The Integumentary System

Skin and all of its accessory structures make up the integumentary system. 

The integumentary system serves many functions. The most important function is protecting the body, but some of the other functions are warmth, sensing the environment, communication, secreting sweat and oils, nails, hair, and much more.

The integumentary is our largest system in terms of size, mainly because it covers our whole body. 

Our skin is made of 3 layers

     -Epidermis (made of epithelial tissue)

     -Dermis (made of dense connective tissue) Includes blood vessels, hair follicles, sweat glands, and other structures.

     -Hypodermis (made of lose connective tissue) Contains adipose tissue, more blood vessels, and nerves. 

The Epidermis

The epidermis is made of Keratinized, stratified squamous epithelium tissue.

Skin cells are called Keratinocytes because they make and store the protein keratin.

The last layer of skin is all dead keratinoctes. There is usually 15-30 layers of dead cells in the last layer of skin. This dry, dead, layer helps pretect the tissue underneath from drying out, and protects it from dangerous microbes.

The third or fourth layer of skin is the new keratinocytes. 

The last layer called the stratum basale is made of basal cells which is the stem cells that constantly go through mitosis making all the new keratinocytes.

Within the last layer of skin are melanocytes. Melanocytes produce melanin, the pigment that gives skin and hair its color. Melanin is important because it protects the epidermis from UV radiation.

There are also merkel cells in found throughout the last layer. Merkel cells send the signal of "touch" to the brain. A merkel cell is connected to a sensory neuron that is in the dermis.

"Thick skin" is found only on the palms of the hands and soles of the feet. Thick skin has 5 layers of epithelium.

Everywhere else on the body is "Thin skin" which has 4 layers.

The Dermis

The dermis is where the blood vessels, nerves, hair follicles, and sweat glands are.

If you scrape yourself, you do not bleed if you did not fully make it through the epidermis. But if you cut yourself and bleed, that means you broke through to the dermis.

The dermis is the core of the integumentary system.

This layer of connective tissue has a lot more going on than the epidermis. It is covered in collagen fibers to provide structure and elasticity. It has phagocytes that engulf any foreign invaders and has lymphatic capillaries which provide lymph fluid. It is full of blood vessels, touch receptors, and nerve endings.

The Hypodermis

(Sometimes called the subcutaneous layer)

The hypodermis is not technically part of the skin. The hypodermis is the part of the integumentary system that connects to the muscular and skeletal system. The hypodermis consists of loose connective tissue and contains adipose tissue (fat). This fat protects the organs underneath from impacts, insulates the organs underneath, and also is used as lipid (food) storage.

Student activity:

Open your coloring book and begin coloring pages 15 and 16. Follow all coloring instructions

Class activity:

We are going to use a special black light to check our skin for damaged skin tissue. Get into groups and use the Derma Specs light to search for damaged tissue. At each station is a picture chart that shows you what to look for.

Students Read:

Lipid Storage

The hypodermis is home to most of the fat that concerns people when they are trying to keep their weight under control. Adipose tissue present in the hypodermis consists of fat-storing cells called adipocytes. This stored fat can serve as an energy reserve, insulate the body to prevent heat loss, and act as a cushion to protect underlying structures from trauma.

Where the fat is deposited and accumulates within the hypodermis depends on hormones (testosterone, estrogen, insulin, glucagon, leptin, and others), as well as genetic factors. Fat distribution changes as our bodies mature and age. Males tend to accumulate fat in different areas (neck, arms, lower back, and abdomen) than do females (breasts, hips, thighs, and buttocks). The body mass index (BMI) is often used as a measure of fat, although this measure is, in fact, derived from a mathematical formula that compares body weight (mass) to height. Therefore, its accuracy as a health indicator can be called into question in individuals who are extremely physically fit.

In many animals, there is a pattern of storing excess calories as fat to be used in times when food is not readily available. In much of the developed world, insufficient exercise coupled with the ready availability and consumption of high-calorie foods have resulted in unwanted accumulations of adipose tissue in many people. Although periodic accumulation of excess fat may have provided an evolutionary advantage to our ancestors, who experienced unpredictable bouts of famine, it is now becoming chronic and considered a major health threat. Recent studies indicate that a distressing percentage of our population is overweight and/or clinically obese. Not only is this a problem for the individuals affected, but it also has a severe impact on our healthcare system. Changes in lifestyle, specifically in diet and exercise, are the best ways to control body fat accumulation, especially when it reaches levels that increase the risk of heart disease and diabetes.

Pigmentation

Pigments give things their color. The pigment that humans make is melanin. There are 2 forms of melanin, Eumelanin and Pheomelanin.

Eumelanin is black and brown

Pheomelanin is red

Humans can only make shades of brown and red since the only pigment we can produce is melanin

The more melanin a person produces the darker their skin will be.

Melanin provides protection against the suns UV radiation. The less melanin in the skin, the more susceptible the person will be to burns from UV radiation.

So melanin protects a person from the sun. However too much melanin can interfere with vitamin D production. So individuals that produce a lot of melanin might struggle to get enough vitamin D.

Sun Exposure

When skin is damaged by the sun or exposed to solar radiation, the body will react by producing more melanosomes to try and create UV protection. We call this a tan. But because melanosomes are temporary, so are tans.

Too much sun exposure causes skin wrinkling because of the destruction of cellular structures. When the sun causes an unusual accumulation of melanocytes in the skin, it is called a freckle. Moles are larger masses of melanocytes.