Cardiology: Blood Supply & Cardiac Cycle

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Questions and Answers

Which artery is responsible for supplying blood to both the left atrium and left ventricle?

Right coronary artery

Pulmonary artery

Left coronary artery (correct)

Aortic artery

What is heart sound S1, commonly referred to as 'lub', caused by?

Beginning of ventricular systole (correct)

Atrial contraction

Closure of the semilunar valves

Filling of the ventricles

During which phase of the cardiac cycle do the semilunar valves open?

Period of falling pressure

Beginning of ventricular systole

Atrial systole

Period of rising pressure (correct)

What structure in the heart serves as the primary pacemaker?

Sinoatrial node Signup and view all the answers

Which event occurs during ventricular diastole?

Semilunar valves snap shut Signup and view all the answers

What is the resting rate of the SA node?

60-100 beats/min Signup and view all the answers

Which part of the heart is primarily supplied by the parasympathetic nervous system?

AV node Signup and view all the answers

What does the P wave in an EKG represent?

Atrial depolarization Signup and view all the answers

What is the primary role of intercalated discs in cardiac muscle cells?

Facilitate quick movement of action potentials Signup and view all the answers

What indicates the beginning of ventricular contraction on an EKG?

QT interval Signup and view all the answers

Which component of cardiac muscle cells allows for rapid transmission of action potentials?

T tubules Signup and view all the answers

Which of the following is a characteristic unique to cardiac muscle compared to skeletal muscle?

More mitochondria Signup and view all the answers

Which of the following correctly describes the QRS complex?

Ventricular depolarization Signup and view all the answers

What occurs in turbulent flow when blood encounters an obstacle?

Blood structure becomes less organized. Signup and view all the answers

What is the systolic blood pressure?

Highest arterial pressure after ventricular contraction. Signup and view all the answers

Which factors contribute to the regulation of blood pressure?

Contractility and blood viscosity. Signup and view all the answers

What role do baroreceptors play in blood pressure regulation?

They detect changes in blood volume and pressure. Signup and view all the answers

What triggers an increase in heart rate and blood pressure in response to CO2 levels?

Increase in PaCO2 concentration. Signup and view all the answers

What is coronary perfusion pressure?

Difference in pressure between the aorta and coronary vessels. Signup and view all the answers

How does autoregulation contribute to coronary circulation?

It ensures continuous coronary artery blood flow despite BP changes. Signup and view all the answers

What is a function of the lymphatic system?

Picks up excess fluids and materials for circulation. Signup and view all the answers

What is afterload in the context of cardiac function?

The pressure the ventricles must overcome to eject blood Signup and view all the answers

How can preload be increased to enhance cardiac output?

By giving IV fluids to increase blood return to the heart Signup and view all the answers

What is the effect of a narrower aortic valve on afterload?

It increases afterload requiring more pressure to open the valve Signup and view all the answers

Which factor most directly influences blood flow through a vessel according to Poiseuille's Law?

The radius of the vessel Signup and view all the answers

What is the relationship between compliance and blood vessels?

Veins possess more compliance than arteries Signup and view all the answers

What happens to blood flow when resistance is increased?

Blood flow is decreased Signup and view all the answers

Which sequence correctly represents the order of blood flow in the cardiovascular system?

Heart → Arteries → Arterioles → Capillaries → Venules → Veins Signup and view all the answers

To decrease preload and subsequently lower cardiac output, you should:

Administer diuretics Signup and view all the answers

What triggers the power stroke in muscle contraction?

Release of ADP and P from myosin Signup and view all the answers

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

To provide for the increased energy demands of the heart Signup and view all the answers

What is the role of intercalated discs in cardiac muscle tissue?

To allow impulses to travel quickly between cardiac tissue Signup and view all the answers

How is cardiac output calculated?

Heart Rate x Stroke Volume Signup and view all the answers

What effect does increased pressure have on the tension in the walls of a hollow cylinder according to Laplace's law?

Increased pressure results in increased tension Signup and view all the answers

Which statement describes the Frank-Starling law of the heart?

Greater blood volume before contraction leads to stronger contraction Signup and view all the answers

What happens to the myosin head after ATP hydrolysis during muscle contraction?

It releases actin and resets in a cocked position Signup and view all the answers

What is the significance of preload in cardiac function?

It indicates the amount of blood in the ventricles after filling Signup and view all the answers

Study Notes

Blood Supply to the Heart

The left coronary artery supplies the left atrium and left ventricle.
The right coronary artery supplies the right atrium, right ventricle, sinoatrial node, and atrioventricular node.

Cardiac Cycle

One cardiac cycle represents one complete heartbeat, encompassing the ventricular contraction and subsequent relaxation.
It starts at the beginning of one ventricular contraction and ends at the beginning of the next.
There are five distinct phases:
- Atrial systole: Both atria contract, pushing blood through the tricuspid and mitral valves into the ventricles. The semilunar valves (pulmonic and aortic) remain closed.
- Beginning of ventricular systole: Both ventricles contract, causing increased pressure that closes the tricuspid and mitral valves. This closure produces the "lub" sound of the heartbeat (S1).
- Period of rising pressure: Ventricular pressure exceeds arterial pressure, forcing the semilunar valves open.
- Beginning of ventricular diastole: Pressure drops below arterial pressure, causing the semilunar valves to snap shut. This closure produces the "dub" sound (S2).
- Period of falling pressure: Blood flows from the atria to the ventricles.

