Blood is a specialized fluid connective tissue that circulates through the cardiovascular system, delivering essential substances like oxygen and nutrients to cells while transporting metabolic waste products away from them. For Nigerian nurses, understanding blood goes beyond simple laboratory values; it is central to managing patients with severe malaria, postpartum hemorrhage, and malnutrition. The circulating volume in an adult is roughly five liters, maintaining homeostasis, regulating body temperature, and providing immune defense through white blood cells and antibodies. Recognizing alterations in blood parameters allows nurses to anticipate clinical deterioration and intervene promptly.
Whole blood separates into two primary components when centrifuged: a liquid extracellular matrix called plasma and formed elements consisting of cells and cell fragments. Plasma constitutes about 55 percent of total blood volume, while the formed elements make up the remaining 45 percent, a ratio quantified clinically as the hematocrit.
Plasma is roughly 90 percent water, serving as a dissolving and suspending medium for solutes. The remaining 10 percent includes critical plasma proteins produced primarily by the liver:
| Protein Type | Primary Function | Clinical Significance |
|---|---|---|
| Albumin | Maintains oncotic pressure | Low levels lead to generalized edema |
| Globulins | Transport and immunity | Gamma globulins act as antibodies |
| Fibrinogen | Essential for blood clotting | Converted to fibrin during hemostasis |
Electrolytes such as sodium, potassium, and chloride also circulate in plasma, maintaining pH balance and osmotic pressure.
The formed elements of blood perform distinct, highly specialized functions necessary for survival.
Erythrocytes are biconcave discs lacking a nucleus, maximizing their surface area to carry hemoglobin and bind oxygen efficiently. In a tropical setting like Nigeria, inherited variations in these cells, such as sickle cell disease, alter their shape and lifespan, leading to vaso-occlusive crises.
Leukocytes protect the body against infection. They are divided into granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes). Neutrophils increase sharply during acute bacterial infections, a common finding on full blood counts.
Platelets are cytoplasmic fragments derived from megakaryocytes. They aggregate at sites of vascular injury to form a primary platelet plug, initiating the clotting cascade.
Hemopoiesis is the continuous production of blood cells, occurring primarily in the red bone marrow of flat bones such as the sternum, ribs, and pelvis. All blood cells originate from a single type of unspecialized stem cell called a hemocytoblast or multipotent hematopoietic stem cell. Depending on chemical signals called colony-stimulating factors and erythropoietin, these stem cells differentiate into either myeloid or lymphoid lineages. Erythropoietin, released by the kidneys in response to low oxygen levels, stimulates red bone marrow to increase red blood cell production. Nurses caring for patients with chronic kidney disease frequently encounter low erythropoietin levels, manifesting as severe anemia.
Hemostasis is the body's physiological process to stop bleeding and repair damaged blood vessels. It involves three rapid, overlapping steps:
The coagulation cascade operates through intrinsic and extrinsic pathways, both converging into a common pathway that activates factor X and leads to fibrin formation. Vitamin K is essential for the liver to synthesize several of these clotting factors.
Clinical assessment of blood involves physical examination for pallor, jaundice, or petechiae, alongside diagnostic laboratory tests like the full blood count and coagulation profile. Common hematological conditions encountered in clinical practice include anemia, characterized by a reduced oxygen-carrying capacity due to low hemoglobin or red blood cell count. In sub-Saharan Africa, iron deficiency, malaria-induced hemolysis, and hemoglobinopathies like sickle cell anemia are leading causes of hospital admissions. Conversely, polycythemia involves an overproduction of red blood cells, increasing blood viscosity. Nurses monitor these parameters closely to administer blood transfusions safely and detect transfusion reactions early.