Objectives:

There are 2 skin organs that you should be able to identify if presented in a practical: thin skin & thick skin. There are 2 structures in the oral cavity that should be identifiable. These include, teeth, tongue. The level of detail required in the unknown identification is summarized in the Differential Diagnosis that occurs at the beginning of each organ.
 
 
 

• Skin:

• Epithel: stratified squamous keratinized
• Dermis (cutis): papillary and reticular layers of CT
• Hypodermis (subcutis): adipose tissue, loose CT.

Before looking at the skin slides, look at the poster of epithelium that is mounted on the door of the lab and find the stratified squamous epithelium of skin. Notice the finger-like projections that extend from the basal side of the stratum basale toward the basal lamina. This is a 3rd level of folding, a subcellular level, that increases the surface contact between cells and the underlying extracellular matrix. It is not easily visualized in the slides in our collection, but in well preserved tissue, it obviously can be seen. When you look at slide 65 (there are only 4 of these slides) keep in mind this picture of an irregular basal surface when you see the distribution of silver under the str. basale and compare it to the silver deposits under the sweat glands and their ducts.

Other feature to keep in mind is the relative arrangement of sweat glands (merocrine), sebaceous glands (holocrine), scent glands (apocrine, present in axillary skin) and arrector pili muscles (smooth muscle). The sebaceous glands and arrector pili muscles are appendages are all found on one side of the hair follicle; they are not spread around the circumference of the hair follicle.

Certain areas of skin, particularly the fingertip and palm, have encapsulated mechanoreceptors, both Meissner and Pacinian. Slide 70, 65 and some slides of 64 have Meissner’s and 65 shows Pacinians.

A. Thin Skin -
There are 9 slides of skin but among these are 16 examples covering a range of different preparations

 
62A Scalp, H&E, Monkey
62B Human scalp, white
62C Scalp, Masson, human
63A Axillary skin, Masson, human
63B Human sweat gland axilla, H&E
66A Skin, Masson, Human
66B Human skin, Caucasian, v.s.
66C Skin, human, Caucasian, trichrome
68 Skin, human, heavily pigmented, H&E
69 Pni. skin, Masson, human
71A Eyelid, monkey, Masson
71B Eyelid, Human, H&E

Epithelium is organized into epidermal ridges with dermal papillae underneath projecting fingerlike into the epidermis.

stratum basale (a.k.a. germinativum),

stratum spinosum (a.k.a.polygonale),

stratum granulosum,

stratum corneum.

 

• Papillary layer: loose connective tissue
• Reticular layer: dense irregular connective tissue
• Hair follicles revealing up to five concentric layers of epithelial cells
• Sebaceous glands found in conjunction with hair follicles
• Arrector pili muscle
• Sweat glands (coiled, tubular) are merocrine (exocytosis of secretory products (proteins).
• Apocrine scent glands are identifiable by large lumen with stored secretory product. If present means that the tissue came from a limited number of possible regions of the skin, e.g. axilla, genitalia.

66C Skin, Caucasian, Mallory stain
Mallory stain brings out several features not readily visualized with regular stains. Particularly in the sweat glands, the dark and clear cells are easily distinguished. The distinction between papillary and reticular layers of the dermis is dramatic. Note in the s. basals of the epidermis the presence of clear cells. These are probably melanocytes. Nerve bundles are easily identified.
 
 

62A Scalp, H&E, Monkey

This slide is rich in hair follicles which should be examined thoroughly. At the base of some hair follicles is a region of more darkly staining cells ,which are the matrix cells. Some slides may show dermal papillae at the base of the hair follicles. The epidermis is relatively thin and contains a cornified layer, relatively easy to distinguish. Eccrine (merocrine) sweat glands and their ducts are present but not in large numbers. At the base of the dermis is a layer of skeletal muscle. Particularly prominent are the arrector pili muscles, which are smooth muscles that connect the hair follicle with the epidermis. Sebaceous glands are associated with each hair follicle, though some follicles lack them. Deep in the dermis are nerve bundles and vasculature.
 
