MEDICAL BIOLOGY, HUMAN ANATOMY, PHYSIOLOGY AND PATHOLOGY - Y.I. Fedonyuk 2010

ANATOMY, PHYSIOLOGY, PATHOLOGY

SECTION 5. BLOOD AND LYMPH CIRCULATION PROCESSES AND THEIR PATHOLOGY

HEART FUNCTION

8. REGULATION OF CARDIAC ACTIVITY

The Innervation of the heart is provided by the Autonomic Nervous system. Sympathetic fibers (cardiac nerves) reach it from the cervical and thoracic ganglia of the Sympathetic trunk.

Parasympathetic innervation is mediated by the Vagus nerve, which helps decrease The Heart rate and contractile force, thereby reducing Cardiac Output. Conversely, activation of the sympathetic cardiac nerves enhances Cardiac Activity.

Stimulation of baroreceptors (by Blood pressure) and chemoreceptors (by chemical agents) in reflexogenic zones triggers reflex changes in cardiac activity. Particularly important reflexogenic zones are located in the aortic arch, the carotid sinus region (branching area of the common carotid artery), and the venae cavae.

When blood pressure in the aortic arch increases, baroreceptors are stimulated, and impulses are transmitted to the parasympathetic depressor center in the Medulla Oblongata, leading to an increase in its tone.

A similar mechanism of altering cardiac activity operates via baroreceptors located in the carotid sinus region (Hering's reflex).

Cardiac Reflexes also include the Bainbridge reflex. Its essence is as follows: baroreceptors within the venae cavae are situated near their junction with the right atrium.

When the Veins are overfilled with blood, these baroreceptors are excited, and nerve impulses are transmitted to the sympathetic cardiac centers in the Spinal Cord. The latter increase their activity and, via sympathetic nerves, stimulate enhanced cardiac performance. As a result, cardiac output increases, relieving The Heart and ensuring that blood outflow matches venous return.