Overview
This lecture introduces the general characteristics, functions, and composition of blood, focusing on key cellular components and the concept of hematocrit.
General Characteristics of Blood
- Blood color varies with oxygen content: bright red (arterial, high oxygen) or dark maroon (venous, low oxygen).
- Blood is slightly alkaline with a pH of 7.35–7.45.
- Blood temperature is about 2°C higher than average body temperature.
- Average blood volume: males 5–6 liters, females 4–5 liters, mainly due to body size differences.
Functions of Blood
- Blood transports oxygen, nutrients, hormones, and waste products throughout the body.
- It regulates body temperature by distributing heat and maintaining core temperature.
- Proteins in blood help maintain fluid volume and blood pressure.
- Blood provides protection through white blood cells (immune defense) and platelets (clotting to prevent blood loss).
Composition of Blood
- Blood is composed of a liquid component (plasma) and solid components (formed elements).
- Plasma (~55%): straw-colored fluid containing water, dissolved nutrients, hormones, waste products, and clotting factors.
- Formed elements (~45%): red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes).
- Upon centrifugation, blood separates into plasma (top), buffy coat (middle, <1%, white blood cells and platelets), and red blood cells (bottom).
Functions of Formed Elements
- Red blood cells (erythrocytes): transport oxygen using hemoglobin.
- White blood cells (leukocytes): immune system defense against infection.
- Platelets (thrombocytes): cell fragments involved in blood clotting to prevent blood loss.
Hematocrit
- Hematocrit is the percentage of blood volume made up of red blood cells (~45%).
- Clinically, hematocrit reflects the oxygen-carrying capacity of the blood.
Key Terms & Definitions
- Erythrocyte — red blood cell; transports oxygen using hemoglobin.
- Leukocyte — white blood cell; involved in immune defense.
- Thrombocyte (Platelet) — cell fragment; aids in blood clotting.
- Plasma — liquid component of blood; contains dissolved substances.
- Formed Elements — collective term for blood's cellular components.
- Hematocrit — percentage of blood volume comprised of red blood cells.
Action Items / Next Steps
- Complete the activity on blood composition and hematocrit in the unit folder.
- Prepare for the next class, which will focus on platelets and the blood clotting process.