👤 By the CinnaEntry Content Team🕐 Updated 2026-09-07🏷️ HESI Anatomy & Physiology🔖 Free to read, print, and share
Also known as: plasma · red blood cells · white blood cells · platelets · hematocrit
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Use this one-page guide to lock in Blood Components for the ATI TEAS 7 and HESI A2. Keep it handy during review and on exam day.
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📒 The 1-minute cheat sheet
📌 By Volume
Plasma ≈ 55% — mostly water, plus proteins, nutrients, wastes
Red cells ≈ 45% — this figure IS the hematocrit
White cells + platelets < 1% — the thin buffy coat
✅ What Each One Does
Erythrocytes (red) — carry O₂ on hemoglobin
Leukocytes (white) — fight infection
Thrombocytes (platelets) — clotting
Plasma — transport medium and clotting proteins
📌 Worth Memorising
Hemoglobin is the iron-containing protein that binds O₂
Red cells have NO nucleus at maturity — more room for hemoglobin
Blood is a connective TISSUE, not just a fluid
📚 Blood Components — full study notes
The cheat sheet above is your quick recall card. These notes go deeper — what it is, what to do first, what must be reported, and what to teach.
Blood is a tissue, not just a fluid. Spun in a centrifuge it separates into three visible layers, and each layer has a job the exam asks about directly.
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Key points
Understand these first
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.
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Study first
Where to start
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.
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Red flags — report now
Escalate immediately
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.
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Commonly tested
What comes up most
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.
❓ Blood Components: TEAS & HESI 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 are the warning signs of Blood Components a nurse must report?
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 TEAS or HESI?
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.
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Quick Tip
Plasma is about 55% of blood volume — mostly water, plus proteins, nutrients, hormones and wastes.