In this article, we are going to study the anatomy of the skin and its functions. Read the article to know more interesting things about your skin that you may not know.
Integumentary System
Skin is part of the Integumentary System, which consists of your skin and skin appendages. Your integumentary system is an outer layer that is the sole protection cover of your internal body systems and organs from direct exposure to the external environment.
The integumentary system is the most important system of your body as it performs various crucial tasks such as:
- Protecting skin from infections, bacteria, germs, excessive sunlight, UV rays, and hazardous objects
- It helps you regulate your body temperature
- It helps you to balance your body fluids
- It is the source of sensory reception from the outer environment
- One of the sources to excrete waste from your body
- An important source for the synthesis of vitamin D
The components of the integumentary system are as mentioned below:
- Skin
- Skin appendages:
- Nails
- Hairs
- Sweat glands
- Oil glands
- Blood vessels
- Nervous system
Now that we know what an Integumentary System is let’s focus on our topic which is skin. We will also discuss skin appendages.
Skin
The skin forms the thickest and largest organ of your body. It weighs about 3 kg to 5kg. It is approximately 2 millimeters thick. Our skin is made up of 3 main layers and other components of the skin are present and working between these layers.
These 3 layers are as mentioned below (the order of the list is outside-in):
- Epidermis
- Hypodermis
NOTE: We are going to learn about the skin from the outermost layer to the innermost layer.
Epidermis
“Epidermis” word is derived from the Greek words epi meaning “outer” and derma meaning skin. So it means outer skin. The epidermis is the outermost layer of the skin which is exposed to the outer environment and is visible to the naked eye. It is made up of Squamous Epithelial Tissue. It is the thinnest of all the layers of the skin.
The epidermal cells grow, die, and re-grow in this layer only. This whole process can take up to 4 – 6 weeks. The epidermis is made up of 5 layers (4 layers of thin skin) along with 4 different types of cells each having its function. These are as mentioned below:
Layers of the Epidermis
Here we will learn about the layers of the epidermis which are made of different cells at different stages of their cell cycle (life cycle).
Stratum Corneum
This is the outermost, toughest, and most visible layer of skin. They are also known as the ‘horny layer’.It is made up of 20-30 layers of flat dead Keratinocytes.
All the dead keratinocytes from the bottom layers are pushed above and stacked upon one another just like brick walls. This layer provides you protection from abrasions, infections, and temperature outside. It also acts as a fatty barrier that monitors the flow of water in and out of the skin.
Stratum Lucidum
This layer is made up of very mature keratinocytes that are nearing the last stage of their life cycle. They are also known as the ‘clear layer’. There are around 2 to 3 layers of less round, flat keratinocytes. This is a very unique layer as it is present in only thick skin (palm of your hand and sole of your feet).
Stratum Granulosm
This layer produces keratine actively. They are also known as the ‘granular layer’. This layer consists of avascular keratinocytes. This means they are mature keratinocytes that do not have their supply system of nutrients and oxygen, thus, they depend upon the cells of the layer beneath them for this supply.
The top layer of these cells loose connection from the bottom layer and starts to flatten and eventually die and reaches the top layer which is the stratum corneum.
Stratum Spinosum
This is the layer where cell generation through mitosis happens. This layer is also known as the ‘spiny layer’. Spiny because when this layer is kept under a microscope it is dried out and it seems to be having spiny filaments holding each other together.
Stratum Basale
This is the thinnest and innermost layer of the epidermis. It is also known as the ‘basal layer’. It consists of only a single layer of columnar cells responsible for the production of new cells required in the epidermis. So, they are also known as the cell factory of the epidermis. This layer connects the epidermis to the dermis.
Cells Present In The Epidermis
There is a total of 4 types of cells present in the epidermis, all of them have their distinct function and work in harmony.
Keratinocytes
These are the cells that produce a fibrous protein called “keratin”. Keratin when mature, hardens and provides a hard, durable, and water-resistant structure. You can find this as the most mature and dead form as your outer visible skin, hair, and nails.
Melanocytes
This is responsible for the production of spider-like structured “melanin”. Melanin is responsible for the pigmentation of the skin. It is found that every individual has the same average number of melanocytes, it is the spread of the cell that is responsible for the different pigments.
