Human Circulatory System: Functions and Components
Circulatory Apparatus: Nutrient and Oxygen Transport
The circulatory apparatus is responsible for transporting nutrients and oxygen to all cells and collecting waste substances, leading them to the organs responsible for elimination.
Components of the Blood System
The blood system is composed of:
- Blood: The liquid responsible for transporting substances.
- Blood Vessels: The conduits where blood circulates.
- Heart: The organ that pumps blood continuously to reach all cells.
Blood Composition
Blood consists of a liquid part called plasma and a cellular suspension including:
- Plasma: A transparent yellow liquid in which blood cells float.
- Red Blood Cells (Erythrocytes): Disk-shaped cells without a nucleus, responsible for oxygen transport. They contain hemoglobin, giving blood its red color.
- White Blood Cells (Leukocytes): Cells with a nucleus, slightly larger than red blood cells, responsible for defending against infections. Types include:
- Granulocytes: Destroy microorganisms through phagocytosis.
- Lymphocytes: Produce antibodies.
- Monocytes: Phagocytic cells.
- Platelets (Thrombocytes): Tiny cells without a nucleus, responsible for blood clotting.
Blood Disorders and Functions
Anemia: A decrease in the number of red blood cells, which can result from hemorrhage, poor diet (iron deficiency), or deficient red blood cell production.
Blood Transport Functions:
- Carries oxygen from the lungs to cells and carbon dioxide from cells to the lungs.
- Transports dissolved nutrients from the intestine to all cells.
- Transports waste products from cells to organs for elimination.
- Transports hormones from endocrine glands to target tissues.
Defense: White blood cells defend the body against microorganisms through phagocytosis or antibody production. Blood clotting prevents blood loss and infection.
Temperature Regulation: Blood distributes heat throughout the body, acting as a coolant and allowing for fast heat dissipation.
The Heart: A Powerful Pump
The heart is the organ that pumps blood continuously through the circulatory system. It is composed of a specific muscle called the myocardium and has four chambers:
- Two upper chambers: Atria
- Two lower chambers: Ventricles
The atria have thin walls, while the ventricles have thick, muscular walls. Coronary arteries and veins supply the heart with blood. Valves between the atria and ventricles ensure unidirectional blood flow.
Blood Flow Through the Heart
- The right atrium receives blood from the vena cava and passes it to the right ventricle, which pumps it to the lungs via the pulmonary artery.
- The left atrium receives oxygenated blood from the lungs via the pulmonary veins and passes it to the left ventricle, which pumps it to the body via the aorta.
Systole is the contraction phase where ventricles eject blood. Diastole is the relaxation phase where ventricles fill with blood.
Blood Vessels and Circulation
There are three types of blood vessels:
- Arteries: Carry blood away from the heart. They have thick, elastic walls.
- Veins: Carry blood back to the heart. They have thinner walls than arteries.
- Capillaries: Connect arteries and veins. Their thin walls allow for gas and nutrient exchange.
The Lymphatic System
The lymphatic system consists of lymph nodes and vessels that circulate lymph, a fluid formed from plasma that leaks out of capillaries. Lymphatic capillaries absorb excess extracellular fluid and return it to the bloodstream.