22 Circulatory Anatomy & Physiology Practice Questions & Answers
Every Circulatory Anatomy & Physiology practice question from the Phlebotomy Technician Practice Test, with the correct answer and a short explanation.
Start practice test →1. In a normal adult, approximately what proportion of whole blood is plasma versus formed elements (cells)?
- A.About 75% plasma and 25% formed elements
- B.About 55% plasma and 45% formed elements✓ Answer
- C.About 90% plasma and 10% formed elements
- D.About 45% plasma and 55% formed elements
Whole blood normally separates into roughly 55% plasma (the liquid portion) and about 45% formed elements, a fraction dominated by red blood cells and reflected in the hematocrit; this ratio is why a spun tube shows a large plasma layer above the packed cells.
Source: Tortora, Principles of Anatomy and Physiology, Blood chapter (composition of whole blood ~55% plasma / ~45% formed elements)Report a problem with this question
2. Plasma is the liquid portion of blood. Approximately what percentage of plasma is water?
- A.About 25% water
- B.About 10% water
- C.About 92% water✓ Answer
- D.About 50% water
Plasma is about 92% water by volume, with the remaining ~8% consisting of proteins (such as albumin, globulins, and fibrinogen), electrolytes, nutrients, gases, and wastes; the high water content is what makes plasma an effective transport and solvent medium.
Source: Tortora, Principles of Anatomy and Physiology (plasma is ~92% water)Report a problem with this question
3. What is the primary function of red blood cells (erythrocytes)?
- A.Transporting oxygen (and some carbon dioxide) via hemoglobin✓ Answer
- B.Defending the body against infection
- C.Producing antibodies against pathogens
- D.Forming clots to stop bleeding
Red blood cells are packed with hemoglobin, an iron-containing protein that binds oxygen in the lungs and releases it to tissues, and also helps carry some carbon dioxide back to the lungs; this gas-transport role is their defining function.
Source: NHA CPT Test Plan, Anatomy & Physiology (function of erythrocytes/hemoglobin)Report a problem with this question
4. What is the primary function of white blood cells (leukocytes)?
- A.Maintaining the blood's osmotic pressure
- B.Carrying oxygen to the tissues
- C.Sealing damaged blood vessels by clotting
- D.Defending the body against infection and foreign invaders✓ Answer
White blood cells are the cells of the immune system; through mechanisms such as phagocytosis and antibody production they identify and destroy pathogens and abnormal cells, which is why an elevated WBC count often signals infection.
Source: NHA CPT Test Plan, Anatomy & Physiology (function of leukocytes)Report a problem with this question
5. What is the primary function of platelets (thrombocytes)?
- A.Regulating body temperature
- B.Transporting oxygen and carbon dioxide
- C.Initiating hemostasis by forming a platelet plug and aiding clotting✓ Answer
- D.Producing antibodies
Platelets are cell fragments that adhere to injured vessel walls and clump together to form a temporary platelet plug, and they release factors that trigger the coagulation cascade; this is why a low platelet count leads to prolonged bleeding.
Source: NHA CPT Test Plan, Anatomy & Physiology (function of thrombocytes/platelets in hemostasis)Report a problem with this question
6. After an anticoagulated blood specimen is centrifuged, from top to bottom the layers are:
- A.Buffy coat, then plasma, then red blood cells
- B.Serum, then buffy coat, then platelets
- C.Red blood cells, then buffy coat, then plasma
- D.Plasma, then buffy coat, then red blood cells✓ Answer
Because centrifugation separates components by density, the lightest plasma rises to the top, the denser red blood cells pack at the bottom, and the intermediate-density white blood cells and platelets form the thin buffy coat between them.
Source: Tortora, Principles of Anatomy and Physiology (layers of centrifuged anticoagulated blood)Report a problem with this question
7. The thin middle layer of a centrifuged anticoagulated specimen, called the buffy coat, consists of:
- A.Plasma proteins
- B.White blood cells and platelets✓ Answer
- C.Red blood cells only
- D.Fibrinogen and clotting factors
The buffy coat is the pale layer between the plasma and packed red cells, and it contains the white blood cells and platelets; their intermediate density places them above the heavier red cells but below the liquid plasma.
Source: Tortora, Principles of Anatomy and Physiology (buffy coat = leukocytes and platelets)Report a problem with this question
8. Which antecubital vein is generally the preferred first choice for routine venipuncture?
- A.Cephalic vein
- B.Basilic vein
- C.Median cubital vein✓ Answer
- D.Brachial vein
The median cubital vein is preferred first because it is typically large, well-anchored, and close to the surface, and it lies away from major arteries and nerves, making the draw both easier and safer for the patient.
