The Heart and Its Chambers

The Heart and Its Structure

• The heart is a four-chambered organ roughly the size of a clenched fist, centrally located in the chest.
• Each heart consists of two atria (upper chambers) and two ventricles (lower chambers), separated by a muscular wall called the septum.
• The right atrium receives oxygen-poor blood from the body, while the left atrium receives oxygen-rich blood from the lungs.
• The right ventricle pumps oxygen-poor blood to the lungs, and the left ventricle pumps oxygen-rich blood to the rest of the body.

Blood Vessels and Valves

• Major blood vessels include the vena cava (largest vein), pulmonary artery, pulmonary veins, and aorta (largest artery).
• The vena cava directs oxygen-poor blood back to the heart; the pulmonary artery transports this blood to the lungs.
• Pulmonary veins bring oxygen-rich blood from the lungs to the left atrium, while the aorta distributes this blood to the body.
• Coronary arteries branch from the aorta to supply blood to the heart itself.
• Valves, including atrioventricular (tricuspid and bicuspid) and semilunar valves, prevent backflow of blood throughout the heart's chambers and vessels.

Types of Blood Vessels

• The circulatory system is closed, meaning blood remains within vessels during its journey.
• Three main types of blood vessels exist: arteries, veins, and capillaries.
• Arteries have thick walls to withstand high blood pressure and primarily transport oxygen-rich blood away from the heart.
• Veins have thinner walls, are more prone to collapse, and carry oxygen-poor blood back to the heart, equipped with valves to prevent backflow.
• Capillaries are the smallest vessels, one cell thick, facilitating the exchange of gases and nutrients between blood and cells.

Composition of Blood

• Blood consists of plasma (55% of blood weight) and corpuscles (45% of blood weight).
• Plasma is a straw-colored fluid containing water, proteins, and small inorganic substances.
• Corpuscles include red blood cells (RBCs), white blood cells (WBCs), and blood platelets (thrombocytes), produced in red bone marrow.

Formed Elements of Blood

• RBCs are biconcave disks without a nucleus, carrying oxygen due to the presence of hemoglobin.
• WBCs defend against infections by secreting antibodies and engulfing pathogens.
• Blood platelets are essential for clotting to prevent excessive bleeding.

Summary

• The heart's chambers work together to maintain blood flow and circulation.
• Blood vessels play distinct roles based on their structure and function.
• The blood transports vital substances and plays a crucial role in the immune response.