CICLO CARDÍACO : Coração como bomba - Fisiologia ( capítulo 9) │Guyton e Hall

Summary

This video explains key concepts in cardiac physiology, focusing on heart sounds, the Frank-Starling mechanism, cardiac output, and autonomic nervous system regulation. It describes how the heart pumps blood with increasing efficiency as venous return rises, and how heart rate and stroke volume are linked to cardiac output. The parasympathetic and sympathetic systems are discussed in terms of their influence on heart rate, cardiac output, and blood pressure, with the parasympathetic system decreasing heart rate and the sympathetic system increasing it. The video provides an accessible overview of how the heart functions and is regulated.

Takeaways

• 😀 The heart operates through a cyclical process involving systole (contraction) and diastole (relaxation).
• 😀 The first heart sound (S1) occurs when the atrioventricular valves close at the beginning of systole.
• 😀 The second heart sound (S2) occurs when the semilunar valves close at the beginning of diastole.
• 😀 Frank-Starling mechanism explains how the heart adjusts its contraction strength based on the volume of blood it receives.
• 😀 The heart functions like an elastic band, becoming stronger the more it stretches, within physiological limits.
• 😀 The sarcomere, consisting of actin and myosin fibers, is responsible for the heart’s contraction force.
• 😀 Cardiac output is the volume of blood the heart pumps per minute, calculated by multiplying stroke volume (70 mL) by heart rate (72 beats per minute).
• 😀 The Frank-Starling mechanism ensures that the heart pumps the volume of blood it receives (preload) forward effectively.
• 😀 The parasympathetic system, through the vagus nerve and acetylcholine, decreases heart rate and blood pressure by causing hyperpolarization of heart cells.
• 😀 The sympathetic system, using norepinephrine, increases heart rate and blood pressure by stimulating heart cells to become more positive, enhancing contraction force.
• 😀 Heart rate and cardiac output are tightly regulated by both the sympathetic and parasympathetic nervous systems to maintain optimal blood pressure and circulation.

Q & A

What causes the first heart sound (S1) during the cardiac cycle?

The first heart sound (S1) is caused by the closure of the atrioventricular (AV) valves during the beginning of ventricular contraction (systole).

What is systolic pressure, and when does it occur?

Systolic pressure is the pressure exerted by the ventricles during contraction when the heart pumps blood into the arteries. It typically measures around 120 mmHg in a healthy individual.

What triggers the second heart sound (S2) in the cardiac cycle?

The second heart sound (S2) is triggered by the closure of the semilunar valves (like the aortic valve) at the end of ventricular systole, marking the beginning of diastole.

What is the Frank-Starling mechanism?

The Frank-Starling mechanism refers to the heart's ability to pump more blood when it receives more blood. As the heart stretches due to increased venous return, the contraction force of the heart increases, allowing more blood to be ejected.

How does the Frank-Starling mechanism relate to the elasticity of the heart?

The heart functions like an elastic band; the more it stretches (due to increased blood volume), the stronger the contraction, up to a certain physiological limit, enhancing the volume of blood pumped out.

What is cardiac output, and how is it calculated?

Cardiac output is the volume of blood the heart pumps per minute. It is calculated by multiplying stroke volume (the volume ejected with each heartbeat) by heart rate. For example, 70 ml per beat multiplied by 72 beats per minute equals a cardiac output of around 5 liters per minute.

What is the role of the autonomic nervous system in regulating the heart?

The autonomic nervous system regulates heart function through its sympathetic and parasympathetic branches. The parasympathetic system decreases heart rate, while the sympathetic system increases heart rate and cardiac output.

How does the parasympathetic nervous system affect heart rate?

The parasympathetic nervous system releases acetylcholine, which causes an efflux of potassium from the heart muscle cells, resulting in hyperpolarization, a more negative charge inside the cells, and a decrease in heart rate.

What neurotransmitter does the sympathetic nervous system use to affect heart rate?

The sympathetic nervous system uses norepinephrine to increase heart rate and cardiac output by stimulating the heart muscle cells to contract more forcefully.

How does the sympathetic nervous system increase blood pressure?

The sympathetic nervous system increases heart rate and cardiac output, which results in a higher volume of blood being pumped throughout the body, thereby raising blood pressure.