Body Systems
Nervous system
The nervous system is the body's master control and communication network. It is divided into the central nervous system (CNS: brain and spinal cord) and the peripheral nervous system (PNS: nerves and ganglia). Using electrical and chemical signals, it integrates sensory input, processes information, and coordinates voluntary and involuntary responses. It enables thought, memory, emotion, perception, and regulates all bodily functions through motor output to muscles and glands.
Immune system
The immune system is a complex defense network that protects the body from pathogens like bacteria, viruses, and fungi, as well as from abnormal cells. It consists of innate (non-specific, immediate) and adaptive (specific, memory-based) components. Key cells include lymphocytes (B and T cells), phagocytes (macrophages, neutrophils), and antigen-presenting cells. It functions via physical barriers, immune surveillance, targeted attacks, and the production of antibodies and cytokines to maintain health and homeostasis.
Respiratory system
The respiratory system facilitates gas exchange between the body and the environment. Its primary organs are the lungs and the airways (nose, pharynx, larynx, trachea, bronchi). The system's core function is to supply oxygen to the bloodstream and remove carbon dioxide. This occurs in the alveoli, tiny air sacs where diffusion takes place. It also plays roles in vocalization, olfaction, and regulating blood pH.
Digestive system
The digestive system is responsible for breaking down food into absorbable nutrients and eliminating solid waste. It consists of the gastrointestinal tract (mouth, esophagus, stomach, intestines, anus) and accessory organs (liver, pancreas, gallbladder). Through mechanical and chemical digestion, it processes food, absorbs water, electrolytes, vitamins, and macronutrients (carbohydrates, proteins, fats), and transports indigestible matter for excretion, providing the body with essential energy and building blocks.
Urinary system
The urinary system, or renal system, is responsible for filtering blood, regulating fluid and electrolyte balance, and excreting metabolic wastes as urine. Its primary organs are the kidneys, ureters, urinary bladder, and urethra. The kidneys filter blood to form urine, reabsorb needed substances, and secrete waste products like urea. This system is critical for maintaining blood pressure, pH balance, red blood cell production (via erythropoietin), and overall homeostasis.