Week 5 Flashcards
Structure of the heart? and basic function?
Epicardium
Myocardium
Endocardium
Receives blood supply via coronary arteries, high demand for oxygen and nutrients
What is myocardial infarction?
blockage in coronary blood flow resulting in cell damage
Exercise training helps protect heart damage during MI
The heart wall structure, characteristics and functions?
Epicardium - Serous membrane including blood capillaries, lymph capillaries and nerve fibres, lubricates outer covering
Myocardium - Cardiac muscle tissue separated by connective tissues and including blood and lymph capillaries, and nerve fibres, provides muscular contractions to eject blood
Endocardium - Endothelial tissue and a thick subendothelial layer of elastic and collagenous fibres, serves as a protective inner lining of the chambers and valves.
Heart Muscle vs Skeletal Muscle – Key Comparison
Contractile Proteins: Actin & Myosin (both)
Fiber Shape: Heart – short, branching; Skeletal – elongated, no branching
Nuclei: Heart – single; Skeletal – multiple
Z-Discs: Present in both
Striations: Present in both
Cellular Junctions: Heart – intercalated discs; Skeletal – none
Connective Tissue: Heart – endomysium; Skeletal – epimysium, perimysium, endomysium
Energy Production: Heart – aerobic (primary); Skeletal – aerobic & anaerobic
Calcium Source: Heart – SR + extracellular; Skeletal – SR only
Neural Control: Heart – involuntary; Skeletal – voluntary
Regeneration Potential: Heart – none (no satellite cells); Skeletal – some (satellite cells present)
Electrical activity of the heart - Conduction system?
Starts at Sinoatrial node (SA) - Pacemaker, initiates depolarization. Originates and travels across atrial wall from SA to AV
Then to Atrioventricular (AV) node - Passess depolarisation to ventricles, brief delay to all ventricle filling. Passes through AV bundle through fibrous skeleton into interventricular system
Bundle branches - connect atria to left and right ventricle. AV bundle divides into left and right bundle branches where AP descends to apex of each ventricle along branches
Finally purkinje fibres - spread wave of depolarisation throughout ventricles, AP carried by fibres from branches to ventricle walls.
Electrocardiogram (ECG)
P Wave - Atrial depolarisation
QRS complex - Ventricular depolarisation and atrial repolarisation
T Wave - Ventricular repolarisation
Rate of intrinsic pacemaker?
Around 100 bpm
Diagnostic use of ECG during exercise?
Observing ECG and BP changes can evaluate cardiac function
ST segment depression suggests myocardial ischemia
Atherosclerosis which is fatty plaque narrows coronary arteries reducing blood flow to myocardium - myocardial ischemia
How does exercise protect the heart?
Reduces incidence of heart attacks/reduces survival of them
Reduces amount of myocardial damage from HA improving antioxidant capacity and function of ATP sensitive potassium channels
Evaluating collapsed athlete
Assess consciousness by checking for pulse which determines the next 1 of 2 paths.
If no pulse = cardiac arrest = life support measure such as CPR which articulates blood to tissues for them.
Time to initiation of chest compressions can determine factors for cardiac arrest
Improving survival outcomes.
67% survival from SCA with immediate defibrillation.
Nearly 4x more neurologically intact survival rate
Exercise stress test for diagnosis of Coronary heart disease?
Tests can detect restricted coronary flow
Coronary Circulation?
- Heart muscle is highly oxidative (high O₂ demand)
- Adenosine is the key metabolic vasodilator- Also β-adrenergic vasodilation (via ANS)
- Blood flow mainly occurs during diastole
- At rest, 80% of coronary flow takes place during diastole because of vessel compression during systole.
- Heavy exercise: 40-50% of flow occurs in systole
- Chronotropic [heart rate increases]
Inotropic [contractility increases]
Coronary circulation in exercise?
- Abundant coronary blood supply to highly oxidative cardiac muscle
- High oxygen extraction
- Metabolic control principally via adenosine
- Flow mainly during diastole
- High potential for ischaemia
Anatomy and role of circulatory system?
