Slides of Skin and Tongue
Thick skin, to be compared with the next slide (thin skin) for thickness of epidermis. Notice also in each slide a duct of sweat gland going down through the dermis.
Thin skin at the same magnification as previous slide. The sweat duct in this case is clearly ending at its coiled secretory portion. Hypodermis in both slides is just beginning at the bottom of the pictures, where you begin to see some fat cells.
Thick skin showing epithelial detail. Cornified (keratinized) stratified squamous epithelium makes up the epidermis. The stratum granulosum is very dark; the stratum lucidum is bright red. The stratum corneum is thick, and very pale.
Detail of epithelium of thick skin from the superficial to deep:
- pale stratum corneum
- bright red stratum lucidum
- purple stratum granulosum
- stratum spinosum
Note the basophilic, keratohyaline granules in the stratum granulosum; their presence indicates that the cells in this layer are beginning to die
Stratum spinosum showing "prickle" appearance of cell contacts. (The cells of this layer are often called "prickle cells".) The cross-lines were once thought to be intercellular bridges.
EM detail of "prickle cell" contact, showing the presence of many desmosomes between cells (arrows). The little fibrillar strands lying in the cytoplasm and inserting on the desmosomes are tonofilaments (F). The cell membranes of the two cells are repeatedly interdigitated, giving the appearance of "intercellular bridges" in light microscopy.
Detail of epithelium of thin skin, showing melanin in the basal layer. The pigment is produced by stellate shaped melanocytes of the dermal layer and then deposited in the basal cells of the epidermis. Melanocytes are of neural crest origin and have to be specifically stained in order to be seen.
Thin skin showing epithelial detail. This is also cornified stratified squamous, but thinner. The granulosum is only about one cell layer thick and is the darkest layer here. There is no stratum lucidum.
Detail of thin skin epithelium. A single layer of dark purple granulosum lies under the rather shredded stratum corneum. The stratum corneum typically sloughs off with wear. Stratum spinosum is at the bottom of the picture.
The next few pictures are various views of sweat glands. This one shows a long straight sweat duct heading down through the dermis. Its epithelial lining is continuous with the basal cells of the epidermal epithelium.
The secretory portions of several sweat glands lie in clusters among the fat cells of the hypodermis, low in the picture. (A bedraggled, shrunken Pacinian corpuscle is in the same area, just left of center.) Sweat glands are simple coiled tubules, so we see many cross-cuts of the coil in a section like this. These are the true (eccrine) sweat g lands of skin and therefore secrete their watery (serous) fluid by merocrine secretion. (Some of the very large sweat glands of the axillary and pubic regions are thought to use apocrine secretion, pinching off small bits of cell cytoplasm or membrane along with the secretory product.) While looking at this picture, note the very dense, irregular connective tissue of the dermis. Right under the epidermis notice a brighter, clearer, quite narrow, pink layer of dermis; this is the papillary layer of the dermis and it forms the dermal papillae which extend up into irregularities of the basal layer of the epidermis, bringing capillary loops and nerve endings closer to the epithelial cells an d to the surface. The bulk of the dermis, below this thinner layer, is the reticular layer; it is more heavily fibrous, with many elastic fibers running among the more numerous collagen fibers. The hypodermis begins with the fat cells.
Detail of sweat duct originating (at lower left) from the basal layer of the epidermal epithelium.
Detail of sweat duct coiling throughout the stratum corneum to the surface of the skin. Since cells are dead here, there is no longer a living duct lining; just the tunneling of its lumen remains.
Detail of sweat gland. The darker circles in the lower part of the field are ducts; the lighter cross-cuts above are the secretory portions.
Three-dimensional drawing of dark, spidery myoepithelial cells surrounding sweat gland tubule. By contracting, they help to squeeze out the secretion.
Detail of myoepithelial cell processes as seen in H&E section. Look at the large tubule on the left for pink "hoops" that seem to be extending from the basement membrane of the upper row of epithelium toward the secretory cell nuclei which lie near the lumen. These "hoops" are the cytoplasmic extensions of the stellate myoepithelial cells. Thes e cells lie within the basal lamina of the tubule.
