Blood Circulation During Exercise
I. INTRODUCTION
Physiological Challenge:
Exercise increases O₂ demand by 15-25x. Circulation must deliver more O₂/glucose to muscles and
remove CO₂/metabolites.
Key Goals:
1. ↑ Cardiac output (CO)
2. Redirect blood to active muscles
3. Maintain BP despite vasodilation in muscles
II. NEURAL & HORMONAL CONTROL
A. Sympathetic Nervous System (SNS) Dominance
Vasoconstriction: In kidneys, gut, skin via α₁-adrenergic receptors.
-Cardiac Stimulation:
-↑ Heart rate (↓ vagal tone + ↑ SNS).
- ↑ Contractility (↑ force of contraction via β₁-receptors).
B. Local Metabolite Override
-Vasodilators in Muscles:CO₂, H⁺, K⁺, lactate, adenosine, nitric oxide (NO).
"Metabolites override SNS vasoconstriction in active muscles – autoregulation > neural control."
C. Hormonal Changes
- Epinephrine/Norepinephrine:↑ HR, contractility, vasoconstriction.
-Vasopressin (ADH):↑ Water reabsorption → maintains blood volume.
-Renin-Angiotensin-Aldosterone: Sodium/water retention.
III. CARDIAC OUTPUT (CO) CHANGES
CO = Heart Rate (HR) × Stroke Volume (SV)
parameter Rest Max exercise Mechanism
Heart rate 60-80bpm 180-200bpm SNS ↑ + Vagal
withdrawal
Stroke volume 70ml 100-150ml ↑ Preload + ↑
I. INTRODUCTION
Physiological Challenge:
Exercise increases O₂ demand by 15-25x. Circulation must deliver more O₂/glucose to muscles and
remove CO₂/metabolites.
Key Goals:
1. ↑ Cardiac output (CO)
2. Redirect blood to active muscles
3. Maintain BP despite vasodilation in muscles
II. NEURAL & HORMONAL CONTROL
A. Sympathetic Nervous System (SNS) Dominance
Vasoconstriction: In kidneys, gut, skin via α₁-adrenergic receptors.
-Cardiac Stimulation:
-↑ Heart rate (↓ vagal tone + ↑ SNS).
- ↑ Contractility (↑ force of contraction via β₁-receptors).
B. Local Metabolite Override
-Vasodilators in Muscles:CO₂, H⁺, K⁺, lactate, adenosine, nitric oxide (NO).
"Metabolites override SNS vasoconstriction in active muscles – autoregulation > neural control."
C. Hormonal Changes
- Epinephrine/Norepinephrine:↑ HR, contractility, vasoconstriction.
-Vasopressin (ADH):↑ Water reabsorption → maintains blood volume.
-Renin-Angiotensin-Aldosterone: Sodium/water retention.
III. CARDIAC OUTPUT (CO) CHANGES
CO = Heart Rate (HR) × Stroke Volume (SV)
parameter Rest Max exercise Mechanism
Heart rate 60-80bpm 180-200bpm SNS ↑ + Vagal
withdrawal
Stroke volume 70ml 100-150ml ↑ Preload + ↑
