Heart Sounds and Blood Pressure
Vocabulary Terms
| aorta
aortic semilunar valve atria baroreceptors cardiac control center cardioacceleratory center cardioinhibitory center diastole diastolic pressure first heart sound homeostasis inferior vena cava left atrioventricular (AV) valve lungs negative feedback loop |
pulmonary artery
pulmonary circuit pulmonary semilunar valve pulmonary veins right atrioventricular (AV) valve second heart sound superior vena cava systemic circuit systole systolic pressure vasoconstriction vasodilation vasomotor center ventricles |
The human heart pumps blood to the lungs and the rest of the body's cells. It is made of two separate pumps working together. The pump on the right receives blood from the body, and then pumps that blood to the lungs. The pump on the left receives blood from the lungs, and then pumps that blood to the rest of the body.
Anatomy of the Heart
| Study the diagram at the right to begin learning the names of the heart chambers and major blood vessels. The human heart is comprised of four chambers. The upper two chambers are called the atria (singular: atrium), and the two lower chambers are called the ventricles. The right atrium is separated from the right ventricle by the right atrioventricular (AV) valve. The left atrium is separated from the left ventricle by the left atrioventricular (AV) valve. Blood from the body cells enters the right atrium through the superior and inferior vena cava. Blood from the lungs enters the left atrium through the pulmonary veins. When the atria contract, blood is forced into the ventricles. When the ventricles contract, the AV valves prevent blood from flowing backward into the atria. Instead, blood in the right ventricle flows through the pulmonary semilunar valve, into the pulmonary artery, and toward the lungs. The blood in the left ventricle flows through the aortic semilunar valve, into the aorta, and then to the rest of the body's cells. The semilunar valves prevent blood from flowing back into the ventricles as the ventricles relax. | |
Redraw a simple diagram of the heart with labels for the following structures.
aorta |
pulmonary artery
pulmonary semilunar valve pulmonary veins right atrioventricular (AV) valve right atrium right ventricle superior vena cava |
Heart Sounds
If you put your ear to someone's chest you can hear a sound that is often described as “lup-dup”, “lup-dup”… etc. As your heart beats, first the atria contract together, and then the ventricles contract together. As the ventricles contract, the right and left atrioventricular (AV) valves close and cause the first heart sound (the “lup”). As the ventricles relax, pressure in the pulmonary artery and the aorta cause the pulmonary and aortic semilunar valves to close, causing the second heart sound (the “dup”). Study the table below to understand more completely how the first and second heart sounds are created, and to review the stages of one heartbeat.
|
|
--- |
|
| Blood that is low in oxygen is carried to the heart by two large veins.
One vein is called the superior vena cava, and the other vein is called
the inferior vena cava.
The superior vena cava carries blood from the head and shoulders
to the heart.
