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BISC 125 The Digestive System


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Types of single cell glands in the digestive system
Goblet cells and enteroendocrine cells
Where do endocrine glands secrete into?
Fenestrated capillaries (into the bloodstream)
What are the two types of exocrine secretory cells in the digestive system?
Mucous-secreting and serous-secreting
What are the two parts of an exocrine gland?
The secretory portion and the ductal portion.
What do myoepithelial cells do (in glands)?
They are modified epithelial cells that contract around the gland to squeeze the secretion out.
What are the three modes of secretion?
Merocrine, apocrine, and holocrine secretion
What is the most common method of secretion and how does it work?
Merocrine secretion: the rough ER produces products that are "packaged" in the Golgi and are released from the cell via exocytosis.
How does apocrine secretion work?
The cell produces secretory materials that are sent to the apex of the cell, and small pieces of cytoplasm containing the product break off.
How does holocrine secretion work?
The cell produces many secretions, packages them, then dies and gives up all secretory material.
What are acinar cells?
Secretory cells arranged like alveoli; one big exocrine duct (secrete mucus and serous in the digestive system)
What do mucous and serous glands look like under a microscope?
Serous cells have a nucleus near the bottom of the cell and stain very blue/purple. Mucous-secreting cells have the nucleus flat against the bottom of the cell and are pale (resemble lipid C.T.)
What is a serous demilune?
A mucous-secreting unit with a small serous-secreting unit on top.
What are the differences between a lobe, a lobule, and a septa?
A lobe is a big division (usually of an organ), a septa is the C.T. that separates lobes, and lobules are smaller divisions within lobes.
What happens if ducts are blocked?
Cells can't get their secretions to the surface, but they keep producing material, so the cells swell and can become painful as the myoepithelial cells contract to expel material.
What is the difference between intralobular ducts and interlobular ducts?
Intralobular are inside the lobules; they are intercalated and striated. Interlobular ducts are outside the lobules.
What type of epithelium lines the oral cavity?
Stratified squamous
What are the three major salivary glands?
The parotid gland, the submandibular gland, and the sublingual gland.
What does the parotid gland secrete?
It is completely serous-secreting.
What does the submandibular gland secrete?
It produces 60-80% of the saliva and is 80% serous-secreting and 20% mucous-secreting.
What does the sublingual gland secrete?
It is 90-95% mucous-secreting.
How many minor salivary glands are there?
about 300
What does mucosa consist of?
Epithelium, lamina propia, and muscularis mucosa
What are the layers of a digestive tubule (starting with the layer exposed to the lumen)?
The epithelium, the lamina propia, the muscularis mucosa, the submucosa, and the muscularis externa (adventitia on outside).
What do "orad" and "caudad" mean?
Orad = towards the mouth, upwards; caudad = down, away from the mouth
What is the esophagus?
A muscular tube linking the pharynx to the stomach.
What type of epithelium lines the esophagus?
Stratified squamous
What layers form the longitudinal folds of the esophagus?
The mucosa and submucosa; the folds disappear transiently and are restored by recoil of elastic fibers in the submucosa.
What layer of the esophagus contains cardiac glands?
The lamina propia (in the lower 1/3 of the esophagus)
What do esophageal cardiac glands do?
They are mucosal tubular glands that secrete mucous to help food slide into the stomach.
Does the esophagus have a muscularis mucosa?
Yes, but only in the lower half; glands from the submucosa fragment it in the upper half.
In what layer of the esophagus are the C.T. papillae located?
The lamina propia.
Where do cardiac esophageal glands secrete to?
Their excretory ducts join a larger duct that opens at the tip of the papilla.
What does the submucosa of the esophagus contain?
Esophageal glands that secrete mucous, lots of blood vessels, and Meissner's plexus
Where does the submucosal venous plexus in the esophagus drain into?
The systematic venous systems and the portal vein system.
What is Meissner's plexus?
A cluster of neurons that stimulate the muscularis mucosa.
What type of muscle makes up the muscularis externa of the esophagus?
Skeletal muscle in the upper 1/3, mixed skeletal and smooth muscle in the middle 1/3, and smooth muscle in the lower 1/3.
Where is Auerbach's plexus located?
In the muscularis externa.