Cardiac Conduction System

The heart's myocardium possesses its own conduction system, driven by pacemaker cells located in two primary sites:
- Sinoatrial node (SA node): Situated in the right atrium, this node acts as the heart's pacemaker, with a resting rate of 60-100 beats per minute. It receives innervation from both the sympathetic and parasympathetic nervous systems.
- Atrioventricular node (AV node): Located just above the tricuspid valve in the atrial wall, this node has a rate of 40-60 beats per minute due to parasympathetic innervation from the vagus nerve.
Bundle of His and Purkinje fibers: These fibers carry the electrical impulse down through the ventricles, facilitating coordinated contraction.

Electrocardiogram (ECG or EKG)

An electrocardiogram is a tool for measuring electrical conduction through the heart.
Depolarization represents contraction, while repolarization signifies relaxation.
P wave: Represents atrial depolarization (contraction).
QRS complex: Represents ventricular depolarization and atrial repolarization.
T wave: Represents ventricular repolarization (return to resting state).
QT interval: Represents the duration of ventricular contraction.

EKG Paper

Voltage is measured on the vertical axis.
Time is measured on the horizontal axis.

Cardiac Muscle Cells - Myocardial Cells

Cardiac muscle cells share similarities with skeletal muscle cells, utilizing the sliding filament theory for movement. However, there are key differences:
- More mitochondria: Cardiac muscle cells have a higher energy demand, requiring more mitochondria for ATP production.
- Single nucleus: Unlike skeletal muscle cells, cardiac muscle cells only have one nucleus.
- Intercalated discs: These specialized junctions facilitate rapid transmission of action potentials between cells, promoting coordinated contraction.
- More T tubules: These structures supply ions, enabling quick action potential transmission.

Cardiac Muscle Contraction

Troponin covers active sites on tropomyosin when they are not in use. During an action potential, calcium binds to troponin, moving tropomyosin and exposing the active sites.
Myosin heads, with ADP and P molecules attached, form cross-bridges with actin by binding to the active sites.
ADP and P are released from the myosin head, causing it to move the actin filament towards the center of the sarcomere in a power stroke.
ATP attaches to the myosin head, causing it to detach from the active site.
This ATP molecule hydrolyzes, cocking the myosin head, readying it for another cycle.

Cardiac Performance: Cardiac Output

Stroke volume (SV): The amount of blood pumped by the heart with each beat.
Cardiac output: The volume of blood pumped by the heart per minute, calculated as SV x HR.
Contractility: The strength of cardiac cell contraction.
Laplace law: This principle from physics states that tension on the walls of a hollow sphere or cylinder depends on the pressure of the contents and the radius. Increased pressure equates to increased tension.
Frank-Starling law of the heart: This law describes the relationship between end-diastolic volume and stroke volume.
- End-diastolic volume (EDV): The amount of blood in the ventricles just before contraction, at the end of the filling phase. It essentially represents the blood volume after diastole.

Preload vs Afterload

Preload: The physiological stretching of the ventricles after diastole, representing the amount of blood filling the ventricles. This primes the heart for pumping blood out.
- Increasing preload: To increase preload, stroke volume, and cardiac output, IV fluids can be used to increase blood return to the heart, or vasopressors can be administered to cause vasoconstriction.
- Decreasing preload: To decrease preload, stroke volume, and cardiac output, diuretics can be used to remove extra fluid and reduce the stretching of the ventricles.
Afterload: The pressure the ventricles must overcome to push blood through the semilunar valves into the lungs or the body.
- High vascular resistance: This results in high afterload, requiring more force to expel blood.
- Narrower aortic valve: Aortic stenosis, or a narrowing of the aortic valve, increases afterload because more pressure is required to open the valve.

Blood Vessel Structure

Understand the order of blood flow through blood vessels:
- Heart  arteries  arterioles  capillaries  venules  veins  heart

Factors Affecting Blood Flow

Pressure: Measured in mmHg, it represents the force exerted on a liquid per unit area.
Resistance: Opposition to blood flow; increased resistance leads to decreased flow.
Velocity: Speed of blood flow.
Poiseuille's law: This law states that a small change in the radius of a vessel causes a large change in blood flow.
Compliance: Ability of a vessel to expand; veins have greater compliance than arteries.
Laminar vs turbulent flow: When blood encounters an obstacle, such as a split in vessels or plaque, it becomes less linear, reducing velocity.

Regulation of Blood Pressure

Systolic blood pressure (top number): Represents the highest arterial pressure after ventricular contraction (systole).
Diastolic blood pressure (bottom number): Represents the lowest arterial pressure during ventricular filling (diastole).
Factors influencing blood pressure: Preload, contractility, vessel diameter, sympathetic nervous activity, blood viscosity.
Humoral regulation: Vasodilation and vasoconstriction contribute to blood pressure regulation.
Baroreceptors: Located in the aorta and carotid sinus, they sense changes in blood volume and send signals to the cardiovascular center in the brainstem.
Chemoreceptors: Also found in the aorta and carotid sinus, they sense changes in blood chemistry and respond to oxygen, carbon dioxide, and pH levels. An increase in PaCO2 or decrease in pH triggers a rise in heart rate, stroke volume, and blood pressure to compensate and reduce CO2.

Regulation of Coronary Circulation

Coronary perfusion pressure: The difference in pressure between the aorta and coronary vessels.
Autoregulation: Ensures constant coronary artery blood flow within a mean arterial pressure range of 60-140mmHg, ensuring adequate blood supply despite variations in blood pressure.
Autonomic regulation: Both the parasympathetic and sympathetic nervous systems contribute to coronary circulation control.

Lymphatic System

The lymphatic system plays a crucial role in collecting excess fluids and materials from the body's tissues and returning them to the bloodstream, allowing the kidneys to filter and eliminate waste products.

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Description

Explore the blood supply to the heart and the phases of the cardiac cycle with this quiz. Understand the roles of the left and right coronary arteries and the dynamics of each cardiac cycle phase. Test your knowledge and grasp of essential cardiac functions!