BIOL 0800 Reading- Chapter 12 Flashcards
What are the two components of blood?
Formed elements and plasma
What is hematocrit?
The percentage of blood volume that is erythrocytes
At any given moment, what percentage of blood volume is in the capillaries?
Only about 5%, even though that’s the percentage that’s doing most of the work
What is the pulmonary circuit?
Blood pumped from right ventricle to lungs to left atrium into systemic circulation
What is the systemic circuit?
Blood pumped from the left atrium to the organs/tissues to the right atrium
What is the aorta?
Where the blood leaves the left ventricle to go to systemic circulation
What is microcirculation?
Arterioles, capillaries, and venules
What is the inferior vena cava? And superior?
Brings all the veins together to bring the blood back to right atrium from below the heart; superior brings back all the blood from above the heart
What is the pulmonary trunk?
Brings blood from the right ventricle to the lungs via two pulmonary arteries (one to each lung)
What is the pulmonary vein?
Brings blood back from the lungs to the left atrium
What pattern does the branching of the capillaries create, and why?
Delivers blood to peripheral organs and tissues in parallel so that each only receives a fraction of the bloodflow
How does circulation to the liver and anterior pituitary gland differ from regular circulation?
Blood passes through two capillary beds in series connected by veins before returning to the heart (called a portal system)
What is a portal system?
When blood passes through two capillary beds in series, connected by veins, before returning to the heart
What is the equation relating flow rate, hydrostatic pressure, and resistance?
F = deltaP/R
What is the equation for resistance?
(8Lviscosity)/(pi*r^4) = R
How are blood viscosity and hematocrit related?
Increase in hematocrit increases blood viscosity
How does flow change if the radius of the blood vessel is halved?
Decreases by 16x, since R = 16x
What are the pericardium, epicardium, and myocardium?
The fibrous sac enclosing the heart; the inner layer of the pericardium; the wall of the heart
What is the difference between the left and right AV valves?
LAB RAT: left is bicuspid, right is tricuspid
How do pressure differences interact with AV valves?
If atrial pressure is greater, valve opens; If ventricular pressure is higher during contraction, valve is forced shut
What is the pulmonary valve?
From the right ventricle to the pulmonary trunk
What is the aortic valve?
From the left ventricle to the aorta
What are the two semilunar valves?
From the ventricles to their respective vessels
What is the conducting system of the heart?
The cells that don’t contract but control normal heart excitation; in electrical contact with cardiac muscle cells via gap junctions
How do sympathetic postganglionic fibers interact with the heart?
Innervate the entire heart: release epi/norepi to beta-adrenergic receptors in atria and ventricles
How do parasympathetic fibers interact with the heart?
Innervate only the atria: release acetylcholine to muscarinic receptors on the atria
Where does initial depolarization of the myocardium begin?
SA node: conducting system cells near the right atrium near the entrance of the superior vena cava
Where is the SA node?
Near the right atrium by the entrance of the superior vena cava
Describe the path of depolarization triggered by the SA node.
Travels to atria (contract at virtually the same time); then to AV node at base of right atrium, which propagates to the ventricle slowly; then down the interventricular septum through the bundle of His; then to Purkinje fibers, which depolarizes both ventricles from the apex up, squeezing blood out
What is the AV node?
Located at base of right atrium; depolarized after atrial contraction; propagates the action potential slowly, allowing the atria to finish contracting before the ventricles contract
Where does the action potential go after leaving the AV node?
To the bundle of His: AV bundle; separates into right and left bundle branches that separate at the apex of the heart (bottom) to enter the left and right wall
What are the Purkinje fibers?
Fibers that rapidly distribute the impulse through the ventricles and make contact with ventricular myocardial cells to depolarize the rest of the ventricle
In what direction does ventricular contraction occur?
From apex to base, aka up the heart as if squeezing blood out
What two parts of the conducting system are the only conductive link between the aria and ventricles?
The AV node and Bundle of His
How do ion concentrations differ during cardiac action potentials from normal ones?
Na permeability up to depolarize and K permeability down; but then no repolarization: K permeability stays low and Ca permeability increases: stays depolarized around 0 mV
Why is there no rapid repolarization in cardiac action potentials?
K channels stay closed, and Ca permeability increases
Why does Ca permeability increase during cardiac action potentials?
Initial depolarization opens Ca channels and influx of Ca: L-type Ca channels
What are L-type Ca channels?
Channels in the myocardial cells that open during initial depolarization to allow an influx of Ca into the cell to balance the eflux of K out after Na influx; modified DHP receptors which were voltage-sensitive for skeletal muscle contraction
Which has a shorter plateau phase, atrial or ventricular cells?
Atrial
What is pacemaker potential?
The gradual depolarization from the plateau caused by Ca influx from L-type Ca channels
What are the three ion channel mechanisms that contribute to pacemaker potential?
