Written by Acel Joy Cimafranca

Living in this world, we have touched and felt many wonders. Most organisms have skins, thick fur, or any covering that helps them thrive and survive. To live without even the skin is unimaginable. It would surprise you that the hair and nails you have are part of the same system. Together, they make up the integumentary system.

This particular system is the body’s biggest organ. It forms a physical barrier between the external and the internal environment. The skin helps protect and maintain our body’s internal structures. It may be from physical, chemical, biological, radiological, and thermal damage. Besides its barrier function, it performs many intricate processes. For example, body temperature regulation, Vitamin D synthesis, and stimuli detection.

The components of the system work together to carry out the following functions:

• Physical protection– its’ most clear function is protection as it covers the body. Each of the layers contributes to the strength of this network of cells knitted tight. Created by layers of dead keratin, the epidermis makes up the outermost layer. This part withstands the wear and tear of the outer environment. The dermis provides the epidermis with an adequate blood supply. It has nerves that announce danger amongst other functions. The hypodermis allows physical cushioning to any mechanical trauma.
• Immunity- the skin is a physical barrier preventing entry of pathogens. Antimicrobial peptides and lipids on the skin act as a biomolecular barrier. They disrupt the bacterial membranes. Resident immune cells are available in the skin. In contrast, dermal dendritic cells travel and activate the more excellent immune system.
• Wound healing- this occurs when our body undergoes trauma with injury. The integumentary system orchestrates wound healing. It does this through hemostasis, inflammation, proliferation, and remodeling.
• Thermoregulation– the skin is very vascularized. It allows it to conserve and release heat through vasoconstriction and vasodilation. The system helps regulate body temperature by association with the sympathetic nervous system. It monitors body temperature and also initiates appropriate motor responses. Sweat glands secrete water, salt, and other substances to cool the body when it becomes warm.

When body temperatures drop, the arterioles will constrict to lessen heat loss. This reduced circulation results in the skin getting pale. Although the skin temperature drops, it prevents passive heat loss. Hence, internal organs and structures remain warm.

• Vitamin D synthesis– the primary sources of vitamin D are sun exposure and oral intake. The epidermal layer synthesizes vitamin D when exposed to UV radiation. With enough sunlight, the body forms vitamin D3 called cholecalciferol. The liver converts cholecalciferol to calcidiol. Vitamin D is critical for the normal absorption of calcium and phosphorous. Healthy bones need this vitamin. Also, it is vital for general immunity against bacterial, viral, and fungal infections. Recent studies are also finding links between insufficient vitamin D and cancer.
• Sensation– the sensory nerve endings cause skin innervation. It allows you to distinguish against pain, temperature, touch, and vibration. Each type of receptor and nerve fiber is unique in its adaptive and conductive speeds. These lead to a wide range of signals used to understand the external environment. It helps the body react the right way.

Why is it called the integumentary system?

The explanation behind this is quite simple. Integumentary is an adjective used when referring to a covering or coating. It derives from integumentum, a Latin word for “a covering.” In a figurative sense, it means a cloak or a disguise. In English, “integument” is a modern word. Its origin traced back to the early seventeenth century. It can mean material or layer that encloses, clothes, or covers in the sense of cladding or coating.

In biology, the integument is the natural covering of an organism or an organ, such as its skin, husk, cover, or peel. An integument is any coating or covering. But, the term refers to the outer layer of natural things like animals and plants most of the time. With that in context, the system’s name comes from its largest organ, the skin. Since it makes up most of the surface area, it is sensible to refer to the system with the word integument.

What organs are in the integumentary system?

The integumentary system consists of the skin, hypodermis, hair, nails, and exocrine glands. These organs have their function in maintaining and protecting the body. Since they are external, you may think of them as accessories. But, they serve essential physiological roles. For further details, read the following:

• Skin- it is the body’s largest organ. The standard square inch of skin has 20 blood vessels, 650 sweat glands. Also, it has more than a thousand nerve endings. It has 60,000 incredible cells producing pigment. All these structures manifest as a stack of cells that is 2 mm thick.

The skin makes up of two prominent layers. These are the superficial epidermis and the deeper dermis.

1. Epidermis– the tough outer layer. It is the first line of defense against the external environment. It comprises squamous epithelial cells that further break down into layers. In the palms and soles is an extra layer between the stratum corneum and stratum lucidum. It makes the skin there thicker.

2. Dermis– the underlying connective tissue framework provides supports to the epidermis. It subdivides into two layers. The dermis is under the epidermis. It contains connective tissues, nervous tissues, blood, and blood vessels. The dermis is way thicker than the epidermis. It also gives the skin strength and elasticity. There are two separate regions: the papillary layer and the reticular layer.

• Hypodermis- rests between the dermis and underlying organs. It is also described as subcutaneous tissue.

This layer encompasses loose areolar tissue and adipose tissue. It provides more cushion and insulation through its fat storage function. Also, it connects the skin to underlying structures such as muscle.

