Describe the wall of an artery
What is the volume of blood within an artery called?
- Extensive elastic fibers and SM
- Stressed Volume
What is the importance of arterioles?
What component of the NS is it innervated by?
- Site of highest resistance - drops the blood pressure.
- Sympathetic NS:
a) B1: the arterioles of the skeletal muscle. Dilatory.
b) A1: the arterioles of the skin, splanchnic, and renal circulations. Constriction
What is the importance of the veins?
What is volume of blood in the veins called?
Are veins innervated by the NS?
- Store the majority of the blood.
- Unstressed Volume
- Yes, the Sympathetic NS. Have Alpha-1 receptors.
What is the equation for:
Velocity of BF
Blood Flow
Resistance
- Velocity of BF: v = Q (flow) / cross-sectional area
- Q = (MAP - RAP) [pressure gradient] / TPR
The pressure is as follows: Arteries>Arteriole>Capillaries>Venules>Veins>RA
- Resistance is proportional to viscosity and length but inversely proportional to radius^4.
What is the importance of Reynold’s number?
Reynold’s number predicts whether the flow of blood is laminar or turbulent.
An increase in Reynold’s number reflects increased tendency for turbulence.
Depends on viscosity and velocity.
Viscosity: decrease viscosity = decrease in resistance = increase velocity
Velocity: decrease radius of BV = increase in velocity.
What is Capacitance?
How does it differ per vessel?
What happens with age? What happens to the BP?
- Capacitance: the distensibility of a blood vessels. Capacitance increases with: lower stiffness, lower elastance
Capacitance decreases with increased stiffness
- Veins have a higher capacitance thus can store more volume without a change in pressure.
- Capacitance decreases with age; vessels become stiffer; systole increases
What is Pulse Pressure?
What’s the most important determinant of PP?
What is the relationship to capacitance?
- PP = Systole P - Diastole P
- SV
- Decreasing capacitance -> increases vessel stiffness –> increases sytolic pressure–> increases PP
What does an increased PP signify?
What does a decreased PP signify?
- Systole is higher due to increased SV - aortic regurgitation, hyperthyroidism (ladder effect of increased HR), age
- Systole is lower due to - aortic stenosis, cardiogenic shock, cardiac tamponade, HF
What do the various components of the ECG mean?
- P: Atrial Depolarization
- PR - the conduction velocity through the AV node.
- QRS: Ventricular Depolarization
- QT: the time it takes for ventricular depolarization and repolarization.
- ST segment: represents the period when the ventricles are depolarized.
- T waves: represent ventricular repolarization.
What are the phases of a cardiac muscle contraction?
Phase 0: Depolarization Phase; Na
Phase 1: K+ efflux, rapid activating K channels
Phase 2: Ca2+ influx
Phase 3: K+ efflux, slow activating K+ channels, Repolarization
Phase 4: RMP @ K Eq = -90mV
What components of the heart rest at -90mV?
What component of the heart has the longest AP?
- Ventricles, Atria, Purkinje Fibers
- Purkinje Fibers
What are the phases of the SA node?
Phase 0: upstroke due to Ca2+ influx
Phase 3: K+ efflux, repolarization
Phase 4: If : Na+
The resting MP: -65mV
Phase 4 is fastest in SA>AV>His/Purkinje
What does chronotropic mean?
Whats a positive chronotrope/negative chronotrope?
Chronotropes produce changes in HR
Positive: Increased HR via increasing firing rate of SA node.
What is a dromotropic effect?
What is a positive dromotropic effect?
Dromotropic effects produce changes in the conduction velocity; primarily throught the AV node.
- Positive dromotrope; increases the conduction velocity through the AV node. Decreases PR interval.
What is the effect of the PaNS on the heart?
- SA, atria, and AV have muscarinic receptors.
Negative chronotropic effect: Decreases HR via slowing down phase 4 depolarization (decreased If flux)
Negative dromotropic effect: Decreases the conduction velocity through the AV node (decreased inward Ca2+, and increased K+ efflux)
What is the effect of the SyNS on the heart?
B1 receptors
- Positive chronotropic effect: increases HR by increasing the rate of phase 4 depolarization; Increased Na+ influx through the If.
- Positive dromotropic effect: increased conduction velocity through the AV node. AP conducted faster to the ventricle - this may compromise the filling time of the ventricle. This occurs due to an increased Ca2+ influx.
In what cell type is the mitochondria more abundant? Skeletal or Cardiac?
What are T-tubules continuous with?
- Cardiac
- The T-tubules are continuous with cell membrane and invaginate the Z-line. T-tubules are well developed in ventricles but not atria.
What receptors are involved with excitation of the cardiac muscle?
- Dihydropyridine R/L-type: the AP causes a conformational change that allows Ca2+ to influx into the cell.
- Ryanodine R: the Ca2+ binds the the RR on the SR = Ca2+ efflux into the cell.
What is inotropism?
What is +ve ionotropism?
- Inotropism: the ability of the heart to contract according to the distension/length of fiber.
- Agents that increase the contraction of the heart.
Can be done via: 1) Increase HR: increasing Ca2+ influx leads to more Ca2+ available for the SR to uptake. By taking up more Ca2+, more will be available for the next contraction. Ladder effect.
- Sympathetic via B1: Increase Ca2+ influx during plateau phase.
Increase Ca2+ ATPase activity on SR via P of Phospholamban.
Cardiac glycoside.
