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Human Skin System - Integumentary System - and Why Hair and Nails Grow After Death

Updated on January 6, 2012

The Skin and Its Appendages

The largest organ system in humans is the skin. The human skin has a surface area of about 2 metres square and the weight of the entire skin system can be as much as 15% of the body weight of a human. The skin and its appendages, which includes the hair, fingernails, toenails, sweat and sebaceous glands, nerve receptors for stimuli, etc, is actually the organ system that is called integumentary system.

Functions of Integumentary (Skin) System

The functions of Integumentary (Skin) System are:

  1. Acts as a barrier between the body internal structures and the external effects of pressure, heat, acids, bacteria, UV radiation, etc.
  2. Regulate the body temperature by production and evaporation of sweat.
  3. Excretes body wastes as sweat.
  4. Senses touch, pain, temperature changes, and emotional sensations.
  5. Produces Vitamin D when exposed to sunlight.
  6. Stores lipids and water.
  7. Acts as absorption medium – as when medicines are absorbed by the body through the skin.
  8. Produces melanin for skin color and protection from ultraviolet radiation.

The Epidermis Layer

The skin has two distinct layers called epidermis and dermis. Epidermis is the outer layer and the dermis is the inner layer. The epidermis has the cells of the type keratinocyte. Keratinocyte contains the fibrous protein called keratin which makes skin tough and waterproof. Within epidermis, another inner sublayer contains Melanocytes cells that produce the pigment melanin. Melanin is what gives the skin its color and provide protection for the skin from ultraviolet radiation. Also within epidermis, the innermost sub-layer has cells called basale. Basale cells are continuously dividing (through a process of open mitosis) and as they form new cells the old cells are pushed toward the skin surface. The old cells will usually move up the strata as they change shape and composition until they finally reach the top layer. The epidermis has no blood vessels and the cells in the deepest layers are fed through diffusion from blood capillaries found extending to the upper layers of the dermis.

The Dermis Layer

Dermis layer is the inner layer after the epidermis layer. Dermis layer is made up of connective tissue which cushions the body against stress and strain. The dermis layer contains the nerve endings (sensory receptors), hair follicles, nails, sebaceous glands, apocrine glands, sweat glands, blood vessels and lymphatic vessels. The cells in the dermis layer together with the basale cells in epidermis layer are fed, and their waste carried, by the blood vessels in dermis layer. The two layers, epidermis and dermis, are attached to hypodermis which connects the skin to the underlying bone and muscle. The hypodermis is not part of the skin. The hypodermis supplies dermis and epidermis with blood vessels and nerves. The hypodermis also contains as much as 50% of the body fats. It’s this fat that is used by skin for padding and insulation.

Anatomy of the human skin. Image Credit:US-Gov Via Wikimedia
Anatomy of the human skin. Image Credit:US-Gov Via Wikimedia | Source

Hair Follicle

Hair is produced by a skin organ called follicle. The hair follicle produces protein that forms the hair. The sebaceous gland secretes the oil that coats the hair shaft. When the follicle becomes infected, it will form a pimple. The sweat glands are located in the subcutaneous tissue and produces sweat that opens to pores on surface of the skin. Eccrine glands and apocrine glands are the two types of sweat glands. Apocrine glands are to be found on armpits and groin areas and will usually produce fluid that bacteria will act on to generate body odors. Fingernails and toenails, like hair and skin, are made of the tougher protein called keratin. The base of the nail is embedded underneath the skin. The nail has several layers of dead, flattened cells. In a nail, cuticle cells are dead cells and the eponychium cells are living cells and that is why the area of eponychium cells will feel pain if cut.

Production of Sweat

In the brain, the area that controls emotions and behavior is called hypothalamus and it’s located in the limbic system of the brain. When body gets hot, the sensory receptors alert the hypothalamus and hypothalamus will send signals to sweat-producing glands on the skin. The sweat producing glands will then start to produce water for cooling the body. At the same time the blood vessels on the skin will dilate thus allowing more blood to flow to transport heat by convection away from the skin surface. When the body gets cold, the sweat glands will constrict and production of sweat will stop. When it gets even colder, the body starts a process called thermiogenesis. In thermiogenesis, the body starts generating heat by increasing body's metabolic rate as well as the body will start shivering.

Body Cooling By Evaporation and Sweating

The skin loses water by evaporation and sweating. When the body sweats, the sweat is deposited on the surface of the skin. The sweat will then evaporate into the atmosphere. The process of evaporation allows sweat to change to water vapour without boiling. For sweat to evaporate, it will require energy, and it gets this energy by utilizing the thermal energy of the sweat itself to complete the evaporation process. The molecules of the sweat that evaporates are only those with the highest kinetic energy. This implies that after evaporation, the temperature of the remaining sweat is lower, and this lower temperature will cool the skin.

Little Yellowish Urine

When it’s hot, you may find your urine is concentrated with minerals, little and yellowish in color. This is because most of the water in the body is lost by skin through evaporation and sweating, and very little water is left for kidneys to convert to urine. When it’s cold, you may find your urine is a lot, dilute in concentration and very clear. This is because very little water in the body is being lost by skin through evaporation and sweating, and all excess body’s water is all left for kidneys to convert to urine.

Do Hair and Nails Grow After Death?

If you watch a dead body of a guy immediately after death and then you see the body again the next day, you will notice that the nails and beard have grown bigger than they were the previous day. This would suggest the hair and nails of dead people continues to grow after death. Scientifically, this is not true.

A Detached Lizard’s Tail Will Continue To Wriggle

If you hold a lizard by its tail, it will detach itself from the tail and leave you holding the tail as it escapes to several metres away. The detached tail will continue to wriggle for several minutes when the brain and heart of the lizard are several metres away. The lizard could be long dead after having been eaten and digested by hawk but the tail is still wriggling somewhere. This would suggest that some parts of a body can continue living by themselves even after the life bearing organs of heart and brain are long dead. In the case of a lizard, the lizard is able to detach itself from the tail in a process called autotomy. This is a self-defense mechanism used by lizards to escape from a predator's grasp. The lost tail will usually regenerate later.

Growth of Human Hair and Nails after Death Is Just an Illusion

The fact that the heart and brain of a lizard can be dead when the tail is still wriggling left and right should not mean that human hair and nails can grow after death? In humans, unlike lizards, when the heart and brain is dead, all the body cells will instantly die. So, in humans, hair and nails do not grow after death. Any growth you may notice on beard and nails of dead people is just an illusion. This happens because the tissues surrounding the hair and nails are losing out water and shrinking faster than the hair and nails. This drying out and shrinking away of skin from the nail folds and hair shafts is what gives the impression of growth.

So, human hair and nails do not grow after death. However, the worms and bacteria in the dead body will grow and multiply very fast. In a cow, the ticks will suck blood, grow and multiply even when the hide has been removed and it’s drying in the sun. If only the ticks could know what will happen in the next few hours they would run very fast and hide.

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