The hypodermis serves as the adaptable connection between the skin, muscles, and bones. The areolar connective tissue in the hypodermis contains elastin and collagen fibers. It allows the skin to stretch and move free of its underlying structures. Fatty adipose tissue in the hypodermis supplies energy.

• Hair- originate from the epidermis. But, it grows its roots deep into the dermis. Its structure splits into the visible hair shaft and the hair follicle within the skin. The hair is an accessory organ of the skin. It is dead keratinocytes found in most body regions.

The hairless parts of the body include the palms, feet, lips, labia minora, and glans penis. The hair protects us from UV radiation by blocking sunlight from striking the skin.

• Nails- form as layers of keratin at the dorsal tips of the fingers and toes. The nail growth set out at the nail matrix generates new cells and drives worn-out cells.

The discernible part of the nail is the nail plate covering the nail bed, where it clings to the finger. Nails operate to protect the fingers and toes. It does so while increasing the accuracy of movements and enhancing sensation. They are keratinocytes congealed and found on the ends of the fingers and toes. Fingernails and toenails strengthen and protect the end of the digits. These also scrape and manipulate small objects.

• Associated Glands– there are four exocrine glands within human skin. These are sudoriferous, sebaceous, ceruminous, and mammary glands.         
• Sudoriferous glands are one of the exocrine glands found in the skin’s dermis. They are also called sweat glands. There are two major types of sudoriferous glands. These are eccrine sweat glands and apocrine sweat glands.
• Sebaceous glands are part of the pilosebaceous group. It includes the hair, hair follicle, and arrector pili muscle. These secrete an oily substance called sebum.
•  Ceruminous glands are special glands located only in the dermis of the ear canals. These produce a waxy secretion known as cerumen to protect the ear canals.

What are the three layers of the skin?

Like our planet Earth, the skin has three prominent layers. These are the epidermis, dermis, hypodermis (subcutaneous tissue)

• Epidermis– the outermost layer of skin. The epidermis provides a waterproof barrier and creates our skin tone.

The epidermis is a water-resistant outer layer of the skin. This layer has 4-5 sublayers of packed cells. The epidermis processes the cell renewal cycle. The dead skin cells shed off the stratum corneum. Then, new, healthy cells generate. The epidermis also consists of your pores that allow oil and dirt to escape your body.

The epidermis contains specialized cells, including:

1. Keratinocyte cells – produce and store keratin (the protein that strengthens skin)

2. Langerhans cells – help prevent infection and defend the immune system

3. Melanocyte cells – produce melanin (the pigment that determines skin color)

4. Squamous cells and basal cells – cause basal cell and squamous cell carcinoma

The epidermis is super thin on selected parts of your body and thicker on others. This layer handles:

a. Making new skin cells

b. Giving skin color

c. Protecting your body

• Dermis – found beneath the epidermis. It contains tough connective tissue, hair follicles, and sweat glands.

The dermis also contains nerve endings that send messages to the brain when you feel. Blood vessels located in this layer help supply your skin with fresh blood. They carry the oxygen as well as the nutrients it needs to be strong.

Within its connective tissues, the dermis makes two essential proteins: Collagen and elastin. The two are responsible for the shape, structure, firmness, and elasticity of your skin. The roles of the dermis include:

a. Making sweat.

b. Helping you feel things.

c. Growing hair.

d. Making oil.

e. Providing blood to your skin.

• Hypodermis (subcutaneous tissue)- composed of fat and connective tissue.

The hypodermis comprises subcutaneous fats, connective tissues, blood vessels, and nerve cells. The blood vessels in this layer are larger. Stored fat helps track body tissue. Also, it cushions your body’s internal organs against negative impact.

The tissue in the hypodermis produces one crucial cell called Adipocytes. These cells store fat used for energy, cushioning, and insulation. The bottom layer of the skin is the subcutaneous fat layer. This layer plays an essential part in your body by:

a. Attaching the dermis to your muscles and bones.

b. Helping the blood vessels and nerve cells.

c. Controlling your body temperature.

d. Storing your fat.

What are the two primary components of the integumentary system?

In this part, we will tackle the two primary components of the integumentary system. These are the cutaneous membrane and the accessory structures.

• Cutaneous membrane- the operational term for our skin. It is a multi-layered membrane composed of epithelial and connective tissues. The apical surface of this membrane subjects itself to the external environment. It is dead, keratinized cells that help protect the body from pathogens. As mentioned, our skin comprises three layers. They are the epidermis, dermis, and subcutaneous tissue.
• Accessory structures- include the hair, nails, sweat glands, and sebaceous glands. These structures originate from the epidermis. Often termed “appendages”, they can extend down through the dermis into the hypodermis.

Accessory structures of the skin consist of not only the hair and nails. This group also includes sweat glands and sebaceous glands. Although these structures appear to be part of the dermis, they come from the epidermis. Dead, keratinized cells make up the hair shaft and get their color from melanin pigments. Nails are also keratinized. They protect the extremities of our fingers and toes from damage. Sweat glands and sebaceous glands create sweat and sebum.

What material makes the epidermis tough?

