Histology: GI Tract Flashcards
What are the two portions of the digestive system?
The alimentary canal and associated/accessory digestive organs
Alimentary canal is also called ______.
The GI tract
What are the organs of the alimentary canal?
Mouth, most of pharynx, esophagus, stomach, small intestine, large intestine
What are the associated/accessory organs of the digestive system?
Tongue, teeth, salivary glands, liver, gallbladder
What are the two functions of the associated/accessory organs of the digestive system? Which organs did which function?
Physical breakdown (come in contact with food): tongue, teeth
Secretions (never contact food, secretions reach GI via ducts, good for chemical breakdown): salivary glands, liver, gallbladder
How long is the GI tract in a cadaver vs. living human?
9meters (30feet) in cadaver
Shorter in living humans because smooth muscle contractions
Food in the lumen of the GI tract is ____ the body
outside
What are the 8 processes of the GI tract?
- Ingestion
- Secretion
- Mixing/propulsion
- Digestion (chemical and mechanical)
- Absorption
- Defacation
- Barrier
- Immunological
Describe the ingestion process of the digestive system
Eating/drinking
Describe the secretion process of the digestive system. how much do we secrete a day through GI?
secretions by glands
we secrete 7L of “stuff” a day - water, hydrochloric acid, buffers, enzymes, mucous
Describe the mixing/propulsion process of the digestive system
smooth muscle moves food downward and also works to break down the food particles
Describe the digestion process of the digestive system
mechanical digesiton: breaks down food into smaller pieces of food (still food) so they have high surface area
chemical digestion: enzymes break bonds of macromolecules to make them micromolecules so that they may cross membrane into body
Describe the absorption process of the digestive system
takes place primarily in the small intestine
Describe the defacation process of the digestive system
defecation of feces
Describe the barrier process of the digestive system
Mucosa is the epithelial lining of the mucous membrane in the GI tract. Mucosa is very selective
Describe the immunologic protection process of the digestive system
when things cross the mucosa epithelial lining of the mucous membrane of the GI tract, the lymph along the mucosa is the first line of defense
Mouth aka ___ aka ____
Mouth aka oral cavity aka buccal cavity
What is the oral cavity bounded by?
Cheeks, hard/solf palate, tongue, floor of mouth
What muscle is in the lips?
Orbicularis oris muscle (skeletal muscle)
What is the posterior aspect of the oral cavity? What does it open into?
The fauces open into the oropharynx
What are the two parts of the oral cavity? describe them both.
- Vestibule: between lips/teeth and between cheeks/teeth
- Oral cavity proper: superior border of hard/solf palate; inferior border of tongue/floor of mouth; posterior border of fauces to oropharynx; all other borders are teeth
What is bolus?
Semi-solid mass of food
“Food” is not what is swallowed in the GI tract.
“Bolus” is swallowed
Describe enamel
96-98% HA crystallites
acellular, mineralized tissue without collagen
Describe central pulp cavity
loose connective tissue that is highly vascularized
Describe periodontal ligaments
fibrous connective tissue (dense and loose) wit lots of collagen
connects root to alveolar bone
Describe gingiva
mucous membrane bound to periosteum of maxillae/mandible
Saliva is ___% water, ____% solutes
99.5% water, 0.5% solutes
On average, humans secrete ____mL of saliva a day
1000mL - 1500mL
What are the 5 functions of saliva?
- Moisten oral mucosa
- Moisten dry food
- Provide medium for food materials to dissolve so they can chemically stimulate taste buds
- Buffer contents of oral cavity
- Contains amylase that partially breaks down starch (polysaccharides)
Why does the oral mucosa need to be moistened?
because it’s a wet membrane that needs to remain wet
Why do taste buds require a medium for food materials?
taste buds are complex chemoreceptors which only respond to chemicals in an aqueous solution
Why does the oral cavity need to be buffered? What helps buffer?
We have an acidic diet
Buffered by bicarbonate and phosphate ions
The pharynx connects the ___ cavity and the __ cavity to the ___ and ____.
the pharynx connects the nasal cavity and the oral cavity to the larynx and esophagus
What are the three portions of the pharynx from superior to inferior?
