Blood and Its Components

Blood Overview

• Blood consists of arteries, arterioles, capillaries, venules, and veins, each playing a crucial role in systemic and pulmonary circulation.

• Arterial blood flow: Oxygenated blood moves from the Artery → Arteriole → Capillary (where oxygen exchange occurs) → Venule → Vein (carrying deoxygenated blood back to the heart).

• Pulmonary circuit: This is a closed loop within the circulatory system where blood is oxygenated in the lungs, involving the heart and lungs.

• Systemic circuit: Includes all circulation outside the pulmonary circuit, delivering oxygen and nutrients to tissues throughout the body and removing waste products.

Detailed Explanation of Blood Components and Functions

• Plasma: Acts as a transportation medium for various substances, including nutrients, hormones, and waste products. It also contains buffering compounds that help maintain blood pH.

• Blood pH: Precisely maintained between 7.35 and 7.45, which is crucial for enzyme activity and overall cellular function; this range must be memorized for physiological relevance.

• Bloodstream functions include:

  • Self-sealing mechanisms (coagulation) to prevent excessive bleeding following injury.

  • Integral involvement in the body's immunological responses, including transporting immune cells and antibodies.

  • Distribution of body temperature, with heat primarily generated by the liver and distributed through the bloodstream to maintain thermal homeostasis.

Plasma and Formed Elements: Composition and Significance

• Hematocrit: Typically around 45% in a spun tube of blood, representing the volume of red blood cells, which is critical for oxygen-carrying capacity.

• Plasma volume: Slightly greater than 50% of total blood volume, providing the fluid matrix for blood cells and dissolved substances.

• Dehydration: Causes a decrease in plasma volume, leading to a higher concentration of blood components and making the blood "sticky," which can impair circulation.

• Plasma content: Primarily composed of water but also includes essential proteins, electrolytes, nutrients, hormones, and waste products.

• Formed elements: Include red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes), each with specific roles in oxygen transport, immune defense, and blood clotting.

Plasma Proteins: Types and Functions

• Plasma proteins: Constitute about 7% of blood composition and include albumin, globulins, and fibrinogen, each with unique functions.

  • Albumin: Crucial for maintaining colloidal osmotic pressure, which prevents fluid leakage from blood vessels; it acts like a "water sponge" to retain fluid within the bloodstream.

  • Insufficient albumin: Leads to edema (swelling) due to poor water reabsorption into the blood, causing fluid accumulation in tissues.

  • Globins: A diverse group including immunoglobulins (antibodies for the immune system) and transport globins like transferrin (for iron transport).

  • Relationship to HDL/LDL ratios (cholesterol): These lipoproteins are critical for cholesterol transport; imbalances can indicate cardiovascular risk.

  • HDL: High-density lipoprotein, often referred to as "good cholesterol," helps remove cholesterol from arteries.