Medical Physiology & Biochemistry: Lymphatics, Anemias, Clinical Enzymology, and Hemostasis

Comprehensive vocabulary flashcards covering lymphatics, hemolytic/hemorrhagic anemias, clinical diagnostic enzymology, and primary/secondary hemostasis.

Lymph

A clear, yellow interstitial fluid derived from capillary filtrate that is not reabsorbed into venous capillaries and instead enters lymphatic vessels; composed of $95\%$ water, plasma proteins (albumin, globulins, fibrinogen, regulatory proteins), glucose, fatty acids, fats, ions, and immune cells.

Lymphatic Vessels

Closed, thin-walled tubes composed of a single layer of overlapping endothelial cells that open when interstitial fluid pressure exceeds intraluminal pressure, equipped with valves to ensure unidirectional flow of lymph toward secondary lymphoid tissues and venous circulation.

Paracortex (Lymph Node)

The diffuse histological zone of a lymph node situated beneath the cortex and adjacent to the medulla that predominantly houses $T\text{ cells}$.

Periarteriolar Lymphoid Sheath (PALS)

A specialized region of the splenic white pulp that surrounds central arterioles and contains $T\text{ cells}$.

Splenic Red Pulp

The splenic compartment that removes effete or damaged red blood cells and recycles iron ($\text{Fe}^{2+}$) from degraded hemoglobin, requiring erythrocytes to squeeze through narrow interendothelial slits (IESs) in the venous sinus walls.

Lymphedema

Significant localized edema that develops following surgical excision of draining lymph nodes (such as during mastectomy), caused by disruption of the regional drainage system amidst postoperative inflammation.

Sepsis

A life-threatening systemic blood infection that can progress to septic shock and death; asplenic patients face a markedly increased risk due to impaired clearance of bloodborne pathogens.

Mean Corpuscular Volume (MCV)

A laboratory index quantifying the average volume/size of a red blood cell, with a normal reference range of $80 - 100\,\text{fL}$; used to classify anemias as normocytic, microcytic, or macrocytic.

Extravascular Hemolysis

The premature destruction of erythrocytes outside of blood vessels, predominantly occurring within the spleen when macrophages phagocytose red blood cells with altered membrane stability, shape, or deformability.

Hereditary Spherocytosis

An extravascular hemolytic anemia resulting from inherited defects in red blood cell membrane skeletal proteins (ankyrin or spectrin), producing rigid, spherical cells lacking central pallor that become trapped and destroyed in the spleen.

Hepcidin

A hepatic regulatory peptide that blocks iron absorption and mobilization by binding and inhibiting the cellular iron efflux channel ferroportin; elevated in states of chronic inflammation via $\text{IL-6}$.

Ferroportin

Transmembrane transport channels that mediate the passage of iron out of cells (enterocytes and storage pools) into the circulation; directly inhibited by hepcidin.

Nuclear-to-Cytoplasm Asynchrony

A cellular feature of macrocytic anemias resulting from vitamin $\text{B}_{12}$ or folic acid deficiency, wherein cytoplasmic maturation proceeds normally while nuclear division lags due to impaired $DNA$ synthesis.

Methylmalonate

A metabolite that accumulates specifically in isolated vitamin $\text{B}_{12}$ deficiency (and not in folic acid deficiency), leading to myelin sheath destruction and neurological symptoms such as ataxia and paresthesias.

Aplastic Anemia

A bone marrow failure syndrome caused by toxic insults, autoimmune attack, or stem cell defects that results in pancytopenia (simultaneous reduction of erythrocytes, leukocytes, and thrombocytes).

Dacrocytes

Teardrop-shaped red blood cells seen on peripheral blood smears when space-occupying marrow lesions (such as metastatic malignancies) mechanically distort hematopoiesis.

Serum

The non-physiological, cell-free fluid obtained by centrifuging fully coagulated whole blood; does not require exogenous anticoagulants but carries a risk of artifactual enzyme release via hemolysis.

Plasma

The physiological fluid, non-cellular fraction of circulating blood collected in the presence of an anticoagulant that prevents in vitro coagulation.

Alanine Aminotransferase (ALT / SGPT)

A predominantly intracellular hepatic enzyme released into plasma upon hepatocellular membrane injury; exhibits greater than $10\text{-fold}$ elevations in acute hepatocellular damage.

Aspartate Aminotransferase (AST / SGOT)

An intracellular enzyme present in hepatocytes and muscle; an $\text{AST}:\text{ALT}$ ratio of at least $2:1$ is strongly characteristic of alcohol-induced liver disease.

Alkaline Phosphatase (ALP)

A cell-surface enzyme localized to biliary canalicular membranes and bone osteoblasts; plasma activity increases more than $3\text{-fold}$ in cholestasis and biliary tract obstruction.

Gamma Glutamyl Transferase (GGT)

A membrane-bound enzyme originating in the liver and pancreas that is elevated in biliary obstruction (cholestasis) and induced by chronic alcohol consumption.

Critical Difference

The percentage threshold difference between serial laboratory test results from a single patient that must be exceeded to demonstrate a statistically significant physiological or pathological change rather than analytical or biological variation.

Isoenzymes (Isozymes)

Multiple physically and structurally distinct molecular forms of the same enzyme that catalyze the identical chemical reaction but differ in quaternary subunit structure, amino acid sequence, electrophoretic mobility, and tissue origin.

