Blood: composition 血液的组成

总体组成 General composition

Blood = plasma + formed elements
Plasma ≈ 55%
Formed elements ≈ 45%

血浆 Plasma

液体成分，主要是水
Liquid component of blood

Water ≈ 90%
Proteins ≈ 7%
Other solutes (electrolytes, nutrients, hormones, waste) ≈ 1–3%

Plasma proteins

Albumin
最多的血浆蛋白
Most abundant plasma protein
Maintains colloid osmotic pressure
Transport of small molecules
Globulins (α, β, γ)
Transport proteins, immune function
γ-globulins = antibodies
Fibrinogen
Coagulation
Converted to fibrin during clotting

有形成分 Formed elements

Erythrocytes (RBCs)

无核
Biconcave shape
Contain hemoglobin
Oxygen transport
~5 million / mm³ (order of magnitude)

Leukocytes (WBCs)

Immune function
~4,000–10,000 / mm³

分类：

Granulocytes: neutrophils, eosinophils, basophils
Agranulocytes: lymphocytes, monocytes

Platelets

Cell fragments
Haemostasis and coagulation
~150,000–400,000 / mm³

血液作为组织 Blood as a tissue

Specialized connective tissue
Cells suspended in extracellular matrix (plasma)

Blood vessels: classification & structure

分类 Classification

Arteries → arterioles → capillaries → venules → veins
Arteries carry blood away from the heart
Veins return blood to the heart
Capillaries are exchange vessels

血管壁的层次 Layers of the vessel wall

（除毛细血管外）

Endocardium
内皮细胞，直接接触血液
Endothelium in direct contact with blood
Myocardium + Fibrous skeleton
平滑肌 + 弹性纤维
Smooth muscle layer, regulates vessel diameter
Epicardium
结缔组织，固定血管
Connective tissue, anchors the vessel

各类血管的结构特点

Elastic arteries

管径大，壁相对薄
Tunica media 富含弹性纤维
Pressure reservoir
Convert pulsatile flow into continuous flow

Muscular arteries

Tunica media 平滑肌多，弹性纤维少
Walls relatively thick
Distributing arteries
Regulate blood flow to organs

Arterioles

管径小，平滑肌比例高
Resistance vessels
Major determinant of peripheral resistance

Capillaries

单层内皮细胞
No tunica media or externa
Exchange of gases, nutrients, wastes
Types: continuous / fenestrated / sinusoids

Veins

壁薄，腔大
Tunica media 薄，tunica externa 最厚
Valves present
Blood reservoir

Blood pressure 血压

定义 Definition

血压：血液对血管壁产生的侧向压力

Blood pressure is the lateral force exerted by blood on vessel walls

血压的产生 Generation

心室收缩产生压力

Ventricular contraction generates blood pressure

动脉血压的两个值

Systolic pressure
心室收缩期动脉内最高压力
Highest arterial pressure during systole
Diastolic pressure
心室舒张期动脉内最低压力
Lowest arterial pressure during diastole

血压沿血管的变化

从左心室向外周逐渐下降
Pressure falls progressively with distance from the left ventricle

血管结构与血压的关系

Elastic arteries

储存心脏射血产生的能量
Pressure reservoir
维持舒张期血压
Maintain pressure during diastole

Arterioles

阻力血管
Resistance vessels
直径变化显著影响血压
Vasoconstriction ↑ → resistance ↑ → blood pressure ↑

Veins

不适合承受高压
Not designed to withstand high pressure
主要功能为容量储存
Capacitance vessels / blood reservoir

影响血压的主要因素

心脏泵血活动
Cardiac pumping activity
血管阻力（主要由小动脉决定）
Vascular resistance (mainly arterioles)

Heart anatomy + systemic circulation 心脏解剖 + 体循环

四腔 Four chambers

右心房 Right atrium (RA)
右心室 Right ventricle (RV)
左心房 Left atrium (LA)
左心室 Left ventricle (LV)

右心 → 肺循环 Right heart → pulmonary circulation
左心 → 体循环 Left heart → systemic circulation

体循环 Systemic circulation flow

Left ventricle → aorta → systemic arteries → arterioles → capillaries → venules → veins → right atrium
左心室 → 主动脉 → 动脉 → 小动脉 → 毛细血管 → 小静脉 → 静脉 → 右心房

Systemic circulation = delivers O₂/nutrients, removes CO₂/waste
体循环 = 供氧供养 + 带走代谢产物

左心与压力 Left heart & pressure

LV wall thick (high pressure pump)
左心室壁厚（高压泵）

Systemic circulation = high pressure
体循环 = 高压系统

肺循环对比 Pulmonary circulation (contrast)

RV → pulmonary artery → lungs → pulmonary veins → LA
右心室 → 肺动脉 → 肺 → 肺静脉 → 左心房

Pulmonary circulation = low pressure
肺循环 = 低压系统

Valves 瓣膜

Atrioventricular valves 房室瓣

Tricuspid (RA→RV) 三尖瓣
Mitral (LA→LV) 二尖瓣/僧帽瓣

Semilunar valves 半月瓣

Pulmonary valve 肺动脉瓣
Aortic valve 主动脉瓣

Valves ensure one-way flow
瓣膜保证单向血流

心脏解剖与血压的直接联系

Left ventricle contraction → systemic arterial pressure
Thicker ventricular wall → higher pressure generation

Systemic blood pressure depends mainly on left ventricular function.

ECG 心电图

ECG 是什么

心电图：记录心脏电活动在体表的表现
ECG records electrical activity of the heart at the body surface
记录的是电位差，不是机械收缩
ECG records potential differences, not contraction

基本波形 Waves

P wave
心房去极化
Atrial depolarization
QRS complex
心室去极化
Ventricular depolarization
T wave
心室复极化
Ventricular repolarization

关键记忆顺序

P → QRS → T
Atria → ventricles → recovery

重要时间间期 Intervals

PR interval
心房到心室传导
Atrial-to-ventricular conduction time
QT interval
心室去极化 + 复极化
Total ventricular electrical activity

AV node 的作用

AV node 延迟传导
AV node delays conduction
约 0.09 s
~0.09 seconds delay

Atria contract before ventricles
心房先收缩，心室后收缩

ECG 记录特点

心肌完全去极化或完全复极化 → ECG = 0
No potential difference → no ECG deflection

ECG 能告诉什么

心律是否正常
Heart rhythm
传导异常
Conduction abnormalities
心肌损伤或缺血
Myocardial damage / ischemia

ECG Leads

导联：心电图中记录电位差的观察方向
A lead is a specific viewpoint that records electrical potential differences

ECG records the potential difference between two electrodes

Standard limb leads 标准肢体导联

Lead I: Left arm − Right arm
Lead II: Left leg − Right arm
Lead III: Left leg − Left arm

三者构成 Einthoven triangle

Einthoven Triangle

Each lead represents a different projection of cardiac electrical activity

导联的基本规则

去极化方向朝向正极 → 向上波形
Depolarization toward positive electrode → positive deflection
去极化远离正极 → 向下波形
Depolarization away from positive electrode → negative deflection