Cardiovascular Review Flashcards
What is the function of the cardiovascular system
Muscular pump for blood - circulates 5 to 6 liters per minute in 70 kg man
Endocrine:
ANP in response to increased atrial pressure
BNP (B-type) in response overstretched ventricles
Describe cardiac muscle
Involuntary muscle with cross striations
Individual cells are connected connected by intercalated discs, allow the heart to contract in synchrony as one unit
Gap junctions allow for the passage of ions between myocytes allowing AP to spread
Describe muscle contraction
Resting state: more Na and Ca outside the cell and more K inside
Phase 0: Na influxes into cardiac myocytes cause depolarization (rapid upstroke)
Phase 1: Inactivation of Na influx and K efflux with a notch of initial repolarization
Phase 2: Ca influx (plateau phase)
Phase 3: Inactivation of Ca influx with continuation of K efflux - rest of repolarization
Phase 4: removal of excess Na and Ca with restoration of the membrane potential using the Na/K ATPase pmp to push Na out and bring K back in
Describe the different refractory periods
Absolute (ARP) - no AP can be initiated regardless of stimulus strength because the Na channels are closed in Phase 1-3
Relative (RRP) AP can be excited, however greater stimulus is needed- extends between the middle of Phase 3-4
Effective refractory period (ERP): From phase 1 to just beyond phase 3 cardiac muscle is incapable of sustained contraction (tetany) as in skeletal muscle because of the relativelylong refractory period
Describe the Frank-Sterling law
Cardiac output is DIRECTLY proportional to venous return
Force of contaction of a myocardial fiber (stroke) is proportional to the lenght of the mycoardial fiber
the greater the amount of blood entering during disastole (venous return) the greater the stretch
A greater stretch results in a greater force of contraction causing an increase in cardiac output
Describe the cardiac cycle
1st heart sound: closure of tricuspid and mitral valves
2nd heart sound: closure of pulmonary and aortic valves
3rd heart sound: occurs after the 2nd heart sound and is seen in congestive heart failure (dubup)
4th hear sound: heard before 1st and seen in hypertrophic ventricles (beLub)
Systole occurs between heart sounds 1 and 2
diastole occurs between heart sounds 2 and 1
Describe the different waves of the electrocardiogram
P - atrial depol proceeds atrial contraction
PR interval - extends from P to start of q
QRS - ventricular depolarization
QT - beginning of Q wave to end of T
ST - extends from the end of S to start of T
T - ventricular repol
Atrial repo is NOT seen on ECG because it is hidden in the QRS complex
Describe the different phases of contraction
Isovolumic:
increase in pressure without change in volume occurs between closure of AV and opening of the aortic valve
ejection of blood - only 70ml of the 120ml in the ventricle expelled ejection faction
Isovolumic relaxation:
decrease in pressure without change in volume
occurs between closing of the aortic valve and opening of AV valves
Describe HR control
Sympathetic T1-5
increases rate. speed. and force of contraction by increasing Ca influx in phase 2
Parasympathetic vagus via cardiac br decreases HR, conduction, and force by decrease Ca influx
Describe blood pressure
systemic BP is 120/80 mm hg
Blood pressure is the product of cardiac output x peripheral resistance
Cardiac output is a product of stroke volume x HR
Describe blood pressure control
Two main mechanisms:
baroreceptors -
fast due to neurotransmitter
High pressure sensor in the carotid sinus and in the aortic arch (afferents carried by CN IX and X) relay information in the medulla
Reflex response to a rise or drop in BP via ANS
a drop in BP causes HR to increase
Low pressure ones located in SVC, IVC and right atrium monitor volume
renin-angiotensin - aldosterone -
slow because hormonal
Describe peripheral resistance
Poiseuille’s Law: peripheral resistance is directly proportional to the viscosity of blood and to length of the vessel and inversely proportional to the radius of the vessel to the 4th power
If blood vessel decreases by half, then resistance increases by a factor of 16
GREATEST resistance in the vascular system is offered by the arterioles
Describe blood flow
La Place’s law: pressure within a blood vessel is related to tension, size, and shape of vessel
inversely proportional to diameter
60% of total blood volume is contained within the venous system at any one time 20% in arteries and arterioles 15% pulmonary system 5% in capillaries
Describe capillary pressure
Intracapillary hydrostatic - tends to force fluids out into the interstitial space intercapillary oncotic (protein) - tends to pull fluids into the capillary intersitial hydrostatic pressure - tends to force fluids into capillary intersitial oncotic - pulls fluid out of capillary
Imbalances of these forces may cause edema
Describe the vascular response to exercise
Stimulates sympathetic:
-increase HR, conduction velocity and cardiac contractility
vasoconstriction of the skin, gut, and inactive muscle
vasodilation of the blood vessels to achieve skeletal muscle
dilation of the coronary
