Integumentary System 2


I need a pithy statement here.


The integumentary system is the organ system that protects the body from various kinds of damage, such as loss of water or abrasion from outside. The system comprises the skin and its appendages (including hair, scales, feathers, hooves, and nails).

  This is material you need to know - there is no use in complaining about it.  Memorize this material and be done.

Characteristics of skin:

Waterproof, stretchable, washable, self-repairing small cuts, rips and burns and  guaranteed to last a lifetime; this is an amazing organ system!

  • Surface area of up to 2.2 square meters

  • 11 pounds

  • 7% of total body weight

  • Pliable yet tough

What causes skin color?

As early humans moved into hot, open environments in search of food and water, one big challenge was keeping cool. The adaptation that was favored involved an increase in the number of sweat glands on the skin while at the same time reducing the amount of body hair. With less hair, perspiration could evaporate more easily and cool the body more efficiently. But this less-hairy skin was a problem because it was exposed to a very strong sun, especially in lands near the equator. Since strong sun exposure damages the body, the solution was to evolve skin that was permanently dark so as to protect against the sun’s more damaging rays.

Why do people from different parts of the world have different colored skin? 

Why do people from the tropics generally have a darker skin color that those who live in colder climates?

Variations in human skin color are adaptive traits that correlate closely with geography and the sun’s ultraviolet (UV) radiation.

Melanin, the skin's brown pigment, is a natural sunscreen that protects tropical peoples from the many harmful effects of ultraviolet (UV) rays. UV rays can, for example, strip away folic acid, a nutrient essential to the development of healthy fetuses. Yet when a certain amount of UV rays penetrates the skin, it helps the human body use vitamin D to absorb the calcium necessary for strong bones. This delicate balancing act explains why the peoples that migrated to colder geographic zones with less sunlight developed lighter skin color. As people moved to areas farther from the equator with lower UV levels, natural selection favored lighter skin which allowed UV rays to penetrate and produce essential vitamin D. The darker skin of peoples who lived closer to the equator was important in preventing folate deficiency. Measures of skin reflectance, a way to quantify skin color by measuring the amount of light it reflects, in people around the world support this idea. While UV rays can cause skin cancer, because skin cancer usually affects people after they have had children, it likely had little effect on the evolution of skin color because evolution favors changes that improve reproductive success.

There is also a third factor which affects skin color: coastal peoples who eat diets rich in seafood enjoy this alternate source of vitamin D. That means that some Arctic peoples, such as native peoples of Alaska and Canada, can afford to remain dark-skinned even in low UV areas. In the summer they get high levels of UV rays reflected from the surface of snow and ice, and their dark skin protects them from this reflected light.

Melanocytes  & Melanin

Pigments in the body

There are three pigments that contribute to skin color

1. Melanin

protein pigment (natural sunscreen)

can range in color from yellow to reddish-brown to black

everyone has the same number of melanocytes but make varying amounts of melanin (differences in skin color)

increased melanin production can be caused by sunlight

Melanin in created in cells called Melanocytes in the Epidermis.  The melanin created in packed into the keratinized cells in the skin

2. Carotene

yellow to orange pigment found in carrots, tomatoes and oranges

most commonly found in the palms or soles. Most intense when large amounts of carotene-rich foods are eaten


3. Hemoglobin

Red blood gives a pinkish hue to fair colored skin

Blood gets its red color from Hemoglobin, an Iron-rich molecule that is used to transport oxygen throughout our bodies. 



These different pigmets combine to cause most of the colors we see in our skin and body tones.

Major appendages of the skin

Skin appendages are skin-associated structures that serve a particular function including sensation, contractility, lubrication and heat loss. In humans, some of the more common skin appendages are hairs (sensation, heat loss, filter for breathing, protection), arrector pilli (smooth muscles that pull hairs straight), sebaceous glands (secrete sebum onto hair follicle, which oils the hair), sweat glands (cool down the skin surface via evaporation) and nails (protection).


  • Sweat (sudoriferous) glands

    • Merocrine (Eccrine) - common sweat glands

      • Hot sweats  vs. Cold sweats

    • Apocrine - produce sweat plus a milky or yellowish substance composed of fat and protein.

      • Found in the arm pits and genitalia

      • Thought to be scent glands.

    • Ceruminous - produce cerumen (ear wax)

    • Mammary glands- produce milk

  • Sebaceous (oil (sebum)) glands

    • Softens and lubricates hair and skin

    • Slows water loss and kills bacteria


  • Senses insects that land on the skin.

  • Hair on the head protects the head from impacts, sunlight and heat loss.

  • Eyelashes shield the eye

  • Nose hairs filter the air


What is hair?

Hair is made in hair follicles.  It is composed of dead, keratinized skin cells.

Hair is made up of two parts:

  • Shaft

    • Medulla(central core)

    • Cortex (bulky layer)

    • Cuticle (heavily keratinized; protects hair)

  • Root


Hair Shaft

Hair Root

The Arrector pili muscles are a band of muscle tissue which connects a hair follicle to the dermis. When stimulated, the arrector pili will contract and cause the hair to become more perpendicular to the skin surface (stand on end).  In mammals with fur, this causes more air to be trapped next to the skin, which acts as inulation.  In humans, it causes "goose bumps".


  • A nail is a scale-like modification of the epidermis

  • Made of tightly compressed keratinized cells

  • Useful tools to pick up small objects or scratch an itch.

  • Nail matrix is the region responsible for nail growth.


Detailed Nail Anatomy