16. Question - Diagram the features seen in a histological section of thin skin. Discuss the structure and function of cells found in thin skin epidermis.
Keratinocytes are the population of cells that form in the basal layer and differentiate as they migrate to the surface and form keratin. Melanocytes (melanoblasts) are derived from neural crest and have many processes. They produce melanin pigment which is not stored but passed on to basal keratinocytes where it accumulates superficial to the nuclei. Langerhans cells belong to the system of mononuclear phagocytes (antigen-presenting cells) and participate in contact dermatitis.
17. Question - Describe the layers of thick skin epidermis.
Five layers are described in the epidermis of thick skin.
18. Question - Describe the layers of the dermis. What is a glomus (arteriovenous shunt)? Explain the innervation of skin.
Papillary dermis is a thin superficial layer that consists of fine collagen fibers (type I). It contains capillary loops that nourish the epidermis and many nerve endings. It continues around hair follicles as the connective tissue root sheath and around ducts of mammary glands as the intralobular connective tissue.
Reticular dermis forms the bulk of the dermis and consists of coarse collagen type I fibers. It contains blood vessel plexuses.
The glomus is an arteriovenous shunt that is surrounded by specialized contractile cells. It regulates the flow of blood to the periphery to help control body temperature.
Free nerve endings (not surrounded by Schwann cell) permeate the epidermis and are found in the dermis especially surrounding hair follicles. They serve multiple purposes; touch, cold, heat and pain. In thick skin they also end in relationship to Merkel's cells (small granule-containing cells in the stratum basale) thought to mediate touch.
Encapsulated ending found in the papillary dermis are Meissner's corpuscles and Ruffini endings. These are touch and mechanoreceptors.
Pacinian corpuscles are usually deep in the dermis and are pressure receptors.
19. Question - Make a line drawing illustrating the histology of the external ear (pinna).
20. Question - Make a line drawing illustrating the histology of the eyelid.
21. Question - Make a line drawing illustrating the histology of the mammary gland; lactating and inactive.
The mammary gland alveolus is large relative to serous acini elsewhere and its lumen is very evident often containing precipitated secretion. Its two major secretions, casein and fat, are secreted by different mechanisms, merocrine (exocytosis) and apocrine respectively. Vacuoles that are seen in these cells in H & E sections are where the fat droplets were stored. These are not fat cells.
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Last Revised: Wed, Jan 24, 2007