Blood, Blood Cells and Blood Types – Comprehensive Study Notes

Components of Blood

• Blood is a connective tissue composed of two major fractions that together equal $100\%$ of total volume.
  • Plasma: $\approx 55\%$ of total blood volume.
  • Formed (cellular) elements: $\approx 45\%$ of total blood volume; subdivided into erythrocytes, leukocytes, and platelets.
• Average adult blood volume ≈ $5\,\text{L}$.
• Brace-map classification ("parts-of-a-whole")
  • Plasma
  • Water, ions, nutrients, gases, wastes, hormones.
  • Plasma proteins: albumin, immunoglobulins (antibodies), clotting factors.
  • Cells (formed elements)
  • Erythrocytes (red blood corpuscles, RBC).
  • Leukocytes (white blood cells, WBC).
  • Platelets (thrombocytes).

Plasma (Liquid Matrix)

• Constitutes $\approx 55\%$ of blood.
• Composition
  • Water: $\approx 92\%$ of plasma; solvent & heat buffer.
  • Plasma proteins: $\approx 7\%$
  • Albumin (osmotic balance, carrier of lipids & hormones).
  • Immunoglobulins (antibodies for immunity).
  • Clotting factors (e.g., fibrinogen ➔ fibrin during hemostasis).
  • Other solutes $\approx 1\%$
  • Electrolytes $\text{Na}^+$, $\text{K}^+$, $\text{Ca}^{2+}$, $\text{Cl}^-$, $\text{HCO}_3^-$.
  • Nutrients (glucose, amino acids, lipids, vitamins).
  • Dissolved gases: $\text{O}<em>2$, $\text{CO}</em>2$.
  • Hormones, metabolic wastes (urea, creatinine, bilirubin).
• Serum = plasma minus clotting factors (laboratory term).</n

Formed Elements (Cellular Fraction)

Overview of Relative Percentages

• Buffy coat (<$1\%$): leukocytes + platelets.
• Erythrocytes (RBC): $\approx 44\%$ of whole blood.
• Platelets: part of buffy coat but often quoted separately at $\approx 1\%$.

Erythrocytes (RBC)

• Shape: biconcave disc; thin central region increases surface-area-to-volume ratio.
• Size: diameter $\approx 7\,\mu\text{m}$.
• Organelles: anucleate, minimal organelles; room for haemoglobin.
• Haemoglobin (Hb)
  • Iron-containing protein binding $4$ $\text{O}<em>2$ molecules (oxyhaemoglobin) or $\text{CO}</em>2$ (carbamino-Hb).
  • Pigment gives blood red colour.
• Flexibility: spectrin cytoskeleton allows passage through $\approx 3\,\mu\text{m}$ capillaries.
• Lifespan: $\approx 120\,\text{days}$ ➔ removed by spleen/liver.
• Functional significance
  • Large surface area + no nucleus ⇒ maximal gas exchange.
  • Clinical link: iron deficiency ↓ haemoglobin ⇒ anaemia ⇒ fatigue due to ↓ cellular respiration.

Leukocytes (WBC)

• Quantity: far fewer than RBC; normal count $\approx 4!\times!10^{9}\,–\,11!\times!10^{9}\,\text{cells/L}$.
• Production: red bone marrow, spleen, lymphatic tissue.
• Characteristics
  • Nucleated (variable shapes).
  • Amoeboid movement; diapedesis through capillary walls.
• Major categories (briefly alluded to in slides)
  • Neutrophils (segmented nuclei; first responders; phagocytosis of bacteria).
  • Others implied: eosinophils, basophils, lymphocytes, monocytes.
• Function: immune defense—phagocytosis, antibody production, cytotoxicity.

Platelets (Thrombocytes)

• Cell fragments from megakaryocytes; diameter $\approx 2\,\mu\text{m}$.
• Lack nucleus.
• Count: $\approx 150!\times!10^{9}\,–\,400!\times!10^{9}\,\text{per L}$.
• Key role in hemostasis
  • Adhere to damaged endothelium.
  • Aggregate with fibrin to form clot/scab.

Microscopic Blood Smear

• Typical slide shows
  • Vast field of RBC (pink biconcave discs).
  • Scattered WBC (larger, purple nuclei).
  • Tiny platelet fragments.
• Identifiable leukocyte: segmented neutrophil pictured.

Vascular Structure (Context for Bleeding)

• Artery: thick smooth-muscle & elastic layers.
• Vein: thinner muscle, larger lumen, valves.
• Capillary: single endothelial layer; site of nutrient/gas exchange.

