- The circulatory system, also known as the cardiovascular system, is a vital biological network that functions to transport blood, oxygen, nutrients, hormones, and waste products throughout the human body.
- It is essential for maintaining homeostasis, supporting cellular activity, defending against pathogens, and regulating body temperature and pH levels. This system integrates with almost every other system in the body, serving as a conduit for sustaining life and promoting internal stability.
- At the core of the circulatory system is the heart, a muscular, four-chambered organ that serves as a powerful pump. The heart consists of the right atrium, right ventricle, left atrium, and left ventricle. It maintains two separate circulatory loops: the pulmonary circulation and the systemic circulation. The pulmonary circulation moves deoxygenated blood from the right side of the heart to the lungs, where carbon dioxide is exchanged for oxygen. The oxygen-rich blood then returns to the left side of the heart, which pumps it through the systemic circulation to nourish tissues and organs throughout the body.
- The blood vessels act as highways within the circulatory system and are categorized into arteries, veins, and capillaries. Arteries carry blood away from the heart under high pressure; their muscular walls help accommodate pulsatile flow. They branch into arterioles and eventually into capillaries, where thin walls facilitate the exchange of gases, nutrients, and waste between blood and surrounding tissues. From there, blood moves into venules and then veins, which return blood to the heart. Valves in veins prevent backflow, especially in the lower extremities, aiding the return of blood against gravity.
- Blood itself is composed of plasma (the fluid component) and formed elements, which include red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes). Red blood cells carry oxygen bound to hemoglobin and remove carbon dioxide. White blood cells are key players in the immune system, defending the body against infections. Platelets contribute to clot formation, helping prevent excessive blood loss after injury.
- The circulatory system is under constant regulation by the autonomic nervous system and endocrine signals. The sympathetic and parasympathetic nervous systems adjust heart rate and vessel diameter in response to internal and external stimuli. Hormones like epinephrine, norepinephrine, angiotensin II, and vasopressin influence vascular tone and fluid balance. Baroreceptors and chemoreceptors located in major arteries monitor changes in pressure and chemical composition, providing feedback to the brain to maintain cardiovascular stability.
- Additionally, the circulatory system includes specialized subsystems such as the coronary circulation, which supplies the heart muscle with oxygenated blood, and the hepatic portal circulation, which routes nutrient-rich blood from the digestive tract to the liver for processing. Closely related is the lymphatic system, which returns excess tissue fluid to the bloodstream and plays a crucial role in immune surveillance and lipid absorption.
- Disorders of the circulatory system are among the leading causes of death globally. Conditions such as hypertension, atherosclerosis, myocardial infarction (heart attack), stroke, and heart failure can result from or lead to disruption in blood flow and oxygen delivery. Lifestyle factors such as diet, physical activity, smoking, and stress, as well as genetics, heavily influence cardiovascular health.
