The musculoskeletal system gives the body its shape, protects vital organs, and enables movement through muscles and bones working together.

Includes bones, muscles, joints, tendons, and ligaments

• Bones form the skeleton, while muscles are attached to bones and allow voluntary movement.

• Works closely with the nervous system

  • The nervous system sends signals to the muscles to contract, which allows movement and coordination.

    
    

The immune system defends against bacteria, viruses, and other harmful invaders that can cause illness.

Includes white blood cells, lymph nodes, spleen, and bone marrow

• White blood cells (like T cells and B cells) identify and destroy threats, while lymph nodes filter harmful substances.

• Works closely with the circulatory system

  • Immune cells travel through the bloodstream to reach infection sites and respond quickly to invading pathogens.

The circulatory system delivers oxygen and nutrients to tissues and organs and removes waste products like carbon dioxide.

Includes key organs like the heart, blood vessels, and blood

• The heart pumps blood through arteries, veins, and capillaries to maintain circulation throughout the body.

• Works closely with the respiratory system

  • The circulatory system picks up oxygen from the lungs (respiratory system) and delivers it to the body while carrying carbon dioxide back to the lungs to be exhaled.

The respiratory system brings in oxygen from the air and removes carbon dioxide from the body.

Includes organs like the lungs, trachea, and diaphragm

• Air enters through the nose or mouth, travels down the trachea, and reaches the lungs where gas exchange occurs in the alveoli.

• Works closely with the circulatory system

  • Oxygen from the lungs enters the bloodstream, and carbon dioxide from the blood is sent back to the lungs to be exhaled.

The endocrine system produces hormones that control growth, metabolism, mood, and more.

Includes glands such as the pituitary, thyroid, adrenal glands, and pancreas

• These glands release hormones directly into the bloodstream to reach organs and tissues.

• Works closely with the nervous system

  • The hypothalamus (part of the brain) controls the pituitary gland, linking the nervous system and endocrine system to maintain balance (homeostasis).

    
    

The reproductive system produces sex cells (sperm in males, eggs in females) and supports fertilization and development of new life.

ncludes organs like the ovaries, uterus, and vagina (females); testes, prostate, and penis (males)

• These organs are responsible for hormone production, gamete creation, and—in females—the development of a fetus.

• Works closely with the endocrine system

  • Hormones like estrogen and testosterone, produced by endocrine glands, regulate sexual development, menstruation, and reproductive functions.