cardiovascular

Question 1

Why is the heart essential for life, and how many times does it contract at an average rate of 75 beats/min?

Answer 1

A: The heart is essential because it pumps blood continuously and never takes a day off. At 75 beats/min, it contracts about 108,000 times per day, >39 million times per year, and around 3 billion times in a 75-year lifespan.

Question 2

Q: Why do cardiac muscle cells have more mitochondria than skeletal muscle cells?

Answer 2

A: Because they rely heavily on aerobic respiration to produce the ATP needed to sustain ~108,000 heartbeats per day, pumping blood and delivering nutrients throughout the body.

Question 3

How much blood does the heart pump at rest, and through what system does it travel

Answer 3

At rest, each beat ejects about 70 mL of blood, equal to ~5 L/min, ~14,000 L/day, and ~5,000,000 L/year. All of this blood travels through the body’s ~95,000 km of blood vessels.

Question 4

Q: What is the size and weight of the heart, and what must we study to understand its function?

Answer 4

A: The heart is about the size of a fist, weighing ~325 g in males and ~275 g in females. To fully grasp its impressive performance, we must understand the anatomy and physiology of the heart.

Question 5

Q: Where is the human heart located, and what protects it?

Answer 5

A: The heart lies in the thoracic cavity, between the lungs in the mediastinum. It is enclosed and separated from other mediastinal structures by the pericardium, a tough protective membrane.

Question 6

Q: How is the heart positioned in the body, and what attaches to its base?

Answer 6

A: The dorsal surface of the heart lies near the vertebrae, while its anterior surface sits deep to the sternum and costal cartilages. The base of the heart (superior surface) is where the great veins (superior & inferior venae cavae) and great arteries (aorta & pulmonary trunk) attach.

Question 7

Where are the base and apex of the heart located?

Answer 7

The base of the heart is at the level of the third costal cartilage. The apex (inferior tip) lies just to the left of the sternum, between the junction of the fourth and fifth ribs.

Question 8

Which chambers are closest to the base and which are closest to the apex of the heart?

Answer 8

The atria are the upper chambers, located nearest the base of the heart. The ventricles are the lower chambers, located nearest the apex.

Question 9

What structures separate the chambers of the heart?

Answer 9

The atrioventricular septum separates the atria from the ventricles, while the interatrial septum separates the right and left atria, and the interventricular septum separates the right and left ventricles.

Question 10

What blood does the right atrium receive, and how does it pass to the right ventricle?

Answer 10

A: The right atrium receives deoxygenated blood from the superior vena cava, inferior vena cava, and coronary sinus. Blood then flows from the right atrium to the right ventricle through the tricuspid (atrioventricular) valve.

Question 11

How does blood leave the right ventricle and where does it go?

Answer 11

The right ventricle pumps blood through the pulmonary semilunar valve into the pulmonary trunk, which branches into the right and left pulmonary arteries that deliver blood to the lung capillaries.

Question 12

What blood does the left atrium receive, and how does it pass to the left ventricle

Answer 12

The left atrium receives oxygenated blood from the pulmonary veins. Blood then flows into the left ventricle through the bicuspid (mitral) atrioventricular valve.

Question 13

How does blood leave the left ventricle, and how does its muscular wall compare to the right ventricle?

Answer 13

The left ventricle pumps blood through the aortic semilunar valve into the systemic circuit. Although both sides pump the same volume of blood per beat, the left ventricle has a much thicker muscular layer than the right ventricle.

Question 14

How do the valves of the heart function, and what prevents backflow into the atria during ventricular contraction?

Answer 14

Heart valves open and close in response to pressure changes during contraction and relaxation. To prevent backflow into the atria, each atrioventricular valve is anchored by chordae tendineae, which are tethered to the ventricular wall via papillary muscles.

Question 15

What are the two distinct but linked circuits in human circulation, and what do they do

Answer 15

Pulmonary circuit: Transports blood to and from the lungs → picks up oxygen, delivers carbon dioxide for exhalation.

Systemic circuit: Transports oxygenated blood to body tissues → returns deoxygenated blood and carbon dioxide to the heart for pulmonary circulation.

Question 16

How does blood flow through the heart chambers supply and drain the myocardium?

Answer 16

Coronary arteries (branches of ascending aorta): deliver oxygenated blood and nutrients to myocardium.

Coronary veins: remove carbon dioxide and wastes, converge at the coronary sinus.

Question 17

How does the aortic valve protect coronary blood flow?

