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152 Cards in this Set
- Front
- Back
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What are the four layers of the alimentary canal?
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Mucosa
Submucosa Muscularis externa Serosa |
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What are the three layers of the mucosa?
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Lining epithelium
Lamina propia - an underlying connective tissue Muscularis mucosae - smooth muscle |
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Where is adventitia found?
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An adventitia made only of connective tissue is found where the wall of the tube is directly attached or fixed to adjoining stuructures i.e. body wall and certain retroperitoneal organs
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What are the three specific functions of the mucosa?
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Protection
Absorption Secretion |
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What protection does the epithelium of the esophagus provide?
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in the esophagus, a stratified squamous epithelium provides protection from physical abrasion by ingested food
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How does the epithelium of the GI tract act as a selectively permeable barrier?
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In the GI portion of the alimentary tract, tight junctions between the simple columnar epithelial cells of the mucosa serve as a selectively permeable barrier
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What is the principal site of absorption of the products of digestion in the small intestine ?
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Villi
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What increases the surface area of the villi?
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microvilli
These are tightly packed microscopic projections of the apical surface of intestinal absorptive cells |
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What are some examples of extramural digestive glands?
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Liver
pancreas |
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What layer of the small intestine contains GALT (gut associated lymphatic tissue)
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Lamina propria contains both the diffuse lymphatic tissue and the lymphatic nodules known as GALT
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What section of the small intestine contain Peyer's patches?
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in the distal small intestine, the ileum
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What side of the ileum is Peyer's patches located antimesentery or mesentery side?
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They tend to be located on the side of the tube opposite the attachment of the mesentery
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What is the arrangement of the musclaris mucosae' s smooth cells?
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The muscularis mucosae, consists of smooth muscle cells arranged in an inner circular and outer longitudinal layer
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What is the deepest layer of the mucosa?
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The muscularis mucosae
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How does the contraction of the muscularis mucosae contribute to the peristaltic movement of the small intestine?
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The contraction of the muscle produces movement of the mucosa, forming ridges and valleys that facilitate absorption and secretion.
This is a localized movement of the mucosa that is INDEPENDENT OF PERISTALTIC MOVEMENT of the entire wall of the digestive tract |
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What layer of the alimentary tract contains the visceral sensory fibers ie sympathetic, parasympathetic, pre and post ganglionic nerve fibers
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Submucosa
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What are the components of the Enteric nervous system?
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the nerve cell bodies of parasympathetic ganglia and their postganglionic nerve fibers
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What is another name for the submucosal plexus ?
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Meissner's plexus
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What is the arrangement of the muscularis externa?
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In the inner layer it is circularly oriented is a tight spiral
In the outer layer it is a longitudinally oriented is a loose spiral |
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Where is the myenteric plexus ( Auerbach's plexus) located?
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in the muscularis externa
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What is contained in Auerbach's plexus?
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The myenteric plexus contains nerve cell bodies (ganglionic cells) of postganglionic parasympathetic neurons and neurons of the ENS
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How does the contraction of the inner circular layer aid to peristalsis?
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Contraction of the inner circular layer of the muscularis externa compresses and mixes the contents by constricting the lumen
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How does the contraction of the outer longitudinal layer aid peristalsis?
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It propels the contents by shortening the tube
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Name the sites in the digestive tube that shows variations of the muscularis externa?
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1. The wall of the proximal portion of the esophagus
2. Around the anal canal 3. The stomach 4. The large intestine |
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What is responsible for the shortening of the tube in the large intestine in order to move food forward?
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The teniae coli
These are three distinct longitudinal bands |
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Where in the gastrointestinal tract does striated muscle form part of the muscularis externa?
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1. In the wall of the proximal portion of the esohagus (pharyngoesophageal sphincter)
2. Around the anal canal (external anal sphincter) |
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What is the function of the pharyngoesophageal sphincter?
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It prevents the entry of air into the esophagus
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Where is the pharyngoesophageal sphincter located?
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It the lowest part of the cricopharyngeus muscle is physiologically referred to as the superior esophageal sphincter
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Name the five places that the circular smooth muscle layer forms sphincters
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1. Pharyngoesophageal sphincter
2. Inferior esophageal sphincter 3. Pyloric sphincter 4. Ileocecal valve 5. Internal anal sphincter |
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What is the function of the internal anal canal?
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It prevents passage of the feces into the anal canal from the undistended rectum
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What is the function of the ileocecal valve?
