Vessel

What is the primary function of arteries?

Carry blood away from the heart under relatively high pressure

What is the primary function of veins?

Return blood to the heart and act as blood reservoirs

What is the primary function of capillaries?

Exchange gases, nutrients, wastes, and fluid between blood and tissues

Which blood vessels have the thickest walls relative to their lumen size?

Arteries

Which blood vessels contain valves that help prevent backflow?

Many veins, especially in the limbs

Which blood vessels have walls only one cell thick?

Capillaries

Why do arteries have thick, elastic, muscular walls?

To withstand high pressure and regulate blood distribution

What are the three layers of a typical artery wall?

Tunica intima, tunica media, and tunica externa

What is the tunica intima?

The innermost vessel layer containing endothelium

What is the tunica media?

The middle layer containing smooth muscle and elastic tissue

What is the tunica externa?

The outer connective tissue layer that supports and anchors the vessel

What is vasoconstriction?

Narrowing of a blood vessel due to smooth muscle contraction

What is vasodilation?

Widening of a blood vessel due to smooth muscle relaxation

How does vasoconstriction affect vascular resistance?

It increases resistance

How does vasodilation affect vascular resistance?

It decreases resistance

What are arterioles?

Small arteries that regulate blood flow into capillary beds

Why are arterioles called resistance vessels?

Their small diameter and adjustable smooth muscle create a major source of peripheral resistance

How does arteriole constriction affect tissue blood flow?

It decreases blood flow into the affected capillary bed

How does arteriole dilation affect tissue blood flow?

It increases blood flow into the affected capillary bed

How does widespread arteriole constriction affect systemic blood pressure?

It generally increases peripheral resistance and raises blood pressure

How does widespread arteriole dilation affect systemic blood pressure?

It generally decreases peripheral resistance and lowers blood pressure

What is blood flow?

The volume of blood passing a point in the circulation per unit time

What is blood pressure?

The force exerted by blood against vessel walls per unit area

What is peripheral resistance?

The opposition to blood flow caused by the friction between circulating blood and the walls of the blood vessels

What is the equation for blood flow?

Flow = ΔPressure / Vascular Resistance

What does ΔP represent in the blood flow equation?

The pressure difference between two points

What happens to blood flow if the pressure difference increases while resistance stays constant?

Blood flow increases

What happens to blood flow if resistance increases while the pressure difference stays constant?

Blood flow decreases

What are the three major sources of vascular resistance?

Blood vessel diameter, blood viscosity, and total vessel length

Which factor has the greatest immediate effect on vascular resistance?

Blood vessel radius

How does vessel radius affect resistance?

Resistance varies approximately inversely with the fourth power of radius, meaning small change in radius causes a massive change in resistance.

What happens to resistance if vessel radius decreases?

Resistance increases sharply

How does increased blood viscosity affect resistance?

The internal friction between the fluid and the vessel walls increases, resistance increases.

How does increased total vessel length affect resistance?

A longer vessel creates a larger inner surface area, increasing the amount of friction between the flowing blood and the vessel walls.

What is local autoregulation of blood flow?

The ability of a tissue to adjust its own blood flow according to its metabolic needs

What happens to local blood flow when tissue metabolism increases?

Local vasodilation increases blood flow

How does low oxygen affect local blood flow in most systemic tissues?

It promotes vasodilation, which increases blood flow.

What is the role of nitric oxide in local blood flow regulation?

It relaxes vascular smooth muscle and causes vasodilation

How does histamine affect local blood vessels?

It promotes vasodilation and increases capillary permeability

What causes redness during inflammation?

Increased blood flow due to vasodilation

Where is systemic blood pressure highest?

In the aorta and large systemic arteries

Where does the greatest pressure drop occur in the systemic circuit?

Across the arterioles

Why does pressure fall substantially across arterioles?

Their high adjustable resistance dissipates pressure

Why is venous blood pressure low?

Pressure has fallen through the resistance vessels and circulation back to the heart

What is systolic blood pressure?

The highest arterial pressure during ventricular contraction

What is diastolic blood pressure?

The lowest arterial pressure during ventricular relaxation

What is pulse pressure?

The difference between systolic and diastolic blood pressure

What is the equation for pulse pressure?

PP = systolic pressure − diastolic pressure

What is the pulse pressure for a blood pressure of 120/80 mmHg?

40 mmHg

What is mean arterial pressure (MAP)?

The average arterial pressure driving blood through the systemic circulation over one cardiac cycle

What is the approximate equation for MAP?

MAP ≈ diastolic pressure + 1/3(pulse pressure)

What is the approximate MAP for a blood pressure of 120/80 mmHg?

Approximately 93 mmHg

What is the baroreceptor reflex?

A rapid negative-feedback reflex that adjusts heart activity and vessel diameter in response to blood pressure changes

Where are the main arterial baroreceptors located?

