Week 1 aka hell week Flashcards
Which node does not have a stable membrane potential
SA node
What causes the pacemaker potential
Decrease in in K+ efflux superimposed on a slow Na+ influx current
What cause the rising phase of the action potential (depolaristation) in the SA node
Activation of voltage-gated Ca+ channels > This results in a Ca+ influx
What cause the falling phase of the action potential (repolaristation) in the SA node
caused by the activation of K+ channels
> Resulting in a K+ efflux
What is responsible for the rising phase (depolarisation) in ventricular muscle
- Fast Na+ influx
What causes the plateau phase of ventricular muscle
influx of Ca+
What causes the falling phase of the action potential (depolarisation)
inactivation of Ca+ channels and activation of K+channels causing a K+ efflux
What effect does the Vagus nerve have on heart rate
Vagal tone slows the intrinsic HR from 100bpm to sound 70bpm
>Vagal tone dominates under restin conditions
What is a negative/positive chronotropic effect?
speeds up/ slows heart rate
What are myofibrils?
- contractile units of muscle. Each muscle cell contains many myofibrils
What are SACROMERES?
SACROMERES is the name given to how actin and myocin are arranged within each MYOFIBRIL
How is cardiac muscle tension produced
by the sliding of actin filaments on myosin filaments
What switches on the cross bridge formation between muscle fibres
Ca+
What element is require to stimulate the release of calcium from the sarcoplasmic reticulum
Ca+
What effect does a positive inotropic effect have on the frank starling curve
Shifts to the left
How could we regulate the cardiac output?
By regulating the stroke volume and Heart rate
What is DIASTOLE
Heart ventricles are relaxed and fill with blood
What is systole?
the heart ventricles contract and pump blood into the: aorta (LV) and pulmonary artery(RV)
Describe the events of PASSIVE FILLING
- Pressure in atria and ventricles close to zero
- AV valves open so venous return flows into the ventricles
- Aortic pressure ~ 80 mmHg, and aortic valve is closed
- Similar events happen in the right side of the heart, but the pressures (right ventricular and pulmonary artery) are much lower
> Ventricles become ~ 80% full by passive filling (due to a simple pressure gradient)
Describe the events of ATRIAL CONTRACTION
The P-wave in the ECG signals atrial depolarisation
The atria contracts between the P-wave and the QRS
> Atrial contraction complete the END DIASTOLIC VOLUME (~ 130 ml in resting normal adult) – the end diastolic pressure is few mmHg)
Describe the events of ISOVOLUMETRIC VENTRICULAR CONTRACTIO
- Ventricular contraction starts after the QRS (signals ventricular depolarisation) in the ECG
- Ventricular pressure rises
- When the ventricular pressure exceeds atrial pressure the AV VALVES SHUT
- This produces the FIRST HEART SOUND (LUB)
- The aortic valve is still shut, so no blood can enter or leave the ventricle
- The tension rises around a closed volume “Isovolumetric Contraction”
The ventricular pressure rises very steeply
Describe the events of VENTRICULAR EJECTION
- When the ventricular pressure exceeds aorta/pulmonary artery pressure
- Aortic/pulmonary valve open
- Stroke Volume (SV) is ejected by each ventricle, leaving behind the End Systolic Volume (ESV)
- Aortic pressure rises
- The T-wave in the ECG signals ventricular repolarisation
- The ventricles relax and the ventricular pressure start to fall
- When the ventricular pressure falls below aortic/pulmonary pressure: aortic/pulmonary valves shut
Describe the events of ISOVOLUMETRIC VENTRICULAR RELAXATION
- Closure of aortic/and pulmonary valves signals the start of the isovolumetric ventricular relaxation
- Ventricle is again a closed box, as the AV valve is shut
- The tension falls around a closed volume “Isovolumetric Relaxation”
- When the ventricular pressure falls below atrial pressure, AV valves open (Remember this is a silent event), and the heart starts a new cycle
What causes the first heart sound?
closure of mitral and tricuspid valves. It sounds like a “lub”
What causes the 2nd heart sound?
caused by closure of aortic and pulmonary valves.
It sounds like a “dub”
What prevents arterial pressure from falling to zero during diastole?
The recoil of the arteries keeps the blood flowing and prevents the pressure from falling
The closure of the aortic valve also contributes to this
What drives blood around the systemic circulation?