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Located at the junction of the small and large intestines --> it prevents reflux of the contents of the colon with its high bacterial count into the distal ileum which has a low bacterial count
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What is the function of the pyloric sphincter?
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It controls the release of chyme
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How does the lower esophageal sphincter work?
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It creates a pressure difference between the esophagus and stomach that prevents reflux of gastric contents
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Where is the serosa continuous with its surroundings?
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With both the mesentery and the lining of the abdominal cavity
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What portions of the digestive tract do not contain a serosa?
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The thoracic part of the esophagus and portions of structuures in the abdominal and pelvic cavities that are fixed to the cavity wall
ie. the duodenum ascending and descending colon rectum and anal canal |
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What is the function of the muscularis mucosae in the upper eosphagus.
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It is unusually thick here and functions to aid in swallowing
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Where can we expect to find striated muscle in the esophagus?
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The upper 1/3 is striated muscle, a continuation of the muscle of the pharynx
In the middle 1/3, striated and smooth muscle are interwoven in the muscularis externa |
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Where in the layers of the alimentary canal are the Esophageal glands proper located?
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The esophageal glands proper lie in the submucosa and are more concentrated in the upper 1/2 of the esophagus
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Where in the layers of the alimentary canal are the esophageal cardiac glands located?
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they are found in the lamina propria of the mucosa and are present in the terminal part of the esophagus
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What type of mucous does the esophageal cardiac glands produce? Why is it important?
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The esophageal cardiac glands produce neutral pH that tend to protect the esophagus from regurgitated stomach contents
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What is responsible for the innervation of the striated musculature of the upper part of the esophagus?
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The striated musculature in the upper part of the esophagus is innervated by somatic motor neurons of the vagus nerve --> from the nucleus ambiguus
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What is responsible for the innervation of the smooth muscle of the lower part of the esophagus?
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The smooth musculature in the lower part of the esophagus is innervated by visceral motor neurons of the vagus --> from the dorsal motor nucleus
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Name the histologic regions of the stomach
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Cardiac region
* near the esophageal orifice, contains the cardiac glands Pyloric region * proximal to the pyloric sphincter, contains the pyloric glands Fundic region * between the cardia and pylorus and contains the fundic or gastric glands |
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What is the difference between the esophagus and gastric tissue?
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Esophagus has stratified squamous epithelium
Stomach has simple columnar epithelium |
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What is the specific makeup of mucous that makes it protective against gastric acid?
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Its high bicarbonate and potassium concentration
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What is the role of prostaglandins in protecting the lining of the stomach?
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They stimulate secretion of bicarbonates and increase thickness of the mucus layer with accompanied vasodilation in the lamina propria.
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How does aspirin damage the gastric mucosa?
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Suppress the production of protective prostaglandins by the gastric mucosa
Aspirin's direct contact with the wall of the stomach interferes with the hydrophobic properties of the gastric mucosa |
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Describe the replacement of cells in the gastric pit from stem cells.
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The isthmus of the fundic gland is a site of stem cells in which stem cells replicate and differentiate
Cells that are destined to become mucous surface cells migrate upward, other cells migrate downward |
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What are the four major components of gastric juice
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HCL
Pepsin Mucus Intrinsic factor |
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What cells produce gastrin?
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enteroendocrine cells
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where is vitamin B12 absorbed?
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in the distal part of the ileum
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which cells secrete intrinsic factor?
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the parietal cells
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What converts pepsinogen to pepsin?
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Pepsin is converted from pepsinogen by HCl at a pH lower than 5
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What cells secrete pepsinogen?
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Chief cells
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How can H. pylori survive the low pH of the stomach
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H. pylori contains large amounts of urease ( hydrolyzes urea) --> this creates a protective basic ammonia cloud around the bacterium that allows it to survive the acidic environment of the stomach
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What is the typical appearance of a fundic gland?
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several glands open into a single gastric pit. Each gland has a narrow, long neck segment and a shorter wider base that usually divides into 2-3 branches
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What are the differences of the surface mucous cell and the mucous neck cells?
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Mucous neck cells
-located in the neck of the fundic gland shorter than the surface mucous cells and has less mucinogen in the apical cytoplasm -secrete a soluble mucous Surface mucous cells make an insoluble or cloudy mucous they line the gastric pit |
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What do chief cells stain blue?
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The abundant rough ER in the basal cytoplasm
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Why do parietal cells stain pink?