What is the upper sphincter (UES) of the esophagus made of (and what's its function)?
It's made of skeletal muscle and it initiates the swallowing reflex.
What is the lower sphincter (LES) of the esophagus made of (and what's it's function)?
It's made of smooth muscle, and it prevent the reflux of gastric contents into the esophagus. It doesn't close very well and can lead to problems.
Is swallowing voluntary?
It can be initiated voluntarily, but once it's started you can't stop it.
What are the regions of the stomach (from the most orad to the most caudad)?
The cardia, the fundus, the body, and the pyloric or antrum region
What two parts of the stomach are histologically the same?
The fundus and the body.
What are the rugae in the stomach (and what is their function)?
Folds on the inside of the stomach that increase SA and stretch when the stomach is full.
What is a gastric pit?
Holes/indentations in the mucosa of the stomach where glands empty their secretions and the secretions are brought to the surface of the stomach.
What parts of the digestive system are lined by simple columnar epithelium?
The stomach, the small intestine, and the large intestine
What do goblet cells secrete and where are they located?
They are mucus-secreting and they are located in the simple columnar epithelium of the stomach, small intestine, and large intestine.
What layer of the stomach contains glands?
The lamina propia (and epithelium--goblet cells)
Are there cardiac glands in the stomach?
Yes, in the lamina propia.
Where are mucous neck cells found and what do they secrete?
They are located at the opening of gastric glands to the pits, and they secrete mucous to protect the gastric surface.
Where are parietal cells found and what do they secrete?
They are found in the lamina propia of the stomach, linked to chief cells; they secrete HCl, intrinsic factor, and HCO3- ions.
What does intrinsic factor do and who secretes it?
Intrinsic factor is secreted by parietal cells, and it allows the body to absorb vitamin B12 which helps the body produce RBCs
What do stem cells in the lamina propia of the stomach do?
Produce new simple columnar and goblet cells
How does the mucosal layer of the stomach neutralize it's surface?
It traps bicarbonate ions, which neutralize the microenvironment adjacent to the apical (upper) region of mucus surface cells to pH 7.0
Where are chief cells located and what do they secrete?
They are located predominantly in the lamina propia of the lower 1/3 of the stomach. They secrete pepsin (breaks down proteins) and lipase (release enzymes, break down fats)
Where are the enteroendocrine cells located and what do they secrete?
They are located throughout the digestive system in endocrine glands, and they produce acetylcholine and gastrin; they also stimulate the parietal cells.
Where are pyloric glands located and what do they secrete?
They are located in the lamina propia of the stomach (in the pyloric region); they secrete mucus, granules containing lysozomes, and gastrin (from their enteroendocrine cells).
Where are Meissner's plexus and Auerbach's plexus located in the stomach?
Meissner's in the submucosa, Auerbach's in the muscularis externa
How many layers of smooth muscle are in the muscularis mucosa and the muscularis externa of the stomach?
Both have three layers (circular, oblique, and longitudinal)
What glands are in the submucosa of the stomach?
What is the submucosa of the stomach made of?
Dense, irregular C.T. (the lamina propia is loose C.T.) and elastic tissue (lots)
Why can bleeding ulcers cause people to lose so much blood?
Because the gastric submucosa contains a rich vascular bed with lots of muscular arteries.
Are Meissner's and Auerbach's plexuses controlled sympathetically or autonomically?
What are the two sphincters of the stomach?
The upper cardiac sphincter, which is weak and can cause regurgitation of food, and the lower pyloric sphincter, which is stronger and thicker.
What is the position of the gastric sphincters during digestion?
They're closed.
What is retropulsion?
When solid contents of the stomach are propelled back into the main body of the stomach because of a closure of the disal antrum (food can also be regurgitated into the esophagus)
What is GERD?
Reflux disease; lots of sinus infections have been linked to this
What is pyloric stenosis and who experiences it?
A condition in which the pyloric sphincter is too tight, and food can't pass from the stomach to the intestine, so it is regurgitated. It has only been diagnosed in male infants.
What is the function of the small intestine?
To absorb digested food after enzymes produced in the intestinal mucosa and pancreas break it down further
What are the three portions of the small intestine (starting from the most orad)?
The duodenum, the jejunum, and the ileum
How does the small intestine increase it's surface area?