|
Blood that is high in oxygen (it has just left the lungs) is carried to the heart by the pulmonary veins. | |
 |
|
|
| Blood from the superior and inferior vena cava flows through the right atrium of the heart, | Blood from the pulmonary veins flows through the left atrium of the heart, | |
|
|
|
| and then through the right atrioventricular (AV) valve, | and then through the left atrioventricular (AV) valve, | |
|
|
|
| and then into the right ventricle. | and then into the left ventricle. | |
|
|
|
| The heart fills from bottom to top: first the right ventricle, and then the right atrium. | The heart fills from bottom to top: first the left ventricle, and then the left atrium. | |
|
|
|
| The right atrium contracts, | The left atrium contracts, | |
|
|
|
| and forces more blood into the right ventricle. | and forces more blood into the left ventricle. | |
|
|
|
| The right ventricle contracts now, | The left ventricle contracts now, | |
|
|
|
| and blood tries to squeeze back into the right atrium, | and blood tries to squeeze back into the left atrium, | |
|
|
|
| but the right atrioventricular (AV) valve closes to prevent blood from flowing back into the atrium. The right and left AV valves close at the same time and cause the first heart sound. | but the left atrioventricular (AV) valve closes to prevent blood from flowing back into the atrium. The right and left AV valves close at the same time and cause the first heart sound. | |
|
|
|
| The right ventricle continues to contract, and the pressure inside the ventricle becomes greater and greater. | The left ventricle continues to contract, and the pressure inside the ventricle becomes greater and greater. | |
|
|
|
| Soon the pressure in the ventricle is so great, that the pulmonary semilunar valve is forced open. | Soon the pressure in the ventricle is so great, that the aortic semilunar valve is forced open. | |
|
|
|
| Blood is squeezed out of the right ventricle, through the pulmonary semilunar valve, and into the pulmonary artery. | Blood is squeezed out of the left ventricle, through the aortic semilunar valve, and into the aorta (the largest artery in the body). | |
|
|
|
| As the right ventricle relaxes, some blood starts to flow backwards into the ventricle. The pulmonary semilunar valve closes to prevent blood from flowing back into the right ventricle. The pulmonary semilunar valve and the aortic semilunar valve close at the same time and cause the second heart sound. | As the left ventricle relaxes, some blood starts to flow backwards into the ventricle. The aortic semilunar valve closes to prevent blood from flowing back into the left ventricle. The pulmonary semilunar valve and the aortic semilunar valve close at the same time and cause the second heart sound. | |
|
|
|
| Blood in the pulmonary artery is carried to the lungs. | Blood in the aorta is carried to the all of the body cells (except the lungs). | |
|
|
|
| In the tiny blood vessels of the lungs, oxygen enters the blood (and carbon dioxide leaves). | In the tiny blood vessels that deliver blood to the body cells, oxygen leaves the blood (and carbon dioxide enters). | |
|
|
|
| The blood is now high in oxygen, and as it leaves the lungs, it enters the pulmonary veins. | The blood is now low in oxygen, and as it leaves the body cells, it will ultimately enter the superior or inferior vena cava. | |
|
|
|
| Blood that is high in oxygen is carried to the heart by the pulmonary veins. | The superior vena cava carries blood from the head and shoulders
to the heart.
The inferior vena cava carries blood from the abdomen and lower limbs to the heart. |
|
|
|
|
| (continued in other column) | (continued in other column) |
If your computer can play sound (wav) files, you can listen to actual heart sounds. This file is an audio recording of two beats of a heart, and you can clearly hear hear "lup-dup", "lup-dup", as first the AV valves close, and then the semilunar valves close, during each of the first and second heartbeats.
Using the list below, pair up the things that happen at the same
time.
1) aortic semilunar valve
closes
2) left atrium contracts
3) left AV valve closes
4) left ventricle contracts
5) pulmonary semilunar
valve closes
6) right atrium contracts
7) right AV valve closes
8) right ventricle contracts
Blood flow through the heart and the rest of the body.
As the heart beats, the right and left halves of the heart contract
at the same time to pump blood to the lungs and the rest of the body cells.
The diagram below illustrates the path of a single red blood cell as it
starts in the right atrium, is pumped to the lungs, circulates back to
the heart, is pumped to the body cells, and then again returns to the heart.
1) The red blood cell starts in the right atrium, |
 |
The portion of the pathway that carries blood to and from the lungs (5 through 8) is called the pulmonary circuit. The portion of the pathway that carries blood to and from the rest of the body cells (13-15) is called the systemic circuit. The pulmonary and systemic circuits are illustrated below.
Starting with a red blood cell in the superior vena cava, list the following structures in the order that the red blood cell will travel through them. You can assume that this particular red blood cell will travel to the brain and back during its journey.
1) aorta |
8) pulmonary artery
9) pulmonary semilunar valve 10) pulmonary veins 11) right atrioventricular (AV) valve 12) right atrium 13) right ventricle 14) superior vena cava |
What blood vessels carry blood that is high in oxygen?
