Week 5 Flashcards
(35 cards)
Structure/Layers of the heart? and basic function of heart and layers?
The heart is a muscular organ that is responsible for receiving blood supply via coronary arteries and pumping blood throughout the body to deliver oxygen and nutrients and remove waste.
It has a high oxygen and nutrient demand, especially in the myocardium
Heart wall layers:
Epicardium – Outer layer; protective membrane
Myocardium – Middle layer; thick muscular layer responsible for contraction and pumping action
Endocardium – Inner layer; smooth lining that reduces friction within chambers
What is myocardial infarction? Efffects of Exercise?
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 and proetects 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?
SA node: Pacemaker; initiates depolarization and spreads it across atria to AV node
AV node: Delays impulse briefly to allow ventricular filling, then transmits to ventricles via the AV bundle
Bundle branches: AV bundle splits into left and right branches, carrying the impulse down the interventricular septum toward the apex
Purkinje fibres: Rapidly distribute depolarization through ventricular walls, ensuring coordinated contraction
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?
Lowers the risk of heart attacks and improves survival if one occurs
Reduces myocardial damage during a heart attack by:
- Enhancing antioxidant capacity
- Improving function of ATP-sensitive potassium channels, which help protect heart cells under stress
Evaluating collapsed athlete?
- Check responsiveness and pulse immediately.
- This step determines the next course of action.
- If no pulse → Cardiac Arrest:
- Initiate life support measures:
– Begin CPR (chest compressions and rescue breaths).
– Goal: circulate blood to maintain tissue oxygenation.
- Time is critical
- Early initiation of chest compressions significantly improves survival chances in cardiac arrest.
How does immediate defibrillation improve survival outcomes in sudden cardiac arrest (SCA)?
Immediate defibrillation leads to 67% survival
Increases chances of being neurologically intact by nearly 4× compared to delayed intervention
Exercise stress test for diagnosis of Coronary heart disease?
It detects restricted coronary blood flow by assessing the heart’s response to exercise—e.g., changes in ECG, blood pressure, or symptoms indicating ischaemia (Chest pain (angina), Shortness of breath, Dizziness, Fatigue)
What are the key features of coronary circulation during rest and exercise??
Cardiac muscle is highly oxidative with high O₂ demand
Adenosine is the main metabolic vasodilator; β-adrenergic vasodilation also contributes via the ANS
Coronary blood flow occurs mostly in diastole
- At rest: ~80% of flow during diastole due to vessel compression in systole
- During heavy exercise: 40–50% of flow can occur in systole
Exercise increases:
- Chronotropy (heart rate)
- Inotropy (contractility), raising O₂ demand
How is coronary circulation adapted during exercise?
The heart has an abundant coronary blood supply to meet the demands of highly oxidative cardiac muscle.
Oxygen extraction is already high at rest (~70–80%), leaving little reserve.
Blood flow increases during exercise, mainly regulated by metabolic vasodilation—especially via adenosine.
Most coronary perfusion occurs during diastole, as systole compresses coronary vessels.
The heart has a high risk of ischaemia during exercise if coronary flow is impaired (e.g. by stenosis), due to its limited capacity to increase oxygen extraction.
Anatomy and role of circulatory system?
Arteries - Blood delivery
Small arteries/arterioles - flow regulation
Capillaries - fluid / nutrient exchange
Venules - collection
Veins - Return
Anatomy and function of peripheral circulation in decreasing size? Principle??
- Conduit arteries
- Diameter: Several mm
- E.g., aorta, major arteries - Feed arteries
- Diameter: ~1 mm
- Supply specific tissues or organs - Resistance arteries
- Diameter: 150–300 μm
- Major site of vascular resistance - Arterioles (resistance arterioles)
- Diameter: 30–150 μm
- Control blood flow into capillary beds - Terminal arterioles
- Diameter: 10–30 μm
- Final branches before capillaries - Capillaries
- Diameter: 4–6 μm
- Site of nutrient and gas exchange
Key Principle: Resistance & Radius
- Resistance increases sharply as vessel radius decreases
- Follows Poiseuille’s Law:
𝑅∝1/𝑟4
- (Small changes in radius → large changes in resistance)
Aspects that control vasodilation/constriction?
