heart

Question 1

how much times does the blood pump

Answer 1

As the heart beats, or contracts, the blood makes continuous round-trips—into and out of the heart, through the rest of the body, and then back to the heart—only to be sent out again. The amount of work that a heart does is almost too incredible to believe. In one day it pushes the body’s supply of 6 quarts or so of blood (6 liters [L]) through the blood vessels over 1,000 times, meaning that it actually pumps about 6,000 quarts of blood (1500 gallons) in a single day!

Question 2

the heart contracts by itself

Answer 2

What makes the heart beat? Unlike skeletal muscle cells, which must be stimulated by nerve impulses before they will contract, cardiac muscle cells can and do contract spontaneously and independently, even if all nervous connections are severed. Moreover, these spontaneous contractions occur in a regular and continuous way. Although cardiac muscle can beat independently, the muscle cells in different areas of the heart have different rhythms. Atrial cells beat about 60 times per minute, but ventricular cells contract more slowly (20–40 times per minute). Therefore, without some type of unifying control system, the heart would be an uncoordinated and inefficient pump.What makes the heart beat? Unlike skeletal muscle cells, which must be stimulated by nerve impulses before they will contract, cardiac muscle cells can and do contract spontaneously and independently, even if all nervous connections are severed. Moreover, these spontaneous contractions occur in a regular and continuous way. Although cardiac muscle can beat independently, the muscle cells in different areas of the heart have different rhythms. Atrial cells beat about 60 times per minute, but ventricular cells contract more slowly (20–40 times per minute). Therefore, without some type of unifying control system, the heart would be an uncoordinated and inefficient pump.

Question 3

intrinsic system

Answer 3

Two systems act to regulate heart activity. One of these involves the nerves of the autonomic nervous system, which act like brakes and gas pedals to decrease or increase the heart rate, depending on which division is activated. We consider this topic later in this chapter. The second system is the intrinsic conduction system, or nodal system, that is built into the heart tissue (Figure 11.7) and sets its basic rhythm like a drummer sets the beat for a rock band playing a song. The intrinsic conduction system is composed of a special tissue found nowhere else in the body; it is much like a cross between muscle and nervous tissue. This system causes heart muscle depolarization in only one direction—from the atria to the ventricles.

Question 4

beats per moment when resting

Answer 4

The atria contract first, pushed by the electrical impulse that starts at the SA node.

Then, after a brief delay at the AV node, the ventricles contract.

This slight difference in timing lets the atria finish squeezing blood into the ventricles before the ventricles contract.

Together, this coordinated sequence happens about 70–75 times per minute in a healthy adult at rest, producing a steady, efficient heartbeat.

So, while the atria and ventricles contract at slightly different moments, their overall rhythm is unified, creating the familiar heartbeat you feel.

Want me to help you visualize this timing with a simple diagram or animation?

Question 5

sinotal node components

Answer 5

One of the most important parts of the intrinsic conduction system is a crescent-shaped node of tissue called the sinoatrial (si″no-a′tre-al) (SA) node, located in the right atrium. Other components include the atrioventricular (AV) node at the junction of the atria and ventricles, the atrioventricular (AV) bundle (bundle of His) and the right and left bundle branches located in the interventricular septum, and finally the Purkinje (pur-kin′je) fibers, which spread within the myocardium of the ventricle walls.

Question 6

the intinsic nodes actual steps

Answer 6

The SA node (sinoatrial node) starts the electrical impulse — it’s the pacemaker of the heart.

The impulse spreads through the atrial walls, causing the atria to depolarize.

Calcium enters the atrial muscle cells, triggering the atria to contract and push blood into the ventricles.

The impulse then funnels into the AV node, where there is a brief delay.
✅ This gives the atria time to finish contracting before the ventricles are stimulated.

After the delay, the signal travels down the:

AV bundle (Bundle of His)

Right and left bundle branches

Purkinje fibers

The signal reaches the apex of the heart and spreads upward through the ventricular myocardium (the thick muscle layer).

Calcium enters the ventricular cells, causing the ventricles to contract.

This contraction pushes blood upward:

Through the pulmonary arteries (from the right ventricle to the lungs)

Through the aorta (from the left ventricle to the body)

Question 7

heart damage

Answer 7

Heart Block: When the AV Node Is Damaged
If the AV node is damaged, the signal from the SA node can’t reach the ventricles properly.

This causes a condition called heart block.

