10. Histology of the Digestive Tract

The stomach mucosa is characterized by what in its luminal surface (hint these are then divided into two important secretory portions of the lumen)?

It is characterized by invaginations in the lumenal surface. These are then divided into gastric pits and gastric glands.

How do paneth cells help the stem cells?

Paneth cells may create a less hostile environment for dividing stem cells by keeping bacterial counts low.

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Flip the deck!

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Gastrointestinal junction Duodenum Pylorus Brunner's Glands Inner circular layer of Muscularis Externa thickens to form the PYLORIC SPHINCTER (aaaaaaaasssssphincter says what? jk, thats not till a later card)

(Ignore the box in top left corner) Yellow Blue Red (bottom left arrows are pointing to same thing) what is it? Bottom right arrow?

What are the 4 histological characteristics of the appendix?

1. Complete outer muscle layer 2. Multiple lymphoid nodules 3. Crypts but no vili 4. Trapped fecal materail in lumen (ask Andy about how important the bird appendix is...............)

1. How is the ileum distinguished? 2. Where do these specific things exist? is there any other spaces that they might occupy? 3. Are these things found else where in the SI? How do we differentiate them from what is found in the ileum?

1. Distinguished by organized collection of lympohoid tissue called Peyer's Patches. 2. Exist in the lamina propria but may break through Muscularis Mucosae and occupy Submucosal space as well. 3. All of digestive tract can have lymphoid aggregates but extensive collections are seen in the slides "screams Peyer's Patches and Ileum" (see here)

Woodbury said that there are 5 cell types to identify, what are the cell types of the small intestine we should know?

1. Enterocytes 2. Goblet cells 3. Paneth cells 4. Enteroendocrine cells (DNES) 5. Stem cells

1. T or F: The small intestine has a weak blood supply. 2. Where does the blood supply to the vili (for the majority of the small intestine) come from? 2. How are fats absorbed?

1. FALSE! ITS ROBUST! 2. Slide says from the SMA 3. Lacteals! Lymphatic lacteals run through the core of the vili to transport fats. They are usually easier to find in vili than the vasculature.

What are two histological differences between the ileum and the large intestine (say at the iliocecal junction?)

1. Large intestine: a. No vili (dont want to hold up the dump!) b. Longitudinal muscle layer reduced to 3 teniae coli 2. Small intestine: a. Vili b. Complete longitudinal muscle layer

What are 3 tissue artifacts that we should know about the large intestine? (hint: poop is now solid)

1. Lots of mucus 2. Enterocytes for reabsorption (of water) 3. No vili but crypts present. GOBLET CELLS INCREASE IN NUMBER as we move from the large intestine to the anus.

What are unique features of the duodenum (2)

1. Neighbors (i.e. the pylorus) 2. Submucosal glands (Brunner's glands: ONLY submucosal glands found in the small intestine and are specific to proximal duodenum).

1. In the fundus/body, what two cell types are present in glands? 2. What are they responsible for secreting? 3. How do they stain? 4. The glands here tend to be (long/short).

1. Parietal cells Chief cells 2. parietal cells = make HCl and intrinsic factor. Chief cells = make pepsinogen 3. Parietal = eosinophilic due to mitochondria Chief = basophilic due to high ribosome content

1. As a review, what cells produce intrinsic factor? 2. What is IF used for? 3. Low amounts of IF lead to what? 4. What are some of the symptoms/how does this condition usually present (~4)?

1. Parietal cells in the fundus/body of stomach 2. Lack of IF and low B12 leads to pernicious anemia 3. Symptoms a. patients complain of fatigue and numbness in hands/feet. b. RBCs are large and decreased in number. c. Tongue is often bright red, smooth and thickened. d. Loss of tongue papillae.

Reviewing Chief cells 1. What to do they secrete? 2. What form? 3. How is the product converted?

1. Pepsinogen 2. Zymogen/inactive precursor of pepsin. 3. converted to pepsin in the acidic environment of the gastric lumen.

How is the surface area of the small intestine increased (3)?

1. Plicae Circularis (i.e. folds int he submucosa/mucosa) 2. Crypts and vili of mucosa 3. microvili on surface of enterocytes

Again (for 1000th time), what are the layers of the esophagus from the lamina moving out? In the lower 1/3 of the esophagus, what type of muscle is present?

