Cardiovascular Physiology Excitation and Conduction Part 1 Flashcards
what are the 3 principle components of the circulatory system
-the heart
- the blood vessels
-the blood
what is the number one cause of death worldwide
cardiovascular disease
what are the most common forms of cardiovascular disease
atherosclerosis and hypertension
what is the function of systemic circulation
-supply O2 and nutrients to tissues
-remove waste
what is the function of the pulmonary circulation
-add O2
-remove CO2
do the right and left side of the heart pump the same amount of blood into each circulation
yes
what chamber of the heart are the pulmonary veins attached to
LA
what chamber of the heart are the pulmonary arteries attached to
RV
what chamber of the heart is the aorta attached to
LV
what chamber of the heart is the vena cava attached to
RA
what are the functions of the heart valves
keep blood flowing in one direction/prevent back flow
what do heart valves open and close due to
changes in pressure
when do the AV valves open? close?
open: pressure in atria > pressure in ventricles
close: pressure in ventricles > pressure in atria
what chambers does the tricuspid valve separate
RA/RV
what chambers does the bicuspid valve separate
LA/LV
when do semilunar valves open? close?
open: pressure in ventricles > pressure in arteries
close: pressure in arteries > pressure in ventricles
where does exchange between plasma and interstitial fluid occur
at capillaries
what are capillaries arranged in when supplying
parallel
how does the distribution of systemic cardiac output change from at rest to strenuous exercise
more blood is distributed to skeletal muscle, skin, heart and brain. less blood is distributed to organs
what are the types of arteries and where are they located
-elastic arteries - heart
- muscular arteries- distribution
- arterioles- capillaries
what is the function of arteries
-carry blood to tissue capillaries from heart
- regulate blood pressure
what are the types of veins and where are they located
-large veins - heart
- medium sized vein -collection
- venules - capillaries
what is the function of veins
-carry blood from heart to tissue capillaries (venous return)
- reservoir of blood (peripheral venous pool)
what are the types of capillaries
-continuous
-fenestrated
-sinusoid
what is the function of capillaries
site of exchange
what is pressure
the force exerted by a fluid in a tube
what is flow
the volume of fluid moved in a given amount of time
what is resistance
how difficult it is for blood to flow between two points at any given pressure difference
-measure of friction that impedes flow
what is Ohm’s law
F= Change in pressure/resistance
what does F stand for in Ohm’s law
volume of blood moved in a unit of time
what is change in pressure calculated by
P1-P2 where P1 = pressure generated by heart beat and P2 = drop in pressure as move further from heart due to friction
what is R controlled by in Ohm’s law
factors defined by Poiseuille’s law
what is poiseuilles law
R = 8nl/pi(r^4)
what 3 factors contribute to cardiovascular resistance
-blood viscosity (n)
- total blood vessel length (l)
-blood vessel radius (r)
what is blood viscosity affected by
blood volume and number of RBC
what do vasodilated vessels do to r and R
increase r
decrease R
what is the main contributor to minute-to-minute control of resistance in the vascular system
blood vessel radius
why do small changes in r lead to big changes in R
because r is to the fourth power
what do Poiseuilles law and Ohms law calculate
flow
which impacts resistance more: diameter or length
diameter
what is the formula for velocity of blood flow and define variables
V = Q/A where Q = blood flow and A = cross sectional area
where is velocity of blood flow slowest and why
the capillaries because there’s more surface area and it allows for exchange and increased O2 delivery to tissues
where are chordae tendinae and papillary muscles located
in AV valves
what is the function of chordae tendinae and papillary muscles
prevent backflow of blood by preventing valve from prolapsing
are all valves open at any given time
no
what are the types of cardiac myocytes and what percentage of each
-conductive muscle fibers- 1%
- contractile muscle fibers- 99%
what are examples of conductive muscle fibers
autorhythmic AR cells, Pacemaker cells
what do conductive muscle fibers do
spontaneously generate AP that lead to heart beat
do conductive muscle fibers contract
very weakly
where are conductive muscle fibers located
in conduction system of heart
what do contractile muscle fibers do
contract and generate heart beat
what are the types of contractile muscle fibers
-atrial myocytes
- ventricular myocytes
describe cardiocytes
striated cells bc functional unit is sarcomeres
anatomy and function of cardiac muscular is similar to ____
skeletal muscle
what are cardiocytes connected by
intercalated discs
what are intercalated discs composed of
-interlocking plasma membrane
-gap junctions
-desmosomes
how are cardiac muscle cells linked
mechanically, chemically, and electrically
how do cardiac cells work together
in a syncytium
what are the two syncytiums in the heart
atrial and ventricular
what are the arteries that supply the myocardium
the coronary arteries
