Cardiovascular Physiology: Hemostasis and Vasculature

Vocabulary-style flashcards based on lecture notes covering platelets, hemostasis clotting pathways, anticoagulants, and the physics of blood flow and microcirculation.

Platelets (Thrombocytes)

Cell fragments derived from megakaryocytes in the bone marrow that play a critical role in hemostasis and blood clotting.

Thrombopoietin

A growth factor that regulates the production and number of platelets; low levels results in poor blood clotting.

Pluripotent Hemopoietic Stem Cell (HSC)

The single source in the bone marrow from which all blood cells are produced, branching into lymphoid and myeloid lineages.

Tissue Factor (TF)

A protein also known as Factor III that is crucial for initiating blood coagulation when blood vessel walls are damaged.

Hemostasis

The process of stopping bleeding, involving four mechanisms: tissue damage-induced vasoconstriction, platelet plug formation, fibrin clot formation, and clot retraction.

von Willebrand factor

A platelet protein that binds to exposed collagen at an injury site to trigger platelet activation and adhesion; it also stabilizes Factor VIII.

Thrombin

A protease enzyme that converts fibrinogen into fibrin and increases its own production through a positive feedback loop involving Factor V and Factor VIII.

Clot Retraction

A process driven by platelet actin and myosin that shrinks the clot and strengthens it, preventing clot fragments from migrating and causing strokes.

Thromboxane A2

A substance released from platelets that stimulates platelet aggregation and constricts blood vessels to prevent blood loss.

Prostacyclin ($PGI_2$)

A substance secreted by healthy adjacent endothelium that inhibits platelet aggregation and vasoconstriction, ensuring clots only form at sites of damage.

Thrombocytopenia

A medical condition characterized by a low platelet count, often presenting as tiny bleeds ($\text{petechiae}$) or large bleeds ($\text{ecchymoses}$).

Common Pathway

The stage of the clotting cascade where Factor Xa cleaves prothrombin into thrombin, eventually leading to the formation of a fibrin clot.

Intrinsic Pathway

The slower clotting pathway initiated by factors inside the blood, such as collagen exposure, which integrates with activated platelets.

Extrinsic Pathway

A fast-acting clotting pathway triggered by external tissue factor (Factor III) from damaged tissues.

Vitamin K

A nutrient required for the carboxylation of pro-coagulant factors II, VII, IX, and X so they can bind calcium and function properly.

Antithrombin III

An anticlotting factor activated by heparin on the endothelial cell surface that inactivates thrombin and other clotting factors.

Fibrinolysis

The active, regulated process of clot removal involving the conversion of plasminogen to plasmin.

Tissue Plasminogen Activator (tPA)

An enzyme released from endothelial cells that converts plasminogen into plasmin at the site of a clot.

Plasmin

An enzyme formed from plasminogen that destroys the fibrin clot matrix and inactivates certain clotting factors.

Blood Flow ($Q$)

The volume of blood per unit of time, calculated by the equation $Q = \frac{\Delta P}{R}$.

Resistance ($R$)

The friction of blood against vessel walls, determined by vessel length, viscosity, and most significantly by radius: $R = \frac{8\eta L}{\pi r^4}$.

Poiseuille’s Law

The law describing the relationship between pressure and flow, expressed as $F = \frac{\Delta P \pi r^4}{8\eta L}$, where changes in radius have the largest effect.

Pulse Pressure ($PP$)

The difference between systolic pressure ($SP$) and diastolic pressure ($DP$), calculated as $PP = SP - DP$.

Compliance

The stretchability of a blood vessel, defined as the change in volume over the change in pressure ($\frac{\Delta \text{Volume}}{\Delta \text{Pressure}}$).

Extraction Ratio ($E$)

A measure of solute movement given by the difference in concentration between arterial and venous blood: $E = \frac{C_a - C_v}{C_a}$.

Oncotic Pressure

The technical term for osmotic pressure generated by plasma proteins in the blood, typically ranging from $18-25\,mm\,Hg$.

Starling-Landis Equation

The equation $J = K \times \{(P_c - P_t) - (OP_c - OP_t)\}$ which balances hydrostatic and oncotic pressures to determine fluid movement across microvasculature.

Edema

A large volume of interstitial fluid that can result from heart failure, kidney failure, or decreased oncotic pressure due to hypoalbuminemia.