Skin

The outer covering of the body that protects it from the environment.

PubMed Health Glossary
(Source: NIH - National Library of Medicine)

How Does the Skin Work?

The skin is one of our body's heaviest and largest organs. Depending on body size and mass, it weighs between 3.5 and 10 kilos (7.5 and 22 pounds) and is 1.5 to 2 m2 in size.

The skin protects the body from harmful environmental factors such as dampness, cold and sunlight, but also from germs and harmful substances. It plays an important role in regulating body temperature. It is through our skin that we pick up sensory information: this is how we feel heat, cold, pressure, itchiness or pain. Some of this information triggers a reflex. For example, we automatically pull our hand back if we accidentally touch a hot burner on the stove.

The body can store water or deposit fat and products of metabolism in the skin. This is also the place where essential vitamin D is produced with the help of sunlight. Many health conditions lead to a change in skin color or structure. People with too few red... Read more about the Skin

Terms to know

Arteries
A blood vessel that carries blood from the heart to tissues and organs in the body.
Basal Cells
A small, round cell found in the lower part (or base) of the epidermis, the outer layer of the skin.
Blood Vessels
Tubes that carry blood to and from all parts of the body. The three main types of blood vessels are arteries, capillaries, and veins.
Body Fat
Excess calories are stored as body fat, providing the body with a reserve supply of energy and other functions.
Body Membrane
A very thin layer of tissue that covers a surface.
Dermis
The inner layer of the two main layers of the skin. The dermis has connective tissue, blood vessels, oil and sweat glands, nerves, hair follicles, and other structures. It is made up of a thin upper layer called the papillary dermis, and a thick lower layer called the reticular dermis.
Epidermis
The outer layer of the two main layers of the skin.
Hair Follicle
The hair follicle is a tube-shaped sheath that surrounds the part of the hair that is under the skin and nourishes the hair.
Hair Shaft
The segment of the hair that projects above the skin surface.
Lymphatic Vessels
A thin tube that carries lymph (lymphatic fluid) and white blood cells through the lymphatic system. Also called lymph vessel.
Melanin
A pigment that gives color to skin and eyes and helps protect it from damage by ultraviolet light.
Melanocytes
A cell in the skin and eyes that produces and contains the pigment called melanin.
Nerves
A bundle of fibers that receives and sends messages between the body and the brain. The messages are sent by chemical and electrical changes in the cells that make up the nerves.
Papillary Dermis
The thin top layer of the dermis (the inner layer of the skin). The papillary dermis has connective tissue and blood vessels that give nutrients to the epidermis (the outer layer of the skin) and that help control the temperature of the skin.
Percutaneous
Passing through the skin, as an injection or a topical medicine.
Pores in the Skin
A tiny opening in the skin.
Reticular Dermis
The thick bottom layer of the dermis (the inner layer of the skin). The reticular dermis has blood vessels and connective tissue that supports the skin. Hair follicles, oil and sweat glands, and other structures are also found in the reticular dermis.
Sebaceous Glands (Oil Glands)
Small glands located within the epidermis, and associated with the hair follicle, that produce and secrete an oily substance that lubricates the skin and hair.
Sebum (Oil)
An oily substance produced by certain glands in the skin.
Squamous Cells
Flat cell that looks like a fish scale under a microscope. These cells cover inside and outside surfaces of the body. They are found in the tissues that form the surface of the skin, the lining of the hollow organs of the body (such as the bladder, kidney, and uterus), and the passages of the respiratory and digestive tracts.
Subcutaneous
Beneath the skin.
Sweat Glands
The small coiled tubes in the skin that produce and secrete sweat.
Tissue
A group of cells that act together to carry out a specific function in the body. Examples include muscle tissue, nervous system tissue (including the brain, spinal cord, and nerves), and connective tissue (including ligaments, tendons, bones, and fat). Organs are made up of tissues.
Veins
Blood vessels that carry blood to the heart.

Terms to know

Arteries
A blood vessel that carries blood from the heart to tissues and organs in the body....
Basal Cells
A small, round cell found in the lower part (or base) of the epidermis, the outer layer of the skin....
Blood Vessels
Tubes that carry blood to and from all parts of the body. The three main types of blood vessels are arteries...
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