- Nasopharynx
- Oropharynx
- Laryngopharynx
Nasopharynx:
- Location?
- Epithelium?
- Food or air?
posterior to nasal cavity, superior to soft palate (when swalloing, soft palate and uvula close off nasopharynx)
AIR ONLY
ciliated psudostratified columnar epithelium (respiratory)
Oropharynx:
- Location?
- Epithelium?
- Food or air?
posterior to oral cavity, between soft palate and epiglottis
air and food
nonkeritanized stratified squamous epithelium
Laryngopharynx:
- Location?
- Epithelium?
- Food or air?
At superior border of upright epiglottis and opens to esophagus and larynx
air and food
nonkeritanized stratified squamous epithelium
General layers of alimentary canal wall structure from lumen to exterior
- Mucosa (epithelial lining, lamina propria, muscularis mucosae)
- Submucosa
- Muscularis externa
- Serosa Adventitia
What are the layers of the mucosa?
epithelial lining, lamina propria, muscularis mucosae
What is the composition of the lining epithelium of the mucous layer of alimentary canal wall?
this is what is right up against the food
Depends where you are on the body
PROTECTION = nonkeritanized stratified squamous epithelium (mouth, esophagus, pharynx, part of anus)
ABSORPTION: simple columnar epithelium (small intestine, large intestine, stomach) which also have tight junctions so it’s highly selective
What is the composition of lamina propria in the mucosa of alimentary canal wall?
loose (areolar) connective tissue of mucous membrane
lots of blood vessels (because overlying epithelium is avascular)
lots of lymph tissues called GALT (gut associated lymph tissue)
Where is GALT located in the alimentary canal wall?
GALT = gut associated lymph tissue
found primarily in the lamina propria layer of the mucosa layer of the alimentary canal wall
What is the composition of the muscularis mucosae in the mucosa of the alimentary canal wall?
smooth muscle (thin layers)
contraction of these smooth muscle layers throw the mucous membrane in different folds
Where is the submucosa layer in relation to the lumen?
submucosa is after the mucosa layer
it is before to the muscularis externa and the adventitia/serosa layer
What is the composition of the submucosa layer?
dense irregular connective tissue is the most common
has many types of glands and lymphoid tissue
Meissner’s plexus (submucosal plexus): part of innervation of GI tract found in submucosal layer. Important in controlling secretory cells/mucosal epithelium
What is meissner’s plexus? Where is it found?
Meissner’s plexus (aka submucosal plexus) found in the submucosal layer of the alimentary canal wall
Part of innervation of GI tract
Important in controlling secretory cells and mucosal epithelium
Where is the muscularis externa in relation to the lumen?
After the mucosa and submucosa layer
Before the adventitia/serosa layer
What is the composition of the muscularis externa?
2 layers of smooth muscle (inner circular layer and outer longitudinal layer)
with Myenteric nerve plexus (aka auerbach’s plexus) between the two smooth muscle layers
What is Myenteric nerve plexus? Where is it found?
aka auerbach’s plexus
Found between the two smooth muscle layers of the muscularis externa portion of the alimentary canal wall
Controls the contraction/relaxation of these two smooth muscles (which control peristalsis)
Describe the two smooth layers of the muscularis externa in detail. What happens when they contract?
Inner circular layer:
- surrounds the lumen
- contraction = constrict lumen, elongate organ
Outer longitudinal layer
- cells at 90deg ang running length of GI tract
- contract = dilate lumen, shorten organ
How does peristalsis occur?
Involuntarily
Alterations of contractions/relaxations of inner circular layer and outer longitudinal layer of muscularis externa on the alimentary canal wall
What does peristalsis do?
Moves products from one location to the next
Also helps break down food physically and chemically by mixing in with secretions
Where in the body is muscularis externae not smooth muscle?
Upper 1/3 of esophagus = skeletal
Outside of anal canal = skeletal
How is a sphincter formed?
the inner circular layer of muscularis externa on the alimentary canal wall thickens so much that it constricts the lumen
sphincters help to regulate flow
Where is the serosa/adventitia layer in relation to lumen?
After the mucosa, submucosa, muscularis externa layers
outermost layer of organ
What determines if an organ has serosa or adventitia on the outermost layer?
