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Regulation of Cardiac Activity

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Different fluids make up the majority of our bodies. Body fluids are crucial for the normal operation of our tissues and perform the crucial tasks of supplying nutrients to live cells and removing toxic toxins created by our systems. Other techniques for facilitating these activities have been created by other animals. However, complex creatures like humans need blood and lymph fluids to carry out the aforementioned functions.

A muscle-filled organ, the heart is made up of specific cardiac muscles. The heart’s primary job is to pump blood to the body’s numerous organs. The human heart can control its activity due to several internal mechanisms, but certain outside forces control cardiac activity. In an autonomic nerve system, substances like hormones, ions, etc. are some of these factors.

Cardiac Cycle

  • The human heart’s activity from the start of one heartbeat to the start of the next is known as the cardiac cycle
  • It consists of two phases: a diastole, in which the heart muscle relaxes and re-fills with blood, and a systole, in which the heart muscle contracts forcefully and pumps blood. 
  • The heart quickly relaxes and expands after emptying to receive a second inflow of blood returning from the lungs and other bodily systems before contracting once more to pump blood to those systems and the lungs.
  • A heart that is typically functioning must enlarge completely before it can pump effectively. Each cardiac cycle, or heartbeat, takes roughly 0.8 seconds to complete the cycle, assuming a healthy heart and a usual rate of 70 to 75 beats per minute.

Regulation of Cardiac Activity

The atrioventricular node (AV node) and sinoatrial node (SA node) nodal tissues automatically control the normal action of the human heart, which is why the heart is known as myogenic.

The autonomic nervous system regulates several physiological processes (ANS). It enhances the heart’s pace and force of contraction. It controls peripheral blood vessel resistance as well. The autonomic nervous system’s sympathetic and parasympathetic divisions cooperate to maintain the body’s equilibrium. The cardiac cycle helps the body’s blood flow throughout it. The cardiac cycle is managed by two fundamental systems.

  1. Intrinsic regulation of cardiac activity  
  2. Extrinsic regulation of cardiac activity 
Regulation of Cardiac Activity


Intrinsic Regulation

The SA-node, AV-node, and a group of His and Purkinje fibers are all involved in the intrinsic regulation of heart rate. The cardiac cycle is accelerated by the SA node, which produces an impulse on its own.

Extrinsic Regulation

There are two kinds of extrinsic regulation. In a mechanism known as neural regulation, sympathetic and parasympathetic nerves regulate the heartbeat. Through hormonal or chemical modulation, hormones like catecholamine and acetylcholine control the heart rate. Other factors, like environmental stress and medications, also control the heartbeat.

Nervous Regulation

  • The modulation of sympathetic and parasympathetic nerves is performed by the ANS (Autonomic Nervous System).
  • Various signals from the cerebral hemispheres are processed by the baroreceptors and chemoreceptors in the cardiac reflex center.
  • Since it is situated in the ventrolateral medulla, the cardiovascular control center also has a significant impact on controlling heart activity.
  • When the cardio-accelerators are released, the sympathetic components cause TACHYCARDIA. 
  • BRADYCARDIA is caused by the parasympathetic component releasing the cardio inhibitors. Acetylcholine, as an example.
  • The control of the heartbeat is another critical function of the CNS. A CNS impulse travels through the medulla’s cardiovascular center. 
  • The heart and blood arteries both react quickly and in unison to modify blood pressure and perfuse tissues appropriately in response to demands. 
  • To control the heart rate, sympathetic and parasympathetic nerves collaborate.