What blood vessels carry blood that is low in oxygen?
Do arteries always carry blood that is high in oxygen?
Do veins always carry blood that is low in oxygen?
What is the difference between arteries and veins?
| Blood Pressure
As the heart beats, it creates large pressure changes in the arteries closest to the heart. These changes become smaller and smaller in blood vessels further away from the heart. When the heart muscle is contracting, that phase of the cardiac cycle is called systole. When the heart muscle is relaxing between heartbeats, this phase of the cardiac cycle is called diastole. The blood pressure in the arteries rises during systole, and falls during diastole. When you measure blood pressure from a large artery, such as the brachial artery in the upper arm, you will measure two pressures, the systolic pressure and the diastolic pressure. The systolic pressure is the pressure in an artery while the heart is contracting (in systole). The diastolic pressure is the pressure in an artery while the heart is relaxing (in diastole). |
 |
| Systole and diastole cause pressure changes in the circulatory system
that can be measured in a clinic or laboratory. To measure the systolic
pressure (during cardiac contraction) and diastolic pressure (during cardiac
relaxation) from the brachial artery (the big artery in the upper arm),
a sphygmomanometer (sfig-mo-mah-nom-eh-ter) is placed over the arm and
a stethoscope is used to listen for the flow of blood. Blood flow
is usually silent because it flows through blood vessels in a non-turbulent,
or laminar, fashion. However, when blood is flowing rapidly through
a small opening, turbulence is produced. This turbulence, or non-laminar
flow, causes the blood to swirl and tumble through the narrow opening and
produce a muffled tapping sound that can be heard with a stethoscope.
This noise is called the "sounds of Korotkoff" after Nicolai S. Korotkoff,
the man who first described them.
The cuff of the sphygmomanometer is inflated until the brachial artery is occluded (closed). If you listen carefully with the stethoscope while slowly deflating the pressure cuff, you will hear a tapping sound when you reach the pressure that blood can just start squeezing through the brachial artery again. This pressure (read from the pressure gauge of the sphygmomanometer) is equal to the systolic pressure. As you continue to deflate the cuff, the sounds of Korotkoff will become muffled, because the blood flow is becoming less turbulent. The pressure at which the sounds of Korotkoff first disappear is the diastolic pressure. At this point the brachial artery is completely open again and laminar flow has resumed. The blood pressure of an individual will vary according to how much blood the heart is pumping out (cardiac output) and how much resistance is encountered in the systemic circulation (peripheral resistance). Blood pressure is most often recorded as the systolic pressure over the diastolic pressure. In healthy adults, this is approximately 120/80 mm Hg when the blood pressure is measured at the brachial artery of the upper arm. |
Regulation of Blood Pressure
As you sleep, run, sit, eat, and do all of the other things you do during your life, your body attempts to maintain fairly constant internal conditions. Homeostasis is the tendency for any living organism to maintain a fairly stable internal environment, even when the external environment is changing. Examples of homeostasis include shivering when the external environment is cold (the shivering raises and maintains your internal body temperature), sweating when the external environment is hot (sweating cools the body to maintain your internal temperature), and urinating a lot when you drink a lot of liquid (the kidneys and rest of the urinary system are dumping the excess water). It is important to realize that the internal environment of your body is not absolutely stable. Your body temperature will fluctuate somewhat, as will the water and salt concentrations of your body fluids, the oxygen levels in your blood, and your blood pressure. Homeostasis maintains your internal environment within a set of limits, attempting to never allow any parameter (temperature, blood pressure, solute concentration, etc.) to become too high or too low.
