[Biology Class Notes] on Structure and Functions of Skin Pdf for Exam

The human skin is the largest organ of the integumentary system and the outer covering of the body. It is made up of up to seven layers of ectodermal tissue and plays  an important role in guarding the underlying muscles, ligaments, bones and internal organs

There are two general types of skin, one is hairy and the other is glabrous skin (hairless). Due to its interfaces with the environment, skin plays an important immunity role in protecting the body against pathogens as well as excessive water loss. Additional functions of the skin include insulation, sensation, temperature regulation, synthesis of vitamin D etc. If the skin is severely damaged it will try to heal by forming scar tissue which is often discoloured and depigmented.

The Anatomy of the Skin Layers

The human skin structure consists of mesodermal cells, pigmentation, such as melanin formed by melanocytes (absorbs a part of the potentially dangerous UV rays in sunlight. It also contains DNA repair enzymes that function by reversing UV damage, such that people lacking the genes for these enzymes suffer high rates of skin cancer. 

The skin has a surface area of between 16.1–21.5 sq ft. for an adult human. The thickness of the skin differs over all parts of the body, and between men and women and the young and the old. For example, the skin on the forearm which is on average 1.3 mm in the human male and 1.26 mm in the human female.  

The Structure of Human Skin Comprises Three Layers. The Three Layers of Skin Are

1. The outer layer of the skin: Epidermis

2. The part that consists of connective tissue: Dermis

3. The deepest layer of the skin: Subcutaneous tissue

1. Epidermis

The outermost layer of the skin is called the epidermis. It gives the skin its tone. We shed more than 500 million skin cells each day. Dead cells are shed continuously from the epidermis as new skin ones take their place  New skin cells are made in the lower layers of the epidermis. For 4 weeks, they make their way to the surface, become hard and replace the dead cells.

The most common type of cells within the epidermis are Keratinocytes; their job is to act as a physical barrier against any type of harmful pathogen, heat, UV rays from the sun, and water loss.

The epidermis contains no blood vessels. The colour of our skin is produced by a pigment called melanin, which is produced by melanocytes; these are also found in the epidermis layer and protect the skin from UV rays.

The Epidermis is Subdivided Into Five Layers

• Stratum corneum

• Stratum lucidum

• Stratum granulosum

• Stratum spinosum

• Stratum germinativum

Between the epidermis and the dermis is a thin sheet of fibres called the basement membrane.

The functions of the epidermis are: producing new skin cells, giving skin colour and protecting the body.

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2. Dermis

Between all the parts of the skin, the dermis mostly consists of connective tissue. It protects the body from strain and stress gives it elasticity and strength.  It is the middle layer of the skin.

If the dermis is stretched a lot, for instance, during pregnancy, the dermis can be torn, which is the reason behind stretch marks.

Most of the receptors that detect pain (nociceptors), pressure (mechanoreceptors) and heat (thermoreceptors) are located in the dermis.

It also houses hair follicles, blood and lymphatic vessels, several glands, including sweat and sebaceous glands (which produce sebum, an oil that lubricates and waterproofs hair).

The Dermis Can Be Divided Into Two Layers

Papillary Region: This region is made of loose connective tissue, and has finger-like projections that push into the epidermis. They provide the dermis with a bumpy surface and are responsible for the patterns we have on our fingertips.

Reticular Region: This region is made of dense, irregularly organised connective tissue. Protein fibres in the reticular region give the skin its strength and elasticity.

The functions of the dermis are providing sensation, making sweat it and oil, growth of hair etc.

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3. Subcutaneous Layer

It is the deepest of the skin and also known as the hypodermis or subcutis. It helps attach the skin to underlying bone and muscle. 

Subcutaneous tissue provides skin with nerves and blood supply as well. The hypodermis is mostly made of fat, connective tissue, and elastin. The high levels of lipid help in the insulation of the body and prevent us from losing too much heat. The lipid layer also acts as protection, padding our bones and muscles. Some hormones are made by fat cells in the hypodermis, vitamin D, for instance.

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Simple Diagram of the Skin

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Skin anatomy diagram

The Function of Skin / What Are the Functions of the Skin?

There are several functions of the skin:

• Protection from the External Environment: This is the most important function of the skin. It keeps dangerous pathogens away so that they do not enter into the skin and cause any harm.

• Prevents Water Loss: Humans possess thick skin and it helps in a lower loss of water. 

• Sensation: Skin is one of the major sensory organs in the human body. It can sense touch, heat, pressure, cold and much more. A network of nerves transmits sensory signals to the brain. Thus we can respond appropriately to a particular stimulus.

• Regulation of Temperature: This is another major function of the skin. It loses water through perspiration, keeps the body cool and in doing so, removes heat from the body. The phenomenon of “goosebumps” is also a temperature regulation response.

• Storage: The skin can store lipids and water in its tissues which can provide extra insulation to our body.

• Excreting Scent Signals: The sweat secreted by the sweat glands of our skin can
  also act as a signal to other organisms.