8.5 - The Heart Flashcards
What is the function of the heart in the circulatory system? What is the difference between a mammals heart and other animal’s heart? Where is it found?
The heart is the organ responsible for moving blood around the body.
In some animals, it is a simple muscular tube, but in mammals, it is a complex four-chambered organ.
It is enclosed by the ribs and sternum for protection.
How does the human heart function as two pumps working together?
Right side of the heart: Pumps deoxygenated blood to the lungs.
Left side of the heart: Pumps oxygenated blood to the body.
The two sides are completely separate, preventing mixing of oxygenated and deoxygenated blood.
What makes cardiac muscle unique compared to skeletal muscle?
Contracts and relaxes in a regular rhythm.
Does not get fatigued, allowing continuous pumping.
What is the role of the coronary arteries?
Coronary arteries supply oxygenated blood to the cardiac muscle.
This ensures the heart has constant oxygen and nutrients to keep contracting.
What are pericardial membranes, and what is their function?
Inelastic membranes surrounding the heart.
Prevent the heart from over-expanding when filling with blood.
Why are sheep or pig hearts commonly used for dissection in biology?
They are similar in shape and size to the human heart.
They allow students to identify key structures of the mammalian heart.
What important structure can be seen on the external surface of the heart during dissection?
The coronary arteries, which supply oxygenated blood to the heart muscle.
Blockage or narrowing of these arteries can cause coronary heart disease and heart attacks.
Why might a heart from a butcher not be completely intact for dissection? (3)
Major blood vessels are often cut back.
The atria may be removed, as they are not typically sold for consumption.
This can make identifying some parts of the heart more difficult.
Why is it important to carefully examine a heart during dissection?
The actual structure is more complex than standard diagrams.
Some parts may be missing or altered, requiring careful identification of the remaining structures.
How does deoxygenated blood enter the heart, and where does it go next?
- Enters the right atrium from the superior and inferior vena cava at low pressure.
- Passes through the tricuspid valve into the right ventricle.
- Right ventricle contracts, forcing blood through the semilunar valves into the pulmonary artery.
- Blood travels to the lungs for oxygenation.
How does oxygenated blood return to the heart and where does it go next?
- Enters the left atrium from the pulmonary veins.
- Passes through the bicuspid (mitral) valve into the left ventricle.
- Left ventricle contracts, forcing blood through the semilunar valves into the aorta.
- Blood is pumped around the body.
What prevents backflow of blood in the heart? (3)
- Atrioventricular (AV) valves (tricuspid & bicuspid) prevent backflow into the atria.
- Semilunar valves prevent blood from flowing back into the ventricles.
- Tendinous cords prevent the AV valves from inverting under high pressure.
Why is the left ventricle wall thicker than the right ventricle wall?
The left ventricle needs to pump blood around the entire body, overcoming higher resistance.
The right ventricle only pumps blood to the lungs, which are close to the heart, so it requires less force.
What is the function of the septum in the heart?
The septum is the inner dividing wall of the heart.
It prevents mixing of oxygenated and deoxygenated blood.
Do the left and right sides of the heart work separately or together?
The right and left sides of the heart fill and empty together, ensuring efficient circulation.
Why is the septum not fully developed in a fetus?
In a fetus, oxygenation occurs in the placenta, not the lungs.
Blood mixes freely in the heart as the septum is not fully formed.
What happens to the septum after birth? What does this ensure?
The gap in the septum closes within the first few days/weeks after birth.
This ensures separation of oxygenated and deoxygenated blood for efficient circulation.
What is a hole in the heart?
A condition where the gap in the septum fails to close after birth.
This allows mixing of oxygenated and deoxygenated blood, reducing oxygen supply to the body.
How can a hole in the heart be detected?
Often heard as a heart murmur using a stethoscope.
Small holes may go undetected if they don’t cause major issues.
What are the potential health effects of a large septal defect? (3)
Reduced oxygenation of blood, leading to fatigue and breathlessness.
Increased workload on the heart, potentially causing heart failure if untreated.
May require surgical correction to repair the hole.
What is the cardiac cycle, and how long does it last in a human adult?
The cardiac cycle refers to the sequence of events in a single heartbeat.
It lasts about 0.8 seconds in a human adult.
What happens during diastole?
- The heart relaxes, and both the atria and ventricles fill with blood.
- The volume and pressure in the heart increase as it fills.
- The pressure in the arteries is at its lowest.
What happens during systole?
- Atrial systole occurs first—atria contract, forcing blood into the ventricles.
- Ventricular systole follows—ventricles contract, pushing blood:
- Right ventricle → lungs via the pulmonary artery.
- Left ventricle → body via the aorta.
- Pressure in the heart increases dramatically during contraction.
How does blood pressure change during the cardiac cycle?
During diastole, blood pressure in the heart is high, but in the arteries, it is low.
During systole, pressure in the heart drops, but arterial pressure reaches its peak.
What are the three main phases of the cardiac cycle?
- Diastole – Heart relaxes, atria and ventricles fill with blood.
- Atrial systole – Atria contract, pushing blood into ventricles.