It has submucosal folds (that encircle the intestinal lumen), villi, and microvilli
What are plicae circulares?
Submucosal folds in the small intestine
What is the difference between villi and microvilli?
Villi are finger-like projections made of epithelium and lamina propia. Microvilli are a "brush border" of tiny projections of microfilaments on the surface of the villi
Where are goblet cells located?
In the simple columnar epithelium of the stomach, small intestine, and large intestine
Where are intestinal glands (aka crypts of Lieberkuhn) found?
In the lamina propia of the small intestine (all three portions)
Which portion of the small intestine has glands in it's submucosa?
The duodenum; it has Brunner's glands, which pierce the muscularis mucosa and secrete alkaline mucous that helps neutralize stomach acid.
How does the duodenum neutralize stomach acid entering with the digested food?
By secreting an alkaline mucous (Brunner's glands), which combines with bile and other pancreatic secretions)
What are Peyer's patches and where are they found?
Permanent lyphatic nodules (primary and secondary) that occupy the lamina propia and submucosa. The overlying epithelium is made of flattened antigen-presenting M-cells.
What is GALT?
Gut-Associated lymphoid tissue; Peyer's patches are the main components of this.
How many layers of smooth muscle are there in the muscularis mucosa and the muscularis externa of the small intestine?
Two layers (in the externa, the inner layer is concentric and the outer is longitudinal)
What do microfilaments do during and after digestion?
They extend during digestion and retract afterwards.
What are two inner components of villi?
Lacteals (which assemble and concentrate lipids; initiate the absorption of fat) and blood vessels (enhances digestion)
What are the types of intestinal glands (located in the lamina propia)?
Stem cells, mucous cells, Paneth cells, and enteroendocrine cells
What are Paneth cells and where are they located?
They are located in the lamina propia at the bottom of intestinal glands (they are bright red). They secrete bacteriostatic material which moderates the amount of bacteria in the intestine.
What do the two layers of the muscularis externa do?
Inner (concentric) layer is for constriction, and the outer (longitudinal) layer is for shortening
What is reverse peristolsis?
When contractions of the smooth muscle around the intestine cause food to travel backwards, towards the esophagus.
What is the function of the large intestine?
To absorb fluid from the digested materials arriving from the small intestine.
What are the five regions of the large intestine?
Ascending, transverse, descending, sigmoid colon (S-shaped), and rectum ("straight" in Latin)
What does the epithelium of the large intestine do?
Participates in the transport of ions and water
What is the purpose of the mucous secretion in the large intestine?
Protection and Lubrication
What part of the large intestine contains intestinal glands and what do they contain?
Intestinal glands are in the lamina propia, and they contain stem cells, mucous-secreting cells, a few absorptive cells, and enteroendocrine cells.
What glands are in the submucosa of the large intestine?
What are taenia coli?
Three longitudinal bands of smooth muscle in the muscularis externa of the large intestine; draws the colon into haustras
What are the layers of the large intestine's muscularis externa?
A complete circular internal layer and an incomplete outer longitudinal layer (contains taenia coli)
What is a haustra and where are they located?
A small sac formed in the muscularis externa of the large intestine (provides space for absorbed materials)
What is diverticulosis?
When food that enters the haustra doesn't leave as fast as it should and attracts bacteria, which cause inflammation. The haustra turns into a diverticulum, an enlarged sac.
What is the appendix?
A tiny extension of the digestive tract; it has lymphatic components
What is special about the lamina propia of the appendix?
It contains multiple lymphatic nodules and lymphocytes infiltrate throughout
What causes appendicitis?
Often result from an illness like the flu; the inflammatory response cause the appendix to swell shut, closing off blood flow, effectively killing the organ
What type of epithelium lines the anal canal?
Simple columnar in the upper portion, stratified squamous in the lower portion
What are the two sphincters in the anal canal?
The internal sphincter (made of smooth muscle) and the external sphincter (made of skeletal muscle)
What are hemorrhoidal plexuses and where are they located?
They are vein plexuses located in the anal canal; they can become inflamed if too much blood is pushed through (causes hemorrhoids)
What does gastrin do?
Gastrin stimulates the production of HCl by the parietal cells and has a tropic effect on the mucosa of the small and large intestine and the fundus of the stomach.

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