Blood Functions Overview

Blood Functions

• Transport:
  • Carries oxygen, carbon dioxide, nutrients, waste products, hormones.
  • Wastes are transported to kidneys, liver, and lungs for elimination.
  • Blood is part of the extracellular compartment, along with interstitial fluid.
• Regulation:
  • Maintains pH, temperature, blood pressure, volume, and osmotic pressure.
  • pH regulation is mediated by bicarbonate ions (HCO3-), electrolytes, and proteins.
  • Temperature regulation is facilitated by blood's high specific heat capacity (due to water content).
  • Blood pressure and volume are closely related: increased blood volume leads to increased blood pressure.
  • Osmotic pressure is controlled by proteins and electrolytes, influencing fluid movement between compartments.
• Protection:
  • Clotting prevents excessive bleeding through coagulation.
  • Immune cells (WBCs), complement system, and immunoglobulins protect against pathogens.
  • Proteins in blood help transport ions, preventing interactions with cells that could alter their structure and function.

Blood Composition

• Plasma:
  • Mostly water (91.5%).
  • Contains solutes: gases, proteins (albumin, fibrinogen, globulins), and electrolytes (mainly NaCl).
  • Albumin is the major protein and contributes to blood's osmotic pressure.
• Formed Elements:
  • Mostly red blood cells (RBCs), constituting 99% of formed elements.
  • White blood cells (WBCs) and platelets make up the remaining 1%.
  • Normal RBC count: 4.8-5.4 million/µL (higher in males).
  • Normal WBC count: 5000-10000/µL.
  • Normal platelet count: 150,000-400,000/µL.
  • Most abundant WBCs are neutrophils, followed by lymphocytes, monocytes, eosinophils, and basophils. Each type has specific functions.

Blood Physical Characteristics

• Mimics water, as water is the solvent of blood.
• Temperature: 38°C (slightly higher than oral or rectal temperature).
• Viscosity: More viscous than water (sticky).
• pH: Slightly alkaline (7.35-7.45), maintained within a narrow range.
• Color: Varies from bright red (oxygenated) to dark red (deoxygenated).
• Blood volume: 5-6 L in males, 4-5 L in females (varies with body size).

Blood Volume Regulation

• Hormonal regulation: RAAS, ANP, ADH.
• RAAS (Renin-Angiotensin-Aldosterone System): Controls sodium (Na+) levels, influencing water reabsorption or excretion by kidneys.
• ANP (Atrial Natriuretic Peptide): Increases Na+ excretion, reducing blood pressure (acts as a natural antihypertensive).
• ADH (Anti-Diuretic Hormone) or Vasopressin: Decreases urine production, conserving water in cases of low blood pressure or dehydration.

Blood Sampling

• Different types of blood sampling tubes are available, each suited for specific laboratory tests.
• Common procedures:
  • Venipuncture: Most common and easiest, obtained from veins.
  • Finger stick or heel stick: Used for capillary blood samples.
  • Arterial stick: Used for arterial blood samples, essential for accurate oxygen saturation measurements.

Formed Elements Under Microscopes

• Light microscope:
  • RBCs appear as biconcave discs.
  • WBCs appear as large, multi-lobed cells with varying colors (blue to red).
  • Platelets appear as small, fragmented cells.
• Electron microscope:
  • Reveals the biconcave structure of RBCs, which increases surface area and is possible because RBCs lack a nucleus.

Interstitial Fluid

• Part of the extracellular fluid (ECF) continuously renewed and modified by blood.
• Provides the environment for cells to acquire nutrients and eliminate waste products.

This quiz explores the essential functions of blood, focusing on its roles in transport, regulation, and protection. Questions cover how blood carries various substances, maintains homeostasis, and protects the body from pathogens. Test your knowledge on the critical functions that blood performs in human physiology.