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Histology Fact Sheet: Skin

 

histology of skinFunctions of the Skin

The skin protects the body. The skin protects the body from water loss. The skin is involved in the production of vitamin D from precursors with the aid of sunlight. There are many sensory receptors in the skin: pain, pressure, fine touch. The skin is also involved in heat regulation.

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Types of Skin

Thick skin is found on the palms of the hand and the sole of the feet. Thin skin is found everywhere else.

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Layers of the Skin

The skin is composed of two layers: the epidermis and the dermis. Underneath these layers lies the hypodermis (subcutaneous tissue). The hypodermis is a layer of loose connective tissue.

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Histology of the Epidermis

The epidermis is formed by stratified squamous epithelium. Keratinization is seen in the epidermis. Keratinocytes, melanocytes Merkel cells and Langerhans cells are all found in the epidermis. The keratinocyte is the most abundant cell in the epidermis. The melanocyte produces melanin, which is responsible for skin pigmentation. The Merkel cell is a mechanoreceptor. The Langerhans cell is a phagocyte. Langerhans cells are macrophages seen in the skin.

The epidermis is divided into five layers: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum.

Stratum Basale

The stratum basale contains the dividing cells. This layer is also called the stratum germinativum.

Stratum Spinosum

The stratum spinosum consists of a layer several cells deep. The cells have pointy or spiny processes on them.

Stratum Granulosum

The cells in the stratum granulosum contain keratohyaline granules.

Stratum Lucidum

The stratum lucidum is present only in thick skin.

Stratum Corneum

The stratum corneum is the outermost layer. It is also called the horny layer. The cells in this layer are essentially bags of keratin. They contain no nuclei or organelles.

Histology hint from Sarah Bellham: The epithelium is classified as "squamous" based on the cells of the surface layer.

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Histology of the Dermis

histology of skin

Beneath the epidermis is the dermis. The dermis is composed of a papillary layer and a reticular layer. The reticular layer of the dermis is made up of dense irregular connective tissue. Fibroblasts are found in the dermis. Fibroblasts produces collagen.

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Histology of the Subcutaneous Layer

The subcutaneous tissue layer (hypodermis) is the loose connective tissue layer underneath the dermis.

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Receptors in the Skin

There are several different sensory receptors in the skin.

Ruffini endings, pacinian corpuscles, meissner's corpuscles, and merkel cells are all encapsulated sensory receptors. Free nerve endings are not encapsulated.

The most abundant sensory receptor are the free nerve endings. Free nerve endings respond to pain and temperature. Ruffini's corpuscles respond to continuous pressure. Pacinian corpuscles respond to vibration and rapidly changing pressure. Krause's end bulbs are a receptor for fine touch which are located in mucous membranes and the tongue. Meissner's corpuscles are also a receptor for fine touch but they are located in the dermis. Pacinian corpuscles are pressure receptors in the skin.

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Skin Appendages

Sweat glands, hair, nails and sebaceous glands are all considered epidermal appendages.

fingernail for Histology - WorldNails

The lunula is the half moon shaped white area on a nail. The anatomical term for the cuticle is the eponychium. The matrix is the region of the nails where there are dividing cells and nail growth. The nail plate rests on the nail bed. The nail root is the proximal portion of the nail that is underneath skin.

Ceruminous Glands

The ceruminous glands of the ear are apocrine sweat glands.

Glands of Moll

The glands of Moll in the eyelid are apocrine sweat glands.

Histology of Sweat Glands

Sweat gland are also called sudoriferous glands.

Classification of Sweat Glands

Sweat glands are divided into apocrine and eccrine. Apocrine sweat glands are found on the areola, external genitalia, axilla, and curcumanal region. Eccrine sweat glands are distributed over most of the body.

Innervation of Sweat Glands

Eccrine sweat glands are innervated by the sympathetic nervous system. The neurotransmitter for the eccrine sweat glands is acetylcholine. Thus, it is cholinergic.

Histology hint from Sarah Bellham: For most postganglionic sympathetic neurons, the neurotransmitter is
norepinephrine. Eccrine sweat glands are an exception to this generalization, as the innervation for eccrine sweat glands is cholinergic sympathetic.

Apocrine sweat glands are innervated by the sympathetic nervous system. The neurotransmitter for the
apocrine sweat glands is norepinephrine. Thus, it is adrenergic.

histology of hairHair

Hair is present over most of the body. It is not found on the palms of the hand, soles of the feet, urogenital openings, and lips. Huxley's layer is a layer in the hair follicle. Henle's layer is a layer in the hair follicle.

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Sources:

Histology: A Text and Atlas
Michael H. Ross/Edward J. Reith