GI Flashcards
-understand histology and physiology of the GI system
The Gi system consists of what two main structures?
ALimentary canal and accessory organs (glands)
General functions of the GI system
transport food/water secretion digestion absorption excretion barrier immune protection
(ADME)
What is the function of the oral cavity? What aids its function?
Function: ingest, masticate, moisten food
*site of initiation of sugar digestion (salivary alpha amylase)
Aided by: salivary glands to form bolus
The tongue is a muscular organ composed of what kind of muscle?
Striated muscle
-3 different planes at rt. angles
*covered by stratified squamous epithelium
The anterior and posterior portions of the tongue are separated by what structure?
Sulcus terminalis
a structure of the tongue that is a remnant of its development, formed by evagination of the embryonic pharynx to form the thyroid
Foramen cecum
The posterior 1/3 of the tongue makes up the
tonsils
The anterior 2/3 of the tongue makes up the
lingual papillae
List the 4 types of lingual papillae:
- Filliform
- Fungiform
- Foliate
- Circumvallate
Lingual papillae are specialized mucosa of the tongue on the dorsal surface (anterior to sulcus limitalis). List the 4 types of lingual papillae:
- Filliform
- Fungiform
- Foliate
- Circumvallate
These Lingual papillae that are located on the entirety of anterior 2/3 of the tongue. They are characterized as being:
- smallest and most numerous
- conical, elongated projections of CT
- stratified squamous DRY epithelium
- *No taste buds
Filliform papillae
Function: break up food (friction)
Lingual papillae that are characterized by their mushroom shaped projections They are located on the dorsal surface of the tongue and are scattered in between filliform papillae.
They contain taste buds and are most numerous near the tip of the tongue.
Fungiform Papillae
-CT covered by stratified squamous epithelium
Foliate papillae are located on the lateral edges of the tongue. They are easily identified in young individuals, but degenerate at by age 2. What are their main characteristics?
Characteristics:
- Parallel low ridges separated by deep mucosal clefts
- ducts from serous glands (Von Ebner) empty into clefts
- CT core covered by stratified squamous epithelium
- *Taste buds on lateral wall of neighboring papilla
Lingual papillae shaped like large, dome shaped structures surrounded by moat like invaginations (weird heart shape). They line the sulcus terminalis (8-12/tongue) and are covered by stratified squamous (dry) epithelium.
Circumvallate papillae
Function:
- Serous glands (von Ebner): empty into moat
- flush out material (allows taste buds to respond to stimuli)
*Taste buds on lateral wall
Taste buds are oval or barrel shaped structures with pale staining bodies that span the width of the epithelium. They are composed of a taste pore and 3 principal cell types. Name these cell types.
Taste pore: small opening at epithelial apex
3 cell types:
- Neuroepithelial (sensory) cells
- Supporting (sustentacular) cells
- Basal cells
Neuroepithelial cells (sensory cells) compose one of the 3 cell types found in taste buds. They constitute the majority of the cells and extend from the basal lamina to the taste pore. They are distinguished by their dark elongated nucleus and microvilli at the apical surface (extending towards the pore).
What are their innervations?
- apical tight junctions
- express only 1 class of taste receptors
- synapse at base w/ afferent sensory: CNVII (facial); CN IX (glossopharyngeal); CN X (vagus)
Sustentacular cells (supporting cells) compose one of the 3 cell types found in taste buds. They constitute less cells compared to neuroepithelial cells. They have a pale staining nucleus and extend from the basement membrane to the taste pore. What are their characteristics?
- microvilli at apical surface
- apical tight junctions
- DO NOT synapse at base with afferent sensory neuron
- immature neuroepithelial cells
What are the 5 taste stimuli. What are their receptors?