Baroreceptor Mechanism

  • Nerve endings present on the walls of arteries are called baroreceptors, sometimes known as pressure receptors. The body contains a significant number of baroreceptors.
    • The internal carotid arteries meet in the region just above the carotid bifurcation, which is known as the carotid sinus.
    • The inner wall of the aortic arch.
  • The medullary centers of the brain organize a response using information from baroreceptors and are in charge of the overall output of the autonomic nervous system.
    •  A rise in arterial pressure triggers the parasympathetic pathway, which lowers the heart rate. This aids in reducing arterial pressure, as does enhance vascular vasodilation.
    • The sympathetic pathway is activated when a drop in arterial pressure is detected, increasing heart rate and contractility. Due to increased artery vasoconstriction, the arterial pressure increases as a result.
  • Baroreceptors react swiftly to changes in artery pressure and are sensitive to them. When blood pressure increases, the baroreceptors are stretched, which causes them to transmit signals to the central nervous system. Following this, “feedback” signals are sent to the circulatory system by the autonomic nervous system, causing arterial pressure to return to a more normal level.
  • The small Hering’s nerve, which connects each carotid sinus to the tractus solitarius in the medulla oblongata of the brain, is where the impulses travel after leaving each carotid sinus. Through the vagus nerves, signals from the aortic arch are sent to the medulla oblongata.

Chemoreceptor Mechanism

Carotid and aortic bodies are the names of these receptors. On the bifurcation of the common carotid artery (at the start of the occipital artery), the carotid, and aortic bodies are present at the arch of the aorta. The sinus and aortic nerves will carry impulses from these receptors’ afferent nerves.

Nerves react to changes in biological fluids, such as a drop in the pO2, an increase in pCO2, and a rise in hydrogen ion concentration. Afferent impulses from chemoreceptors are transported by sinus and aortic nerves when they are triggered by any of the above conditions. Because of that, a heart rate will be the eventual effect.

Bainbridge Reflex

In the walls of large veins, stretch receptors are present. They are referred to as volume receptors or low-pressure receptors. The dilation of the great veins stimulates these receptors. Afferent impulses from these receptors will be carried by the vagus nerve. Afferent impulses along the vagus also activate neurons in the brainstem, enhancing sympathetic nerve activity. Afferent signals decrease the cardioinhibitory center’s function, increasing heart rate. The heart’s sympathetic activity is increased, which raises the heart rate.

Chemical Regulation

Norepinephrine is the chemical secreted from the end of the vasoconstrictor nerves (noradrenaline). The medulla of the adrenal endocrine glands secretes norepinephrine (=nor- adrenaline). The primary functions of epinephrine and norepinephrine are to increase metabolism and prepare organisms to deal with certain conditions brought on due to physical stress, such as a drop in blood pressure or blood sugar, rage, anxiety, fear, and so on.

Under normal conditions, norepinephrine regulates blood pressure. Which causes a restriction of almost all of the body’s blood arteries.  In addition to adrenal hormones, the medulla of the adrenal glands also secretes epinephrine (adrenaline). Every part of the body receives this hormone through the bloodstream, where it affects cells directly. Norepinephrine does not have the same effect on heart activity as epinephrine.

In contrast to the noticeably stronger constriction brought on by norepinephrine, it also causes a minor narrowing of muscle blood vessels. As a result, the heart rate is increased by adrenal medullary hormones.

FAQs on Regulation of Cardiac Activity

Question 1: What do you understand by the regularity of cardiac activity?


The regulation of heart activity involves the dynamic and continuous interaction of two different types of control systems, one neurological and one chemical.

Question 2: What makes the cardiac cycle significant?


The heart’s primary function in the cardiac cycle is to circulate blood around the body. It is defined as the electrical impulses that regulate the filling and emptying of the blood vessels as well as the contraction and relaxation of the heart muscles.

Question 3: Name the receptors that are present in the Chemoreceptor Mechanism.


Carotid and aortic bodies are the receptors that are present in the Chemoreceptor Mechanism.

Question 4: Which hormones control heart function?


The heart rate is raised by substances released by the sympathetic nervous system (SNS) (catecholamines – epinephrine and norepinephrine). The parasympathetic nervous system is responsible for producing the hormone acetylcholine, which slows heart rate (PNS).

Question 5: Mention the name of two systems in the cardiac cycle.


Two main systems control the cardiac cycle:

  • Intrinsic regulation 
  • Extrinsic regulation 

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Last Updated : 04 Dec, 2022
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