Blood circulation

General characteristics and history of study

The closed nature of the circulatory system was scientifically established by William Harvey in 1628. The main function of the heart as a pump is to maintain a continuous blood flow. The quantitative indicators of cardiac muscle performance are impressive: over a lifetime, the heart pumps about 200 million liters of blood. Cardiac output can dynamically change from 3 to 30 liters per minute, adapting to the body's current demands.

Coronary circulation of the myocardium

The myocardium works continuously and requires a steady supply of oxygen. Its primary energy source is fatty acids, while glucose and lactate play an additional role (meeting up to 40% of its needs).

Physiological features of coronary blood flow:

• Phasic nature: blood enters the vessels primarily during diastole. During systole, blood flow stops because the capillary ostia are covered by the aortic semilunar valves, and the contracted myocardium mechanically compresses the vessels.
• Role of myoglobin: during relaxation, myoglobin stores oxygen, releasing it to the tissues during systole.
• Effect of heart rate: in tachycardia, diastole is shortened, which severely limits blood flow, whereas bradycardia lengthens the rest phase and reduces myocardial workload.

Hemodynamics during pregnancy

The gestation period is accompanied by major cardiovascular remodeling. The circulatory organs experience increased stress, which can cause latent pathologies to manifest for the first time.

Key hemodynamic changes:

• Circulating blood volume increases by 40–60%.
• Cardiac output increases by 40–50%.
• A decrease in total peripheral vascular resistance is recorded.
• A new vascular network is formed—the placental complex.

Pathologies and clinical features

Cardiovascular diseases rank first among extragenital pathologies in pregnant women. Special attention is paid to congenital and acquired heart defects, as well as essential hypertension. The most common heart disease in pregnant women is mitral valve prolapse (MVP), in which the valve leaflets bulge into the left atrial cavity. Against the background of physiological hemodynamic changes, the degree of prolapse often decreases, and in the absence of significant regurgitation, the pregnancy proceeds favorably. Pulmonary hypertension presents a completely different picture, where adaptive changes lead to decompensation; therefore, pregnancy is strictly contraindicated in this condition.

Class and exam questions

What else to study on this topic

• Anatomic structure of coronary arteries and Thebesian veins
• Arteriovenous anastomoses and shunts of the coronary bed
• Etiological classification of mitral valve prolapse
• Role of the autonomic nervous system in cardiac innervation
• Pathogenesis of decompensation in pulmonary hypertension during pregnant women

Other topics in the "Additional Topics" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.