Human Body Structure and Skin

Basic Structures I

• The human body consists of chemicals, cells, tissues, organs, and systems that work together to form the entire organism.
• The skin is the body's largest and heaviest organ, consisting of two layers: the epidermis (superficial layer) and the dermis (deep underlying layer).

Skin

• The epidermis contains keratin, a protein that toughens the skin, and keratinocytes, which produce keratin.
• The epidermis also contains melanin, a natural skin pigment that determines hair, skin, and eye color in people.
• The dermis is a layer of connective tissue that contains fat, nerve, and vessel.
• Skin appendages include hair, nails, and cutaneous glands (sebaceous and sweat glands).

Deep Fascia

• The deep fascia is a layer of dense connective tissue that lies beneath the subcutaneous tissue.
• Inward extensions of the deep fascia form the intermuscular septa, which separate muscles.

Muscle

• Muscle is a tissue that generates tension through contraction.
• There are three types of muscle: smooth muscle, cardiac muscle, and skeletal muscle.
• Smooth muscle is found in organs and blood vessels, cardiac muscle is confined to the heart, and skeletal muscle is responsible for voluntary movements.

Muscle Structure

• A muscle cell is also known as a myocyte.
• Skeletal muscle cells are long and threadlike, and are bound together into bundles or fascicles.
• The connective tissue of the muscle includes the epimysium, perimysium, and endomysium.

Tendons

• Tendons are formed by the collagen fibers of the epimysium, perimysium, and endomysium, and connect muscles to bone, cartilage, or skin.

Blood Vessels

• The cardiovascular system consists of the heart and blood vessels.
• There are three types of blood vessels: arteries, capillaries, and veins.
• Arteries are thick-walled and carry blood away from the heart.
• Capillaries are the smallest vessels and allow for exchanges between the blood and tissues.
• Veins contain unidirectional valves that direct the flow of blood towards the heart.

Lymphatic System

• The lymphatic system collects tissue fluid through open-ended channels called lymphatic vessels.
• Lymphatic vessels drain into aggregations of lymphoid tissue (lymph nodes), which filter lymph.
• Lymph eventually drains into the venous system.