Skin and Its Functions- Definition, Structure, and Functions of the Skin

Skin and its Functions: Do you know which is the largest organ of our body? It isn’t the stomach, brain, liver, or not even intestines. Then, what is it?  Yes, you are right; it’s the skin. Skin is the main barrier between our bodies and the outside world. There is no doubt that skin is one of the fascinating organs in the human body that is a lot more complex than we may have thought. It is made up of different layers and cells with specific and important functions to keep us safe and healthy. In this article, we will learn everything about the skin, its structure, and the important functions performed by these structures of the skin.

The Skin

The human skin is known to be the largest organ of the integumentary system and is the outermost covering of the human body. It consists of seven layers of ectodermal tissue and has a very important role in guarding the underlying muscles, bones, ligaments, and internal organs. Its functions are to protect the body against pathogens, regulate heat and permit the sensation of touch, cold, or heat.

The skin has a unique feature of healing itself when severely damaged. It also includes the nails, hair, and exocrine glands. The colour of the skin is produced by special cells called melanocytes, which produce the pigment melanin. Melanocytes are located in the epidermal layer of the skin. To understand the functions of different layers and cells of the skin, we need to know the basic structure. Let us learn more about skin cells and structure.

Fig: Structure of the Skin

Skin Cells

Skin cells are the basic building blocks of the large, complex structure of the skin. We often notice that the skin gets dry, flaky, and falls off but again gets replaced with new skin cells; this process of developing new skin cells slows down as age increases but never ends. Skin cells grow and divide in the basement membrane.

The new cells are pushed from the basement membrane to the epidermis, where the cells no longer get blood and nutrients. Hence, they begin to die and are replaced by new ones. The outermost layer that we see is nothing but the dead cells. There are mainly four types of skin cells, namely Keratinocytes, Melanocytes, Langerhans cells, and Merkel cells. We will learn about these cells under the epidermis of the skin as these are mainly present in the epidermis.

Structure of the Skin

Our skin looks like a very simple organ externally, but when we dig a little deeper, we can find out that it’s actually made up of multiple layers and different kinds of skin cells. We have already learned about different types of cells present in the skin, now we will learn about the three main layers of skin. The structure of skin consists of three layers, the outermost epidermis layer, the connective layer called the dermis, and lastly, the deepest subcutaneous layer.

Epidermis

It is the outermost layer of the skin that provides skin with its tone. It is also the thinnest than the other three skin layers. Let us learn more about the four important cells present in the epidermis:

1. Keratinocytes: Keratinocytes, also known as basal cells, are the most common type of skin cells (about 90-95%). The primary function of these cells is to form a complex and waterproof layer against UV radiation from the Sun, harmful chemicals, and other infectious agents.
2. Melanocytes: These are the second type of skin cells that produce a special pigment called melanin. Melanin is a dark pigment contained inside melanosomes that determines the colour of the skin. Melanin also provides protection against Ultra-Violet (UV) radiation and support the immune system.
3. Langerhans cells: These are the third type of skin cells also called dendritic cells (Antigen-Producing Immune Cells – APC). These cells act as the outermost protective guard of the cutaneous immune system. They are known to induce the first reactions against harmful pathogens encountered through the skin.
4. Merkel cells: These are also known as Merkel-Ranvier cells or tactile epithelial cells. These are oval-shaped cells responsible for light, touch, and sensation.

Fig: Types of Skin Cells

The epidermis layer is further divided into five different layers:

1. Stratum corneum (horny layer)
2. Stratum lucidum ( found on palms of the hands etc., where the skin is thick)
3. Stratum granulosum (granular layer)
4. Stratum spinosum (prickle layer)
5. Stratum germinativum (germinative layer)

Fig: Structure of the Epidermis

Dermis

This layer is mainly composed of connective tissue and is a thicker layer than the epidermis. The dermis is the middle layer of the skin that protects the body from strain and stresses and also provides strength and elasticity.      

The dermis layer consists of receptors that identify pain (nociceptors), heat (thermoreceptors), and pressure (mechanoreceptors). Hair follicles, several glands including sweat and sebaceous glands, etc., are present in this layer. The dermis layer functions are to provide sensation, growth of hair, etc.

