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The NAVL of the heart are the nerves, arteries, veins and lymphatics which influence the actions of the heart.
Page 2 Controls of Heart Function
Control of heart functions can be divided into the following areas:
• Extrinsic controls (control from outside the heart)
• Intrinsic controls (control from inside the heart)
• Humoral control, where some substances transported by the blood can accelerate or slow the action of the heart.
Page 3 Extrinsic controls
A number of cardiac nerves arise from both the sympathetic and parasympathetic portions of the nervous system.
(Fibers from the sympathetic portion leave the central nervous system at the thoracic and lumber portions of the spinal cord, while those from the parasympathetic nervous system leave from the brain stem and the sacral region of the spinal cord.)
The sympathetic portion accelerates the action of the heart, while the parasympathetic portion slows it down.
These portions are both controlled by cardiovascular centers in the medulla of the hind-brainstem.
In addition, as everyone is well aware, various emotional states can affect the actions of the heart.
Page 4 Intrinsic Controls
Within the substance of the heart, certain fibers of the myocardium have been transformed from contracting muscle tissue to impulse-transmitting fibers. These are called Purkinje's fibers. Together, these fibers
provide intrinsic control for the action of the heart.
The sinoatrial (SA) node is a collection of these fibers in the interatrial septum. The SA node is often called the pacemaker of the heart because it initiates each cycle of the contractions of the heart chambers.
The atrioventricular (AV) node is another group of these fibers just above the interventricular septum.
Descending from the AV node is the bundle of His, which branches into the right and left septal bundles. These branches pass down on either side of the interventricular septum.
Page 5 Intrinsic Controls
Impulses begin in the SA node, pass to the AV node, and then descend through the septal bundles to stimulate the myocardium of the ventricular walls to contract.
Page 6 Coronary Arteries
Previously, we have described the flow of blood through the chambers of the heart. This blood, upon which the heart acts, is called functional blood.
Now, we wish to discuss the supply of nutrient blood to the heart. This blood nourishes the tissues of the heart. The nutrient blood supplies oxygen and food materials to the tissues of the heart and removes waste materials.
This nutrient blood is supplied to the walls of the heart by the right and left coronary arteries.
Page 7 Coronary Arteries
The openings leading into the coronary arteries are located in the base of the ascending aorta, just above (behind the cusps of) the semilunar valve (aortic valve). When this valve is open, its cusps cover the openings of the coronary arteries.
When the valve is closed, the backpressure of the blood in the aorta fills the coronary arteries with blood. The coronary arteries then distribute the blood to all of the tissues of the relaxed heart.
Page 8 Coronary Arteries
Many of the branches of the coronary arteries are of the end artery type.
This means that such a branch is the sole supply of nutrient blood to a specific area of the heart.
If the branch should be closed for any reason, the tissue in that area will due to lack of oxygen and nourishment.
Page 9 Cardiac Veins, Coronary Sinus and Thebesian Veins
The blood from the tissues of the heart is collected by the cardiac veins.
These veins empty into the coronary sinus, a vessel, which in turn empties into the right atrium.
The thebesian veins are many minute sinuses found in the myocardium of the ventricles. They extend from the lumen into the myocardium of each ventricle.
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