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They stain with eosin because of the extensive amount of membrane comprising the intracellular canaliculus, tubulovesicular system, mitochondria
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Where are parietal cells found?
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in the neck of the fundic glands among the mucous neck cells, they are most numerous in the upper and middle portions of the neck
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What is the most common cause of vitamin B12
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lack of intrinsic factor
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What are other causes ( besides lack of intrinsic factor) of vitamin B 12 deficiency?
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1. Gram neg anaerobic bacterial overgrowth in the small intestine
2. peptic ulcer disease 3. achlorhydria 4. parasitic tapeworm infections |
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How does gram neg bacteria cuase vitamin B 12 deficiency
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The bacteria bind to the vitamin B12- intrinsic factor complex --> prevents its absorption
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Which class of drugs do not affect intrinsic factor H2 receptor antagonists or proton-pump inhibitors
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Proton-pump inhibitor
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Why does the tubovescicular system reduce or disappear in an actively secreting cell?
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The membranes of the tubovesicular system serve as a reservoir of plasma membrane containing active proton pumps
In an actively secreting cell this membrane material can be inserted into the plasma membrane of the canaliculi to increase their surface area and the number of proton pumps |
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How is H. pylori able to maintain a chronic infection?
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The lipopolysaccharide antigens that are expressed on its surface mimic those on human gastric epithelial cells --> this causes an initial immunological tolerance to it
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How many types of membrane receptors are there for HCl secretion
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Gastrin receptors
histamine H2 receptors Acetylcholine M3 receptor |
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How are H+ ions produced in the parietal cells?
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Carbonic anhydrase hydrolyzes carbonic acid to H+ and HCO3-
The CO2 necessary for synthesis of carbonic acid diffuses across the basement membrane into the cell from the blood capillaries in the lamina propria |
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How is Cl- transported into the lumen of the canaliculus?
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Cl- ions from the parietal cell cytoplasm into the lumen of the canaliculus through the activation of K+ and Cl- channels
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How is H+ ions transported to the lumen of the canaliculus?
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the transport of H+ ions from the cytoplasm across the membrane to the lumen of the canaliculus by the H+/K+-ATPase proton pump
K+ from the canaliculus is transported into the cell cytoplasm in the exchange for the H+ ions |
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What is the drug of choice in HCl hypersecretion ie Zollinger-Ellison syndrome?
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Proton-pump inhibitors
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In Zollinger-Ellison syndrome, there is an excessive secretion of _____ that leads to continuously stimulated ______ cells
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gastrin
parietal |
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What cell serve as the primary chemoreceptors?
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Open enteroendocrine cells
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What regulates the secretion of the open vs the closed enteroendocrine cells
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* The open enteroendocrine cells sample the contents of the gland lumen and release hormones based on the info from these samples
* secretion from closed cells is regulated by luminal content indirectly through neural and paracrine mechanisms |
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what Hormones are responsible for inhibiting gastric emptying?
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Glucagon -like peptide
Peptide YY Cholecystokinin |
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Which hormones stimulate pancreatic enzyme secretion; pancreatic bicarbonate ion secretion; pancreatic growth?
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Cholecystokinin
Secretin |
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What hormones stimulates insulin release?
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Gastric inhibitory peptide
Glucagon- like peptide 1 |
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What hormone stimulates appetitie and perception of hunger
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Ghrelin
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what is the life span of the parietal cells
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150-200 days
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what is the lifespan of the surface mucous cells
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3-5 days
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what hormones stimulates gastric acid secretion?
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histamine
gastrin |
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How many layers of muscularis externa?
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Three
outer longitudinal layer middle circular layer inner oblique layer |
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what structures are the gastric serosa continuous with in the abdomen?
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It is continuos with the parietal peritoneum of the abdominal cavity via the greater omentum and with visceral peritoneum of the liver at the lesser omentum
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What are the three anatomic portions?
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Duodenum
Jejunum Ileum |
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what is the largest portion of the small intestine?
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the lower 3/5 of the small intestine
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Where are the enzymes (disaccharidase, dipeptidase) in the small intestines located?
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In the glycocalyx of the microvilli of the enterocytes
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What are the valves of Kekring?
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The valves of Kekring or plicae circulares are permanent transverse folds with a core of submucosa
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Villi are folds of what layer of small intestine?
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mucosa
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What is responsible for giving the apical region of enterocytes a striated region?
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The microvilli
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What is found in the core of the villus?
