Riddle: Microanatomy

Front 1

How does the composition of the muscularis externa differ among the upper, middle and lower esophagus?

Are other layers of the esophageal wall systematically different among the upper, middle and lower regions?

Back 1

In humans, muscularis externa of upper esophagus has skeletal muscle, lower esophagus smooth, and middle has mixed bundles of skeletal and smooth.

Muscularis mucosa becomes more prominent in middle and lower esophagus; esophageal cardiac glands (in lamina propria) more common in lower (and sometimes upper) esophagus.

Front 2

What type(s) of extracellular fibers would you expect to find in the connective tissue of the submucosa in the esophagus. Why?

Back 2

Need a mix of collagenous fibers for strength and elastic fibers to permit esophagus to expand as food bolus is swallowed and then recoil.

Front 3

What change(s) might you expect to find at the esophagogastric junction in an individual suffering from GERD?

Back 3

The normally distinct border between the stratified squamous epithelium of the esophagus and simple columnar epithelium of the stomach is altered with GERD, showing signs of inflammation; the esophageal mucosa eventually can become eroded, exposing the underlying submucosa.

Front 4

Describe the cytological appearance of surface mucus cells (in a typical H&E stained section), relating the major structural feature(s) to the cells’ primary function

Back 4

Apical portion of the surface mucus cells appears only lightly or unstained in H&E because mucus, produced to protect the mucosal surface from the acidic contents of the stomach, is largely washed away in tissue processing.

Front 5

Describe the cytological appearance of parietal cells (in a typical H&E stained section), relating the major structural feature(s) to the cells’ primary function.

Back 5

Cytology of parietal cells is dominated by eosinophilic staining of the cytoplasm, due in large part to the large numbers of mitochondria, required to produce the ATP needed to drive the activity dependent transporters involved in HCl production.

Front 6

Describe the cytological appearance of chief cells (in a typical H&E stained section), relating the major structural feature(s) to the cells’ primary function.

Back 6

Basophilic staining of cytoplasm due to large amount rER needed for protein synthesis and eosinophilic staining of apical cytoplasm where zymogen granules contain enzyme precursors.

Front 7

Describe the cytological appearance of enteroendocrine cells (in a typical H&E stained section), relating the major structural feature(s) to the cells’ primary function.

Back 7

Cytoplasm usually very lightly stained because hormone containing granules are very small and not evident. Cell often does not extend apically to lumen of gland; cell products secreted basally, into extracellular fluid and bloodstream.

Front 8

Describe briefly the major changes in the ingesta from the time it enters the stomach to the time that it is released into the duodenum.

Back 8

Food enters stomach after being partially ground during chewing and moistened with saliva. Is reduced to liquid and mixed with digestive enzymes before being gradually released into the duodenum.

Front 9

How does the glandular epithelium differ between the pyloric and fundic region of the stomach? What is the major functional significance of that difference?

Back 9

Histologically gastric pits are deeper in the pyloric region and glands are more coiled and branched; more important functionally is the lower frequency of parietal and chief cells and higher density of mucus producing cells in the pyloric region.

Front 10

Which layer of the muscularis externa is enlarged to form the pyloric sphincter?

Back 10

Middle circular layer (outer longitudinal layer could not effectively occlude the lumen).

Front 11

If neuronal cell bodies are present in these plexi what kind(s) of neurons might they represent? For the neuron type(s) that you might expect to find there, briefly describe the effects that activation of those neurons might have on the gastric mucosa and/or smooth muscle in the muscularis externa?

Back 11

Neuronal cell bodies in wall of gut could represent enteric neurons or parasympathetic neurons (sympathetic cell bodies are in ganglia near spinal cord). See lecture for review of nervous system control of GI function.

Front 12

Describe the cytological appearance of absorptive cells in a typical H&E stained section and the key ultrastructural features you could see if we hauled an electron microscope into the lab. Describe how these ultrastructural features are key to the cells’ functions.

Back 12

Apical “brush border” represents apical microvilli (increase surface area for absorption). Cytoplasm eosinophilic due to secretory products (remember these cells secretory as well as absorptive). At ultrastructural level would see tight junctions among cells in the apical regions, restricting movement through the paracellular pathway, wider intracellular spaces basalaterally, and abundant sER in the apical cytoplasm, which plays a role in transport of absorbed nutrients by the cells (see lecture).

Front 13

Describe briefly a) the anatomical relationship between absorptive cells and the vascular and lymphatic capillaries and b) the significance of that relationship for the absorption of amino acids, sugars and fatty acids

Back 13

Vascular capillaries in lamina propria immediately beneath lamina propria of the epithelium; lymphatic capillaries in center of lamina propria core. Amino acids and sugars transported by the absorptive cells enter the vascular capillaries but the chylomicrons involved in lipid transport enter the larger and more permeable lymphatics.

Front 14

Describe the cytological appearance of goblet cells (in a typical H&E stained section), relating the major structural feature(s) to the cells’ primary function.

