Blood Characteristics, Components, and Plasma Proteins

Overview & Lecture Context

• Builds on the previous recording in which students observed
  • Micrographs of blood smears
  • 3-D blood-cell models
  • Demonstrations of red-blood-cell (RBC) surface antigens
  • Common instruments used in blood testing
• Present lecture will
  • Define the characteristics of whole blood
  • Break down formed elements (RBCs, WBCs, platelets) in detail
  • Cover plasma composition
  • Preview future topics: clotting vs agglutination and the full clotting cascade

Composition of Whole Blood

• Whole blood = Plasma + Formed Elements
• Typical proportion (remember it is always a range, not a fixed value)
  • Formed elements: 37\%\text{–}54\%
  • Plasma: 46\%\text{–}63\%
  • “Text-book” shortcut often quoted: 45\% cells, 55\% plasma
• Formed Elements
  • 99.9\% of formed elements = erythrocytes (RBCs)
  • < 0.1\% = leukocytes (WBCs)
  • < 0.1\% = platelets (thrombocytes)
• Hematocrit (Hct)
  • Laboratory fractionation of a spun blood sample
  • Definition = percentage of formed elements in the sample
  • Normal range: 37\%\text{–}54\% (value is gender-, age-, and hydration-dependent)
  • Plasma % can be found by 100-Hct
• Buffy Coat
  • Thin, whitish layer between packed RBCs and plasma after centrifugation
  • Contains all WBCs + platelets

Physical & Chemical Characteristics of Blood

• Temperature: \approx 38\,^\circ\text{C} ( 100.4\,^\circ\text{F} ), slightly warmer than core body T°
• Viscosity: \sim5× that of water
  • Viscosity ↑ with dehydration → ↑ cardiac workload ("water → syrup → molasses" analogy)
• pH: 7.35\text{–}7.45 (slightly alkaline)
  • < 7.35 ⇒ acidemia; > 7.45 ⇒ alkalemia (even though both values still sit near neutral on standard pH scale)
• Blood volume
  • ≈ 7\% of body mass
  • Formula: \text{Blood Vol}\,(L)=\text{Body Wt}\,(kg)\times0.07
  • Adults: 4\text{–}6\;L overall; males tend toward the upper end because of larger average body size

Functions of Blood

1 Transportation

• Nutrients to tissues (glucose, amino acids, lipids, vitamins, minerals)
• Gases: O2 to, CO2 away from cells; nitrogen also present in solution
• Metabolic waste → kidneys & liver for removal
• Hormones & endocrine peptides to target tissues
• Stem cells circulating from bone marrow

2 Regulation

• Fluid Balance
  • Plasma water reservoir (≈92\% of plasma) can be borrowed during dehydration → ↓ blood volume & pressure
• pH Buffering
  • Hemoglobin accepts or donates H$^+$ to stabilize extracellular pH
• Thermoregulation
  • Heat distribution: vasodilation (heat loss) vs vasoconstriction (heat conservation)

3 Defense

• Inflammation limits spread of infection & starts repair
• Leukocytes destroy microbes & malignant cells; neutralize toxins
• Platelets start clot formation and secrete chemicals that modulate immunity & healing

Movement of Substances In/Out of Capillaries

• Capillaries possess inter-endothelial gaps → exchange site
• Driving forces
  • Hydrostatic pressure ( = blood pressure) pushes fluid out
  • Concentration gradients drive diffusion (high → low)
  • Osmosis = water diffusion specifically (high H_2O concentration → low)
• Net result: more fluid leaves than re-enters; excess collected by lymphatic vessels and returned to circulation

Plasma – Detailed Composition

• Makes up 46\text{–}63\% of whole blood
• \approx92\% = water
• Remaining \approx8\% solute fraction includes:
  • Plasma proteins (major contributor to solute concentration & viscosity)
  • Electrolytes (Na$^+$ ≈ 90\% of extracellular cations, K$^+$, Ca$^{2+}$…)
  • Nutrients, gases, nitrogenous wastes, hormones, enzymes

Plasma Proteins (do NOT leave capillaries)

Production Sites

• > 90\% of plasma proteins synthesized by liver
  • Liver pathologies (cirrhosis, hepatitis) ↓ production → bleeding disorders, edema, transport deficits
• Gamma globulins (antibodies) : secreted by plasma cells (differentiated B-lymphocytes)
• Peptide hormones : secreted by respective endocrine glands

Nitrogenous & Other Solutes

• Nitrogenous wastes (urea, uric acid) – from protein / nucleic-acid catabolism
• Nutrients – glucose, amino acids, fatty acids, cholesterol, phospholipids, vitamins, minerals absorbed in the gut
• Dissolved gases – O2, CO2, N_2

Formed Elements & Hematopoiesis

• Erythrocytes (RBCs) – >99.9\% of cellular fraction
• Leukocytes (WBCs) – immune cells; five major types
  • Neutrophils, Eosinophils, Basophils, Monocytes, Lymphocytes (B & T)
• Platelets (Thrombocytes) – cytoplasmic fragments essential for hemostasis
• Hematopoiesis (hemato = blood, poiesis = production) produces all formed elements – will be addressed in coming lectures
• Fractionation = laboratory separation of whole blood; diagnostic form is the hematocrit

Blood-Volume & Hematocrit Calculations – Worked Example

1. Patient weighs 70\;kg.
2. Estimated blood volume = 70 \times 0.07 = 4.9\;L.
3. Centrifuged sample yields Hct =44\%.
   • Formed elements volume ≈ 0.44 \times 4.9 = 2.16\;L.
   • Plasma volume ≈ 4.9 - 2.16 = 2.74\;L (or 100-44 = 56\% of 4.9 L).

Clinical & Real-World Connections

• Dehydration → ↓ plasma water → ↑ viscosity → ↑ cardiac workload & ↓ blood pressure
• Liver failure → ↓ albumin & clotting factors → peripheral edema, ascites, spontaneous bleeding
• Blood donation / hemorrhage – acute ↓ volume triggers vasoconstriction, ↑ HR, mobilization of interstitial fluid into plasma
• ADH (antidiuretic hormone), previously studied, conserves water → affects plasma water fraction and BP

Key Terminology Recap (Study-Sheet Ready)

• Whole blood = plasma + formed elements
• Hematocrit (Hct) = % formed elements (normal 37\text{–}54\%)
• Buffy coat = WBC + platelets layer in centrifuged sample
• Viscosity = thickness; blood ≈5× water
• Osmolarity = solute concentration; largely determined by albumin & Na$^+$$$
• Hydrostatic pressure = blood pressure at capillary wall
• Hematopoiesis = production of formed elements
• Thrombocyte = platelet; thromb = clot, cyte = cell
• Agglutination vs Clotting (future lecture): agglutination = antibody-mediated RBC clumping; clotting = fibrin mesh hemostasis

Self-Check / “Time-Out” Prompts
• Can you calculate blood volume from body mass?
• Explain why dehydration changes blood viscosity and BP.
• List the three major plasma proteins and their roles.
• Describe the forces that govern capillary exchange.