1. See picture 2. Smooth muscle layers

1. Cardia tissue of the stomach has (long/short) glands and are (branching/linear) which (will/will not) allow us to see cross-sectional profiles. 2. What % of the glands are mucus-secreting? 3. When looking at a histo slide, what is the best criteria for determining a pit from a gland in the cardia/pyloric region?

1. Short glands branching will allow us to see cross-sectional profiles 2. Almost 100% mucus-secreting 3. LOCATION, LOCATION, LOCATION. Near the lumen = pits; near the muscularis mucosae = gland

Much of the Enteric Nervous System is found in (ganglia, spread out in networks). They are found between what two layers (hint: think of a muscularis layer)

1. Spread out in networks 2. found deep to the longitudinal muscular level and the circular muscle layer. Talking to Woodbury, he noted that the Enteric Nervous System is throughout the whole digestive tract, not just in the esophagus (just in case it was unclear during lecture).

What are the 4 layers of tissue that make up the esophagus? (from the lumen moving outward)

1. Stratified squamous epithelium 2. Muscularis mucosae 3. Esophageal glands 4. Muscularis externa on the next slide he does mention that there is lamina propria, but its pretty small compared to the other layers

1. What type of epithelium lines the pharynx? 2. What sphincter is located at the junction of the pharynx and the esophagus?

1. Stratified squamous epithelium 2. Upper Esophageal Sphincter (UES)

Histology of the Esophagus: 1. What type of epithelium lines the esophagus? 2. Are there mucosal glands? Submucosal glands? Names/locations of them? 3. What type of muscle is present in the esophagus?

FEAST YOUR EYES! 1. Stratified Squamous epithelium 2. Cardiac glands in the mucosal layer, only found in the upper and lower esophagus. Esophageal glands found in the submucosal layer and found throughout. 3. Skeletal, Skeletal/Smooth, Smooth

Duodenum Jejunum Ileum At low power it is really easy to tell these 3 apart, but we will use more than just the vili to tell each of these apart.

From left to right, where would each be found?

Gastric vs. Intestinal stem cells 1. Where are they found in each?

Gastric are found in the Isthmus (where the gastric pits and the gastric glands meet) Intestinal stem cells are found in crypts near the paneth cells

Where do we find the myenteric plexus (of Auerbach) in esophageal tissue?

In the muscularis externa, between the longitudinal and circular muscle patterns

In the pylorus, the pits are often (very deep/very shallow). The glands tend to be (linear, branched). They tend to produce mostly (acid, mucus). T or F: There are occasional parietal cells found in the pylorus.

In the pylorus, the pits are often very deep often extending half way to the Muscularis Mucosae. The glands tend to be branched. They tend to produce mostly mucus to protect the downstream duodenum True; there are occasional parietal cells found in the pylorus.

Internal and External Anal Sphincters: 1. What is the histological difference between the two?

Internal sphincter: expansion of the inner circular layer of muscularis externa (i.e. SMOOTH MUSCLE/involuntary control) External Sphincter: Skeletal muscle (voluntary control)

What is the Enteric Nervous System? Does it require sympathetic or parasympathetic control in order to function?

(Talked with Woodbury after lecture to make sure this is clear) The Enteric Nervous system is the network of nerves the controls in large part the majority of the peristaltic action that takes place in the GI. Some parasympathetic interaction takes place from the esophagus to the stomach, but from the duodenum on, the Enteric nervous system reigns.

1. How do Peyer's Patches appear on luminal surface of Ileum? 2. Are the epithelium enterocytes and goblet cells here?

1. They appear as small domes amongst the vili. 2. Epithelium are not enterocytes and goblet cells but specialized M-cells that take in bacteria from the lumen and expose to the underlying Immune system

1. What do enteroendocrine cells do? 2. Where are they found? 3. How can we identify them? 4. Where are their secretions directed (lumen/lamina propria)?

