Heart as a pump I - Physiology

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Questions and Answers

What is the primary function of the pericardial fluid?

To support blood circulation in the heart

To increase the pressure in the heart chambers

To provide lubrication and reduce friction between pericardial layers (correct)

To supply oxygen to the heart muscle

Which of the following best describes pericarditis?

Weakening of the heart valves

Inflammation of the heart muscle

Inflammation of the pericardial sac causing friction (correct)

Constriction of the coronary arteries

How does the structure of the myocardium contribute to its function?

It is made of skeletal muscle fibers which are stronger and more efficient

It consists of interlacing bundles of cardiac muscle fibers that allow for effective contraction (correct)

It has a uniform layer that creates a single contraction pattern

It is composed of smooth muscle which allows for quick relaxation

What layer of the heart wall is primarily responsible for its pumping action?

Myocardium Signup and view all the answers

Which layer of the heart directly contacts the blood within the heart chambers?

Endocardium Signup and view all the answers

What factor differentiates the left pump of the heart from the right pump?

The left pump has thicker walls and pumps at a higher pressure Signup and view all the answers

Which characteristic of coronary arteries is crucial for their function?

They penetrate heart muscle at a 90° angle Signup and view all the answers

What is the main function of the heart's wall structure?

To contract and pump blood throughout the body Signup and view all the answers

Which of the following is a common cause of pericarditis?

Viral infections or autoimmune diseases Signup and view all the answers

What role do heart valves play in cardiac mechanics?

They prevent backward flow of blood during heart contractions Signup and view all the answers

What characteristic is essential for cardiac muscle function?

Ability to contract rhythmically and autonomously Signup and view all the answers

Which layer covers the heart and provides protection?

Pericardium Signup and view all the answers

What prevents the AV valves from being forced open in the opposite direction during high ventricular pressure?

Papillary muscles attaching to chordae tendinae Signup and view all the answers

During which stage does blood flow primarily occur in the subendocardial portion of the left ventricle?

Diastole Signup and view all the answers

What action causes the heart valves to open and close?

Pressure differences across the valves Signup and view all the answers

Why is backflow of blood from the atria into the veins usually not a significant issue?

The venae cavae are compressed during atrial contraction Signup and view all the answers

Which type of junction is known for mechanically holding cardiac muscle cells together?

Desmosomes Signup and view all the answers

Which structure supports the heart valves and separates the atria from the ventricles?

Fibrous skeleton Signup and view all the answers

What percentage of oxygen is typically pumped by the heart at rest for every unit of blood volume?

65% Signup and view all the answers

What occurs when there is a forward pressure gradient regarding heart valve function?

The valve opens Signup and view all the answers

What is the role of chordae tendinae in heart valve function?

They prevent the valve leaflets from everted Signup and view all the answers

What type of valve is the left AV valve also known as?

Bicuspid or mitral valve Signup and view all the answers

Study Notes

Heart as a Pump

The heart is a hollow muscular organ, the size of a clenched fist, located in the middle of the thoracic cavity.
It has a broad base (upper) and an apex (lower).
The heart has two separate pumps (left and right halves), each with two chambers (atria and ventricles).
Veins return blood from the body to the atria.
Arteries carry blood away from the ventricles to the tissues.
A septum, a continuous muscular partition, separates the left and right sides of the heart, preventing oxygen mixing.
Blood travels continuously through the circulatory system to and from the heart through two separate vascular loops: the pulmonary circulation and the systemic circulation.

Pulmonary Circulation

The right side of the heart receives deoxygenated blood from the systemic circulation and pumps it into the pulmonary circulation.
The pulmonary circulation is a low-pressure, low-resistance system.
The pulmonary circulation transports blood through the lungs, where it picks up oxygen and releases carbon dioxide.

Systemic Circulation

The left side of the heart receives oxygenated blood from the pulmonary circulation and pumps it into the systemic circulation.
The systemic circulation, in contrast to pulmonary circulation, may be viewed as a series of parallel pathways that deliver oxygenated blood throughout the body.
The systemic circulation is a high-pressure, high-resistance system.