A Pressure Gradient between the Aorta (AO) and the Right Atrium (RA)
A MAP of what pressure is needed to perfuse vital organs?
60 mmHg
What is the normal mean range for MAP
70 —–> 105
Where are the two groups of baroceptors located??
(1) Aortic Arch
(2) Carotid Sinus
How is information relayed to the medulla
via the Vagus nerve and glossopharyngeal nerve
What stops the firing of baroceptors
if high blood pressure is sustained
What is responsible for the long term control of MAP
Blood Volume
What two factors affect extracellular volume
Water excess or deficit
Na+ excess or deficit
What is - The Renin-Angiotensin- Aldosterone System - RAAS?
Plays an important role in the regulation of plasma volume and TPR and hence the regulation of MAP
Where does Renin come from and what does it do?
Renin is released from the kidneys and stimulates the formation of angiotensin I in the blood from angiotensinogen (produced by the liver)
What is the name of the enzyme which converts AngiotensinI into Angiotensin II
ACE (produced by pulmonary vascular endothelium)
What are the two jobs of ANGIOTENSIN II?
- stimulates the release of Aldosterone from the adrenal cortex
- Causes systemic vasoconstriction - increases TPR
What is the function of ALDOSTERONE?
a steroid hormone
acts on the kidneys to increase sodium and water retention – increases plasma volume
How is the Renin-Angiotensin- Aldosterone System regulated?
(1) Renal artery hypotension -caused by systemic hypotension (decreased blood pressure)
(2) stimulation of renal sympathetic nerves
(3) Decreased [Na+] in renal tubular fluid – sensed by macula densa (specialised cells of kidney tubules)
What is Atrial Natriuretic Peptide?
28 amino acid peptide synthesised and stored by atrial muscle cells (atrial myocytes)
Released in response to atrial distension (hypervolaemic states)
What is the primary purpose of ANP?
Causes excretion of salt and water in the kidneys, thereby reducing blood volume and blood pressure
Acts as a vasodilator - decreases blood pressure
Decreases Renin release
What is ADH?
Peptide hormone derived from a prehormone precursor synthesised by the hypothalamus and stored in the posterior pituitary
Secretion stimulated by
1) reduced extracellular fluid volume or
2) increased extracellular fluid osmolarity (main stimulus)
What is the normal osmolarity of extracellular fluid?
280 milli-osmoles/l
What is the function of ADH?
ADH acts in the kidney tubules to increase the reabsorption of water (conserve water) - i.e. concentrate urine (antidiuresis)
This would increase extracellular and plasma volume and hence cardiac output and blood pressure
What is the function of osmoreceptors?
To monitor the plasma osmolality?
What is the main site of TOTAL PERIPHERAL RESISTANCE
The arterioles
What system supplies the vascular smooth muscle?
SYMPATHETIC nerve fibers.
The neurotransmitter is NORADRENALINE acting on alpha receptors
Define Vasomotor tone
Vasomotor tone is the amount of tension in the smooth muscle inside the walls of blood vessels, particularly in arteries
What would increase vasomotor tone and thereby causing vasoconstriction
- Increased sympathetic discharge
What would decrease vasomotor tone and thereby causing vasodilation
Decreased sympathetic discharge
What is the effect of adrenaline of alpha receptors?
causes vasoconstriction
What is the effect of adrenaline of beta receptors?
vasodilation
what factors cause relaxation of arteriolar smooth muscles resulting in VASODILATATION:
- Decreased local PO2
- Increased local PCO2
- Increased local [H+] (decreased pH)
- Increased extra-cellular [K+]
- Increased osmolality of ECF
- Adenosine release (from ATP)
Name 3 humoral agents which cause relaxation of arteriolar smooth muscles resulting in VASODILATATION
- Histamine
- Bradykinin
- Nitric Oxide (NO) - this is continuously released by endothelial cells of arteries and arteriole
Name 3 humoral agents which cause contraction of arteriolar smooth muscles resulting in VASOconstriction
Serotonin
Thromboxane A2
Leukotrienes
Endothelin - this is a potent vasoconstrictor released from endothelial cells. Its production is stimulated by various agents which cause vasoconstriction
What effecr does increased VENOmotor tone have?
Increased venous return, SV and MAP
