General Science: Human Blood

Blood is a fluid connective tissue that circulates in the body, delivering necessary substances like nutrients and oxygen to the cells. The average pH of human blood is slightly basic at 7.4.

Composition of Blood

• Plasma (55%): A straw-colored liquid consisting mostly of water, proteins, and electrolytes.
• RBCs (Erythrocytes): Contain Hemoglobin for oxygen transport. They have a lifespan of approx. 120 days.
• WBCs (Leukocytes): Part of the immune system; they help the body fight infections and foreign invaders.
• Platelets (Thrombocytes): Tiny blood cells that help the body form clots to stop bleeding.

Blood Groups and Transfusion

• ABO System: Discovered by Karl Landsteiner.
• Universal Donor: Blood group O negative (can be given to anyone).
• Universal Recipient: Blood group AB positive (can receive from anyone).
• Rh Factor: An antigen found on the surface of RBCs; its presence makes blood “positive.”

Question for you: Which organ in the human body is known as the “Graveyard of RBCs”?

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