Blood, a specialized fluid circulating throughout the body, constitutes approximately 7% to 8% of an individual’s total body weight. It transports various substances, supporting numerous bodily processes and ensuring the proper functioning of organs and tissues. Understanding its primary components provides insight into how blood performs its many functions.
Blood Plasma
Blood plasma serves as the liquid matrix of blood, appearing as a light yellowish or straw-colored fluid. It makes up about 55% of the total blood volume and is predominantly water, accounting for 90% to 92% of its composition.
The remaining 8% to 10% consists of dissolved solids, including proteins like albumin, fibrinogen, and antibodies, along with salts, sugars, fats, and hormones. Plasma transports these substances, blood cells, and waste products throughout the body. It also contributes to maintaining fluid balance and blood pressure.
Plasma helps regulate body temperature by absorbing and releasing heat. It collects cellular waste products and carries them to organs like the kidneys and liver for excretion.
Red Blood Cells
Red blood cells, or erythrocytes, are the most abundant type of blood cell, making up 40% to 45% of blood volume. Their characteristic red color comes from hemoglobin, an iron-containing protein crucial for binding and transporting gases.
The primary function of red blood cells is to carry oxygen from the lungs to tissues and transport carbon dioxide from tissues back to the lungs for exhalation. Mature red blood cells have a biconcave disc shape and lack a nucleus, allowing them to be flexible and efficiently maneuver through narrow blood vessels. This shape also maximizes their surface area for effective gas exchange.
These cells develop in the bone marrow. Once released into the bloodstream, red blood cells have an average lifespan of about 120 days. Their production is regulated by erythropoietin, a hormone.
White Blood Cells and Platelets
White blood cells, or leukocytes, are an integral part of the immune system, circulating through the bloodstream and tissues. While less numerous than red blood cells, accounting for about 1% of the blood, they defend the body against infections, foreign invaders, and abnormal cells. Different types of white blood cells exist, each with specialized roles in immune responses.
Platelets, also called thrombocytes, are small cell fragments that lack a nucleus. They are fundamental to blood clotting, known as hemostasis, which prevents excessive bleeding. When a blood vessel is injured, platelets quickly gather at the site, sticking together to form a plug that helps seal the damaged vessel.
Both white blood cells and platelets are produced in the bone marrow. Platelets have a lifespan of about 8 to 12 days.