Control of heart function Flashcards
What are the 3 major tissues that control heart function?
CNS
Blood Vessels
Kidneys
Where is the SAN found?
Junction of crista terminalis; upper wall of right atrium & opening of superior vena cava
What molecule regulates the AVN?
Ca2+
Where is the AVN found?
Triangle of Koch at base of right atrium
What kind of cells are in the bundle of His and describe the pathway
Specialised myocytes.
AV node: His bundle > branches at intraventricular septum > apex
What are the purkinje fibres made of?
Specialised conducting fibres
3 phases: 0, 3, 4
Ca2+ influx
K+ efflux
Na+ influx
What kind of channels create the pre-potential present in the SAN?
‘Funny’ channels
How do action potentials vary across the heart?
Have different action potential shapes
-Due to different ion currents flowing and different ion channel expression in cell membrane
How and why are cardiac muscle APs different to nerve APs?
Compared to nerves, cardiac AP is long (200-300 ms vs. 2-3 ms)
-Duration of AP corresponds to duration of contraction
-Long contractions necessary for effective pumping
def Absolute refractory period
Time during which no AP can be initiated regardless of stimulus intensity
def Relative refractory period
Period after ARP where an AP can be elicited but only with larger stimulus strength
How many phases are in a cardiac muscle AP and what are they?
5
What causes the upstroke in a cardiac muscle AP?
Na+ influx
What is different about K+ efflux and Na+ influx in cardiac muscle cells and SA node cells?
SA node has K+ efflux only during AP, cardiac muscle AP has K+ efflux continuously, apart from the first influx of Ca2+
SA node has Na+ infux continuously, but cardiac muscle cell has Na+ influx only at the upstroke
How does the sympathetic and parasympathetic nervous system innervate the heart?
Sympathetic: Controls SAN, AVN and lower heart fibres
Parasympathetic(Vagus nerve): Controls SAN and AVN only
What is the effect of sympathetic innervation of the heart?
‘fight or flight’
↑ HR (chronotropy) – increases the slope of phase 4
↑ force of contraction (inotropy) – increases Ca2+ dynamics
What is the effect of parasympathetic innervation of the heart?
‘Rest & digest’
↓ heart rate (HR) – decreases the slope of phase 4
What are the neurotransmitters in pre and post ganglionic fibres in the SNS?
Pre-ganglionic fibres use ACh
Post ganglionic fibres use noradrenaline
What is the neurotransmitter in pre and post ganglionic fibres in the PNS?
ACh
Between the cardiac plexuses and spinal cord where do sympathetic fibres pass through first?
Sympathetic chain(Paravertebral ganglia)
What are the SNS and PNS useful for in heart control?
PNS: Heart rate
SNS: Circulation
When innervating the heart, where do the parasympathetic and sympathetic fibres arise from?
SNS: Thoracic + Lumbar vertebrae
PNS: Cervical + Sacral vertebrae
What is the function of the vasomotor centre and what comprises it?
Transmits impulses distally through spinal cord to almost all blood vessels
Composed of:
-Vasoconstrictor (pressor) area
-Vasodilator (depressor) area
-Cardio-regulatory inhibitory area
Where is the vasomotor centre located?
VMC(Vasomotor centre) located bilaterally in reticular substance of medulla & lower third of pons
What different functions do the lateral and medial portions of the vasomotor centre control?
Medial: Transmits signals via vagus nerve to heart that tend to decrease heart rate.
Lateral: Controls heart activity by influencing heart rate and contractility
At the SAN, what kind of receptors do Ach(PNS) and NA(SNS) bind to?
G-protein coupled receptors which activate a protein cascade(ATP>cAMP>PKA)
How is the vasomotor centre excitatorily/inhibitorily controlled?
Higher centers of the brain such as the hypothalamus can exert powerful excitatory or inhibitory effects on the VMC.
By what 3 means is kidney function controlled?
Sympathetic innervation(No PNS)
Blood volume
Blood pressure
How does decreased blood volume alter kidney function?
↑renin secretion > ↑angiotensin-II production: vasoconstriction & ↑blood pressure(via aldosterone)
How does increased sympathetic innervation alter kidney function
α1-adrenoceptor > vasoconstriction > ↓ glomerular filtration > ↓Na+ excretion: increase in blood volume (aldosterone)
What are changes in blood volume detected by?
Venous volume receptors
How are changes in blood pressure detected?
Arterial baroreceptors
Where do renal sympathetic fibres innervate on the kidney?
Afferent and efferent arterioles
What is the site of storage, synthesis and release of renin?
Juxtaglomerular cells
What do kidney B1-adrenoceptors control?
Renin secretion
How do baroreceptors control blood pressure in the CP circuit?
(Decrease in filling)/Distension > Less/More baroreceptors firing > More/Less SNS activity
Which nerves do volume+pressure sensors (also atria & right ventricle) send signals through?
Glossopharyngeal + Vagus
In the arterial circuit, how do pressure sensors control heart rate?
Decrease/Increase in pressure > Less/More baroreceptors firing > More/Less SNS activity
What factors are SNS activity based off of in the cardiopulmonary and arterial circuit?
CP: Volumes
Arterial: Pressures
What are the 2 circulations in the body?
Two circulations: pulmonary and systemic
Right heart > lungs > left heart > body
What does constriction in veins cause?
-Reduced compliance
-Increased venous return
What is peripheral venous volume affected by?
Peripheral venous tone(SNS)
Gravity
Skeletal muscle pump
Breathing
What does central venous pressure dictate?
Amount of blood flowing back to the heart, and thus preload and stroke volume
What does constriction determine in arteries?
Blood flow to downstream organs
Mean arterial blood pressure
The pattern of blood flow to organs
Top is atrial pressure
What is the function of Nitric oxide (NO) and is it a local or systemic factor for blood flow regulation?
Local vasodilator
What is the function of Prostacylin and is it a local or systemic factor for blood flow regulation?
Local vasodilator
What is the function of Noradrenaline/Adrenaline and is it a local or systemic factor for blood flow regulation?
Systemic vasoconstriction
What is the function of Atrial natriuretic peptide (ANP) and is it a local or systemic factor for blood flow regulation?
Systemic vasodilator
What is the function of Vasopressin (ADH) and is it a local or systemic factor for blood flow regulation?
Systemic vasoconstriction
What is the function of Angiotensin II and is it a local or systemic factor for blood flow regulation?
Systemic vasoconstrictor
What is the function of Kinins and is it a local or systemic factor for blood flow regulation?
Systemic vasodilator
What is the function of Endothelins (ET) and is it a local or systemic factor for blood flow regulation?
Local vasoconstrictors
What is the function of Thromboxane A2 (TXA2) and is it a local or systemic factor for blood flow regulation?
Local vasoconstrictor
What is the difference between systemic and local blood flow regulators?
Local: Intrinsic to the smooth muscle (or closely associated)
Important for reflex local blood flow regulation within an organ
Systemic: Extrinsic to the smooth muscle
These include the autonomic nervous system & circulating hormones
What is the effect of SNS innervation on the afferent glomerular arterioles?
α1-adrenoceptor > vasoconstriction
↓ in glomerular filtration rate > ↓Na+ filtered > Increased blood volume
What is the function of aldosterone
Increase Na+ reabsorption
Increase K+ excretion
What is renins’ effect on aldosterone?
Renin increases aldosterone
