Blood: Structure, Function, and Disorders

Introduction

Blood is a specialized connective tissue that plays a vital role in maintaining homeostasis within the human body. It serves as the primary transport medium for nutrients, gases, hormones, and waste products, and is essential for regulation and protection mechanisms.

Functions of Blood

Transport

Blood acts as the life-sustaining vehicle of the cardiovascular system, performing several key transport functions:

• Delivery of Oxygen and Nutrients: Blood transports oxygen (O2) from the lungs and nutrients from the digestive tract to all body cells.

• Removal of Metabolic Wastes: Blood carries carbon dioxide (CO2) to the lungs for exhalation and transports other metabolic wastes to the kidneys for elimination.

• Transport of Hormones: Blood delivers hormones from endocrine organs to target tissues and organs throughout the body.

Example: Insulin, a hormone produced by the pancreas, is transported via blood to regulate glucose uptake in tissues.

Regulation

Blood helps regulate several critical physiological parameters:

• Body Temperature: Blood absorbs and distributes heat throughout the body, helping to maintain a stable internal temperature.

• pH Balance: Blood contains buffers, such as bicarbonate ions, to maintain normal pH (7.35–7.45).

• Fluid Volume: Blood proteins and salts help maintain adequate fluid volume in the circulatory system.

Equation: The bicarbonate buffer system is represented as:

Protection

Blood provides protection against blood loss and infection:

• Prevention of Blood Loss: Platelets and plasma proteins initiate clot formation to prevent excessive bleeding.

• Defense Against Infection: White blood cells (leukocytes) and antibodies defend the body against pathogens.

Example: Neutrophils, a type of white blood cell, rapidly respond to bacterial infections by phagocytizing invading microbes.

Composition of Blood

Plasma

Plasma is the straw-colored, sticky fluid portion of blood, making up about 55% of total blood volume. It consists of:

• Water (about 90%): Acts as a solvent for carrying other substances.

• Plasma Proteins: Includes albumin (maintains osmotic pressure), globulins (immune function), and fibrinogen (clotting).

• Solutes: Electrolytes (Na+, K+, Ca2+, Cl-, HCO3-), nutrients, gases, hormones, and waste products.

Formed Elements

The formed elements of blood include:

• Erythrocytes (Red Blood Cells, RBCs): Transport oxygen and carbon dioxide.

• Leukocytes (White Blood Cells, WBCs): Provide defense against disease.

• Platelets (Thrombocytes): Involved in blood clotting.

Key Terms and Definitions

• Hemoglobin: The oxygen-carrying protein in erythrocytes, composed of globin and heme groups.

• Plasma: The liquid, non-cellular component of blood.

• Leukocyte: A white blood cell involved in immune defense.

• Platelet: A cell fragment that plays a crucial role in blood clotting.

Summary Table: Functions of Blood

Additional info: These notes are based on Chapter 17 of Marieb & Hoehn's "Human Anatomy & Physiology" and are suitable for college-level Anatomy & Physiology students.