Prep Guide: Circulatory System

Key Concepts (Recall & Understanding)

Components of Blood:
- Plasma: Liquid matrix.
- Red Blood Cells (RBCs/Erythrocytes): Transport oxygen via hemoglobin; lack a nucleus in mammals.
- White Blood Cells (WBCs/Leukocytes): Part of the immune system.
- Platelets (Thrombocytes): Responsible for blood clotting.
The Heart: A four-chambered pump (two atria, two ventricles).
- Right Side: Handles deoxygenated blood.
- Left Side: Handles oxygenated blood.
Double Circulation: Blood passes through the heart twice per circuit.
- Pulmonary Circulation: Heart → Lungs → Heart.
- Systemic Circulation: Heart → Body Tissues → Heart.
Blood Vessels:
- Arteries: Carry blood away from the heart; thick, muscular walls.
- Veins: Carry blood towards the heart; thinner walls, have valves.
- Capillaries: Microscopic vessels for exchange of substances with tissues.
Hepatic Portal System: A unique system of veins that carries blood from the digestive organs to the liver for processing before it enters the main circulation.
Blood Groups: Based on antigens on RBCs (ABO system and Rh factor).
Lymphatic System: A network including lymph, lymph vessels, and organs like the spleen and tonsils, which returns tissue fluid to the blood and is crucial for immunity.

Application Corner

Why do athletes often train at high altitudes to improve their performance?
- Answer: At high altitudes, the air has a lower oxygen concentration. To compensate, the body produces more red blood cells to increase its oxygen-carrying capacity. When the athlete returns to lower altitudes, this higher RBC count allows their blood to carry more oxygen, enhancing their endurance and performance.
A person with blood type A can safely receive a blood transfusion from a person with blood type O, but not from a person with blood type B. Explain why.
- Answer: A person with type A blood has anti-B antibodies in their plasma. If they receive type B blood, these antibodies will attack the B antigens on the incoming RBCs, causing a dangerous transfusion reaction. Type O blood has no antigens, so it does not trigger an immune response in a type A recipient.

Analytical Thinking

Odd One Out: Aorta, Vena Cava, Pulmonary Artery, Hepatic Portal Vein.
- Odd One: Hepatic Portal Vein.
- Category: The rest are major blood vessels that connect directly to the chambers of the heart.
Scenario: The valves in a person's leg veins are faulty and do not close properly. What would be a likely consequence of this condition?
- Answer: Veins have low blood pressure, and valves are crucial for preventing the backflow of blood, especially in the legs where blood has to move against gravity. If the valves are faulty, blood would pool in the leg veins. This would increase pressure in those veins, causing them to stretch and bulge, a condition known as varicose veins. It could also lead to swelling in the ankles and feet.

Atherosclerosis is a condition where plaque (made of fat, cholesterol, and other substances) builds up inside the arteries, causing them to narrow and harden. The coronary arteries, which supply oxygen-rich blood to the heart muscle itself, are often affected. If a piece of this plaque ruptures, a blood clot can form. If this clot completely blocks a coronary artery, the part of the heart muscle supplied by that artery is starved of oxygen and begins to die. This event is a myocardial infarction, or heart attack. This case study demonstrates the critical importance of the circulatory system in supplying oxygen to all tissues, and how a blockage in even a small artery can have life-threatening consequences.

Assertion-Reason Practice

Assertion (A): The wall of the left ventricle is thicker than the wall of the right ventricle. Reason (R): The left ventricle has to pump blood to the entire body, while the right ventricle only pumps blood to the lungs.

(a) Both (A) and (R) are true and (R) is the correct explanation of (A). (b) Both (A) and (R) are true but (R) is not the correct explanation of (A). (c) (A) is true but (R) is false. (d) (A) is false but (R) is true.

Answer: (a) Both (A) and (R) are true and (R) is the correct explanation of (A). The left ventricle needs a more muscular wall to generate the high pressure required to push blood through the extensive systemic circulation, whereas the pulmonary circulation to the lungs is much shorter and requires less pressure.

HOTS (Higher-Order Thinking Skills) Question

All arteries carry oxygenated blood and all veins carry deoxygenated blood." Is this statement strictly correct? Justify your answer with specific examples from the human circulatory system.

Answer: The statement is not strictly correct. The defining characteristic of an artery is that it carries blood away from the heart, and a vein carries blood towards the heart, regardless of oxygen content.
- Exception for Arteries: The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs.
- Exception for Veins: The pulmonary veins carry oxygenated blood from the lungs to the left atrium. These two vessels are the major exceptions to the general rule.

Specimen Prep - Circulatory System