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Notes for 7th grade obtained from Holt Science and Technology: Life Science. Austin: Holt Rinehart & Winston, 2007. Print.
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Chapter 22 Section 4
List 4 functions of the skin
Describe the 2 layers of the skin
Describe the structure and function of hair & nails
Describe 2 kinds of damage that can affect skin
1 sq. inch of skin can hold as many as: 650 sweat glands 20 blood vessels More than 1,000 nerve endings
No 2 people have the same fingerprints
More than ¾ of the dust in some homes is made up of dead skin cells!!!!!!
Only mammals have true hair
Visible signs of aging occurs most in this system: age spots, wrinkles, gray hair, less active seat glands
Hair that is kept short grows an average of 2cm per month; growth slows to 1cm per month for hair longer than 30 cm
Fingernails grow ~ 2 cm each year (middle finger is the fastest!) 3x quicker than toenails!
Composed of the skin, hair, nails
Covers your body and helps to maintain homeostasis
1. Protects: keeps water in your body and foreign particles out
2. Nerve endings keep you in touch with the outside world; you can feel the world around you
3. Helps to regulate body temperature (sweat glands)
4. Helps to get rid of wastes; removed in sweat
Skin color is determined by melanin
A lot of melanin, skin is dark; little melanin, light
Melanin absorbs UV light from the sun
Helps to reduce damage that can lead to skin cancer (all skin still needs to be protected!)
Skin is a complex organ:
Composed of: Blood vessels Nerve fibers Hair follicles Muscle fibers Oil glands Sweat glands
http://www.factmonster.com/images/ESCI351SKIN003.gif
Skin is the largest organ in the body
In an adult it covers an area of about 2m²
2 main layers Epidermis: outermost layer
Dermis: the thicker layer that lies beneath
Made of epithelial tissue
Made of many layers of cells, but is only as thick as 2 sheets of paper (thicker on palms of hands & soles of feet)
Most cells here are dead
The cells are filled with a protein called keratin (makes the skin tough)
http://www.naturalrussia.com/nr/images/skin_structure.gif
http://www.dermnetnz.org/doctors/principles/images/epidermis.jpg
Lies beneath the epidermis
Has many fibers made of a protein called collagen (fibers that provide strength)
Collagen fibers let skin bend without tearing
Contains many smaller structures Sweat glands, follicles, nerve fibers, fat cells,
blood vessels, oil glands, muscle fibers
http://1stholistic.com/Beauty/images/skin-section.GIF
Important part of the system
Like skin, hair & nails are made of living & dead cells
Hair forms at the bottom of a tiny sac called a hair follicle
Hair grows as new cells are added at the hair follicle
Older cells get pushed upward
Only living cells are in the follicle
Like skin, hair gets its color from melanin
Hair helps protect skin from UV light
Keeps particles (dust, insects) out of eyes and nose
Helps regulate temperature (muscles in follicles contract) – trap warm air and warm body
http://www.infovisual.info/03/037_en.html
Nails grow from living cells in the nail root at the base of the nail
As new cells form, the nail grows longer
Protect the tips of fingers and toes
Allows your fingers and toes to remain sensitive for touch
http://www.drstandley.com/images/fingernail.gif
Your skin can usually repair itself when injured
Damage to genetic material can cause skin cancer
Skin is also affected by hormones (over produce in oil glands) – leads to acne when bacteria clog hair follicles
http://www.path.cam.ac.uk/partIB_pract/P03/image04.jpg
A blood clot forms over a cut to stop bleedingKeeps bacteria from entering the woundBacteria fighting cells come to kill bacteria in the areaDamaged cells are replaced through cell divisionA scar is all that is left on the surface
What are the 4 functions of the skin?
Describe 2 layers of the skin