Cardiovascular L4: Regulation of Heart Rate and Cardiac Output Flashcards
What is cardiac output?
volume of blood pumped by each ventricle per minute
What 2 things determine cardiac output?
Heart rate (HR) Stroke volume (SV)
What stimulation increases heart rate and what stimulation decreases heart rate?
Heart rate is decreased by parasympathetic stimulation and increased by sympathetic stimulation
What are 2 things that determines stroke volume?
Stroke volume is determined by:
- sympathetic activity
- venous return (how much blood coming back to heart from veins)
What is the equation for cardiac output (CO)?
Heart rate (bpm) x stroke volume (ml) = Cardiac output (CO)
On average at rest, what is the CO (cardiac output) for each ventricle?
72 bpm x 70 ml = 5040 ml/min 5.04 L
Overview of the autonomic nervous system. What does the sympathetic and parasympathetic nervous system do?
To all organs, glands,blood vessels and tissues (other than skeletal muscle)
What are 3 key facts about the autonomic nervous system?
- Most organs dually innervated
- Mostly opposite effects
- Balance shifts to meet demands
What is the sympathetic nervous system? Specify length of pre and post fibres.
- ganglia are close to spinal column
- short pre and long post
What is the parasympathetic nervous system? Specify length of pre and post fibres.
- ganglia are close to effector organ
- long pre and short post
Diagram of Autonomic nervous system
What does the sympathetic nervous system innervate?
Innervates SA and AV nodes, myocardium &conduction system
MORE TO ADD
What does the parasympathetic nervous system innervate?
Innervates SA and AV nodes &atrial muscle
MORE TO ADD
How is cardiac output affected by autonomic control (heart rate and stroke volume)?
Cardiac output = Heart rate x Stroke volume Heart rate: influenced by both parasympathetic and sympathetic nervous systems Stroke volume: influenced by sympathetic nervous system only (but in two ways…)
How is heart rate controlled by the nervous system?
Parasympathetic & Sympathetic innervation: both have chronotropic effects (changing heart rate) and ionotropic effects (activating or deactivating voltage-gated ion channels)
Heart rate is a balance between parasympathetic (______) and sympathetic (______) control
inhibitory; excitatory
- Sympathetic- keeps it going If left to own devices, heart rate would speed up
- Thus, is constantly slowed down by the parasympathetic system
What is ‘vagal tone’?
The heart has an intrinsic rate of 100-110 bpm, but at rest, HR is 60-80 bpm, suggesting that it is under constant inhibitory control
An increase in HR would ______ (increase/decrease) parasympathetic activity and ______ (increase/decrease) sympathetic
decrease; increase
What happens to HR if the vagus nerve is cut?
Lose vagal tone –> accelerate HR
What is produced by the parasympathetic nervous system to control heart rate (change the pacemaker)? What does that cause?
Acetylcholine decreases slow inward Na+ and Ca2+ (slower depolarisation); increases K+ out in AP (more hyperpolarisation) = longer time to reach threshold Take longer to reach threshold –> decrease/slower HR
What happens to AP in normal self induced contraction?
What is produced by the sympathetic nervous system to control heart rate (change the pacemaker)? What affect does it have on HR?
Noradrenaline
increases slow inward Na+ and Ca2+ (faster depolarisation); decreases K+ out in AP (less hyperpolarisation) = shorter time to reach threshold
Takes faster to reach threshold –> increased/faster HR
What are the 2 ways that the sympathetic stimulation has of influencing stroke volume?
- Directly by excitatory innervation of the myocardium (atria & ventricles), increases strength of contraction, results in larger stroke volume = ‘extrinsic control’
- Indirectly by stimulating the Adrenal Medulla to produce Adrenaline, acts on veins to cause venoconstriction
- increases venous return (more blood returned to heart)
- increases ventricular filling and leads to increased EDV
- results in a larger stroke volume, through length–tension relationship called the ‘Frank–Starling law’ = ‘intrinsic control’
When controlling stroke volume, the sympathetic control as extrinsic and intrinsic effects to increase SV. Explain this.
- Extrinsic: direct increase in muscle contractility = increase SV
- Intrinsic: indirectly causes increase in venous return, increased EDV = increase SV
What is the Frank Starling Law?
The heart has the capacity to automatically adjust its output (Stroke Volume) to match its input (End Diastolic Volume)
Cardiac muscle fibre length depends on the extent of _______. Normally, fibre length is _____ (more/less) than optimal length for developing max tension. What happens to SV when there is an increase in venous return?
venous filling; less
Increased venous return → increased EDV → stretches fibres closer to optimal length → increased tension → stronger contraction → increased SV.
How is EDV increased in the Frank-Starling Law?
This would be the effect if only EDV increases, but we also get effects of extrinsic control
How to increase contractility (extrinsic control) in the Frank-Starling Law?
Extrinsic control shifts the curve to the left: same EDV, more SV (to meet the demands of the body)
How does intrinsic and extrinsic effects affect the Frank-Starling Law to increase SV?
- Intrinsic effect shifts up curve through increased EDV Extrinsic effect shifts curve to the left through increased contractility Combined together to give a larger response
How is the Frank-Starling Law important in heart failure? What happens to the curve?
Frank–Starling curve shifts downward and to the right - SV decreases at normal EDV Damage = decrease contraction = decrease SV = weaker
How does the Frank-Starling Law compensate in heart failure?
Sympathetic stimulation increases contractility, shifting curve to the left Increase in blood volume increases EDV, increases muscle fibre length = able to get normal SV
Summary: What are 2 things that the parasympathetic innervation does?
- inhibits SA and AV nodes, decreasing heart rate and increasing AV node delay
- inhibits atrial muscle, weakening atrial contraction
Summary: What are 4 things that the sympathetic innervation does?
- stimulates SA and AV nodes, increasing heart rate and decreasing AV node delay
- excites conduction pathways, increasing conduction
- stimulates myocardium increasing atrial &ventricular contractility and stroke volume
- causes venoconstriction increasing venous return & EDV = increased SV
Why does the heart get its own blood supply through the coronary arteries? List 3 reasons
- the coronary arteries branch off the aorta close to aortic valve, but during contraction, the open aortic valve partially blocks their entrances
- the contracting myocardium compresses the major branches of the coronary arteries (can get blood when contract)
- but, cardiac muscle very good at getting O2 out of blood, and can use multiple sources of energy
Coronary blood flow normally _____ to keep pace with cardiac oxygen needs
varies
Coronary artery disease, particularly the development of ______, can occur due to ______, ______ and _______.
atherosclerosis (plaque); hypertension; hyperlipidemia; hyperglycaemia
Atherosclerotic plaques in coronary arteries can cause partial or full ______, leading to _______, _______ and ______ → _______ of muscle wall
obstructions; angina; ischemic heart disease; myocardial infarction (no blood supply which damages tissue); death