 

62B Human scalp, white
This darkly stained slide reveals some follicular papilla extremely clearly. Hair follicles are very prominent. A layer of adipose tissue underlies the dermis and in some sections with a layer of dense irreguar connective tissue under it. Within this connective tissue layer are several peripheral nerve fibes. The deep connecive tissue extends finger-like projections into the dermal layer. A layer of skeletal muscle can be found underlying the deep connective tissue. Within the epidermis, the 4 layers can be clearly distinguished. There is a very distinct gradation in the staining between the papillary layer and the underlying reticular layer. The reticular layer is also more highly cellular.
 
 

62C Scalp, HE, human

This slide presents a completely different picture from 93. The stain is only part of the difference. Much more prominent are the eccrine sweat glands and sebaceous glands. The 4 layers of the epidermis are also more visible. Where the section reveals the base of the hair follicle, the matrix cells are clearly seen. Much more prominent also are the dermal papillae below the epidermis. In places they appear as rows interrupted by the occasional epidermal ridge. A layer of adipose tissue is found in about the middle of the section. Notice how connective tissue extends vertically toward the surface at nearly regular intervals starting at just below the layer of adipose tissue. Also at about this level is some large vasculature as well as nerve fibers. Arrector pili muscles are more difficult to see. They can be detected by the fact that the long axis of the cell nuclei run parallel with the fiber bundle. Smooth muscle in vessels will run perpendicular to the long axis of the vessel. The eccrine sweat glands do not show obvious dark and clear cells, but there are two shades of stain in the cell nuclei of the glands. Myoepithelial cells at the base of the glands appear as a layer of squamous (flat) cells. Where sections run obliquely through the gland, the myoepithelial cytoplasmic processes can be seen as rods. Hair follicles show clear layering. The internal root sheath stains darker than the external root sheath. Erythrocytes stain brown, a fact that should help you identify the capillaries in the section. Peripheral nerve bundles are found throughout the section running parallel to the larger blood vessels.
 

63A Axillary skin, HE, human

Compare this slide with 92 and note the very prominent apocrine scent (modified sweat) glands. Some slides show ducts that can be followed nearly to the surface. Myoepithelial cells are very prominent in the glandular tissue. In glancing section, they appear as rods. In the epidermis, melanin granules can be observed surrounding the nucleus of the str. basale cells. The staining brings out the difference in connective tissue of the papillary layer and the underlying reticular layer. In the sebaceous glands, the secretion product appears as non-staining granules. The secretion product of the glands appears blue and apparently contains some cellular material, apparently sloughed off by the glandular epithelium. In the picture above, p. l. stands for papillary layer and r.l. stands for reticular layer.
 
 

63B Sweat gland, human, skin
This slide is a completely different preparation from 63a but also shows both apocrine and eccrine sweat glands, although the apocrine are the more prominent and are distinguishable by the large lumen of the glands. Myoepithelial cells are pretty prominent and their finger-like structure is visible where you see an oblique section through the gland.
 
 

66A Skin, Masson, Human
This section is devoid of hair follicles, the epidermis is relativley thin and 5 layers are not visible in the epidermis. So probably this is from a "hairless" region of thin skin. Noteable is the presence of dark and clear cells in the eccrine sweat glands and very prominent myoepithelial cells. This is one of the few slides that reveal the two types of secretory cell in the sweat glands.
 

66B Human skin, white, v.s.

This is a thick section so that where nuclei are concentrated is very dark. Unfortunately, you will not be able to observe melanin granules in the str. basale but you can see the 4 layers of the epidermis. In the sweat glands, myoepithelial cells are distinguishable by their squamous appearance. Dark and clear cells are not easily distinguished. Nerve bundles can be seen in several places. There is a hypodermal layer deep to the dermis in some sections..
 
 

68 Skin, pigmented, human 
Examine this slide only for the epidermis. The rest of the slide is unremarkable. Note the deposits of brown granules around the basal cells. The other 3 layers of the epidermis are also clearly resolved. The reticular layer can be distinguished from the papillary layer by the relatively low number of cells. The papillary layer has several blood vessels runing parallel the epidermal surface.
 
 

69 Penile skin, Masson, human
This slide is remarkable for the large venous sinuses in the dermal layer and the lack of hair follicles which suggests skin from a specialized location, i.e. the penis. However, the epidermis will provide you with another view of melanin granules, which are arranged like little "hats" on top of the basal cell nuclei.
 

