Epidermis of skin : microscopic and clinical anatomy

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Epidermis of skin : microscopic and clinical anatomy 

Skin : It has two  layers  

1.      Epidermis

2.     Dermis

Sometimes, hypodermis consider as third layer of skin contain subcutaneous fat.

Epidermis

It  is the superficial layer of skin which is formed by  keratinized stratified squamous epithelium.

Cells of epidermis:  It is composed of four cell types:

1.      Keratinocytes,

2.     Melanocytes,

3.     Langerhans cells, and

4.     Merkel cells.

The keratinocytes are arranged in five layers, and the remaining three cell types are interspersed between them .

 Five layers of the epidermis: deep to superficial

1. Stratum Basale :

A single layer of cuboidal to columnar cells that stand on the basement membrane. This is a region of cell division.

It also contains melanocytes and Merkel cells.

2. Stratum Spinosum: it is composed by many layers of polyhedral prickle cells bearing intercellular bridges. Mitotic activity is also present.

It also contains Langerhans cells and processes of melanocytes.

3. Stratum Granulosum : it is composed by flattened cells which contain keratohyalin granules.

It is absent as a distinct layer in thin skin.

4. Stratum Lucidum A thin, translucent layer that is also absent in thin skin.

5. Stratum Corneum it is composed of squamous cells packed with keratin. Superfi cial squamous cells  are desquamated.

 

        Location of skin cells and functions

Difference between location, functions & development of different skin cells

Cells of skin	Location	Functions	Development
Keratinocytes	New skin cells develop at the bottom layer of your epidermis (stratum basale) and travel up through the other layers as they get older.	It forms barrier against environmental damage by heat, UV radiation, dehydration, pathogenic bacteria, fungi, parasites, and viruses.	Surface ectoderm
Melanocytes	Stratum basale	Melanocytes are well known for their role in skin pigmentation, and their ability to produce and distribute melanin has been studied extensively	Neural crest
Langerhans cells	Stratum spinosum	These cells act as the outermost guard of the cutaneous immune system and are likely to induce the first reactions against pathogens encountered via the skin	Fetal Langerhans cells from Primitive yolk sac in fetal life , in adult Langerhans cells  from fetal monocytes
Merkel cells	Stratum basale	It is also known as tactile epithelial cells, which is an  oval-shaped mechanoreceptors essential for light touch sensation	Surface ectoderm

Keratinocytes, reach the outermost layer of your epidermis after about a month, where the skin cells shed from your body as new cells develop at the bottom layer.

Albinism

 It is a congenital disorder characterized by the complete or partial absence of melanin pigmentation in the skin, hair,  iris of eye, and eyelashes.

 It is an autosomal recessive/X -linked disorder. 

 Although the melanocytes are present, but genetic mutation results in lack of tyrosinase enzyme, which catalyzes the production of melanin from tyrosine.

People with albinism have skin that is very sensitive to light and sun. Sunburn is one of the most serious complications of albinism.

This allows light to shine through the irises and makes the eyes extremely sensitive to bright light.

Vitiligo

 It is s a clinical condition with presence of spots without melanin in the skin, which occurs due to partial or complete absence of melanocytes.