Arteries - Blood delivery
Small arteries/arterioles - flow regulation
Capillaries - fluid / nutrient exchange
Venules - collection
Veins - Return
Anatomy of peripheral circulation in decreasing size?
Conduit arteries - several mm
Feed arteries - about 1 mm
Resistance arteries 150-300 um
Resistance arterioles - 30-15- arterioles
Terminal arterioles 10-30um
Capillaries 4-6 um
Resistance is higher the lower the radius
Aspects that control vasodilation/constriction?
Neural - SNS = adrenaline
Hormonal = similar to above, norepinephrine
Myogenic = flow and pressure varies depending on what is needed eg exercise
Mechanical - Skeletal muscle pump/moving
Metabolic
Endothelial derived relaxing factors (EDRF)
Metabolic regulation of resistance vessels?
Blood flow increases in relation to the metabolic activity of a tissue / organ –
HYPERAEMIA
such as
* Tissue hypoxia
* CO2 increase
* pH decrease
* lactate production
* breakdown products of ATP
- e.g. adenosine, inorganic phosphate
* potassium
* osmolality
Endothelial derived relaxing factors (EDRFs)
Blood flow creates shear stress on endothelial cells, triggering the conversion of L-arginine to nitric oxide (NO). NO promotes vasodilation and supports vascular health. In many cardiovascular diseases, NO production is impaired, reducing vessel function.
Arachidonic acid is converted into prostaglandins (PGs), which cause inflammation.
Short-term: Beneficial—boosts blood flow and aids muscle recovery
Long-term: Harmful—leads to chronic inflammation increases blood flow which helps muscle recovery.
Redistribution of Blood Flow During Exercise?
Increase blood flow to working skeletal muscle.
* At rest, 15 to 20% of cardiac output to
muscle.
* ↑ to 80 to 85% during maximal exercise.
Decrease in blood flow to less active organs.
* Liver, kidneys, GI tract.
* Redistribution depends on metabolic rate.
* Exercise intensity.
Regulation of Local Blood Flow during Exercise?
Skeletal muscle vasodilation causes decrease vascular resistance
This is also known as Autoregulation (blood flow regulation) which controls based off of needs.
* Blood flow increases to meet metabolic demands of tissue.
* Magnitude of vasodilation in proportional to the size of recruited muscle
mass.
* Due to changes in local factors (Increase nitric oxide, prostaglandins, ATP and
adenosine).
Vasoconstriction to visceral organs and inactive tissues increases vascular resistance
* SNS vasoconstriction - due to release of hormones such as norepinephrine etc
* Blood flow reduced to 20 to 30% of resting values
Redistribution of cardiac output aided by catecholamines?
Circulating levels of noradrenaline and adrenaline increase during
exercise and act to vasoconstrict in most organs.
‘Noradrenaline spillover’ from muscle represents SNS activation
Adrenaline:
* Dilates skeletal muscle blood vessels
via β receptors in light exercise
* Vasoconstricts via α receptors in heavy
exercise as more blood is needed
Cardiac output redistribution during exercise?
Skeletal muscle can take up to 90% of cardiac output at maximal exercise
Other major users of cardiac output in exercise – skin, coronary circulation
Circulation through ‘special’ regions during exercise
- Sympathetic vasoconstriction in inactive
organs (resting skeletal muscle, skin,
splanchnic, renal) - Metabolic vasodilation in active organs
(active skeletal muscle, coronary) - Thermoregulatory vasodilation in skin
- BUT: In severe exercise – competing
demands of active muscle and
thermoregulation and need to maintain
blood pressure
What is Splanchnic circulation?
The splanchnic circulation supplies blood to the liver, GI tract, pancreas, and spleen.
30% of the blood comes via the hepatic artery (from the aorta)
70% via the portal vein (draining GI organs)
This region holds about 20–25% of total blood volume
Splanchnic circulation during rest vs during exercise?