There are 2 forms of melanin, pheomelanin (reddish yellow) and eumelanin (brownish black). The main function of melanin is to protect against UV rays, Thus it is said that historically those who lived in an area that had more solar radiation (near the equator) have a high concentration of melanin pigment compared to those who live in an area that has less solar radiation (near poles).
It is also responsible for the synthesis of vitamin D, the only vitamin that our body can produce on its own.
Langerhans Cells
These cells are part of the most important system of your body, the Immune System. They are star-shaped cells that are produced in bone marrow as most immune system cells do. They are spread across your skin in millions. They provide you protection against pathogens, and viruses that may enter your body through the skin. This cell works the hardest.
Markel Cells
These are present near the last layer of the epidermis. They act as the connection between the epidermis and dermis. They act as sensory receptors, meaning they are connected to the nerve endings of the nerve present in the layer below, which are responsible for providing sensation and transmitting sensory response between the outer world and the brain.
Functions of Epidermis
- To produce new cells of the skin
- Protection against the harmful pathogen, UV rays, and hazardous chemicals
- Transferring sensory responses back and forth from the skin to the brain
- Maintaining the temperature of the body
- Last stage of excretion of waste from the body
Dermis
The dermis is the middle layer of the skin, also known as the corium. The dermis is made up of Collagen Fibre and Elastin Fibres that makes this layer strong and elastic. This layer is also the origin and home of blood vessels and capillaries, nerve fibers, and various skin appendages like hair follicles, oil glands, and sweat glands. This thick layer provides strength and structure to the skin so that it can move and stretch as you wish and retain body shape.
Layers of Dermis
There are a total of two layers of the dermis,
Papillary Dermis
This layer is made up of collagen fiber, fibroblasts, blood vessels, nerve fibers, touch receptors like Meissner corpuscles, and Areolar connective tissues. This is a thin layer that has dermal papillae, which are small wiggly finger-like structure on the top that helps to connect and form a strong bond with the last layer (basal layer) of the epidermis above it.
These dermal papillae are responsible for providing unique friction ridges so that you can hold objects with a grip.
Reticular Dermis
It is the thick layer, which comprises 80% of the dermis. It is made up of elastin fiber, collagen fiber, blood vessels, various glands, lymphatics, and nerve cells. Some glands and hair follicles originate here and get extended to the outermost layer of the skin which is the Stratum Corneum.
Functions of Dermis
- Providing sensory receptors for sensory communication
- Provide a protective barrier to organs from the harsh external forces
- Provide cellular support to the epidermis as some of its cells an avascular
- Produce hair through hair follicles in various parts of the body
- Produce excrete oil, secretions, and waste using the oil glands and other glands
Hypodermis
The hypodermis is the innermost layer of the skin, also known as the “subcutaneous layer”. This layer is made up of connective tissues (prominently fatty connective tissue is adipose tissue), blood vessels, lymphatic vessels, and nerves. As the majority of components of the hypodermis are fats, their thickness differs in various parts of the body as well as depending upon hormones and genetics.
Functions of Hypodermis
- It acts as a connection between the dermis and muscles
- The fat present in this layer helps to maintain body temperature according to the external environment
- Acts as a cushion to minimize any sudden impact on internal organs
- Stores energy in the fat cells
Functions of Skin
- It acts as the major sensory receptor of the body
- It stores about 5% of our total body blood, in case an urgent blood supply is needed
- It provides an immune barrier against external bacteria, pathogens, and viruses
- It regulates body temperature as per the external environment
- It excretes some waste out of the body
- It is responsible to provide strong rigid support to the body to move and stretch
- In case of small skin damage, the skin has the regenerative ability with help of skin appendages.
- Sometimes, the pigment of the skin can be useful in the diagnosis of diseases. For example:
- Cyanosis (blue skin): indicates a severe respiratory issue or heart failure
- Jaundice (yellow skin): liver disorder
- Erythema (red skin): fever, inflammation, or allergies
Skin Appendages
Skin appendage refers to the components of skin that reside in between the 3 layers of the skin. This includes:
Hair
Your single strand of hair originates from the dermis and it is extended out of the skin from the pores present on the epidermis. This pore is called a hair follicle it has a tunnel-shaped structure. It is made from keratin.