In the carotid sinuses and aortic arch

What do baroreceptors detect?

Stretch of arterial walls caused by changes in blood pressure

What happens to baroreceptor firing when blood pressure rises?

Baroreceptor firing increases

How does the brain respond to increased baroreceptor firing?

It decreases sympathetic output and increases parasympathetic output to the heart

What happens to baroreceptor firing when blood pressure falls?

Baroreceptor firing decreases

How does the brain respond to decreased baroreceptor firing?

It increases sympathetic output and reduces parasympathetic output

How does sympathetic activation affect cardiac output?

It increases heart rate and contractility, increasing cardiac output

How does sympathetic activation affect peripheral resistance?

It causes vasoconstriction in many systemic vessels, increasing resistance

What is the chemoreceptor reflex?

A reflex in which changes in blood oxygen, carbon dioxide, and pH trigger responses supporting ventilation and circulation

Where are the main peripheral chemoreceptors located?

In the carotid bodies and aortic bodies

What do peripheral chemoreceptors detect?

Low arterial oxygen, elevated carbon dioxide, and decreased pH

What is the primary role of the sympathetic nervous system in blood pressure regulation?

Rapidly adjusts heart function, vessel diameter, and venous return

How does sympathetic stimulation affect arterioles?

It generally causes vasoconstriction through alpha-1 adrenergic receptors

How does sympathetic stimulation affect veins?

It causes venoconstriction, increasing venous return to the heart

What is cardiac output?

The volume of blood pumped by one ventricle per minute

What is the equation for cardiac output?

CO = heart rate × stroke volume

What is epinephrine?

A hormone released by the adrenal medulla during stress that affects the heart and blood vessels

How does epinephrine affect the heart?

It increases heart rate and contractility through beta-1 receptors

What is norepinephrine?

A hormone and neurotransmitter that strongly promotes alpha-1-mediated vasoconstriction, it is released continuously by nerves to maintain baseline blood pressure.

How does norepinephrine usually affect blood pressure?

It increases peripheral resistance and usually raises blood pressure

What is antidiuretic hormone (ADH)?

A hormone that promotes water conservation by the kidneys and can cause vasoconstriction at high concentrations

How does ADH affect blood volume?

It increases water reabsorption by the kidneys, helping maintain or increase blood volume

What is aldosterone?

A hormone from the adrenal cortex that increases sodium reabsorption by the kidneys

How does aldosterone affect blood volume?

Sodium retention promotes water retention, increasing extracellular fluid volume

What is atrial natriuretic peptide (ANP)?

A hormone released mainly by atrial heart muscle cells in response to increased stretch

How does ANP affect blood volume and pressure?

It promotes sodium and water excretion, decreasing blood volume and blood pressure

What is the renin-angiotensin-aldosterone system (RAAS)?

A hormonal system that raises blood pressure and helps restore blood volume when low blood pressure is detected.

What triggers renin release from the kidneys?

Low blood pressure, low sodium delivery, sympathetic nervous system activation

What does renin do?

Cleaves angiotensinogen to form angiotensin I

Which enzyme converts angiotensin I to angiotensin II?

Angiotensin-converting enzyme (ACE)

What is the main effect of angiotensin II on arterioles?

Causes vasoconstriction that increases peripheral resistance and blood pressure.

How does angiotensin II affect aldosterone secretion?

It stimulates aldosterone release from the adrenal cortex

How does RAAS increase blood pressure over time?

Vasoconstriction and sodium and water retention increase pressure and blood volume

What is capillary exchange?

The movement of gases, nutrients, wastes, and fluid between blood and surrounding tissues

How do oxygen and carbon dioxide cross capillary walls?

By diffusion down their partial pressure gradients

What is filtration in capillary exchange?

Movement of fluid from capillary blood into the interstitial space

What is reabsorption in capillary exchange?

Movement of fluid from the interstitial space into capillary blood

What is capillary hydrostatic pressure?

The pressure exerted by blood against the capillary wall that tends to push fluid outward

What is blood colloid osmotic pressure?

The osmotic force produced mainly by plasma proteins that tends to draw fluid into capillaries

What is net filtration pressure (NFP)?

The net pressure resulting from forces that promote fluid filtration versus fluid reabsorption

What does positive net filtration pressure indicate?

Net movement of fluid out of the capillary

What does negative net filtration pressure indicate?

Net movement of fluid into the capillary

What can cause increased capillary filtration?

Increased capillary hydrostatic pressure or increased interstitial oncotic pressure

What is edema?

Excess accumulation of fluid in the interstitial tissues

How can increased capillary hydrostatic pressure cause edema?

It pushes more fluid out of capillaries into tissues

How can low plasma protein concentration cause edema?

It reduces plasma oncotic pressure, decreasing the force drawing fluid into capillaries

What is the role of the lymphatic system in fluid balance?

It returns excess interstitial fluid and leaked proteins to the bloodstream