- bitter: T2Rs + G-protein
- sweet: T1R2, T1R3 + G-protein
- umami: T1R1;T1R3 + G-protein
- sour: H+; Ca2+ proton channel
- salt: Na+;Ca2+ channel
Describe the process by which bitter, sweet, and umami tastants stimulate receptor
- receptor stimulation by tastant
- G protein
- PLC activation
- IP3 activated – open Na channel (depolarization of neuroepithelial cell)
- Voltage gated Ca2+ channel opened – Ca2+ influx
- NT release
- binds gustatory afferent nerve fiber
Umami
glutamate, aspartate, asparagus, tomatoes, cheese, meat, monosodium glutamate
Sour taste is detected by hydrolysis of acidic compounds (H+) protons. Describe the process by which sour taste is detected
- H+ enter neuroepithelial cell (amiliride sensitive Na+ channel or taste specific H+ channel)
- voltage sensitive Ca2+
- NT release – action potential in gustatory afferent
* H+ block K+ channel = no depolarization
Salty taste results from the taste of Na+ ions. Describe mechanism of signalling in neuroepithelial cell
- Na2+ enters amiloride-sensitive Na channel
- depolarization
- voltage sensitive Ca2+ channels and Na+ channels
- NT release (afferent nerve)
Describe innervation of the tongue
- Posterior 1/3:
- General: glossopharyngea (IX)l & vagus (X)
- Taste: glossopharyngeal and vagus - Anterior 2/3:
- General: mandibular branch of trigeminal (V)
- Taste: chorda tympani (facial nerve VII)
Name the layers of the gut (in order)
- Mucosa
- epithelium (endoderm)
- lamina propria (CT)
- muscularis mucosa (SM) - Submucosa (CT)
- Muscularis (SM & SK)
- muscular circular
- muscular longitudinal
4. Adventitia (CT attached to body wall) OR Serosa (CT hanging in a cavity)
*see slide 26 GI Lecture 1
Name the elements of the GI tract (in order)
Esophagus; Stomach; Duodenum; Jejunum; Ileum; Colon
List the functions of the mucosa
- Protection
- barrier; chemical abrasion - Secretion:
- mucous, digestive enzymes, hormones - Absorption
- permeable barrier
* increase absorptive surface are (villi; microvilli)
List the layers of the Mucosa
- Epithelium
- changes for fxn - Lamina propria
- CT beneath epithelium - Muscularis mucosa
- SM under lamina propria
- inner (circular); outer (longitudinal)
- movement of absorption and secretion
Submucosa
- Dense, irregular CT
- BV’s and LV’s
- Nerve plexi (Meissner’s plexus)
- -(sympathetic sensory)
- -(pre and post parasympathetic & enteric)
- Esophageal and duodenal submucosa have glands
Muscularis externa
2 layers of SM
- inner: circular (sphincters) = mix luminal contents
- outer: longitudinal = propels luminal contents
CT between muscle layers have:
-blood and lymph
**Myenteric (Auerbach’s plexus)
(post-ganglionic parasympathetic & enteric)
*forms sphincters
Adventitia/Serosa
Outermost layer (dense, irregular CT)
Serosa: Serous membrane
- simple squamous mesothelium
- some CT
- “visceral peritoneum”
Adventitia: CT only
-covers tract not lined by serosa
As the gut progresses caudally, the lumen widens and the surface area increases. What structures aid in surface area?
- Epithelial invaginations: pits and crypts
- Epithelial evaginations: Villi (Small intestine only)
- Epithelium and underlyaing layers evaginate: Plicae
Glands located in the esophagus
- Mucosa: mucosal gland
2. Submucosa: Esophageal submucosal gland
Glands of the stomach
Mucosa: Gastric gland
Glands of the duodenum
- Mucosa: Crypts of Lieberkuhn
2. **Submucosa: Brunner’s glands
Villi are found in what structures?
Duodenum; Jejunum and Ileum (Small Intestine)
*goblet cells 1st seen in duodenum….
Esophagus starts at the level of the cricoid cartilage and descends
posterior to the trachea
-exits thorax through the esophageal hiatus of the diaphragm
The esophagus is a fixed muscular tube connecting the pharynx and the stomach. Which part is fixed to the body wall? Which is free and covered by serosa?
Body wall: thoracic; adventitia
Free: abdominal esophagus; serosa
Esophageal mucosa: lamina propria
Lamina propria:
- lymph tissue
- cardiac esophageal glands
- mucous
- acid reflux
Esophageal Muscularis Mucosa
Beneath the lamina propria
- longitudinal and thick
- swallowing?