The dermis layer is also sub-divided into two layers:

1. Papillary region: They have finger-like projections made up of loose connective tissues and capillaries. This region is responsible for patterns present on an individual’s fingers.
2. Reticular region: This region is made up of connective tissues which are dense, irregularly organised. The reticular region contains protein fibres which provide skin its strength and elasticity.

Hypodermis layer

The hypodermis layer is also called the subcutaneous or subcutis layer. It is the deepest part of the skin. This layer is the attachment of the skin to bones and muscles. It is mostly composed of fat, elastin, and connective tissue.

Subcutaneous tissues work to provide the skin with nerves and blood supply. The lipids present in this layer are in high amounts, which helps in the insulation of the body and prevents too much heat loss from the body. The lipid layer also functions to give protection to our bones and muscles.

Functions of Skin

We already know that the primary function of the skin is to provide protection, but there are other important functions too. Some of these functions are mentioned below:

Fig: Functions of the Skin

Protection

1. The skin acts as an overlaying protective barrier from the outside environment and pathogens while also contributing to the adaptive immune system.
2. Each layer of the skin contains some important elements which help to protect the body against various harm.
3. A tough protein called keratin helps to guard tissues, organs, and structures located underneath the skin against physical damage like minor cuts, scratches, and abrasions.
4. The waterproof nature of the skin helps to protect internal organs from several chemical irritants. This feature also ensures that important molecules remain within the body.
5. A layer known as the malpighian layer produces skin pigment, which acts as a protective layer against harmful UV radiation.
6. A chemical reaction between perspiration and oil produces an acid-like barrier that prevents harmful bacteria from entering the skin.
7. Oil glands present consist of sebum which prevents the skin from drying and gives easy access to bacteria to reach the skin’s surface and enter the blood supply. During this period of bacteria entering into the skin, if any unwanted bacteria has entered, then the part of the skin swells and recognizes it by Langerhans cells which alert the body, and in response, the body releases its defences to the infected area.
8. Fat cells present in subcutaneous layers provide protection against trauma. This layer also acts as an energy source.

Role of Skin as a Part of the Immune System

1. In addition to being a physical barrier against the external environment, the skin is also an active immune organ.
2. It has an immune system that protects the body from infection, cancer, toxins and attempts to prevent autoimmunity.
3. The skin immune system is also known as skin-associated lymphoid tissue (SALT), which includes peripheral lymphoid organs such as the spleen and the lymph nodes.
4. Langerhans cells and Keratinocytes are two key immune cells that are found in the epidermis.
5. The dermis has blood and lymph vessels and numerous immune cells, including dermal dendritic cells, Lymphocytes like T cells, B cells, natural killer (NK) cells, and Mast cells.
6. Keratinocytes act as the first line of innate immune defence against the infection.

Sensation

1. The sensation is one of the important features of the body, without which the body might face a lot of dangers. It also enables the body to feel pleasure too.
2. Nerve endings found in the skin carry impulses to the brain and allow us to feel the heat, cold, pleasure, touch, pressure, pain, and also an itch. 
3. The receptors for touch and pain lie closest to the surface of the skin, whereas the pressure receptors are found deepest. The heat and cold receptors are settled between these.

Body Temperature Regulation

1. The skin helps the body to maintain the body temperature within a very precise range.
2. When the body gets too cold (hypothermia), the arrector pili muscles cause the hair to stand up, giving goosebumps.
3. The thin layer of air caught between the hair and the body functions as an insulator to keep the body warm.
4. The blood vessels present within the dermis also constrict by a process called vasoconstriction. Constricting the vessels at the skin’s surface helps the skin cool while maintaining the accurate blood temperature for the body’s core and critical organs.
5. If the body becomes too warm, the sudoriferous glands release sweat. As the sweat evaporates, it helps to cool down the skin.
6. The blood vessels also play an important role in reducing the body temperature by dilating (vasodilation). The vessels relax and allow more blood to flow from the body’s core, bringing the heat along with it. The heat then evaporates through the skin.

