I have always found the Human body amazing but the skin and what it does, is one of the most amazing feats of engineering, so i thought i would bore the pants of everyone (lol only joking) and explain why its so amazing.
Our skin is part of the Integumentary System, which also comprises of our Nails, Hair, Sweat and Sebaceous glands. Our skin is the largest and the heaviest organ in our bodies— it covers approx 1.7 to 1.9 square metres, and weighs 2.3 to 3.2 kilos which is about 16% of an adult’s total body weight (Silverthorn, 2004)! Our skin is made up of about 20% water and is at its thinnest on the eyelids where it is 0.04mm thick and at its thickest on the soles of our feet at 6mm thick. Over the rest of the body the skin is generally about 0.1mm thick.
The skin is also our interface with the rest of the world—it’s the first thing that another person might notice about us. The numerous essential functions of the skin make it extremely important to maintain the health of this large organ.
The skin protects our body from the environment, including from ultra-violet radiation and certain microorganisms. The skin also regulates our internal temperature, excretes waste, guards against dehydration, and aids in the production of vitamin D. With its many sense receptors, the skin also allows us to feel and sense what is going on in our external environment. You can use the Acronym PASTES to help you remember the functions of the skin.
Protection: The Skin Protects the moist, warm, internal environment from the dangers of the external environment in which we live.
- The Acid Mantle on the surface keeps the skin supple and provides a waterproof barrier to prevent the entry pf Pathogens and Dehydration.
- Melanin cells absorb UV Rays
- Connective tissues cushion and protect the underlying organs.
(Interesting Fact about the Acid Mantle: This is a protective layer on the surface of the epidermis. It comprises of a mixture of Sebum, Dead Skin Cells & Sweat).
Absorption: There is limited permeability through the skin but it can absorb certain substances, eg drugs.
Sensory Organ: Nerve endings in the dermis relay sensations of pain, pressure, heat, cold and touch. These inform the Central Nervous System of changes in the external environment.
Temperature Regulation: Assists to keep the skin at a temperature of 37oC/ 98.6oF through vasodilation and Vasoconstriction.
Excretion: Sweat removes limited amounts of waste, eg Urea, Uric acid and ammonia.
Synthesis of Vitamin D: Certain fatty substances in the skin are converted into Vitamin D by Ultra Violet (UV).
Within the skin, there are three main layers:
The epidermis is the outer layer of the skin. It contains no blood vessels, all nutrients must pass from the blood vessels in the dermis and be transported from there to the epidermis. The layers of the epidermis are;
- Stratum corneum
- Stratum lucidum
- Stratum granulosum
- Stratum spinosum
- Stratum germinatum
The dermis contains connective tissue (tissue that connects, supports, or surrounds other tissues and organs); sweat glands that secrete a salty fluid to cool the body off; hair follicles; sebaceous glands that secrete sebum, a fatty mixture that is meant to lubricate the skin and hair; muscles that pull the hair follicles into a vertical position to create goose bumps; nerve endings that monitor the external environment; and blood vessels.
The Dermis has 2 layers:
A superficial papillary layer consisting of loose connective tissue (collagen and elastin), Small finger like projections extend into the epidermis to feed and nourish the tissue through an extensive capillary network.
The Deep reticular layer, consists of dense connective tissue:
- Collagen; A major constituent of the dermis and an important structural protein in the body. These wavy white fibres are arranged in an intricate network giving strength. It also resists stretching. It is collagen that makes meat tough.
- Elastin; Also a protein, it Consists of yellow fibres, which provide flexibility. Once stretched these fibres have the ability to snap back to there normal shape.
Other Structures in the Dermis are:
- Blood Vessels
- Lymphatic Vessels
- Nerves: Sensory for tactile sensation & Motor for Muscular Tissue
- Sweat Glands: These help regulate the body temperature by excreting excess water. This evaporates, releasing heat off the surface of the body. There are 2 types.
A) Eccrine Glands; These tiny coiled tubes extend up through the skin and open onto the surface. They are found all over the body. Their function is to regulate body temperature and eliminate waste materials.
B) Apocrine Glands; These glands secrete into hair follicles and are found in the greatest numbers under the arms and groin. They develop and become active at puberty. The glands produce thick sticky secretion. the odour only becomes unpleasant when bacteria multiply and decompose the sweat.
5. Sebaceous Glands; These are found all over the skin. Most open into hair follicles via little ducts. They are found in their greatest numbers on the scalp, face & back. The glands secrete an oily substance called sebum which contains waxes, fatty acids, cholesterol and dead cells. Sebum keeps the hair soft and the skin moist. it also provides an oily film that retards water loss from the surface of the skin and inhibits the growth of certain bacteria.
The Hypodermis or subcutaneous: This layer is structurally unique, The fat cells are organised into chambers that are surrounded by strands of connective tissue. Its main purpose is to insulate and protect the internal organs. The subcutaneous layer is composed of adipose tissue, areolar tissue, blood, lymph and nerve endings. Below the subcutaneous layer is the sub-dermal layer. This layer allows the skin to move freely over the muscular tissue beneath it.