Term
| what are the 4 layers that make up the digestive tract? |
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Definition
Mucosa (mucous membrane)
Submucosa
Muscularis externa
Serosa (or Adventitia)
These layers vary depending upon the functions of the different regions of the tract. |
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Term
| what are the 3 layers of mucosa? |
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Definition
epithelium with its basal lamina - derived from endoderm. The type of epithelium reflects function.
lamina propria - a loose connective tissue containing blood vessels, nerves, lymphatics, lymphoid tissue and in some regions, glands.
muscularis mucosae - typically two layers of smooth muscle, a thin inner circular and an outer longitudinal layer. The muscularis mucosa separates the mucosa from the submucosa. |
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Term
| describe the submucosa and what it contains |
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Definition
Typically a dense irregular connective tissue
Contains
blood vessels
Lymphatics
a nerve plexus, the submucosal Meissner's plexus.
Part of enteric nervous system.
Neural crest derived.
The submucosa in some regions contains glands and lymphoid tissue. |
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Term
| describe the muscularis externa |
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Definition
Typically an inner circular and an outer longitudinal layer of smooth muscle.
Between these two muscle layers is the myenteric (Auerbach's) plexus.
Part of enteric nervous system.
Neural crest derived |
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Term
| what is the serosa/adventitia? |
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Definition
layer of loose connective tissue with blood vessels, lymphatics and nerves.
In the case of a serosa it is covered by mesothelium.
In the case of an adventitia, it is surrounded by and blends into the adjacent connective tissue. |
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Term
| describe the mucosa in the esophagus |
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Definition
Stratified squamous non-keratinized epithelium.
The lamina propria has esophageal cardiac glands at its lower end near the stomach.
These glands secrete mucus which has a neutral pH. Protects the esophagus from regugitated acid.
The muscularis mucosae (smooth muscle) is thicker than other parts of tract and is only longitudinally oriented |
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Term
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Definition
Excessive gastric reflux results in pyrosis or what is more commonly described as heartburn.
Persistent reflux can cause metaplasia of the epithelium. There is a change from a stratified squamous epithelium to a simple columnar epithelium.
Incidence of Barrett esophagus is increasing, particularly among males.
Alcohol and smoking are risk factors.
As with all epithelial metaplasia, Barrett esophagus can undergo transformation into a malignancy, adenocarcinoma. |
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Term
| what can be found in the esophageal submucosa? |
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Definition
Over the entire length of the esophagus, the submucosa contains groups of small mucus-secreting glands called esophageal glands proper.
The secretion of these glands is slightly acid and functions to lubricate the lumen of the esophagus. These glands tend to be most numerous in the lowermost region of the esophagus. |
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Term
| describe the 3 regions of the muscularis externa in the esophagus |
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Definition
Has two layers, an inner circular layer and an outer longitudinal layer
Region of esophagus, upper, middle and lower can be identified by muscle types in externa.
upper third has a muscularis externa composed of skeletal muscle only
middle 1/3 has a mixture of skeletal and smooth
lower 1/3 -SMOOTH MUSCLE ONLY |
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Term
| describe the adventitia above the diaphragm |
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Definition
| loose connective tissue containing longitudinally-oriented blood vessels, nerves and lymphatics |
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Term
| describe the serosa below the diaphragm |
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Definition
| free part of esophagus just before the stomach is covered with mesothelium |
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Term
| what are the 4 grossly identifiable regions of the stomach? |
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Definition
cardia (at T11)
fundus
body
pyloris |
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Term
| what are rugae in the stomach? |
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Definition
| longitudinal folds of mucosa and submucosa seen in empty organ called magenstrasse (German for stomach streets) by gross anatomists |
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Term
| describe the gastric mucosa |
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Definition
Characterized by gastric pits or foveolae.