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the lamina propria
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Which sugars can be directly absorbed into venous capillaries
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galatose
glucose fructose |
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The action of lactase is to split lactose into ______ and _____
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galatose and glucose
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Where in the digestive tract is trypsinogen converted into trypsin?
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Duodenum
in the plasma membrane of the apical microvilli |
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What is responsible for converting trypsinogen into trypsin?
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Enteropeptidase
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What is the action of trypsin?
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1. Trypsin converts additional trysinogen into trypsin
2. Trypsin converts other pancreatic zymogens into active enzymes |
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How does the enterocyte absorption of glucose and galactose differ from the absorption of fructose?
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1. glucose and galatose are absorbed by the enterocyte via an active transport using Na- dependent glucose transporters
( SGLT1) 2. Fructose enters the cell via facilitated Na - independent transport using GLUT5 |
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How are monosaccharides absorbed into the blood capillaries?
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All the monosaccharides pass through the basal membrane of the enterocytes using GLUT2 into the underlying capillaries of the portal circulation
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What products of triglycerides?
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Triglycerides are broken down into glycerol, monoglycerides, and long- and short- chain fatty acids
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Where are chylomicrons formed?
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The newly resynthesized triglycerides appear first in apical vesicles of the smooth ER , then in the Golgi where they are converted into chylomicrons
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What is Hartnup's disease
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A disorder of amino acids
Free amino acids appear in the blood when dipeptides are fed to patients but not when free amino acids are fed |
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Which products of the triglyceride metabolism do not need to included in the chylomicron?
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Short chain fatty acids and glycerol can leave the intestine exclusively via capillaries
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what is the function of Paneth cells?
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The primary function is to maintain mucosal innate immunity by secreting antimicrobial substances
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Where can lacteals be found?
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In the lamina propria of the villus
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What causes movement of the microvilli?
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Each microvillus has a core of vertically oriented actin microfilaments that insert into the terminal web , a horizontally oriented contractile microfilaments
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what is the function of the lateral plasma membrane Na+/K+ - ATPase pump
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It transiently reduces the cytoplasmic concentration of Na+ by transporting it across the lateral plasma
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Describe the path of water and Na+ in the small intestine.
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1. the Na+/K+ - ATPase pump in the lateral plasma membrane reduces Na+ in the cytoplasm by moving it intercellularly
2. The high intercellular Na+ concentration causes water to move from the cell into the intercellular space 3. The low water and Na+ concentrations inside the cell cause water and Na+ to enter in at the apical surface |
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The sodium pumps in the colon and small intestine create a ____ intracellular Na+ concentration.
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transiently low
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what structures in the enterocyte are involved in the absorption of fatty acids?
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Tubules and cisternae of the smooth ER are involved in the absorption of fatty acids and glycerol and in the resynthesis of neutral fat
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___increase the apical surface area and _____ increaed the lateral surface of the enterocytes
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microvilli
lateral plications |
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Why does the small intestine also secrete water and electrolytes?
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It maintains the normal state of liquid chyme
The absorption of fluid by the villus enterocyte is balanced by the secretion of fluid by the gland enterocyte |
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In the small intestine, goblet cells ____ in number from the duodenum to the terminal ileum
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increase
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What is the role of the alpha-defensins that are secreted by the Paneth cells
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Alpha- defensins are homologs of peptides that function as mediators in cytotoxic CD+8 T lymphocytes
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What is the role of lysozyme?
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Lysozyme digests the cell walls of certain groups of bacteria
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Where are Paneth cells occasionally found?
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They are occasionally found in the normal colon in small numbers but their numbers increase in certain pathologic conditions
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What are the origins of the neurocrine hormones
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They are secreted by the nerve cells in the Meissner's and Auerbach's plexuses
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What are the neurocrine hormones of the GI tract
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VIP, bombesin, the enkephalins
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Somatostatin and Histamine are considered ____ hormones
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paracrine
They do not circulate in the bloodstream and have a local effect |
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The open enteroendocrine cells are located ______ of each villus
The closed enteroendocrine cells are concentrated in the _____. |
At all levels of each villus
in the lower portion of the intestinal gland |
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Where are M cells located?
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M cells are epithelial cells that overlie Peyer's patches and other large lymphatic nodules
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Why are M cells considered antigen transporting cells?
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They take up microorganisms and macromolecules from the lumen in endocytotic vesicles
The vesicles are transported to the basolateral membrane where they discharge their contents into the epithelial intercellular space in the vicinity of CD4+ T lymphocytes |
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Why are M cells considered antigen presenting cells?
