# HUMAN BODY The human body relies on 10 major interconnected organ systems working in harmony to maintain homeostasis — regulate vital functions, process nutrients, support movement, and fight disease — * Nervous * Integumentary * Circulatory * Endocrine * Respiratory * Digestive * Reproductive * Urinary * Muscular * Skeletal NICER DRUMS (Nervous, Integumentary, Circulatory, Endocrine, Respiratory, Digestive, Reproductive, Urinary, Muscular, Skeletal) Nervous Primary Function: Coordinates voluntary and involuntary actions, and transmits signals between different parts of the body. Key Organs: Brain, spinal cord, and sensory organs. Cardiovascular (Circulatory) System Primary Function: Pumps blood to deliver oxygen, nutrients, and hormones to cells, and removes waste products. Key Organs: Heart, blood vessels, and blood. Respiratory System Primary Function: Supplies oxygen to the blood for cellular use and expels carbon dioxide waste.Key Organs: Lungs, trachea, bronchi, and diaphragm. Digestive System Primary Function: Breaks down food, absorbs nutrients, and eliminates solid waste. Key Organs: Stomach, intestines, liver, gallbladder, and esophagus. Urinary (Excretory) System Primary Function: Filters blood to remove excess water, salts, and waste products, while regulating pH balance. Key Organs: Kidneys, ureters, and bladder Skeletal System Primary Function: Provides structural support, protects internal organs, produces blood cells, and stores minerals. Key Organs: Bones, cartilage, ligaments, and tendons Muscular System Primary Function: Allows for voluntary and involuntary movement, maintains posture, and generates heat. Key Organs: Skeletal, smooth, and cardiac muscles. Endocrine System Primary Function: Produces and secretes hormones to regulate metabolism, growth, and reproduction. Key Organs: Pituitary gland, thyroid, pancreas, and adrenal glands. Lymphatic & Immune System Primary Function: Defends the body against infections, diseases, and foreign invaders. Key Organs: Lymph nodes, spleen, thymus, and bone marrow. Reproductive System Primary Function: Produces sex cells and hormones, facilitating sexual reproduction and the development of offspring. Key Organs: Ovaries, uterus, testes, and prostate. The Integumentary System, which includes the skin, hair, and nails, is frequently included as an 11th primary system, functioning as a protective barrier