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Double Circulation & Regulation of Cardiac Activity Notes | Study Biology Class 11 - NEET

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Regulation of Cardiac Activity
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The circulatory system is responsible for the transportation of nutrients and gases like oxygen, for the body and metabolic waste products away from the body. The heart and the lungs play an important role in circulating and purification of blood throughout the body. But is the heart the only organ that helps in purification? Let’s have a brief study on double circulation and the relevant organs involved.
Double Circulation & Regulation of Cardiac Activity Notes | Study Biology Class 11 - NEET

Types of Circulatory Systems
In animals, there are two types of circulatory systems: open circulatory system and closed circulatory system. The majority of mammals, including humans, use a double circulatory system. The closed circulatory system is further classified into two, based on the number of times blood circulation takes place through the heart:

Single Circulation

  • In a single circulatory system, the blood will pass through the heart to gills, then after purification, blood will be distributed to different parts of the body. Only one cardiac cycle is completed, hence the name single circulation. For example: single circulation is mainly seen in birds, fish, reptiles, etc.

Double Circulation

  • The heart is the key organ for blood circulation and the double circulation is an efficient way of circulation as it provides an effective way of circulation. The main difference is that the blood follows two routes – one for oxygenated blood and the other for deoxygenated blood. Hence, the name “double circulation.” The majority of mammals, including humans utilize a double circulatory system.

The human heart is divided into four chambers:

  • Left Atria
  • Right Atria
  • Left Ventricles
  • Right Ventricles

Further, the heart is connected to the lungs through the pulmonary artery and vein. In double circulation, there are two pathways in which the blood flows. They are:

Systemic circulation

Systemic circulation carries oxygenated blood from the left ventricles to the tissue capillaries.

  • The oxygen-rich blood is transferred to the aorta for circulating into various parts of the body.
  • Later, the veins and venules collect the deoxygenated blood – which is rich in carbon dioxide from various parts of the body.
  • The deoxygenated blood is pumped back into the superior vena cava and then to the right atrium.
  • Once, after receiving the deoxygenated blood, the right atrium carries blood to the right ventricle for pulmonary circulation.

Pulmonary circulation

In the pulmonary circulation, the blood circulation starts from the right atrium to the left atrium. In this pathway:

  • The pulmonary artery collects the blood from the right ventricle and carries to lungs for oxygenation.
  • Once, after the purification process, the oxygenated blood is pumped back to the left atrium through the pulmonary vein which is carried to the left ventricles.
  • The left ventricles pump the oxygenated blood to the aorta for systemic circulation.

Double circulation supports a strict separation of both oxygenated and deoxygenated blood. Therefore, this circulation ensures that the body always has a dedicated supply of oxygen and also, it improves body efficiency. This is also one of the reasons why mammals can maintain their body temperatures. Apart from the double circulation, a third portal system also exists to improve circulation efficiency.

Regulation of Cardiac Activity

The heart is a muscular organ composed of specialized muscles called cardiac muscles. The main function of the human heart is to pump blood to various parts of the body. There are several internal factors which enable the human heart to regulate its activities on its own, but there are some external influences as well which regulates the cardiac activity. These factors include an autonomic nervous system, chemicals like hormones, ions etc.


Autonomic regulation-Sympathetic and Parasympathetic Nerves

Cardiac output variation and rhythmic control can also be achieved by the autonomic nervous system (ANS) impulse generation. Medulla oblongata in the brain is responsible for this ANS activity. ANS consists of two nerves- sympathetic nerves and parasympathetic nerves, which contradict each other. Stimulation of sympathetic nerves leads to stronger ventricular and atrial contraction which increases the cardiac output. It also increases heart rate. In contrast to sympathetic action, parasympathetic stimulation reduces the contraction of atria and ventricles. This results in less cardiac output and heart rate.


Chemical Regulation-Hormones and Ions

Apart from autonomic regulation, there are certain chemicals which can affect the regulation of cardiac activity. These chemicals include hormones like epinephrine, nor-epinephrine, thyroxine etc. They can increase the contraction and heart rate. Ions are the other chemicals that have an impact on the heart.

The regulation of cardiac activity is influenced not only by these factors. Even gender of an individual can influence it.

The document Double Circulation & Regulation of Cardiac Activity Notes | Study Biology Class 11 - NEET is a part of the NEET Course Biology Class 11.
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