The Heart and circulation 25.

The Heart: Function & Basic Structure

• Primary Function:​ The heart is a muscular organ responsible for pumping blood around the entire body.

• Muscular Composition:​ The heart walls are almost entirely made of muscle tissue called cardiac muscle. these muscles are striated and branched.

• Myogenic (肌源性的) Activity:​ The heart is myogenic, meaning it has the intrinsic ability to contract without requiring an external stimulus (like nerve impulses) to initiate each heartbeat.

• Energy Requirements:​ Because the heart beats continuously throughout a person's life, it requires a constant supply of oxygen and glucose from the blood to sustain its activity.

• Coronary Artery (冠状动脉) System:​ To meet its energy needs, the heart has its own dedicated blood supply. The blood vessels that supply oxygen to the heart muscle cells are the coronary arteries.

Chamber Identification & Location

• Right Atrium（心房）:​ Located at the top right; receives deoxygenated blood.

• Right Ventricle（心室）:​ Located at the bottom right; pumps blood to the lungs.

• Left Atrium:​ Located at the top left; receives oxygenated blood.

• Left Ventricle:​ Located at the bottom left; pumps blood to the rest of the body.

Major Blood Vessels

• Vena Cava 腔静脉 (Superior & Inferior):​ Large veins that transport deoxygenated blood from the body into the Right Atrium.

• Pulmonary 肺的 Artery:​ Carries deoxygenated blood from the Right Ventricle to the Lungs.

• Pulmonary Vein:​ Transports newly oxygenated blood from the Lungs into the Left Atrium.

• Aorta 主动脉:​ The largest artery in the body; carries oxygenated blood from the Left Ventricle to the systemic circulation.

Heart Valves (Preventing Backflow)

• Tricuspid Valve 三尖瓣:​ Positioned between the Right Atrium and Right Ventricle. It closes when the right ventricle contracts to prevent backflow into the atrium.

• Pulmonary Valve:​ Located at the exit of the Right Ventricle into the Pulmonary Artery.

• Bicuspid Valve 二尖瓣 (Mitral Valve):​ Positioned between the Left Atrium and Left Ventricle. It closes to prevent backflow when the left ventricle contracts.

• Aortic Valve:​ Located at the exit of the Left Ventricle into the Aorta.

• The Double Pump Sequence:

  • Right Side (Pulmonary Circuit):​ Blood enters the Right Atrium​ via the vena cava. It flows down through the Tricuspid Valve​ into the Right Ventricle. Upon contraction, the Pulmonary Valve​ opens, forcing blood into the Pulmonary Artery​ to travel to the Lungs to pick up oxygen.

  • Left Side (Systemic Circuit):​ Oxygen-rich blood returns via the Pulmonary Veins​ into the Left Atrium. It passes through the Bicuspid Valve​ into the Left Ventricle. Upon contraction, the Aortic Valve​ opens, and the Left Ventricle pumps oxygenated blood into the Aorta.

• Wall Thickness:​ The muscle wall of the Left Ventricle​ is significantly thicker than anywhere else in the heart. This structural adaptation allows it to generate the high pressure required to pump blood throughout the entire body.

The Circulatory System & Major Organs

• Pulmonary Circulation:

  • Blue Path (Deoxygenated):​ Travels from the Heart to the Lungs via the Pulmonary Artery.

  • Red Path (Oxygenated):​ Returns from the Lungs to the Heart via the Pulmonary Vein.

• Systemic Circulation:

  • Aorta:​ Distributes oxygenated blood (red) from the Left Ventricle to all parts of the body.

  • Vena Cava:​ Collects deoxygenated blood (blue) from the body and returns it to the Right Atrium.

• Key Organ Interactions:

  • Liver:​ Receives nutrient-rich blood directly from the Gut via the Hepatic 肝的 Portal 门静脉 Vein. It also receives oxygenated blood via the Hepatic Artery. Deoxygenated blood leaves via the Hepatic Vein.

  • Gut:​ Receives oxygenated blood from the mesenteric 肠系膜的 artery to support digestion.

  • Kidneys:​ Receive oxygenated blood from the Renal 肾的 Artery to filter waste. Deoxygenated blood is returned to the circulatory system via the Renal Vein.

  • Other Organs:​ Represent the general musculature and tissues that receive oxygenated blood and return deoxygenated blood to maintain bodily functions.