Cardiovascular System – Exam Review

Cardiovascular Physiology – MAP, CO, TPR, Vascular Control & Capillary Dynamics

Why must blood be pressurized in the circulatory system?

Pressure provides the driving force that moves blood through vessels and ensures delivery of oxygen and nutrients to tissues.

What is blood flow and what units are used to quantify it?

Blood flow is the volume of blood moving past a point per unit time, usually expressed in liters per minute (L · min⁻¹) or milliliters per minute (mL · min⁻¹).

Is blood flow identical in every organ? Why or why not?

No. Organs receive different fractions of cardiac output based on metabolic demand and local vascular resistance.

Define blood pressure and state its standard units.

Blood pressure is the force exerted by blood on vessel walls, measured in millimeters of mercury (mm Hg).

In a medical office, which circuit’s pressure is typically measured when taking blood pressure?

Systemic arterial circuit (specifically pressure in large systemic arteries).

Why does arterial blood pressure vary over time?

Because the heart ejects blood intermittently; pressure peaks during ventricular systole and falls during diastole.

Define systolic pressure.

The maximum arterial pressure achieved during ventricular systole.

Define diastolic pressure.

The minimum arterial pressure reached just before the next ventricular ejection (during diastole).

How do you calculate mean arterial pressure (MAP) from systolic and diastolic pressures?

MAP ≈ DP + 1⁄3(SP − DP).

Is blood pressure the same in capillaries and veins? Explain.

No. Pressure drops along the circulation; capillary and especially venous pressures are much lower because energy is lost to resistance.

Do capillaries and veins show large pressure fluctuations? Why or why not?

No. Pulsatile fluctuations are dampened by the high resistance of arterioles and the compliance of distal vessels.

Define total peripheral resistance (TPR).

The combined resistance to blood flow offered by all systemic blood vessels.

Name three major sources of resistance to blood flow.

1) Blood viscosity, 2) total vessel length, 3) vessel radius (inverse fourth-power relationship).

How does the sympathetic nervous system alter vessel radius?

Baseline sympathetic tone causes partial vasoconstriction; increased tone tightens smooth muscle (vasoconstriction), decreased tone relaxes it (vasodilation).

State the equation that links MAP, CO, and TPR.

MAP = CO × TPR.

If cardiac output rises while TPR stays constant, what happens to MAP?

MAP increases proportionally.

If arterioles dilate widely, how is MAP affected (assuming CO unchanged)?

TPR falls, so MAP decreases.

What are baroreceptors and where are the main ones located?

Stretch-sensitive mechanoreceptors that detect arterial pressure; major sites are the carotid sinus and aortic arch.

How do baroreceptors convey pressure information to the cardiovascular control center?

Stretch opens mechanically gated channels → receptor potentials → action potentials in glossopharyngeal (carotid) and vagus (aortic) nerves to the medulla.

Outline the baroreceptor reflex for maintaining arterial pressure.

↑MAP → ↑baroreceptor firing → medulla decreases sympathetic & increases parasympathetic output → HR, SV, and TPR fall → MAP returns to set point (and vice versa for ↓MAP).

How do changes in blood volume influence blood pressure?

More blood volume raises venous return and CO, elevating MAP; reduced volume lowers MAP.

Describe the kidney’s long-term role in blood-pressure control.

By adjusting salt and water excretion and releasing hormones (e.g., renin → angiotensin II → aldosterone), kidneys alter blood volume and thereby MAP.

What is autoregulation in arterioles and capillaries?

Intrinsic ability of tissues to adjust their own blood flow by changing arteriolar resistance independent of neural or hormonal input.

Differentiate metabolic vs. myogenic local control.

Metabolic: vasodilation in response to local buildup of CO₂, H⁺, K⁺, adenosine, low O₂. Myogenic: vascular smooth muscle contracts when stretched and relaxes when intraluminal pressure falls, stabilizing flow.

Define hyperemia and active hyperemia.

Hyperemia is increased blood flow to a tissue; active hyperemia is flow rise caused by elevated metabolic activity (e.g., contracting skeletal muscle).

Why is active hyperemia confined to the local level?

Metabolic by-products that trigger dilation are produced and cleared within the working tissue, so their effects do not spread systemically.

List three processes by which materials cross capillary walls.

1) Diffusion, 2) bulk flow/filtration-reabsorption, 3) vesicular transport (transcytosis).

Name the forces that move water across capillary walls.

Capillary hydrostatic pressure (Pc), interstitial hydrostatic pressure (Pi), capillary colloid osmotic pressure (πc), and interstitial colloid osmotic pressure (πi).

Overall, what is the net movement of water between capillaries and interstitial space?

Slight net filtration out of capillaries, balanced by lymphatic return.

How can changes in Starling forces alter fluid movement?

↑Pc or ↑πi promotes filtration; ↑πc or ↑Pi promotes reabsorption; pathological shifts (e.g., high venous pressure, low plasma proteins) can cause edema.