Serosa = visceral peritoneum (within peritoneal cavity)
Adventitia = retroperitoneal position / outside of peritoneal cavity
What is the composition difference of serosa and adventitia?
Serosa = mesothelium = simple squamous epithelium on top of loose areolar connective tissue
Adventitia = loose areolar connective tissue
What is the physical location of the esophagus? (superior, inferior and posterior)
Superior to the stomach, inferior to the laryngopharynx and posterior to the trachae
How long is the esophagus?
10 inches in length (collapsable)
Where does the esophagus pierce the diaphragm?
T10 at the esophageal hiatus
What kind of mucosa layer does the esophagus have?
nonkeritanized stratified sqaumous epithelium
the muscularis mucosae is “blotchy”
What type of muscularis externa layer does the esophagus have?
Varies within the esophagus
Upper 1/3 = skeletal muscle
Middle 1/3 = mixed skeletal and smooth
Lower 1/3 = smooth muscle
What type of serosa/adventitia layer does the esophagus have?
Pre-T10 (at diaphragm), it is only adventitia
Once passed the esophageal hiatus, now fully in the paritoneal cavity so fully serosa until reach the stomach
What digestive activity is occurring in the esophagus?
None. The esophagus transports food from point a to point b. little secretion takes place here.
What types of mucous glands to the esophagus have?
Two types:
- Proper esophageal glands
- Esophageal cardiac glands
Proper esophageal glands: where are they found? what do they do?
Found in submucosa
Along entire length of esophagus but especially concentrated in upper half
Produce mucous for protection and to keep membrane wet
Esophageal cardiac glands: where are they? what do they do?
Found in lamina propria (of mucosa)
Found as you get closer to the stomach
Produce mucous for protection and to keep the membrane wet
What special relationship do the esophageal cardiac glands have with hydrochloric acid?
The stomach produces hydrochloric acid. As the sphincter to the stomach opens, we can get gastric reflux.
Esophageal cardiac glands at distal end of esophagus help with this reflex by producing mucous
Histology change at junction of stomach and esophagus?
immediate change between non-keritinized stratified squamous of esophagus to simple columnar of stomach.
What are the 4 anatomical subdivisions of the stomach?
Cardia, Fundus, Body, Pylorus
What kind of glands are found in the cardia region?
Cardia glands (secrete mucous)
What kind of glands are found in the pyloric region?
Pyloric glands (secrete mucous)
How do you tell the difference between a cardiac gland and a pyloric gland on a slide?
Both produce mucin which releases to produce mucous when mixed with water.
Pyloric glands have longer gastric pits
What kind of glands are found in the body and fundus?
Fundic glands (some secrete HCl, some secrete pepsinogen)
What are rugae? What do they do?
Rugae are stomach folds - NOT FOR SURFACE AREA.
They have a submucosa core
They are present for expansion. When stomach is full - rugae disappear
What kind of mucosa layer does the stomach have?
Simple columnar epithelium
(immediate change from esophagus non-keritinized stratified squamous)
Has surface mucous cells
Have gastric pits leading to simple branched tubular. Name these pits baed on region (cardiac region = cardiac glands)
What kind of submucosa layer does the stomach have?
No glands from mucosa extend in this layer
Still has lymph tissue and blood vessels but does not have glands
What kind of muscularis externa does the stomach have?
Additional layer!! (Usually inner circular and outer longitudinal)
Stomach has 3 because food is present for 3-4 hours here and needs a lot of smooth muscle to churn.
Inner oblique, middle circular, outer longitudinal
What kind of serosa/adventitia layer does the stomach have?
Serosa.
Because completely covered in mesothelium because in peritoneal
Has surface mucous cells (PITS) What’s at bottom of pit depends where you are in the stomach
Where are goblet cells located in the stomach?
NOWHERE. When these are present in the stomach we have a special name for mucous cells depending no the area (cardiac/fundic/pyloric)
Term “goblet cell” mostly for small intestine
What are mucous neck cells in the stomach?
Found in fundic glands of the stomach
produce mucous - found in neck region of fundic gland
What are parietal cells in the stomach?