71A Eyelid, monkey, Masson
This slide has both keratinized and non-keratinized str. squamous epithelium. Hair follicles can be seen on one surface, the glands on the opposite surface are probably the Meibomian glands which are sebaceous-type glands. In the axis of the section look for the tarsal plate consisting of elastic cartilage. Skeletal muscle fibers are found in the inner part of the eyelid, these are fibers of the levator palpebrae muscle . The non-keratinized epithelium is very thin in places.
 
 

71B Eyelid, Human, H&E
Very similar to 107 with all the same structures, but stained differently.
 

B. Thick Skin
 

64 Plantar skin, human, H&E
65 Palmar skin, silver, human
67 Intercellular bridges
70 Meissner’s corpuscles

 
1. Epidermis - keratinized stratified squamous epithelium consisting of 5 layers: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, stratum corneum.

2. Epithelium is organized into epidermal ridges with dermal papillae underneath projecting fingerlike into the epidermis.

3. Dermis: dense irregular fibroelastic connective tissue arranged in 2 layers:

a. Papillary layer: loose connective tissue
b. Reticular layer: dense irregular connective tissue

4. Dermal ridges ("finger prints")

5. Merocrine (eccrine) sweat glands (coiled, tubular, simple cuboidal) and their ducts (stratified cuboidal)

6. Sensory specializations for pressure sensing

a. Meissner's corpuscles located in the dermal papillae
b. Pacinian corpuscles located deep in the dermis

7. No hair follicles

65 Palmar skin, silver impregnation, human
This slide is impregnated to reveal the reticular fibers that underlie the basal lamina. Some basal lamina is also visible. Silver grains are found in the stratum basale, around the sweat glands and their ducts, adipocytes and within the Pacinian corpuscles. You can also find Meissner’s corpuscles in the dermal papilla. There is very little cellular staining. Note that the sweat gland ducts stain more heavily than the glandular epithelium and that the thin matrix around the adipocytes also is impregnated.
 
 

67 Intercellular bridges
This section of thick skin is stained to bring out the bridges that connect cells in the str. basale and str.spinosum. They can be seen as very fine processes extending across the pale staining zone between cells.
 

70 Meissner’s corpuscles
This slide was examined several weeks ago in the nerve tissue lab. The dermis contains many sweat glands and the layering of the epidermis is clear. You should also be able to find the ducts of the sweat glands in the str. corneum, identifiable by their coiled appearance.
 
 

 
A. Tooth. There are 3 slides of developing teeth. Most of you have 72b and 72c, which are relatively similar but some have 72a. Slide 72b & 72c are more complicated looking. You have nearly enough knowledge to find your way about this slide but I have written a description that you will find on a separate page at the end of the lab. Hint: the section slices through the whole skull from mouth through the brain case.

1. Layered structure consisting of a dental papilla consisting of loose connective tissue with vasculature.
2. Dental papilla lined by columnar cells, the odontoblasts. Odontoblasts in turn covered by striated layer, the dentine.
3. Developing enamel layer lined by a columnar epithelium - the ameloblasts
4. Enamel organ filled with stellate reticulum

72A Early dentine formation, pig

72A Early dentine formation

This slide has a nicely oriented slice of early tooth formation. At one end of the slide is a piece of epidermis.
The enamel organ is defined by the outer enamel epithelium (OEE).
Underlying it is the stellate reticulum (SR).
Tooth structures consist of the

dental papilla (DP),

odontoblasts (O) and

ameloblasts (A).

72B Developing tooth, Mallory
This slide may be perplexing to look at, initially. There are two groups of slides. Most have a large block of tissue and these are the ones that this description is for.

B. Tongue
There are many different examples of tongue, particularly slide 74. You do not need to look at all of them. The most intersting is the slide with the taste buds, slide 75.

1. Muscular organ covered by a mucous membrane consisting of a stratified squamous epithelium and a dense irregular connective tissue. Epithelium is mostly non-keratinized.
2. Skeletal muscle arranged in 3 mutually perpendicular layers
3. Taste buds observed in the epithelium is selected areas

a. Foliate papillae - parallel ridges separated by deep mucosal clefts with taste buds
b. Fungiform papillae- mushroom shaped papillae,  taste buds (rare) can be on their dorsal surface
c. (Circum)vallate papillae- dome-shaped papilla surrounded by a cleft populated by taste buds

4. Connective tissue may contain serous secreting (von Ebner's) and mucous secreting glands.
 
 

73B Vallate papillae, v.s. 

