Chapter 6: The Circulatory System Knowledge Drill 6-3: True/False Activity The following statements are all false: 1. The three layers of the heart are the epicardium, the myocardium, and the pericardium. 2. Cardiac contraction is initiated by an electrical impulse generated from the bundle of His, also called the pacemaker. 3. Veins carry blood away from the heart. 4. A heart attack or death of the heart muscle due to occlusion is called a myocardial infarction. 5. When renal blood is collected by a syringe, the pressure normally causes the blood to pump into the syringe artery. 6. Venules are microscopic, one-cell-thick vessels that connect the arteries and arterioles. 7. The venous distribution patterns are so named because the major veins on the arm resemble the shape of an “H” or a “4”. 8. The AC fossa is the shallow depression in the arm that is inferior and above the bend of the elbow. 9. The “H-shaped” venous distribution pattern displayed by approximately 50% of the population includes the median cephalic vein, cephalic vein, and basilic vein. 10. The main function of RBCs is to transport oxygen. 11. Blood that is removed from the body will clot within 10 to 15 minutes. 12. The blood cells are enmeshed in a fibrin network, and the remaining fluid portion is called plasma. 13. Tests for lymphatic disorders include D-dimer, prothrombin time, and partial thromboplastin time. 14. The femoral artery is a major artery in the antecubital area. 15. Blood type O is the most common blood type. 16. Thrombin is an elastic threadlike protein involved in clot formation.
The Correct Answer and Explanation is:
Corrected Statements:
- False → The three layers of the heart are the epicardium, myocardium, and endocardium.
- False → Cardiac contraction is initiated by an electrical impulse generated from the sinoatrial (SA) node, also called the pacemaker.
- False → Arteries carry blood away from the heart, while veins carry blood toward the heart.
- True – A heart attack or death of the heart muscle due to occlusion is called a myocardial infarction.
- False → When venous blood is collected by a syringe, the pressure causes the blood to flow into the syringe; not arterial pressure.
- False → Capillaries, not venules, are the microscopic, one-cell-thick vessels that connect arterioles and venules.
- True – The venous distribution patterns are named “H-shaped” or “M-shaped” based on vein patterns in the arm.
- False → The antecubital (AC) fossa is the shallow depression in front of the elbow, not above it.
- False → The “H-shaped” pattern includes the median cubital, cephalic, and basilic veins.
- True – The main function of red blood cells (RBCs) is to transport oxygen.
- True – Blood removed from the body will typically clot within 10 to 15 minutes unless anticoagulants are used.
- False → After clotting, the fluid portion is called serum; plasma is the liquid before clotting.
- False → Tests like D-dimer, PT, and PTT evaluate coagulation, not lymphatic disorders.
- False → The femoral artery is located in the thigh, not the antecubital area.
- True – Blood type O is the most common.
- False → Fibrin, not thrombin, is the elastic threadlike protein that forms a clot matrix.
Explanation
The circulatory system is vital for delivering oxygen and nutrients while removing waste products. It includes the heart, blood vessels, and blood. The heart has three distinct layers: the outer epicardium, the thick muscular myocardium, and the inner endocardium. The SA node, located in the right atrium, initiates electrical impulses that trigger cardiac contraction—this is why it’s termed the pacemaker.
Arteries transport blood away from the heart, and veins carry it back. One common mistake is confusing capillaries with venules; capillaries are the microscopic vessels where gas exchange occurs, connecting arterioles and venules. In the arm, superficial veins such as the median cubital, cephalic, and basilic form recognizable patterns used in phlebotomy.
Red blood cells carry oxygen using hemoglobin, while white cells defend against pathogens and platelets help with clotting. When blood clots, fibrin, a protein, forms a mesh that traps blood cells; the fluid left after clotting is serum, whereas plasma is the fluid portion before clotting.
Some tests, like PT, PTT, and D-dimer, assess blood clotting—not lymphatic issues. The femoral artery is in the leg, not the elbow area. Understanding these anatomical and physiological distinctions is crucial for accurate diagnostics and treatment in healthcare.
