Blood and Red Blood Cells Overview

Study Notes

Erythrocytes
Shape: Biconcave discs, can appear as rouleaux in slow blood stream.
Size: 6-9 µm (average 7.5 µm).
Color: Single RBC is greenish yellow due to minimal hemoglobin, while stained sections appear red due to the large number of RBCs. Acidophilic with a pale center.
Number:
- Males: 5-5.5 million /mm3.
- Females: 4.5 - 5 million /mm3 (decreased due to menstruation and female sex hormones).
Structure & Adaptation to Function:
- Biconcave disc increases surface area for gas exchange.
- Plasticity allows squeezing through narrow vessels without rupture.
- Selective permeability facilitates the exchange of oxygen and carbon dioxide while retaining hemoglobin.
- Absence of nucleus and organelles allows for more space to accommodate hemoglobin for gas exchange.
- Contains carbonic anhydrase for transporting CO2 from tissues to the lungs.

	Neutrophils	Eosinophils	Basophils
Percentage	60-75%	2-5%	0.5-1%
Size	10-12 μm	12-15 μm	10-12 μm
Nucleus	Single, Segmented (2-5 segments)	Bilobed or horse-shoe shaped.	Large, Irregular.
Cytoplasm	Fine neutrophilic granules.	Large acidophilic refractile granules.	Obscured by cytoplasmic granules.
Function	Defense mechanism: Phagocytosis of bacteria, foreign bodies, leading to pus formation.	Anti-allergic action by phagocytosing Ag-Ab complex. Contains histaminase & sulphatase to destroy excess histamine and other allergy-causing substances.	Produce histamine & heparin during allergy.

	Monocytes	Lymphocytes
Percentage	3-8%	25-30%
Diameter	15 μm	6-8 μm (B&T)
Nucleus	Large & pale. Kidney or horse-shoe shaped.	Dark. Rounded.
Cytoplasm	Abundant. Pale basophilic.	Little rim around nucleus. Pale basophilic.
Function	Migrate into connective tissue and become macrophages.	B lymphocytes: Responsible for humoral immunity. T lymphocytes: Responsible for cell-mediated immunity.

Structure: Cytoplasm covered with a membrane, no nucleus (not true cells).
Counts: 150,000-400,000/mm3.
Shape: Oval or rounded discs.
LM:
- Outer pale blue part (hyalomere)
- Central granular part (granulomere)
Origin: megakaryocyte.
Function: Hemostasis (stopping bleeding).
- Serotonin: Vasoconstriction to reduce blood loss.
- Platelet aggregation (white thrombus): Adherence to injured vessel walls.
- Red thrombus (coagulation): Secrete Thromboblastin which activates prothrombin into thrombin, converting fibrinogen into a fibrin network, attracting RBCs, and closing the blood vessel to stop bleeding.