Back 14

Large unstained region in apical cytoplasm where abundant mucinogen granules (largely lost in processing) were located; mucus produced by cells help lubricate and protect luminal surface of the GI tract.

Front 15

Describe the cytological appearance of Paneth cells (in a typical H&E stained section), relating the major structural feature(s) to the cells’ primary function.

Back 15

Basophilic basal cytoplasm (rER) and intensely acidophilic apical secretory vesicles containing the antimicrobial factors intrinsic to the cells function.

Front 16

How do the mucosa and submucosa of the ileum differ from that in the duodenum?

Back 16

Mucosa of the ileum has relatively more goblet cells in the epithelium (and fewer of the other cell types); submucosa contains more and larger lymphoid nodules (Peyer’s patches).

Front 17

How do the structure and function of M cells differ from those of absorptive cells?

Back 17

The M cells overlying lymphoid nodules are cuboidal rather than columnar. They have extensive apical folds rather than microvilli and have recesses in which lymphocytes may sit. The M cells play a role in antigen transport and presenting, rather than nutrient absorption.

Front 18

What are the major differences between the mucosa of the small intestine and that of the colon? Relate these structural differences to differences in function between the small and large intestine.

Back 18

Fewer absorptive cells in large intestine since less, and more restricted (water and salts mostly), absorption there; no Paneth cells (might kill the normal flora of the large bowel); more goblet cells in large intestine as the remaining waste matter from the ingesta becomes more compacted and more lubrication is needed; mucus from the goblet cells also helps bind the waste together for elimination.

Front 19

What is the primary difference between the muscularis externa of the small intestine and that of the colon? Speculate on the functional significance of the difference(s).

Back 19

The accumulation of the longitudinal smooth muscle in the outer layer of the muscularis externa into discrete bundles, the tenia coli, may provide for stronger contractions and greater ability to move the compacted waste through the colon.

Front 20

What is the primary function of absorptive cells in the large intestine? Describe briefly and generally how they accomplish that function, noting the role of critical structural features of the cell.

Back 20

Critical features are apically located tight junctions that require that most things move by the regulated, transcellular rather than paracellular route and differential distribution of channels and transporters in apical versus basal-lateral membrane.

Front 21

What identifies the center of a classical hepatic lobule? What defines the margins?

Back 21

Center is central vein (aka terminal hepatic venule); margins defined by portal triads (branches of hepatic artery and hepatic portal vein and bile ductile)

Front 22

What type(s) of cells form the walls of the sinusoids and central venule?

Back 22

Both sinusoids and central veins have lining of endothelial cells; sinusoids also have Kupffer cells associated with their walls.

Front 23

What is the functional significance of the microvilli?

Back 23

Increases the plasma membrane surface area over which hepatocytes can secrete and absorb materials.

Front 24

4. What type of epithelium is found in the gall bladder and how does it function?

Back 24

The gall bladder is lined by a simple columnar epithelium that actively transports sodium and chloride ions into the intercellular space in the basal-lateral compartment of the epithelium. Water moves from the lumen of the gall bladder into the intercellular space, following the osmotic gradient established by the ion transport; the fluid then moves into the subepithelial connective tissue and then into fenestrated capillaries and venules that underlie the epithelium.

Front 25

How would you distinguish this from small intestine?

Back 25

Distinguish gall bladder from small intestine by villi (present in sm. Intestine but not in gall bladder), cell types in epithelium (all columnar absorptive cells in gall bladder, other cell types in intestine), distinct brush border on sm. intestinal epithelium, absence of muscularis mucosa and submucosa in gall bladder, much more distinct cell layers in muscularis externa in intestine.

Front 26

4 major cell types in gastric epithelium

Back 26

Surface mucous cells: nucleus basally displaced by large mucous cup and apical cytoplasm poorly stained because of loss of soluble mucus.

Mucous neck cells: similar surface mucous cells except apical cytoplasm often appears more granular because contains many smaller granules containing mucinogen (rather than a single large mass as in the surface cells).

Parietal cells: large oval cells with central nucleus. Large size and acidophilic staining of cytoplasm function in part of high level of metabolic activity and large number of mitochondria required to provide ATP need to drive ion transport functions related to production of HCl.

Chief cells: basophilic cytoplasm due to abundant rER required for peptide production; apical cytoplasm typically acidophilic because presence zymogen granules (but not so much in this virtual slide, which is rather darkly stained).

Front 27

the function of the M cells

Back 27

M cells are restricted to the epithelium overlying the lymphoid nodules. The epithelium in this region lacks the cell types typically seen in the small intestinal epithelium (primarily enterocytes and goblet cells) and instead the cells have a more cuboidal appearance. These cells transport peptide antigens from the lumen and release them into the interstitial fluid within the nodule where they are taken up by antigen presenting cells and presented to lymphocytes in the nodule.