12 & 13. Hematology, Lymphatic System, and Immunity

Comprehensive vocabulary flashcards covering hematology, blood composition, leukocytes, erythropoiesis, blood clotting, the lymphatic system, and immune mechanisms.

Erythrocyte

A biconcave-disc shaped, anucleate red blood cell devoid of organelles that is specialized to carry hemoglobin and transport oxygen.

Leukocyte

A white blood cell containing a nucleus and organelles that defends the body against infection, disease, and foreign invaders.

Thrombocyte

A platelet; an anucleate cytoplasmic fragment budded off from a megakaryocyte that functions in hemostasis by forming blood clots.

Plasma

The liquid portion of whole or unclotted blood, composed of approximately $90\%$ water with the remainder consisting mostly of plasma proteins.

Serum

The liquid portion of clotted blood that is separated from cells and clot elements, lacking clotting proteins such as fibrinogen.

Buffy Coat

The thin intermediate layer consisting of leukocytes and platelets that forms between plasma and packed erythrocytes when whole blood is centrifuged.

Lavender-Top Tube (LTT)

A blood collection vacutainer containing an anticoagulant that prevents clotting in order to harvest plasma or whole blood cells.

Albumin

The most abundant plasma protein ($60\%$ of total plasma proteins) responsible for maintaining blood oncotic/osmotic pressure.

Globulins

A class of plasma proteins ($35\%$ of plasma proteins) comprising transport proteins and antibodies (immunoglobulins) that function in immune defense.

Fibrinogen

A plasma protein ($4\%$ of plasma proteins) converted into insoluble fibrin strands by thrombin during the coagulation cascade; present in plasma but absent in serum.

Hemolysis

The destruction or rupture of erythrocytes, causing plasma or serum to turn pink or red.

Icterus (Jaundice)

Yellow discoloration of plasma, serum, or mucous membranes caused by high circulating concentrations of bilirubin from hepatic disease, bile duct obstruction, or severe hemolysis.

Lipemic

A milky or cloudy white appearance of plasma or serum caused by high concentrations of suspended lipids/fats.

Elliptocytes

Oval-shaped erythrocytes that are normally found in camelids, such as llamas.

Erythropoiesis

The production and development of red blood cells within spongy bone marrow, stimulated in response to hypoxia.

Hemoglobin

The iron-containing quaternary protein packed within erythrocytes that binds oxygen in the lungs and delivers it to peripheral tissues.

Heme

A non-protein iron-binding prosthetic group; each hemoglobin molecule contains $4$ heme units, each capable of holding a single iron atom ($\text{Fe}^{2+}$) that binds oxygen.

Methemoglobinemia

A condition induced in animals by acetaminophen toxicity where normal hemoglobin is converted into methemoglobin, which binds oxygen but cannot release it, resulting in tissue hypoxia.

Biliverdin

A green pigment formed as an initial waste byproduct from the enzymatic breakdown of heme during erythrocyte recycling.

Bilirubin

A yellow waste pigment derived from the breakdown of biliverdin that travels to the liver for metabolism and excretion.

Cyanosis

A bluish-purple discoloration of mucous membranes and thin tissues resulting from unoxygenated, dark-red blood during severe hypoxia.

Red Pulp

The region of the spleen responsible for filtering, inspecting, and recycling aging or abnormal erythrocytes via fixed macrophages.

White Pulp

The lymphoid region of the spleen that mounts immune responses against blood-borne pathogens.

Diapedesis

The process by which leukocytes squeeze through the intact endothelial cells of capillary walls into tissues in response to chemical stimuli.

Chemotaxis

The oriented movement of white blood cells along a chemical concentration gradient toward the site of tissue injury or infection.

Neutrophil

A phagocytic granulocyte acting as the body's primary first responder against bacterial infections; its nucleus becomes segmented with age.

Band Neutrophil

An immature neutrophil characterized by a horseshoe-shaped or unsegmented nucleus, indicating premature bone marrow release.

Lymphocyte

The smallest leukocyte, featuring a large, round nucleus that occupies most of the intracellular space; acts as the primary cellular mediator of adaptive immunity.

Monocyte

The largest leukocyte, lacking granules and containing visible cytoplasmic vacuoles; acts as a second responder during infection and matures into a macrophage upon migrating into tissues.

Eosinophil

A granulocyte containing granules that stain reddish-pink with eosin; primarily involved in allergic reactions and parasitic defenses.

Basophil

The rarest leukocyte, containing dark blue-staining granules filled with histamine (to initiate allergic inflammation) and heparin (an anticoagulant).

Leukopoiesis

The biological process of producing white blood cells within the bone marrow in response to specific inflammatory or pathogenic signals.

