Regulation Of Cardiac Activity: Definition And Diagram

The regulation of cardiac activity involves mechanisms that ensure the heart functions efficiently to meet the body's needs. It is controlled by intrinsic factors, such as the heart's conduction system, and extrinsic factors, including neural and hormonal influences. In this article, the cardiac cycle, basic anatomy and physiology of the heart, mechanisms of cardiac regulation, cardiac output and its regulation, cardiac control in different physiological conditions, and disorders related to cardiac regulation are discussed. Regulation of cardiac activity is a topic of the chapter Body Fluids and Circulation in Biology.

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This Story also Contains

1. The Cardiac Cycle
2. Basic Anatomy and Physiology of the Heart
3. Regulation of Cardiac Activity
4. Regulation of Cardiac Output
5. Cardiac Control in Different Physiological Conditions
6. Disorders Related to Cardiac Regulation

The Cardiac Cycle

The cardiac cycle refers to the events occurring in a single heartbeat. It is the alternate contraction and relaxation of the chambers of the heart. It involves two major phases: systole, when the ventricles contract and blood is pushed out of the heart, and diastole when the heart muscle relaxes and allows the chambers to fill with blood. The effect of this cycle is an effective blood flow to the body, delivering needed oxygen and nutrients to tissues and taking away wastes.

Basic Anatomy and Physiology of the Heart

This part provides a general overview of the structure of the heart and its basic functions. A view of the four-chambered organ: two atria and two ventricles. Circulating blood is managed effectively through the flow of blood coordinated in these chambers. Cardiac cycles, including systole and diastole, are systematically controlled by the sinoatrial and atrioventricular nodes.

Regulation of Cardiac Activity

Neural Control

• Cardiac output variation and rhythmic control can also be provided by the autonomic nervous system ANS impulse generation.

• The ANS activity takes place in the brain's medulla oblongata.

• There exist two kinds of nerves in the system: the sympathetic nerves and the parasympathetic nerves, which are opposite to each other.

• The sympathetic nerves increase the strength of ventricular and atrial contraction when stimulated.

• This will result in an increased cardiac output.

• Heart rate is also increased.

• Compared to a sympathetic action, parasympathetic stimulation reduces the contraction of atria and ventricles, hence giving less cardiac output and heart rate.

Hormonal regulation

• Apart from autonomic regulation, there are certain chemicals which can affect the regulation of cardiac activity.

• These chemicals include the hormones like epinephrine, norepinephrine, and thyroxine.

• They can increase contraction and heart rate.

• The other chemicals that impact the heart are ions.

• Not only these factors but also the gender of an individual has an impact on the regulation of cardiac activity.

Intrinsic Regulation

• The Frank-Starling Law of the Heart describes an event where, when the volume of blood filling the heart increases, the stroke volume increases.

• This intrinsic regulation implies that the more blood that comes back to the heart, the more the heart is going to pump out in a very nice balancing act for circulation.

Reflex Mechanisms

• Baroreceptor Reflex: The baroreceptors, located within the carotid arteries and aorta, sense changes in blood pressure. The impulses that are impinged through it are transmitted to the brain, which responds by modifying the heart rate together with the diameter of the blood vessels, hence keeping the blood pressure stable.

• Chemoreceptor Reflex: These chemoreceptors are found in the carotid bodies and aorta. They establish reflexes responding to alterations in blood gases, primarily carbon dioxide and oxygen. Those reflexes, via these receptors, play a huge role in the regulation of respiration and cardiovascular activities.

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• MCQ Practice on Regulation of Cardiac Activity
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Regulation of Cardiac Output

• Cardiac output refers to the volume of blood pumped by the heart in one minute. It is determined by heart rate and stroke volume.

• The factors that influence cardiac output are venous return, peripheral resistance, and the strength of contraction of the ventricles.

• The cardiac output must be maintained at a level sufficient to provide adequate blood supply to all tissues.

Heart Rate Variability (HRV)

• Heart rate variability is the measure of time variation between each heartbeat and acts as an index for sympathetic-parasympathetic balance.

• HRV is an important index for cardiovascular health and autonomic nervous system function.

• The methods physically offered for the measurement and techniques of HRV include time-domain, frequency-domain, and nonlinear analyses.

Cardiac Control in Different Physiological Conditions

• Cardiac regulation adapts to different physiological conditions:

• During exercise, there is an increase in heart rate and stroke volume as an attempt to meet the oxygen demand of muscles, which is higher.

• In response to stress, the sympathetic nervous system is activated, and heart rate and cardiac output increase.

• The parasympathetic dominance is the sleep stage, during which the heart rate is lower.

• Ageing may affect cardiac regulation; there is a general decline in cardiac output and a predisposition to arrhythmias.

Disorders Related to Cardiac Regulation

Several disorders are associated with impaired cardiac regulation:

• Hypertension: This may be a constant straining of the heart that could cause intermittent injuries in blood vessels over time.

• Arrhythmias: These are irregularities in the heartbeat, which prevent the smooth flow of blood and can lead to severe consequences.

• Heart Failure: The inability of the heart to pump blood effectively could be due to a weakening of the cardiac muscle or some defect in the structure.

• Chronic Diseases: Conditions such as diabetes mellitus and hyperthyroidism are also known to affect the heart and its regulations.

Understanding the mechanism of cardiac regulation has been evolving over the years, and recent research into the mechanisms has resulted in innovative treatments or therapies. Improvements in medical technology, such as the invention of pacemakers and cardiac imaging, have dramatically changed the early diagnosis and management of cardiac disorders.

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