Chapter 29 – The Human Body Section 1 – An Inside View of the Human Body Section 2 – Skin Section 3 - Bones Section 4 - Muscles

Section 29.1 – An Inside View of the Human Body All of the trillions of cells of the body come from a single cell – the fertilized egg. All the cells look the same at the beginning, but the cells start to become specialized to carry out specific tasks. Cells that are the same group together to become tissues. A tissue is a group of similar cells that work together to perform a specific function – such as movement or protection

The four types of tissue Epithelial tissue Muscle tissue Nervous tissue Connective tissue Epithelial tissue covers and protects. The cells are tightly connected and are arranged in flat sheets. Epithelial tissue prevents damage to the cells that lie beneath it. Examples of epithelial cells Skin Exocrine glands like sweat glands and digestive glands

Muscle tissue – it moves the parts of your body Muscle tissue – it moves the parts of your body. Even while you are sitting, muscles move food through your digestive system, move blood through your heart and maintain your posture. Muscle fibers respond to electrical stimulus from the nerves. The fibers contract to shorten and then relax. Examples: Heart or cardiac muscles – generate their own electrical signals, nerves to the heart control how fast Skeletal muscles – attached to the bones, work in pairs, under voluntary control Smooth muscle – not under conscious control, found in blood vessels, pupil of eye, walls of internal organs.

Nervous tissue sends electrical signals through the body. Nervous tissue is found in your brain, nerves, and sense organs. The cells are called neurons and they transfer the electrical impulses long distances along long extensions.

Connective tissue cells are spaced far apart, the contain few cells Connective tissue cells are spaced far apart, the contain few cells. Some connective tissues are fluids; others more like crystals. There are three types of connective tissue: Defensive – tissue that defends the body; example white blood cells Structural – tissue that supports the body; example bone, cartilage, ligaments, tendons, and fibroblasts Sequestering – tissue that stores particular compounds; example red blood cells, fat, and melanin in the skin

Section 29.2 - Skin The skin is composed of two main parts: The epidermis-the outer layer, thin The dermis – the thicker, under layer. The dermis is composed mainly of connective tissue. Fibers in the dermis make your skin tough, flexible and elastic. The dermis also contains nerves, muscles, blood vessels, hair follicles and glands. The nerves enable you to sense pressure, temperature and pain. The dermis also has tiny muscles that are attached to the hairs in your skin.

Blood vessels in the skin carry nourishment, remove waste, and cool the body. Blood radiates heat into the air as it passes near the surface of the skin. If your body becomes too hot, the tiny blood vessels enlarge, allowing more blood to flow through the dermis near the body surface. Sweat is another way that your body removes excess heat. Your skin contains about 100 sweat glands per square centimeter. The evaporation of sweat from the surface of your skin removes the heat much more efficiently. Without sweat, you would have difficulty cooling your body on a hot day or after exercising.

Not all your skin is alive Not all your skin is alive. These cells were formed two to four weeks earlier in the innermost layer of the epidermis, a region called the basal layer. After the cells are formed, they are pushed outward by the new cells forming underneath. As the epithelial cells move far away from the nutrient source and fill with keratin, the cells die. A strand of hair is made of dead, keratin-filled cells that overlap like roof shingles. Hair grows from specialized cells called hair follicles. Each hair on your head grows for several years before it goes into a resting phase for a few months. While the follicle is dormant, the hair falls out. The inner epidermal cell is the most active region for cell division.

Skin Disorders Skin is colored by cells that produce a brown pigment called melanin. The amount of melanin produced depends on two factors: a genetic trait that varies from person to person the length of time one is exposed to ultraviolet radiation. The longer you are exposed to the sun, the darker your melanin becomes. This darkening protects you from further burning. Your skin is not only a protective barrier, but also the most exposed part of your body.

Oil glands do produce oil at the base of the hair follicle to waterproof your skin and hair. During adolescence the increased hormones also increase the amount of oil produced. The oil combines with cellular debris and bacteria to clog follicles which produces the skin eruptions. The pimple is evidence that the body is fighting skin damage and invading bacteria. Ultraviolet rays caused by sun exposure or tanning beds results in a thickening of the skin, more rapid skin aging, a loss of elasticity, greater wrinkling and cancer of the skin. The best protection from sunburn is reducing your exposure to ultraviolet rays and remaining covered when in the sun. Stay out of the sun from 10 am – 3 pm Cover up with hat, UV-filtering eyeglasses and clothes You can still be burned on a cloudy day Avoid tanning beds and lamps

Continued exposure to ultraviolet light can trigger cellular mutations in DNA, which can cause cells to lose the ability to stop dividing. Basal cell cancer is the most common skin cancer and easily treated if found in the early stages. This cancer is believed to be due to exposure to the sun. Another kind begins in the flattened cells of the epidermis. They begin as flat, scaly, reddish patches on the skin, an indication that the skin has been damanged. A malignant melanoma usually occur on a mole. They result in 75% of all deaths from skin cancer. Sunburns before age 18 increases risk of skin cancer later in life.

Chapter 29.3

Anabolic steroids are used to increase the size of their muscles Anabolic steroids are used to increase the size of their muscles. They are powerful synthetic compounds that chemically resemble the male sex hormone, testosterone. There are very serious side effects and health problems associated with its use. If used before complete maturity, the steroids stop the bones from growing