73A Vallate papillae, human
Some of these slides show taste buds and some do not. The taste buds are not very well preserved. The glands are mostly serous with some mucous. In the slides there are a number of peripheral nerves
 

74A Tongue, H&E, Human
This slide contains only the epithelium and the underlying muscle and conective tissue. There are apparently no glands and no taste buds. Some dark staining material on the surface of the epithelium is apparently post mortem tissue degradation. There are some very large veins under the epithelium.
 
 

74B Tongue, Masson, Human
This is a slice through no particular region of the tongue and lacks taste buds. The glands are numerous and are mosty serous secreting.
 
 

74D Tongue, MA, Human
There is quite a bit of variation along these slides in terms of the amount of material. This slide is stained with Mallory-Azan. Connective tissue stains a dark blue color. The epithelial tissue and muscle stain red to purple. There is only a surface epithelium, underlying connective tissue and the muscle layer. The stain gives a different impression than the other slides.
 

74C Tongue, H&E, Human
There is some variation among these slides as well. The slides have a surface epithelium and numerous submucosal serous glands with some mucous glands. There are no taste buds. Some slides have lymph nodules underneath the epitheium.
 
 
 

74F Tongue, Mucicarmine, Human
 This is an unusual stain which brings out the mucous glands to the exclusion of almost everything else. Skeletal muscle is identifiable by the arrangement of nuclei which do stain well. The mucous glands are a pale purple-brown color. Their cytoplasm looks vesicular and their nuclei are basal and flattened, sure signs of a mucous secreting gland.
 
 
 

75A Foliate papilla with taste buds
This is an iron hematoxylin stained section of foliate papilla from rabbit. Taste buds line the cavity between the papilla. You will have to search for buds that show the tiny pore that opens to the lumen enabling the buds to sample the contents of the lumen. A stratified squamous epithelium covers the papilla. Extensive serous secreting glands are present in the submucosa and seromucous glands in the muscularis.
 
 

 

Integument  General  thick skin  thin skin Epidermis  keratinocytes  tonofilaments  tonofibrils  keratohyaline granules  lamellar bodies  melanocytes  premelanosomes  Langhans cell  Merkel cell  Merkel’s corpuscle  stem cells  stratum basale  stratum germinativum  stratum spinosum  stratum granulosum  stratum lucidum  stratum corneum  water barrier  Dermis  dermal papillae  epidermal ridges  rete ridges  hemidesmosomes  anchoring filaments  anchoring fibrils  papillary layer  reticular layer  Pacinian corpuscle  Meissner’s corpuscle  Ruffini endings  hair follicles  bulb  external root sheath  matrix cells  internal root sheath  keratogeneous zone  sebaceous glands  sebum  pilosebaceous canal  arrector pili muscles  eccrine sweat glands  clear cells  dark cells  myoepithelial cells  duct cells  apocrine sweat glands  Hypodermis  superficial fascia  panniculus adiposus  TONGUE  General  vestibule  oral cavity proper  palatine tonsil  pharyngeal tonsil  lingual tonsil  masticatory mucosa  lining mucosa  Tongue  sulcus terminalis  foramen cecum  filiform papillae  fungiform papillae  circumvallate papillae  foliate papillae  Taste Buds  taste pore  neuroepithelial cells  supporting cells  basal cells

TEETH  General  clinical crown  anatomical crown  cusps  neck/cervix  cementoenamel junction  peridonal ligament  peridontal membrane Enamel  hydroxyapatite  rods  prisms  amelogenesis  ameloblasts (secretory/maturation)  Tomes’ process  stratum intermedium  papillary cells  amelogenins  enamelins  tuft protein  Cementum  socket/alveolus  cementocytes  cementoblasts  periodontal ligament  Sharpey’s fibers  oxytalan fibers  Dentin  odontoblasts  dentinal tubules  predentin  peritubular dentin  intertubular dentin  abacus bodies  apical foramen  Gingiva  gingival mucosa  masticatory mucosa  attachment epithelium  gingival sulcus  crevicular epithelium  periodontium