Control of Heart Function Flashcards
What 3 sources control function of the heart?
- CNS
- kidneys
- blood vessels
What parts of the ANS control the heart?
cardio-regulatory centre + vasomotor centres in medulla + Vagus nerve
How does the parasympathetic NS control heart rate?
- rest + digest
* vagus nerve decreases HR by decreasing slope of phase 4
How does the sympathetic NS control heart rate?
- fight or flight
- cardiac nerves from lower cervical + upper thoracic ganglia increase HR by increasing slope of phase 4 + increasing force of contraction (which increases Ca2+ dynamics)
What is chronotropy?
increase of heart rate
What is inotropy?
increase of force of contraction
How does the renal system control heart rate?
- decreased glomerular filtration = increased Na+ excretion = increase in blood volume
- increased renin secretion = increase in angiotensin-II production = vasoconstriction
How are changes in blood volume detected by the blood vessels?
increase in blood volume is detected by venous volume receptors
How are changes in blood pressure detected by the blood vessels?
increase blood pressure is detected by arterial baroreceptors
How do large pulmonary vessels detect + communicate changes in volume?
volume sensors (also in atria + right ventricle) send signals through glossopharyngeal + vagus nerves
What do volume sensors do when there is a decrease in filling?
reduced baroreceptors firing + increased SNS activity
What do volume sensors do when there is distention?
increases baroreceptors firing + decreased SNS activity
What vessels are part of the arterial circuit?
aortic arch + carotid sinus + afferent arterioles of the kidneys
How are changes in pressure detected in the arterial circuit?
pressure sensors send signals through glossopharyngeal + vagus nerves
What do pressure sensors do when there is a decrease in pressure?
decreased baroreceptors firing + increased SNS activity
What do pressure sensors do when there is a increase in pressure?
increased baroreceptors firing + decreased SNS activity
What does the sympathetic nervous system do?
• Pre-ganglionic fibres use acetylcholine as their
neurotransmitter
• Post ganglionic neurotransmitter is noradrenaline
• SNS is important for controlling the circulation
What does the parasympathetic nervous system do?
• Pre- and post-ganglionic fibres use
acetylcholine as neurotransmitter
• Muscarinic (M2) and Nicotinic receptors
• PNS is important for controlling the heart rate
Where is the vasomotor centre?
located bilaterally in reticular substance of medulla + lower 1/3 of pons
What effects do higher centres of the brain (e.g. hypothalamus) have on the vasomotor centre?
can exert powerful excitatory + inhibitory effects
How are impulses transmitted to the blood vessels?
distally through the spinal chord (to almost all the blood vessels)
What does the lateral portion of the vasomotor centre do?
controls heart activity by influencing heart rate + contractility
What does the medial portion of the vasomotor centre do?
transmits signals via vagus nerve to heart - tends to decrease heart rate
What 3 zones is the vasomotor centre split into?
- Vasoconstrictor (pressor) area
- Vasodilator (depressor) area
- Cardio-regulatory inhibitory area
What is the name of the network of nerves that supplies the heart?
cardiac plexus - receives contributions from right + left vagus nerve + sympathetic trunk
What does the right vagus nerve primarily innervate?
SA node
What does the left vagus nerve primarily innervate?
AV node
What receptors does the heart have? What binds to them?
adrenoceptors or adrenergic receptors - binds to adrenergic agonists such as noradrenaline + epinephrine
What receptors does the parasympathetic nervous system act on? How?
M2-receptors, causes inhibition of
ATP ➜ cAMP ➜ PKA
What receptors does the sympathetic nervous system act on?
β1-receptors + β2-receptors, causes more
ATP ➜ cAMP ➜ PKA
What happens when a β1-receptor is bound by a β1-agonist?
- heart rate increases (positive chronotropy)
- conduction velocity increases (positive dromotropy)
- contractility increases (positive inotropy)
- rate of myocyte relaxation increases (positive lusitropy)
When do β2-receptors become functionally more important than β1-receptors? Why?
heart failure - β1-receptors become down-regulated
What else can noradrenaline bind to? What is the effect?
α1-adrenoceptors found on myocytes to produce small
increases in inotropy
What else can bind to the α + β receptors in the heart?
Circulating catecholamines (epinephrine) released by the adrenal medulla
What happens when acetylcholine binds to M2 muscarinic receptors?
- negative chronotropy and dromotropy in the heart
* negative inotropy and lusitropy in the atria
How do the sympathetic nerve fibres affect the glomerulus + nephron tubule cells?
innervate the afferent + efferent arterioles
What is the primary site of sympathetic activity in the renal system?
afferent arterioles
What is the significance of α1-adrenoceptors in the renal system?
causes vasoconstriction = decreased glomerular filtration rate = decreased Na+ filtered
What is the significance of β1-adrenoceptors in the renal system?
causes renin secretion = conversion of angiotensin I to angiotensin II = vasoconstriction
What 4 factors is venous volume distribution affected by?
- peripheral venous tone
- gravity
- skeletal muscle pump
- breathing
What does central venous pressure determine?
amount of blood flowing back to heart
How does constriction affect veins?
reduces compliance + venous return
What does constriction in arterioles determine?
- Blood flow to downstream organs
- Mean arterial blood pressure
- Pattern of blood flow to organs
What is meant by local mechanisms for blood flow regulation?
mechanisms from endothelial or muscle cells
Why are local mechanisms for regulating blood flow important?
important for reflex local blood flow regulation within an organ
What are 4 endothelium derived mediators?
- Nitric oxide (NO): potent vasodilator, diffuses into vascular smooth muscle cells
- Prostacylin: vasodilator that also has antiplatelet & anticoagulant effects
- Thromboxane A2 (TXA2): vasoconstrictor that is also heavily synthesised in platelets
- Endothelins (ET): vasoconstrictors generated from nucleus of endothelial cells
What is meant by systemic mechanisms for blood flow regulation?
extrinsic to the smooth muscle, include the ANS & circulating hormones
What are 5 non-endothelium derived mediators?
• Kinins: bind to receptors on endothelial cells & stimulate NO synthesis – vasodilator effects
• Atrial natriuretic peptide (ANP): secreted from the atria in response to stretch – vasodilator effects to
reduce BP
• Vasopressin (ADH): secreted from pituitary gland. Binds to V1 receptors on smooth muscle to cause
vasoconstriction
• Noradrenaline/Adrenaline: secreted from adrenal gland (& SNS); causes vasoconstriction
• Angiotensin II: potent vasoconstrictor from the renin-angiotensin-aldosterone axis. Also stimulates ADH
secretion
