Anatomy & Physiology of Skin MCQs

Explanation: The correct order of epidermal layers from deepest to most superficial is: Stratum basale -single layer of mitotically active keratinocytes Stratum spinosum -cells with desmosomal "spines" Stratum granulosum- keratohyalin granules present Stratum corneum- outermost layer of dead, keratinized cells Epidermal layers (deep to superficial): S.basale : Stem cell layer, melanocytes, Merkel cells S.spinosum : Thickest living layer, Langerhans cells S.granulosum : Granular layer, barrier formation S.lucidum : Present only in thick skin (palms, soles) S.corneum : Anucleate keratinized layer providing protection

Tyrosinase is a copper dependent enzyme that catalyzes the conversion of L-tyrosine into L-DOPA, the rate-limiting stage in melanin synthesis. Reference: Rooks textbook of dermatology, 9 th edition, chapter 88, page 5

The basal layer is the mitotically active layer, divides to give rise to outer population of cells that constitutes the spinous layer. These two epidermal layers together are referred to as the Malpighian layer. Reference: Rooks textbook of dermatology 9th edition, chapter 2, page 5

During development of the epidermis, first layer to form is S. Basale and subsequently, layers form from below upwards. Thus, stratum corneum is the last layer to develop and is underdeveloped (only 2-3 layers) in preterm/ very low birth weight (VLBW) infants in initial one week. In these babies, stratum corneum is thin and permeable, leading to more fluid/heat losses. It becomes similar to the adult and full term infant after 2 to 3 weeks postnatal maturation. Reference: Rooks textbook of dermatology 9th edition, chapter 2, page 7

Odland bodies/lamellar bodies/membrane-coating granules, are present in the stratum granulosum. They contain lipids/sterols and discharge lipid components into the intercellular space that play the role of intercellular cement in the stratum corneum and perform the barrier function. Reference: Rook's Textbook of Dermatology, 9th Edition, Page Number-7.

In palm and soles, stratum lucidum is sandwiched between the granulosum and corneum. These cells are nucleated and are referred to as 'transitional' cells. Eleidin granules are present in this layer. Their refractile nature gives this layer a translucent appearance, because of which it is also called as clear cell layer. Reference: Rooks textbook of dermatology 9th edition, chapter 2, page 7

Stratum corneum, outermost layer, consists of cells without the nucleus and hence it is dead layer This layer functions as a mechanical barrier and prevents the entry of microbes/allergens/irritants from the environment into the body as well as prevents loss of fluids/electrolytes from the body. As keratinocytes divide and move up to the stratum corneum from stratum basale, they undergo the following changes: Loss of nucleus and ability to divide Increase in size Flattening of cells Dehydration of cell Focussed metabolic activity Reference: Rooks textbook of dermatology 9th edition, chapter 2, page 1

MelanoCytes originate from neural crest and are present in the stratum basale. They produce melanin and transfer to keratinocytes. Epidermal Melanin unit : Ratio of 1:36 (melanocyte : keratinocyte) Reference: Rooks textbook of dermatology 9th edition, chapter 2, page 1