Blood

• Blood consists of four main components: red blood cells, white blood cells, platelets, and plasma.
• Red blood cells, which make up almost half of our blood by volume, carry oxygen from the lungs to our body's tissues.
• Red blood cells contain a red pigment called hemoglobin which combined with oxygen to become oxyhemoglobin.
• Once red blood cells have traveled around the body to the tissues, the oxyhemoglobin can split back into hemoglobin and oxygen again, allowing the oxygen to diffuse into our tissues.
• Red blood cells have two adaptations that contribute to their role in transporting oxygen: they don't have a nucleus, which means there's more space for hemoglobin and oxygen, and they're shaped like a biconcave disc, which gives them a large surface area for absorbing oxygen.
• White blood cells, which make up less than 1% of our blood by volume, are an essential part of our immune system which defends us against infection.
• White blood cells can do a range of useful things for us, including phagocytosis, juicing antibodies, and producing anti toxins.
• Unlike red blood cells, white blood cells do have a nucleus.
• Platelets, which aren't actual cells but small fragments of cells, float about in our blood waiting until we get a cut at which point they rush to the wound and act like a glue patching up the hole.
• The main reason we need platelets is to stop blood from pouring out of us whenever we get a cut.
• Another important reason for having platelets is to prevent microorganisms from getting in as they could cause an infection.
• Plasma, which makes up just over half of the blood's volume, is a pale stool-colored liquid that carries everything including the red blood cells, white blood cells, and platelets.
• Plasma carries nutrients like glucose and amino acids, waste products like carbon dioxide and urea, as well as hormones, proteins, and the antibodies and toxins produced by the white blood cells.
• Most adults have five liters of blood flowing through their circulatory system at any one time.
• If this drops too much due to a knife wound or surgical complications, there might not be enough blood left over to deliver the required oxygen to the tissues.
• Doctors can give the patient new blood in the form of a blood substitute, which consists of salt water, to replace the lost volume in the circulatory system.
• A better option is a blood transfusion in which a person is given a real blood that's been donated by blood donors, which comes with its own red blood cells.
• Red blood cells are essential for surviving blood loss.