Histology Flashcards
Difference in alimentary canal and digestive system
Alimentary canal- digestive tract (from oral cavity to anus) while the digestive system is the alimentary canal + the digestive glands (salivary, liver, pancreas, gallbladder)
What are the four layers throughout the GI tract
- Mucosa- which consists of epithelium, lamina propria and muscularis mucosa
- Submucosa– dense irregular CT
- Muscularis Externa– which has an inner circular and an outer longitudinal layer
- Serosa (or Adventitia)– mesenteric covering
Features of the mucosa
Has three main components- epithelium and lamina propria and muscularis mucosa
Epithelia function
- barrier between lumen (environment) and body tissues –keeps out pathogens, antigens, toxins, encloses undigested food. Maintains barrier via tight junctions
2.protection from abrasion via stratified type of epithelia
3.absorption – of nutrients and water
4.secretion – via glandular tissue
. Provides lubrication, enzymes, HCl, buffer,
hormones
What does the lamina propria house?
1.Microvasculature – for nutrient absorption
2.Lacteals– lipid uptake
3.Glands (are embedded in and surrounded by LP)
4.Diffuse lymphatic tissue (lymphocytes, plasma cells)
5.Lymphatic Nodules with germinal centers
-Both diffuse and nodular lymphatic tissue in the GI tract is called Gut-Associated Lymphatic Tissue (
GALT)
6. Other leucocytes that function in CT compartments
Two locations where there is an abrupt change in epithelium
Esophageal-cardiac and the rectal-anal junction
Features of the muscularis mucosa
Part of the mucosa (with epithelium and lamina propria)
- Inner circular and outter longitudinal smooth muscle
- Functions- contraction of the muscularis mucosa produces movement that make transient ridges and facilitates absoption/secretion (NOT FOR PERISTALIC MOVEMENT)
Features of the submucosa and what does it contain
Dense irrefular CT layer (fibroblast and collagen)
- larger blood vessels (which send/receive branches to/from other three layers)
- Lymphatics
- Submucosal nerve plexus comprised of parasympathetic ganglia (nerve cell bodies) and nerve fibers (both motor and sensory)- controls mucosal/submucosal motility and secretory activity of glands
- Submucosal glands (present only in selected regions of GI tract)
Features of the muscularis externa
3 main components
- Inner circular layer spirals around the gut tube- contracts to constrict the lumen— Also forms sphincters
2 Outter longitudinal layer that contracts to shorten the tube (peristalsis)
- Myenteric nerve plexus- located between the two layers of muscle. Comprised of parasym ganglia and nerve fibers (sensroy and motor) and also has sympathetic input that controls mucosa and submucosa
Function of the outermost layer of the gut tube. What does it suspend?
Serosa- has a thin layer of squamous epithelium that prodcues serous fluid lubricate that reduces friction
Serous covers protions of the GI tract suspended in the peritoneal cavity (intraperitoneal)
What is adventitia? What organs have it? Difference between serosa
Dense irregular CT that is found in organs fixed to abdominal wall– retroperitoneal.
If found between two organs it acts to adhere them where it may have adipose as a shockabsorber rather than the dense CT
When would an organ have both serosal and adventitia coverings?
Organs/parts of organs that have both coverings? (4)
When one surface is bound to another organ and the other is suspended.
The gallbladder is adventitia where it is bound to th eliver but serosa the rest of the surface.
Ascending, descengin and esophagus have both coverings
What is the gut mainly controlled by? How is this control center organized?
by the enteric nervous system which is self contained system comprised of repeating ganglia organized into two plexuses 1. Submucosal and 2. Myenteric
Features of the submucosal
It’s one of the plexuses that make the enteric system
AKA Mesissner
- has neuronal cell bodies located in the submucosa
- Motor component: controls mucosal and submucosalgland secretion and blood flow
- Sensory component: consists of mucosal mechanosensitive neurons (convey info
regarding luminal contents, secretory status)
Features of the myenteric
AKA the Auerbachs
- Has nueronal cells between the circular and longitudinal layers of the muscularis externa
- Motor component that controsl the GI motility (contraction and relaxatin)
- Sensory component that controsl the tension-senstivie neurons and the chemosenstive neurons
What other innervation does enteric system have except self?
Self contrain through the submucosal and myenteric plexus but also parasym and sym
Para syme- 1. via vagus 2. Stimulates peristalsos and inhibits sphincters 3. Triggers secretory
Sym- 1. via splanchnic nerves, inhibits peristalisis, and activates sphincters
Vascular and lymphatics of the gut
Aterial is from the celiac trunk and segmetnal branches of the superior and inferior mesenteric arteries
Lymphatics- lacteals in the villus of the SI. Provide route for lipds from intestinal absorptive cells where they join proteins to make CHYLMICRO and drain externally to the musculars and into the mesenteric lympaics to the para-aortic lymphatics to the thoracic duct into genreal circulation
Function of esophagus
Type of epothelium? And why?
What’s special about the proximal side?
Esophagusa fixed tube that conveys food/liquid from the pharynx to the stomach
Has stratified (non keritinzied epithelium) that provides from abrasion as the bolus passes down
The proximal has thick muscularis mucosa to aid in swallowing
Upper 1/3 muscularis externa is skeletal muscle
What happens at the esophageal cardiac junction?
How is it protected>
There is an abrupt change in epithlium from stratified squamous to simple columnar
The esophageal glands in the submucosa secrete neutral pH mucus protecting the junctional region from the stoamch acids
The muscularis externa becomes thickened to form the inferior esophageal sphincter
Location and function of the stomach
What are the parts
Stomach– The stomach is an expanded part of the gut tube and lies beneath the diaphragm.
Function: mixes and partially digests food to produce a mixture called chyme
.
It has three histologically distinct regions:
1.Cardiac region
- Fundic/Body region
- Pyloric region
4 distinguishing features of the stomach
- Epothelium comprised of surface mucus cells and gastric gland which are embedded in the lamina propria
- Longitudinal submucosal folds that are called rugae are present that allow the stoamch to expand when food is present
- Muscularis externa has three poorly distinguished layers. Inner oblique, middle circular, and outer longitudinal
- Outter most is serosa
Special features of the cardiac region
Cardiac gastric glands are shallow simple mucus glands form gastric pits
Esophageal glands in the submucosa under transition zone
Features of the fundic region of the stomach
- Gastric pits 2-3 gastric glands
- Mucus gastric cells line the lumen
- Relatively thick mucosa due to the bits and fundic glands
Cells present
1 Mucus neck cells
- Parietal- upper half of glands
- Cheif- bottom half of glands produce pepsinogen and lipase
- Enteroendorcine cells- usually in bottom half secrete across basal lamina
G-cells- make gastrin that produces HCl
D Cells- produces somatostain that inhibits gastrin
Enterochromaffin- produce histamine which stimulates HCl
Pyloric features
Shallow glands
Simple tubular glands that appear s-curves
Secrete highly basic mucus to neutralize the acidity of chyme before it enters the duodenum
No epithelial transition here
Histo of Stomach Wall Identify
