Introduction
Circulation is the process of blood moving through the body to deliver essential substances and remove waste. Human circulation involves the heart, blood vessels, and blood.
The heart pumps blood, acting like a powerful engine. Blood vessels, like highways, carry the blood. Arteries carry oxygen-rich blood away from the heart, like roads leading out. Veins bring oxygen-poor blood back, like roads returning home.
Blood carries oxygen and nutrients to body cells, like a delivery service. It also picks up waste like a garbage collector, taking it to the lungs and kidneys for cleaning. This continuous journey keeps us healthy and alive.
Types Of Circulation
- Open Circulation
- Close Circulation
Open Circulation: Open circulation is a type of circulatory system in which the blood is not enclosed in blood vessels but instead flows freely through the body cavity.
In an open circulatory system, the heart pumps blood into a large cavity called the hemocoel. The blood then flows through the hemocoel and bathes the organs and tissues. The oxygen and nutrients in the blood are exchanged with the cells of the organs and tissues, and the waste products of metabolism are removed. The blood then flows back to the heart through a series of openings called ostia.
Open circulation is less efficient than closed circulation, but it is also simpler and less costly to maintain. As a result, it is well-suited for small animals with simple body plans.
Examples – This type of circulation is found in arthropods, such as insects and crabs, and in most mollusks.
Closed Circulation: Closed circulation is a type of circulatory system in which the blood is enclosed in a network of blood vessels.
In a closed circulatory system, the heart pumps blood through a series of arteries, capillaries, and veins. The arteries carry blood away from the heart, and the veins carry blood back to the heart. The capillaries are the smallest blood vessels, and they are where the exchange of oxygen and nutrients with the cells of the body takes place.
Closed circulation is more efficient than open circulation because it allows for a more rapid and complete exchange of oxygen and nutrients with the cells of the body. As a result, closed circulation is better suited for large animals with complex body plans.
Example – This type of circulation is found in vertebrates, such as fish, amphibians, reptiles, birds, and mammals.
Composition Of Blood
The blood consists of :
- Plasma – The fluid part, constitutes 55 per cent of blood.
- Cellular elements – red and white cells, and platelets, 40-45 per cent of blood.
Plasma: The plasma is a light-yellow-coloured, alkaline liquid. It mainly consists of :
- Water – 90 – 92%
- Proteins – 7-8%
- Inorganic salts – 1%
- Other substances – traces
The inorganic salts include mainly sodium chloride and sodium bicarbonate. Among other substances contained in the plasma are glucose, amino acids, fibrinogen, hormones, urea, etc. The plasma from which the protein fibrinogen has been removed is called serum.
Some Functions of Plasma:
- Transports nutrients, hormones, and other important substances throughout the body.
- Helps to regulate body temperature.
Red Blood Cell (RBC): Red blood cells (RBCs), or erythrocytes, are small, biconcave discs that transport oxygen throughout the body. Their size, around 7 microns in diameter, aids efficient oxygen absorption due to a large surface area. This design enables them to navigate narrow capillaries in a single file, ensuring effective circulation. In adults, males have about 5 million RBCs per cubic mm of blood, slightly less in females. The vital component, haemoglobin (Hb), resides within RBCs. Haemoglobin, composed of iron-rich haemin and globin protein, binds oxygen for delivery to tissues, crucial for sustaining life.
Some Functions of RBC:
- RBCs transport oxygen from the lungs to the tissues.
- RBCs transport carbon dioxide from the tissues back to the lungs.
Life and Death of RBC
- In adults, the RBCs are produced in the marrow of long bones, especially in the ribs, breast bone and ilium of the hip girdle.
- In an embryo, they are produced in the liver and spleen.
- In children, the RBCs are produced in the bone marrow of all bones until 5 years of age.
- The mature red blood cells have no nuclei, but when they are being produced, they have one. As they mature, the nuclei are lost, i.e., they become enucleated.
