Fifteen systems

Skeleton

Bones form the supporting framework of the body, protect organs, and provide attachment points for muscles. Their internal tissue also stores minerals and produces blood cells.

Muscles

Skeletal muscles generate movement by pulling on their attachments. Together with tendons, they move joints, stabilize posture, and produce heat.

Heart

The heart is a muscular pump with four chambers. Its valves direct blood forward through the pulmonary and systemic circuits.

Sensory organs

These structures contribute to special senses, including sight, hearing, and balance. Their specialized tissues detect stimuli and work with the nervous system to convey information.

Arteries

The heart drives blood through the circulation. Arteries carry blood away from the heart to supply tissues or, in the pulmonary circuit, to the lungs.

Veins

Veins return blood toward the heart. Superficial and deep networks collect blood from the tissues; the pulmonary veins bring oxygenated blood back from the lungs.

Nervous system

The brain, spinal cord, and peripheral nerves carry and process signals. They support sensation, movement, coordination, and automatic regulation of body functions.

Respiratory

The airways conduct air to the lungs, where oxygen and carbon dioxide move between air and blood. Breathing depends on pressure changes produced by respiratory muscles.

Digestive

The digestive tract breaks down food, absorbs nutrients and water, and moves waste onward. Accessory organs contribute bile and digestive enzymes.

Urinary

The kidneys filter blood and regulate fluid, electrolyte, and acid-base balance. Urine travels through the ureters to the bladder and exits through the urethra.

Lymphatic

Lymphatic vessels return excess tissue fluid to the circulation. Lymph nodes and other lymphoid organs support immune surveillance and responses.

Endocrine

Endocrine organs release hormones into the blood to coordinate processes such as metabolism, growth, stress responses, and reproduction.

Reproductive

The male reproductive structures represented here contribute to sperm production, maturation, transport, and the production of sex hormones.

Body surface

The body surface provides an outer anatomical reference. The integumentary system forms a protective barrier and contributes to sensation and temperature regulation.

Connective tissue

Cartilage, ligaments, and other connective tissues support, connect, and separate structures. Their roles include stabilizing joints and distributing mechanical loads.