Found in fundic glands of the stomach
Produce HCl and Intrinsic Factor
Large, pyramidal with large central spherical nucleus.
HCl production needs lots of mitochondria so parietal cells stain very eosinophilic
What is intrinsic factor?
Produced by parietal cells in fundic glands
Important for converting vitamin B12 in intestines
What are chief cells in the stomach?
Found in fundic glands of the stomach
aka Zymogen cells
have zymogen granules
produce pepsinogen and gastric lipase
Do chief cells produce active pepsin or pepsinogen?
Chief cells produce pre-cursor pepsinogen because you don’t want active pepsin in the cell - you want that in the lumen.
What are G-cells in the stomach?
Found in fundic glands of the stomach
Entero-endocrine cells (secrete hormones)
found in bottom portion of the gland
Produce gastrin which stimulates the parietal cells to secrete HCl
What is the relationship between G-cells and parietal cells?
G-cells (lower down in the fundic gland pit) produce gastrin which stimulates parietal cells (more towards the surface of the fundic gland pit) to secrete HCl
Small intestine role
absorption and to continue to move chume via peristalsis
What are the lengths of the 3 portions of the small intesinte?
duodenum - 25cm
jejunum - 2.5m
ileum - 3.5m
Difference in length of small intestine in a living human vs. a cadaver?
Living human = 10 ft, cadaver = 21 feet
What are plicae circularis in the small intestine?
“circular folds” seen best at the jejunum but also seen in all of small intestine
What is the core of plicae circularis in the small intestine?
Submucosa
Are plicae circularis temporary or permanent?
permanent.
What are villi of small intestine?
fingerlike projections of the mucosa
How long are villi of small intestine?
0.5 - 1.5mm in length
Where are villi located in small intestine?
Located on each plicae circularies
What is the core of villi in small intestine?
Lamina propria
What is the general shape of villi in small intestine?
in the duodenum they are leaf like (wider)
in jejunum and ileum they are fingerlike (thinner)
What are microvilli?
Projections of apical membrane of intestine absorptive cell
What forms a striated border?
microvilli being so uniform in shape and so common in the small intestine
What is the core of microvilli?
actin
What is the epithelium of the mucosa of the small intestine?
simple columnar epithelium
What is found in the epithelium of the mucosa of small intestine? 4 things
Absorptive cells (enterocytes)
Striated border
Goblet cell
Secretory cells
Enterocyte definition
a cell of the small intestine
Where are goblet cells most prominent in the small intestine?
Number of goblet cells increase while moving distally in small intestine
What do secretory cells do in the epithelium of the mucosa of the small intestine?
secrete enzymes to break down macromolecules
What are Crypts of Lieberkuhn and where are they found?
intestinal glands found in the mucosa layer of small intestine
T/F: the Crypts of Lieberkuhn extend beyond the muscularis mucosae layer.
FALSE.
Crypts of Lieberkuhn stay within the mucosa layer.
What is found within the crypts of lieberkuhn? 6 things.
Enterocytes Goblet cells Stem cells Paneth cells tubular glands enteroendocrine cells
Where in crypts of lieberkuhn are stem cells located and what do they do?
They are located at the junction of the villus and intestinal gland opening
They differentiate and either move up or down in the process
Where in crypts of lieberkuhn are paneth cells and what do they do?
located at the bottom of the crypt
secrete lysozymes (exocrine)
keep bacterial flora in check
produce hormones to keep GI regulated
What glands are found in the submucosa layer of the small intestine?
Glands in submucosa are only found in teh duodenum
Called brunner’s gland.
Brunner’s gland aka _____
duodenal gland
What do brunner’s glands do?
produce alkaline to neutralize the chyme
Where are brunner’s glands located?
submucosa layer of the duodenum (only)
What is the muscularis externa layer like in the small intestine?
back to 2 layers (after stomach added the inner oblique layer)
only has: inner circular and outer longitudinal
Does the small intestine have serosa or adventitia?
depends if it’s intraperitoneal or retroperitoneal
duodenum is both retro and intra
What are Peyer’s patches? Where are they located?
grouped lymphatic nodules / “aggregated lymphatic follicles”
Located in the lamina propria and the submucosa of the ileum
Are peyer’s patches eosinophilic of basophilic?
