Nutrient Distribution and the Circulatory System
The Distribution of Nutrients and the Circulatory System
The body needs to distribute nutrients and oxygen to cells and remove waste products like CO2, which will be eliminated by the excretory organs. This is the primary function of the circulatory system.
Components of the Circulatory System
- Blood: The means of transport for nutrients, oxygen, and waste.
- Blood Vessels: A network of tubes through which blood circulates.
- Heart: An organ that acts as a pump, making blood circulate.
Blood Vessels
- Arteries: Carry blood *from* the heart *to* the organs. Their walls are thick and elastic. They branch into smaller vessels called arterioles, and then into capillaries.
- Veins: Carry blood *from* the organs *to* the heart. Their walls are less elastic and contain internal valves to prevent the backflow of blood. Small veins called venules carry blood from the capillaries to the veins.
- Capillaries: Very thin-walled vessels. The exchange between blood and tissue cells (nutrients, wastes, and gases) occurs in the capillaries.
Blood Vessels of the Heart
Blood vessels that reach the heart:
- Right Atrium: Receives blood from the two venae cavae (superior and inferior).
- Left Atrium: Receives blood from the four pulmonary veins.
Blood vessels that leave the heart:
- Left Ventricle: The aorta, the largest artery in the body, exits from here.
- Right Ventricle: The pulmonary artery exits from here.
Coronary System: The set of small arteries and veins that carry blood to the heart’s own tissues.
Blood Composition
- Blood Plasma: A yellow liquid consisting of water, mineral salts, glucose, and proteins.
- Cellular Components: Make up about 40% of blood volume (called the hematocrit). A decrease in hematocrit indicates anemia.
- Red Blood Cells (Erythrocytes): Responsible for oxygen transport.
- White Blood Cells: Defend the body against parasites and tumor cells. Three types exist: lymphocytes, granulocytes, and others.
- Platelets: Cell fragments involved in blood clotting.
Blood Transfusions
The administration of blood or its components from one person (donor) to another (recipient).
Excretion
The elimination of waste substances from cellular activity. Organs involved in excretion include:
- Kidneys: Form urine from blood.
- Lungs: Remove CO2 from cell metabolism.
- Sweat Glands: Excrete sweat through the skin.
- Liver: Processes substances from the degradation of hemoglobin, which are then sent to the intestine.
Risk Factors
- Cardiovascular Diseases: Often don’t manifest until a blood vessel is blocked.
- Respiratory Diseases: Are directly related to tobacco consumption.
- Renal Impairment: Symptoms include tiredness, swelling of feet and ankles, and increased need to urinate.
Renal Function
The kidneys maintain the constant chemical composition of blood and regulate water loss in the urine.
Blood Circuits
- Pulmonary Circuit: Begins when oxygen-poor blood leaves the right ventricle through the pulmonary artery and goes to the two lungs. It returns to the left atrium of the heart.
- Systemic Circuit: Oxygenated blood is pumped from the left ventricle through the aorta and distributed throughout the body. It returns, via the vena cavae, to the right atrium.
Cardiac Cycle
- Ventricular Systole: The cycle begins with the contraction of the ventricles, which forces blood out of the heart through the aorta and pulmonary artery, preventing backflow into the atria.
- Ventricular Diastole and Atrial Systole: The ventricles relax and fill with blood. At the same time, the atria contract.
- Atrial Diastole: The atria relax and fill with blood coming from the veins.
Circulation in Veins
Blood circulates through the vessels due to the pumping action of the heart. Each heartbeat consists of a contraction movement (systole) followed by a relaxation movement (diastole).