The integumentary, skeletal, and muscular systems are all very different, but they all work together to achieve one purpose- to protect your body and to keep it staying up and moving.

The integumentary system is made up of specialized structures that make up the skin, hair, and nails. It protects the body from injury, defends against pathogens, regulates body temperature, and prevents the body from drying out.

Skin is a major part of the integumentary system. Skin has three layers:

1. Epidermis- This is the outermost layer formed of flattened dead cells. It contains keratin, which makes skin tough and waterproof. The inner layer of the epidermis produces melanin, or pigment that gives skin its color.
2. Dermis- This layer is made of living cells (nerve, blood, and skin cells, as well as hair follicles). Blood vessels regulate temperature, and sweat glands produce sweat, which removes heat. An oil called sebum is also produced in this layer- it keeps skin flexible and waterproof.
3. Subcutaneous tissue- This layer is mostly fat. It acts as a shock absorber and insulator. Energy is stored here, and the layers of fat anchor the skin to the organs that it covers.
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The skeletal system is the framework for your body. The human body has 206 bones in it. There are several different types of bone- long bone, short bone, flat bone, and irregular bones. Each bone has different parts to it:

1. Compact bone has a hard outer covering and is made of dense connective tissue. Mineral rings are found inside of it, as well as series of tubes called Haversarian canals. This kind of bone contains blood vessels.
2. The inner layer is spongy bone. This is a loosely structured network of connective tissue. This is where bone marrow, or the material inside of bones, is found.
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The human skeleton is divided into two parts: the axial skeleton (skull, sternum, ribs, vertebral column) and the appendicular skeleton (upper and lower extremities, shoulder and pelvic girdle). Bones connect to each other with ligaments, while muscles connect to bones with tendons.
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The human body contains more than 650 individual muscles that allow the body to move by contracting. Muscles come in pairs; when one contracts, the other expands, and movement occurs. There are two major classifications of muscle:

  1. Voluntary: Muscles we consciously control, such as our limbs.
  2. Involuntary: Muscles that work independent of conscious thought, such as the heart.
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There are three main types of muscle.

  1. The cardiac muscle is the heart itself. Unlike other muscles, it is not attached to any bones, but rather is a functioning unit by itself. Cardiac muscle is involuntary muscle.
  2. Skeletal muscle makes up about 40% of an adult’s weight and is voluntary muscle. They provide movement through contraction.
  3. Smooth muscle is what makes up the body’s internal organs. These muscles are involuntary and are often controlled by the nervous system and other hormones.

1) What system provides the framework of the body?
A) Muscular B) Skeletal C) Endocrine D) Integumentary
2) What is the outemost layer of skin called?
A) Epidermis B) Dermis C) Compact Skin D) Dead Skin
3) Describe how muscles work in pairs to provide movement.
4) Why do some muscles need to be involuntary?

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