1. They produce hormones that directly effect the function of the GI tract. 2. They are throughout the stomach, small and large intestine, and pancreas (they are the body's largest endocrine organ); specifically in the SI they are found in crypts alongside the paneth cells. 3. They have a complete lack of staining. 4. They direct their secretions to the lamina propria so their juices can be taken up by the capillary system

1. Longitudinal (on the left) Circular (on right) 2. Myenteric plexus

1. What type are the orientation of the muscle fibers shown here? 2. What is betwixt the muscle fibers (black arrow)?

1. How do intestinal cells replace themselves? 2. Where do these cells reside? 3. What do they give rise to?

1. With STEM CELLS! 2. They reside in the crypts intermingled witht he paneth cells. 3. give rise to all lineages of the epithelium while maintaining their own population.

1. Where are Paneth cells found? 2. How can we identify them with H&E staining? 3. What do they make? 4. What does bacterial cell counts look like in the small intestine (high/low)? 5. Are crypts and vili continuous?

1. found deep in the crypts 2. they are intensely eosinophilic and dont need any other special staining other than H&E for them to be found (check it out) 3. Make lysozyme and other bactericidal/bacteriostatic molecules 4. in small intestine is kept low in part due to secretions from paneth cells. 5. YES! even though crypts and vili appear to be separate entities in most images the epithelium that covers them is continuous.

1. Where are the gastric stem cells found? 2. If they migrate toward the lumen, how long is their life? 3. If they migrate toward the gland base how long is their life?

1. in the ISTHMUS! 2. 2-3 days 3. 2-3 weeks

1. What do gastric pits produce? 2. Are gastric pits similar throughout the stomach? 3. T or F: Products of gastric glands are the same throughout the different regions of the stomach. 4. What is produced by gastric glands? 5. In the stomach, is the lamina properia a discrete layer still? Explain.

1. they produce an insoluble protective mucus 2. YES! 3. FALSE! Products of gastric glands varies with stomach region. 4. In cardia and pyloric regions: soluble mucus as a protective layer. In fundus and body: acid and enzymatic product 5. NO! due to the invaginations of epithelium. Lamina propria surrounds and supports the pits and glands.

Blue: Enteroendocrine cell Red: paneth cell

Blue Box? Red box?

Blue box: internal and external anal sphincters Yellow: smooth muscle and it is called the internal sphincter Green: skeletal muscle, external sphincter

Blue box: what tissue is this? Yellow: what tissue type is this? what is the name of this? Green: what tissue type is this? the name?

BB: Microvili, have actin core, not tubulin RB: Enterocyte with Microvili YB: Goblet Cell

Blue boxes (hint: what is at the core of this structure?)? Red Box? Yellow box?

blue: Enteroendocrine cell (non-staining) red: paneth cell yellow: stem cell (mitosis)

Blue? Red? Yellow?

What are Brunner's Glands and what makes them important?

Brunner's Glands are THE ONLY submucosal glands found in the small intestine. They are specific to proximal duodenum. Make bicarb rich secretion to combat the stomach acid.

Bl: Z-line Red: Gastric mucosa (simple columnar) Yel: Stratified squamous (esophagus)

Cell type/organ Blue? Red? Yellow?

What is Barrett Esophogus? This increases the risk of what condition if not addressed?

Chronic Gastroesophageal Reflux Disease (GERD) can resutl in Barrett Esophagus where the normal stratified squamous epithelium is relplaced by something more suite to withstand acid exposure. Mucosal changes increase risk of neoplasm if underlying GERD is not addressed. Images on slide to come

Top is the smooth muscle Bottom is skeletal muscle Because both are present would assume we are in the middle 1/3 of the esophagus

Muscularis Externa (outer longitudinal layer) What are the two lines pointing to? What portion of the esophagus are we in (top, middle, bottom)?

1. Support cell & fibroblast nuclei 2. Neuron cell body 3. Capsule 4. Myenteric plexus ganglia 5. Inner circularly oriented muscle 6. Outer longitudinally oriented muscle

Myenteric Plexus Ganglia: 1. Box in top right 2. Box in top left 3. Box in bottom left 4. Red dotted line 5. Line in bottom left 6. Line in top right

1. Stratified squamous epithelium 2. Lamina propria 3. Muscularis mucosae 4 (red arrows). Lots of vessels 5 (purp). Esophageal glands 6. Muscularis mucosae The muscularis externae is all smooth muscle, meaning that we would be in the lower 1/3 portion of the esophogous

Name the arrows (starting from top left going counter clockwise) Based off the histology of the bottom layer (muscularis externae), what level are we in the esophagus (top, middle, lower 1/3)?

