Blood Circulation | GCSE Edexcel 生物：血液循环 考点精讲

📚 Blood Circulation | GCSE Edexcel 生物：血液循环 考点精讲

The circulatory system is a vast network of organs and vessels that ensures every cell in the body receives oxygen and nutrients while waste products are removed. It plays a central role in maintaining homeostasis by transporting hormones, regulating temperature and fighting infection. In GCSE Edexcel Biology, understanding the components of blood, the structure of the heart and the double circulation is fundamental.

循环系统是由器官和血管组成的庞大网络，确保体内每个细胞都能获得氧气和营养物质，同时将废物清除。它在维持内环境稳态中起着核心作用，负责运输激素、调节体温并抵抗感染。在GCSE爱德思生物学中，理解血液成分、心脏结构以及双循环是基础。

1. Overview of the Circulatory System | 循环系统概述

The human circulatory system is composed of the heart, blood vessels and blood. It is a closed, double circulatory system, meaning that blood passes through the heart twice during one complete circuit of the body. The right side of the heart pumps deoxygenated blood to the lungs, while the left side pumps oxygenated blood to the rest of the body.

人类循环系统由心脏、血管和血液组成。它是一个封闭的双循环系统，这意味着血液在一次完整的体循环中两次经过心脏。心脏右侧将缺氧血泵送至肺部，左侧将富氧血泵送至全身各处。

2. The Heart: Structure and Function | 心脏的结构与功能

The heart is a muscular organ located between the lungs, protected by the ribcage. It has four chambers: the right atrium and right ventricle on the deoxygenated side, and the left atrium and left ventricle on the oxygenated side. The left ventricle has a much thicker muscular wall because it must pump blood at high pressure around the entire body.

心脏是位于两肺之间、受胸腔保护的肌肉器官。它有四个腔室：右侧的右心房和右心室处理缺氧血，左侧的左心房和左心室处理富氧血。左心室的心肌壁要厚得多，因为它必须以高压将血液泵送至全身。

Valves between the atria and ventricles (atrioventricular valves) and at the exits of the major arteries (semilunar valves) prevent backflow of blood. The tricuspid valve sits between the right atrium and right ventricle, while the bicuspid (mitral) valve is on the left side.

房室之间的瓣膜（房室瓣）以及主要动脉出口处的瓣膜（半月瓣）可防止血液倒流。三尖瓣位于右心房和右心室之间，而二尖瓣位于左侧。

3. Blood Vessels: Arteries, Veins and Capillaries | 血管：动脉、静脉和毛细血管

Arteries carry blood away from the heart. They have thick, muscular walls with elastic fibres to withstand and smooth out the high pressure generated by the heart’s contractions. The lumen (central cavity) is relatively narrow, helping maintain pressure. The largest artery is the aorta.

动脉将血液从心脏运出。它们的管壁厚实，富含肌肉和弹性纤维，以承受并缓冲心脏收缩产生的高压。管腔相对狭窄，有助于维持血压。最大的动脉是主动脉。

Veins return blood to the heart. They have thinner walls and a wider lumen than arteries, as the blood pressure is much lower. Many veins, especially those in the limbs, contain valves to prevent the backflow of blood. The vena cava is the major vein entering the right atrium.

静脉将血液送回心脏。它们的管壁较薄，管腔比动脉宽，因为血压要低得多。许多静脉（尤其是四肢的静脉）含有瓣膜，以防止血液倒流。腔静脉是进入右心房的主要静脉。

Capillaries are microscopic vessels that form networks at the organs and tissues. Their walls are only one cell thick (a single layer of endothelial cells), which allows for efficient diffusion of gases, nutrients and wastes between blood and cells. Capillaries link arteries to veins.

毛细血管是微观血管，在器官和组织中形成网络。它们的管壁仅有一层细胞厚（单层内皮细胞），这使得气体、营养物质和代谢废物能够在血液与细胞之间高效地扩散。毛细血管连接动脉和静脉。

4. The Double Circulatory System | 双循环系统

Humans have a double circulation consisting of the pulmonary circulation and the systemic circulation. In the pulmonary circuit, deoxygenated blood is pumped from the right ventricle to the lungs via the pulmonary artery. Gas exchange occurs in the alveoli: carbon dioxide diffuses out of the blood and oxygen diffuses in. The now oxygenated blood returns to the left atrium through the pulmonary veins.

人类拥有双循环，包括肺循环和体循环。在肺循环

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