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1 Describe the different types of layer formed during the embryological development of human skin, and name the dendritic cells found within the epidermis.
Answer: The three main layers formed during embryological development are the ectoderm, which gives rise to the epidermis and associated appendages. This sits on the mesoderm, which produces the mesenchymal cells of the dermis and subcutis. Finally, there is the periderm, which develops later within the epidermal tissue and eventually gives rise to the granular cell layer. The dendritic cells found within the epidermis include the melanocyte and the Langerhans cells.
2 Describe the constituents that make up the structural components (layers) of the epidermis and basement membrane zone.
Answer: The epidermis is composed of five layers of cells, which can only be distinguished effectively using high-power light microscopy, or, better still, electron microscopy. These layers from the basement membrane upwards include the stratum basalis or germinativum, stratum spinosum, stratum granulosum, stratum lucidum and finally the stratum corneum. The basement membrane is composed of three main structural networks, the hemidesmosome and anchoring filaments, the basement membrane proper, and the mooring and supportive anchoring fibrils.
3 Describe the structures and functions of the components of the pilosebaceous unit.
Answer: The pilosebaceous unit is composed of the hair, the hair follicle and associated sebaceous gland. The main function of the pilosebaceous unit is thermoregulatory control. The arrector pili muscle attaches to the hair follicle shaft and can raise the hair to trap warm air close to the skin when the body surface is cold; conversely, it can pull the hair flat when the body needs to lose heat. The sebaceous glands produce sebum in the form of sweat to cool the surface of the skin when hot.
4 Describe the corpuscles found within skin. What are their functional roles?
Answer: The main corpuscles or mechanoreceptors of the skin include the Meissner corpuscle, which is the receptor that responds to touch. The other main mechanoreceptor is the Pacinian corpuscle, which reacts to vibration and pressure stimuli. There are three other types: the Ruffini, Krause and genital corpuscles. The distribution of these corpuscles does vary throughout the skin depending on anatomical site.
5 Describe the use of antibodies to evaluate normal and pathological breast tissue.
Answer: The range of markers used to evaluate breast tissue is extensive. Broadly speaking, luminal cells express cytokeratins of molecular weight 7, 8, 18 and 19; myoepithelial cells express lower molecular weight cytokeratins, which include 5/6, 14 and 17. In addition, myoepithelial cells will be positive for S100, smooth muscle actin, calponin and CD10. The basal lamina is positive for collagen type IV and also laminin.