Physio Exam 2 (cardiovascular system)

Describe Path of Blood Flow (Starting from Right Atrium):

1. Right Atrium (deoxygenated blood from Vena Cava)

2. Through Tricuspid Valve

3. Right Ventricle

4. Through Pulmonary Semilunar Valve

5. Pulmonary Trunk —> Pulmonay Arteries (to lungs)

6. Lungs (dumps CO2, picks up O2)

7. Pulmonary Veins (oxygenated blood)

8. Left Atrium

9. Through Bicuspid Valve

10. Left Ventricle

11. Through Aortic Semilunar Valve

12. Aorta —> Systemic Circulation (to entire body)

13. Returns to Right Atrium via Vena Cava

What are interdigitating folds and why are they important in cardiac muscle?

They are folds where adjacent cardiomyocytes interlock, increasing surface area for cell-to-cell contact → improves communication and coordination between cells.

What is the difference between mechanical and electrical gap junctions in cardiac muscle?

• Mechanical (desmosomes): hold cells together so they don’t pull apart during strong contractions

• Electrical (gap junctions): allow ions to flow between cells → spread depolarization

Why does the heart contract as a syncytium (functional unit)?

Electrical gap junctions let ions move between cells → action potentials spread quickly →

• atria contract together

• ventricles contract together

→ makes the heart pump efficiently as one unit

What is the main function of the cardiovascular system?

Because cells have constantly changing metabolic demands → need continuous delivery of O₂/nutrients and removal of waste

What are the two main components of the cardiovascular system?

Heart (pump) + blood vessels

What do arteries, veins, and capillaries do?

Arteries —> Away from heart

Veins —> back to heart

Capillaries —> exchange (O2, nutrients)

What is the functional difference between pulmonary and systemic circuits?

• Pulmonary → gas exchange (low pressure system)

• Systemic → delivers O₂ to tissues (high pressure system)

What drives blood flow through the heart?

Pressure gradient

What would happen if the heart valves failed?

Backflow —> reduced efficiency or circulation

If blood flows backward from ventricle → atrium, which valve is faulty?

AV valve (tricuspid or bivalve)

What would happen if gap junctions were blocked in cardiac muscle?

Loss of coordinated contraction → heart would not pump efficiently

Why is electrical coupling essential in cardiac muscle?

Ensures depolarization spreads → synchronized contraction

Why is the SA node the primary pacemaker?

It has the fastest intrinsic depolarization rate

Why must atria contract before ventricles?

To complete ventricular filling before ejection

What happens if the AV node fails?

Atria contract normally, but ventricle may not —> loss of coordination

Why does the SA node depolarize spontaneously?

Slow NA+ influx —> gradual depolarization to threshold

Key difference between SA node and cardiomyocyte depolarization?

• A node → Ca²⁺ drives depolarization

• Cardiomyocyte → Na⁺ drives depolarization

Why do cardiomyocytes have a plateau phase?

Ca²⁺ influx balances K⁺ efflux → prolongs AP

Why is tetanus impossible in cardiac muscle?

Long plateau —> long refractory period

What do desmosomes (mechanical junctions) do?

Prevent cells from pulling apart during contraction

What do electrical gap junctions allow?

Ion flow —> spread of depolarization

Why do cardiac muscle cells have interdigitating folds?

Increase contact → better communication

What is the SA node?

Primary pacemaker —> initiates depolarization

What does the P wave represent?

Atrial depolarization

What does the QRS complex represent ?

Ventricular depolarization

What does the T wave represent ?

Ventricular repolarization

Why don’t we see atrial repolarization on EKG?

It’s masked by larger ventricular signal

What is the formula for heart rate from EKG?

HR = 60 / RR interval (seconds)

Why must RR interval be in seconds?

Units must match (60sec/min)

What happens if the RR interval increases?

HR decreases

Why do Ca²⁺ channel blockers reduce cardiac & smooth muscle contraction but not skeletal?

• Cardiac + smooth → rely on extracellular Ca²⁺

• Skeletal → uses SR Ca²⁺

Why does depolarization come before contraction?

Electrical activity triggers mechanical contraction

Why does systole follow depolarization?

AP —> Ca2+ influx —> contraction

Why does diastole follow repolarization?

Repolarization —> Ca2+ removed —> relaxation

What is the pathway of electrical conduction in the heart?

SA node → atrial myocardium → AV node → ventricular myocardium

What determines whether a valve opens or closes?

Pressure gradients (not active movement)

When do AV valves open vs semilunar valves?

AV : Atrial Pressure > ventricular

Semilunar: Ventricular Pressure > Arterial

Why are systole and diastole usually referring to ventricles?

Ventricles generate the pressure that drives circulation

What happens during ventricular filling? (PHASE 1)

• AV open, semilunar closed

• Blood flows into ventricles

• Volume ↑

What defines isovolumetric contraction? (PHASE 2)

• ALL valves closed

• Pressure ↑

• Volume stays same

Why must all valves be closed during isovolumetric contraction?

