The Mammalian Cardiovascular System | 哺乳动物心血管系统详解

📚 The Mammalian Cardiovascular System | 哺乳动物心血管系统详解

The cardiovascular system is a remarkable transport network that delivers oxygen and nutrients to every cell and removes metabolic waste. In mammals, the system is double and complete, meaning blood passes through the heart twice per circuit and oxygenated blood never mixes with deoxygenated blood.

心血管系统是一个卓越的运输网络，它将氧气和营养物质输送到每个细胞，并清除代谢废物。哺乳动物的循环系统为双重且完全的双循环，这意味着血液在每次循环中两次经过心脏，且含氧血与去氧血从不混合。

1. The Structure of the Mammalian Heart | 哺乳动物心脏的结构

The human heart has four chambers: two atria and two ventricles. The right side deals with deoxygenated blood; the left side with oxygenated blood. A muscular septum separates the two sides, preventing mixing.

人类心脏有四个腔室：两个心房和两个心室。右侧处理去氧血；左侧处理含氧血。肌肉质的室间隔将两侧隔开，防止血液混合。

The atrioventricular valves (tricuspid on the right, bicuspid/mitral on the left) are attached to flap-like chordae tendineae, which anchor them to papillary muscles and prevent inversion when ventricles contract.

房室瓣（右侧为三尖瓣，左侧为二尖瓣/僧帽瓣）连接着腱索，腱索将其固定于乳头肌上，防止心室收缩时瓣膜翻转。

Semilunar valves lie at the openings of the pulmonary artery and aorta. They prevent backflow of blood from arteries into ventricles during diastole.

半月瓣位于肺动脉和主动脉的开口处，防止舒张期血液从动脉回流进入心室。

2. The Cardiac Cycle | 心动周期

The cardiac cycle has three stages: atrial systole, ventricular systole and cardiac diastole. During atrial systole, both atria contract to push blood through the AV valves into the ventricles. Ventricular systole then closes the AV valves and opens the semilunar valves, forcing blood into the aorta and pulmonary artery.

心动周期包括三个阶段：心房收缩、心室收缩和全心舒张。在心房收缩期，两个心房收缩将血液通过房室瓣推入心室。随后心室收缩，关闭房室瓣并打开半月瓣，将血液压入主动脉和肺动脉。

During cardiac diastole, the heart relaxes, pressure falls and blood fills the atria. The semilunar valves close, producing the ‘lub-dub’ heart sounds. The volume changes reflect these pressure changes.

在心脏舒张期，心脏放松，压力下降，血液回流入心房。半月瓣关闭，产生”扑通-扑通”的心音。这些容积变化反映了压力的变化。

Cardiac output (CO) = Heart rate (HR) × Stroke volume (SV)

心输出量（CO）= 心率（HR）× 每搏输出量（SV）

For a typical adult at rest, HR = 70 beats/min and SV = 70 cm³/beat, so CO ≈ 4900 cm³/min (about 5 dm³/min).

对普通成年人休息时，心率 = 70 次/分钟，每搏输出量 = 70 cm³/次，所以心输出量 ≈ 4900 cm³/分钟（约 5 dm³/分钟）。

3. Electrical Control of the Heart | 心脏的电控制

Cardiac muscle is myogenic: it contracts without a nerve impulse. The sinoatrial node (SA node) in the right atrial wall is the pacemaker. It generates impulses that spread across both atria, causing atrial systole.

心肌是肌源性的：无需神经冲动便能自行收缩。右心房壁上的窦房结（SA node）是起搏器。它产生冲动，扩散至两个心房，引起心房收缩。

Impulses then reach the atrioventricular node (AV node), where a slight delay allows the atria to finish emptying. The impulse travels down the bundle of His and through Purkinje fibres, causing ventricular contraction from the apex upwards.

随后冲动到达房室结（AV node），在此有一短暂延迟，使心房完全排空。冲动沿希氏束向下传导，并通过浦肯野纤维传导，使心室从心尖向上收缩。

This sequence can be recorded by an electrocardiogram (ECG), where the P wave indicates atrial depolarisation and the QRS complex the

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