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They have MHC II molecues on their surface
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How do intermediate cells work in the amplifying compartment of the intestinal stem cell?
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They usually undergo one or two divisions before they become committed to differentiation into either absorptive or goblet cells
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What acts as the immunologic barrier of the intestinal tract
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GALT
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Describe the appearance of the intermediate cells
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They have short microvilli with long core filaments extending deep into the apical cytoplasm. Small mucin-like secretory granules form a column in the center of the supranuclear cytolplasm
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What is prinicipal immunoglobulin of mucosal immunity?
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Secretory IgA
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What are the differences between dIgA and sIgA?
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Most of the plasma cell in the lamina propia of the intestine secrete dimeric dIgA. It is composed of two monomeric IgA subunits and a polypeptide J chain.
Secretory IgA is IgA with an extracellular binding domain of the pIgR |
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Where are Brunner's glands located?
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They are located in the submucosa of the duodenum
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What is the function of Brunner's glands
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The secretion of these glands has a pH of 8.1 to 9.3 and contains neutral and alkaline glycoproteins and bicarbonate ions
This secretion neutralizes the acid- containing chyme and brings the intestinal contents close to the optimal pH for the pancreatic enzymes that are delivered to the duodenum |
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What is the function of secretory IgA?
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It prevents the attachment and invasion of viruses and bacteria into the mucosa by either inhibitin their mobility, causing microbial aggregation or masking pathogen adhesion sites of the epithelial surface
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What is the purpose of segmentation contractions?
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Segmentation are local contractions that serve to circulate the chyme locally, mixing it with digestive juices and moving it into contact with mucosa for absorption
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What muscle layer is involved in segmentation?
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primarily the circular layer
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What direction does segmentation contraction move intestinal contents?
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both proximally and distally
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What direction does peristalsis move intestinal contents?
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distally
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Where are stem cells located within the intestinal gland?
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At the base
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what is the lifespan of the Paneth cells.
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4 weeks
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What are the three identifiable characteristics of colon
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Teniae coli
Haustra coli Omental appendices |
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What layer composes teniae coli?
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Teniae coli are three narrowed thickened equally spaced bands of the outer longitudinal layer of muscularis externa
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What are omental appendices?
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They are small fatty projection of serosa observed on the outer surface of the colon
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Why does the mucosa of the large intestine have a smooth appearance?
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It has neither plicae circulares nor villi are present
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what mechanism that the large intestine cells use to absorb water and electrolytes?
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Na+/K+ - ATPase pump
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What is distinguishes the rectum from the rest of the distal colon?
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Transverse rectal folds
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What are the three zones of anal canal?
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Colorectal zone
Anal transitional zone Squamous zone |
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What epithelium should we expect in the colorectal zone of the anal canal
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Simple columnar epithelium
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What epithelium is found in the anal transitional zone
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There is a transition between the simple columnar epithelium of the rectal mucosa and the stratified squamous epithelium of the perianal skin
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Where do carcinoid tumors originate?
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Carcinoid is a type of tumor that originates from enteroendocrine cells of lining mucosa
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At what level do teniae coli end?
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At the level of the rectum
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When does the muscularis mucosa end?
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The muscularis mucosa disappears at the level of the ATZ, where the circular layer thickens to form the internal anal sphincter
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What veins can cause internal hemorrhoids?
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The enlargement of submucosal veins of the rectal plexus make up internal hemorrhoids
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Why can mucosal adenomas be treated by removal of only the polyp?
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Due to the absence of the lymphatic tissue from the lamina propria
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What disease can cause proliferation of lymphatic vessels and blood vessels in the lamina propria?
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Ulcerative colitis
It is a disease of chronic inflammation of the colon and rectum with the formation of granulation tissue associated with proliferation of lymphatic vessels and blood vessels in the lamina propria? |
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What is the difference in appendix histology vs the cecum?
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The cecum histology resembles the rest of the colon.
The appendix has a uniform layer of longitudinal muscle in the muscularis externa and it has a large number of lymphatic nodules that extend into the submucosa |
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Describe lymphatic vessel drainage.
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Small lymphatic vessels at the bases of the intestinal glands --> these drain into the lymphatic network within the muscularis mucosa --> then the lymphatic plexuses in the submucosa and muscularis externa before lymph leaves the wall of the large intestine
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