Esophageal Submucosa
CT: dense irregular
-blood/lymph vessels
- diffuse lymph
** Meissner’s plexus
(innervates muscularis mucosa)
Esophageal glands proper :
- secrete acidic mucus (lubricate/protect)
- concentrated in upper half
- compound, tubuloalveolar glands - duct lined by stratified squamous
- -cysts due to viscous secretion
Muscularis externa of Esophagus
2 layers; Circular and longitudinal
Upper 1/3: Skeletal; CN X
Middle 1/3: SM and Skeletal; CN X (somatic/visceral)
Lower 1/3: SM; CN X (visceral)
At what site of the GI system do we start to see food mixing and digestion (chyme)
Stomach
*absorption of water, salt, lipid soluble drugs
What are the three histological regions of the stomach?
- Cardiac: cardiac glands
- Fundic: gastric and fundic glands
- Pyloric: pyloric glands
- Rugae: inner longitudinal ridges
- -don’t alter surface area
Mucosa of the Stomach (e.g. gastric mucosa) contains pits and glands. Define these terms
Gastric pits: opening in mucosal surface
Gastric glands: open into bottom of pits
The transition from the esophagus to the stomach involves a change in epithelum. Describe the transition
Esophagus: Stratified squamous wet
Stomach: Simple columnar with pits and glands
—invagination of the epithelium
What are the cells types found in the Fundic (gastric) glands?
- Mucous neck cells
- chief cells
- parietal (oxyntic cell)
- enteroendocrine cell
Enterocytes???
*Isthmus: between pit & gland is site of cell replication and migration
Surface mucous cells of Stomach provide a physical barrier between gastric mucosa and luminal contents. What are their features?
- Simple columnar
- Elongated nucleus
- Secrete mucous (cloudy) = protection & HCO3-
- Stain H&E, Touidine blue, PAS
Gastric juice contains
water, electrolytes, HCL, pepsin, mucous, Intrinsic Factor (IF)
Mucous neck cells of the Stomach are located in the neck region of the fundic gland. They are shorter than surface mucous cells. What are their features?
- less mucinogen (no prominent mucous cap)
- spherical nucleus
- Vagal stimulation = secrete soluble nucleus
- *No secretion in resting stomach
Chief cells are protein secreting cells that stain basophilic under H & E. They are concentrated in the basal 1/3 of the fundic gland. What do these cells secrete?
- Pepsinogen (proteolytic enzyme)
- activated by HCl (hydrolyzes peptides) - Lipase
- Leptin
- zymogen granules
- most abundant near Muscularis mucosa layer
Parietal cells are large, (sometimes binucleate) cells with a triangular appearance. They contain a spherical nucleus and stain eosinophilic (due to presence of mitochondria). What do they secrete?
HCL & Intrinsic factor
*canaliculi in cytoplasm w/ microvilli
Tubulovesicular system within parietal cells provide a reservoir for what?
H+ pump - containing plasma membrane
-inserts into the canaliculi
Intrinsic factor is secreted by parietal cells. It is a glycoprotein that binds what?
Vitamin B12
- essential for absorption of B12 in the small intestine
- most common cause for B12 deficiency = absence of IF
HCl is secreted by parietal cells to initiate digestion by acid hydrolysis. It helps activate pepsinogen to pepsin. Describe HCl production
*stimulated by gastrin, histamine and Ach
- CO2 (from blood) + OH- = H2CO3 (carbonic acid)
Broken down = H+ and HCO3- - Move CL- into cell
- exchange HCO3- with Cl-
- anion exchange channel at basal surface
- HCO3- enters bloodstream - Movement of K+ into cell (lumen)
- K+ enters cell via basolateral Na+/K+ ATPase
- –exchanges Na+ for K+ entry
- K+ transported into lumen via K+ uniporter - Exchange H+ for K+
- H+ transported into lumen
- exchange with K+ via H+/K+ ATPase proton pump
- —- H+ out; K+ into cell from lumen
- K+ removed from cell at basal surface - HCl production
-Cl- transported into lumen of canaliculus by Cl- channel
Cl- + H+ = HCl
Helicobacter pylori cause 95% of ulcers in the human stomach. How do they survive in the acidic environment?
use urease to create a basic ammonia cloud
Peptic ulcers are open sores located on the lining of the esophagus, stomach or small intestine. What are they symptoms? What are causes?