Basophilic
What are M cells?
Microfold cells
Specialized epithelial cells that are overlying peyer’s patches
Cannot see them - just know they’re there
What do M cells do?
Help detect antigens by taking samples of materials from the lumen and transferring them to macrophages
What is the main function of the large intestine from a histology standpoint?
Re-absorption of electrolytes and water
Not enough water absorbed = _____
Too much water absorbed = _____
not enough = dehydration
too much = constipation
Where are plicae circularis in the large intestine?
Nowhere.
plicae circularis only found in the small intestine
Where are villi found in the large intestine?
nowhere.
What are teniae coli?
grouped together outer longitudinal smooth muscle seen on surface
Where are teniae coli seen in the large intestine?
everywhere but rectum, anal canal and appendix
What are haustra?
they are pockets seen in colon and rectum (??????)
Ommental appendages aka _____
epiploic appendages
What are ommental appendages? Where are they found?
aka epiploic appendages
They are fatty projections of serosa that hang off of haustra. They can sometimes twist off and float in peritoneal space
What are anal columns?
folds of mucosa in anal canal
What is the epithelial layer of mucosa of the large intestine?
simple columnar epithelium
Do the large intestines have paneth cells? Why/why not?
No.
Paneth cells are antibacterial. That is what you want in the small intestine, not the large intestine.
What is a colonocyte?
an absorptive cell of the large intestine
What is within the crypts of lieberkuhn? 5 things
tubular gland intestinal absorptive cell (colonocyte) goblet cell enteroendocrine cells stem cells
Why are goblet cells so prevalent in the large intestine?
In the large intestine we are re-absorbing water which creates friction.
Goblet cells are increasingly prevalent the more distal you go (which has more friction) because mucous helps prevent friction
What is found in the lamina propria of large intestine?
galt (gut associated lymph tissue)
not as aggregated as it was in the small intestine - ie no peyer’s patches
What is found in the submucosa of the large intestine?
lots of lymphoid cells, lymphoid nodules, galt
What is found in the muscularis externa layer of the large intestine?
two layers: inner circular and outer longitudinal
outer longitudinal groups together to form tenia coli everywhere except anal canal, rectum and appendix
Where are teniae coli found?
everywhere in the large intestine except the anal canal, the rectum and the appendix
Where is the veriform appendix located?
hangs off of the cecum as an evagination of the cecum
What is the shape of the veriform appendix lumen?
small and irregular
What is the veriform appendix made up of?
lymphatic nodules
What is known as the tonsile of the abdomen and why?
the veriform appendix because it’s made up of lymphatic nodules
Does the veriform appendix have crypts of lieberkuhn?
Yes but they are small and rare
What is the total length of the anal canal?
4cm
What are the three zones of the anal canal and how are they divided?
Divided based on epithelial lining
- Colorectal zone (superior 1/3)
- ATZ (anal transition zone) (middle 1/3)
- Squamous zone (inferior 1/3)
How long is the colorectal zone?
1-2cm in length
What epithelium is in the colorectal zone?
simple columnar epithelium
What is significant about the crypts of lieberkuhn in the colorectal zone?
crypts of lieberkuhn start to look irregular in this area
What is the ATZ zone epithelium?
mixed simple columnar, stratified columnar or cuboidal, and stratified squamous 3-4 layers thick
How long is the ATZ zone?
0.3 - 1.1 cm
What is the distinguishing marker showing that you are in ATZ?
When muscularis mucosi is no longer present - this is the ATZ
What is the epithelium of the squamous zone?
non-keritinized stratified squamous - THICK (as opposed to the mixed stratified squamous which was only 3-4 cells thick)
What is located in the submucosa of the anal canal? How is this different than the rest of the GI tract?
Most of the GI tract doesn’t have glands in the submucosa
Anal canal has glands that extend into the muscularis externa.