Epithelium
simple columnar epithelium - mucus secreting cells (NOT GOBLET CELLS)
Lamina propria
loose C.T.
lymphatic tissue
branched tubular gastric glands that open into the gastric pits
Muscularis mucosae
inner circular, outer longitudinal smooth muscle |
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Term
| where are gastric glands located? |
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Definition
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Term
| what are the regional specializations of gastric glands? |
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Definition
cardia region
mainly mucus-secreting cells
fundus and body
short gastric pits
long gastric glands empty into these pits
pyloric
deep pits
short glands |
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Term
| what do gastric surface cells secrete? |
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Definition
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Term
| where are parietal/oxyntic cells located in the gastric glands and how do they stain? |
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Definition
| Parietal or oxyntic cells, located mainly upper part of gastric glands, are round or pyramidal shaped, very eosinophilic cells |
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Term
| where are chief or zymogenic cells located in the gastric glands and how do they stain? |
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Definition
| Chief or zymogenic cells, located in the lower portions of the gastric glands, are very basophilic |
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Term
| do parietal cells secrete HCl? |
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Definition
no
Elaborate hydrochloric acid.
Contain carbonic anhydrase.
It dissociates H2CO3 into H+ and HCO3-. The H+ combines with Cl- to form HCl in the lumen.
It is improper to say that parietal cells secrete HCl.
They actively transports H+ across their apical membranes.
Cl- is actively transported across the basal membrane and passively crosses the apical membrane to enter the lumen.
Secret intrinsic factor needed for absorption of vitamin B12. |
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Term
| how do parietal cells stain and what are they characterized by? |
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Definition
Very acidophilic
Characterized by:
intracellular canaliculi
Numerous mitochondria
Very little RER |
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Term
| describe what happens in an individual with B12 deficiency |
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Definition
Lack of intrinsic factor due to such conditions as atrophic gastritis can lead to pernicious anemia.
Low RBC count, low hemoglobin.
B12 deficiency can lead to central nervous system degeneration.
For example, B12 deficiency can cause subacute combined degeneration of the spinal cord. This can occur in very strict vegetarians since B12 is not found in vegetables and fruits.
Presents as a burning sensation in soles of feet and other sensory disturbances.
May present like multiple sclerosis |
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Term
| describe chief (zymogenic) cells |
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Definition
Located in the lower portions of the gastric glands.
Very basophilic because of their high content of RER.
Have secretory (zymogen) granules and release pepsinogen.
Pepsinogen becomes pepsin in the very acid environment of the lumen |
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Term
| how do chief cells stain and what are they characterized by? |
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Definition
Very basophilic
Characterized by:
Lots of RER
Secretory (zymogen) granules |
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Term
| all enteroendocrine cells secrete their protects into what layer? |
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Definition
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Term
| what do gastric enteroendocrine cells produce? |
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Definition
| gastrin that stimulates acid production |
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Term
| the fundic stomach has what type of pits and glands? |
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Definition
| shallow pits, long glands |
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Term
| the pyloric stomach has what type of pits and glands? |
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Definition
| deep pits and short glands |
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Term
| what are the 3 layers of smooth muscle in the gastric muscularis externa |
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Definition
inner - oblique
middle circular - forms the pyloric sphincter
outer longitudinal |
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Term
| what are some general features of mucosa in the small intestine? |
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Definition
Plicae circulares (valves of Kerkring) - core of submucosa
Villi - core of lamina propria - has central lymphatic vessel or lacteal
Absorptive cells with microvilli - core of microfilaments (actin filaments)
Crypts of Lieberkuhn - intestinal glands within the lamina propria.
PANETH CELLS in the base of crypts have large eosinophilic granules which contain lysozyme an antibacterial enzyme that breaks down bacterial cell walls.
Other cell types - GOBLET CELLS and enteroendocrine cells |
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Term
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Definition
| epithelial cells with microvilli |
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Term
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Definition
| single celled mucous glands |
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Term
| what do paneth cells secrete? |
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Definition
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Term
| what do enteroendocrine cells secrete? |
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Definition
| paracrine and endocrine hormones |
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Term
| what are M (microfold) cells? |
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Definition
| modified enterocytes that cover lymph nodules of lamina propria |
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Term
| what is the small intestine specialized for? |
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Definition
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Term
| what are the 3 levels of folding that increase the surface area for absorption in the small intestine? |
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Definition
Plicae circulares
Permanent submucosal folds and as such, they have a core of submucosa
Villi
Leaf-shaped or finger-like projections of mucosa.
Core of lamina propria.
Microvilli
Cellular projections
Core of microfilaments |
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Term
| describe the layers in the small intestine? |
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Definition
Lamina propria
loose connective tissue
Contains lymphocytes, mast cells, macrophages
Blood vessels
Central lacteals
Submucosa
Dense irregular CT
Only in duodenum contains glands.
