Blood Pressure

What is the reason MAP must be homeostatically maintained?

To ensure constant, adequate blood flow and perfusion to all organs, especially the brain and heart.

How does heart-to-brain distance relate to MAP in animals like giraffes?

Greater distance requires a higher MAP at the heart level to overcome gravity and perfuse the brain.

What is the MAP formula using pulse pressure?

MAP = ((PS − PD)/3) + PD.

What is the MAP formula using flow and resistance?

MAP = CO × TPR.

What does systolic pressure (PS) reflect?

Cardiac Output (CO). (↑ PS ≈ ↑ CO)

What does diastolic pressure (PD) reflect?

Total Peripheral Resistance (TPR).

What is the formula for Cardiac Output (CO)?

CO = HR × SV.

What factors can alter heart rate (HR)?

Autonomic nervous system (via SA node) or the hormone epinephrine from the adrenal medulla.

What does End Diastolic Volume (EDV) determine regarding stroke volume?

Depends on venous return and heart rate (filling time); ~60% of EDV is ejected as SV (Starling's Law).

How does contractility affect stroke volume?

Controlled by SANS; increased contractility increases velocity and increases ejection fraction.

What problem does standing upright create for venous return?

Gravity tends to pool blood in the lower extremities.

What mechanisms help maintain venous return?

Skeletal muscle pump; respiratory pump; venoconstriction.

How does the skeletal muscle pump increase venous return?

Muscle contraction compresses veins, pushing blood toward the heart past one-way valves.

How does the respiratory pump increase venous return?

Inspiration decreases thoracic pressure, drawing blood into the chest cavity.

How does venoconstriction increase venous return?

SANS stimulation increases smooth muscle contraction in veins, raising venous pressure and pushing blood to the heart.

Which branch of the ANS innervates veins?

Sympathetic Nervous System (SANS).

What autonomic output leads to venoconstriction?

Increased SANS output.

What is the effect of venoconstriction on venous return?

Increases venous return.

What autonomic output leads to venodilation?

Decreased SANS output.

What is the effect of venodilation on venous return?

Decreases venous return.

What does increased SANS do to venous smooth muscle?

Causes venous smooth muscle to contract.

What does decreased SANS do to venous smooth muscle?

Causes venous smooth muscle to relax.

What factors alter Peripheral Resistance?

Vessel length; blood viscosity; vessel diameter (arterioles).

Which factor controls Peripheral Resistance moment-to-moment?

Vessel diameter (arterioles).

How does vasodilation affect blood flow?

Increased diameter → decreased resistance → increased flow through tissues.

How does vasoconstriction affect blood flow?

Decreased diameter → increased resistance → decreased flow through tissues.

How does vasoconstriction affect PD and MAP?

Increased vasoconstriction → increased TPR → increased PD → increased MAP.

How does vasodilation affect PD and MAP?

Increased vasodilation → decreased TPR → decreased PD → decreased MAP.

Which branch of the ANS innervates arterioles?

Sympathetic Nervous System (SANS).

What autonomic output leads to vasoconstriction?

Increased SANS output.

What autonomic output leads to vasodilation?

Decreased SANS output (less tone).

What is the effect of increased SANS on arteriolar smooth muscle?

Causes smooth muscle in the arterioles to contract.

What is the effect of decreased SANS on arteriolar smooth muscle?

Causes smooth muscle in the arterioles to relax.

What is sympathetic tone (vasomotor tone)?

Continuous, basal sympathetic stimulation that maintains partial arteriolar constriction.

How is arteriolar diameter controlled systemically?

By SANS control of vasomotor tone.

How is arteriolar diameter controlled locally?

By metabolic by-products that override sympathetic vasoconstriction in active tissues.

What is the stimulus of the baroreceptor reflex?

↑ stretch with ↑ MAP; ↓ stretch with ↓ MAP.

Where are the receptors for the baroreceptor reflex located?

Baroreceptors in the aortic arch and carotid sinus.

What is the integrator (control center) for the baroreceptor reflex?

Medulla (Vasomotor Center and Cardiac Center).

Why does PD remain constant during exercise?

Local metabolic vasodilation in active muscle overrides SANS vasoconstriction → ↓ TPR → constant or slightly ↓ PD.

Why is hypertension called the silent killer?

Because it often has no symptoms yet causes progressive damage to blood vessels and organs.

How is hypertension diagnosed?

By repeated blood pressure measurements showing persistently elevated MAP.