They are branched, tubular and produce mucous
Orient the pancreas in the abdomen according to head/body/tail position
Head sits in c-shaped part of duodenum
Body is going across midline
Tail is pointing to the hilum of spleen
98-99% of pancreas function is ____, the other 1-2% of pancreas function is ____
exocrine; endocrine
What are islets of langerhan?
part of the endocrine function of the pancreas
Islets of langerhan aka ______
pancreatic islets
How does pancreatic juice exit the pancreas?
pancreatic juice exits pancreas via main pancreatic duct
____ and ____ join together to form the hepatopancreatic ampulla
main pancreatic duct and common bile duct
main pancreatic duct and common bile duct join together to form _______
hepatopancreatic ampulla
Leaving the pancreas/liver, where does the hepatopancreatic ampulla go? To do what?
Joins the small intestine at the major duodenal papilla to secrete exocrine
What is an acini?
secretory component
What makes up pancreatic acini?
aciner cells (protein secreting)
What is at the apical portion of pancreatic acini?
apical cytoplasm of pancreatic aciner has zymogen granules
What are aciner cells?
protein secreting cells that make up pancreatic acini
What do zymogen granules contain? Where are they found?
inactive enzymes for digestive tract
These are found in the apical cytoplasm of the pancreatic acini
Staining: what is the difference between pancreatic acini and pancreatic islets? Why?
Pancreatic acini stain darker
Pancreatic islets stain lighter
General: What is the difference between pancreatic acini and pancreatic islets?
Pancreatic acini are for exocrine function
Pancreatic islets are for endocrine function (aka islets of langerhan)
Where does blood come from that supplies the liver?
Proper hepatic artery brings 25% of blood to liver - oxygenated
Portal vein brings 75% of blood to liver - nutrient rich and deoxygenated
What does the proper hepatic artery supply to the liver?
25% of blood supply
oxygenated blood
What does the portal vein supply to the liver?
75% of blood supply
deoxygenated nutrient rich blood
Where do the portal vein and proper hepatic artery deliver their blood supply?
To the liver sinusoid
What does the liver sinusoid receive blood from?
Portal vein (75%) and proper hepatic artery (25%)
What is the liver sinusoid?
Leaky capillaries for blood to bathe in hepatocytes (to detoxify it)
What are hepatocytes?
aka hepatic cells aka liver cells
specialized liver cells work to detoxify blood
Pathway of blood from liver sinusoid back to heart
Liver sinusoid -> central vein -> hepatic vein -> inferior vena cava -> right atrium of the heart
Portal vein system has how many capillary beds?
- with a portal vein system between the 2 capillary beds.
What is a classic hepatic lobule?
the structural and functional unit of the liver
What is the structure of a hepatic lobule?
6 sided structure (hexagon or polyhedral)
The hepatic lobule consists of stacks of ______ surrounding _____
stacks of hepatocyte plates surrounding a central vein
What are hepatic plates separated by?
anastomosing sinusoids
What are anastomosing sinusoids lined by?
discontinuous endothelium
Hepatocyte apical specializations?
hepatocytes have microvilli that extend into the perisinusoidal space
Perisinusoidal space of hepatic lobule aka _____
space of disse
Where is the space of disse? Space of disse aka _____
aka perisinusoidal spcae
the space between endothelial cells and hepatocytes
What are Kupffer cells?
Stellate macrophages
Where are kupffer cells?
larges cells lining the sinusoid
What is kupffer cell function?
involved in breakdown of old/damaged RBCs from spleen
phagocytosis
What are kupffer cell’s derived from?
monocytes
think: kupffer cells are macrophages. macrophages are derived from monocytes
Hepatic stellate cells aka _____
Ito cells
Ito cells aka _____
hepatic stellate cells
What is hepatic stellate cell function?
aka ito cells
store hepatic vitamin A
Where are hepatic stellate cells found?
aka ito cells
found in perisinusoidal space
Where is the portal canal found in relation to a classic hepatic lobule?
On the corner
What is within the portal canal?
the portal triad
What is within the portal triad?
portal vein (75% of deoxygenated, nutrient rich blood), hepatic portal artery (25% oxygenated blood) and branch of bile duct system
What is the branch of the bile duct system epithelium?
lined with simple cuboidal cells
What are the 4 important cell types of the liver?
Hepatocytes, endothelial cells, kupffer cells, hepatic stellate cells
