Understanding Blood: Composition, Function, and Disorders
What is Blood?
Blood is a liquid tissue that circulates throughout the body, delivering essential elements to cells for vital functions like breathing, energy production, and defense against infections. All organs rely on blood flow through arteries, veins, and capillaries. The blood volume in a person varies with age, weight, sex, and height, but adults typically have between 4.5 and 6 liters.
Blood is considered a highly specialized connective tissue.
Role of Blood Cells
Red Blood Cells (RBCs): Carry oxygen to body cells and remove carbon dioxide.
White Blood Cells (WBCs): Responsible for various functions related to the body’s defense system.
Platelets: Involved in primary hemostatic mechanisms, including coagulation and anticoagulation processes.
Blood Circulation
Major Circulation (Systemic Circulation):
Begins in the left ventricle, travels through the aorta and its branches to reach capillaries throughout the body. Blood returns through veins that eventually drain into the superior and inferior vena cava, ending in the right atrium.
Minor Circulation (Pulmonary Circulation):
Begins in the right ventricle, exits through the pulmonary trunk, and continues along the right and left pulmonary arteries to the lungs. Blood returns through venules that converge to form four pulmonary veins (two from each lung), which drain into the left atrium.
Blood Coagulation
A. Spontaneous Coagulation:
B. Separation:
- Liquid
- Solid
Hematocrit:
B. Separation by an anticoagulant:
- b.1. Liquid
- b.2. Solid (Elements Figurations)
A. Liquid – Plasma (55%):
Complex mix of:
- Water
- Proteins (Albumin, Globulin)
- Lipids
- Carbohydrates
- Vitamins, Enzymes, Antibodies, etc.
B. Solid – Figurative Elements (45%):
- Red Blood Cells
- White Blood Cells
- Platelets
Anemia
Anemia is a condition characterized by a lack of red blood cells, leading to poor oxygenation of the body. This can cause problems with growth and development in children and requires prompt treatment. Anemia is caused by low blood hemoglobin levels, which can result from various factors that affect the production, number, quality, or destruction of red blood cells.
Anemia can be severe because the lack of oxygen to vital organs like the heart, brain, and lungs can lead to death or irreversible damage. In young children, it can also cause growth and developmental problems.
General Symptoms of Anemia:
- Low weight and appetite
- Fatigue and weakness
- Excessive paleness and lack of color in mucous membranes, especially eyes
- Rapid heart rate
- Respiratory problems
- Chest pain
Human Blood
This preparation is stained with hematoxylin-eosin to study different types of blood cells, starting with red blood cells and platelets.
General Features of White Blood Cells:
- Colorless
- Nucleated with cytoplasm
- Amoeboid features
- Functional in small amounts
Function of White Blood Cells:
- Actively participate in the defense and integrity of the body
Formation of White Blood Cells:
- In red bone marrow
Polymorphonuclear Granulocytes
1. Neutrophils:
The most numerous type of white blood cells. They have a multilobed nucleus (2-5 lobes connected by thin chromatin bridges), abundant homogeneous cytoplasm with fine granules stained dark purple or lilac. Neutrophils are the first line of defense against invading foreign bodies and constitute 60-70% of total leukocytes in adults. They have a high capacity for phagocytosis.
2. Eosinophils:
Similar in size to neutrophils but found in lesser amounts (1-3% of total leukocytes). The cytoplasm is slightly basophilic but often obscured by numerous coarse granules. The nucleus generally has two lobes.
3. Basophils:
The least abundant type of polymorphonuclear leukocyte (less than 1%). They are slightly smaller than neutrophils and eosinophils, with an average diameter of 10 mm. Their cytoplasm is acidophilic and covered by large, irregular, purplish-black granules that also cover the nucleus, making it difficult to see its shape.
Polymorphonuclear Agranulocytes
1. Lymphocytes:
Constitute approximately 30% of total white blood cells. They vary in size (large, medium, and small), with small lymphocytes being the most common. The nucleus is round and basophilic, with possible chromatin aggregates and a small notch in the outline. The cytoplasm is a narrow strip around the nucleus and generally lacks visible granules.
Larger lymphocytes have a nucleus shifted to the periphery, more cytoplasm, and a few azurophilic granules. The basophilic cytoplasm is due to high RNA content and can become deeper blue when stimulated. A perinuclear halo can often be seen, and in medium and large lymphocytes, the negative image of the Golgi complex may be visible near the nucleus.
2. Monocytes:
The largest leukocytes, with a diameter of 15-20 mm. The nucleus is large and polymorphic, often round, oval, or horseshoe-shaped (the most characteristic). The chromatin is loose and has a reticular appearance. The cytoplasm is abundant, slightly basophilic, blue-gray in color with scattered azurophilic granules. It lacks the characteristic perinuclear halo of lymphocytes and appears slightly “dirty” compared to the “translucent” appearance of lymphocytes.
Platelets (Thrombocytes)
Platelets are not cells but fragments of the cytoplasm of megakaryocytes, giant cells found in bone marrow. They are very small (2-3 mm), irregularly shaped, but appear rounded in peripheral blood smears. They have a slight brownish color and can be seen isolated or in clumps, as they play a crucial role in forming plugs to prevent bleeding. Their normal count is between 200,000 and 400,000 per ml of blood, making them easily visible in blood smears.