Integumentary system: Structure and function

The integumentary system is the largest organ in our body. It is made up of the skin and its accessory structures, which include the nails; hair; sebaceous, or oil, glands; and sweat glands.

The primary functions of the integumentary system are covering and protecting our internal organs and tissues, preventing the entry of microbes or harmful substances, preventing excess water loss and dehydration, storing fat and water, regulating our body temperature, providing sensory information, and producing vitamin D.Now, the skin is divided into the epidermis and the dermis.

The epidermis is the outermost and thickest layer, and it's made of multiple layers of developing cells, which are called keratinocytes because they produce keratin: a protein that makes our skin resistant to water.

Now, keratinocytes start their life at the lowest layer of the epidermis and then migrate upwards to form the other layers of the epidermis in a process that takes approximately a month.

Now, the lowest layer of the epidermis also contains another group of cells called melanocytes, which secrete a protein pigment, or coloring substance, called melanin.

The relative quantity and type of melanin defines a person’s skin and hair color. In addition, melanin acts as a natural sunscreen that protects keratinocytes from excessive exposure to ultraviolet light from the sun.

However, a little exposure is necessary daily because ultraviolet rays stimulate keratinocytes to synthesize vitamin D, which is needed for calcium absorption.

Okay, so as keratinocytes mature, they migrate up into the next layer, which also contains immune cells, called Langerhans cells, that lurk around, constantly looking for invading microbes.

Finally, as new keratinocytes push up, older, dead cells are sloughed off, forming skin flakes or dandruff. Now, below the epidermis lies the dermis, which is made up of elastic connective tissue that gives flexibility to the skin.

The dermis lies above the hypodermis, or subcutaneous tissue, which is made of fat and connective tissue. The hypodermis helps insulate deeper tissues, provides padding to the body, and anchors the skin to the underlying muscle.

The dermis contains the skin’s accessory structures, which include nails, hair follicles, and sebaceous and sweat glands.

Nails protect the fingers and toes and are made up of keratin and dead cells that grow from the nail root on the tips. Hair is made of keratin and melanin, which gives it its color.

Hair is found nearly everywhere, except for the palms, soles, and lips. Its main function is to help maintain our body temperature and keep us warm.

Sebaceous, or oil, glands are associated with the hair follicle and skin pores to secrete an oily substance, called sebum.

Sebum softens the hair shaft, preventing it from becoming brittle, and lubricates the skin to prevent moisture loss. In addition, sebum is slightly acidic, which helps to deter pathogens.

And of course, sweat glands secrete sweat, which contains mostly water with small amounts of electrolytes, like sodium, and waste products for elimination.

But the main purpose of sweat is to regulate body temperature. When body temperature rises, like during a workout or while being under the sun, sweat helps cool the body by taking the heat from the skin and helping it dissipate into the air with every drop of sweat that evaporates away.Now, the dermis also contains blood vessels, which help regulate our body temperature as well.

When body temperature rises, blood vessels dilate, which brings more blood closer to the skin surface and that allows heat to get lost to the outside environment.

On the other hand, when it’s cold outside, blood vessels constrict, diverting blood flow away from the skin and conserving body heat.

Finally, the dermis also contains nerve receptors, which detect pain, touch, pressure, and temperature.Now, as we get older, our integumentary system undergoes some visible changes, like graying of hair, age spots and wrinkles in the skin, and thickening of the nails.

Gray hair appears due to the progressive loss of melanin production in the hair follicle. On the other hand, age spots are benign pigmented skin areas caused by increased melanin deposits over time, typically in the face and hands.

Wrinkles appear because, throughout our lifespan, there’s progressive loss of the connective tissue of the dermis as well as thinning of the supportive fatty tissue that makes up the hypodermis.

In addition, keratinocytes in the epidermis slow down their maturation and migration, and sebaceous glands decrease in number and produce less sebum.

Because of these factors together, the skin gradually becomes thin, dry, and fragile. As a consequence, this skin can be easily injured and takes longer to heal.

Additionally, the slow down of keratinocytes leads to slower nail growth. As a result, dead cells pile up, and nails can become thicker and yellowish.

Finally, the number of sweat glands and the blood flow to the skin tend to decrease over the years. As a consequence, older people can somewhat lose the ability to regulate their body temperature.

All right, as a quick recap… The integumentary system is the largest organ of the body. It is made up of the skin, which is divided into two layers: the epidermis and the dermis.

The epidermis is made of multiple layers of keratinocytes. The dermis is made up of elastic connective tissue and contains the skin’s accessory structures, which include nails, hair follicles, and sebaceous and sweat glands.

Nails protect the tips of fingers and toes. Hair helps maintain our body temperature.

Sebaceous glands secrete sebum, which lubricates the skin, prevents moisture loss, and deters microbes. Sweat glands secrete sweat to cool our body temperature.

In addition, the dermis also contains blood vessels that help regulate body temperature by dilating or constricting as well as nerve receptors for sensation.

Finally, the hypodermis is made of fat and connective tissue that helps insulate deeper tissues, provides padding to the body, and anchors the skin to the underlying muscle.

Now, as we get older, our integumentary system undergoes some visible changes, like graying of hair, age spots, wrinkles, and thickening of nails.

In addition, the skin becomes thin, dry, and fragile and becomes less