Blood Circulation in Human Beings

The circulatory system is also known as the cardiovascular system and consists of the heart, blood and blood vessels—capillaries, veins and arteries. Blood circulation in human beings is carried out in a double manner: the pulmonary circulation and the systemic circulation. In the pulmonary circulation, blood is carried towards the heart to be oxygenated. In the systemic circulation, the blood that has been enriched by oxygen is transported to other organs. This double circulation also aids with the maintenance of the optimal body temperature. The transport of materials such as oxygen, food, carbon dioxide and excretory products in human beings is also a function of the circulatory system. 

Our Pump-The Heart

The heart is a muscular organ that is as big as our fist.

• It has different chambers to prevent mixing oxygen-rich blood with blood containing carbon dioxide

• The carbon dioxide-rich blood must reach the lungs for the carbon dioxide to be removed
• The oxygenated blood from the lungs must be delivered again to the coronary heart. This Oxygen-rich blood is then pumped to the rest of the body

• Oxygen-rich blood from the lungs comes to the skinny-walled upper chamber of the coronary heart at the left, the left atrium. The left atrium relaxes while it’s collecting this blood
• It then contracts, while the subsequent chamber, the left ventricle, relaxes so that the blood is moved to it. Right when the muscular left ventricle contracts in its turn, the blood is pumped out of the body
• Deoxygenated blood comes from the body to the upper chamber on the right at the atrium as it relaxes
• As the right atrium contracts, the corresponding lower chamber, the right ventricle, dilates. This transfers blood to the right ventricle, which in turn pumps it to the lungs for oxygenation
• Ventricles pump blood into numerous organs so that they have thicker muscular walls than atria
• Valves make sure that blood does not flow backwards when the atria or ventricles contract

Schematic representation of transport and exchange of oxygen and carbon dioxide

Blood Circulation in various organisms

• The separation of the right side and the left side of the coronary heart is beneficial to preserve oxygenated and deoxygenated blood from blending and permits highly efficient delivery of oxygen to the body
• This is beneficial in animals that have excessive energy desires, along with birds and mammals, which continuously use power to preserve their body temperature
• Animals, like amphibians or other reptiles, have three-chambered hearts and tolerate mixing of the oxygenated and deoxygenated blood streams except crocodiles which have 4 chambered hearts
• Fishes have only two chambers to their hearts. The blood is pumped to the gills, oxygenated there, and passes at once to the rest of the body. Thus,  only once do blood goes through the heart in the fish during one cycle of passage via the body
• On the other hand, it goes via the heart two times during every cycle in different vertebrates. This is called double circulation

Blood Pressure

• The force that is applied by the blood against the wall of a vessel is blood pressure
• This pressure is a lot more prominent in arteries than in veins
• The pressure of blood inside the vein during ventricular systole (tightening) is called systolic pressure, and pressure in the artery during ventricular diastole is called diastolic pressure
• The standard systolic pressure is around 120 mm of Hg, and diastolic pressure is 80 mm of Hg
• It is assessed with an instrument called a sphygmomanometre
• High blood pressure is similarly called hypertension. It can provoke the rupture of an artery and cause internal bleeding

The Tube – Blood vessels

• Arteries are the vessels that deliver blood from the heart to numerous organs of the body. Since the blood emerges from the heart under excessive pressure, the arteries have thick, elastic walls
• Veins acquire the blood from specific organs and convey it again to the heart. They do not require thick walls as the blood is not under pressure now. Instead, they have got valves that make sure that the blood flows only in a single direction
• Once it reaches an organ or tissue, the artery separates into smaller and smaller vessels to pass on the blood in contact with all the cells
• The smallest vessels have walls that are one-cell thick and are known as capillaries. The exchange of material among the blood and surrounding cells takes place through this thin wall
• The capillaries then come together to form veins that convey the blood far from the organ or tissue

Platelets

The blood has platelet cells that flow across the body and plug any leaks by assisting in blood clotting at the time of injury. 

• They assist in minimising the loss of blood from the system
• They prevent any loss of blood pressure which might reduce the working of the pumping system

Lymph

• Lymph is a biological fluid
• It is a colourless fluid
• Acts as a filter against microbes and other toxins
• Used in transportation of nutrients to the cells
• Helps in intercellular communication between the cells

Conclusion

Blood is a connective tissue that helps in the circulation of blood and transport essential substances to the cells and carries waste from there. Lymph is another fluid that also helps in the transportation of essential substances. Fluid matrix, plasma and formed elements constitute the components of blood. Formed elements constitute RBCs, WBCs and platelets. Humans have the following blood group, A, B, AB, and O based on the presence or absence of 2 surface antigens. Humans have a closed blood circulatory system. The human circulatory system has a muscular pumping organ, a network of blood vessels and a fluid, blood. Heart muscle is auto-excitable. SAN (Sino-atrial node) or pacemaker produces the maximum number of action potentials per minute (70-75/min). 

The action potential causes the atria and the ventricle to contract (systole) followed by relaxation (diastole). Atria on contraction forces the blood to ventricles the pulmonary artery and the aorta. Sequential events in the heart create a cardiac cycle and this cycle is repeated continuously and thus called the cardiac cycle. A healthy person shows a 72/min cardiac cycle. Electrical activity of the heart can be recorded with the help of an electrocardiograph and the obtained recording is called an electrocardiogram (ECG). The double circulation pathway ensures the oxygenated supply of blood to the human body. Human heart functions can be moderated by neural and hormonal mechanisms.