Flow = 1500 ml/min, 25% of CO2 vs 350 ml/min 5% of CO2
O2 Consumption = 50-60ml/min vs 50-60ml/min
O2 Extraction - 15-20% vs 75%
Blood flow decreases through sympathetic vasoconstriction
and circulating catecholamines
Oxygen extraction increases to compensate
Splanchnic Circulation & Exercise Response?
During exercise:
Splanchnic blood flow decreases significantly
Blood is redirected to muscles and the heart to meet increased metabolic demands
Flow returns to baseline post-exercise
Physiological effects:
Vasoconstriction in splanchnic vessels helps increase venous return by shifting blood back to the heart
Vasoconstriction is more intense during exercise in heat, allowing more cardiac output to be directed to the skin for cooling
Temporary reduction in GI blood flow also limits digestive activity to prioritize active tissues
Skin(cutaneous) circulation ?
Rest - 100-300ml/min per m^2 of body surface
Max - 7-8 L/min per m^2 of body surface
More during max to maintain thermoregulation eg sweating during exercise by redirecting blood to skin
Sympathetic neural control of skin blood vessels?
- Adrenergic vasoconstrictor
(non-hairy skin e.g. palms, sole of foot, lips)
Adrenergic: noradrenaline as neurotransmitter - Cholinergic vasodilator
(hairy skin)
Cholinergic: acetylcholine as neurotransmitter
Skin (cutaneous) circulation – thermoregulation?
Cold stress leads to vasoconstriction (VC)
Heat stress leads to vasodilation (VD)
Vasoconstriction
= sympathetic constrictor activity Increases (Adrenergic)
Vasodilation
= sympathetic constrictor activity decreases (non-hairy) = sympathetic dilator activity increases (hairy) (Cholinergic
Skin circulation during exercise ?
During dynamic exercise, active vasodilation occurs at a higher threshold
than during heating at rest
Mechanism of active vasodilation in exercise
(hairy skin) sympathetic cholinergic nerves and
nitric oxide, peptides
Skin (cutaneous) circulation – blood pressure regulation?
Skin circulation can determine the performance of the
heart
In heat, blood flow is shifted from core to surface
Muscle pump cannot assist in aiding venous return
Filling of heart is reduced. Vasoconstriction must occur
to maintain BP.
BUT – in extreme conditions, skin vasoconstriction
compromises thermoregulation
Skin (cutaneous) circulation – integrative control?
Reflex inputs: Thermoregulatory = internal, skin temp
Non-thermoregulatory = baroreceptors, exercise
Sympathetic controllers:
Vasodilator and Vasoconstrictor
Central modifiers:
Circadian rhythm, hydration, acclimatization, menstrual cycle, training
Summarised Skin circulation?
Use diagram. ABC
In dynamic exercise - competing influences
* Vasoconstriction at onset with
sympathetic activation (A)
* Active vasodilation occurs at a threshold
core temperature to lose heat (B)
* Vasoconstriction during prolonged
exercise to maintain central blood volume
and venous return (C)
Renal blood flow Rest vs Exercise?
Flow: 1200 ml/min 20% of CO vs 360ml/min 4% of CO
O2 extraction: 6% vs 18%
Sympathetic neural control
Vasoconstriction in exercise
Potential for proteinuria in intense exercise
Why is Brain blood flow (BBF) Vital? What are functional consequences and the continuum they fall on?
- Survival: Supplies oxygen and substrates to the brain.
- High Demand: Brain is 2-3% of body mass but uses 20% of cardiac output.
- If under/over perfused it can result in Strokes
- Functional Consequences:
- Performance and cognitive function.
- Impairments linked with diseases (e.g., dementia, stroke, TBI).
- Prognostic value for cardiovascular mortality
- Continuum of Impairment:
- Acute: Fainting, stroke.
- Chronic: Hypertension, dementia, concussion/TBI
Physical Activity, Ageing, and Brain Health?
- Ageing and Inactivity: Linked to a decline in BBF.
