Hematology: Red Blood Cells and Hemopoiesis

A comprehensive vocabulary set covering the components of blood, plasma composition, erythrocyte characteristics and function, bone marrow structure, and the stages of hemopoiesis and erythropoiesis.

Blood

A specialized connective tissue consisting of formed elements suspended in a fluid extracellular matrix called plasma, accounting for approximately $7\%$ of total body weight and an average volume of about $5\,dm^3$ in adults.

Plasma

A slightly alkaline fluid ($pH\,7.4$) that acts as the liquid extracellular matrix, consisting of $91-92\%$ water, $7-8\%$ proteins, and $1-2\%$ other solutes.

Hematocrit (Packed Cell Volume)

The bottom layer of centrifuged blood (approximately $44-45\%$) composed almost entirely of erythrocytes.

Buffy Coat

A thin, translucent middle layer (<1\%) of centrifuged blood containing leukocytes and platelets.

Albumin

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

Globulins

Plasma proteins ($35\%$) including alpha, beta, and gamma types (immunoglobulins) that serve as antibodies and transport proteins.

Fibrinogen

A large plasma protein ($4\%$) essential for the process of blood clotting (coagulation).

Erythrocytes (Red Blood Cells)

Biconcave, anucleated cells with a diameter of $7.5\,\mu m$ and a life span of $120\,\text{days}$, specialized for the transport of oxygen and carbon dioxide.

Hemoglobin

A protein inside erythrocytes that binds oxygen in the lungs and releases it in tissues, also facilitating the transport of $20-27\%$ of $CO_2$ as carbaminohemoglobin.

Carbonic Anhydrase

The enzyme inside red blood cells that converts most $CO_2$ into bicarbonate ions ($HCO_3^{-}$).

Nitric Oxide (NO)

A potent vasodilator bound and released by hemoglobin to help regulate local blood flow by relaxing smooth muscles of vessel walls.

Leukocytes (Normal Count)

White blood cells with a total normal count between $4,500\text{ and }11,000\text{ per }\mu L$.

Platelets (Thrombocytes)

Small, membrane-bound cytoplasmic fragments with a normal count of $150,000-400,000\text{ per }\mu L$ and a life span of $7-10\,\text{days}$.

Bone Marrow

Soft, highly vascularized tissue found in medullary cavities; it is the primary site of hemopoiesis in adults.

Red Bone Marrow

Active marrow rich in hemopoietic cells and sinusoidal capillaries where blood cells are actively produced.

Yellow Bone Marrow

Inactive marrow heavily infiltrated with adipocytes (fat cells) that can revert to red marrow during severe blood loss.

Sinusoidal Capillaries (Sinusoids)

Wide, thin-walled blood vessels with discontinuous endothelium in the bone marrow that allow mature blood cells to enter general circulation.

Hemopoiesis

The continuous process by which the formed elements of blood (erythrocytes, leukocytes, and platelets) are formed from established precursor cells.

Hematopoietic Stem Cells (HSCs)

Pluripotential cells capable of self-renewal and asymmetric division, morphologically resembling small lymphocytes.

Progenitor Cells

Also called transit amplifying cells or Colony Forming Units (CFUs), these are committed to specific lineages and divide rapidly but lose self-renewal capacity.

Precursor Cells (Blasts)

The first cells in a lineage (e.g., proerythroblasts) to show distinct morphological characteristics of the final cell type.

Proerythroblast

The earliest recognizable precursor of the erythroid line; a large cell with a large nucleus and several nucleoli.

Basophilic Erythroblast

A stage of erythropoiesis where the cytoplasm is intensely basophilic due to polyribosomes synthesizing hemoglobin.

Orthochromatophilic Erythroblast (Normoblast)

A stage where the nucleus becomes small and pyknotic before being eventually extruded from the cell.

Reticulocyte

A young, anucleated RBC containing a few ribosomes that enters circulation and matures into a functional erythrocyte within $1-2\,\text{days}$.