Blood circulating throughout the body is a transport network that carries oxygen, nutrients, and waste products. Let us examine the structure of the heart, the central pump.
Basic Knowledge
The human heart is divided into four chambers: right atrium, right ventricle, left atrium, and left ventricle.
Blood flow (two circulations):
① Pulmonary circulation (lesser circulation): right ventricle → pulmonary artery → lungs (gas exchange) → pulmonary vein → left atrium
② Systemic circulation (greater circulation): left ventricle → aorta → whole body (delivers oxygen and nutrients and receives CO₂ and waste products) → vena cava → right atrium
Three types of blood vessels:
・Artery: blood leaving the heart; thick and elastic walls
・Vein: blood returning to the heart; thin walls and valves (prevent backflow)
・Capillary: a narrow blood vessel connecting arteries and veins; the site of material exchange
Components of blood:
・Red blood cells: carry oxygen using hemoglobin (disc-shaped; no nucleus)
・White blood cells: immunity (attack bacteria and other substances)
・Platelets: stop bleeding (coagulation)
・Plasma: the liquid component; carries nutrients, waste products, and hormones
Atria and ventricles (atria=receiving chambers, ventricles=pumping chambers; two of each, four chambers total)
Pulmonary and systemic circulation (the two blood circulation routes between the heart and lungs and between the heart and the whole body)
Arteries, veins, and capillaries (vessels leaving the heart, returning to the heart, and exchanging materials)
Red blood cells and hemoglobin (cells that carry oxygen and the oxygen-binding protein inside them)
Arterial and venous blood (bright red blood containing much oxygen / dark red blood containing much CO₂)
Tissue fluid (fluid that leaks from capillaries and bathes cells; mediates material exchange between cells and blood)
Further Study (Background and Significance)
Arterial blood and an artery are different concepts. Arterial blood means “blood rich in oxygen,” while an artery is “a blood vessel leaving the heart.” They usually correspond, but the pulmonary artery leaves the heart while carrying venous blood (rich in CO₂), and the pulmonary vein returns to the heart while carrying arterial blood (rich in oxygen).
Hemoglobin is a protein containing iron (Fe). It binds to oxygen in the lungs, where the oxygen concentration is high, and releases it in tissues. Iron deficiency causes anemia, a condition in which the amount of hemoglobin decreases and oxygen transport is reduced.
The heart beats about 70 times per minute (in an adult at rest) and about 100,000 times per day. It pumps about 70mL per beat and about 7,000L per day, making it an amazing organ that pumps hundreds of thousands of liters of blood during a lifetime.
Capillary walls consist of only one layer of cells, so materials can easily enter and leave. Some blood plasma leaks through the walls and becomes tissue fluid, bathing cells and delivering nutrients and oxygen. Some of it collects in the lymphatic vessels and eventually returns to the veins.
- Heart=four chambers (right atrium, right ventricle, left atrium, left ventricle)
- Pulmonary circulation: right ventricle→lungs→left atrium
- Systemic circulation: left ventricle→whole body→right atrium
- Arteries=outward/veins=returning/capillaries=connecting
- Veins have valves (prevent backflow)
- Red blood cells+hemoglobin=oxygen transport
- Plasma=liquid component; transports nutrients and waste products
Points of Caution (Easily Confused)
① Arteries (vessels leaving the heart) and arterial blood (oxygen-rich blood) are different concepts. Venous blood flows through the pulmonary artery. ② Atria are the entering side, and ventricles are the outgoing side. Do not reverse them. ③ Veins have valves, but arteries do not. The valves return blood to the heart against gravity. ④ Red blood cells have no nucleus, a characteristic unique to mammals that allows them to transport oxygen more efficiently.
Practice
- Name the chamber that pumps blood from the heart to the whole body.
- Between the pulmonary artery and pulmonary vein, which carries oxygen-rich blood (arterial blood)?
- Name the protein inside red blood cells that carries oxygen.