Cardiovascular System

Question 1

Heart Circulation

Answer 1

• Pulmonary Circulation: The right side of the heart accepts deoxygenated blood returning from the body and moves it to the lungs through the pulmonary arteries. The right side of the heart is less muscular.
• Systemic Circulation: The left side of the heart receives oxygenated blood from the lungs through the pulmonary veins and forces it out to the body through the aorta. The left side of the heart is more muscular.
• The atria are separated from the ventricles by atrioventricular valves; the Tricuspid Valve separates the right atrium from the right ventricle, while the Bicuspid (Mitral) Valve separates the left atrium from the left ventricle (the right lung is larger, the left lung has heart indentation).
• The ventricles are separated from the vasculature by semilunar valves; the Pulmonary Valve separates the right ventricle from the pulmonary circulation, while the Aortic Valve separates the left ventricle from the systemic circulation.

Question 2

Electrical Conduction

Answer 2

• Sinoatrial (SA) Node initiates impulses without any neurological input.
• Depolarization wave spreads from SA node to Atrioventricular (AV) Node at the junction of the atria and ventricles.
• Signal then travels down the Bundle of His (AV Bundle) and its branches embedded in the Intraventricular Septum.
• Signal then reaches the Purkinje Fibers which distribute the electrical signal through the ventricular muscle. The intercalated discs in cardiac muscle allow for coordinated ventricular contraction.
• Circulatory system is under autonomic control; sympathetic signals speed up the heart rate and increases the contractility of cardiac muscle, while parasympathetic signals (provided by Vagus Nerve) slow down the heart rate.
• During Systole (ventricular contraction), AV valves are closed and blood is pumped out of ventricles. During Diastole (ventricular relaxation), semilunar valves are closed and blood from atria fills the ventricles.

Question 3

Vasculature

Answer 3

• All blood vessels are lined with Endothelial Cells, which release chemicals to stimulate vasodilation and vasoconstriction, allow passage of leukocytes from blood into tissues during inflammatory responses, and release chemicals when damaged that are involved in the formation of blood clots to repair the vessel and stop bleeding.

• Arteries: Pressure reservoirs; have more smooth muscle than veins and are highly elastic as a result. Arterioles are high resistance vessels and experience the largest drop in blood pressure so as not to damage capillaries.
• Veins: Blood reservoirs; thin-walled and inelastic due to smaller amount of smooth muscle in the vein walls but can stretch to accommodate larger quantities of blood.
• At the arterial end of a capillary bed, hydrostatic pressure is much larger than oncotic pressure, resulting in the net efflux of water from circulation. At the venule end of a capillary bed, oncotic pressure is much larger than hydrostatic pressure, resulting in the net influx of water back into circulation.

Question 4

Hematopoiesis

Answer 4

• Hematopoietic stem cells produce all of the components of blood.
• Erythropoietin is secreted by the kidneys to stimulate erythrocyte development.
• Thrombopoetin is secreted by the liver and kidneys to stimulate platelet development.

Question 5

Blood Antigens

Answer 5

• A and B antigens are codominant. People with O blood do not express either antigen and have a homozygous recessive genotype.
• People with Type O blood are universal donors but can receive only Type O blood.
• People with Type AB blood are universal recipients but can donate only to others with Type AB blood.
• Antibodies to the lacking blood antigens exist spontaneously in the blood (person lacking the A allele has anti-A antibodies), however antibodies to Rh factor are not produced prior to exposure to Rh-negative blood.
• Erythroblastosis Fetalis: Occurs when an Rh-negative mother is sensitized to Rh factor during the birth of an Rh-positive child, complicating subsequent pregnancies with Rh-positive fetuses.

Question 6

Gas Transport and Cooperative Binding

Answer 6

• Oxygen and Carbon Dioxide are both nonpolar and thus has low solubility in the aqueous plasma. Oxygen is primarily bound to hemoglobin in the blood (with a very small amount dissolved in plasma). Carbon Dioxide exists primarily as bicarbonate ions in the blood (with a small amount bound to hemoglobin with low affinity and a very small amount dissolved in plasma).
• Carbon Dioxide (CO₂) entering blood cells is reversibly combined with Water (H₂O) by Carbonic Anhydrase to form Carbonic Acid (H₂CO₃), which is a weak acid that dissociates into a proton (H+) and a Bicarbonate anion (HCO₃-).
• Cooperative Binding: Form of allosteric regulation in which the binding of an oxygen molecule to the first heme group induces a conformational change (from taut to relaxed) that continually increases hemoglobin’s affinity for oxygen for every subsequent molecule of oxygen that binds to the remaining three unoccupied heme groups. As the first oxygen molecule leaves a fully loaded hemoglobin molecule, it induces a conformational change that makes it progressively easier for more oxygen to be removed.
• Cooperative binding results in the classic sigmoid (S-shaped) Oxyhemoglobin Dissociation Curve. Oxygen saturation of Hb is 100% in the lungs but decreases in tissues during rest, and decreases even more in tissues during exercise so that more oxygen can be unloaded from Hb and provided to the tissues. Unloading of oxygen is further facilitated by shifts in the hemoglobin curve that occur during exercise.

Question 7

Shifts in Oxyhemoglobin Dissociation Curve

Answer 7

• Exercise is the RIGHT thing to do; increased activity causes a right shift in the Oxyhemoglobin Dissociation Curve due to increased PₐCO₂, increased [H+] (decreased pH), increased temperature, or increased 2,3-bisphosphoglycerate (2,3-BPG) levels.
• Left shifts are caused by decreased PₐCO₂, decreased [H+] (increased pH), decreased temperature, or decreased 2,3-BPG levels. Fetal Hemoglobin (HbF) has a left-shifted curve compared to Adult Hemoglobin (HbA) because of its higher oxygen affinity.
• Bohr Effect: Hemoglobin’s affinity for oxygen decreases under acidic conditions caused by high CO₂ levels. When rates of cellular metabolism are high, CO₂ production increases (along with oxygen demand). This increased CO₂ production shifts the bicarbonate buffer system to the right, raising [H+] and lowering pH. The accumulation of lactic acid also lowers the pH. These hydrogen ions bind to hemoglobin and reduce its affinity for oxygen, which allows more oxygen to be unloaded at the tissues.

Question 8

Coagulation

Answer 8

• Damaged endothelium exposes Collagen and Tissue Factor proteins. Platelets come into contact with exposed collagen and begin to aggregate. Coagulation Factors secreted by liver sense tissue factor and initiate coagulation cascade. At the end of the cascade, Thromboplastin activates Prothrombin to form Thrombin, which cleaves Fibrinogen into Fibrin. Fibrin forms mesh-like structures that strengthen the platelet plug.
• Clots are broken down by Plasmin, which is generated from Plasminogen.