3.2 The Cardiovascular System: Blood Distribution and Blood Flow

Vocabulary flashcards covering cardiovascular hemodynamics, blood distribution, pressure regulation, vascular resistance mechanisms, flow velocity, and venous return pumps.

Blood reservoirs

The systemic veins and venules that hold the largest portion of the body's blood at rest ($64\%$).

Blood flow

The volume of blood that flows through any tissue in a given time period, typically expressed in units of $mL/min$.

Factors affecting blood flow

The four primary variables governing the movement of blood: blood pressure, vascular resistance, velocity of blood flow, and venous return.

Systolic blood pressure (SBP)

The highest arterial pressure reached during ventricular systole.

Diastolic blood pressure (DBP)

The lowest arterial pressure reached during ventricular diastole.

Sphygmomanometer

The device used clinically to measure arterial blood pressure.

Blood pressure difference ($\Delta P$)

The pressure gradient between two points along a vessel ($P_1 - P_2 = \Delta P$); as $\Delta P$ increases, blood flow increases.

Normal blood pressure

A blood pressure category defined by a systolic blood pressure less than $120\,mmHg$ and a diastolic blood pressure less than $80\,mmHg$.

Prehypertension

A blood pressure category characterized by a systolic blood pressure of $120\text{–}139\,mmHg$ or a diastolic blood pressure of $80\text{–}89\,mmHg$.

High Blood Pressure (Hypertension) Stage 1

A blood pressure category characterized by a systolic blood pressure of $140\text{–}159\,mmHg$ or a diastolic blood pressure of $90\text{–}99\,mmHg$.

Vascular resistance

The friction encountered by blood as it passes through vessels, determined by lumen diameter, blood viscosity, and total vessel length.

Systemic vascular resistance (SVR)

All of the vascular resistance offered by systemic blood vessels (also known as total peripheral resistance, TPR); it is controlled primarily by arteriole vasoconstriction and vasodilation, not by arteries or veins.

Vessel radius-resistance relationship

The mathematical relationship where vascular resistance ($R$) is inversely proportional to the fourth power of the vessel radius ($r$), represented as $R \propto \frac{1}{r^4}$.

Blood flow formula

The equation relating flow to pressure gradient and resistance: $\text{Blood Flow} = \frac{\Delta P}{R} = \Delta P \times r^4$.

Vasoconstriction

A decrease in blood vessel radius that elevates vascular resistance, decreases blood flow, and increases friction because more blood cells contact the vessel wall.

Vasodilation

An increase in blood vessel radius that lowers vascular resistance, increases blood flow, and reduces friction because fewer blood cells contact the vessel wall.

Blood viscosity

The thickness of blood, which increases with elevated red blood cell counts (such as from EPO injection) or dehydration, and decreases during hemorrhage.

Total blood vessel length effect

The physiological factor wherein an increase in total vessel length—such as from additional vessels supporting adipose tissue in obesity—increases vascular resistance and elevates hypertension risk.

Velocity of blood flow

The speed of blood movement ($cm/s$), which is inversely related to the total cross-sectional area of the vascular bed.

Capillary cross-sectional area and velocity

The extensive total combined area ($4500\text{–}6000\,cm^2$) of systemic capillaries that slows blood velocity to approximately $0.1\,cm/s$, allowing efficient exchange of substances between blood and tissues.

Circulation time

The time required for blood to complete a circuit through the systemic and pulmonary systems, which is about $1\text{ minute}$ in a resting individual.

Venous return

The volume of blood returning to the heart through systemic veins, driven by cardiac pressure, the skeletal muscle pump, and the respiratory pump.

Skeletal muscle pump

A mechanism of venous return where skeletal muscle contractions compress deep veins, forcing blood upward through the proximal valve while distal valves close to prevent backward flow.

Respiratory pump during inhalation

The phase of the respiratory pump where the diaphragm contracts and flattens, increasing intra-abdominal pressure to compress the inferior vena cava and pump venous blood into the right atrium.

Respiratory pump during exhalation

The phase of the respiratory pump where the diaphragm relaxes and domes upward, decreasing intra-abdominal pressure to produce a vacuum effect that pulls blood from lower limbs into the inferior vena cava.