Hemostasis

The physiological process that arrests bleeding from injured blood vessels through vascular spasm, platelet aggregation, and fibrin mesh formation.

Thrombus

A stationary blood clot formed within an intact or injured blood vessel lumen.

Embolism

The sudden mechanical blockage of a blood vessel by an abnormal travelling mass (such as an air bubble, fat globule, or displaced clot fragment).

Thromboembolism

The occlusion of a blood vessel by a detached blood clot (thrombus) that has moved through the bloodstream from its site of origin.

Thrombocytopenia

A condition characterized by an abnormally low circulating platelet count (below the normal range of $160{,}000\text{--}625{,}000\text{ per }\mu\text{L}$ in dogs and cats).

Petechiae

Tiny, pinpoint, and numerous hemorrhages seen as small red/purple spots on the skin or mucous membranes as a result of thrombocytopenia.

Ecchymosis

A larger, confluent area of hemorrhagic bruising covering a broader area of skin or tissue than petechiae.

Anemia

The reduced oxygen-carrying capability and/or capacity of red blood cells, which leads to tissue hypoxia.

Packed Cell Volume (PCV)

A clinical laboratory value measuring the percentage of whole blood volume occupied by erythrocytes using microhematocrit capillary tubes.

Polychromatophil

An immature erythrocyte that exhibits a bluish-tinted cytoplasm on a Wright's-stained blood smear due to retained ribosomal RNA, indicating regenerative anemia.

Lymph

The clear-to-yellowish biological fluid found inside lymphatic vessels, derived from collected interstitial fluid.

Interstitial Fluid

The extracellular fluid occupying the microscopic interstitial spaces surrounding tissue cells, formed by blood plasma filtering across capillary walls.

Lacteal

A specialized central lymphatic capillary located inside a small intestinal villus that absorbs digested dietary lipids.

Chyle

A milky-white fluid consisting of lymph emulsified with digested fats and triglycerides absorbed by intestinal lacteals.

Edema

An abnormal accumulation of excess fluid within interstitial tissue spaces caused by compromised lymphatic drainage or reduced physical mobility.

Primary Lymphatic Organs

The anatomical structures where immature lymphocytes undergo maturation and become immunocompetent, specifically the bone marrow, thymus, and Bursa of Fabricius.

Secondary Lymphatic Organs

Peripheral structures where mature lymphocytes reside, encounter filtered antigens, and initiate adaptive immune responses (e.g., lymph nodes, spleen, and Peyer's patches).

Thymus

A bilobed primary lymphoid organ in the cranial mediastinum where T-lymphocytes mature; it is largest in young animals and atrophies with age.

Bursa of Fabricius

A specialized primary lymphoid diverticulum situated dorsal to the cloaca in birds where avian B-lymphocytes undergo differentiation and maturation.

Peyer's Patches

Aggregated lymphoid nodules embedded within the submucosa of the small intestines, especially concentrated in the ileum, providing mucosal GI immunity.

Lymph Node

A small, bean-shaped secondary lymphoid organ distributed along lymphatic pathways that filters lymph and houses abundant B-cells and macrophages.

Popliteal Lymph Node

A peripheral lymph node located caudal to the stifle joint in the popliteal fossa that drains lymph from the distal pelvic limb.

Innate Immune System

The nonspecific first and second lines of defense (skin, mucous membranes, phagocytic cells, inflammation, fever) providing rapid, non-targeted protection against pathogens.

Adaptive Immune System

The antigen-specific, acquired arm of the immune system mediated by B-cells and T-cells that develops memory and generates specialized responses upon prior exposure.

Cardinal Signs of Inflammation

The $5$ hallmark clinical manifestations of acute tissue inflammation: pain, heat, redness, swelling, and loss of function.

Pyrogen

Any fever-inducing agent (exogenous microbial toxin or endogenous cytokine like IL-1, IL-6, and TNF) that resets the hypothalamus to raise body temperature.

Antigen

Any molecule or foreign substance that is recognized as nonself and triggers an immune response, specifically stimulating antibody production.

Antibody

A Y-shaped immunoglobulin protein produced by plasma cells that contains unique antigen-binding sites specific to a single target antigen.

Plasma Cell

A fully differentiated, effector B-lymphocyte that actively synthesizes and secretes large quantities of soluble antibodies into the circulation.

Memory Cell

A long-lived lymphocyte formed following an initial immune response that retains antigen specificity to mount an accelerated reaction during subsequent infections.

Cytokines

Soluble protein chemical messengers secreted by T-lymphocytes and antigen-presenting cells that coordinate, recruit, and regulate other immune cells.

ELISA Snap Test

An enzyme-linked immunosorbent assay in-clinic diagnostic tool used to identify the presence of specific antigens or antibodies in a patient blood sample via colorimetric detection.