Fig: Body Temperature Regulation

Secretion

1. Sweat glands, also known as sudoriferous glands, are responsible for secreting waste substances.
2. These sweat glands are influenced by the sympathetic nervous system and are divided into two categories, apocrine and eccrine glands.
3. The apocrine sweat glands are found in the genital and axillary areas. They secrete water, salts, cellular waste, and fatty substances onto the skin through the hair follicles during perspiration. When these substances reach the surface of the skin, they combine with bacteria on the skin and create body odour. These glands also excrete pheromones that play an important role in sexual attraction.
4. The eccrine sweat glands are found all over the body but are mostly present across the forehead, the palms of the hands, and soles of the feet. These glands secrete mainly water and also some salts, urea, and other water-soluble substances.

Excretion

1. Skin also plays a role in excretion through the production of sweat from the sweat glands present in the dermis.
2. Though the main role of sweat production is to keep the body cool and maintain temperature homeostasis, it also helps to eliminate excess water and salts, as well as a small amount of urea.
3. The sebaceous glands (also called oil glands) excrete an oily substance known as sebum which gives an individual healthy skin.
4. These glands are present in the entire skin but mostly on scalps, face’s T-zone, and cheeks.
5. Sebum is secreted from the hair follicles and acts as a lubricant to hair as well skin.

Synthesis of Vitamin D

1. The skin involves some biochemical processes, for example, the synthesis of vitamin D in the presence of sunlight.
2. Vitamin D is produced in the two innermost layers of the epidermis, the stratum basale, and stratum spinosum.
3. Vitamin D synthesized in the skin is inactive, and the process of activation needs enzymatic conversion in the liver and kidney.
4. Vitamin D is essential for the normal absorption of calcium and phosphorus that are needed for healthy bones.

Absorption

1. The absorptive capabilities of the skin helps in the administration of certain medications through the skin.
2. The most commonly known mechanisms of drug administration through the skin are the use of ointments or adhesive patches, like the nicotine patch or Iontophoresis, etc.

Summary

The skin is the largest organ in the human body that supports several bodily functions associated with our immune system, sensory perception, and body homeostasis. There are mainly four types of skin cells, namely Keratinocytes, Melanocytes, Langerhans cells, and Merkel cells. These are mainly present in the epidermis. The skin consists of three main layers, epidermis, dermis, and hypodermis (subcutaneous), and many sublayers of epidermis that all perform different actions to keep us healthy.

Protection of the body from harmful pathogens such as bacteria, viruses, fungi, etc., is the primary function of the skin. Not only protection, thermal regulation, excretion of waste products, sensation, absorption, and secretion, are other important functions performed by the skin. The sensation is one of the important functions of the skin that makes life more exciting and less dangerous. Vitamin D needed for healthy bones is also synthesized by the skin. Learning these important functions helps us better understand why it is important to maintain skin and keep it healthy for as long as possible.

Frequently Asked Questions (FAQs) on Skin and Its Functions

Q.1. What is your largest organ?
Ans: The human skin is known to be the largest organ of the integumentary system. It is the outermost covering of the human body.

Q.2. What is skin and its functions?
Ans: Skin is the outermost covering of the body. It totally consists of seven layers of ectodermal tissue and has a very important role in guarding the underlying muscles, bones, ligaments, and internal organs. Protection of the body, thermal regulation, excretion of waste products, sensation, absorption, and secretion are major functions of the skin.

Q.3. What is the importance of skin?
Ans: Skin performs several functions such as protection, heat regulation, sensation, excretion, and absorption of essential substances, and a lot more. It is the first defense mechanism of the body against a wide range of harmful pathogens. Hence, it is very important to have healthy skin.

Q.4. How many layers are there in the skin?
Ans: The structure of skin has three main layers. Following are three main layers of skin;
1. Epidermis layer
2. Dermis layer
3. Subcutaneous layer

Q.5. What are the main skin cells?
Ans: Skin cells are the basic building blocks of the large, complex structure of the skin. There are mainly four types of skin cells, Keratinocytes, Melanocytes, Langerhans cells, and Merkel cells. Keratinocytes constitute 90-95% of the skin structure.

We hope this article on Skin and its Functions helps you in your preparation. Do drop in your queries in the comments section if you get stuck and we will get back to you at the earliest.