Cardiovascular System: Blood Vessels and Circulation Study Notes

Cardiovascular System

Blood Vessels and Circulation

The cardiovascular system is responsible for the transport of blood, nutrients, gases, and waste products throughout the body. Blood vessels are the conduits through which blood flows, and they are classified into arteries, veins, and capillaries based on their structure and function.

Blood Vessels

Types of Blood Vessels

• Arteries: Carry blood away from the heart, typically oxygenated except for pulmonary arteries.

• Veins: Carry blood toward the heart, typically deoxygenated except for pulmonary veins.

Vessel Wall Structure

Blood vessel walls are composed of three main layers, each with distinct functions:

• Lumen: The central blood-containing space.

• Tunica Intima:

  • Innermost smooth layer.

  • Prevents blood clots by secreting biochemicals.

  • Releases nitric oxide, relaxing smooth muscle.

• Tunica Media:

  • Middle layer.

  • Strong and flexible, contains smooth muscle and elastic fibers.

  • Responsible for vasoconstriction and vasodilation.

• Tunica Externa:

  • Outermost layer.

  • Composed of connective tissue, irregular elastin, and collagen.

  • Provides structural support and protection.

Capillaries

Structure and Function

Capillaries are the smallest-diameter blood vessels and serve as the primary sites for the exchange of nutrients, gases, and waste products between blood and tissues.

• Connect smallest arterioles and venules.

• Facilitate exchange of nutrients and gases.

• The density of capillary networks is higher in tissues with greater metabolic rates.

• If all capillaries in an adult were unwound, they would measure approximately 25,000–60,000 miles in length.

Pathologies

Common Blood Vessel Disorders

• Pulmonary Edema:

  • Fluid accumulation in the lungs.

  • Results in suffocation due to impaired gas exchange.

• Peripheral Edema:

  • Fluid buildup in the body, especially in extremities.

  • Caused by a weak right ventricle, leading to blood backing up into the body.

  • Results in ascites (painful swelling of the abdomen).

Venules & Veins

Structure and Function

• Venules are microscopic vessels that continue from capillaries and merge into veins.

• Veins have valves that prevent backflow and aid in blood returning to the heart.

Blood Pressure Factors

Determinants of Blood Pressure

• Vascular Resistance:

  • Determined by luminar diameter; smaller diameter increases resistance.

• Blood Viscosity:

  • Greater viscosity leads to greater resistance.

• Systolic vs. Diastolic Pressure:

  • Systolic pressure is the peak pressure during heart contraction.

  • Diastolic pressure is the minimum pressure during heart relaxation.

• Hypertension vs. Hypotension:

  • Hypertension: abnormally high blood pressure.

  • Hypotension: abnormally low blood pressure.

Blood Pressure

Key Concepts

• Stroke Volume: The volume of blood that enters the arterial system per heartbeat. Example: Average male at rest: 70 mL.

• Cardiac Output: The volume of blood discharged by the heart per minute. Formula: $\text{Cardiac Output} = \text{Stroke Volume} \times \text{Heart Rate}$

• Blood Volume: Total blood volume varies but is about 8% of body weight (~5L in adults).

Arteries/Veins

Highlighted Arteries and Veins

Refer to the provided handout for detailed information on specific arteries and veins.

Additional info:

• Vasoconstriction refers to the narrowing of blood vessels, increasing blood pressure.

• Vasodilation refers to the widening of blood vessels, decreasing blood pressure.

• Capillary exchange is driven by hydrostatic and osmotic pressures, as illustrated in the provided diagram.