Bleeding & Hemostasis Sequence

• Vessel injury ➔ bleeding (internal = bruise, external wound).
• Immediate responses
  • Vasoconstriction.
  • Platelet plug formation (platelet adhesion & aggregation).
  • Activation of clotting cascade (plasma clotting factors ➔ fibrin network).
• Benefits
  • Seals wound, prevents blood loss.
  • Flushes microbes out; WBC migrate into tissue (inflammation).
  • Tissue fluid accumulation causes swelling (edema).

Genetics & Biochemistry of Blood Types

ABO System

• Antigens (glycoproteins) on RBC membrane: $A$ and $B$.
• Genes (alleles): $A$, $B$, $O$.
  • $A$ and $B$ are codominant; $O$ is recessive (no antigen produced).
  • Genotype ➔ phenotype:
  • $AA$ or $AO$ ➔ Type $A$.
  • $BB$ or $BO$ ➔ Type $B$.
  • $AB$ ➔ Type $AB$ (both antigens present).
  • $OO$ ➔ Type $O$ (no antigens).
• Plasma antibodies (naturally occurring):
  • Type $A$: anti-$B$.
  • Type $B$: anti-$A$.
  • Type $AB$: none.
  • Type $O$: anti-$A$ and anti-$B$.

Rh (Rhesus) System

• Antigen $D$ (Rh factor) present ➔ $+$; absent ➔ $-$.
• Individuals lack pre-formed anti-Rh antibodies.
  • First exposure of Rh-negative person to Rh-positive blood produces antibodies.
  • Subsequent exposure ⇒ haemolytic reaction (clumping/destruction).
• Obstetric relevance: Rh-negative mother carrying Rh-positive fetus ➔ risk of haemolytic disease of newborn in subsequent pregnancies; prophylaxis with anti-D immunoglobulin.

Transfusion Compatibility

• Principle: avoid introducing RBC antigens for which recipient has antibodies.
• Compatibility chart (recipient perspective)
  • Type $O^-$: universal donor (no $A$, $B$, or $Rh$ antigens).
  • Type $AB^+$: universal recipient (has $A$, $B$, $Rh$ antigens; no anti-antibodies).
• Immune mechanism
  • Antibodies (Y-shaped) bind matching foreign antigen ⇒ agglutination ⇒ haemolysis ⇒ potentially fatal.
• Example scenario from transcript
  • Type $A$ recipient given type $B$ blood ➔ anti-$B$ antibodies bind $B$ antigen ➔ clumping.

Clinical Connections & Applications

• Iron–haemoglobin–anaemia link: inadequate dietary iron ↓ Hb synthesis ⇒ anaemia ⇒ fatigue (↓ $\text{O}_2$ delivery and cellular respiration).
• Blood typing & cross-matching essential before transfusion.
• Platelet & clotting factor disorders lead to excessive bleeding or thrombosis.
• Inflammation sequence during tissue injury integrates vascular, immune, and clotting responses.

Numerical & Statistical References

• Whole blood composition: $55\%$ plasma : $45\%$ cells.
• Buffy coat volume: <$1\%$.
• Average adult blood volume: $5\,\text{L}$.
• Cellular percentages in some slides: $44\%$ RBC, $1\%$ platelets.
• Lifespan of RBC: $120\,\text{days}$.
• WBC count: $4!\times!10^{9}$ – $11!\times!10^{9}\,\text{L}^{-1}$.
• Platelet count: $150!\times!10^{9}$ – $400!\times!10^{9}\,\text{L}^{-1}$.

Real-World & Ethical Considerations

• Safe blood banking relies on accurate typing, donor screening, and cross-matching to prevent transfusion reactions.
• Rh prophylaxis programs have dramatically reduced haemolytic disease of the newborn—a public-health success.
• Anaemia worldwide often linked to malnutrition, parasitic infection; social determinants of health influence prevalence.
• Ethical allocation of blood products (scarcity, emergencies) requires evidence-based triage.

Study Tips & Mnemonics

• "P.A.N.G." for plasma solutes: Proteins, Albumin, Nutrients, Gases (plus wastes, ions).
• "Never Let Monkeys Eat Bananas" (Neutrophils, Lymphocytes, Monocytes, Eosinophils, Basophils) to recall leukocyte types.
• Surface-area mnemonic for RBC: "Biconcave = Bigger Contact."