Blood circulation system

An Overview

The blood circulatory system (cardiovascular system) delivers nutrients and oxygen to all cells in the body. It consists of the heart and the blood vessels running through the entire body. The arteries carry blood away from the heart; the veins carry it back to the heart. The system of blood vessels resembles a tree: The “trunk” – the main artery (aorta) – branches into large arteries, which lead to smaller and smaller vessels. The smallest arteries end in a network of tiny vessels known as the capillary network.

There isn’t only one blood circulatory system in the human body, but two, which are connected: The systemic circulation provides organs, tissues and cells with blood so that they get oxygen and other vital substances. The pulmonary circulation is where the fresh oxygen we breathe in enters the blood. At the same time, carbon dioxide is released from the blood.

In the systemic circulation, the left ventricle pumps oxygen-rich blood into the main artery (aorta). The blood travels from the main artery to larger and smaller arteries and into the capillary network. There the blood drops off oxygen, nutrients and other important substances and picks up carbon dioxide and waste products. The blood, which is now low in oxygen, is collected in veins and travels to the right atrium and into the right ventricle.

This is where pulmonary circulation begins: The right ventricle pumps low-oxygen blood into the pulmonary artery, which branches off into smaller and smaller arteries and capillaries. The capillaries form a fine network around the pulmonary vesicles (grape-like air sacs at the Human blood circulation comprises mainly 2 forms of circulations, the pulmonary and systemic circulations. During pulmonary circulation, the human blood is oxygenated after a loop through the lung. As for systemic circulation, the blood is circulated (loop) through the rest of the body to provide oxygenated blood.

Blood circulation helps to move nutrients, gases or even waste, to and from cells. This would then help in fighting diseases and stabilizing blood temperature and pH to maintain homeostasis.

Types of blood circulation

Double circulation

A type of circulation in which blood flows through the heart twice is called double circulation. This type of circulatory system has a separate systemic circulation and pulmonary circulation.

• Systemic circulation – The flow of oxygenated blood from the left ventricle of the heart to various parts of the body and deoxygenated blood from various parts of the body to the right atrium is called systemic circulation. The systemic arteries arising from the aorta carry oxygenated blood from the left of the ventricle to various parts of the body. The systemic veins carry deoxygenated blood from various parts of the body to the right atrium of the heart.
• Pulmonary circulation – The flow of deoxygenated blood from the right ventricle to the lungs and the return of oxygenated blood from the lungs to the left atrium is called the pulmonary circulation. The pulmonary trunk( right and left pulmonary artery) carries blood from the right ventricle to the lungs where the exchange of gases takes place. The oxygenated blood from the lungs returns to the left atrium of the heart through two pulmonary veins, one from each lung.
Hepatic portal circulation – The flow of deoxygenated blood from the digestive organ to the liver before returning to the heart is called Hepatic portal circulation. A vein that does not carry blood directly to the heart but forms a network of capillaries in another organ before reaching the heart is called a portal vein. Blood enters the liver from two sources. The hepatic artery supplies oxygenated blood from the abdominal aorta and the hepatic portal vein carry deoxygenated blood from the digestive organs to the liver.

Circulation of blood in the heart

The circulation of blood within the different chambers of the heart is described below:

Right atrium:

• Deoxygenated blood enters the right atrium from
• The anterior region of the body via the superior vena cava and the posterior region of the body via the inferior vena cava.
• This causes an expansion of the right atrium.

Right ventricle

• When the right atrium contracts, the tricuspid valve is opened.
• As a result, the blood flows from the right atrium into the right ventricle.
• When the right ventricle contracts, the blood is forced into the pulmonary artery due to the opening of the pulmonary semilunar valves. The pulmonary artery carries the blood to the lungs for oxygenation.

Left atrium

• After oxygenation, four pulmonary veins bring the blood back from the lungs into the left atrium.
• This makes the left atrium expand.

Left ventricle

• When the left atrium contracts, the bicuspid valve is opened.
• As a result, the blood flows from the left atrium into the left ventricle.
• When the left ventricle contracts, the oxygenated blood is pushed into the aorta via the aortic semilunar valves.
• The aorta then carries the oxygenated blood to different parts of the body.

Human Circulatory System

1. The Human Circulatory system is an organ system that contains the heart and the blood vessels and moves blood throughout the body in a closed network of blood capillaries.
2. Humans have a closed circulatory system.
3. The human circulatory system functions to transport blood and oxygen from the lungs to the various tissues of the body.
4. The human heart consists of four chambers – two ventricles and two auricles.
Circulatory System: Blood
Blood is a fluid connective tissue that consists of blood cells, plasma, and platelets. It always keeps on circulating through blood vessels delivering oxygen and nutrients to various cells and tissues. It forms about 88 to 1010 of our body weight.

Blood consists of two major parts:

1. Plasma, which is nearly 5555 to 5858.
2. Formed (cellular) elements or blood corpuscles are nearly 4242 to 4545.

These are of three types, i.e.,

1. Red Blood Cells or RBCs – Red Blood Cells (RBCs) are also known as erythrocytes. They contain a complex chemical compound called haemoglobin which has iron.
2. White Blood Cells – White Blood Cells (WBCs) are also known as leukocytes. These blood cells fight against pathogens and other foreign bodies and thus protect our bodies from diseases.
3. Blood Platelets – Platelets are also known as Thrombocytes. These platelets help in preventing the loss of blood from our body as they causeclotting of blood at the site of injury.

Functions of Circulatory System

The functions of the Circulatory System are given below:
1. The circulatory system helps in transporting oxygen throughout the body.
2. It circulates oxygen and removes carbon dioxide from the body.
3. It transports blood, nutrients, hormones, etc., throughout the body.
4. It helps in the removal of the waste products of metabolism to the excretory organs for disposal.
5. It protects the body against disease and infection.
6. It acts as an interface for cell-to-cell interaction.

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