Skin

           The skin is a thin layer that covers your whole entire body.  It's almost like a "wrapper" that holds your body together, but does many more things.  It is practically your primary line of defense for your body.  It protects your inner tissues from drying out and also provides you with a sense of touch, grows hair and nails, and even keeps pathogenic microorganisms out of your body. 
            To the right a simple diagram of human skin is shown, also the structure of hair.  The skin is composed of two basic layers, the top is the epidermis, the inner is the dermis, and below the dermis is the hypodermis.  The hypodermis binds the skin to the outer lying tissues.
            The top layer of the epidermis is a layer of dead cells and the inner layer is of living cells.  The living cells are constantly reproducing in this layer of skin.  The dead cells in the epidermis are firm and sturdy and this is what mainly protects your body from pathogenic organisms because it is hard for them to penetrate through.
            Your skin also has hair.  About the only place your skin does not produce hair is in such areas as the palms of your hands and the soles of your feet.  Hair comes from a structure known as a hair follicle which are like tiny pits in the epidermis.  The lowest part of the hair follicle is called the matrix which have cells that rapidly reproduce.  When you get cold, the muscle that controls your hair automatically contracts pulling the hair straight up.  This causes a little bump and keeps in the warm which is usually called a goose pimple.
             Your hair also has sensation so that when your hair is moved or moving it sends signals to your brain telling you that something is touching your skin.  Since hair is so little even a gentle breeze sends off the sensation.
            Your skin also has sweat glands.  The sweat is produced in your sweat glands, travels up through the dermis in the sweat duct, and then pours out onto your skin through your sweat pores cooling you down.  Sweat also feed helpful bacteria and fungi that live on your skin.
            Have you ever wondered why people have different colors of skin?  It depends on how much of a chemical called melanin they have. This chemical is called a pigment because it tends to give off color to whatever it's on.  The more melanin someone has, the darker the skin they have but if someone has a less amount of melanin, they will have lighter skin.
            In the same way, hair's color depends on melanin too.  Dark hair has a lot of melanin in it, whereas, light hair has very little.  Red hair has a mixture of melanin and red pigment.  Without any melanin, the hair is white.

Smooth muscles and Cardiac muscles

Smooth muscles

            Smooth muscles have their name for a reason; unlike skeletal muscles, which are long and have orderly striped muscles, they appear smooth even under a microscope. Also unlike skeletal muscles, smooth muscles are involuntary muscles, which means that it doesn't take a conscious thought, they just do it on there own. The bicep and triceps, as seen to the right, would be an example of a smooth muscle.

          

Cardiac muscles

           The cardiac muscles are striped, similar to the skeletal muscles but smaller. Since the cardiac muscles are shaped like skeletal muscles, but are involuntary like smooth muscles they're kind of like a mix between the two. A heart, like on the right, is a type of cardiac muscle. The heart is controlled by something called a sinoatrial node. The sinoatrial node sets a pace for the heart; therefore it’s called a pacemaker.

Skeletal muscles

           There are three types of muscles in your body: skeletal muscles, smooth muscles, and cardiac muscles. We are going to focus on skeletal muscles. Skeletal muscles are the muscles that help with posture and balance.
           The first thing about your skeletal muscles is that they are voluntary muscles; which means they move when you want them to move, not just by themselves.
           Skeletal muscles, however, are not connected straight to your bones; they are connected by tendons, which attach to the skeleton.
           Although skeletal muscles do all these amazing things for us, they wouldn't be much good without joints.
           There are 4 different types of joints: Hinge joint (elbow), Ball and socket joint (shoulder), Saddle joint (ankle), and Washer joint (vertebrae).

  

    

                                                                   
   1. Hinge joint     2. Ball and socket joint     3. Saddle joint     4. Washer joint

           Around the joints is something called an air capsule, this produces joint fluid for the joint called synovial fluid, joints that contain this fluid are called synovial joints.
          Back to skeletal muscles; there are two main muscles that support your head: sternocleidomastoid muscles and the posterior triangle muscles, one of each on each side.

                                                            Outside muscle: Prostior triangle muscles
                                                          Inside muscle: Sternocleidomastoid muscles

                                                                     

            Muscles and joints work together to make a perfect creation by God.

Skeletal body

    The skeleton is split up into two parts: the axial skeleton (in the pink), and the appendicular skeleton (in the blue). The axial skeleton consists of the skull, vertebrae, and the rib cage; and the appendicular skeleton consists of the arms, legs, shoulder blades, collarbones, and the pelvis.

•     Axial skeleton- The portion of the skeleton that supports and protects the head, neck, and trunk.
•     Appendicular skeleton- The portion of your skeleton that connects to the axial skeleton and has the limbs attached to it.

        Your whole skeleton together is called your endoskeleton (usually referred to as just "skeleton"). The most important part of the endoskeleton is the vertebral column, usually called the vertebrae or backbone. Depending on whether an animal has vertebrae or not divides two different classifications. Therefore, humans are vertebrates along with rabbits, horses, foxes, and many others.
           The arms are connected to your body by something called the pectoral girdle; and your legs are connected to your body by your pelvic girdle. All of these work together to make a complete endoskeleton and keep your body staying upward.

Human Bones

   Bones are an important part of the human superstructure. They keep the body upright and allow bends in joints and sockets. There are three main parts to a bone: the compact bone, the spongy bone, and the medullary cavity, (as seen in the picture to the right).

        Bones are made up of collagen and minerals. The collagen is the flexible part of the bone made up of chemicals called proteins, the minerals are the hard part of the bone and are made up of chemicals called calcium.
         Both the compact bone and the spongy bone are made of the same substance (collagen and, the only difference is the substances are packed differently. In the compact bone the substances are packed hard to make a hard, tough substance; where as the spongy bone there are little holes throughout the hard bone, which gives it a spongy look, although it is quite hard giving support without much weight.

          The medullary cavity consists of red bone marrow, yellow bone marrow, and blood vessels. The red bone marrow produces the cells in your blood, and the yellow bone marrow is composed of fats being stored in your body.

            The bone is then covered by a substance called periosteum that is the white part of the bone that you see. This part of the bone contains blood vessels for nutrition in your bones. It also contains nerves to send signals to your brain if it gets damaged.