Overview of the Integumentary System

Introduction

The integumentary system is the body system that provides protective coverage for your internal organs. This integumentary system comprises the skin, hair, nails, sweat glands, and sebaceous (oil) glands. Nails protect the ends of fingers and toes. The skin, hair, sebaceous glands, and sweat glands enable the body to regulate temperature.

 

Skin

Although the skin may appear to be an inactive sheet of tissue, it's a dynamic organ with blood vessels and nerves just like any other organ. The skin is a vital organ that interacts with several other organ systems and has several functions. 

Some of the skin's functions are as follows:

• The skin provides protection from the outer environment.
• The skin acts as a barrier against foreign pathogens.
• The skin sends the pain, temperature, pressure, and touch stimuli to the brain.
• When skin is exposed to the sun, it helps in synthesizing vitamin D, an essential vitamin needed to carry out various body functions.

The skin weighs somewhere between seven and nine pounds and takes up, on average, 20 square feet. There are about 300 million skin cells. Each square centimeter of your skin contains about four meters of small branches of the peripheral nerves. This intricate system of nerves allows you to sense very subtle changes in the immediate environment.

 

Your skin senses touch, pressure, temperature, and pain with different types of nerve fibers. These then send a signal to the brain; the brain decodes the signal and sends a response to the affected body part.

 

A single centimeter of skin contains meter-long blood vessels. In addition to supplying blood and essential nutrients to the skin, blood vessels allow the skin to help regulate body temperature. Think of the last time you exercised. Whenever you exercise, your heart rate increases to deliver more oxygen to your working muscles. The metabolism of your muscles generates heat. To maintain a stable body temperature, your body must get rid of this extra heat. This occurs mainly through sweating. Evaporation of sweat from your skin carries away heat. The tiny blood vessels in your skin dilate to lose heat, making your skin warm and flushed.

In the opposite situation, when you're exposed to extremely cold temperatures, the blood vessels in your skin become more constricted. This shunts blood flow, along with heat, away from skin and inward to protect vital organs. Shivering also is an attempt of your body to produce heat to counteract extremely cold temperatures.

*Your skin is an organ that can grow on its own. Skin grafting is commonly used to grow and repair blood vessels, trauma wounds, deep injuries, and burns. Grafting is a process of taking a piece of your own skin or a piece of donor skin and transplanting it to the affected site to grow and repair.

 

Sweat and Sebaceous Glands

Sweat glands are located deep in the dermal layer, very close to the subcutaneous layer of the skin. There are two types of sweat glands: eccrine and apocrine. There are both sweat glands and modified sweat glands.

Eccrine sweat glands are numerous, important, and widespread throughout your body. These tiny coiled tubes reach the epidermis through crooked ducts called pores. Eccrine sweat glands produce a watery sweat.

Apocrine sweat glands are found primarily in the axillae (armpits) and in the pigmented skin areas around the genitals. The apocrine sweat glands produce a thicker, milky secretion that can be odorous.

The milk-producing mammary gland is actually a modified sweat gland, but it doesn't work full time like the sweat gland. The mammary gland secretes milk only after the birth of a child.

Other modified sweat glands are the ceruminous glands, located in the skin that lines the external auditory canals (your ears). Instead of sweat, these glands secrete earwax, or cerumen. 

Flask-shaped sebaceous glands are also located in the dermis. Commonly attached to hair follicles, the sebaceous glands secrete an oily substance called sebum, which is released through ducts into the hair follicles. Sebum oils the hair, lubricates the skin, and prevents water loss.

*Approximately two million sweat glands work together to help your body maintain its proper temperature. As muscle movement and physical activity generate body heat, the sweat glands secrete water, more commonly known as perspiration. As the perspiration evaporates, the body becomes cooler. On average, a person sweats approximately one quart of water each day. That's why it's important to drink enough water to replenish body fluids.

 

Hair and Nails

Hair and nails are modified forms of the epidermis. In both, the horny cells, filled with keratin, are pushed through the epidermis. Because hair and nails are composed of dead cells, no pain is felt when they're cut. Hair and nails provide protection.

Hair keeps heads warm and serves as a filter system for ears, eyes, and nose. Each strand of hair on your body is a complex entity with a full support system. Some parts of the human body have no hair, such as the palms of the hands and the soles of the feet. But other parts have an abundance of hair. Your hair is constantly shed and replaced as more horny cells move upward from hair follicles through the hair shaft.

Nails protect the ends of fingers and toes. Nails provide physical support to the fingertips to allow you to pick up small objects.

Hair

Hair fibers are composed of a tightly fused meshwork of horny cells. A single hair is composed of four basic parts—the hair shaft, hair root, hair follicle, and the papilla. The hair shaft is the visible part of the hair. The hair root is embedded in the dermis. If you pluck a hair from the root, you'll see the hair follicle, a bulblike attachment at the end of the hair. The follicle consists of the root and its coverings. The papilla is a loop of capillaries enclosed within connective tissue.

Nails

Nails are hard, keratin-filled plates that are composed of tightly cemented, horny cells. A nail grows from the lunula, the white crescent at the base of the nail. Fingernails grow indefinitely at the rate of about one millimeter a week unless they're cut or broken. Toenails also grow indefinitely, but at a slower rate than fingernails. The cuticle is the narrow band of the epidermis that extends from the nail wall onto the surface. The pinkish color seen beneath the nail is produced by underlying capillaries. 

 

Key Points

• The three layers of your skin are called the epidermis, dermis, and hypodermis.
• The epidermis provides protection and physical barrier to foreign pathogens.
• The dermis contains sweat glands, sebaceous glands, and hair follicles and provides protection against disease-causing pathogens and releases histamine to protect the skin against allergens.
• The hypodermis produces and stores fat and connects the skin to the body organs to give shape to your body.
• Sebaceous glands produce oil that keeps hair and skin lubricated as well as prevent water loss.
• Sweat glands produce sweat to maintain body temperature.