ASVAB Practice

Human Body Systems

Circulatory: Heart pumps blood through arteries (away from heart) and veins (toward heart). Left ventricle → aorta → body. Right ventricle → pulmonary artery → lungs. Capillaries are tiny vessels where gas/nutrient exchange occurs.

Respiratory: Nose → trachea → bronchi → bronchioles → alveoli (gas exchange: O₂ in, CO₂ out). The diaphragm contracts (flattens) to inhale.

Digestive: Mouth → esophagus → stomach (acid + enzymes) → small intestine (most absorption) → large intestine (water reabsorption). Enzymes are proteins that accelerate chemical reactions. Pancreas secretes digestive enzymes.

Nervous: Brain + spinal cord = CNS. All other nerves = PNS. The medulla oblongata controls involuntary functions: breathing, heart rate, blood pressure. Neurons transmit electrical signals.

Endocrine: Glands secrete hormones into the bloodstream. - Pituitary: "master gland" — controls other glands - Thyroid: metabolic rate - Adrenal cortex: cortisol (stress response, raises blood glucose) - Pancreas: insulin (lowers blood glucose), glucagon (raises blood glucose)

Muscular: Skeletal (voluntary), smooth (involuntary, in organs), cardiac (involuntary, only in heart). Tendons connect muscle to bone. Ligaments connect bone to bone.

Immune: White blood cells fight pathogens. Antibodies recognize specific antigens.

Excretory: Kidneys filter blood and produce urine; also regulate blood pH by excreting H⁺ ions and retaining bicarbonate (HCO₃⁻) during acidosis.

Integumentary: Skin (body's largest organ), hair, nails. Regulates temperature, prevents water loss, blocks pathogens. Contains exocrine glands (sweat, sebaceous).