Control Of Heart Function Flashcards
Endogenous (within the heart) regulation of heart function:
What are the 3 main anatomical components of the heart and what are their respective functions?
Muscle cells (cardio-myocytes): can contract and relax in response to electrical stimuli. Essential for pumping blood around the body
Specialised electrical cells: cells that create spontaneous currents and those that transmit currents exist within the heart. Essential for regulating contraction of the cardio-myocytes
Vessels: major blood vessels responsible for transporting blood in and out of the heart, while coronary blood vessels supply blood to the heart.
Main components of the heart:
List the two types of nodes and their characteristics
Nodes:
Sinoatrial (SA) node:
Pacemaker of the heart ; 60-100 bpm
Junction of Crista terminalis; upper wall of right atrium & opening of superior vena cava
Atrioventricular (AV) node:
Has pacemaker activity - slow calcium mediated action potential
Triangle of Koch at base of right atrium
Main components of the heart:
List the types of tracts and their characteristics
- Bundles of His & bundle branches
- specialised myocytes. AV node: his bundle -> branches at intraventricular septum -> apex
Purkinje fibres:
Specialised conducting fibres
The sinoatrial node - pacemaker
Detail the nodal cell action potential
How many phases?
What are the phases?
Resting membrane potential?
Nodal cell action potential (AP):
Nodal AP only has 3 phases (0,3&4)
Upstroke (inc) due to Ca2+ influx
Repolarisation (decreases) due to K+ efflux
Nodal cells don’t have a resting membrane potential - only a pre potential due to Na+ influx through a funny channel
Why do different parts of the heart have different action potential shapes?
Different parts of the heart have different ion currents flowing and different ion channel expression in cell membrane
Cardiac muscle action potential:
Describe the length of cardiac muscle APs
What does the duration of the AP control?
What type of contraction is needed to produce an effective pump
What is the definition of the absolute refractory period (ARP)?
Define the term relative refractory period (RRP)
Compared to nerves, cardiac AP is long (200-300 ms vs 2-3 ms)
Duration of AP controls duration of contraction of heart
Long, slow contraction is required to produce an effective pump
AP has 5 phases (0-4)
Absolute refractory period (ARP) = time during which no AP can be initiated regardless of stimulus intensity
Relative refractory period (RRP) = period after ARP where an AP can be elicited but only w larger stimulus strength
Exogenous (outside the heart) regulation of heart function:
List the 3 major organ systems that modulate the activity of the heart and their respective roles
- Brain/central nervous system - can effect immediate changes through nerve activity or slower changes through hormonal activity
- Kidneys - heart and kidneys share a bi-directional regulatory relationship through indirect mechanisms
- Blood vessels - regulate amount of blood that goes to and from the heart the heart the blood vessels are able to influence cardiac activity
Control of the heart - CNS:
Which nervous systems are involved in the control of heart function and what effects do they have on heart rate and the phases of action potentials?
Autonomic nervous system:
Cardio regulatory centre & vasomotor centres in medulla
Parasympathetic nervous system:
Rest and digest
Decreases heart rate (HR) - decreases slope of phase 4
Sympathetic nervous system:
Fight or flight
Increases heart rate (chronotropy) - increases the slope of phase 4
Increases force of contraction (inotropy) - increases Ca2+ dynamics
More on the autonomic nervous system:
Describe the features of the parasympathetic and sympathetic nervous systems:
Neurotransmitters used by ganglionic fibres?
Functions?
Anatomical positions?
Parasympathetic:
Rest and digest
Pre ganglionic fibres use ACh as neurotransmitter
PNS post ganglionic NT = ACh
PNS is important for controlling the heart rate
Parasympathetic arises from cranial part of spinal cord
PNS arises from sacral part of spinal cord
Sympathetic:
Fight or flight
Pre ganglionic fibres use ACh as their neurotransmitter
SNS post ganglionic NT = NA
SNS is important for controlling the circulation
Sympathetic arises from thoracic vertebra
Sympathetic arises from lumbar vertebra
The vasomotor centre:
Where is the VMC located?
What is the VMC composed of? (3 areas)
How does the VMC transmit impulses to almost all blood vessels?
What effect can higher centres of the brain like the hypothalamus have on the VMC?
How do the lateral portions of the VMC control heart rate?
How does the VMC decrease heart rate?
VMC located bilaterally in reticular substance of medulla and lower third of pons
VMC is composed of:
Vasoconstrictor (pressor) area
Vasodilator (depressor) area
Cardio regulatory inhibitory area
Transmits impulses distally through spinal cord to almost all blood vessels
Many higher centres of the brain eg hypothalamus can exert powerful excitatory or inhibitory effects on the VMC
lateral portions of VMC controls heart activity by influencing heart rate and contractility
Medial portion of VMC transmits signals via vagus nerve to heart that tend to decrease heart rate
Control of the heart - kidneys
What effect does the renal system have on:
Sympathetic nerves
Blood volume
Blood pressure
Sympathetic nerves:
Increase activity
Decrease glomerular filtration -> decreased Na+ excretion: increase in blood volume (aldosterone)
blood volume:
Detected by venous volume receptors
Increased activity
Increased renin secretion —> increases angiotensin II production: vasoconstriction & increases blood pressure
Blood pressure:
Detected by arterial baroreceptors
Renal system:
Sympathetic nerves - what do they innervate in the glomerulus?
Afferent arterioles - what are they the site of? How do they decrease the amount of Na+ filtered What are juxtaglomerular cells What receptor regulates renin secretion
Sympathetic nerves:
Innervate afferent and efferent arterioles of the glomerulus (and nephron tubule cells)
Afferent arterioles:
Primary site of sympathetic activity
Alpha 1-adrenoceptor -> vasoconstriction
Decrease in glomerular filtration rate —> decrease in Na+ filtered
Juxtaglomerular cells are the site of synthesis, storage & release of renin
Beta1 adrenoceptor —> renin secretion
Control of the heart via blood vessels:
Cardiopulmonary circuit:
What types of vessels?
How does the cardiopulmonary circuit lead to an increase in SNS activity
How does the cardiopulmonary circuit decrease SNS activity?
Cardiopulmonary circuit - volumes:
Large pulmonary vessels
-volume sensors (also atria & right ventricle): send signals through glossopharyngeal & vagus nerves
-decrease in filling —> decreased baroreceptor firing —> increased sympathetic nerve (SNS) activity
-distension -> increased baroreceptor firing —> decreased SNS activity
Control of the heart via blood vessels:
Arterial circuit:
What structures does it consist of?
What is the function of the pressure sensors
How does the arterial circuit increase and decrease SNS activity
Arterial circuit - pressures:
Aortic arch, carotid sinus & afferent arterioles of kidneys
- pressure sensors: send signals through glossopharyngeal & vagus nerves
- decrease in pressure —> decrease in baroreceptor firing —> increase in SNS activity
- increase in pressure -> increases baroreceptor firing —> decreased SNS activity
Circulatory system - volumes:
What are the two blood circulations?
What is venous volume distribution affected by?
What does central venous pressure determine?
What determines stroke vol?
What is the effect of constriction in veins
What does constriction determine in arterioles? (3)
Two circulations: pulmonary and systemic
Right heart —> lungs —> left heart —> body
Venous:
Venous volume distribution affected by peripheral venous tone, gravity, skeletal muscle pump & breathing
Central venous pressure (mean pressure in the right atrium) determines amount of blood flowing back to heart
Amount of blood flowing back to the heart determines stroke volume
In veins construction reduces compliance and increases venous return
In arterioles constriction determines:
Blood flow to downstream organs
Mean arterial blood pressure
The pattern of blood flow to organs
