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.