Lecture 19. PHYSIOLOGY OF BLOOD CIRCULATION. REGULATION OF CARDIAC ACTIVITY

Plan

► Classification of regulatory mechanisms of cardiac activity.

► Neuroreflex regulation of cardiac activity:

• receptors and reflexogenic zones of cardiac reflexes;

• afferent part of cardiac reflexes;

• nerve centers of cardiac reflexes;

• efferent part of cardiac reflexes; role of sympathetic and parasympa-thetic nerves in control of cardiac activity.

► Humoral regulation of cardiac activity.

► Intracardiac mechanisms of regulation of cardiac activity:

• myogenic regulatory mechanisms

• neuroconducting regulatory mechanisms

Classification of Regulatory Mechanisms of Cardiac Activity

Mechanisms of regulation of cardiac activity are classified into extracardiac (extrinsic) and intracardiac (intrinsic).

Extracardiac mechanisms include neuroreflex and humoral mechanisms, and intracardiac mechanisms include neuroconducting and myogenic mechanisms.

Fig. 19.1. Classification of mechnisms of regulation of heart activity

Neuroreflex Control of Cardiac Activity

Neuroreflex mechanisms are divided into hereditary (unconditioned) and acquired (conditioned). Any reflex arc comprises five basic elements: receptors, afferent nerve, nerve center, efferent nerve and effector organ.

Receptors and Reflexogenic Zones of Heart Reflexes

Basic receptors for cardiac reflexes are baroreceptors controlling arterial pressure, and volume receptors controlling the volume of circulating blood. Baroreceptors are located within the walls of arteries and are mainly concentrated in paired carotid sinuses (the zone of bifurcation of the common carotid artery into external and internal carotid arteries), in the aortic arch and in the pulmonary artery. Volume receptors are mainly concentrated in the right heart.