Anatomy & Circulatory System for Phlebotomy

Four Chambers of the Heart

Blood Components

Hand Veins (Dorsal Metacarpal Veins)

Location: On the back (dorsal surface) of the hand.
When to use: Antecubital veins inaccessible (burns, IV lines, mastectomy, edema), elderly with fragile arm veins.
Considerations: Use smaller needle (23 gauge), use butterfly/winged infusion set for better control, veins are more fragile and roll easily, more painful for patient, increased risk of hemolysis with small veins.

Wrist Veins

Location: On the ventral (palm) side of the wrist, about 1 inch above the wrist crease.
When to use: When hand and antecubital veins are unavailable.
Considerations: Very painful due to high concentration of nerve endings, high risk of nerve damage, increased risk of tendon injury, use as last resort only.

Ankle and Foot Veins

Location: Dorsal surface of the foot, ankle area.
When to use: Only with physician's permission. Never use without authorization.
Considerations: High risk of blood clots (DVT), poor circulation in diabetics and elderly, increased infection risk, extremely painful, contraindicated in diabetics and patients with peripheral vascular disease.

High-Yield Exam Topics

• Three main antecubital veins: median cubital (first choice), cephalic (second choice), basilic (last choice — close to artery/nerve)
• Arterial vs. venous blood: bright red pulsating vs. dark red steady, thick walls vs. thin walls, deep vs. superficial
• Signs of arterial puncture: bright red spurting blood, rapid tube filling, sharp pain, immediate hematoma
• Four heart chambers: right atrium → right ventricle → lungs → left atrium → left ventricle → body
• Blood composition: plasma (55%), RBCs (45%), WBCs and platelets (<1%)
• Hematopoiesis occurs in red bone marrow (flat bones and proximal ends of long bones in adults)
• Five types of WBCs: neutrophils (most common, 50-70%), lymphocytes, monocytes, eosinophils, basophils
• Normal values: RBC 4.5-5.5 million/µL, WBC 4,500-11,000/µL, platelets 150,000-400,000/µL

What are the three main superficial veins used for venipuncture?

The three primary superficial veins in the antecubital fossa (elbow crease) are: (1) Median cubital vein — first choice, runs diagonally between cephalic and basilic veins, large and well-anchored; (2) Cephalic vein — second choice, located on the thumb side (lateral), can roll easily; (3) Basilic vein — third choice, located on the pinky side (medial), close to brachial artery and median nerve, higher risk of complications. Always assess all three and choose the best vein based on size, depth, and stability.

Why is the basilic vein a last-choice option for venipuncture?

The basilic vein is located on the medial (pinky) side of the arm and runs very close to the brachial artery and median nerve. Accidental arterial puncture can cause hematoma, severe pain, and nerve damage. The median nerve injury can cause permanent numbness, tingling, or loss of function in the hand. The basilic vein also tends to roll more than the median cubital vein. Use the basilic vein only when the median cubital and cephalic veins are not accessible, and use extra caution to avoid deep probing near the artery and nerve.

How can you tell if you accidentally punctured an artery?

Signs of accidental arterial puncture: (1) Bright red, pulsating blood that spurts into the tube; (2) Tubes fill very rapidly under high pressure; (3) Patient reports sharp, shooting pain radiating down the arm; (4) Hematoma forms immediately around puncture site. If arterial puncture occurs: remove needle immediately, apply firm pressure for at least 5 minutes (longer for patients on anticoagulants), monitor for continued bleeding or neurological symptoms, and document the incident. Never attempt venipuncture at the same site again.

What is the difference between an artery and a vein?

Arteries carry oxygenated blood away from the heart to tissues (except pulmonary artery). They have thick, muscular, elastic walls to withstand high pressure, and blood is bright red and pulsates with heartbeat. Veins carry deoxygenated blood back to the heart (except pulmonary vein). They have thinner walls, contain valves to prevent backflow, and blood is darker red and flows smoothly without pulsing. For phlebotomy, veins are superficial and easily accessed, while arteries are deeper and must be avoided during routine venipuncture.

What are the four chambers of the heart?

The heart has four chambers: Right atrium (receives deoxygenated blood from body via superior and inferior vena cava), Right ventricle (pumps deoxygenated blood to lungs via pulmonary artery), Left atrium (receives oxygenated blood from lungs via pulmonary veins), and Left ventricle (pumps oxygenated blood to body via aorta — the body's largest artery). Blood flows in one direction through the heart: right side handles deoxygenated blood going to lungs, left side handles oxygenated blood going to body. Valves between chambers prevent backflow.

What is hematopoiesis and where does it occur?

Hematopoiesis is the process of blood cell formation. In adults, it occurs primarily in red bone marrow found in flat bones (sternum, ribs, pelvis, skull) and the ends of long bones (femur, humerus). Stem cells in bone marrow differentiate into red blood cells (carry oxygen), white blood cells (fight infection), and platelets (blood clotting). Understanding hematopoiesis is important because certain diseases (leukemia, anemia, thrombocytopenia) affect blood cell production, and many laboratory tests evaluate blood cell counts and function.