Creatine Kinase Isoenzyme Electrophoresis

An analytical technique performed at alkaline pH ($\text{pH } 8.6$) to separate dimeric creatine kinase into three distinct bands based on net negative charge migrating toward the anode: $\text{CK1 (BB)}$, $\text{CK2 (MB)}$, and $\text{CK3 (MM)}$.

Troponin Complex

A heterotrimeric cardiac biomarker complex consisting of Troponin I (inhibitory), Troponin T (tropomyosin-binding), and Troponin C (calcium-binding); plasma levels of Troponin I and T rise within $3 - 12\,\text{hours}$ post-myocardial infarction and remain elevated for $5 - 14\,\text{days}$.

Primary Hemostasis

The initial phase of hemostasis triggered by vascular endothelial injury, characterized by platelet adhesion, activation, mediator secretion, and aggregation to form an unstable primary platelet plug.

Thrombocytopenia

A pathological reduction in circulating platelet concentration below $100{,}000/\mu\text{L}$ of blood (reference range: $150{,}000 - 300{,}000/\mu\text{L}$), predisposing patients to spontaneous mucocutaneous bleeding.

von Willebrand Factor (vWF)

A large adhesive plasma and subendothelial multimeric glycoprotein that bridges exposed collagen to the platelet $Gp\,\text{Ib-IX-V}$ receptor complex and stabilizes circulating Factor VIII.

Glycoprotein IIb-IIIa (Gp IIb-IIIa)

A platelet surface integrin receptor that undergoes a conformational activation change allowing it to bind bivalent fibrinogen with high affinity, thereby cross-linking adjacent platelets during aggregation.

Bernard-Soulier Disease

A rare autosomal recessive disorder of primary hemostasis caused by an inherited quantitative or qualitative defect in the platelet membrane $Gp\,\text{Ib-IX}$ receptor complex, preventing normal adhesion to vWF.

Glanzmann Thrombasthenia

A rare autosomal recessive bleeding disorder of primary hemostasis resulting from defective or deficient platelet integrin $Gp\,\text{IIb-IIIa}$, rendering platelets incapable of binding fibrinogen and aggregating.

Aspirin

An antiplatelet drug that irreversibly acetylates and inactivates platelet cyclooxygenase-1 (COX-1), permanently halting the synthesis of pro-aggregatory thromboxane $\text{A}_2$ ($\text{TXA}_2$) for the lifespan of the platelet.

Clopidogrel (Plavix)

An oral antiplatelet therapeutic agent that antagonizes platelet $\text{P2Y}_{12}$ adenosine diphosphate (ADP) receptors, preventing ADP-mediated activation of the $Gp\,\text{IIb-IIIa}$ complex and subsequent aggregation.

Tissue Factor (Factor III)

A membrane-bound procoagulant glycoprotein exposed upon subendothelial vascular injury that forms an active complex with Factor VIIa to initiate the extrinsic pathway of secondary hemostasis.

Factor XIIIa

A transglutaminase enzyme activated by thrombin in the presence of $\text{Ca}^{2+}$ that catalyzes covalent cross-linking between fibrin monomers, transforming a soft fibrin clot into a mechanically stable clot.

Gamma-Carboxyglutamate (Gla) Residues

Dicarboxylated glutamic acid residues produced post-translationally by vitamin K-dependent gamma-glutamyl carboxylase on Factors II, VII, IX, and X, enabling negative charges that coordinate $\text{Ca}^{2+}$ bridges to platelet membrane phospholipids.

Hemophilia A

An X-linked recessive coagulopathy resulting from a quantitative deficiency or functional defect in Factor VIII, which impairs intrinsic tenase complex amplification and causes recurrent hemarthroses.

Hemophilia B

An X-linked recessive bleeding disorder caused by deficiency of Factor IX (Christmas factor), clinically identical to Hemophilia A due to impairment of the identical intrinsic coagulation reaction converting Factor X to Factor Xa.

Antithrombin (ATIII)

A circulating serine protease inhibitor that irreversibly neutralizes thrombin and Factor Xa; its inhibitory rate is accelerated by several orders of magnitude upon binding to endothelial heparan sulfate or exogenous heparin.

Protein C / Protein S Pathway

An endogenous anticoagulant system wherein thrombin binds endothelial thrombomodulin to activate Protein C; activated Protein C (Protein Ca) then partners with cofactor Protein S to inactivate Factors Va and VIIIa via proteolysis.

Factor V Leiden

The most prevalent inherited thrombophilia, characterized by a point mutation in the Factor V gene that confers resistance to proteolytic inactivation by activated Protein C (Protein Ca), leaving Factor Va persistently active.

Warfarin

An oral anticoagulant that functions as a competitive inhibitor of vitamin K epoxide reductase (VKOR), halting the regeneration of active vitamin K and impairing the gamma-carboxylation of zymogens II, VII, IX, and X.

Fibrinolysis

The enzymatic dissolution of a secondary hemostatic clot wherein plasmin cleaves insoluble cross-linked fibrin networks into soluble fibrin degradation products (FDPs) and D-dimers.

Tissue Plasminogen Activator (t-PA)

An endothelial serine protease released in response to thrombi or stasis that selectively binds to fibrin clots and cleaves plasminogen into the fibrin-cleaving enzyme plasmin.