Skin Anatomy

Skin Anatomy 

  • The skin is the largest organ of the body.
  • Cells have an average life span of 19 – 34 days.
  • The average person is covered by 2 ½ square yards of skin that weighs around 9 pounds.
  • The average human grows about 1000 completely new outer skins during a lifetime.
  • Red blood cells wear out at a rate of 3 million every second, requiring the body to make over 200 billion new ones every day.
  • The body’s entire supply of red blood cells is completely renewed every four months. • Blood platelets last only 7-10 days in the body. They are one of the shortest lived elements in the human body.

The Skin

Skin has two major tissue layers, The Epidermis, a thin layer of non vascular tissue and the dermis, a dense layer of vascular connective tissue the subcutaneous layer (below the dermis) is a thick layer composed of fatty connective tissue that varies in thickness in each person.

A unique characteristic of the epidermis is its ability to regenerate tissue continuously. This process of shedding and renewing and renewing of epidermal tissue is called desquamation, taken from the Latin ‘desquamatous’ that means to scale off.

The outer layer of healthy skin is moist and approximately 10% water.

Intercellular cement is the lipid substance between the cells of the epidermis that keep the skin from dehydrating and helps to shield the skin from aggravating substances.

The layers of the epidermis have no blood vessels.

In order of their distance from the surface:

Stratum Corneum: Horny Layer: The outer layer of skin. This layer is the thickest of the epidermal layers and is exposed to the outer elements. The cells in this layer are dry and flat. This layer may have between 18-23 layers of flat dry cells that are cemented together by lipids, peptides, sebum and ceramides.

Stratum Lucidum: Is only present on the palms and soles of the feet. Thickness may vary from 0.5 to 0.8MM on the palms and soles of the feet and can be less than 0.1mm on the eyelids.

Stratum Granulosum: In this layer the lipids separate from the keratin (a non-living substance), ands cells lose a considerable amount of fat and moisture. These cells are approximately 80% keratin and less than 20% water.

Stratum Spinosum: This layer is several layers thick and flattens out as it rises upward. It is called the spiny or prickle cell layer due to the spiky appearance of the cells.

Stratum Germinativum: The basel layer is the only living layer of the epidermis where mitosis takes place. Mitosis is the process by which body cells divide to form two identical cells. This layer of skin does not have any blood vessels in it. Melanin is also in this layer.

Layers of the Dermis

Papillary Layer: This Layer of skin is directly below the epidermis.

Reticular Layer: This Layer contains the following:

  • Nerves.
  • Lymph Vessels.
  • Oil Glands.
  • Elastin.
  • Blood Vessels.
  • Hair Follicles.
  • Sweat Glands.
  • Fat Cells.
  • Arrector pili muscles.
  • Collagen.

One Square inch of skin contains:

  • 9,500,000 Cells
  • 65 Hairs
  • 19-20 Yards of Blood Vessels
  • 13 Sensory apparatuses for cold
  • 19,500 Sensory cells at the ends of nerve fibres
  • 1,300 nerve endings to record pain
  • 650 Sweat glands
  • 95-100 Sebaceous glands
  • 78 sensory apparatuses for heat
  • 78 yards of nerves
  • 160-165 pressure apparatuses for the perception of tactile stimuli.

Why does the skin age and what happens when it does?

How skin ages will depend on a variety of factors: lifestyle, diet, heredity, and other personal habits. For instance, smoking can produce free radicals, once-healthy oxygen molecules that are now overactive and unstable. Free radicals damage cells, leading to, among other things, premature wrinkles. There are other reasons, too. Primary factors contributing to wrinkled, spotted skin include normal aging, exposure to the sun (photo aging) and pollution, and loss of subcutaneous support (fatty tissue between your skin and muscle). Other factors that contribute to aging of the skin include stress, gravity, daily facial movement, obesity, and even sleep position.

Skin Changes That Come with Age

As we grow older, changes like these naturally occur:

  • Skin becomes rougher.
  • Skin develops lesions such as benign tumours.
  • Skin becomes slack. The loss of the elastic tissue (elastin) in the skin with age causes the skin to hang loosely.
  • Skin becomes more transparent. This is caused by thinning of the epidermis (surface layer of the skin).
  • Skin becomes more fragile. This is caused by a flattening of the area where the epidermis and dermis (layer of skin under the epidermis) come together.
  • Skin becomes more easily bruised. This is due to thinner blood vessel walls.

Skin Facts

  • The skin guards the body from injury and bacterial invasion.
  • The perceived colour of a person’s skin depends on the intensity of the state of contraction or dilation of the superficial vessels and on the extent of oxygenation of the blood.
  • Our skin has a limited capacity for absorption.
  • Freckles are an uneven distribution of melanin in the epidermis.
  • Skin is about 1mm thick on your eyelids, 3mm thick on the palms of your hands and the soles of your feet and about 2mm thick everywhere on the body.
  • The nerve endings are small and separate so that sensation is distributed not uniformly but in small areas. Individuals who are insensitive to pain have defective development of certain nerve structures.
  • When cells are injured, histamine (a chemical that dissolves protein) is released and these irritate the sensory nerve endings to cause varied degrees of discomfort.
  • When ice is applied to the skin the capillaries constrict, less blood and histamine flows and pain is alleviated.
  • When the skin is stroked firmly, the contractile cells of the vessels are mechanically stimulated, and capillary constriction produces immediate blanching. When these cells relax, the vessels dilate, and redness appears that flares to a small distance from the actual site of the stimulus. The flare depends on the integrity of nerve tissue and does not occur when the skin nerves have degenerated. If the stroke is injurious, histamine is released from damaged cells, water moves from the capillaries into the tissues and a swelling ensues. This is called a wheal and flare reaction or a hive.
  • Keratin in the basal layer is a protein that aids in protecting the skin against invasion.

The Function of the Skin

The skin has many functions, these include:

Secretion – The skin secretes sebum from the underlying sebaceous glands. This natural oil helps to keep the skin supple.

Heat Regulation – The body temperature is regulated through the skin. Sweating helps to cool the skin, while shivering helps to warm the body up.

Absorption – Substances can be absorbed through the skin which can be transported into the blood stream.

Protection – The skin acts as a protective barrier against germs and bacteria. The skin also contains Melanocytes which produce Melanin, and this helps protect the skin against UV radiation.

Excretion – The skin contains sweat glands which help to excrete excess waste and toxins out of the body.

Sensation – The skin contains thousands of nerve endings which act as sensors for pain. Heat or cold.

Vitamins – The skin helps make Vitamin D which Is created by a chemical reaction to Sunlight