lecture 23

Question 1

What are the main functions of each part of the vasculature?

Answer 1

Arteries: create bulk flow + driving pressure
Arterioles: control/regulate blood flow to specific tissues
Capillaries: site of gas + nutrient exchange only
Veins/venules: return blood to the heart (flow reservoir)

Question 2

How do sympathetic and parasympathetic systems control heart rate from rest to maximal exercise?

Answer 2

🟩 Back:
At rest (~60 bpm):

Parasympathetic (vagal tone) dominates
Keeps heart rate low

During exercise → max (~200 bpm):

Parasympathetic activity decreases (withdrawal of vagal tone)
Sympathetic activity increases
→ raises heart rate

Key idea:

Rest = “brake on” (parasympathetic)
Exercise = “gas on” (sympatheti

Question 3

Stroke volume

Answer 3

The volume of blood
pumped during one beat of the heart
* Difference in ventricular volume at the end
of diastole and end of systole
* SV = EDV – ESV
* Units = mL/beat

Question 4

Ejection fraction

Answer 4

Ejection fraction (EF) = % of blood pumped out of the left ventricle per beat
Formula: EF = SV / EDV
SV = stroke volume
EDV = end-diastolic volume
Expressed as a percentage (%)

Question 5

How does cardiac structure and function differ in athletes vs untrained individuals?

Answer 5

🟩 Back:
Athletes:

❤️ Larger heart
↑ EDV (more filling)
↑ Stroke volume (more blood per beat)
EF: little/no major change

Key idea:

Bigger cardiac capacity, not much change in efficiency (%)

Question 6

What is cardiac output and how does it change with training and exercise?

Answer 6

🟩 Back:

Cardiac output (Q̇) = total blood pumped per minute
Formula: Q̇ = HR × SV
Units: L/min

At rest:

Untrained: ~5 L/min (70 bpm × 71 mL)
Trained: ~5 L/min (45 bpm × 111 mL)
👉 Same total output, different HR + SV

During maximal exercise:

Q̇ increases a lot (~20–35 L/min or more)
Example: 185 bpm × 180 mL ≈ 33 L/min

Question 7

What is the Fick Equation for oxygen uptake (V̇O₂)?

Answer 7

🟩 Back:

V̇O₂ = Q̇ × (a–v̄O₂ difference)
V̇O₂ = oxygen uptake (L/min)
Q̇ = cardiac output (HR × SV)
a–v̄O₂ difference = amount of O₂ extracted by tissues

Question 8

How does the a–v̄O₂ difference change with exercise intensity?

Answer 8

aO₂ stays ~constant (arterial O₂ saturation remains high)
Ventilation increases → keeps blood well oxygenated
v̄O₂ decreases (more O₂ extracted by muscles)
→ muscles use more O₂ at higher intensity
✔️ Result: a–v̄O₂ difference widens with intensity

Question 9

🟥 Front:
Why does heart rate increase linearly with exercise intensity?

Answer 9

Heart rate increases with intensity due to combined regulation:

1. Intrinsic control:

SA node sets basic rhythm (~100 bpm)

2. Extrinsic control (adjusts HR ~25–200 bpm):

↓ Parasympathetic (vagal withdrawal)
↑ Sympathetic stimulation

Additional inputs:

Central command (brain feedforward)
Endocrine: epinephrine & norepinephrine
Peripheral feedback:
Mechanical (muscle + vessels)
Chemical (metabolites → group III/IV afferents)

Question 10

🟥 Front:
How do stroke volume (SV), heart rate (HR), and cardiac output (Q̇) change during increasing exercise intensity?

Answer 10

🟩 Back:

HR and Q̇ increase linearly with exercise intensity
SV increases at first, then plateaus (~30–50% VO₂max)
After plateau, further increases in Q̇ come mainly from HR

SV = EDV − ESV

EDV depends on:

Venous return
Ventricular distensibility

ESV depends on:

Ventricular contractility
Aortic/pulmonary artery pressure (afterload)

Question 11

Venous return is aided by 3
factors:

Answer 11

Muscle pump
* Respiratory pump
* Valves located in veins

Question 12

During prolonged constant-intensity exercise, there is a gradual decrease in SV due to ________. This results in ________.

Answer 12

🟩 Back:

Due to decreased venous return (reduced plasma volume / dehydration + increased blood flow to skin for thermoregulation)
This results in increased heart rate to maintain cardiac output (cardiovascular drift)

Question 13

What is the Frank-Starling Law of the Heart?

Answer 13

🟩 Back:

↑ End-diastolic volume (EDV) → ↑ stretch of ventricular walls
↑ stretch → ↑ force of contraction
→ leads to ↑ stroke volume (SV)
Works within physiological limits

Key idea:
👉 The more the heart fills, the more it pumps ou