Mechanisms Flashcards
In an MI, what artery is most likely occluded?
Left anterior descending artery
Give 2 equations that can be used to calculate mean arterial pressure MAP
1.MAP=DP+(1/3PP)
(PP=SP-DP)
2.MAP=COxTPR
What 2 factors effect flow (volume passing in a certain time)?
Resistance (higher R, slower flow)
Pressure (higher P, faster flow)
Regarding haemodynamics, what does velocity mean?
What factor effects this?
Distance travelled in a given time
Area (larger the SA:V, higher the velocity)
Describe when in the cardiac cycle each valve in the heart opens
and closes.
Include when you will hear S1-lub and S2-dub sounds
DIASTOLE:
1) Atrial contraction - SLV: closed AVV: open
SYSTOLE: (ventricles contracting)
1) Isovolumetric contraction - SLV: closed. AVV: closed S1 lub sound
2) Rapid ejection - SLV: open AVV: closed
3) Reduced ejection - SLV: open AVV: closed
DIASTOLE: (ventricles filling)
1) Isovolumetric relaxation - SLV: closed S2 dub sound. AVV: closed
2) Rapid filling - SLV: closed AVV: open
3) Reduced filling - SLV: closed AVV: open
What causes mitral valve stenosis?
Rheumatic fever causes commissural fusion
Name 3 factors that lead to RV hypertrophy in mitral valve stenosis, as a result of LA dilation
Dyspnoea
Pulmonary oedema
Pulmonary hypertension
What causes dysphagia in mitral valve stenosis?
Oesophagus is compressed as a result of LA dilation
Why do patients with mitral valve stenosis have a higher chance of getting a stroke?
LA dilation leads to atrial fibrillation, stasis of blood in atria leads to thrombus formation, this can emboli and travel to the brain
What sound would be heard in mitral valve stenosis?
When would this sound be heard:
A) Diastole or systole
B) closure or opening of atrioventricular valves?
Diastolic rumble/mid diastolic murmur
Be heard in diastole, when the AVV open
Describe the pathophysiology of mitral valve regurgitation
Chordae tendineae and papillary muscle weakness leads to the prolapse of the mitral valve during systole (when they are meant to be closed)
What chamber undergoes hypertrophy in mitral valve regurgitation?
And how?
LV as during systole more blood flows back into the LA so the preload, for the next cycle is greater.
What sound would be heard in mitral valve regurgitation?
Specifically, when would the sound be beard?
Holosystolic/pan-systolic murmur heard in systole all the way from S1 (AVV closure) to S2 (SLV closure)
Name 3 causes of aortic valve stenosis
Calcification
Fibrosis
Chronic rheumatic fever - commissural fusion
Congenital - bicuspid instead of tricuspid valve formation
What abnormal valve function can lead to left sided heart failure?
How?
Aortic valve stenosis as there is more blood in the LV, leading to increased LV kpa so get LV hypertrophy but as time goes on tissue undergoes necrosis and cannot pump as much blood to the body (so get syncope) through the aorta.
Why do you get angina in aortic valve stenosis?
Not enough O2 blood entering the coronary arteries (via the aorta) to supply the heart muscle
What sound do you hear in aortic valve stenosis?
When is it heard?
Crescendo-decrescendo/ejection systolic murmur
Heard shortly after the 1st heart sound in systole
What type of anaemia does aortic valve stenosis cause?
Microangiopathic haemolytic anaemia
In aortic valve regurgitation, when does blood flow back into the LV (systole/diastole)?
What heart murmur is heard
Name 4 clinical signs seen in this condition
Diastole
Early (decrescendo) diastolic murmur
- Increase in systolic kpa (>120 mmHg)
- Decrease in diastolic kpa (<80 mmHg)
- Quinke’s sign
- Head bobbing (with each beat of the heart)
What is Quinke’s sign?
Nail bed goes pink then pale with each beat of the heart
What does the ductus arteriosus connect?
What does it by pass?
Pulmonary trunk to aorta
Lungs
What does the foramen ovale connect?
What does it by pass?
RA to LA
By pass right ventricle and lungs
What does the ductus venosus connect?
What does it by pass?
Placenta to IVC
By pass liver
How do the shunts close?
Respiration begins:
- increasing the kpa in the LA so foramen ovale closes
- DA contracts
Removal of placenta:
- DV close
What is the pathophysiology of an acyanotic heart defect?
Give 5 examples
Blood flowing from the left side of the heart to the right:
- Ventricular septal defect
- Atrial septal defect
- Patent ductus arteriosus
Not enough blood leaving the heart
- Aortic valve stenosis
- Coarctation of the aorta
The formation of the 4th and 6th arch arteries will eventually become the great vessels.
List all the arteries that supply pharyngeal arches 1-6.
PA 1 + PA 2: Pharyngeal arteries (eventually regress)
PA 3: ICA
PA 4: L - Arch of aorta R - Brachiocephalic artery
PA 6: Pulmonary arch arteries
Name a congenital malformation of the great heart vessels that does not lead to cyanosis.