The ventricles then beat on their own at a much slower rate (like 20–40 bpm), because they have a backup rhythm, but it’s weak and slow.

Partial heart block: some signals get through.

Complete heart block: no signals get through — atria and ventricles beat independently.

🛠️ What if the SA Node Fails?
If the SA node is damaged, the heart beats more slowly, because other parts (like the AV node) take over at a lower rate.

In these cases, doctors may install an artificial pacemaker — a small device that sends electrical signals to keep the heart beating at a safe rate.

❤️‍🩹 Ischemia and Fibrillation
Ischemia = not enough blood supply to the heart muscle.

It can damage the heart’s electrical system.

This can lead to fibrillation, which is:

A rapid, uncoordinated, useless quivering of the ventricles.

The heart doesn’t pump blood — it’s like a bag of wiggling worms.

This is a medical emergency and can lead to sudden death.

⚡ AEDs Save Lives
AED = Automatic External Defibrillator

It gives a controlled shock to the heart to stop fibrillation and help restore a normal rhythm.

AEDs are in many public places now, and training people to use them saves lives.

Question 8

systole and diastole

Answer 8

Heartbeat Timing in a Healthy Heart:
The atria contract together first (at the same time).

Then, as the atria relax, the ventricles begin to contract.

This coordinated timing is what keeps blood flowing smoothly through the heart and out to the lungs and body.

🕒 Key Terms:
Systole = contraction
👉 (Think: “Squeeze”)
Usually refers to ventricular contraction, when blood is pushed out of the heart.

Diastole = relaxation
👉 (Think: “Dilate” or “Drift open”)
Refers to the time when the ventricles relax and fill with blood.

Even though both the atria and ventricles go through systole and diastole, when doctors say “systole” and “diastole,” they’re usually talking about the ventricles, since they do most of the pumping work.

🧠 Easy Way to Remember:
Systole = Squeeze

Diastole = Dilate (relax and fill)

Question 9

cardiac cycle

Answer 9

1. Atrial Diastole (Ventricular Filling Begins)
   The heart is completely relaxed

Pressure is low

AV valves open, semilunar valves closed

Blood flows passively from the atria into the ventricles

2. Atrial Systole (Ventricular Filling Completed)
   Atria contract

Push the remaining blood into the ventricles

Ventricles are still in diastole (relaxed and filling)

3. Isovolumetric Contraction
   Atrial systole ends, and ventricular systole begins

Ventricular pressure rises, closing the AV valves

All valves are closed, so volume stays the same (“isovolumetric” = same volume)

4. Ventricular Systole (Ejection Phase)
   Ventricles contract forcefully

Intraventricular pressure rises above arterial pressure

Semilunar valves open, and blood is ejected into:

Aorta (from the left ventricle)

Pulmonary artery (from the right ventricle)

Meanwhile, atria are in diastole, filling with blood again

5. Isovolumetric Relaxation
   Ventricular diastole begins

Pressure drops, and semilunar valves close (to prevent backflow)

All valves are briefly closed again

Once ventricular pressure falls below atrial pressure, the AV valves open, and the cycle restarts

🔁 In Simple Terms:

Question 10

lub dup sound

Answer 10

When using a stethoscope, you can hear two distinct sounds during each cardiac cycle. These heart sounds are often described by the two syllables “lub” and “dup,” and the sequence is lub-dup, pause, lub-dup, pause, and so on. The first heart sound (lub) is caused by the closing of the AV valves. The second heart sound (dup) occurs when the semilunar valves close at the end of ventricular systole. The first heart sound is longer and louder than the second heart sound, which tends to be short and sharp.

Question 11

heart murmurs

Answer 11

Abnormal or unusual heart sounds are called heart murmurs. Blood flows silently as long as the flow is smooth and uninterrupted. If it strikes obstructions, its flow becomes turbulent and generates sounds that can be heard with a stethoscope. Heart murmurs are fairly common in young children (and some elderly people) with perfectly healthy hearts, probably because their heart walls are relatively thin and vibrate with rushing blood. However, murmurs in patients who do not fall into either of these groups most often indicate valve problems. For example, if a valve does not close tightly (is incompetent), a swishing sound will be heard as the blood flows back through the partially open valve after that valve has (supposedly) closed. Distinct sounds also can be heard when blood flows turbulently through stenosed (narrowed) valves.

Question 12

Tachycardia
Bradycardia

Answer 12

Tachycardia = Fast heart rate (over 100 bpm)
Bradycardia = Slow heart rate (under 60 bpm)