Blood Overview

General Properties of Blood

Blood is a fluid connective tissue that plays a vital role in maintaining homeostasis and supporting physiological functions throughout the body. An average adult has about 5 liters of blood, which constitutes approximately 8% of total body weight and circulates continuously through blood vessels.

• Blood composition: Blood consists of two major components: plasma (the liquid extracellular matrix) and formed elements (cells and cell fragments suspended in plasma).

• Visible layers: When blood is centrifuged, it separates into three layers: plasma (top), buffy coat (middle, containing leukocytes and platelets), and erythrocytes (bottom).

• Formed elements: Include erythrocytes (red blood cells), leukocytes (white blood cells), and platelets (cell fragments).

Example: A blood sample in a test tube will show plasma as a pale yellow liquid at the top, a thin buffy coat in the middle, and a dense layer of erythrocytes at the bottom.

Functions of Blood

Major Physiological Roles

Blood performs several essential functions necessary for life and health.

• Exchanging gases: Transports oxygen from the lungs to tissues and carbon dioxide from tissues to the lungs.

• Distributing solutes: Plasma carries ions, nutrients, hormones, and wastes, helping regulate ion concentrations in tissues.

• Performing immune functions: Transports leukocytes and immune system proteins throughout the body to defend against pathogens.

• Maintaining body temperature: Blood absorbs and distributes heat produced by metabolic reactions.

• Blood clotting: Platelets and certain proteins form clots to seal damaged blood vessels and prevent blood loss.

• Preserving acid-base homeostasis: Blood maintains a pH between 7.35 and 7.45 using buffering systems.

• Stabilizing blood pressure: Blood volume is a major factor in determining blood pressure.

Example: During exercise, blood redistributes heat from active muscles to the skin, helping regulate body temperature.

Blood Plasma

Composition and Functions

Plasma is the liquid portion of blood, making up about 55% of its volume. It is primarily water (about 90%), which determines the viscosity (thickness) of blood.

• Water: Acts as a solvent and helps transport substances.

• Plasma proteins: Make up about 7% of plasma volume and have various functions:

  • Albumin: Maintains osmotic pressure and transports solutes.

  • Globulins: Produced by leukocytes; function in immunity and transport hydrophobic compounds.

  • Fibrinogen: Involved in blood clotting.

• Other solutes: Include nutrients (amino acids, glucose), electrolytes, gases (oxygen, carbon dioxide), and wastes.

Example: Albumin helps retain water in the bloodstream, preventing excessive fluid loss to tissues.

Table: Major Components of Plasma and Their Functions

Clinical Note: Cirrhosis

Liver Disease and Plasma Proteins

Cirrhosis is a chronic liver disease caused by factors such as cancer, alcoholism, or viral hepatitis. It leads to decreased production of plasma proteins, resulting in reduced colloidal osmotic pressure and fluid loss to tissues (edema), especially in the abdomen (ascites). Clotting factor deficiency also causes easy bruising and delayed clotting.

• Symptoms: Edema, bruising, delayed clotting

• Consequences: Severe cases may be fatal due to impaired blood clotting and fluid imbalance

Example: A patient with cirrhosis may develop ascites and be at increased risk for bleeding.

*Additional info: Academic context and table structure inferred from fragmented notes and images.*