- Ventricular systole – Ventricles contract, forcing blood into arteries.
Why does atrial pressure remain low throughout the cardiac cycle?
Atrial walls are thin and do not generate much force.
Pressure peaks when the atria contract (atrial systole).
When the AV valves close, pressure drops but rises again as the atria refill with blood.
When is atrial pressure at its highest?
During atrial systole, when the atria contract to push blood into the ventricles.
What happens to ventricular pressure as blood fills the ventricles?
It starts low and gradually increases as the ventricles fill with blood.
Why does ventricular pressure increase sharply?
When the ventricular walls contract during ventricular systole, forcing blood into the arteries.
What happens when ventricular pressure exceeds aortic pressure?
The semilunar valves open, allowing blood to be ejected into the aorta.
When does ventricular pressure drop?
After blood is ejected and the semilunar valves close, ventricular pressure falls.
What happens to ventricular volume during atrial systole?
It increases as the ventricles fill with blood.
What happens to ventricular volume when the semilunar valves open?
It drops suddenly as blood is ejected into the aorta.
Why does aortic pressure stay relatively high?
The elasticity of the aorta helps maintain pressure and create a recoil action to keep blood moving.
What causes a temporary rise in aortic pressure during relaxation?
The recoil action of the aorta after blood is ejected from the ventricles.
What causes the ‘lub’ and ‘dub’ sounds of the heart?
Lub – Closing of atrioventricular (AV) valves.
Dub – Closing of semilunar valves.
What does an ECG (electrocardiogram) measure?
The electrical activity of the heart.
Between what timings does atrial systole occur?
0.0 - 0.1s: Atrial systole (Atria contract, pushing blood into ventricles).
Between what timings does ventricular systole occur? What occurs at the beginning of this phase?
0.1 - 0.4s: Ventricular systole (Ventricles contract, blood is ejected into arteries).
Lub sound (AV valves closing) occurs at the start of this phase.
What marks the beginning of the ventricular systole on an ECG Graph?
QRS complex on ECG marks the beginning of ventricular systole.
Between what timings does Diastole occur? What occurs at the beginning of this phase?
0.4 - 0.8s: Diastole (Heart relaxes, chambers refill with blood).
T wave on ECG marks the start of diastole.
What marks the beginning of the Diastole on an ECG Graph?
Dub sound (Semilunar valves closing) occurs at the start of this phase.
What is the primary cause of the sounds in the heartbeat?
The sounds of the heartbeat are caused by blood pressure closing the heart valves. The two main sounds are the result of the closing of the atrioventricular valves and the semilunar valves.
What are the two distinct heart sounds and when do they occur?
First sound (Lub): Occurs when the atrioventricular valves (tricuspid and bicuspid) close as the ventricles contract.
Second sound (Dub): Occurs when the semilunar valves (aortic and pulmonary) close due to the backflow of blood as the ventricles relax.
What does the term “myogenic” mean in reference to cardiac muscle?
“Myogenic” means that cardiac muscle has its own intrinsic rhythm, meaning it can generate its own electrical impulses and contract without external nervous stimulation.
What is the average resting heart rate of an adult, and what factors influence it?
The average resting heart rate of an adult is around 70 beats per minute. This can be influenced by factors such as exercise, excitement, and stress, which can increase the heart rate.
How is the basic rhythm of the heart maintained?
The basic rhythm is maintained by a wave of electrical excitation, not by a nerve impulse, and this wave triggers the contraction of the heart muscles.
What is the role of the Sino-atrial Node (SAN) in the heartbeat?
The SAN is the pacemaker of the heart, initiating the electrical wave that triggers the contraction of the atria and starts the heartbeat.
Why can’t the electrical excitation pass directly to the ventricles from the SAN?
A layer of non-conducting tissue between the atria and ventricles prevents the direct passage of electrical excitation, ensuring proper sequence of contractions.
What is the role of the Atrio-ventricular Node (AVN) in the conduction of the heartbeat?
The AVN receives the electrical activity from the SAN and imposes a slight delay before passing the signal to the Bundle of His, ensuring that the atria have time to contract before the ventricles.
What is the Bundle of His, and what is its role in the conduction system of the heart
The Bundle of His is a bundle of specialized conducting tissue that carries the electrical impulse from the AVN to the apex (bottom) of the heart, where it is then passed to the Purkyne fibers.
What happens at the apex of the heart in the conduction process?
At the apex, the electrical impulse is passed to the Purkyne fibers, which spread out through the walls of the ventricles. This triggers the ventricles to contract, starting from the apex.
Why is it important for ventricular contraction to start at the apex of the heart?
Starting the contraction at the apex allows for more efficient emptying of the ventricles, as the contraction pushes blood upward toward the outflow valves (aortic and pulmonary).
How does the delay at the AVN ensure proper coordination of the heart’s contractions?
The delay at the AVN ensures that the atria have finished contracting and emptying blood into the ventricles before the ventricles begin their contraction, preventing inefficient or premature contraction.
What does an electrocardiogram (ECG) measure?
An ECG measures the electrical activity of the heart, specifically the tiny electrical differences in the skin that result from the heart’s electrical activity.
