logo Structure and function key points test.

Introduction to dermatology

Structure and function key points test

Keratinised epidermis is derived from: *! Basal cell keratinocytes * Langerhans cells * Melanocytes * Fibroblasts Explanation: The epidermis is created by active proliferation of basal cell keratinocytes, which differentiate to produce squamous cells and their protective protein, keratin. Desmosomes are found in: *! Keratinocytes * Langerhans cells * Melanocytes * Fibroblasts Explanation: Desmosomes are the cellular structure responsible for adherence of keratinocytes within the epidermis. Hemidesmosomes bind the basal cells to the basement membrane. Antigen-presenting cells in the skin are known as: * Keratinocytes *! Langerhans cells * Melanocytes * Fibroblasts Explanation: Langerhans are modified macrophages that act as intraepidermal antigen presenting cells. Which of the following statements are correct: * Basement membrane zone is a communication channel between keratinocytes and Langerhans cells * Dermis is mainly composed of elastin * Subcutaneous tissue stores glycogen *! Appendages include hair, nails, sebaceous glands, eccrine and apocrine glands Explanation: Collagen makes up about 70% of the dry weight of the dermis, whereas elastic tissue only accounts for 2%. The basement membrane zone is a complex structure between keratinocytes and the dermis. Subcutaneous tissue stores fat in adipocytes. Epidermal appendages refer to the pilo-sebaceous unit and sweat apparatus. To protect against microbial attack, skin pH is: * 4.5 *! 5.5 * 6.5 * 7.5 Explanation: The pH of skin is 5.5 (the acid mantle). Arrange the parts of the body according to skin thickness with the thinnest first (1) and the thickest last (4). Mix and match: [table] Eyelid: 1 Forearm: 2 Upper back:3 Sole:4 Explanation: Eyelid is the area with the thinnest skin, then forearm and upper back. The sole is the thickest. Identify the layers of the skin Mix and match [table] epidermis :A basement membrane :B dermis :C subcutaneous tissue :D In normal skin, melanin is found in which layer of skin: *! Epidermis * Basement membrane zone * Dermis * Subcutaneous tissue Explanation: Melanin is formed in the basal layer of the epidermis. It does not occur deeper unless there has been injury to the basal layer (post-inflammatory pigmentation is dermal) or there is a compound or dermal melanocytic naevus. Melanin is increased by: # Corticosteroids #! Ultraviolet radiation # Zinc paste #! Pregnancy Explanation: Melanin pigmentation is promoted by ultraviolet radiation, hormones (MSH, ACTH, androgens, oestrogens, progesterones), inflammation and friction. It may be reduced by melatonin and corticosteroids. UV-induced pigmentation is blocked by sunscreens including zinc paste. Name the stage of the hair cycle Mix and match: [table] A:anagen B:catagen C:telogen Explanation: The growth phase of the hair cycle is known as anagen, and the resting phase is telogen (bulb hairs) with catagen as the in-between phase. Name the components of the nail apparatus Mix and match [table] A:hyponychium B:nail plate C:lateral nail fold D:nail bed E:lunula F:cuticle G:proximal nail fold H:matrix Match the cell with its function. Explanation: Keratinocytes produce the protein keratin but also lipids (for waterproofing and pliability) and cytokines for immune and wound healing functions. Langerhans cells are antigen presenting immune cells; melanocytes produce the pigment melanin to protect the skin from ultraviolet radiation injury; sebaceous glands are active post-puberty and produce a variety of lipids; eccrine glands produce a watery salt solution to cool the body by evaporation. Mix and match Keratinocytes:Produce protein, lipids, cytokines Melanocytes:Produce pigment Langerhans cells:Antigen-presenting cell Sebaceous glands:Produce phospholipids, cholesterol, triglycerides Eccrine glands:Produce water, sodium chloride, urea, ammonia, uric acid Eccrine glands: # Are rare in the axillae # Produce a hypertonic salt solution #! Are under hypothalamic control #! Increased production with heat, emotional stress and spicy foods Explanation: Eccrine sweat glands produce a hypotonic solution of water, sodium chloride, urea, ammonia and uric acid. They are most dense on palms, soles, axillae and forehead and are absent on the lips, labia minora, glans penis and prepuce. The glands are dermal structures under hypothalamic control. Sweat is produced in response to exercise and high temperature (internal or environmental) and reaches the skin surface via a coiled duct. Apocrine glands: # Produce hypotonic salt solution # Are common on the palms and soles #! Are active after puberty # Smell derived from nitrogenous waste products Explanation: Apocrine glands are found in axillae and perianal regions and become active after puberty. They produce a thick secretion that rapidly becomes colonised by bacteria resulting in characteristic body odour. The ducts open into the pilosebaceous follicle. Which of the following statements are true? * Water can permeate through intact epidermis to the dermis * The epidermis is significantly damaged by thermal injury at 39C *! Commensal organisms protect against pathogenic attack * The skin pH of 5.5 encourages bacterial colonisation Explanation: Epidermis is water resistant and cannot permeate to the dermis. It is injured by contact with temperatures greater than 41C but not by 39C. Commensal organisms protect to a degree against pathogenic attack. The skin pH of 5.5 discourages bacterial colonisation. Which of the following statements are true? *! Melanin is found throughout the epidermis in black skin * Continuous sweating is necessary to prevent the skin drying out * Goose bumps occur to protect the hairs from cold * Apocrine gland secretion prevents overheating Explanation: Melanin is found throughout the epidermis in black skin, within keratinocytes. Sweating is intermittent. Goose bumps (contraction of arrector pili) produces heat to protect the body rather than hairs (these are resistant to cold injury). Eccrine gland secretion prevents overheating whereas apocrine gland secretion appears to have a sexual function.