Your body maintains homeostasis with negative feedback loops,
which are self-correcting systems that do not allow your internal environment
to fluctuate outside a set of limits. If something is too high (blood
pressure, body temperature, etc.), then a negative feedback loop will lower
it. Conversely, if something is too low, then a negative feedback
loop will raise it. Negative feedback loops maintain the homeostasis
of blood pressure.
| Blood pressure is monitored by specialized nerve cells called baroreceptors. These baroreceptors are found in the large arteries closest to your heart. If your blood pressure is going up, the baroreceptors will generate more and more action potentials. If your blood pressure is decreasing, then the baroreceptors will generate fewer and fewer action potentials. The action potentials travel up sensory (afferent) neurons to the brain. |  |
At the base of the brain (in the medulla oblongata), are circuits of neurons that can adjust blood pressure. One circuit of neurons, the cardiac control center, can increase and decrease heart rate. Another circuit of neurons, the vasomotor center, can adjust the diameter of the blood vessels (vasoconstriction is when blood vessels become narrower, vasodilation is when blood vessels become wider).
The cardiac control center has two parts, the cardioacceleratory center and the cardioinhibitory center. The neurons of the cardioacceleratory center stimulate motor (efferent) neurons that cause the heart to beat faster and harder. These motor neurons are called sympathetic motor neurons, because they prepare the body for stressful activities.
The neurons of the cardioinhibitory center stimulate motor neurons that cause the heart to beat slower. These motor neurons are called parasympathetic motor neurons, because they prepare the body for restful or quiet activity.
The baroreceptors, medulla oblongata, and heart and blood vessels form
a negative feedback loop that can regulate blood pressure. A rise
in blood pressure is sensed by the baroreceptors, which respond by generating
more action potentials. The action potentials travel to the brain,
and cause different responses in different circuits.
When more action potentials are being delivered by the baroreceptor sensory neurons, the cardioacceleratory center neurons respond by generating fewer action potentials. This results in fewer action potentials traveling down the sympathetic motor neurons to the heart, and the heart will beat slower and with less force. |
 |
All three of these responses combine to lower the blood pressure. Remember, this is how negative feedback loops maintain homeostasis. If something like blood pressure is too high, then the negative feedback loop will attempt to reverse the situation and lower the blood pressure.
Circle the correct option listed in the brackets to answer the next four questions.
As a person's blood pressure rises, you expect the baroreceptors to generate [more fewer the same number] of action potentials per second.How will each of the responses you listed above affect blood pressure?As a person's blood pressure rises, you expect the cardioinhibitory center to generate [more fewer the same number] of action potentials per second.
As a person's blood pressure rises, you expect the cardioacceleratory center to generate [more fewer the same number] of action potentials per second.
As a person's blood pressure rises, you expect the vasomotor center to generate [more fewer the same number] of action potentials per second.
If a person loses a lot of blood, the blood pressure will drop.
The baroreceptors respond by generating fewer action potentials.
The action potentials travel to the brain, and again cause different responses
in different circuits.
When fewer action potentials are being delivered by the baroreceptor sensory neurons, the cardioacceleratory center neurons respond by generating more action potentials. This results in more action potentials traveling down the sympathetic motor neurons to the heart, and the heart will beat faster and with greater force. |
 |
The responses of the cardioacceleratory center, cardioinhibitory center, and vasomotor center combine to increase blood pressure.
The baroreceptors in your body are constantly monitoring your blood pressure, so that the negative feedback loop controlling blood pressure can make constant adjustments based on your activity, posture, and overall health. This is how your body maintains blood pressure homeostasis.
Circle the correct option listed in the brackets to answer the next four questions.
If a person has been injured in an accident, and is losing a lot of blood, you expect the baroreceptors to generateHow will each of the responses you listed above affect blood pressure?
[more fewer the same number] of action potentials per second.If a person has been injured in an accident, and is losing a lot of blood, you expect the cardioinhibitory center to generate
[more fewer the same number] of action potentials per second.If a person has been injured in an accident, and is losing a lot of blood, you expect the cardioacceleratory center to generate
[more fewer the same number] of action potentials per second.If a person has been injured in an accident, and is losing a lot of blood, you expect the vasomotor center to generate
[more fewer the same number] of action potentials per second.