Contains nerve plexus (Meissner's plexus)
Muscularis externa
Inner circular -outer longitudinal smooth muscle.
Between layers there is a nerve plexus and postganglionic neurons (Auerbach's plexus) |
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Term
| M cells are specialized epithelial cells that cover what region? |
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Definition
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Term
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Definition
| They phagocytose microorganisms and macromolecules from the intestinal lumen and present the antigens to CD4+ T lymphocytes in the lamina propria |
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Term
| plasma cells in the lamina propria secrete what substance? |
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Definition
IgA
IgA is bound to a secretory component in enterocytes and transported to the lumen |
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Term
| describe what is found in the epithelium of the duodenum |
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Definition
Leaf-shaped villi
Typical intestinal epithelium
columnar cells with microvilli
Goblet cells
Short simple tubular glands - crypts of Lieberkuhn within the lamina propria
Brunner's glands are found in the submucosa, i.e. outside the muscularis mucosa |
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Term
| when chyme, material from the stomach, enters the duodenum, which gland secretes an alkaline secretion to buffer the acidic chyme? |
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Definition
Brunner's glands
Optimizes pH for pancreatic enzymes |
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Term
| what substances do enteroendocrine cells of the duodenum secrete specifically and what is the function of each? |
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Definition
cholecystokinin (CCK), gastric inhibitory protein (GIP) and secretin
CCK stimulates gall bladder contractions, pancreatic enzyme secretion and pancreatic bicarbonate secretion. It inhibits gastric emptying.
GIP shuts off acid production in stomach.
Secretin stimulates pancreatic secretion and inhibit gastric acid production |
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Term
| one can see the _____ _____ at the gastroduodenal junction. |
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Definition
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Term
| what occurs at the gastroduodenal junction? |
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Definition
There is a transition from pyloric mucosa (Pmuc) to intestinal mucosa (Imuc). Here one finds villi and, for the first time, goblet cells.
If one follows the muscularis mucosa into the duodenum, one sees that there are glands within the submucosa |
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Term
| compare the jejunum and the ileum histologically |
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Definition
Jejunum
Most well-developed plicae circulares.
Villi are rounded - fingerlike
More goblet cells than duodenum
Ileum
Club-like villi
Peyer's patches (lymphoid nodules) in lamina propria.
More goblets cells than jejunum |
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Term
| what are paneth cells and where are they located? |
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Definition
| Paneth cells reside at the base of the crypts of Lieberkühn. They have secretory granules which have antibacterial enzymes within them |
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Term
| what is the function of the large intestine (colon) and what can be found there? |
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Definition
Function is to absorb water, compact feces, and lead to its elimination.
This function is reflected in absorptive cells with rather meager microvilli and lots and lots of goblet cells to provide lubrication for the movement of the stool.
NO VILLI
There are crypts of Lieberkuhn containing many goblet cells
NO PANETH CELLS IN CRYPTS, BUT SOME ENTEROENDOCRINE CELLS
MUSCULARIS EXTERNA -inner circular, outer longitudinal composed of three distinct longitudinal bands called the teniae coli |
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Term
| what can be viewed to differentiate the large intestine from the small intestine? |
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Definition
| the tenia coli or longitudinal bands of smooth muscle |
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Term
| what is the appendix and how is it characterized? |
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Definition
Once believed to be a vestigial organ, the appendix is now viewed as a lymphoid organ.
Characterized by a mucosa like that of the colon and numerous secondary lymphoid nodules amongst diffuse lymphoid tissue.
Does NOT have teniae coli. |
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Term
| what is the internal anal sphincter? |
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Definition
The internal sphincter is smooth muscle and is a thickening of the inner circular layer of the muscularis externa.
It relaxes under the influence of the parasympathetic nervous system and tightens under sympathetic control |
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Term
| what is the external anal sphincter and what is it innervated by? |
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Definition
| The external sphincter is skeletal muscle innervated by the inferior anal (rectal) nerves, branches of the pudendal nerve (S2, S3, S4). |
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Term
| what kind of transition occurs at the anorectal junction? |
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Definition
Transition from a simple columnar epithelium to a stratified squamous non-keratinized epithelium (black arrow).
At the anal orifice, there is a second transition to stratified squamous keratinized epithelium (red arrow). |
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