- Habitual Exercise:
- Offsets age-related decline in BBF (~10-year delay).
- Positive correlation between aerobic fitness and BBF.
Measurement of Brain Blood Flow?
- MRI (Magnetic Resonance Imaging):
- Structure and functional imaging.
- High spatial resolution but limited use during exercise.
- Doppler Ultrasound:
- Measures blood velocity as an index of flow.
- Advantages: Beat-to-beat changes, robustness, and ease of use.
- Commonly used with the Middle Cerebral Artery (MCA).
- NIRS (Near-Infrared Spectroscopy):
- Measures oxygen supply and demand at the capillary level.
- Assesses brain activation (neurovascular coupling).
- Portable and robust for exercise studies.
- Arterial Spin Labelling (ASL):Brain perfusion imaging technique
- Measures cerebral perfusion at rest.
- Region-specific cerebral blood flow (CBF) analysis.
- Phase Contrast Angiography: Brain perfusion imaging technique
- Analyzes flux and velocity across cardiac cycles.
- High spatial resolution but challenging to use during exercise.
- Should be chosen based on what question is being asked.
Multimodal Approach:
- Combining different imaging methods enhances assessment of brain health.
- Accounts for both structural and functional aspects.
Key Regulators of Brain Blood Flow?
- Blood Pressure - Perfusion pressure
- Neurogenic - Cerebral SNA
- Metabolism - links to nerve cell activity
- Chemical - Arterial PCO2
- Cardiac Output
Large changes in blood pressure can occur during and following exercise…
- What are the consequences for brain blood flow and brain function?
Fainting
Cerebral blood flow factors and link to exercise?
- Arterial Blood Pressure (ABP)
- Cerebral Autoregulation
- Cardiac Output
- Baroreflex
- Sympathetic and Parasympathetic Nervous Activity
- Cerebral Neural Activity
- Metabolism:
- Glucose, lactate, oxygen, and carbon dioxide.
- Nitric Oxide (NO)
Exercise affects these things at the same time, complex interactions. we can use this to look at processes such as chemoreflex, baroreflex etc
Brain blood flow responsiveness to CO2?
BBF highly sensitive to changes in arterial partial pressure of carbon dioxide (PaCO2).
During exercise it increases till about 65% vo2 max then declines due to increase hyperventilation and reduction in H+ ions so less Co2 produced in processes
BBF Response to Exercises, intensities and modalities?
- Intensity:
- Incremental increase in BBF with mild to moderate exercise (20-80% Wmax).
- Maximal exercise (90-100% Wmax) may lead to a plateau or decrease due to hyperventilation-induced hypocapnia.
- Modality:
- Different patterns observed between rowing, running, and cycling.
- Rowing and Running:
- BBF patterns mirror blood pressure profiles.
- Cycling:
- Shows modality- and fitness-specific profiles at high intensities (>65% VO2max).
- Aquatic Treadmill Exercise:
- BBF changes similar to land running but influenced by hydrostatic pressure.
- Mechanism: Increased venous return leading to higher cerebral perfusion
High-Intensity vs. Moderate Exercise for BBF?
- High-Intensity Interval Training (HIIT):
- BBF decreases during 30s sprints but rebounds immediately after.
- Associated with enhanced neurotrophic factor circulation.
- Moderate Intensity Continuous Training (MICT):
- Maintains relatively stable BBF throughout.
- Different BBF profiles could indicate varied adaptations from HIIT vs. MICT.
Practical Implications for Brain Health?
-
Regular Physical Activity:
- Counteracts age-related BBF decline.
- Maintains cognitive function and reduces risk of neurodegenerative diseases.
-
Exercise Modality and Intensity:
- Influence the magnitude and pattern of BBF responses.
- Tailoring exercise prescriptions can optimize brain health benefits.
-
Potential for Targeted Interventions:
- Utilizing exercise to improve neurovascular coupling and cognitive function.
- Customizing interventions based on fitness levels and health conditions