The base of the hair follicle the roots get the necessary supplies for its growth from the blood vessels for the production of keratin. The sebaceous glands (oil glands) attached to the hair follicle helping to provide lubrication to hair and scalp. New hair cells generate through active keratinization (a process of producing keratin) at the roots and the cells that push upward toward the skin surface as they mature. The hairs that you see are all dead keratin cells.
Hair can be used as one of the ways people want to present themselves.
Functions of Hair
- Hair can give you protection from external harms such as pathogens, and infectious viruses.
- Hairs can help you as sensation receptors.
- They can help you with thermoregulation.
Nails
The nail visible to you are all dead cells. The nail cells generate in the matrix that is located near the lunula (white crescent at the base of your nail.) These nail cells actively generate and have their life cycle in the lunula. Then they are pushed upward and they slowly come to the end of their life cycle.
The hard nail that is to cut, paint, and file is called a nail plate they are all dead keratin cells, and it is situated just above the nail bed (the cells below the nail plate that holds the nail in place). The hyponychium is the skin that holds the nail plate and nail bed, it's also where the free edge of the part that you usually trim starts.
Paronychium is the skin surrounding the nail's side it provides a protective barrier, if not taken care of this layer then it can cause harm to the nail. The skin which is folded above the lunula is called the cuticle, they are dead skin that was once surrounding and protecting the matrix. You can trim it off to maintain healthy nails.
Read more about the structure of the nail.
Functions of Nails
- The hard nail plate gives strength to do daily tasks and also helps in providing strength for grip from the blood vessels present in the nail bed.
- They protect the sensitive fingertip and prevent bacteria from entering the nail bed and your body.
- They act as a sensory organ as it has nerve cells in the nail bed.
- It can aid you in motor movement like scratching any surface, separating two sticky surfaces, etc.
Sudoriferous or Sweat Glands
Two types of sweat glands differ based on their biological structure, distribution in the body, and functions. These two types are the Eccrine Gland and Apocrine Gland. Let's understand them one by one.
Eccrine Gland
These are distributed along your whole body except some areas such as lips, external ear canal, nail beds, glans penis, clitoris, and labia minora, which do not contain sweat glands. These glands usually consist of sweat glands and hair follicles. They originate in the dermis and extend out through the epidermis. The thick skin that is the palm and sole of the feet, only have sweat glands and no other skin appendage like nail, hair, or oil glands.
Functions Of Eccrine Gland
- They regulate body temperature by sweating and removing water as sweat when body temperature rises than usual.
- They act as emotional and thermal receptors of the body.
Apocrine Gland
The number of these glands on your skin is low, they usually develop during and after puberty. They usually grow around armpits, private parts of both males and females. These are the glands that are known to produce a bad odor when exposed to bacteria.
There is some modified apocrine gland that has the function of unique secretion based on the location. These are the mammary gland (for lactation) and the ceruminous gland in the ear canal (secrete ear wax).
Functions Of The Apocrine Gland
- They stimulate under the effect of sex hormones.
- Secrete waste (earwax) or provide glands for lactation.
Read more about the sudoriferous/ sweat glands.
Sebaceous or Oil Glands
As the name suggests they produce oil for various purposes naturally in the skin. They are usually attached to the hair follicles and secrete the oil from the epidermis. These glands release sebum. Sebum is made up of lipids (fatty molecules). And thus they can provide protection and lubrication to skin and hair.
They are located throughout your body and originate in the dermis. They are not present in thick skin. The number of glands on your face and scalp is more compared to your body. Sebum production is less in the childhood stage, highly active in adulthood and slowly reduces as you age.
Functions Of Sebaceous/ Oil Gland
- Provide natural lubricant to the body to retain moisture.
- Provide a protective layer of lipids that protects skin from scratching and scraping.
- Provide moisture and lubrication to hair and scalp.
- They contribute to forming body odor.
Frequently Asked Questions
Why Is My Skin Dry And Patchy?