Discuss why
Patent ductus arteriosus (failure of the DA contracting post birth) as blood flows from aorta to pulmonary trunk
In PDA, a continuous murmur will be heard, throughout systole and diastole. What is this murmur called?
Machinery murmur
What happens to the LV in PDA?
Discuss.
Get LV hypertrophy due to the increased preload into the LV as a result of a greater volume of blood entering the pulmonary trunk and then back to the left ventricle.
What 4 factors make up Tetralogy of Fallot?
Pulmonary stenosis
Right ventricular hypertrophy
Overriding aorta
Ventricular septal defect
What is an overriding aorta
Instead of the aorta being connected to the left ventricle, it is connected to the ventricular septal defect
Fully discuss 2 congenital malformations of the heart vessels that lead to cyanosis
Tetralogy of fallot:
Pulmonary stenosis worsens RV hypertrophy thus the shunting of the ventricular septal defect is right to left and the overriding aorta leads to the distribution of mixed blood.
Transposition of the great vessels:
Aorta is connected to the right ventricle so deoxygenated blood redistributed.
Formation of the inter-atrial septum
- Ostium primum is an inital opening in the septum primum
- Septum primum fuses with the endocardial cushions (from neural crest cells) and an ostium secundum forms
- Septum secundum forms and foramen ovale forms
Formation of the inter-ventricular septum
- Muscular wall of the the ventricular septum grows up towards the endocardial cushions
- Small gap is left
- Endocardial cushions produces connective tissue to close the small gap - forms membranous portion of the ventricular septum
What are the resting potentials of
A) SkM
B) Cardiac muscle
C) Nerve cells
D) Smooth muscle
A) -90 mP
B) -80 mP
C) -70 mP
D) -50 mP
How is the resting potential, -80 mP, of a cardiac myocyte generated?
Passive efflux of K+
Describe the processes of excitation - contraction coupling in
ventricular myocardial cells.
Depolarisation of the sarcolemma leads to the opening of the L-type VGCC in the T tubule. Leading to an influx of Ca2+ into the cytoplasm. Ca2+ binds onto the RYANODINE receptor on the sarcoplasmic reticulum (contributes to 75% of Ca2+ causing contraction), this leads to the opening of the CICR (calcium induced calcium release receptor) on the sarcoplasmic reticulum. Ca2+ in the cytoplasm now acts on the actin-myosin complex.
What is hypokalaemia’s effect on the heart?
Get EADs - early after depolarisations, which lead to oscillations in the cardiac membrane, leading to ventricular fibrillations (cardiac arrest)
Describe the actin-myosin theory in cardiac myocytes
Ca2+ binds to Troponin I and T, leading to conformational change of tropomyosin, the myosin binding site is now revealed on the actin filament. Myosin head, along with its ATPase, can now bind on its binding site (ADP + Pi formed, leading to power stroke)
After cardiac myocyte contraction, how are cytoplasmic Ca2+ levels reduced?
- Sarcolemma Ca2+ ATPase
- SERCA (SR/SR Ca2+ ATPase)
- Sodium-calcium exchanger (NCX, 3NA+-Ca2+-exchanger)
Describe two ways in which the myosin light chain:
A) cannot be phosphorylated
B) is dephosphorylated
thus leading to the vasodilation of vascular smooth muscle (so arteries and veins)
A) B2 adrenoceptor on VSM has (physiological) adrenaline bound to it (released from sympathetic postganglionic cells) leading to the activation adenyl cyclase thus more ATP is converted to cAMP. More cAMP activates PKA. PKA phosphorylates MLCK thus inhibiting Myosin Light Chain Kinase from phosphorylating the myosin light chain
B) Myosin light chain phosphatase dephosphorylates the myosin light chain (this process is always working)
Describe the excitation-contraction process of smooth muscles
focus on the main pathway
Noradrenaline binds to a1 adrenoceptor (or adrenaline when its levels are above physiological levels) (on SM cell membrane), activating this receptor and thus the Gq receptor. This then activates Phospholipase C, thus catalysing this reaction PIP2 -> IP3 + DAG. IP3-R on the sarcoplasmic reticulum membrane opens, thus allowing the efflux of Ca2+. Ca2+ binds to and activates calmodulin. This new complex activates and binds to MLCK. This new complex phosphorylates the myosin light chain thus activating myosin so its power strokes with the actin molecule can now happen.
Activation of which receptors in the ANS lead to an
A) increase in heart force of contraction and heart rate
B) decrease in heart force of contraction and heart rate
Are each receptor found in the SNS or PNS?
A) B1 in the SNS
B) M2 in the PNS
When the parasympathetic preganglionic vagus nerve synapses in the AVN and SAN, what happens next?
chronotropic - HR
ACh is released from the postganglionic cells, and binds to M2 receptors causing a reduction in heart rate (- chronotropic effect) and a decrease inAVN conduction velocity