Chapter 19: The Cardiovascular System – Blood

Fluids of the Body

Main Body Fluids

The cells of the body are serviced by two primary fluids: blood and interstitial fluid. These fluids are essential for the transport of nutrients, gases, and wastes throughout the body.

• Blood: Composed of plasma and a variety of cells, blood transports nutrients and wastes to and from body tissues.

• Interstitial Fluid: This fluid bathes the cells of the body, providing a medium for the exchange of substances between blood and cells.

• Diffusion: Nutrients and oxygen diffuse from the blood into the interstitial fluid and then into the cells, while wastes move in the reverse direction.

• Hematology: The study of blood and blood disorders.

Functions of Blood

Major Roles of Blood

Blood performs several vital functions necessary for maintaining homeostasis and overall health.

• Transportation: Blood transports oxygen (O2), carbon dioxide (CO2), metabolic wastes, nutrients, heat, and hormones throughout the body.

• Regulation:

  • Helps regulate pH through buffers.

  • Regulates body temperature via the coolant properties of water and vasodilatation of surface vessels to release heat.

  • Maintains water content of cells by interacting with dissolved ions and proteins.

• Protection: Blood protects the body from disease (immune response) and prevents loss of blood through clotting mechanisms.

Physical Characteristics of Blood

Properties and Volume

Blood has unique physical and chemical properties that distinguish it from other body fluids.

• Viscosity: Blood is thicker (more viscous) than water and flows more slowly.

• Temperature: The temperature of blood is approximately 100.4°F (38°C).

• pH: Blood is slightly alkaline, with a pH of 7.4 (normal range: 7.35–7.45).

• Body Weight: Blood constitutes about 8% of total body weight.

• Blood Volume:

  • Average male: 5 to 6 liters

  • Average female: 4 to 5 liters

• Homeostasis: Hormonal negative feedback systems maintain constant blood volume and osmotic pressure.

Major Formed Elements of Blood

Blood Cell Types

Blood contains several types of formed elements, each with specialized functions.

• Erythrocytes (Red Blood Cells): Responsible for oxygen transport.

• Leukocytes (White Blood Cells): Involved in immune defense.

• Platelets (Thrombocytes): Cell fragments essential for blood clotting.

Example: The provided image (Slide 1) shows a microscopic view of blood, labeling erythrocytes, platelets, and leukocytes.

Additional info:

• Hematology is a branch of medicine focused on the study of blood, blood-forming organs, and blood diseases.

• Blood's viscosity is due to the presence of cells and plasma proteins, which also contribute to its osmotic pressure.