Comprehensive Study Notes on Blood Composition, Functions, and Characteristics

Components and Separation of Blood

• Blood is a complex fluid that separates into three primary layers when processed, organized by density from top to bottom:   - Plasma: The topmost layer, which is the lightest and has a watery consistency. It accounts for approximately $55\%$ of whole blood.   - Buffy Coat: A thin, middle layer that makes up less than $1\%$ of the blood volume. It contains leukocytes (white blood cells) and platelets, which are essential for immune function and clotting.   - Erythrocytes: The bottom layer, also known as red blood cells (RBCs). These are the most dense components and comprise approximately $45\%$ of whole blood.
• Collectively, blood is composed of plasma (the liquid portion) and formed elements (the cellular portion).

Correcting Misconceptions: Blood Coloration

• A common myth suggests that deoxygenated blood is blue. This is incorrect.
• Blood is always red, regardless of its oxygenation state.
• Oxygenated blood (oxygen-rich) is a bright, scarlet shade of red.
• Deoxygenated blood (oxygen-poor) is a darker shade of red.

Principal Functions of Blood

• Blood serves as the body’s internal transport system and performs three primary roles:

Transport Functions

• Oxygen and Nutrients: Delivering oxygen for cellular respiration and nutrients to all body cells.
• Waste Elimination: Transporting metabolic waste products to the lungs and kidneys for removal from the body.
• Hormone Delivery: Carrying hormones from the endocrine system glands to their specific target organs.

Regulatory Functions

• Body Temperature: Maintaining thermal balance by absorbing and distributing heat throughout the body.
• pH Balance: Maintaining a normal pH range (typically between $7\text{.35}$ and $7\text{.45}$, though broad ranges are sometimes cited as $7$ to $7\text{.4}$).
• Buffer Systems: Utilizing the bicarbonate buffer system to neutralize acids (hydrogen ions) or bases, providing an "alkaline reserve" of bicarbonate ions. This system actively counters external influences, such as drinking alkaline water (pH $8$, $9$, or $10$), to return the blood to a neutral state.

Protective Functions

• Preventing Blood Loss: Initiating clot formation via plasma proteins and platelets when a vessel is damaged.
• Preventing Infection: Carrying agents of immunity, including antibodies, complement proteins, and white blood cells, to defend against foreign invaders.

Histological Classification: Blood as Connective Tissue

• Blood is formally classified as a connective tissue, sharing properties with other tissues like bone and cartilage.
• Reasoning for Classification:   - Like bone (containing osteoblasts and phosphate in the matrix) and cartilage (containing chondrocytes), blood is composed of specialized cells suspended in an extracellular matrix.   - The cellular portion consists of formed elements (red blood cells, white blood cells, and platelets).   - The extracellular matrix is the liquid plasma.   - Tissue Fibers: Unlike solid connective tissues, the fibers in blood are soluble proteins that only become visible as solid fibers during the process of blood clotting.

Physical Characteristics and Quantitative Data

• Viscosity: Blood is an opaque, viscous fluid with a metallic taste. It is approximately $5$ times more viscous than water, primarily due to the presence of erythrocytes ($45\%$ of blood volume).
• pH Level: The physiological pH of blood is maintained between $7\text{.35}$ and $7\text{.45}$.
• Weight and Volume:   - Blood accounts for approximately $8\%$ of total body weight.   - In average adult males, the blood volume is approximately $5$ to $6\,L$.   - In average adult females, the blood volume is approximately $4$ to $5\,L$.

Detailed Composition of Blood Plasma

• Plasma is a straw-colored, sticky fluid consisting of approximately $90\%$ water.
• It contains over $100$ different dissolved solutes, including:   - Nutrients: Glucose, carbohydrates, and amino acids.   - Gases: Dissolved oxygen and carbon dioxide (noting that carbon dioxide is handled carefully to avoid bubbling in the blood).   - Hormones: Including lipid-soluble hormones carried by proteins.   - Wastes: Such as urea, creatinine, and uric acid.   - Inorganic Ions: Various electrolytes required for cellular function.   - Plasma Proteins: The most abundant solutes, mostly produced by the liver.

The Specific Role of Albumin

• Albumin is the most prominent plasma protein, accounting for $60\%$ of the total plasma protein content.
• Functions of Albumin:   - Carrier Protein: Transports lipid-soluble hormones that cannot dissolve directly in the watery plasma.   - Blood Buffer: Acts to help maintain the constant pH of blood.   - Osmotic Pressure Management: Albumin is a large, negatively charged protein that remains inside the capillaries when water and nutrients are forced out to feed the tissues. Because it is polar and negatively charged, it creates osmotic pressure that attracts water back into the blood vessel. Without sufficient albumin, water would remain in the tissues, leading to edema (swelling).