Circulatory system Flashcards
What are the main components of blood, and their percentages?
Plasma (55%): Water, proteins (albumin, globulins, fibrinogen), electrolytes, hormones.
Erythrocytes (45%): Red blood cells (RBCs) for oxygen transport.
Buffy coat (<1%): Platelets and leukocytes (WBCs).
What is the role of hemoglobin in RBCs?
Binds oxygen in the lungs and releases it to tissues. Composed of 4 subunits (2α + 2β globin chains), each with a heme group containing iron.
How is erythropoiesis regulated?
Controlled by erythropoietin (EPO) from kidneys in response to low oxygen. Stimulates bone marrow to produce RBCs.
What causes pernicious anemia?
Vitamin B₁₂ deficiency due to lack of intrinsic factor (needed for B₁₂ absorption in the gut).
Universal donor and recipient blood types?
Donor: O-negative (no A/B antigens).
Recipient: AB-positive (no anti-A/B antibodies).
List the three steps of haemostasis.
Vascular spasm: Constriction of damaged vessels.
Platelet plug formation: Platelets adhere to collagen via vWF.
Coagulation: Fibrin mesh stabilizes the plug.
Differentiate intrinsic vs. extrinsic clotting pathways.
Intrinsic: Triggered by exposed collagen (factor XII).
Extrinsic: Triggered by tissue factor (factor III) from damaged tissues.
How does aspirin affect clotting?
Inhibits thromboxane A₂ synthesis in platelets, reducing aggregation.
Name the four heart valves and their locations.
Atrioventricular (AV): Tricuspid (right), Mitral (left).
Semilunar: Pulmonary (right ventricle), Aortic (left ventricle).
How do chordae tendineae prevent valve prolapse?
Anchor AV valve cusps to papillary muscles, preventing inversion during ventricular contraction.
Compare systemic vs. pulmonary circulation.
Systemic: Left ventricle → body → right atrium (oxygenated to deoxygenated).
Pulmonary: Right ventricle → lungs → left atrium (deoxygenated to oxygenated).
Sequence of electrical conduction in the heart.
SA node → AV node → Bundle of His → Purkinje fibers → Ventricular myocardium.
What causes the delay at the AV node?
Ensures atrial contraction completes before ventricular depolarization (~0.1 sec delay).
ECG waves and their meanings:
P wave: Atrial depolarization.
QRS complex: Ventricular depolarization.
T wave: Ventricular repolarization.
What does ventricular fibrillation look like on an ECG?
Chaotic, irregular waves with no discernible PQRST pattern.
How do cardiac muscle action potentials differ from skeletal muscle?
Cardiac APs have a plateau phase (Ca²⁺ influx prolongs depolarization).
Role of intercalated discs in cardiomyocytes?
Contain gap junctions for electrical coupling and desmosomes for structural support.
Why can’t cardiac muscle undergo tetanus?
Long refractory period (~250 ms) ensures relaxation between contractions.
Factors affecting vascular resistance (Poiseuille’s Law):
R ∝ (viscosity × vessel length) / radius⁴
Most impactful factor: radius (small changes → large resistance changes).
How does vasodilation affect blood flow?
↑ Vessel radius → ↓ resistance → ↑ flow (F = ΔP/R).