Detail of Pacinian corpuscle. Note the onion-like layers of the specialized capsule. The nerve ending itself is buried in the center (which looks pink here). The cell body for this dendritic ending lies in a spinal ganglion related to this particular dermatome of skin.
Whole mount of a Pacinian corpuscle, to give a more three-dimensional view. The dendritic ending is the darker "rod" in the middle.
Section of thick skin, as of finger tip. Projections of pale-staining dermal connective tissue push up into the bottom layers of the darker staining epithelium, carrying capillaries and nerve endings with them. In the projection on the farthest left, you can see an encapsulated Meissner's corpuscle, a sensory receptor ending for touch. Speciali zed connective tissue cell nuclei can be seen running in a circular direction around the corpuscle. The cell body for this ending lies in a spinal ganglion related to this particular dermatome of skin. (NOTE: In the stratum granulosum of this epidermis, the cells are stained dark purple.)
Detail of Meissner's corpuscle lying in dermal papilla. The arrows point to nuclei of the specialized connective tissue sheath that surrounds the dendritic ending that is twining around inside, among the sheath cells. Silver stain would make the ending visible. You get the feeling that this corpuscle has some substance to it, i.e. that you coul d shell it out as a more or less solid unit, from the surrounding loose areolar connective tissue.
Hair follicles of scalp, with associated pale sebaceous glands. The follicles extend down into the hypodermis, which is largely adipose tissue. Notice the arrector pili muscle running diagonally toward the upper right-hand corner of the field. Its lower end would at some point attach to the follicle sheath.
Cross-sections of many hair follicles. The yellow centers are the hairs themselves. The surrounding pink cellular sheaths are continuous with the surface epithelium of the skin. A clear pink connective tissue sheath lies outside the epithelial sheath. The fat cells of the hypodermis surround the follicles.
Overview of the scalp, again showing collagen fibers of dense irregular c.t. clearly. A sweat gland duct is extending down from the surface epithelium near the top center of the field. At the extreme right, a hair is seen extending from the top of a follicle, and pale sebaceous glands are emptying into the follicle lower down.
Detail of sebaceous gland. Cells look foamy because of loss of lipid droplets during tissue fixation. This gland exhibits holocrine secretion, in which whole cells swell up, degenerate, and are desquamated as part of the oily secretion (sebum). The secretion is emptied into the hair follicles and eventually reaches the surface of the skin.
View of tongue, showing location of papillae. Most of the surface of the human tongue is covered with filiform papillae, with some fungiform papillae interspersed. A row of circumvallate papillae lie toward the back of the tongue. The lymphoid tissue labelled is lingual tonsil.
Cut-away section of tongue to show three-dimensional view of papillae and underlying c.t. and muscle.
Section of surface of tongue, showing one rather tangentially cut fungiform papilla at the left and some filiform papillae with sharp, semicornified tips at the right. Cornification is less extensive in human tongue than in cats, dogs, etc.
Higher magnification of tongue surface, showing two filiform papillae. They are obviously extensions of stratified squamous epithelium.
View of foliate papillae, typical of rabbit and some other animals. These have a characteristic 3-pronged connective tissue pattern extending up into the papilla, and there are taste buds on the outside walls. Notice the bundles of skeletal muscle down below.
Detail of skeletal muscle and secretory glands of the body of the tongue. Mucous cells are to the left, with their flattened, basal nuclei, while serous cells are in the center and to the right, with their round nuclei.
Section of tongue through circumvallate papilla. Notice glands immediately below it; also the interlacing skeletal muscle strands deeper in the section.
Detail of circumvallate papilla, showing pale taste buds opening into the lumen of the furrow that surrounds the papilla.
Higher magnification of taste buds (from the foliate papillae of rabbit in this case). In the lower buds note surface pores through which salivary fluids in the lumen of the furrow reach sensory nerve endings within the taste bud capsule. The cell bodies for these dendritic endings are pseudounipolar and lie within the sensory ganglion of a cran ial nerve (such as Nerve VII).
