Human Anatomy , The integumentary system is the outer layer of the body. It protects the body from the environment, helps to regulate body temperature, and produces vitamin D. The integumentary system includes the skin, hair, nails, and sweat glands.
- Skin: The skin is the largest organ in the body. It is made up of three layers: the epidermis, the dermis, and the hypodermis. The epidermis is the outermost layer of skin. It is made up of dead cells that are constantly shed. The dermis is the middle layer of skin. It is made up of living cells that produce sweat, oil, and hair. The hypodermis is the deepest layer of skin. It is made up of fat cells that insulate the body and help to store energy.
Hair: Hair is made up of keratin, the same protein that makes up nails. Hair grows from hair follicles in the dermis. The hair follicle is a small sac in the skin that contains a hair root. The hair root is attached to a muscle that can make the hair stand up straight.
Nails: Nails are made up of keratin. They grow from nail beds in the dermis. The nail bed is a layer of tissue that supports the nail. The nail plate is the hard, visible part of the nail.
Sweat glands: Sweat glands are found all over the body. They produce sweat, which helps to cool the body down. Sweat glands are most concentrated in the armpits, palms, and soles of the feet.
The musculoskeletal system is responsible for movement. It includes the bones, muscles, and joints.
- Bones: Bones are the hard structures that make up the skeleton. They provide support for the body, protect the organs, and produce blood cells. Bones are made up of two types of tissue: compact bone and spongy bone. Compact bone is the hard, outer layer of bone. Spongy bone is the soft, inner layer of bone.
Muscles: Muscles are the tissues that allow us to move. They are made up of muscle fibers that contract and relax. There are three types of muscles: skeletal muscles, smooth muscles, and cardiac muscles. Skeletal muscles are the muscles that we control voluntarily. Smooth muscles are the muscles that control involuntary movements, such as digestion and blood flow. Cardiac muscles are the muscles that make up the heart.
Joints: Joints are the places where bones meet. They allow bones to move relative to each other. There are three types of joints: immovable joints, slightly movable joints, and freely movable joints. Immovable joints, such as the joints between the bones of the skull, do not allow any movement. Slightly movable joints, such as the joints between the vertebrae, allow limited movement. Freely movable joints, such as the joints in the elbows and knees, allow a wide range of movement.