Plasma is about 55% of blood volume — mostly water, plus proteins, nutrients, hormones and wastes.
Before you read
Test yourself first: 5 questions
Question 1 of 5
Which blood vessel carries oxygenated blood from the lungs back to the heart?
Answer: B. The pulmonary veins carry oxygenated blood from the lungs to the left atrium. The pulmonary artery is the exception that carries deoxygenated blood (heart → lungs).
Question 2 of 5
Blood in the pulmonary artery is:
Answer: A. The pulmonary artery is the exception to 'arteries carry oxygenated blood': it carries oxygen-poor blood from the right ventricle to the lungs. The pulmonary VEINS are the matching exception on the return side.
Question 3 of 5
Which chamber of the heart pumps oxygenated blood out to the body?
Answer: D. The left ventricle is the most muscular chamber; it pumps oxygenated blood into the aorta and out to the body. The right ventricle pumps deoxygenated blood to the lungs.
Question 4 of 5
Which type of blood vessel carries blood away from the heart?
Answer: B. Arteries carry blood away from the heart; veins return it. (Remember: Artery = Away.)
Question 5 of 5
Which type of blood vessel returns blood to the heart?
Answer: B. Veins carry blood back toward the heart.
Keep the streak going with more questions like these, each with a full rationale.
Key points
- Plasma is about 55% of blood volume — mostly water, plus proteins, nutrients, hormones and wastes.
- Red blood cells (erythrocytes) are about 45% and carry oxygen on hemoglobin; that 45% figure is the hematocrit.
- White blood cells (leukocytes) fight infection and are less than 1% of volume.
- Platelets (thrombocytes) are cell fragments that begin clotting.
- Red cells are made in RED bone marrow; yellow marrow stores fat.
Study first
- A patient's hematocrit is reported as 45%. That means red cells occupy 45% of the blood volume — a normal adult value.
- An infection raises the white cell count; it does not raise the hematocrit, because those are different components.
Commonly tested
- Picture the spun tube: straw-colored plasma on top, a thin pale band, dark red cells at the bottom. The picture gives you the percentages.
- Match each component to ONE verb: plasma carries, red cells oxygenate, white cells defend, platelets clot.
Watch out for
- Confusing plasma (the liquid, still containing clotting factors) with serum (plasma after clotting).
- Assigning oxygen transport to white cells — that is the red cells' job.
- Calling platelets whole cells; they are fragments of larger cells.
Blood Components: FAQs
What should I focus on first when studying Blood Components?
A patient's hematocrit is reported as 45%. That means red cells occupy 45% of the blood volume — a normal adult value. An infection raises the white cell count; it does not raise the hematocrit, because those are different components.
What is most often missed on Blood Components?
Confusing plasma (the liquid, still containing clotting factors) with serum (plasma after clotting). Assigning oxygen transport to white cells — that is the red cells' job. Calling platelets whole cells; they are fragments of larger cells.
What do I need to know about Blood Components for the HESI A2?
Plasma is about 55% of blood volume — mostly water, plus proteins, nutrients, hormones and wastes. Red blood cells (erythrocytes) are about 45% and carry oxygen on hemoglobin; that 45% figure is the hematocrit. White blood cells (leukocytes) fight infection and are less than 1% of volume. Platelets (thrombocytes) are cell fragments that begin clotting.
What are the most commonly tested points on Blood Components?
Picture the spun tube: straw-colored plasma on top, a thin pale band, dark red cells at the bottom. The picture gives you the percentages. Match each component to ONE verb: plasma carries, red cells oxygenate, white cells defend, platelets clot.
