# Structural Biochemistry/Cell Signaling Pathways/Integumentary System
## Integumentary System

Out of all of the organs in the human body, the largest one is the integumentary system. The integumentary system consists of the skin and the skin’s derivatives, such as hair, nails, glands, and receptors.
The overall purpose and functions of the integumentary system is to protect the body’s internal living tissues from foreign particles, damage, and water dehydration. The integumentary system acts as a receptor for touch, pain, pressure, heat and cold. It also protects the underlying tissues and organs, the body from water loss and against abrupt changes in temperature, protects the body against the invasion by infectious organisms; helps dispose waste materials and store water, fat, and vitamin D.

## Structure and Function

The structure and functions of the integumentary system varies depending on certain organisms. For humans, the skin has two main layers: the epidermis and dermis.
The outer layer of the skin is the epidermis, which is made up of epithelial cells. The epidermis contains many types of cells, such as squamous cells, which are the flat cells that lie on the surface of the skin, and melanocytes which gives the skin it’s color.
The second layer that lies beneath the epidermis is the dermis, which includes the secretion glands, blood vessels, hair follicles, and most of the receptors.
The dermis has two layers, the upper papillary, which has receptors that communicate with the central nervous system, and the lower reticular layers which houses hair follicles, nerves, and certain glands.
The dermis contain glands such as the sebaceous glands, which secretes natural oils in order to keep the skin and hair moist, the sudorferous glands, which secrete sweat in order to regulate the temperature in the body, and the ceruminous glands, which secrete wax in order to prevent dust from entering the ear. On every part of the body, except for the palms and soles, there is hair, which helps maintain body temperature. Underneath the dermis, is the subcutaneous tissue, which is the “fatty cushion below the skin that separates the dermal layers from the underlying tissues”.

## Examples in invertebrates and vertebrates

In invertebrates, such as the lobster, its body is covered by a strong and impermeable exoskeleton. Its exoskeleton is composed of chitin and layers of protein, and lobsters shed their exoskeletons and secrete a larger external skeleton in a molting process.
As for a non-mammal vertebrate, such as the bird, its integumentary system includes the skin, feathers, and appendages (beak and claws). Birds have three tissues, the epidermis, dermis, and hypodermis. The epidermis consists of three separate layers: the outermost layer being the horny cell layer, the transitional layer joins both the outer layer to the inner layer, and the innermost layer is the columnar layer. The main component of the dermis is collagen and it has a thin and uniformed structure. The hypodermis is more loosely arranged compared to the dermis and also contains fewer cells. Feathers are the epidermal derivatives, and each feather follicle undergoes telogen, which is the mechanical process where the molting of the feather generates the growth of a new feather.

## Similarities and differences between humans, invertebrates, and vertebrates

The human, invertebrate, and non-mammalian vertebrate share both differences and similarities in their integumentary systems.
The similarities include the integumentary system of a human and bird, where the functions of their epidermis and dermis provide a thermal insulation in order to regulate body temperature, their nerve endings are sensed through the central nervous system, and their skin produces vitamin D in the presence of sunlight. Similarities that the invertebrate and non-mammalian vertebrate shares are the molting process of their exoskeleton and feathers.
Differences are that the human skin is made up of glands, hair, and nails, whereas a vertebrates integumentary system is comprised of skin, scales, feather, hair, and glands, and a strong and permeable external skeleton protects the internal organs of an invertebrate.

## Interesting facts about the integumentary system in humans

Asides from being the largest organ system of the human body, the integumentary system has many fascinating aspects to it. Some interesting aspects are that a whole new layer of skin is produced every month, forty pounds of skin is shed in an average lifetime, and an adult has approximately twenty square feet of skin. Also, melanin absorbs and reflects ultraviolet radiation from the sun, and the skin has the ability to produce vitamin D just in the presence of sunlight.

## Diseases affiliated with the integumentary system

Out of the many diseases that are associated with the integumentary system, such as acne, herpes, blisters, and melanoma, two diseases that are typically known are alopecia areata and athletes foot.
Alopecia areata is a non-contagious autoimmune disorder where the immune system attacks the hair follicles on the human body. Hair loss may be in a few or all regions of the body, but is most commonly lost on the scalp, which results in baldness. “In males and females, the spot baldness condition affects 0.1% - 0.2% in early childhood to young adulthood, however, the disease affects people of all ages”.
As for the more commonly known disease known as athlete’s foot, the disease is a fungal infection that causes scaling, flaking, and itching in various areas of the skin. Although this condition typically affects the feet, it can spread to other areas such as the groin. This condition is transmitted in moist areas where people typically walk barefoot such as in the shower, and prevention of athlete’s foot is to maintain good hygiene.

### References

* ↑ Integumentary System & Personal BILD 2 Essay.