Lecture 15 - The Heart and Circulation - Central Flashcards
What are the 4 major parts of the cardiovascular system?
- heart (pump)
- arteries (outflow conduits)
- capillaries (drop/pick-up site)
- veins (return flow conduits)
what are the 4 chambers of the heart?
- right atria
- left atria
- right ventricle
- left ventricle
what is the role of the atria?
- receiving chambers (top)
what is the role of the ventricles?
- pumping chambers (bottom)
what is the “right heart”?
- pulmonary circulation
- pumps deoxygenated blood from body to lungs
- superior/inferior vena cava –> RA –> tricuspid valve –> RV –> pulmonary valve –> pulmonary arteries –> lungs
what is the “left heart”?
- systemic circulation
- pumps oxygenated blood from lungs to body
- lungs –> pulmonary veins –> LA –> mitral valve –> LV –> aortic valve –> aorta
what is cardiac muscle? and its characteristics?
- muscle of the heart
- contracts as one single unit
- fibres are interconnected end-to-end by intercalated discs
- “all or nothing” muscle
what is coronary circulation?
- primary blood supply to heart is provided by coronary arteries which arise from aorta
- cardiac veins return deoxygenated blood to the inferior and superior vena cava
- requires oxygen and energy for contraction
how do you match O2 supply with O2 demand?
- as ATP demand increases, demand for oxygen increases
- oxygen supply also increases because they have to be equal/equivalent (supply and demand)
What is the heart’s contribution to exercise?
- generates pressure to drive oxygenated blood through vessels to skeletal muscle
- driven by the demands for active skeletal muscle for O2
- also driven by the need to remove CO2, transport hormones, support temperature, fluid regulation and acid-base balance (pH)
- works harder when O2 demands are higher
what is the equation for matching systemic O2 with O2 demand?
- VO2 = Q x a-vO2difference
- where VO2 = O2 uptake
- Q = HR x SV, flow of O2 rich blood
- a-vO2difference = CaO2 - CvO2 (O2 extraction)
- this is known as Fick’s principle
how can you measure CaO2?
- with a catheter
- with hemoglobin –> concentration of hemoglobin, saturation of hemoglobin and partial pressure of O2 in the blood
what has the biggest influence on Vo2 uptake?
- Q
- cardiac output needs to increase significantly to keep us exercising for long periods of time or at higher levels
what is normal VO2 at rest?
- 4-6 L/ minute
- Q increases at a 6:1 ratio as VO2 increases
what is cardiac output (Q)?
- total volume of blood pumped by the ventricle each minute
- measured in L/min
- HR x SV
how does HR contribute to Q? (2)
- intrinsic control
- extrinsic control
what is intrinsic control?
- internal rhythm controls in the heart
- heart can generate it’s own electrical signal
- pacemaker (SA node) - establishes sinus rhythm
- can reach 100 bpm without external control
what is extrinsic control?
- systems that modulate intrinsic electrical impulses
- causes HR to increase
- adjusts HR at rest (for endurance athletes, it’s very low)
- HR can reach up to 220 during maximal effort
- works like a dial
- requires brain signals
what are the components of an ECG?
- P wave = atrial depolarization
- QRS wave = ventricular depolarization
- ST segment= ventricular repolarization
- T wave = ventricular repolarization
- PR interval = includes AV delay
- QT interval = ventricular depolarization and repolarization
what is the route of myocardial impulse transmission?
- sinoatrial node
1.5. atria - atrioventricular node
- A-V bundle or bundle of His
- Purkinje fibres (AV bundle)
4.5. ventricles
what happens in the SA node?
- spontaneous depolarization and repolarization to provide “innate” heart stimulus
what happens in the AV node?
- delays impulse around 0.10 second to provide sufficient time for atria to contract and force blood into the ventricles
what is the role of Purkinje fibres?
- speed impulse rapidly through ventricles
what 3 extrinsic systems modulate HR?
- parasympathetic nervous system
- sympathetic nervous system
- endocrine system
what is the role of the parasympathetic nervous system in modulating HR?
- vagus nerve
- slows the heart rate and conduction velocity
- uses acetylcholine
what is the role of the sympathetic nervous system in modulating HR?
- from the ganglia
- increases HR
- uses norepinephrine (improves conduction)
- dilate coronary arteries
what is the role of the endocrine system in modulating HR?
- releases epinephrine (from adrenal medulla)
- slows heart rate
- dilates coronary vessels
- accelerates SA node discharge
- increases myocardial metabolism
how does SV contribute Q?
- stroke volume is the amount of blood pumped in one heartbeat
- pressure changes/generation throughout the heart
- through the cardiac cycle
what is normal SV?
- 70mL/beat
what are the phases of the cardiac cycle?
- contraction phase = systole
- relaxation phase = diastole
- always some volume in the left ventricle (never at 0)
- *understand the cardiac cycle image (slide 19)
how do you calculate SV?
- during systole
- EDV - ESV = SV
what is EF?
- ejection fraction
- % of EDV pumped (end-diastolic volume)
- SV /EDV = SV
- clinical index of heart contractile function
- typically between 60-65%
what is preload?
- the volume of blood received by the heart during diastole (EDV)
- a component of SV
- increased venous return
what is the Frank-Starling Law of the Heart?
- the relationship between contractile force and resting length of heart’s muscle fibres
- force is proportional to it’s initial length
- preload stretches the ventricle is diastole to produce a more forceful ejection of blood (increased EDV = increased SV)
what is contractility?
- a component of SV
- can we get cells to contract more forcefully
- inotropy
what is inotropy?
- enhanced contractile force (increased tension)
- augments stroke power and facilitates emptying
- length-independent
- increased inotropy = increased SV
- fires sympathetic nerves, decreases parasympathetic nerves, increases circulation of Epi and NE
what is afterload?
- a component of SV
- pressure the heart must generate to open aortic valve
- higher afterload = higher pressure needed to open aortic valve
how do you overcome afterload?
- reduction of afterload is normal during exercise
- high afterload = greater pressure generated by left ventricle
what is the relationship between stroke volume and oxygen uptake?
- consistent relationship
- exponential relationship (ending with evening out)
what are the 5 determinants off cardiac output?
- heart rate
- stroke volume
- preload
- contractility
- afterload
what is the Fick Principle?
- need to match O2 supply with O2 demand
- cardiac output is very closely linked to oxygen supply and demand
