Red Blood Cells: Structure and Function (II)

Comprehensive vocabulary flashcards covering red blood cell membrane composition, metabolic pathways, poikilocyte morphologies, and hemoglobin catabolic pathways.

Poikilocyte

An abnormally shaped red blood cell whose specific morphology provides diagnostic evidence of underlying red blood cell pathology or systemic disease.

Red Blood Cell Cytoskeleton

The structural protein network beneath the lipid bilayer—composed of spectrin, actin, protein 4.1, and ankyrin (protein 2.1)—that determines and maintains cell shape, provides viscoelastic properties, and delimits deformability.

Elastic Deformation

The physiologic, reversible mechanical stretching of the hexagonal cytoskeletal lattice that enables red blood cells to squeeze through narrow capillaries and promptly return to their resting biconcave discoid shape.

Plastic Deformation

The pathologic, irreversible distortion of the erythrocyte hexagonal cytoskeletal lattice, leading to permanent shape alteration and failure to return to normal resting conformation.

Cholesterol (Membrane Biomechanics)

A lipid bilayer constituent that intercalates between phospholipids and stiffens the erythrocyte membrane; excess incorporation into the outer leaflet induces irregular membrane projections.

Ovalocyte

An ovoid red blood cell shape that is normal in camelids, as well as in birds and reptiles (where red blood cells also retain their nucleus).

Echinocyte

A crenated erythrocyte bearing regularly spaced, sharp projections; commonly caused artifactually by drying or underfilled EDTA tubes, or pathologically by electrolyte disturbances, uremia, or rattlesnake envenomation.

Acanthocyte

An erythrocyte with irregularly distributed, blunt, or club-like projections resulting from excess cholesterol incorporation into the outer lipid bilayer; seen normally in pigs, calves, and rabbits, and pathologically in hepatic disease, lipid disorders, fragmentation, or neoplasia.

Codocyte (Target Cell)

An abnormally shaped erythrocyte displaying a target-like appearance with a central area of hemoglobin surrounded by a clear ring; pathologically seen in regenerative anemia, iron deficiency, and hepatobiliary disease.

Schistocyte

An irregular red blood cell fragment produced when circulating cells are sheared and torn by intravascular fibrin strands (microangiopathy), commonly seen in disseminated intravascular coagulation (DIC), thrombosis, or vascular tumors.

Keratocyte

A fragmented erythrocyte with one or two sharp horn-like projections, formed via intravascular mechanical trauma and shearing against fibrin strands in conditions such as DIC, thrombi, or vascular tumors.

Spherocyte

A small, darkly staining, spherical red blood cell lacking central pallor, formed when splenic macrophages partially phagocytose antibody-coated membrane and the remainder reseals; a diagnostic hallmark of immune-mediated hemolytic anemia (IMHA) when markedly abundant.

Heinz Body

A round intraerythrocytic inclusion formed by oxidized, denatured globin chains that clump and bind to the inner membrane surface; up to $5\%$ of red blood cells may contain them in healthy cats due to high numbers of oxidant-sensitive sulfhydryl groups.

Eccentrocyte

A red blood cell exhibiting condensation of hemoglobin toward one side of the cell with an apposed, clear, crescentic zone of fused membrane, caused by oxidative injury to membrane proteins and lipids.

Howell-Jolly Body

A small, round, basophilic nuclear remnant remaining within an erythrocyte; found in very low numbers in healthy mammals, but increased during regenerative anemia or splenic pathology.

Agglutination

The cross-linking and macroscopic clumping of red blood cells caused by surface-bound antibodies; alongside spherocytes, it represents a hallmark of immune-mediated hemolytic anemia (IMHA).

Embden-Meyerhof Pathway

The anaerobic glycolytic pathway responsible for generating ATP in mature red blood cells to sustain membrane shape, fuel contractile proteins, and operate cation transport pumps.

Canine and Feline Erythrocyte Cation Profile

A unique species difference where dogs and cats maintain high intracellular $\text{Na}^+$ and low intracellular $\text{K}^+$, whereas most other mammalian species maintain high intracellular $\text{K}^+$ and low intracellular $\text{Na}^+$.

Methemoglobin Reductase Pathway

An erythrocyte metabolic pathway that utilizes NADH produced during glycolysis to reduce oxidized ferric iron ($\text{Fe}^{3+}$) back to functional oxygen-carrying ferrous iron ($\text{Fe}^{2+}$) within hemoglobin.

Pentose Phosphate Shunt

An erythrocyte metabolic pathway that utilizes glucose-6-phosphate dehydrogenase (G6PD) to generate NADPH, providing reducing equivalents to maintain glutathione in its active reduced state.

Reduced Glutathione (GSH)

An intracellular antioxidant peptide that serves as a sacrificial molecule, reducing hydrogen peroxide ($\text{H}_2\text{O}_2$) to $\text{H}_2\text{O}$ via glutathione peroxidase and protecting globin sulfhydryl groups from oxidation.

Glutathione Peroxidase

A selenium-dependent antioxidant enzyme that uses reduced glutathione (GSH) to convert harmful hydrogen peroxide ($\text{H}_2\text{O}_2$) into water ($\text{H}_2\text{O}$), forming oxidized glutathione disulfide (GSSG).

Biliverdin Reductase

The enzyme responsible for reducing biliverdin to bilirubin within macrophages during hemoglobin catabolism; it possesses minimal activity in birds, reptiles, and amphibians.

Unconjugated Bilirubin (Indirect Bilirubin)

The lipid-soluble bilirubin product released from macrophage heme breakdown that circulates bound to albumin in plasma prior to hepatic uptake.

Conjugated Bilirubin (Direct Bilirubin)

Water-soluble bilirubin that has been conjugated with glucuronide inside hepatocytes and excreted into bile.

Stercobilin

The brown bile pigment end-product produced by bacterial degradation of intestinal urobilinogen, which is eliminated from the body via feces.

Erythrocyte Senescence

The natural end-of-life process of red blood cells caused by progressive ATP depletion, loss of reducing capacity, hemoglobin oxidation, and binding of senescence antibodies that promote splenic macrophage phagocytosis.