Symptoms:
- Peritonitis: if penetrates wall
- Burning pain & inc. emptying
Causes:
- H. pylori
- -aggrevated by stress, smoking, spicy
Treat: Antibiotics, antifungals, H+ pump inhibitors
Pernicious anemia is a disruption of RBC formation in the bone marrow. It is due to a deficiency in what? What are its causes?
–Vitamin B12 deficiency
Causes:
-Autoimmune gastritis (Abs against H+/K+ ATPase; less HCl and less Intrinsic Factor)
Treatment: monthly injection B12
Enteroendocrine cells are small cells that rest on a basement membrane. They do not always reach the lumen. They secrete their contents basally, and their zymogen granules usually appear eosinophilic. What are Meek’s names for enteroendocrine cells?
Enterochromaffin cells, argentaffin cells, argyrophil
- stain with salts, chromium and silver
- > 20 secretions
Zollinger Ellison syndrome is a pancreatic tumor that is caused by increased HCl from parietal cells (stomach). What leads to inc. HCL production? What are symptoms?
Gastrin inc. HCl production in parietal cells
Symptoms:
- peptic ulcers (stomach & duodenum)
- recurrent infections (resistance)
Treat:
-proton pump inhibitors or surgery
Rare
Cardiac region of the stomach is located at the cardioesophageal junction and is composed of tubular, branched glands known as cardiac glands. What are the cells of the cardiac region?
Mucous secreting cells
Enteroendocrine cells
- mucous, gastric juice, protective
- glands and pits are about equal in length
Pyloric glands have deep _____, making up about 1/2 of the mucosa and shallow _____.
Deep pits; shallow glands
Cell types of pyloric glands
Primary: similar to surface mucous cell
–secretes viscous secretion
Enteroendocrine
Parietal cells
The Lamina propria of the stomach is restricted to spaces around gastric pits and gastric glands. It is composed of
reticular fibers, fibroblasts, SM and immune cells
The muscularis mucosa of the stomach is composed of 2 layers of smooth muscle. What are these layers?
Inner circular
Outer longitudinal
The submucosa of the stomach is composed of dense CT with adipose, blood vessels, nerve fibers and submucosal nerve plexi known as
Meissner’s plexus
- innervate vessels of submucosa
- innervate SM of muscularis mucosa
- Muscularis externa of the stomach is composed of 3 layers of Smooth Muscle (only place with 3 layers). Name the layers and their importance.
- What important structure is found in between the muscle layers?
Inner oblique
Middle circular
Outer longitudinal
-important in mixing and movement of chyme
- Myenteric (Auerbach’s) plexus
- innervate muscle
- group of ganglion cells and unmyelinated nerve fibers
Gastric reflux and Barrett’s esophagus
Reflux:
- low pH enzymes in esophagus
- heart burn
Barrett’s esophagus:
- change from strat. sq. wet (esophagus) to gastric epithelium
- high risk for esophageal adenocarcinoma
- block acid secretion = no change
Serosa of the stomach
mesothelium + CT
-continuous w/ parietal peritoneum of abdominal cavity
The small intestine is the longest component of the GI tract and is the principal site of digestion and absorption (via pancreatic enzymes and bile). What are the three anatomical regions of the small intestine?
Duodenum (shortest/widest)
Jejunum (upper 2/5)
Ileum (lower 2/5)
Plicae circulares (valves of Kerckring) are found in the small intestine. What are these structures?
*look like tree fronds
-permanent transverse folds (w/ core of submucosa)
- Villi attached
- extend around lumen
**most found in distal duodenum
function: inc. absorptive surface area
Fingerlike projections of mucosa that extend from mucosal surface into lumen, and completely cover
surface of small intestine
VIlli
- Located in small intestine
- covered by a core of lamina propria
Mucosa of the small intestine contains villi as well as what other cells?
fibroblasts, SM, immune cells (lymphocytes), fenestrated capillaries, lacteals (lymph vessels)
Crypts of Lieberkuhn are found in the mucosa of the small intestine. These are simple, tubular structures that extend from the muscularis mucosa to the lamina propria and open onto luminal surfaces beneath the villi. What are they composed of?
