AP 2 4.3 Physiology of the Cardiovascular System Flashcards
Blood Flow through the Heart
Blood flow through the heart is controlled by the four heart valves. These valves assure that the blood flows in one direction: forward from vessels into the atria, into the ventricles, and then out of the ventricles. The heart is a double pump because it has two circuits.
pulmonary circuit
The right circuit is called the pulmonary circuit, and it sends deoxygenated blood to the lungs to be oxygenated.
systemic circuit
The left circuit is called the systemic circuit, and it sends the oxygenated blood from the heart to the cells of the body
Blood follows a one-way path
Blood follows a one-way path through the heart, lungs, and body. The pathway is best described as it returns (in a deoxygenated form) from the cells of the body entering the heart.
inferior and superior vena cavae
Two large veins called the inferior and superior vena cavae return deoxygenated blood to the right atrium
tricuspid valve
From the right atrium blood flows through the tricuspid valve into the right ventricle.
pulmonary arteries
The right ventricle pumps blood through the pulmonary valve into the pulmonary arteries to the lungs. The pulmonary arteries are the only arteries in the body carrying deoxygenated blood away from the heart.
pulmonary veins
After the blood is oxygenated in the capillary bed of the lungs (also losing its carbon dioxide), it is carried by the pulmonary veins to the heart entering the left atrium.
bicuspid valve
This oxygenated blood flows through the bicuspid valve (mitral valve) into the left ventricle, which pumps it through the aortic valve into the aorta, the largest vessel in the body.
aortic arch
The aortic arch turns posteriorly, carrying oxygenated blood to supply the cells of all body tissue with oxygen and nutrients. Deoxygenated blood is then returned to the right atrium through the vena cavae, which completes the circuit
The Cardiac Cycle
The heart contracts, or beats, about seventy times a minute, and each heartbeat lasts about 0.85 seconds.
systole
The term systole refers to contraction of heart chambers,
diastole
the word diastole refers to relaxation of these chambers.
heart to function as a pump
For the heart to function as a pump, it must contract and relax in a cyclical pattern
heart sounds
When the heart beats, the heart sounds are called lub-dub sounds as the valves of the heart close. The first lub sound is heard when the atrioventricular (bicuspid and tricuspid) valves close. The dub is heard when the semilunar valves close. The heart sounds can be heard using a stethoscope
Systolic pressure
Systolic pressure results from blood being forced into the arteries during ventricular systole.
cardiac cycle
Each heartbeat, or cardiac cycle, consists of three general phases. First, the atria contract for about 0.15 seconds while the ventricles relax. Second, the ventricles contract for about 0.30 seconds while the atria relax. Finally, all chambers relax for about 0.40 seconds. The short systole of the atria occurs because the atria send blood only a short distance into the ventricles. The ventricles contract for a longer period to pump blood into the much larger systemic and pulmonary circulatory circuits.
Blood Pressure
Contraction of the left ventricle forces blood into the arteries under pressure.
Diastolic pressure
Diastolic pressure is the pressure in the arteries during ventricular diastole.
sphygmomanometer
Blood pressure is measured with a piece of medical equipment called a sphygmomanometer (Figure 4.18). Blood pressure measures the amount of pressure required to stop the flow of blood through an artery, typically the brachial artery.
bulb and bladder
The bulb portion is squeezed to inflate the bladder with air.
cuff
The bladder is held in place over an artery by the cuff.
stethoscope
A stethoscope is used to listen to the first and last sounds of the blood flow displayed on the manometer. A blood pressure reading consists of two numbers, for example, 120/80—which represents systolic and diastolic pressures, respectively.
valve
The pressure inside the bladder is slowly released by turning the valve, emptying the bladder of air and allowing blood to flow through the artery again
manometer
The manometer displays the pressure in millimeters of mercury.
As blood flows from the aorta into the various arteries and arterioles
As blood flows from the aorta into the various arteries and arterioles, blood pressure falls within the arteries to the arterioles. The difference in pressure between systolic and diastolic pressure gradually diminishes as blood reaches the arterioles. In the blood capillaries, there is a slow, even flow of blood to allow for diffusion of oxygen and wastes in and out of the capillary beds. Blood pressure in the veins is very low and can even approach zero in some cases. Several factors enable blood to return to the heart from the veins. First, there is low resistance in the venous walls, meaning that veins can stretch to accommodate a larger volume. Second, the presence of internal valves prevents the backward flow of blood. Finally, the assistance of muscular contraction in the limbs and chest enables blood in the veins to maintain a flow rate significant enough to return the blood to the heart.
Electrical Impulses
The heart has an elaborate electrical system that is responsible for maintaining its intrinsic rhythmic abilities . The contractions of the cardiac muscle begin within the heart muscle itself, making it somewhat independent of any nerve supply from the central nervous system. If removed from the body, the heart can continue to beat on its own with proper nutrients and oxygen.
heart rate
The nervous system and endocrine systems regulate the heart rate (number of beats per minute) through neurotransmitters such as norepinephrine and acetylcholine. The interaction of the nervous and endocrine systems enables the heart to change blood pressure with emotional and physical stressors.
SA node (sinoatrial node)
The electrical impulse that controls the cardiac cycle begins at the SA node (sinoatrial node) found in the right atrium . The SA node is known as the “pacemaker” of the heart because it begins the electrical impulses necessary for the cardiac cycle. The SA node is a small mass of specialized cardiac muscle that contains both cardiac and nervous tissue characteristics. The electrical impulse begins at the SA node and spreads through the atria, creating left and right atrial systole.
AV node (atrioventricular node or AV bundle)
The impulse then travels through the AV node (atrioventricular node or AV bundle) into the bundle of His.
EKG, or ECG, (electrocardiogram)
The EKG, or ECG, (electrocardiogram) is a device used to measure electrical impulses in the heart (Figure 4.20). Different parts of the ECG tracing represent the rhythmic electrical impulses and corresponding mechanical events in the heart. Medical personnel commonly use ECGs to monitor and diagnose patient conditions.
Purkinje fibers
Next, the impulse continues to travel towards the ventricular apex (downward point of the heart). Finally, it travels through the Purkinje fibers, causing the left and right ventricles to contract
Atrial depolarization
Atrial depolarization (active firing of a nerve impulse) and atrial systole are denoted as the P-wave
Ventricular depolarization and ventricular systole
Ventricular depolarization and ventricular systole are denoted as the QRS complex
Ventricular repolarization
Ventricular repolarization (returning to rest) and ventricular diastole are denoted as a T-wave
no way to note the repolarization of the atria
There is no way to note the repolarization of the atria, as its activity is lost within the QRS complex.