Source: NHA CPT Test Plan, Site Selection (median cubital preferred; least movement, away from artery/nerve)Report a problem with this question
9. In the common H-shaped antecubital vein pattern, which three veins are involved?
- A.Great saphenous, femoral, and popliteal veins
- B.Cephalic, median cubital, and basilic veins✓ Answer
- C.Jugular, subclavian, and axillary veins
- D.Brachial, radial, and ulnar veins
The H-pattern of the antecubital fossa is formed by the cephalic vein (lateral), the basilic vein (medial), and the median cubital vein connecting them; these are the primary superficial veins targeted in arm venipuncture.
Source: NHA CPT Test Plan, Anatomy of antecubital veins (H-pattern: cephalic, median cubital, basilic)Report a problem with this question
10. On the antecubital area, the cephalic vein is located on which side of the arm?
- A.The lateral (thumb) side✓ Answer
- B.The medial (little-finger) side
- C.Directly over the brachial artery
- D.The posterior (back) surface
In the anatomical position, the cephalic vein runs along the lateral (thumb-side) aspect of the forearm and antecubital area, whereas the basilic vein lies on the medial (little-finger) side; knowing this orientation helps locate veins consistently.
Source: Tortora / NHA CPT (cephalic = lateral, basilic = medial in antecubital fossa)Report a problem with this question
11. Why is the basilic vein generally chosen last among the antecubital veins?
- A.It is too small to accept a needle
- B.It carries oxygen-poor blood and cannot be sampled
- C.It always collapses when a tourniquet is applied
- D.It lies near the brachial artery and median nerve, raising the risk of injury✓ Answer
The basilic vein is the last choice because it sits close to the brachial artery and the median nerve; puncturing there increases the chance of accidentally hitting the artery or nerve, causing pain, hematoma, or nerve damage.
Source: NHA CPT Test Plan, Site Selection (basilic vein last due to proximity to brachial artery and median nerve)Report a problem with this question
12. Which structural feature is found in veins but not in arteries, and helps prevent the backflow of blood?
- A.An external elastic membrane
- B.A thick tunica media of smooth muscle
- C.One-way valves✓ Answer
- D.A pulsatile lumen
Veins contain one-way valves that keep blood moving toward the heart against gravity and prevent backflow, a feature arteries lack because arterial blood is propelled under high pressure directly from the heart.
Source: Tortora, Principles of Anatomy and Physiology (veins contain valves; arteries do not)Report a problem with this question
13. In the systemic circulation, in which general direction do veins carry blood?
- A.Toward the lungs to pick up oxygen
- B.Only within a single organ
- C.Toward the heart✓ Answer
- D.Away from the heart
By definition veins return blood toward the heart, while arteries carry blood away from the heart; this is why venipuncture collects venous blood flowing back through the superficial veins of the arm.
Source: Tortora, Principles of Anatomy and Physiology (veins carry blood toward the heart)Report a problem with this question
14. The walls of both veins and arteries are composed of three layers. From innermost to outermost, these tunics are:
- A.Tunica interna (intima), tunica media, tunica externa (adventitia)✓ Answer
- B.Tunica media, tunica interna, tunica externa
- C.Tunica externa, tunica media, tunica interna
- D.Endocardium, myocardium, epicardium
Blood vessel walls are built from the tunica interna (intima) lining the lumen, the muscular tunica media in the middle, and the connective tissue tunica externa (adventitia) on the outside; arteries have a thicker tunica media than veins to withstand higher pressure.
Source: Tortora, Principles of Anatomy and Physiology (three tunics of vessel walls)Report a problem with this question
15. Capillaries are uniquely suited for the exchange of gases and nutrients because their walls are:
- A.Only a single layer of endothelial cells thick✓ Answer
- B.Composed of three thick muscular tunics
- C.Made of dense connective tissue
- D.Reinforced with one-way valves
Capillary walls consist of just a single layer of endothelial cells (a thin tunica interna), and this minimal thickness allows oxygen, carbon dioxide, nutrients, and wastes to diffuse readily between blood and tissue cells.
Source: Tortora, Principles of Anatomy and Physiology (capillary wall = single endothelial cell layer)Report a problem with this question
16. Which pathway correctly describes the pulmonary circulation?
- A.Right side of the heart to the lungs and back to the left side of the heart✓ Answer
- B.Aorta directly to the capillaries of the arms
- C.Left side of the heart to the body and back to the right side
- D.Heart to the digestive organs and back to the heart
Pulmonary circulation carries oxygen-poor blood from the right side of the heart to the lungs, where it picks up oxygen and releases carbon dioxide, then returns the oxygenated blood to the left side of the heart for distribution to the body.
