Your skin is your body’s largest organ. It covers and protects your body. Your skin holds body fluids in, preventing dehydration Keeps harmful microbes out, preventing infections. Helps you feel things like heat, cold, and pain. Keeps your body temperature even. etc.
Summary
Your skin is your body’s largest organ. It covers and protects your body. Your skin
- Holds body fluids in, preventing dehydration
- Keeps harmful microbes out, preventing infections
- Helps you feel things like heat, cold, and pain
- Keeps your body temperature even
- Makes vitamin D when the sun shines on it
Epidermis
The epidermis is the outermost layer of the skin, and protects the body from the environment. The thickness of the epidermis varies in different types of skin; it is only .05 mm thick on the eyelids, and is 1.5 mm thick on the palms and the soles of the feet. The epidermis contains the melanocytes (the cells in which melanoma develops), the Langerhans’ cells (involved in the immune system in the skin), Merkel cells and sensory nerves. The epidermis layer itself is made up of five sublayers that work together to continually rebuild the surface of the skin:
The blood vessels supply nutrients and oxygen to the skin and take away cell waste and cell products. The blood vessels also transport the vitamin D produced in the skin back to the rest of the body.
The lymph vessels bathe the tissues of the skin with lymph, a milky substance that contains the infection-fighting cells of the immune system. These cells work to destroy any infection or invading organisms as the lymph circulates to the lymph nodes.
The hair follicle is a tube-shaped sheath that surrounds the part of the hair that is under the skin and nourishes the hair.
- Apocrine glands are specialized sweat glands that can be found only in the armpits and pubic region. These glands secrete a milky sweat that encourages the growth of the bacteria responsible for body odor.
- Eccrine glands are the true sweat glands. Found over the entire body, these glands regulate body temperature by bringing water via the pores to the surface of the skin, where it evaporates and reduces skin temperature. These glands can produce up to two liters of sweat an hour, however, they secrete mostly water, which doesn’t encourage the growth of odor-producing bacteria.
The lymph vessels bathe the tissues of the skin with lymph, a milky substance that contains the infection-fighting cells of the immune system. These cells work to destroy any infection or invading organisms as the lymph circulates to the lymph nodes.
Sebaceous, or oil, glands, are attached to hair follicles and can be found everywhere on the body except for the palms of the hands and the soles of the feet. These glands secrete oil that helps keep the skin smooth and supple. The oil also helps keep skin waterproof and protects against an overgrowth of bacteria and fungi on the skin.
The dermis layer also contains pain and touch receptors that transmit sensations of pain, itch, pressure and information regarding temperature to the brain for interpretation. If necessary, shivering (involuntary contraction and relaxation of muscles) is triggered, generating body heat.
The dermis is held together by a protein called collagen, made by fibroblasts. Fibroblasts are skin cells that give the skin its strength and resilience. Collagen is a tough, insoluble protein found throughout the body in the connective tissues that hold muscles and organs in place. In the skin, collagen supports the epidermis, lending it its durability. Elastin, a similar protein, is the substance that allows the skin to spring back into place when stretched and keeps the skin flexible.
- The Papillary Layer: The upper, papillary layer, contains a thin arrangement of collagen fibers. The papillary layer supplies nutrients to select layers of the epidermis and regulates temperature. Both of these functions are accomplished with a thin, extensive vascular system that operates similarly to other vascular systems in the body. Constriction and expansion control the amount of blood that flows through the skin and dictate whether body heat is dispelled when the skin is hot or conserved when it is cold.
- The Reticular Layer: The lower, reticular layer, is thicker and made of thick collagen fibers that are arranged in parallel to the surface of the skin. The reticular layer is denser than the papillary dermis, and it strengthens the skin, providing structure and elasticity. It also supports other components of the skin, such as hair follicles, sweat glands, and sebaceous glands.
The lymph vessels bathe the tissues of the skin with lymph, a milky substance that contains the infection-fighting cells of the immune system. These cells work to destroy any infection or invading organisms as the lymph circulates to the lymph nodes.
The Dermis
The dermis is located beneath the epidermis and is the thickest of the three layers of the skin (1.5 to 4 mm thick), making up approximately 90 percent of the thickness of the skin. The main functions of the dermis are to regulate temperature and to supply the epidermis with nutrient-saturated blood. Much of the body’s water supply is stored within the dermis. This layer contains most of the skins’ specialized cells and structures, including:
The basal cell layer contains cells called melanocytes. Melanocytes produce the skin coloring or pigment known as melanin, which gives skin its tan or brown color and helps protect the deeper layers of the skin from the harmful effects of the sun. Sun exposure causes melanocytes to increase production of melanin in order to protect the skin from damaging ultraviolet rays, producing a suntan. Patches of melanin in the skin cause birthmarks, freckles and age spots. Melanoma develops when melanocytes undergo malignant transformation.
The basal cell layer contains cells called melanocytes. Melanocytes produce the skin coloring or pigment known as melanin, which gives skin its tan or brown color and helps protect the deeper layers of the skin from the harmful effects of the sun. Sun exposure causes melanocytes to increase production of melanin in order to protect the skin from damaging ultraviolet rays, producing a suntan. Patches of melanin in the skin cause birthmarks, freckles and age spots. Melanoma develops when melanocytes undergo malignant transformation.
Merkel cells, which are tactile cells of neuroectodermal origin, are also located in the basal layer of the epidermis.