- The average life of an RBC is about 120 days.
White Blood Cell (WBC): White blood cells, or leukocytes (leuko : white), differ from red blood cells in having a nucleus and do not contain haemoglobin. Their number is much less, usually about 4000-8000 per mm3 of blood. Most WBCs are amoeboid and can produce pseudopodia with which they can squeeze through the walls of the capillaries into the tissues (diapedesis dia: across, pedesis: oozing out).
Some Functions of WBC
- WBCs defend against infections and invaders.
- They detect, destroy, and aid in healing.
Structure of the Human Heart
- Location: The heart is right in the centre between the two lungs and above the diaphragm. The narrow end of the roughly triangular heart is pointed to the left side and during working, the contraction of the heart is most powerful at this end giving a feeling that the heart is on the left side.
- Covering: The heart in adult humans is about the size of our closed fist – 12 cm in length and 9 cm in width. It is protected by a double-walled membranous covering called the pericardium
- Structure of the heart: The heart consists of four chambers – two upper atria (singular – atrium) and two lower ventricles. The atria (also called auricles) have thinner walls because their major function is to receive blood from the body and pump it into the very next ventricles. The ventricles have thick muscular walls because they have to pump blood over long distances.
The right atrium receives blood from the body. This blood is low in oxygen. The right ventricle pumps this blood to the lungs. The lungs oxygenate the blood and then send it back to the left atrium. The left ventricle pumps this oxygenated blood to the rest of the body.
The arteries carry blood away from the heart and the veins carry blood back to the heart. The largest artery in the body is the aorta. The aorta carries oxygenated blood from the left ventricle to the rest of the body.
Double Circulation
Systemic Circulation: Systemic circulation is the part of the circulatory system that pumps oxygenated blood from the heart to the rest of the body.
The oxygenated blood leaves the left ventricle of the heart and travels through the aorta, the largest artery in the body. The aorta branches into smaller arteries, which then branch into even smaller arteries called arterioles. The arterioles lead to capillaries, which are the smallest blood vessels in the body. The capillaries are where the exchange of oxygen and nutrients with the cells of the body takes place. The deoxygenated blood then travels from the capillaries through venules and veins back to the heart.
Systemic circulation is essential for life because it delivers oxygen and nutrients to the cells of the body. Without systemic circulation, the cells would not be able to survive.
Pulmonary Circulation: Pulmonary circulation is part of the circulatory system that pumps deoxygenated blood from the heart to the lungs and then returns oxygenated blood back to the heart.
The deoxygenated blood leaves the right ventricle of the heart and travels through the pulmonary artery to the lungs. The pulmonary artery branches into smaller arteries, which then branch into even smaller arteries called arterioles. The arterioles lead to capillaries, which are the smallest blood vessels in the body. The capillaries are where the exchange of oxygen and carbon dioxide with the air in the lungs takes place. The oxygenated blood then travels from the capillaries through venules and veins back to the heart.
Pulmonary circulation is essential for life because it allows the blood to be oxygenated. Without pulmonary circulation, the blood would not be able to carry oxygen to the cells of the body.
Acknowledgement
I would like to express my special thanks of gratitude to my English teacher _____ (Name of the teacher) as well as our principal _____ (Name of the principal) who gave me the golden opportunity to do this wonderful project on the topic _____ (Write the topic name). Secondly, I would also like to thank my parents and friends who helped me a lot in finalizing this project within the limited time frame.
Lastly, I like to thank all my supporters who have motivated me to fulfil their project before the timeline.
Bibliography
To successfully complete my project file. I have taken help from the following website
- Flash Education – A helpful website with educational content. (Website: FlashEducation.online)
- Wikipedia – An online encyclopedia where I found useful facts. (Website: Wikipedia)
- Topper.com – Another website that provided valuable information. (Website: topper.com)
- Freepik.com – Another website that provided valuable infographics (Website: Freepik.com)
