When differentiating the pyloris (thick d/t sphincter) of the stomach and the duodenum of the SI, what layer is important to look at?
the submucosal layer
What is different about the submucosal layer of the of the duodenum compared to the pyloris? hallmark
There are abundant Brunner’s glands in the submucosa, deep to muscularis mucosae
Brunner’s glands in the duodenum in the intial SI produce alkaline secretion which neutralize the acidic chyme. What does the duodenum collect?
Collects bile and pancreatic secretion via the hepatopancreatic ampulla (2nd descening part of duodenum at L2-L3)
What part has the longest finger-like villi of the SI, with no submucosal glands or peyer’s patches?
Jejunum
What part of the SI has shorter finger-like villi than the jejunum, and has island like PEYER’s patches?
Ileum
Food is propelled from the ileum to cecum through the ileoceccal valve. Here we can see an abrupt transition from villi of SI to?
glandular epithelium of LI
What is the main job of the large intestine?
absorb water, sodium, vitamins, minerals
Opening of tubular intestinal glands (crypts of Lieberkuhn) are hallmark of the LI mucosa. What are 3 other hallmarks!
intestinal glands
goblet cells
NO intestinal villi
The mucosa of the LI ha simple columnar epithelium and a lamina propria and muscularis mucosae are present. What is extensive here and may penetrate the submucosa?
GALT
The LI submucosa is typical along with the inner layer of muscularis externa. What is different about the outer longitudinal layer?
it is organized into taeniae coli which form the haustra to help propel food
The veriform appendix is a diverticulum of the cecum with layers similar to those of LI. What are characteristic of the mucosa, submucosa, muscularis and serosa here?
Mucosa has simple columnar epithelium and goblet cells
Sub has ADIPOCYTES and dense ireg CT
Muscularis has undeveloped outer longitudinal layer
Covered in Serosa!
What disease is due to mutations in the RET gene which causes failure of neural crest cells (NCC) to migrate and develop the plexuses of the bowel segment?
Hirschprung’s Disease
(85% are short segment confined to rectosigmoid, 10% long-segment from rectosigmoid to splenic flexure, 5% affects entire colon)
Hirschprung’s disease occurs 1:5000 neonates. Presents with constipation, poor feeding and abdominal distention. How does one treat this?
Surgical removal of the affected colon segment and reattach ends
IBD, inflammatory bowel disease, includes ulcerative colitis and chron’s disease. Characterized by diarrhea, pain and relapses. Chron’s can affect any reion while ulcerative colitis affects?
the mucosa of the LI
Chrons is observed in the LI and terminal ileum. Inflammatory cells produce cytokines that damage the intestinal mucosa. Neutrophils infiltrate into the crypts of lieberkuhn and destroy intestinal glands due to crypt abscesses
just FYI I think
The rectum proper (upper part) has typical mucosa with tubular intestinal glands and transverse folds. The anal canal (lower part) has what three things?
Anal columns with mucosal folds
Anal sinuses: depressions between columns
Anal glands: extend into submucosa/muscularis externa
What is the main job of anal sinuses?
to keep poop inside :)
The ENS stops at the pectinate line and what begins for the external anal sphincter?
skeletal muscle
The anal canal has three zones, what are they?
colorectal zone
anal transitional zone (ATZ)
squamous zone
The colorectal zone is simple columnar epithelium identical to the rectum (upper 1/3 of anal canal) while the squamous zone is?
nonkeratinized stratified squamous epithelium continous with perineal skin (lower 1/3 of anal canal)
The ATZ is where simple squamous epithelium becomes?
Stratified squamous epithelium of perianal skin (middle 1/3 of anal canal)
What layer forms the internal anal sphincter?
the inner circular layer of the muscularis externa thickens
At the recto-anal junction, what two types of cells can be seen?
nonkeratinized stratified squamous epithelium and simple columnar with tubular intestinal glands
