Skin & Integument

Atlas:
Ross & Pawlina (6th ed.), Plates 42-46, pgs. 513-522
Text:
Ross & Pawlina (6th ed.), Ch 15, pgs. 488-512, Integumentary System

Overview:

Your attention in this work period is directed to the epithelial differentiations that serve the functions of a multifunctional organ, skin.  At the same time you should review the various tissue types that make up this organ. 

Remember:  You must derive the three dimensional morphology of the structures you are studying from essentially two dimensional tissue sections under the microscope.  Try to visualize how various profiles result from sections at different angles and levels through solid geometrical forms.

A few reminders about the most effective use of each webslide with the available tools:

  1. Understand what you expect to see based on the lectures, lab manual, computer atlas (Histology Time), and textbook (Histology: A Text and Atlas by Ross and Pawlina).
  2. Survey a webslide first with the lowest objective setting and then observe it at progressively higher objective settings. 
  3. Attempt to locate exemplary areas that resemble figures in your atlas or text as closely as possible.
  4. Try to develop a sense of continuity of structure from whole organ to histological architecture, to cellular detail, to intracellular microstructure, to macromolecular arrangement.
  5. It is often helpful to work as teams.
  6. Please ask your instructor when you need assistance.

 

 

Slide Descriptions

Webslide 0058_L:  Thin Skin, human, H & E
[Aperio ImageScope] [Aperio WebScope]

A. Examine this slide at low power to observe major structural characteristics and variations of the epidermis.  How thick is the epidermis?  The cornified layer?

Observe the distinctive appearance of the dermis:  dense, irregular connective tissue characterized by thick dermal papillae, sections of criss-crossing collagen fiber bundles, and masses of tubular sweat glands cut in various sections.  Subtle textural differences separate the upper papillary layer from the lower reticular layer.

The separation between dermis and hypodermis is less easily made with the microscope than in the gross lab.  In the latter, skin is separated from superficial fascia at the dermis-hypodermis junction by careful dissection, taking care that the fat that characterizes hypodermis does not come away with the peeled skin.  In the slide, the spongy masses of fat mark the indistinct boundary.

B.    Observe at high power the following features.

Epidermis:

  1. Appearance of typical keratinocytes.
  2. Cells of the Stratum Granulosa. What do the granules represent?
  3. Note the progression of cell changes from S. basale to S. granulosum.
  4. The melanosomes - especially in the basal cells. Is there any particular orientation to their deposition?  What functional significance might this have?
  5. Clear melanocytes and Langerhans cells.  Where are they located in the epidermis?

Dermis:

  1. Dermal papillae containing capillary loops.
    1. Are there capillaries in the epidermis?
    2. What are the advantages of draping the epidermis upon dermal papillae?
  2. The appearance of nerve and blood vessels.
  3. Sweat glands and ducts passing toward the epidermis.
    1. How do coiled tubes appear in sections?
    2. What modifications of cell structure distinguish duct from gland?
    3. Do ducts penetrate the epidermis?

 

 

Webslide 0059_L: Eyelid, monkey, H&E
[Aperio ImageScope] [Aperio WebScope]

On this slide, two free epithelial surfaces are visible, the outermost epidermis (on the top) and the moist (conjunctival) surface that moves over the eye (on the bottom).  What two obvious structural modifications enable you to identify which surface is which? 
       
Note the large mass of mucus glands in the dermis under the moist epithelial surface. 

The large mass of skeletal muscle in the center line of the section is part of the sphincter-like orbicularis oculi.  It serves to close the lid and is one of the muscles of facial expression innervated by the 7th cranial nerve.  Smaller isolated patches of skeletal muscle, many longitudinally oriented, probably represent the voluntary skeletal muscle for raising the upper lid, levator palpebrae superioris.
 
Nerve bundles, especially where cut transversely, should be recognizable.  Large diameter blood vessels are also present.

 

 

Webslide 0093_N: recto-anal junction, mammal, H&E
[Aperio ImageScope] [Aperio WebScope]

This slide contains good examples of apocrine sweat glands.

Under lowest power, locate the keratinized stratified squamous epithelium of the recto-anal junction on the far left hand side.  In this region, you will observe hair follicles with hair shafts, and associated sebaceous glands.  Deeper in the dermis, closer to the adipose tissue of the hypodermis, there are dilated glandular elements with clear lumina.  The diameter of each lumen is about 5-10 times the thickness of the surrounding epithelium.  These structures are apocrine sweat glands.

Examine the glandular epithelium at higher powers.  It is cuboidal to low columnar in structure.  Between these principal epithelial elements and the basal lamina, you will see a series of dark, flattened nuclei.  The latter are nuclei of the myoepithelial cells that act to express the apocrine secretion onto the surface of the skin.