Answer 17

aortic valves stop the high pressure blood from going to the aritires

Question 18

What unique properties allow cardiac muscle to conduct impulses effectively?

Answer 18

Branch freely → form a network for coordinated contraction.

Intercalated discs with desmosomes → hold cells together during contraction.

Gap junctions → allow ions to flow directly between cells, enabling rapid electrical conduction.

Question 19

What is autorhythmicity in cardiac muscle, and how is heart rate controlled?

Answer 19

Autorhythmicity: Cardiac myocytes can initiate their own electrical potential at a fixed rate.

Electrical signals spread through gap junctions to coordinate contraction.

Heart rate is mainly modulated by the endocrine and nervous systems, despite autorhythmicity.

Question 20

What are the two main types of cardiac cells and their roles?

Answer 20

Myocardial contractile cells (~99%): Conduct impulses and generate contractions that pump blood.

Myocardial conducting cells (~1%): Form the conduction system, initiate and propagate action potentials throughout the heart.

Question 21

The components of the cardiac conduction system include

Answer 21

• The sinoatrial node
• The atrioventricular node
• The atrioventricular bundle
• The atrioventricular bundle branches
• The Purkinje cells

Question 22

What establishes normal cardiac rhythm and why is it called the heart’s pacemaker?

Answer 22

Sinoatrial (SA) node: Located near the superior vena cava.

Has the highest inherent rate of depolarization → sets the pace for the heart.

Initiates sinus rhythm, the normal electrical pattern of heart contractions.

Question 23

What is the role of the atrioventricular (AV) node in cardiac conduction

Answer 23

Location: Within the atrioventricular septum.

Function: Ensures the impulse passes through the AV node before reaching the ventricles.

Critical pause: AV node depolarization creates a delay, allowing atria to finish contracting before ventricular contraction.

Question 24

Why is there a delay at the AV node, and what is its physiological significance?

Answer 24

Delay: Impulse takes ~100 ms to pass through the AV node due to slower conduction.

Purpose: Allows atria to complete contraction, adding ~20% more blood to ventricles (atrial kick) before ventricular contraction.

Maximum rate: Under extreme sympathetic stimulation, AV node can conduct up to 220 impulses/min.

Question 25

How does the cardiac impulse travel from the AV node to the ventricles?

Answer 25

AV node → atrioventricular (AV) bundle / bundle of His: Travels along interventricular septum. Bundle branches: Divide into left and right branches toward the apex. Purkinje fibers: Spread the impulse to ventricular myocardial contractile cells, triggering contraction.

Question 26

What happens to heart rate if parts of the conduction system fail?

Answer 26

AV node blocked: AV bundle fires at ~30–40 bpm. Bundle branches: Inherent rate ~20–30 bpm. Purkinje fibers: Inherent rate ~15–20 bpm. Example: Athlete Miguel Indurain had HR as low as 28 bpm – an example of bradycardia.

Question 27

How do action potentials differ between cardiac conductive cells and contractile cells?

Answer 27

Cardiac conductive cells: Have autorhythmicity → spontaneous depolarization. Show slow depolarization to threshold, then fast upstroke. Lack a true resting potential. Cardiac contractile cells: Depolarization triggered by incoming impulses. Exhibit a plateau phase (sustained contraction) due to Ca²⁺ influx. Have a stable resting potential.

Question 28

How does the action potential in cardiac conductive cells (autorhythmic cells) occur?

Answer 28

Prepotential (pacemaker potential): Slow Na⁺ influx gradually depolarizes the cell. Threshold (-40 mV): Ca²⁺ channels open, causing rapid depolarization up to +15 mV. Repolarization: Ca²⁺ channels close, K⁺ channels open, allowing K⁺ outflow. Return to prepotential (-60 mV): Cycle repeats spontaneously.

Question 29

Contractile cells

Answer 29

demonstrate a much more stable resting phase than conductive cells at approximately −80 mV for cells in the atria and −90 mV for cells in the ventricles * Once activated, there is rapid depolarization (Na+ influx) * Followed by a plateau phase (depolarization maintained through slow Ca2+ channels) * Then repolarization occurs (outflux of K+ which results in repolarization)

Question 30

What is the significance of the absolute and relative refractory periods in cardiac contractile muscle?

Answer 30

Absolute refractory period: ~200 ms; relative refractory period: ~50 ms; total ~250 ms. This extended refractory period allows ventricular filling and rest. Prevents premature contractions that would disrupt coordinated heart function and could be life-threatening.