Cardiovascular System: Blood Vessels – Structure, Function, and Hemodynamics

Chapter 18: The Cardiovascular System – The Blood Vessels

Learning Objectives

• Describe the location and structure of major arteries, veins, and capillaries.

• Explain the physiology of blood flow.

• Discuss the factors that regulate blood pressure.

• Summarize the process of atherosclerotic plaque formation.

Blood Vessels: General Overview

Vasculature and Its Functions

The vasculature consists of billions of blood vessels that transport blood to tissues for exchange of gases, nutrients, and wastes, and then return it to the heart. Collectively, blood vessels measure over 60,000 miles in length.

• Regulate blood flow to tissues

• Control blood pressure

• Secrete a variety of chemicals

Blood flow pathway: veins → heart → arteries → capillaries

Overview of Arteries, Veins, and Capillaries

Functional Classification

• Arteries – Distribution System: Carry blood away from the heart, branching into vessels of progressively smaller diameter. In the pulmonary circuit, arteries carry deoxygenated blood; in the systemic circuit, they carry oxygenated blood.

• Capillaries – Exchange System: Smallest diameter vessels, forming branching networks called capillary beds. They facilitate exchange of gases, nutrients, and wastes between blood and tissues.

• Veins – Collection System: Drain blood from capillary beds and return it to the heart. Small veins merge to become larger veins. In the pulmonary circuit, veins transport oxygenated blood; in the systemic circuit, veins transport deoxygenated blood.

Structure and Function of Arteries and Veins

Specialized Receptors

• Baroreceptors: Pressure receptors found in the aorta and common carotid artery. They detect changes in blood pressure.

• Chemoreceptors: Detect concentrations of blood oxygen, carbon dioxide, and hydrogen ions, helping regulate respiratory and cardiovascular responses.

Introduction to Hemodynamics

Physiology of Blood Flow

Hemodynamics is the study of blood flow in the cardiovascular system. The heart creates a pressure gradient that drives blood through the vessels, with the highest pressure near the heart.

• Blood Pressure: The outward force exerted by blood on vessel walls. Ranges from about 120 mm Hg in large systemic arteries to 10–15 mm Hg in large systemic veins.

• Blood Flow: The volume of blood that flows per minute (L/min). Closely related to cardiac output (CO).

Key Equation:

• $\text{Blood Pressure} = \text{Cardiac Output} \times \text{Peripheral Resistance}$

Additional info: Cardiac output (CO) is the amount of blood the heart pumps per minute, and peripheral resistance is the opposition to blood flow due to vessel diameter, length, and blood viscosity.