Question

What two layers make up the skin? What do we call the pigment-producing cells in our skin? List the five different strata of cells found in thick skin. Which layer contains cells that are dividing? Which layer is thickest? What type of protein fibers are present in the dermis? The hypodermis is primarily composed of what type of tissue? Identify ONE (1) way in which hair and nails are similar and ONE (1) way in which they differ. What role do sweat glands and sebaceous glands play in the skin? What vitamin do we begin making in our skin?

Answer 1

Skin is the outer most covering of our body,we can say largest organ of our body.It has 2 layers_outer epidermis and inner dermis.below dermis -layer of tissue is called as hypodermis.

epidermis is mainly a cellular layer.majority are keratinocytes_which have keratin filaments and they produce keratin.Other cells such as Melanocytes_melanin pigment producing cells are dendritic cells present in between keratinocytes.These cells synthesize melanin and transfer it to to the keratinocytes.one melanocyte for nearly 36 keratinocytes.No blood vessels,lymphatics or nerves present in this layer.other cells like langerhan cells_macrophages, and merkel cells_touch receptors.

Epidermis is divided into 5 strata_outer to inner is_stratum corneum(dead skin layer,here keratinocytes do not have nucleus)--stratum lucidum(this layer is present only over palms and soles making them thickest skin and provides strength)--stratum granulosum(pingment granules present inside the keratinocytes in this layer)--stratum spinosum(spine like projections over the hexagonal keratinocytes)--stratum basale(it is the inner most layer a single layer of tissues capable of dividing present here).stratum spinosum is the thickest layer of epidermis.

Dermis is more of a fibrous layer _collagen,elastc fibres & ground substances like mucopolysaccharides,chondritin sulphate,glycoproteins present here.Embeded nerves,blood vessels,lymphatics,muscles,pilosebaceous glabds,eccrine&apocrine glands present.Cellular contents -fibroblast,histiocytes,mast cells,langerhan cells.etc present.

hypodermis composed primarily of adipose tissues.fat cells are mainly present.

Both hair and nail are skin appendages but they are different in type of keratin present.hard keratin present in nails.and hair is a dermal appendage.

sweat glands secrete sweat.2 types of sweat glands_eccrine (duct opend directly on the skin surface)and apocrine glands(opens along with hair follicle).

Sebaceous glands produce sebum(waxy substance) generally present with hair follicles called pilosebaceous unit.It opens into upper hair follicle.

Both have excreatory function also helps in innate immunity.

Vitamin D formation starts in skin. It receives sunlight and converts 7 dehydrocholesterol into cholecalciferol(inactive form of vitaminD3),which is then converted into 25 hydroxy cholecalciferol in liver which is again converted into 1,25-dihydroxy cholecalciferol(active form of vitamin D3).