Look at your toes, your face, and your hands. What you’re watching are your keratinocytes. They put together over 90% of the epidermis cells, the outermost layer of the skin. The keratinocytes make the epidermis strong. The skin on every part of your body is not the same. This difference is due to toughness. The number of keratin proteins produced in certain parts causes this distinction. Keratin is an intermediate filament protein made by keratinocytes.

The main aim of these keratin-producing cells is to preserve. It may be against microbial, viral, fungal, and parasitic invasion. They also protect us against UV radiation. Apart from that, they cut the heat, solute, and water loss.

Keratinocytes are very well specialized. They play an indispensable role in protection because they form a tight barrier. It prevents foreign substances from entering the body. Also, they shorten the loss of moisture, heat, and other constituents. In maintaining them in their locations, they form tight bonds with the other cells. Also, keratinocytes function as immunomodulators following skin injuries.

Which layer of the skin does hair grow from?

Your hair is a keratinous filament growing out of your epidermis. Dead and keratinized cells predominate this layer. Strands of hair originate in an epidermal permeation called the hair follicle.

The hair shaft is part of the hair. It is not anchored to the follicle, and much of this is visible at the skin’s surface. The rest of the hair lies below the surface of the skin. This is the hair root. The hair root stops deep in the dermis at the hair bulb. It also includes a layer of active basal cells called the hair matrix. The hair bulb surrounds the papilla hair. It contains blood capillaries and nerve endings from the dermis.

The basal layer of the epidermis creates the layers of epidermis that get shoved to the surface. This happens as the dead skin sheds. The same cells of the hair bulb divide and push cells out in the hair root and shaft. It occurs as the hair grows. The medulla structures the core of the hair. The cortex surrounds it. The cuticle covers this layer of compressed keratinized cells.

Hair grows, then sheds, and the new hair replaces it. There are three stages to this. The first is the anagen phase, when cells at the hair’s root divide, pushing the hair shaft up and out. We use years to measure this phase, and it usually lasts between 2 and 7 years.

Also, the catagen phase lasts only 2 to 3 weeks. It announces the end of the growth phase of the hair follicle. Finally, the hair follicle is dormant throughout the telogen period. By this time, no new growth occurs. A new anagen phase begins after this phase, which lasts roughly 2 to 4 months. As the growth cycle repeats, the basal cells in the hair matrix generate a new hair follicle. It pulls the old hair out. During the anagen phase, hair develops at a rate of 0.3 mm every day. Every day, about 50 inches fall out. Hair loss happens when the amount of hair shed exceeds the amount of hair restored. It can occur due to hormonal or nutritional changes.

REFERENCES:

American Academy of Dermatology Association. (2021). What kids should know about the layers of the skin. https://www.aad.org/public/parents-kids/healthy-habits/parents/kids/skin-layers

American Hair Loss Association. (2010, March 1). Hair Loss: The Science of Hair. WebMD. https://www.webmd.com/skin-problems-and-treatments/hair-loss/science-hair

Betts, J. G., Young, K. A., & Wise, J. A. (2013). Anatomy and Physiology. OpenStax.

Biga, L. (2021). Anatomy and Physiology (1st ed.). Pressbooks. https://open.oregonstate.education/aandp/chapter/4-1-types-of-tissues/

Hoffman, M. (2021, August 1). The Skin (Human Anatomy). WebMD. https://www.webmd.com/skin-problems-and-treatments/picture-of-the-skin

Kim, J., & Dao, H. (2021, May 9). Physiology Integument. National Center for Biotechnology Information. https://www.ncbi.nlm.nih.gov/books/NBK554386/

Lumen Candela. (2020, August). The Skin. Lumen Learning. https://courses.lumenlearning.com/boundless-ap/chapter/the-skin/

Martini, N., & Ober, K. (2018). Visual Anatomy and Physiology (3rd ed.). Pearson. https://www.palmbeachstate.edu/slc/Documents/AandPch05LecturePearson.pdf

Mohs Skin Cancer Surgery. (2020, January 30). The Layers of Skin. Florida Dermatology and Skin Cancer Center. https://fldscc.com/2020/01/30/three-layers-skin/

Pane, C. (2020, September 27). Keratinocytes. PromoCell. https://promocell.com/cell-culture-basics/keratinocytes/#

Physiopedia. (2020, October 23). The Integumentary System. https://www.physio-pedia.com/Integumentary_System

Reina, O. (2016, September 13). Keratinocytes: Their Purpose, Their Subtypes and Their Lifecycle. Tempo Bioscience. https://www.tempobioscience.com/blog/keratinocytes-their-purpose-their-subtypes-and-their-lifecycle/

Taylor, T. (2021, May 17). Integumentary System. Innerbody Research. https://www.innerbody.com/anatomy/integumentary#continued

Xandrea, P. (2019, December 9). Skin 2: accessory structures of the skin and their functions. Nursing Times. https://www.nursingtimes.net/clinical-archive/tissue-viability/skin-2-accessory-structures-of-the-skin-and-their-functions-09-12-2019/