- Neural Control:
- Sympathetic Nervous System (SNS) → Releases adrenaline → vasoconstriction or dilation depending on receptor type.
- Hormonal Control:
- Hormones like norepinephrine act similarly to SNS signals, influencing vessel tone.
- Myogenic Mechanism:
- Blood vessels respond to changes in pressure and flow automatically (e.g., constrict if pressure increases to maintain flow).
- Mechanical Factors:
- Skeletal muscle pump and movement enhance venous return and influence vessel diameter.
- Metabolic Control:
- Local metabolites (e.g., CO₂, H⁺, adenosine) cause vasodilation to match blood flow with metabolic demand.
- Endothelial Factors:
- Endothelium releases EDRF (e.g., nitric oxide) causing smooth muscle relaxation and vasodilation.
Metabolic regulation of resistance vessels?
Blood flow increases according to tissue/organ metabolic activity — called hyperaemia.
Metabolic factors causing vasodilation include:
- Tissue hypoxia (low oxygen)
- Increased CO₂
- Decreased pH (acidosis)
- Lactate accumulation
- ATP breakdown products (e.g., adenosine, inorganic phosphate)
- Increased potassium (K⁺)
- Changes in osmolality
Endothelial derived relaxing factors (EDRFs)
EDRFs are substances released by the endothelium (inner lining of blood vessels) that cause vasodilation — relaxing the smooth muscle in vessel walls to increase blood flow. Two key EDRFs are:
Nitric Oxide (NO): Formed from L-arginine in response to shear stress.
- → Enhances blood flow, reduces blood pressure, and supports vascular health.
- → In cardiovascular disease, NO production is often impaired, reducing vessel function.
Prostaglandins (PGs): Formed from arachidonic acid.
- → Cause vasodilation but are pro-inflammatory.
- Short-term: Beneficial—increases blood flow and aids muscle recovery.
- Long-term: Harmful—chronic inflammation can damage vessels
Redistribution of Blood Flow During Exercise?Depends on? Purpose?
To Active Muscles:
- At rest: ~15–20% of cardiac output goes to skeletal muscle
- During maximal exercise: increases to 80–85%
- Supports oxygen and nutrient delivery to meet increased metabolic demands
Away from Less Active Organs:
- Reduced flow to liver, kidneys, and gastrointestinal tract
Degree of redistribution depends on:
- Exercise intensity
- Metabolic activity of tissues
Purpose:
- Optimises blood flow to where it’s most needed during physical exertion.
How is Local Blood Flow Regulated during Exercise?
Active skeletal muscle: Vasodilation reduces vascular resistance (via autoregulation)
- Blood flow increases to meet metabolic demand
- Magnitude of vasodilation depends on the amount of muscle recruited
- Mediated by local factors: ↑ nitric oxide, prostaglandins, ATP, adenosine
Inactive tissues & visceral organs: Vasoconstriction increases resistance
- Caused by SNS activation (e.g. norepinephrine)
- Blood flow can fall to 20–30% of resting levels to prioritize active muscles
How do catecholamines aid redistribution of cardiac output during exercise? Determinants?
Noradrenaline & adrenaline levels rise, causing vasoconstriction in most organs
- This helps redirect blood to active muscles
Noradrenaline spillover reflects increased SNS activation
Adrenaline effects depend on intensity:
- Light exercise: Vasodilation in skeletal muscle via β-receptors
- Heavy exercise: Vasoconstriction via α-receptors as demand increases
Cardiac output redistribution during exercise?
At maximal exercise, skeletal muscle can receive up to 90% of cardiac output
Other significant recipients include the skin (for cooling) and coronary circulation (to meet increased heart demand)
Circulation through ‘special’ regions during exercise?
Sympathetic vasoconstriction reduces flow to inactive organs (e.g. resting muscle, skin, splanchnic, renal)
Metabolic vasodilation increases flow to active muscle and coronary circulation
Thermoregulatory vasodilation boosts skin blood flow for heat loss
In severe exercise, there’s competition between muscle demand and thermoregulation, with blood pressure maintenance taking priority
