| Alveoli | Tiny air sacs in the lungs where gas exchange occurs |
| Antibody | Protein produced by the immune system that neutralizes harmful substances |
| Atrium | Upper chamber of the heart that receives blood |
| Axon | Part of a neuron that carries impulses away from the cell body |
| Bile | Digestive fluid produced by the liver that helps break down fats |
| Capillary | Smallest blood vessel where nutrients and gas exchange occurs |
| Cerebrum | Largest part of the brain; controls thinking, memory, and voluntary movement |
| Diaphragm | Muscle below the lungs that helps with breathing |
| Digestive enzyme | Protein that helps break down food into smaller nutrients |
| Endocrine gland | A gland that releases hormones directly into the bloodstream |
| Epidermis | Outer layer of the skin |
| Hormone | Chemical messenger that regulates body functions |
| Involuntary muscle | Muscle that works automatically, such as in the heart or intestines |
| Joint | Place where two or more bones meet |
| Kidney | Organ that filters blood and produces urine |
| Ligament | Tough connective tissue that links bones together |
| Lymph | Fluid that circulates through lymphatic vessels and contains immune cells |
| Melanin | Pigment that gives skin its color and protects against UV rays |
| Neuron | Nerve cell that transmits electrical signals |
| Ovary | Female organ that produces eggs and hormones |
| Pancreas | Gland that produces insulin and digestive enzymes |
| Peristalsis | Wave-like muscle contractions that move food through the digestive tract |
| Pituitary gland | Master gland that controls other endocrine glands |
| Red blood cell | Blood cell that carries oxygen using hemoglobin |
| Reflex | Automatic, rapid response to a stimulus |
| Sarcomere | Unit of muscle contraction in skeletal muscle |
| Skeletal muscle | Voluntary muscle attached to bones |
| Spinal cord | Nerve bundle that carries messages between brain and body |
| Synapse | Gap between neurons where nerve signals are transmitted chemically |
| Tendon | Connective tissue that attaches muscle to bone |
| Testosterone | Hormone that controls male development and reproduction |
| Thyroxine | Hormone that regulates metabolism (produced by the thyroid gland) |
| Uterus | Female organ where a fetus develops |
| Ventricle | Lower chamber of the heart that pumps blood out |
| White blood cell | Immune cell that fights infection |