what is the path of the coronary arteries
they exit from behind the aortic valve cusps and lead to a branching network of small arteries, arterioles, capillaries, venules and veins similar to those in other organs
what do most of the cardiac veins drain into
the coronary sinus which empties into the right atrium
what is systole
contraction
what is diastole
relaxation
what are the events in the cardiac cycle
-atrial systole
-ventricular systole/atrial diastole
- ventricular diastole
what must the heart do before systole can occur
depolarize
what must the heart do before diastole can occur
repolarize
what is the pathway of excitation of the heart
SA node -> internodal pathways -> AV node -> bundle of his (AV bundle) -> down bundle branches -> up purkinje fibers
what controls the heart rate
the area that makes AP at the highest rate which is the SA node
how long is AV delay
0.1 sec
what do purkinje fibers supply and what does it do
papillary muscles - contract during ventricular contraction to tighten chordae tendinae and prevent AV valves from prolapsing into the atria
what do pacemaker cells do
generate AP leading to contractile cell contraction
what is the order of activation sequence in the heart
SA node -> AV node -> AV bundle -> right/left bundle branches -> purkinje fibers
why is the conduction velocity in the AV node so low
because of AV delay
why is atrial repolarization not seen on an EKG
because ventricular depolarization is much larger and takes over and they happen at the same time
what does the P wave represent
atrial depolarization
what does the QRS complex represent
ventricular depolarization/atrial repolarization
what does the T wave represent
ventricular repolarization
describe pacemaker potential
AR cells do not have a steady resting membrane potential
what are the channels of pacemaker potential
-F type channels - VG Na+ channels
-Ca2+ (T) - transient VG Ca2+ channel
what is pacemaker potential due to
F type channels and Ca2+ T channel
what are the channels of AP
Ca2+ (L) - long lasting VG Ca2+ channel
K+ channel - VG K+ channel
what is depolarization of AR cells due to
calcium entering the cell
what NT is released in autonomic NS control of AR cells and what is the receptor
NE and EPI - beta 1 adrenergic receptors
what does NE/EPI do to AR cells
-increase probability of F and Ca2+ (T) channels are open
-decreases time to threshold
-increases HR
-positive chronotropic agent
what is a positive chronotropic agent
agents that increase HR
what is the NT released in parasympathetic stimulation of the AR cells and what receptor
AcH- muscarinic
what does AcH do to AR cells
-decreases probability of F channel open
- increases probability of K+ channel opne
- hyperpolarizes Vm
- increases time to threshold
- decreases HR
- negative chronotropic agent
what is the SA node spontaneous rate
about 100 bpm
at rest what control is the heart under
parasympathetic
what depolarizes contractile cells
signal from AR cells
what are the phases of the action potential in contractile cells and what happens in each
- phase 4 - resting Vm
-phase 0 - depolarization spike, fast voltage gated Na+ channel open (both gates) - phase 1 - partial repolarization- fast VG Na+ channels close
-phase 2- plateau, transient K+ channels close, L- type Ca2+ channels open
-phase 3 - repolarization, L-type Ca2+ channels close, slow K+ channels open
what ion depolarizes contractile cells
Na+
Describe the steps of ECC in cardiocytes
-AP enters from adjacent cell
-VG Ca2+ channels open. Ca2+ enters the cell
-Ca2+ induces Ca2+ release through ryanodine receptor channels
-local release causes Ca2+ spark
-summed Ca2+ sparks create a Ca2+ signal
-Ca2+ ions bind to troponin to initiate contraction
-relaxation occurs when Ca2+ unbinds from troponin
- Ca2+ is pumped back into the sarcoplasmic reticulum for storage OR
-Ca2+ is exchanged with Na+
-Na+ gradient is maintained by the Na+ K+ ATPase
how is contraction in skeletal muscle different than cardiac muscle
calcium in cardiac muscle can be pumped out of the cell or stored back in the SR. in skeletal muscle calcium can only be pumped out
what is the difference between the AP and muscle tension in skeletal muscle and cardiac muscle
- in skeletal muscle the AP ends before the contraction begins
- in cardiac muscle the action potential lasts as long as the muscle contraction
why is it important that the AP in cardiac muscle lasts as long as the contraction
it prevents summation and tetanus which we dont want in the heart
describe cardiac muscle contractions
they are graded
in the resting state when calcium is released from AP in cardiac cells do troponin sites get saturated
no
what does the strength of contraction in cardiac cells depend on
calcium concentration
what are inotropic agents
substances that alter the force of contraction of cardiocytes by changing caclium concentration in the cytosol
what is the pathway of sympathetic control of contractile cells
-EPI and NE bind to B1 receptors
-B1 receptors activate cAMP second messenger system
-resulting in phosphorylation of VG Ca2+ channels and phospholamban
- resulting in more forceful contraction and shorter duration of action
what does the cardiac cycle include
all the events involved with blood flow through the heart during one heart beat
