Hematology
Blood composition
Blood is composed of plasma, buffy coat (platelets/WBCs), and RBS.
Plasma (55%)
Plasma is 90% water and 10% proteins.
Protein composition
- Albumin (60%): Responsible for fluid retention by oncotic pressure. Transports bilirubin.
- Globulins (35%): Immunoglobulins/antibodies (Ig), hormones
- Fibrinogen (4%): Clotting factor (blood serum is plasma without fibrinogen)
Also in plasma
- Lipids
- Carbohydrates
- Amino acids
- Organic wastes (urea, creatinine, bilirubin)
- Electrolytes
Buffy coat (1%)
-PHILS (Granulocytes): Neutrophils, eosinophils, basophils. Have lobated nuclei and recognizable granules.
-CYTES (Agranulocytes): Lymphocytes, monocytes. Have uniform nuclei and few/no granules.
Platelets
Derived from megakaryocytes and are important for hemostasis, clotting, and vascular repair. They are produced in the bone marrow and does not have a nucleus. Releases granule content through the open canalicular membrane system.
The membrane contains integrins used for platelet aggregation. These bind vWF and fibrinogen. It turns into a sphere upon clotting.
Structure
Has a hyalomere (peripheral area) containing microfilaments and microtubules which will stain LIGHT BLUE. Also has a granulomere which is used for secretory storage (e.g. serotonin for vasoconstriction, PD growth factor for endothelial mitosis and vascular repair) which will stain PURPLE.
Neutrophils
Accounts for 60-70% of WBCs. Phagocytose bacteria with production of oxygen radicals and hydrogen peroxide (H2O2), or by using lysosomes.
Neutrophilic stains will turn it PINK. Azurophilic stains will also turn its lysosomes PURPLE.
Travel by squeezing through endothelial cells of blood vessels (diapedesis), navigating via chemotaxis. Will form pus at site (usually a collection of neutrophils).
Structure
Has a multilobated nucleus. The Dumstick/Barr body is a remnant of inactivated X-chromosomes in women which can be seen in a small percentage of neutrophils.
Eosinophils
Accounts for 2-4% of WBCs. Attacks parasites. Will limit inflammation by inactivating leukotrienes and histamine. Are recruited by basophils which secrete eosinophil chemotactic factors.
Structure
Has a bilobed nucleus, although not as lobed as the neutrophil. Its banded appearance is histologically unique. The external area contains peroxidase and hydrolytic enzymes. The internal space is crystalline and contains major basic protein (which kills parasites), eosinophil cationic protein, and neurotoxin.
Eosinophilic stains will turn it ORANGE. Azurophilic stains will also turn its lysosomes PURPLE.
Basophils
Accounts for 0.5% of WBCs. These promote inflammation and are responsible for many immune diseases like hypersensitivity allergy/asthma. They express IgE which binds foreign agents and causes degranulation to be induce inflammatory response. Will recruit eosinophils to fight against parasites.
Structure
Have a segmented nucleus, although less so than neutrophils.
Basophilic stains will turn it BLUE. Basophilic stains will color the large granules which contain heparin (anti-coagulant), proteases, histamine (for vascular permeability), and eosinophilic chemotactic factor. Azurophilic stains will also turn its lysosomes PURPLE.
Lymphocytes
Accounts for 28% of WBCs. Are the B and T cells of the immune system which mediate specific and acquired immunity. B cells produce antibodies, T cells destroy pathogens.
Structure
Large/round/uniform nucleus and sparse cytoplasm. Has a few granules which turn PURPLE with azurophilic stain.
Monocytes
Accounts for 5% of WBCs. These are the progenitors of macrophages and secrete cytokines involved in host defense/inflammation. They will phagocytose foreign antibodies and is an antigen-presenting cell (APC).
Structure
Large nucleus which looks indented (not to be confused with eosinophils which have clear granules). Has more cytoplasm than lymphocytes.
Its cytoplasm will stain gray/blue. A few azurophilic granules may be present.
Erythrocytes/Red blood cells (45%)
Responsible for gas exchange (O2 and CO2).
Structure
No nucleus, non-motile. Have a biconcave appearance which increases the surface area for gas exchange.
Membrane composition
- Glycophorin (on surface): Carries sugar moiety
- Anion transport channel (on surface): Allows for gas exchange
- Ankyrin (within cell): Anchors submembrane skeleton to transporter and maintains cell shape
ABO blood groups
H/O antigen: Core of the glycan, Type O blood only has the H antigen (no A/B)
Type A: Enzyme adds N-acetyl galactosamine
Type B: Enzyme adds galactose
Measuring RBC volume (Hematocrit)
For calculation of specific volume, see Body Fluid Compartments > Measurement of Compartments
The volume of red blood cells is usually expressed as a percentage. Normal value is between 40-50% depending on age. Anemia would be low HCT, polycythemia would be high HCT.
Life cycle
Production starts in bone marrow as reticulocytes which mature in blood, but have limited lifespan because of a lack of a nucleus. Aging RBCs will degenerate via hemolysis.
Extravascular blood is destroyed in the spleen, liver, and bone marrow.
Intravascular blood is destroyed via phagocytosis by macrophages.
Differential count
Never Let Monkeys Eat Butt
NLMEB
- Neutrophil (60-70%): Attack bacteria
- Lymphocyte (28%): Mediate humoral/cellular immunity
- Monocyte (5%): Phagocytic macrophages
- Eosinophil (2-4%): Attack parasites
- Basophil (0.5%): Mediate inflammation
Diagnostic tool
Elevated levels of any NLMB type will indicate an issue ingoing in the body. For example, if eosinophils are elevated, there may be a parasitic infection.
Hemostasis
Step 1: Vasoconstriction
Narrowing of blood vessels to avoid blood loss.
Step 2: Platelet Aggregation
Platelets adhere to subendothelial collagen, forming a platelet plug. Von Willebrand's factor (vWF) expressed during vascular injury binds to factor VIII from blood plasma, forming fibrin.
Step 3: Clot formation
Coagulation cascade (secondary hemostasis). Thrombin formed, converting fibrinogen to fibrin. Fibrin will then form a definitive hemostatic plug.