–simple columnar epithelium with microvilli and goblet cells
–continuous w/epithelium of villi
The epithelium of the small intestine is composed of simple columnar cells known as ______, microvilli, and mucous secreting ____ cells.
- Enterocytes (simple columnar cells)
- Microvilli
- goblet cells
*amplify luminal surface
Enterocytes are the absorptive cells of the small intestine. They are tall, columnar cells with basal nucleus and apical microvilli. They contain ____ junctions between cells, requiring active transport.
tight junctions
*secrete: glycoprotein enzymes, water and electrolytes
Digestive enzymes occur as zymogens and must be activated. What is the process of activation of these enzymes?
- Enterokinase (on enterocyte microvilli) converts trypsinogen to trypsin
- Trypsin converts:
- chymotrypsinogen
- proelastase
- procarboxypeptidase A & B
- prophospholipase A2
Absorption in the small intestine occurs by
- tight junctions: restrict enzymes
- Lateral plications
- -Na/K ATPase on lateral membrane
- -Na moves out; water follows
Goblet cells are first seen in the Duodenum and extend throughout the small intestine. What are features of goblet cells?
1:4 goblet cell:absorptive cell
–H&E: appear empty due to
apical mucinogen granules
Paneth cells are located at the base of (small) intestinal glands. Describe their features and their secretions
Features:
- basophilic basal cytoplasm
- acidophilic, apical secretory granules
Secrete:
- lysozyme (degrades peptidoglycan)
- alpha defensins (antimicrobial; ion channels)
- phospholipase A2
- TNF alpha (pro-inflammatory)
*phagocytosis - bacterial flora
Enteroendocrine cells of the small intestine are similar to the enteroendocrine cells of the stomach. They are located in the lower region of the intestinal gland. What hormones do they contain?
Same as stomach:
- CCK
- Secretin
- GIP: insulin release
- Motilin
- Somatostatin
- Histamine
CCK
- stimulate pancreas/gallbladder
- inhibit gastric secretory fxn and motility
Secretin
same as CCK
GIP
insulin release in pancreas
Motilin
Gastric and intestinal motility
Histamine
paracrine: stimulates gastric acid secretion
M cells
epithelial cells (overlying Peyer’s patches)
- no microvilli
- Antigen transporting cell (to basolateral surface)
Submucosa of the small intestine has dense CT with localized sites of adipose tissue. What types of glands are located in the submucosa?
Brunner’s glands (submucosal glands)
- zymogen and mucous secreting cells
- pH = 8,1-9.3
- neutral & alkaline proteins
- bicarbonate
The muscularis externa of the small intestine is composed of 2 layers of SM: inner (circular) and outer (longitudinal). What plexus can be found in between these layers? What types of contraction occur?
Myenteric (Auerbach’s plexus)
- Segmentation: local
- circulate chyme
- digest/absorb - Peristalsis
- coordination of 2 layers
- moves contents distally
The duodenum is retroperitoneal and is covered by ____ on the posterior surface, and ____ on the anterior surface. The jejunum and ileum are both covered by _____ which is continuous iwth the mesentery.
Duodenum:
- adventitia on posterior
- serosa on anterior
Jejunum and Ileum: Serosa
The large intestine is involved with absorption of water and electrolytes. It has NO villi. What structures constitute the large intestine?
- Ileocecal jxn: joins small intestine
- Appendix
- Cecum
- Colon
- Rectum
- Anal canal
Distinguishing features of Large intestine
teniae coli & Haustra (colon and cecum)
*No Villi in mucosa
The ileocecal junction is the junction between the ileum and the large intestine. It is formed by what folds? What is the function of the ileocecal valve?
FOrmed by: mucosal and submucosal folds
–inner part of muscularis externa enlarged = support
Ileocecal valve: prevents reflux of colon (inc. bacteria)
The mucosa of the Large Intestine contains Intestinal glands known as
Crypts of Lieberkuhn
- stem cells
- no digestive enzymes
What: are the cells of the mucosa of the Large Intestine?
4:1 eneterocyte to goblet cell
Enterocyte: abosrption; no digestion
Goblet: mucous/lubrication
**No Paneth cells
The lamina propria of the large intestine has large lymphatic nodules that extend into the submucosa. However, it does not contain lymph vessles. Where are the lymph vessels?