There can be many reasons for your dry and patchy skin, such as deficiency of vitamins, less oil production in oil glands, depleting layers of natural oils, or any infections. If it is a depletion of the oil layer you can moisturize your skin regularly. Even if the problem is very intense you should consult a dermatologist for professional treatment.
What Causes Acne?
A lot of people these days face the problem of acne, some even face severe painful acne problems. Acne is caused by a blockage that happens in hair follicles and oil gland openings. This blockage can be caused by several reasons such as excess oil production, accumulation of dirt and other products in the pores, lack of proper cleaning of the pore, or genetics too. A proper skincare routine of cleaning and moisturizing can prevent or lessen the acne problem significantly, however, it is advised to consult a doctor for better treatment.
How Does A Tattoo Work On The Skin?
Love for tattoos has been there through ancient times. Some people tattoo something that means a lot to them and some do it because they just like a tattoo. Tattoos are done by injecting ink into the skin of the person in the pattern of their choice. And for this, the needle used to draw the tattoo has to penetrate the dermis layer to effectively color the skin. As the needle is injected into the dermis, it bleeds and the immune system of the skin is alerted thus it may swell a little.
Why Is Skin Color Different In Different Body Parts?
There can be several reasons decolorization of the skin may happen for various reasons ranging from genetics to lifestyle habits. Some of these causes are Vitiligo (a skin disorder that happens when pigment are destroyed by the immune system), Melasma (brown or gray patches on the skin), and Age Spot (some area of your skin becomes darker compared to other due to long exposure to UV rays and sunlight)
Summary
From this article, we understood that skin is our largest and a very crucial organ. It performs many tasks ranging from providing stable structure to your body, protecting the muscles and vital organs, regulating the temperature of the body, acting as an immune system to prevent bacteria and other hazardous pathogens from entering your body, excreting waste in different forms, growing hair and oils essential for the body, regenerating new skin cells to maintain healthy skin (Your entire skin is replaced in the period of 4 to 6 weeks) and many more.
Skin is mainly made up of 3 layers:
- Epidermis: Outermost layer made up of stratum corneum, stratum lucidum (only present in thick skin), stratum granulosum, stratum spinosum, stratum basle and consists of keratinocytes, melanocytes, Langerhans cells, and markel cells.
- Dermis: Middle layer is made up of the papillary layer and the reticular layer. It is made up of collagen fiber and elastin fiber. It consists of blood capillaries and blood vessels.
- Hypodermis(subcutaneous layer): Innermost layer is made up of adipose connective tissues and fats.
It’s important to understand that the skin is not just these 3 layers it also has skin appendages such as hairs, nails, sweat glands, and oil glands. Each has its significance and functions such as:
- Nails protect sensitive skin at top of the fingertips and also provide a grip
- Sweat glands work as thermoregulator
- Oil glands produce natural oils and lubrication to provide protection and moisture to the scalp and skin to sustain against the external conditions
It can be said that your skin and skin appendages work in harmony to provide for better survival and protection of your muscles and vital organs. It is the most essential organ and it should be properly taken care off, to survival without the skin is impossible.
References
- Lumen Learning. Layer of the Skin. (https://courses.lumenlearning.com/suny-ap1/chapter/layers-of-the-skin/). Accessed 12/28/2022
- Cleveland Clinic. Integumentary System. (https://my.clevelandclinic.org/health/body/22827-integumentary-system). Accessed 12/29/2022
- Health and Safety Executive. Structure and function of skin. (https://www.hse.gov.uk/skin/professional/causes/structure.htm). Accessed 29/12/2022
- Cleveland Clinic. Epidermis. (https://my.clevelandclinic.org/health/body/21901-epidermis). Accessed 12/29/2022
- SkinKraft . Hair Follicles: The Complete Structure, Functions & Related Diseases. (https://skinkraft.com/blogs/articles/hair-follicle). Accessed 12/29/2022
- Musculoskeletal key. Anatomy and Physiology of the Fingertip. (https://musculoskeletalkey.com/anatomy-and-physiology-of-the-fingertip/). Accessed 12/29/2022
- National Center for Biotechnology Information. Anatomy, Skin Sweat Glands
- (https://www.ncbi.nlm.nih.gov/books/NBK482278/). Accessed 12/29/2022