Source: Tortora, Principles of Anatomy and Physiology (pulmonary circulation: right heart → lungs → left heart)Report a problem with this question
17. The systemic circulation is best described as the circuit that carries blood:
- A.Only within the walls of the heart itself
- B.From the left side of the heart to the body's tissues and back to the right side✓ Answer
- C.Only between the heart and the brain
- D.From the right side of the heart to the lungs and back
Systemic circulation delivers oxygenated blood from the left ventricle through the aorta to all body tissues and returns oxygen-poor blood to the right atrium; it is the larger circuit that supplies the organs and limbs, including the arm veins used for venipuncture.
Source: Tortora, Principles of Anatomy and Physiology (systemic circulation: left heart → body → right heart)Report a problem with this question
18. What is the first vascular response of hemostasis immediately after a blood vessel is injured?
- A.Dissolving of the clot by fibrinolysis
- B.Formation of a mature fibrin clot
- C.Vasoconstriction (vascular spasm) of the injured vessel✓ Answer
- D.Release of oxygen from red blood cells
The first step of hemostasis is vascular spasm (vasoconstriction), in which the smooth muscle of the injured vessel contracts to reduce blood flow and limit blood loss, buying time for the platelet plug and coagulation to follow.
Source: Tortora, Principles of Anatomy and Physiology (hemostasis step 1: vascular spasm)Report a problem with this question
19. Place the three main stages of hemostasis in their correct order:
- A.Vascular spasm, platelet plug formation, coagulation (blood clotting)✓ Answer
- B.Fibrinolysis, vascular spasm, platelet plug formation
- C.Platelet plug formation, coagulation, vascular spasm
- D.Coagulation, platelet plug formation, vascular spasm
Hemostasis proceeds in order as vascular spasm, then platelet plug formation, then coagulation; each stage builds on the last, with vasoconstriction slowing flow, platelets forming a temporary seal, and the coagulation cascade producing a stable fibrin clot.
Source: Tortora, Principles of Anatomy and Physiology (three stages of hemostasis)Report a problem with this question
20. During coagulation, which insoluble protein forms the meshwork that traps blood cells to create a stable clot?
- A.Albumin
- B.Hemoglobin
- C.Fibrin✓ Answer
- D.Fibrinogen (in its soluble form)
In the final step of coagulation, the enzyme thrombin converts soluble fibrinogen into insoluble fibrin threads, which weave a mesh that traps red cells and platelets to form a stable clot; the soluble precursor fibrinogen itself cannot form the mesh until converted.
Source: Tortora, Principles of Anatomy and Physiology (thrombin converts fibrinogen to fibrin)Report a problem with this question
21. How does serum differ from plasma?
- A.Serum contains fibrinogen but plasma does not
- B.Serum contains red blood cells while plasma does not
- C.Serum is collected only in anticoagulant tubes
- D.Serum is the liquid remaining after clotting and lacks fibrinogen and clotting factors✓ Answer
Serum is the fluid that remains after blood is allowed to clot, so the fibrinogen and clotting factors have been consumed in forming the clot; plasma, obtained from anticoagulated blood, still contains fibrinogen because clotting was prevented.
Source: Tortora, Principles of Anatomy and Physiology (serum = plasma minus fibrinogen and clotting factors)Report a problem with this question
22. In standard anatomical position, the term 'distal' describes a location that is:
- A.Closer to the point of attachment or trunk
- B.Toward the midline of the body
- C.Farther from the point of attachment or trunk (e.g., the wrist relative to the elbow)✓ Answer
- D.Toward the front surface of the body
'Distal' means farther from the trunk or point of attachment, while 'proximal' means closer to it; for example the wrist is distal to the elbow, and using these terms precisely helps phlebotomists describe and locate venipuncture sites.
Source: Tortora, Principles of Anatomy and Physiology (directional terms: proximal vs distal)Report a problem with this question
Concept-focused practice questions based on CLSI GP41 (venous blood collection), the CLSI order of draw, and the OSHA Bloodborne Pathogens Standard (29 CFR 1910.1030). Not affiliated with the NHA, ASCP, or CLSI, and not medical advice. Facility protocols and current CLSI standards take precedence — always follow your employer's procedures. About the CPT exam →