Black = lamina propria Red: muscularis mucosae Purp: esophageal glands Circ: Lymphoid inflitrate

Name the arrows: Black Both red arrows Purple Purple circle

Blue: Gastric pit Yellow: Gastric gland Red: Parietal cell

Name the boxes: Blue Yellow Red

Red: Glands Blue: Muscularis Mucosae Yellow: Pits

Name the boxes: Red Blue Yellow

Blue: Cardia of Stomach Red: Esophagogastric junction Yellow: Esophagus Woodbury says that in this region we should expect to see cardia glands associated with the esophogus but none are evident here

Name the following organs (be specific) Blue? Red? Yellow?

1. Stratified Squamous Epithelium 2. Muscularis mucosae 3. Esophageal Glands 4. Muscularis externa

Name the layers which the arrows are pointing

Should there be any issue confusing the lymphoid tissue of the ilem (what is it called again?) and the lymphoid tissue of the appendix (what are they known by?)?

No, please dont Peyer's Patches and Lymphoid nodules of the appendix are very different

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The glands int he cardia and pylorus make an (acidic/alkaline) (soluble/insoluble) mucus that helps to protect the esophagus and duodenum.

The glands int he cardia and pylorus make an alkaline soluble mucus that dissolves in the acid solution and helps to protect the esophagus and duodenum.

The presence of what organ on a histological slide helps you to know you have reached the duodenum?

The pancreas! Check it out!

Check out this sweet pick Woodbury made...

Things to note: 1. Mucosal layer (cardiac glands) 2. Esophageal glands 3. Circular and longitudinal muscle layers int he mucsuclaris externa 4. Esophogus has robuts blood supply and prominent submucosal venous plexus

Check out the Myenteric Plexus Ganglia!

Things to note: 1. The outer longitudinal muscle 2. Myenteric plexus ganglia (red dotted line) 3. Capsule 4. Neuron cell body 5. Suppor cells and fibroblast nuclei 6. The inner circular muscle tissue.

Where would we most likely find cardiac glands in the esophagus? (i.e. where along the esophagus and where in the layers of the tissue?)

Top 1/3 and bottom 1/3 just superficial to the muscularis mucosae

Couple of reminders for the pharynx...

Wanted to make sure that we knew that the lumen from the pharynx to the esophagus narrows significantly. so if you swallow a coin it gets stuck in there!

Teniae Coli Large intestine

What are the blue boxes? Where would we find this tissue?

Top: pits Bottom: glands this is characteristic of the fundus/body of the stomach

What are the two boxes (top and bottom) and where would this tissue type be found in the digestive tract?

blue: Muscularis mucosa red: cardiac cells

What is the blue box? What is the red box? (hint: this is the lower 1/3 of the esophagus)

The pylorus Very deep pits, often extending half way to the Muscularis Mucosae; glands are branched, generating cross-sectional profiles.

What portion of the stomach would this tissue be found?

Rectoanal junction! Red: Simple columnar without microvili and goblet cells Yellow: Stratified squamous Light Blue: Keratinized stratified squamous

What tissue is this (dark blue box) Red (cell type present)? Yellow? Light Blue?

Ileum! Plicae Circularis Peyer's Patches!

What tissue is this? Blue Box? Red Box?

THE APPENDIX! Blue: Complete outer muscle layer Red: Multiple Lymphoid Nodules Yellow: Crypts but no vili Brown: Trapped fecal material in lumen

What tissue is this? Blue? Red? Yellow? Brown?

Duodenum! RA: Pancreas = presence of the pancrease is also a good indicator of duodenum OB: Brunner's glands that are enveloping the duodenal mucosa DBB: Mucosa RB: Muscularis Mucosae YB: Submucosa GB: Muscularis Externa LBB: Brunner's glands

What tissue is this? Red arrow? Orange box? Dark blue box? Red box? Yellow Box? Green Box? Light blue box?

Blue: Parietal cell HCl IF Large Eosinophilic Central Nucleus Red: Chief cells Pepsinogen Smaller Basophilic Deep in glands

what are the cell types present here (blue and red)? What do they secrete? Compared to one another, size difference? Staining? Nucleus location?