Downing: Histology of Stomach and Small Intestine Flashcards
What are important histological features of the stomach?
- Mucosa
Simple columnar epithelium
LP: contains gastric glands, pyloric glands, cardiac glands
Muscularis mucosa - Submucosa: LCT, large blood vessels and submucosal plexus
- Muscularis exerna: 3 layers (myenteric nerve plexus between M and O layer)
- Serosa
What layers thicken in the pyloric region of the stomach to form the pyloric sphincter?
Inner and middle layer
Describe the surface region and glandular region of the body and fundic regions of the stomach?
Surface region
- Surface- simple columnar epithelium
- Mucus secreting cells.
- LP forms a gastric pit (1/4 the thickness of the mucosa)
- Constant turn over every 4-6 days
Glandular region
- Simple columnar
- From gastric pit to muscularis mucosae
- Isthmus, neck
- Mucous neck cells and Parietal cells
What parts of the glandular region have mitotically active cells?
Isthmus (germinative zone from which surface cells are renewed)
Neck (mucous neck cells and parietal cells)
What do mucus neck cells secrete?
Secrete clear mucus to protect gland from HCL and proteolytic enzymes
Columnar cells or cuboidal cells
Where are parietal cells most numerous in the stomach?
In the neck region of gland and upper body
What are the functions of parietal cells?
Produce secretory glycoprotein called IF that is necesary for absorption of vitamin B from the ileum
Produce HCL
Eosinophilic!
What stimulates parietal cells to secrete acid?
cholinergic nerve endings (ACh)
histamine (HR)Gastrin (MR) target G cells in the pyloric region
Where are chief cell most numerous?
Basal region of the gland
Why are chief cells basophilic?
D/tRER and eosinophilic d/t protein stored in zymogen granules
What do chief cells secrete?
Zymogen granules in chief cells contain pepsiniogen that is released from the GA and stored in the cytoplasm. Once released pepsinogen is activated by the acidic environment to pepsin. Pepsin can convert proteins to peptides.
Enteroendocrine cells produce substances that are secreted where?
They are NOT secreted into the lumen but rather secreted on the other side of hte basement membrane, where they accumulate and enter the vasculature.
What are three hormones produced by enteroendocrine (DNES) cells?
Gastrin
Secretin
Cholecystokinin
Gastrin
G cell
pylorus
Stimulates gastric acid secretion
Secretin
S cell
Small intestine
Pancreatic and biliary bicarbonate and water secretion
Cholecystokinin
I cell
Small intestine
Pancreatic enzyme secretion and gall bladder contraction
How does the pyloric region of the stomach differ from the fundic and body regions?
- Surface region
- also simple columnar w/ mucus secreting cells to protect the epithelium
- LP forms gastric pits that are 2/3!! the thickness of hte mucosa - Glandular
- also simple columnar
- also has mucus cells nad enteroendocrine cells
What is unique about the mucosa of the cardiac region?
Gastric pits are 1/2 the thickness of the mucosa
Glands are NOT DEEP and are mostly the mucous neck type
What are the functions of the stomach?
Produce chyme
Produce IF for absorption of B12 from the ileum
VERY little absorption
What are the functions of the small intestine?
Mostly digestion and absorption
What are plicae circulares?
Prominent circular folds in the duodenum and upper jejunum but NOT in teh ileum
Extend half way around the lumen and can increase the intestinal SA by a factor of 3
What is commonly seen in the mucosa of the small intestine?
Villi formed by mucosal lining
Distinct muscularis mucosae to separate the mucosa and underlying submucosa
Plicae circulares are mucosal folds w/ submucosal cores
What is commonly seen in the submucosa of the SI?
Core of the plicae circulares
larger blood vessels
submucosal nerve plexus
What is the muscularis of the SI made up of?
ONly TWO layers of smooth muscle (Inner circular and outer longitudinal)
Myenteric plexus in between!
Where is serosa found in the SI?
Every where except in areas that are retro-peritoneal
Describe the epithelium of the SI.
Villus epithelium- simple columnar
- absorptive columnar, goblet and enteroendocrine cells
Crypt epithelium- simple columnar
- the three above + Paneth cells and undifferentiated cells
Lymphocytes
Cells held together by junctional complexes
Describe the lamina propria of the SI.
Forms the CT core of each villus
contains a central lymphatic vessel known as a lacteal
Very cellular
What is a characteristic feature of the small intestine?
intestinal villi
What are the crypts of lieberkuhn?
located in the small intestine they open up at the base of hte villi
paneth cells are found at the base of the crypt and mitotic cells are present
What are the absorptive columnar cells of hte small intestine?
Specialized for absorption and have tones of microvilli
Brush border of these cells contains enzymes that facilitate digestion and absorption
What do goblet cells do and what happens to them as you pass form the duodenum to the colon?
secrete mucus
number of cells INCREASES
Where are DNES cells found in the SI and what do they do?
found adjacent to the basement membrane
secrete peptide hormones
Where are paneth cells found in the SI and what do they do?
Paneth cells are found at the base of crypts and contain zymogen granules taht contain a bacteriolytic lysozyme. They are believed to regulate intestinal bacteria.
What is unique about the undifferentiated cells in the SI?
contain free ribosomes and undergo frequent mitosis
What cells of the SI are associated wtih intestinal carcinoma?
undifferentiated cells
What are brunner’s glands found?
In the submucosa of the Duodenum!
What do brunner’s glands do?
Secrete alkaline mucus material into the duodenum that NEUTRALIZES the acid chyme of the stomach.
Where can you find adventitia and serosa in the SI?
Duodenum- adventitia
Jejunum/ileum- serosa
Where are peyer’s patches found?
Ileum opposite the mesentery attachment
What are peyer’s patches?
aggregates of lymphatic nodules taht provide the precursors for plasma cells to produce IgA
What are M cells?
Cells found in peyer’s patches that endocytose antigen and transport it to underlying lympahtic tissue
What may be small, few or altogether absent from the distal ileum though it’s a prominent feature throughout much of hte SI?
plicae circulares
Are there more or less goblet cells in ileum compared to the rest of the SI?
MORE
What is the significance of tight junctions in the intestinal epithelium?
- compartmentalizes membrane proteins
2. forces material to be absorbed to pass into the absorptive cell
