Overview
This lecture introduces the functions and properties of blood as part of the cardiovascular system, emphasizing its roles in transport, regulation, and protection.
Functions of Blood
- Blood transports oxygen, nutrients, waste, and hormones throughout the body.
- Blood helps regulate body temperature by holding and dispersing heat due to its high water content.
- Blood maintains pH homeostasis (normal pH: 7.35–7.45) using buffering systems like bicarbonate.
- Blood regulates its fluid content, which affects blood pressure and maintains proper circulation.
- Blood protects against blood loss via clotting (platelets) and infection via white blood cells and antibodies.
Regulation by Blood
- Water in blood helps absorb and distribute heat without large temperature changes.
- Blood disperses heat to the skin for cooling through blood flow adjustments.
- The bicarbonate buffer system (HCO₃⁻ and H₂CO₃) maintains pH by neutralizing excess acids or bases.
- Blood proteins (mainly albumin) create osmotic pressure to draw water back into vessels, ensuring proper fluid balance and blood pressure.
Structure and Composition of Blood
- Blood is a connective tissue with cells, a fluid matrix (plasma), and fibers visible only during clotting (fibrin).
- Three main types of blood cells: red blood cells (transport oxygen), white blood cells (immune defense), and platelets (clotting).
- Blood plasma (55% of blood) is 90% water and contains solutes: nutrients, gases, hormones, proteins, and ions.
- Red blood cells make up most of the formed elements (45% of blood), with less than 1% each for white blood cells and platelets.
Plasma Proteins and Ions
- Proteins are the most abundant plasma solute by mass, mostly made by the liver; they transport non-polar substances, maintain osmotic pressure, and assist in clotting.
- Key plasma proteins: albumin (main transporter), globulins (transport, immune functions), fibrinogen (clotting), antibodies (immune defense).
- Ions (like bicarbonate) are most abundant by number; they help buffer pH and maintain proper osmotic conditions.
Key Terms & Definitions
- Plasma — Liquid component of blood, mostly water, that carries dissolved substances.
- Formed Elements — Collective term for blood cells: red blood cells, white blood cells, platelets.
- Osmotic Pressure — The force exerted by solutes (mainly proteins) drawing water into blood vessels.
- Bicarbonate (HCO₃⁻) — Ion that buffers blood pH.
- Albumin — Major plasma protein responsible for transport and maintaining osmotic pressure.
- Fibrin(ogen) — Protein that forms fibers during blood clotting.
Action Items / Next Steps
- Review the characteristics and functions of blood listed in the module's first link.
- Learn the key buffer system equations and the roles of plasma proteins.
- Prepare for upcoming lectures on the heart and blood vessels.