What is a stratum of the skin?

Answer 1

As best I can tell it seems to be a typo or OCR error for "stratum corneum," which is the outermost layer of skin cells.

Answer 2

There are 3 layers of skin named: the epidermis, dermis, and subcutaneous tissue.

1. Epidermis

The epidermis is composed of 4 or 5 layers depending on the region of skin being considered. Those layers in descending order are:

• cornified layer (stratum corneum):

The top layer of the epidermis, the stratum corneum, is made of dead, flat skin cells that shed about every 2 weeks. It is Composed of 10 to 30 layers of polyhedral, anucleated corneocytes (final step of keratinocyte differentiation), with the palmsand soles having the most layers. Corneocytes are surrounded by a protein envelope (cornified envelope proteins), filled with water-retaining keratin proteins, attached together through corneodesmosomes and surrounded in the extracellularspace by stacked layers of lipids. Most of the barrier functions of the epidermis localize to this layer.

• clear/translucent layer (stratum lucidum): only in palms and soles
• granular layer (stratum granulosum): Keratinocytes lost their nuclei and their cytoplasm appears granular. Lipids, contained into those keratinocytes withinlamellar bodies, are released into the extracellular space through exocytosis to form a lipid barrier. Those polar lipids are then converted into non-polar lipids and arranged parallel to the cell surface. For example glycosphingolipids becomeceramides and phospholipids become free fatty acids.

• spinous layer (stratum spinosum): Keratinocytes become connected through desmosomes and start produce lamellar bodies, from within the Golgi, enriched in polar lipids, glycosphingolipids, free sterols,phospholipids and catabolic enzymes.Langerhans cells, immunologically active cells, are located in the middle of this layer.

• basal/germinal layer (stratum basale/germinativum): The bottom layer of epidermis, the stratum basale, has cells that are shaped like columns. In this layer the cells divide and push already formed cells into higher layers. As the cells move into the higher layers, they flatten and eventually die. it is mainly composed up of proliferating and non-proliferating keratinocytes, attached to the basement membrane by hemidesmosomes. Melanocytes are present, connected to numerous keratinocytes in this and other strata through dendrites. Merkel cells are also found in the stratum basale with large numbers in touch-sensitive sites such as the fingertips and lips. They are closely associated with cutaneous nerves and seem to be involved in light touch sensation.

The epidermis is separated from the dermis, its underlying tissue, by a basement membrane.
2. Dermis:

The dermis also varies in thickness depending on the location of the skin. It is .3 mm on the eyelid and 3.0 mm on the back. The dermis is composed of three types of tissue that are present throughout - not in layers. The types of tissue are:

• collagen
• elastic tissue
• reticular fibers
• Layers of the Dermis

The two layers of the dermis are the papillary and reticular layers.

• The upper, papillary layer, contains a thin arrangement of collagen fibers.
• The lower, reticular layer, is thicker and made of thick collagen fibers that are arranged parallel to the surface of the skin.

Specialized Dermal Cells

The dermis contains many specialized cells and structures.

• The hair follicles are situated here with the erector pili muscle that attaches to each follicle.
• Sebaceous (oil) glands and apocrine (scent) glands are associated with the follicle.
• This layer also contains eccrine (sweat) glands, but they are not associated with hair follicles.
• Blood vessels and nerves course through this layer. The nerves transmit sensations of pain, itch, and temperature.
• There are also specialized nerve cells called Meissner's and Vater-Pacini corpuscles that transmit the sensations of touch and pressure.

3. Subcutaneous TissueThe subcutaneous tissue is a layer of fat and connective tissue that houses larger blood vessels and nerves. This layer is important is the regulation of temperature of the skin itself and the body. The size of this layer varies throughout the body and from person to person.

The skin is a complicated structure with many functions. If any of the structures in the skin are not working properly, a rash or abnormal sensation is the result. The whole specialty of dermatology is devoted to understanding the skin, what can go wrong, and what to do if something does go wrong.