How does an ECG detect electrical activity in the heart?
An ECG doesn’t directly measure the electrical activity of the heart. Instead, it detects the tiny electrical differences in the skin caused by the heart’s electrical impulses.
How are electrodes used in ECG testing?
Electrodes are painlessly stuck to clean skin to ensure good contact, which is necessary for obtaining reliable results. These electrodes pick up the electrical signals from the heart.
How is the electrical signal from the electrodes used in an ECG?
The electrical signal from each electrode is fed into a machine, which processes it and produces an ECG recording.
What is the main medical use of an ECG?
ECGs are primarily used to diagnose heart problems, such as detecting irregularities in electrical activity that may indicate conditions like heart attacks.
How can an ECG be used to diagnose a heart attack?
During a heart attack, recognizable changes occur in the heart’s electrical activity, and an ECG can capture these changes to diagnose the problem and assist in timely treatment.
What is tachycardia?
Tachycardia is when the heartbeat is very rapid, over 100 beats per minute.
When can tachycardia occur normally?
Tachycardia can occur during exercise, when you have a fever, or when you are frightened or angry.
What causes abnormal tachycardia?
Abnormal tachycardia can be caused by problems in the electrical control of the heart.
How is abnormal tachycardia treated?
Abnormal tachycardia may need treatment through medications or surgery to restore normal rhythm.
What is bradycardia?
Bradycardia is when the heart rate slows down to below 60 beats per minute.
When is bradycardia considered normal?
Bradycardia is normal in fit individuals because training makes the heart beat more slowly and efficiently.
When is bradycardia dangerous?
Severe bradycardia can be dangerous and may result in inefficient heart function.
What treatment is required for severe bradycardia?
Severe bradycardia may require an artificial pacemaker to keep the heart beating steadily.
What is an ectopic heartbeat?
An ectopic heartbeat is an extra heartbeat that occurs outside of the normal rhythm.
How common are ectopic heartbeats?
Most people have at least one ectopic heartbeat per day.
Are ectopic heartbeats normally a cause for concern?
Ectopic heartbeats are usually normal and harmless, though frequent ones may indicate underlying health conditions.
What is atrial fibrillation (AF)?
Atrial fibrillation is an arrhythmia where rapid electrical impulses are generated in the atria, causing them to contract very fast, up to 400 times per minute.
Why is atrial fibrillation an abnormal rhythm?
The atria contract very fast but in an uncoordinated manner, which is called fibrillation.
How does atrial fibrillation affect the ventricles?
Only some electrical impulses from the atria are passed to the ventricles, causing them to contract less frequently than normal.
How does atrial fibrillation affect heart function?
Atrial fibrillation reduces the efficiency of blood pumping, as the heart does not pump blood properly.
Why is atrial fibrillation considered a serious condition?
Atrial fibrillation can lead to poor circulation and increases the risk of stroke and other heart-related complications.
What factors affect blood pressure?
Blood pressure is affected by the contraction of the ventricles and the diameter of blood vessels. Narrowing of the arteries can influence local blood flow and increase blood pressure.
What is the significance of narrowing the arteries in relation to blood pressure?
Narrowing of the arteries can increase blood pressure and may lead to severe health problems if the changes are permanent.
How is blood pressure commonly expressed?
Blood pressure is expressed as two figures: the first (higher) number represents the systolic pressure, and the second (lower) number represents the diastolic pressure.
What device is traditionally used to measure blood pressure?
Blood pressure is traditionally measured using a manual sphygmomanometer, which consists of a cuff connected to a mercury manometer.
How is the sphygmomanometer used to measure blood pressure?
The cuff is placed around the upper arm and inflated until blood flow to the lower arm is cut off. A stethoscope is positioned over the blood vessel at the elbow as the cuff is slowly deflated.
What happens when the cuff pressure is released during a blood pressure reading?
As the cuff pressure is released, blood sounds are first heard as a slight tapping sound. The point at which this sound first appears corresponds to the systolic blood pressure.
What does the systolic blood pressure represent?
The systolic blood pressure corresponds to the pressure when the left ventricle of the heart contracts strongly, forcing blood through the arteries.
How is the systolic blood pressure measured with the sphygmomanometer?
The systolic blood pressure is recorded by the height of the mercury column when the first blood sounds are heard, indicating the highest pressure in the arteries.
What does the diastolic blood pressure represent?
The diastolic blood pressure represents the pressure in the arteries when the heart is in diastole, or resting phase, and the pressure is low enough for blood to flow through the cuff.
How is diastolic blood pressure measured using the sphygmomanometer?
The diastolic blood pressure is recorded when the blood sounds return to normal, indicating that the lowest pressure during diastole is sufficient for blood to pass through the cuff.
What is considered a normal blood pressure reading?
A normal blood pressure reading is generally 120/80 mmHg, where 120 is the systolic pressure and 80 is the diastolic pressure.
What is a newer alternative to the traditional sphygmomanometer for measuring blood pressure?
A simpler digital sphygmomanometer is often used nowadays, which works on the same principles, but the stethoscope is built into the cuff applied around the arm.