To build pressure without ejecting blood

What triggers ventricular ejection?

Ventric. Pressure> Arterial Pressure

What defines isovolumetric relaxation? (PHASE 4)

• ALL valves closed

• Pressure ↓

• Volume constant

Why are there TWO isovolumetric phases?

• One builds pressure (contraction)

• One releases pressure (relaxation)

What is EDV?

End Diastolic Volume; Max ventricular volume (end of filling)

What is ESV?

Remaining blood after contraction

What is stroke volume?

SV = EDV - ESV

What does stroke volume represent physiologically?

How much blood is actually pumped per beat

What is ejection fraction and why is it important?

EF = SV / EDV —> measures how well heart pumps

What does a low EF indicate?

Heart failure / poor contractility

What causes the “lub” sound?

AV valves closing

What causes the “dub” sound?

Semilunar valves closing

Why do valve closures produce sound?

Turbulent blood flow

What is the MAP formula?

MAP = (SP + 2DP) / 3

Cardiac Output Equation

CO = SV * HR

CO = 90 mL/beat × 90 beats/minute = 8100 mL/minute

Why can CO increase without increasing HR?

By increasing stroke volume

What determines heart rate?

SA node firing rate

How does parasympathetic input affect HR?

Decreases HR (open K+ channels; K+ efflux slows depolarization)

How does sympathetic input affect HR?

Increases HR (Na+ and Ca2+ influx speeds depolarization)

Recruits "funny" (Na⁺) channels and T-type Ca²⁺ channels on SA Node.

Noise during systole (ventricular contraction):

• Whistling: Stenotic semilunar valve (aortic/pulmonary).


• Gurgling: Leaky AV valve.

Noise during diastole (ventricular relaxation/filling):

• Whistling: Stenotic AV valve.


• Gurgling: Leaky semilunar valve.

Blood Velocity Equation

v = Q ÷ A

A= Cross-sectional area.


• Key Point: Velocity is slowest in the capillary beds because they have the greatest total cross-sectional area, allowing for efficient nutrient/waste exchange.

Why is pressure gradient considered the driving force of blood flow?

Because without a difference in pressure, no flow occurs

What are the 3 factors controlling stroke volume?

Contractility, Preload (EDV), Afterload

What is preload ?

Initial stretch of ventricle (EDV)

What does Starling’s law state?

More filling —> more stretch —> stronger contraction

What does increased EDV increase SV?

Optimal overlap of actin-myosin —> stronger contraction

What does sympathetic stimulation do to contractility?

Increases Ca2+ —> stronger contraction

What is afterload?

Pressure ventricle must overcome to eject blood

What happens to SV if afterload increases?

SV decreases (harder to eject blood)

What happens to SV if venous return increases?

Preload ↑ → SV ↑

What happens during sympathetic activation?

Contractility ↑ → SV ↑

What happens with hypertension?

Afterload ↑ → SV ↓

If SV increases but HR stays constant, what happens to CO?

CO increases

If HR increases but filling time decreases, what happens to CO?

Depends → HR ↑ increases CO, but ↓ filling may ↓ SV

How do you calculate CO if given EF and EDV?

1. SV = EF × EDV

2. HR from EKG

3. CO = SV × HR

What is the intrinsic firing rate of the SA node?

~100 bpm

How does parasympathetic input affect HR?

Opens K⁺ channels → slows depolarization → ↓ HR

How does sympathetic input affect HR?

Opens Na⁺ + Ca²⁺ channels → faster depolarization → ↑ HR

What ion change increases contractility?

↑ intracellular Ca²⁺

Why does more Ca²⁺ increase contraction strength?

More cross-bridge formation → stronger contraction

What increases EDV?

• ↑ venous return

• ↑ filling time

• ↑ atrial pressure

What does a whistling sound indicate?

Stenotic valve

What does a gurgling sound indicate?

Leaky (regurgitant) valve

Murmur during systole → which valves likely?

• Semilunar stenosis

• AV regurgitation

Murmur during diastole → which valves likely?

• AV stenosis

• Semilunar regurgitation

What determines blood flow?

Flow = ΔP / R

What happens to flow if resistance increases?

Flow decreases

Why must flow be equal in systemic and pulmonary circuits?

To prevent blood backup

Why is pulmonary resistance lower than systemic?

Lower pressure gradient → must lower resistance to keep flow equal

What is Poiseuille’s law for resistance?

R ∝ (length × viscosity) / radius⁴

Which factor has the biggest effect on resistance?

Radius

Why is radius the most important regulator of blood flow?

Because resistance ∝ 1/r⁴ → small changes = huge effect

What decreases resistance?

Vasodilation (↑ radius)

What increases resistance?

Vasoconstriction (↓ radius)

What is the difference between flow and velocity?

• Flow = volume/time

• Velocity = distance/time

Why is velocity slowest in capillaries?

Largest total cross-sectional area

What is the relationship between CO, MAP, and resistance?

CO = MAP / TPR

If resistance increases and MAP stays constant, what happens to CO?

CO decreases