Histology of the Lower GI Tract Flashcards
What is chyme?
semifluid mass of partly digested food expelled by the stomach into the duodenum
What are villi in the small intestines?
folds of the mucosa projecting into the lumen. cover entire surface of S.I. increase the absorptive surface of the mucosa
Extend deep into mucosa to form crypts of lieberkuhn and end at muscularis mucosae
What are plicae circularis?
permanent folds that are distinct in jejunum what include mucosa and submucosa
begin in duodenum and disappear in mid-ileum
What are crypts of lieberkuhn?
intestinal simple tubular glands that increase surface areaby adding another separate fold btwn the villi
What epithelium lines the crypts and what 4 types of cells are included in crypts of lieberkuhn?
Lined by simple columnar epithelium Absorptive, goblet, paneth, and enteroendocrine cells
What are enterocytes?
Absoprtive cells: epithelial cells lining the lumen that have microvilli on apical surface
Have tight junction barrier linking adjacent enterocytes
What do the length of the villi depend on ?
degree of distention of intestinal wall and contraction of Sm m in villus core
What are microvilli?
evagination of apical part of enterocytes to increase SA
Produce brush border on apical border of enterocytes
Contain intramembranous enzymes, including lactase, maltase, sucrase, for terminal digestion of carbs
What layer is the main site of blood and lymph vessels?
submucosa
What covers the serosa (thin layer of loose CT)?
visceral peritoneum (mesothelium) - a membrane composed of simple squamous cells taht forms the lining of several body cavities
What is mesothelioma?
an aggressive form of cancer affecting the membrane lining the pericardial, pleural or peritoneal cavities
What is segmentation ?
pattern of annular contraction of sm m layers in walls of SI which temporarily seems to cut the region affected into individual compartments; mixes chyme and controlled by ANS
NOT coordinated
What is peristalsis?
Contents advance along intestine when proximal contraction is corrdinated with relaxtion below
The arterioles derived from the submucosal plexus enter the mucosa of the SI and give rise to two capillary networks called….
villus capillary plexus: intestinal villus and upper portions of crypts of L
Pericryptal capillary plexus: lower half of crypts
Where are lacteals located? what is the function?
In the core of villus
Single blind-ending central lymphatic vessel
pull material (chyle) in and send to lymphoid follicles and follow the portal vein
What is chyle?
lymph containing lipids absorbed from the meal and packaged in chylomicrons
There are brunner’s glands in the submucosa
Relatively few goblet cells
and leaf-like villi
What part of the intestines is this in?
Duodenum
Well developed plicae circulares Irregular villi more goblet cells NO brunners glands or peyer's patches What part of the intestines is this in?
Jejunum
Many lymphoid nodules (peyer’s patches) in LP and submucosa
Finger-like villi and the most goblet cells
What part of the intestines is this in?
ileum
Oligosaccharides reduce carbs to hexoses in enterocyte microvilli and can now be transported into the enterocyte by what?
carrier proteins
Why does lactose sometimes cause gas, irritation, and increased motility?
Lactose intolerance due to lack of lactase
Bacteria instead ferment lactose producing organic acids and gas
What are goblet cells?
columnar mucus-secreting cells scattered among enterocytes
Secretory product: glycoproteins
Exocytosis
Protective gel coat from abrasion and bacterial invasion
Enteroendocrine cells secrete secretin. What does secretin do?
stimulate prancreatic bicarb secretion and enhances insulin secretion
What does CCK do?
released by enteroendocrine cells: acts on pyloric sphincter to slow emptying, stimulates release of bile and pancreatic enzymes