See if you can distinguish ductal components of the glands.

 

 

Webslide 0012_A: Ear, monkey, glutaraldehyde perfusion, 1.5 µm GMA section, AF-TB.
[Aperio ImageScope] [Aperio WebScope]

 Examine this slide carefully at all powers.
 A.   Low Power Objective Setting:  Note:

Epidermis on both sides.
Dermis relatively free of dermal papillae.
Hair follicles, largely cut transversely.
Clusters of irregular, empty, fat locules.
Sebaceous glands.
Large blood vessels.
Long bar of cartilage median in section.
Striated muscle.
Nerve (cut transversely).
Dense, irregular connective tissue.

B.    High Power Objective Setting:

  1. Epidermis:
    1. Stratum basale with intracellular pigment granules.
    2. Stratum corneum layers have become separated during tissue processing and therefore can be seen in detail.
  2. Dermis:
    • Sebaceous glands.  What accounts for the swollen, foamy appearance of the cells? 
  3. Hypodermis:
    • Fat (adipose) cells.  Each irregular, empty locule represents an adipose cell whose cytoplasm has been stretched to the thin attenuated shell that you see by the accumulation of a huge droplet of fat.  The fat was extracted during alcohol dehydration and embedding of the tissue, allowing the shell to collapse partially.

 

 

Webslide 0097_L: Finger tip, monkey, glutaraldehyde fixation, 2 um GMA section, AF-TB
[Aperio ImageScope] [Aperio WebScope]

This slide contains some fixation artifacts, and is not as suitable as the previous slides for examination of most skin structures.  However, the following specific features are visible here that are not as evident in the other slides.  In particular. use this slide to look for:

  • Stratum spinosum in the epidermis. What intercellular junction gives rise to the spinous processes of the “prickly cells” in the stratum spinosum?
  • The presence of hemidesmosomes at the base of the epidermis.
  • Meissner’s Corpuscles in the dermis.  They can often be spotted at low power in the dermal papillae by virtue of their being relatively non-nucleated.  Refer to relevant plates in your atlas.
  • Pacinian Corpuscles in the dermis.  This multilayered structure has the appearance of an onion.  Why do you think that these structures would be abundant in sections of the fingertip?

 

 

DO THIS AFTER YOU HAVE DONE EVERYTHING ELSE

Webslide 0065_L: Skin, foot, human, 6 um paraffin, H&E
[Aperio ImageScope] [Aperio WebScope]

This slide was prepared from a piece of glutaraldehyde-fixed human plantar skin (sole of foot).  It has the following noteworthy features:
 l)    Moderately thick stratum corneum.
2)    Moderately numerous sweat glands and sweat gland ducts.
3)    Prominent stratum spinosum.

 

EXTRA SLIDES

Webslide 0306_D:  Plantar Skin, H&E
[Aperio ImageScope] [Aperio WebScope]

This slide is from the plantar (sole) surface of the foot similar that shown in Webslide 0065 above and offers another opportunity to study the structure of thick skin, which is very well preserved in this specimen such that it is very easy to distinguish the delicate collagen fibers of the papillary dermis from the thicker, coarse collagen fibers in the reticular dermis. Also well preserved are the eccrine sweat glands present at the interface between the fatty hypodermis and fibrous dermis. The ductal portions of the glands are darker and you can clearly see that they are lined by a stratified cuboidal epithelium. The secretory portions of the glands are also very preserved such that you can see the inner cuboidal secretory cells and the darker-staining "shell" of myoepithelial cells (the myoepthelial cells contain actin and myosin and contract in response to neural signals to propel sweat out of the glands).

 

 

Slide UMich 104-2: Thin skin, human, H&E
[Aperio ImageScope] [Aperio WebScope]

Like Webslide 0058 above, this slide features thin skin. However, this particular specimen was taken from thin skin in the region of the axilla and features excellent examples of eccrine and apocrine sweat glands. The dermal papillae are quite deep and exhibit quite obvious capillary loops. A few hair follicles and sebaceous glands can be seen. Finally, this particular specimen is from a darker-skinned individual making it very easy to see cytoplasmic melanin granules in the basal cells in contrast to the clear cytoplasm of the melanocytes. Recall that the melanocytes actually package melanin into melanosomes and rapidly secrete it in a cytocrine manner to the adjacent basal cells via numerous delicate extensions --the reason why the melanocyte cell bodies are clear is that the melanosomes are concentrated in the extensions rather than the bodies.

 

 

Slide UCSF 180: fingertip, human, H&E
[Aperio ImageScope] [Aperio WebScope]

This slide is similar to Webslide 97 above and features some excellent examples of Meissner's and Pacininan corpuscles.

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