AP151 LEX EXAM 4: Cardiac Output, Blood Pressure, Blood Flow

AP151 LEC

What are the Factors that Affect Cardiac Output? (Five Answers)

Heart rate

Stroke volume

Venous return

Sympathetic stimulation (increases HR and contractility)

Parasympathetic stimulation (decreases HR)

What are the Sympathetic Effects on the Heart?

Increases heart rate

Increases contractility

Speeds AV node conduction

Increases cardiac output

Describe the Events of an Action Potential in Autorhythmic Cells

Funny channels let sodium in, gradually reaching the threshold. Calcium channels then open, causing rapid depolarization. Finally, potassium channels open, leading to repolarization

How does the Sympathetic Nervous System Affect the Firing Rate of Autorhythmic Cells?

Increases the rate of firing by making depolarization faster

How does the Parasympathetic Nervous System Affect the Firing Rate of Autorhythmic Cells?

Decreases the rate of firing by slowing depolarization

What are the Factors that Affect Stroke Volume?

EDV, Contractility (Inotropy), Afterload (Resistance)

How does Preload Affect Stroke Volume?

Increasing preload, meaning increases ventricular stretch, which results in increase stroke volume

How does Contractility (Inotropy) Affect Stroke Volume?

Increased contractility decreases ESV and increases stroke volume.

How does Afterload (Resistance) Affect Stroke Volume?

Increased afterload increases ESV and decreases stroke volume

What is the Frank-Startling Law?

Stroke volume that is proportional to end diastolic volume (EDV) 

Is the Frank-Starling Law an Intrinsic or Extrinsic Control of the Heart?

Intrinsic control of the control

How is the Frank-Starling Law Important for the Heart during Increased Peripheral Resistance or Increased Pulmonary Circulation?

It allows the heart to pump more forcefully when ventricular filling increases, helping overcome higher peripheral resistance or handle more pulmonary blood flow

What might be Some Intrinsic Controls of the Contractility of the Heart?

Stretch of cardiac muscle fibers (Frank-Starling law) and cellular Ca²⁺ availability.

What are the Main Factors that Affect Venous Return?

Blood volume

Venous pressure

Skeletal muscle pump

Respiratory pump

How does the Skeletal Muscle Pump Assist Venous Return?

Muscle contractions push blood toward the heart, helping overcome low venous pressure

How does the Respiratory Pump Affect Venous Return?

Negative thoracic pressure during breathing draws blood toward the heart

How does Venous Return Relate to Stroke Volume?

Higher venous return increases end-diastolic volume (EDV), which stretches the myocardium and increases stroke volume through the Frank-Starling mechanism

What are Some Factors that Affect the Release of ADH?

High plasma osmolality and low blood volume or pressure

Can you Describe the Osmoregulator Response to Decreased Blood Volume?

ADH is released, which increases water reabsorption in the kidneys and raises blood volume

Where in the Vessel System is Blood Flow Regulated?

Arterioles

What is the Most Influential Factor on Blood Flow?

Vessel Radius

How does Vessel Radius Mathematically Affect Blood Flow?

Blood flow is proportional to the fourth power of the vessel’s radius (r^4), meaning small changes in radius cause large changes in blood flow. △PR4/(𝜋)NL (8)

What is Total Peripheral Resistance?

The sum of all resistances within the systemic circulation; important for the regulation of blood pressure

What happens to Cardiac Output when Total Peripheral Resistance Increases?

Cardiac output decreases to help maintain stable blood pressure

What happens to Cardiac Output when Total Peripheral Resistance Decreases?

Cardiac output increases to keep blood pressure steady

What are the Sympathetic Effects on Blood Pressure?

Increasing heart rate, contractility, and causes vasoconstriction, which raises cardiac output and total peripheral resistance, ultimately increasing blood pressure

How does EDV stay similar during exercise compared to rest, even with less time between heartbeats? 

Increased venous return from the skeletal muscle and respiratory pumps fills the ventricles faster, and stronger atrial contractions add more blood to the ventricles

What accounts for Greater Stroke Volume in Athletes? How would this Cause Greater Stroke Volume?

Increased ventricular size and contractility lead to higher end-diastolic volume and stronger contractions, which result in a higher stroke volume

How do Blood flow and Cross-Sectional Area Relate?

Blood flow velocity is inversely proportional to cross-sectional area (Velocity ∝ 1/area)

How do Different Blood Vessels vary in Blood Flow Velocity and Cross-Sectional Area?

Arteries have high velocity and a small area, Capillaries have low velocity and a large area, and veins are intermediate in both

What would be the Result of Atrial Natriuretic Peptide regarding Blood Pressure and Blood Volume?

• Increased venous return stretches the left atrium, which stimulates ANP release

• ANP increases urine output and decreases blood volume

• ANP also decreases ADH release, enhancing water loss

• Overall effect: Lowers blood volume and blood pressure

What Forces Drive Blood through the Vessels? 

Pressure Gradient (From high to low pressure) 

How is Blood Pressure Measured? 

Using a sphygmomanometer and a stethoscope. Inflate the cuff to stop blood flow, then slowly release it while listening for Korotkoff sounds to determine systolic and diastolic pressures

How do you Calculate Pulse Pressure?

Systolic Pressure − Diastolic Pressure

How do you Calculate Mean Arterial Pressure (MAP)?

Diastolic Pressure + ⅓ × (Systolic Pressure − Diastolic Pressure), or Diastolic Pressure + ⅓ × Pulse Pressure.

Why is More Value Given to the Diastolic Pressure in the MAP Equation?

The heart spends more time in diastole than in systole

What is Hypertension?

High blood pressure, often called a “silent killer,” increases afterload, can damage cerebral vessels, and contributes to atherosclerosis

What can Cause Hypertension?

• Increased total peripheral resistance

• Increased blood volume

• Excess sympathetic activity

• Lifestyle factors: smoking, alcohol, obesity, high salt intake

What Factors that Affect Blood Pressure do Hypertension Drugs Alter?

• Diuretics: Decrease blood volume

• Beta blockers: Decrease heart rate and contractility

• ACE inhibitors / ARBs: Reduce vasoconstriction and blood volume