Submucosa and Muscularis externa
*slow metastasis of certain cancers?
Parietal cells are activated by
Ach, Gastrin & Histamine
The lamina propria of the large intestine contains a thick layer of collagen and proteoglycans referred to as the collagen table. It is located between the basement membrane and fenestrated venous capillaries. What is its function? What disease is it associated with?
Regulates water and electrolyte transport
Human hyperplastic colonic polyps:
-3x normal thickness
The lamina propria of the large intestine contains a structure called Pericryptal fibroblast sheath. It is a population of fibroblasts that undergo regular replication.
**FIX
The outer longitudinal layer of the Muscularis externa of the Large intestine is known as ________. Taenia are not found in the rectum, anal canal or appendix!!
Taenia coli
3 thickened areas of S.M.
*contraction leads to formation of Haustra
Haustra are sacculations of external surface of cecum and colon formed by contraction of Taenia coli. What is the function of haustra?
allows segments to contract independently (segmentation)
2 types of contraction:
- -segmentation (local)
- -peristalsis - distal mass movements
Serosa/Adventitia of the Large intestine
Mostly retroperitoneal
- Anterior: serosa
- Posterior: Adventitia
True/False: The Cecum of the intestine is a small, blind pouch of large intestine that is histologically identical to the colon. The appendix is a diverticulum of the cecum that contains cellular debris
True
The appendix differs from the large intestine in that it does not have
taenia coli
- uniform outer longitudinal layer
- no villi
- *lymph nodules extending into submucosa
- *lots of lymphocytes
The Mucosa of the Large Intestine has what types of cells?
- enterocytes
- goblet cells
- *Lots of lymphocytes
The lamina propria of the Large intestine has lots and lots of what types of cells?
Lymphocytes
The muscularis mucosa is difficult to distinguish in the large intestine due to
lots of lymphocytes!!
*Submucosa also has lots of lymphocytes and lymph nodules!!
the muscularis externa of the large intestine does not have what structure?
No taenia coli
Inflammatory Bowel Disease
- ulcerative colitis (mucosa) & Crohn’s (any segment of intestinal tract)
- diarrhea, pain and relapses
Crohn’s:
- chronic inflammation from autoimmunity
- damage intestinal mucosa (progresses downward)
Crohn’s Disease
- bowel obstruction
- deep ulcerations in gut wall
Start: adolescence/early adulthood
Symptoms: diarrhea, severe abdominal pain, nausea, fever, weakness, chills, weight loss
SIde effects: malnutrition, fisutlas
- no cure
- corticosteroids/antibiotics; anti-inflammatories
Hirschsprung’s Disease
-Aganglionic megacolon
Newborns:
-intestinal obstructions
Congenital defects (gene mutations):
- failure of NCC’s to migrate
- Down’s syndrome
- colon lacks enteric ganglia – non-peristaltic
Symptoms of Hirschsprung’s disease
delayed initial bowel movement in newborns
vomiting
constipation
abdominal distension
rupture of cecum
*Treat: surgery - remove non-innervated
The rectum and anal canal function in the elimination of waste. The rectum is the dilated portion of the alimentary canal. It is split into upper region and distal colon by what structures?
Transverse rectal folds
Mucosa: 1;1 enterocyte to goblet (see tons of goblet cells)
The anal canal is the most distal region of the alimentary canal. It is composed of anal columns and anal sinuses. Distinguish between the two
Columns: Longitudinal; upper region
Sinuses: Depressions between columns
True/False: The Anal-rectal junction is located above the anal columns and anal sinuses (above the pectinate line)
True
3 Zones of the Anal Canal
Upper 1/3: Colorectal
- -simple columnar w/goblet
- less glands
Middle 1/3: Anal Transitional Zone
- pectinate line
- simple columnar to strat. sq. wet
Lower 1/3: Squamous zone
-strat. sq. dry
Circumanal canals
-large apocrine glands
- skin around anal orifice
- hair follicles
- sebaceous glands
Muscularis externa of the Large intestine has no taenia coli. It is composed of 2 layers: Inner circular and outer longitudinal. Discuss
Inner:
- -thick
- internal anal sphincter
Outer:
- -longitudinal
- -External anal sphincter (striated muscle)