The squamous cell layer is located above the basal layer, and is also known as the stratum spinosum or “spiny layer” due to the fact that the cells are held together with spiny projections. Within this layer are the basal cells that have been pushed upward, however these maturing cells are now called squamous cells, or keratinocytes. Keratinocytes produce keratin, a tough, protective protein that makes up the majority of the structure of the skin, hair, and nails.
The squamous cell layer is the thickest layer of the epidermis, and is involved in the transfer of certain substances in and out of the body. The squamous cell layer also contains cells called Langerhans cells. These cells attach themselves to antigens that invade damaged skin and alert the immune system to their presence.
The keratinocytes from the squamous layer are then pushed up through two thin epidermal layers called the stratum granulosum and the stratum lucidum. As these cells move further towards the surface of the skin, they get bigger and flatter and adhere together, and then eventually become dehydrated and die. This process results in the cells fusing together into layers of tough, durable material, which continue to migrate up to the surface of the skin
The stratum corneum is the outermost layer of the epidermis, and is made up of 10 to 30 thin layers of continually shedding, dead keratinocytes. The stratum corneum is also known as the “horny layer,” because its cells are toughened like an animal’s horn. As the outermost cells age and wear down, they are replaced by new layers of strong, long-wearing cells. The stratum corneum is sloughed off continually as new cells take its place, but this shedding process slows down with age. Complete cell turnover occurs every 28 to 30 days in young adults, while the same process takes 45 to 50 days in elderly adults.
The Subcutis
The subcutis is the innermost layer of the skin, and consists of a network of fat and collagen cells. The subcutis is also known as the hypodermis or subcutaneous layer, and functions as both an insulator, conserving the body’s heat, and as a shock-absorber, protecting the inner organs. It also stores fat as an energy reserve for the body. The blood vessels, nerves, lymph vessels, and hair follicles also cross through this layer. The thickness of the subcutis layer varies throughout the body and from person to person.
Subcutaneous Tissue
The hypodermis is beneath dermis which is beneath epidermis. It is used mainly for fat storage.
A layer of tissue lies immediately below the dermis of vertebrate skin. It is often referred to as subcutaneous tissue though this is a less precise and anatomically inaccurate term. The hypodermis consists primarily of loose connective tissue and lobules of fat. It contains larger blood vessels and nerves than those found in the dermis.
Artery
Arteries meaning ‘windpipe, artery are blood vessels that carry blood away from the heart. While most arteries carry oxygenated blood, there are two exceptions to this, the pulmonary and the umbilical arteries. The effective arterial blood volume is that extracellular fluid which fills the arterial system.
The arteries are part of the circulatory system, which is responsible for the delivery of oxygen and nutrients to all cells, as well as the removal of carbon dioxide and waste products, the maintenance of optimum pH, and the circulation of proteins and cells of the immune system. In developed countries, the two leading causes of death, myocardial infarction (heart attack), and stroke, may each directly result from an arterial system that has been slowly and progressively compromised by years of deterioration.
Hair Shaft
The hair shaft (HS) is a key cornified component of the mature hair follicle (HF), situated at the center of the HF. HS is formed during upward growth and differentiation of the matrix cells and is comprised of three distinct cell layers: the innermost medulla, the cortex and the hair shaft cuticle. The number of medulla cell columns defines the thickness of the hair.
While the sebaceous glands are present just about all over the skin, they are notably absent on the palms of the hands and the soles of the feet. The sebum being excreted by your body today began production around 8 days ago.
Lymph Vessel
Lymph travels around the body through a network of vessels in much the same way that blood travels around the body through the blood vessels. Whereas the blood carries nutrients and other substances into our tissues, the lymph vessels drain fluid from the tissues and transport it to the lymph nodes. These small gland-like masses of tissue filter out and destroy bacteria and other harmful substances. The bigger lymph vessels then carry the cleaned fluid back to the vein called the superior vena cava, where it enters the blood stream.
The lymph or lymphatic system is an important part of our body’s system to defend us against infections.
Nerve
The entire surface of your skin receives its nerve supply from the central nervous system (CNS) and the autonomic nervous system (ANS).
Your central nervous system receives sensory information about touch, pressure, temperature and pain from areas of your skin. These areas of skin are referred to as dermatomes.
Receptors in different areas of your skin send nerve impulses or messages via spinal nerves to the spinal cord. This information is then transmitted up the sensory or ascending spinal tracts in your spinal cord to the brain.
The autonomic nervous system controls the blood vessels, sweat glands and oil (sebaceous) glands in your skin.
Vein
Superficial vein is a vein that is close to the surface of the body. This differs from deep veins that are far from the surface.
Superficial veins are not paired with an artery, unlike the deep veins, which typically have an artery with the same name close by.
Superficial veins are important physiologically for cooling of the body. When the body is too hot the body shunts blood from the deep veins to the superficial veins, to facilitate heat transfer to the surroundings. Superficial veins can be seen under the skin. Those below the level of the heart tend to bulge out. This can be readily witnessed in the hand: raised above the heart and the blood should drain; lowered below the heart and it will fill. Veins become more visually prominent when lifting heavy weight, especially after a period of proper strength training.
Physiologically, the superficial veins are not as important as the deep veins (as they carry less blood) and are sometimes removed in a procedure called vein stripping, which is used to treat varicose veins.