Blood Flow and Pressure

Blood flows down a pressure gradient (from an area of higher pressure to an area of lower pressure).
Pressure (P) is the force exerted on the vessel walls by the blood pumped into them by the heart.
Resistance (R) is the opposition of blood flow (caused by friction between the flowing blood and the vessel wall).
The left side of the heart works harder because it pumps an equal volume of blood at a higher pressure into a higher-resistance and longer system.
The heart muscle on the left side is thicker (stronger pump) than the muscle on the right side.

Heart Wall and Coverings

The heart is enclosed in the double-walled, membranous pericardial sac.
The pericardial sac consists of two layers: a tough, fibrous outer layer and a secretory lining.
The fibrous outer layer attaches to the connective tissue partition that separates the lungs, anchoring the heart in its correct position within the chest.
The secretory lining of the sac secretes pericardial fluid, which lubricates the pericardial layers, preventing friction as they glide over each other during each heartbeat.

Pericarditis

Pericarditis is inflammation of the pericardial sac that results in painful friction between the two pericardial layers.
Pericarditis can occur due to viral or bacterial infections.

Myocardium

The myocardium is the middle layer of the heart wall and is composed of cardiac muscle.
Cardiac muscle fibers are arranged spirally around the circumference of the heart.
When the ventricular muscle contracts, the diameter of the ventricular chambers is reduced, and the apex is simultaneously pulled upward toward the base of the heart in a rotating manner.

Oxygen Supply to The Heart

The coronary arteries and their branches supply oxygen to the heart.
The coronary arteries originate at the root of the aorta, run along the heart surface, and penetrate the muscle at a 90° angle.
Myocardium compresses its blood vessels upon contraction.
During systole (contraction) of the left ventricle (LV), pressure inside the LV is slightly higher than in the aorta.
Blood flow in the arteries that supply the subendocardial portion of the LV only occurs during diastole (relaxation).
At rest, the heart pumps about 65% of the oxygen contained in every unit of blood volume.
The heart can only increase its oxygen intake if blood flow is enhanced.

Heart Valves

Heart valves are located within the heart to ensure unidirectional blood flow, from veins to atria to ventricles to arteries.
The valves open and close passively due to pressure differences.
A forward pressure gradient (a greater pressure behind the valve) forces the valve open, while a backward pressure gradient (a greater pressure in front of the valve) forces the valve closed.

Types of Heart Valves

Right AV Valve (Tricuspid): Has three cusps or leaflets.
Left AV Valve (Bicuspid or Mitral): Has two cusps or leaflets.

Chordae Tendinae and Papillary Muscles

The edges of the AV valve leaflets are fastened by chordae tendinae, tough thin cords of tendinous-type tissue.
The chordae tendinae prevent the valve from everting (being forced by high ventricular pressure to open in the opposite direction into the atria).
The chordae tendinae extend from the edges of each cusp and attach to small, nipple-shaped papillary muscles that protrude from the inner surface of the ventricular walls.

Absence of Valves Between Atria and Veins

Backflow of blood from the atria into the veins is typically not a major problem for two reasons:
- Atrial pressures are usually not much higher than venous pressures.
- The sites where the venae cavae enter the atria are partially compressed during atrial contraction.

Fibrous Skeleton

Four interconnecting rings of dense connective tissue, known as the fibrous skeleton of the heart, surround and support the four heart valves.
The fibrous skeleton also separates the atria from the ventricles and provides rigid support for the cardiac muscle.

Membrane Junctions

Desmosomes are a type of adhering junction that mechanically holds cells together, contributing to the structural integrity of the heart.

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Description

Test your knowledge on the structure and function of the heart as a pump. This quiz covers topics like the heart's anatomy, chambers, and the difference between pulmonary and systemic circulation. Perfect for students learning about human physiology!