K channels, F-type channels, and T-type Ca channels
What are F-type channels?
Funny channels: nonspecific cation channels that open at negative membrane potential values: conduct an inward depolarizing Na current
What are T-type Ca channels?
Ca channels that open briefly and contribute to inward Ca current to boost depolarization in pacemaker potential
Why do SA node cells initiate action potentials rather than AV node cells, if they’re similar in shape?
Because pacemaker currents of SA node cells are brought to threshold more rapidly than AV node cells
Why is the AV node so slow at propagating cardiac excitation?
Because depolarization in nodal cells is caused by Ca influx from L-type Ca channels, which depolarize the membrane more slowly than voltage-gated Na channels do
What is the P wave?
Corresponds to atrial depolarization
What is the QRS complex?
Corresponds to ventricular depolarization
What is the T wave?
Ventricular repolarization
Why isn’t atrial repolarization evident in an EKG wave?
Because it occurs at the same time as the QRS complex
What is Lead I?
Right hand (-) to left hand (+), ground at right ankle
What is Lead II?
Right hand (-) to left ankle (+), ground at right ankle
What is Lead III?
Left hand (-) to left ankle (+), ground at right ankle
How do augmented leads work?
Combine two electrodes into a single central electrode
What is Lead aVR?
Left arm and leg (-) to right arm (+); points up toward right shoulder [combines Lead III]
What is Lead aVL?
Right arm and left leg (-) to left arm (+); points up toward left shoulder [combines Lead II]
What is Lead aVF?
Right arm and left arm (-) to left leg (+); points down [combines Lead I]
What is the difference between partial block and complete block in EKG readings?
Partial block is when AV node damage permits only every other impulse to the ventricles; Complete block is when there is no synchrony between atrial and ventricular electrical activity and the ventricles are contracted by the slow bundle of His activity
How does excitation-contraction coupling with in cardiac muscle cells?
The Ca influx from L-type Ca channels during prolonger depolarization triggers greater release of Ca from ryanodine receptors in the SR, for standard thin filament binding and crossbridge cycling
Is ventricular muscle capable of contraction summation?
No: because of long absolute refractory period
What is the absolute refractory period of the heart?
The period during and following an action potential when the heart can’t be re=excited: due to prolonger plateau of depolarization
What is systole?
The period of ventricular contraction and blood ejection
What is diastole?
The period of ventricular relaxation and blood filling
What are the two parts of systole?
IVC and ejection
What are the two parts of diastole?
IVR and filling
When is the only time during the cardiac cycle that all valves are closed?
IVC and IVR
What is EDV?
The amount of blood in the ventricle after ventricular diastole
What is ESV?
The amoutn of blood remaining after ejection
What is stroke volume?
EDV-ESV
What is a typical stroke volume for an adult at rest?
135-65 = 70 mL
How does the T wave correspond to action potentials?
Represents the end of the plateau phase of the action potential: onset of ventricular repolarization
What is the dicrotic notch?
The decrease and rebound of aortic pressure caused when the aortic valve closes (since aortic pressure is greater than the relaxing ventricular pressure), due to blood rebounding against the valve
How does typical pulmonary artery sys/dias differ from systemic?
Much lower: 25/10 vs 120/80
What is “lub?”
The first heart sound: closing of the AV valves, onset of systole
What is “dup?”
The second heart sound: closing of the pulmonary and aortic valves: onset of diastole
What is stenosis?
Abnormally narrowed valves
What is cardiac output?
The volume of blood each ventricle pumps, in L/min: volume of blood flowing through either the systemic or pulmonary circuit per minute
What is the formula for cardiac output?
CO = HR x SV
What is a normal cardiac output for a resting adult?
5.0 L/min
What is typical total blood volume?
5.0 L
Without any nervous system input, what is resting heart rate? Why is typical resting heart rate different?
100 bpm; but more parasympathetic input than sympathetic, so closer to 70 bpm
How does sympathetic NS increase heart rate?
Increases pacemaker potential slope by increasing F-type channel permeability: faster depolarization, SA nodal cells reach threshold faster, heart rate increases
How does parasympathetic NS decrease heart rate?
Decreases pacemaker potential slope due to reduction of inward current, so threshold is reached slowly and heart rate decreases; increased SA node cell permeability to K+
What are the three main factors that affect stroke volume?
Changes in EDV, changes in sympathetic NS input magnitude, and changes in afterload
What is preload?
The volume of blood in the ventricles just before contraction
What is afterload?
The arterial pressures against which the ventricles pump
What is the Frank-Starling mechanism?
Stroke volume increases as EDV increases
Why does the Frank-Staling mechanism work?
Because greater EDV stretches the ventricular sarcomeres before contraction, allowing a more forceful contraction later on, which puts out more SV
Why does cardiac muscle cell force increase more steeply as a function of sarcomere length than in skeletal muscle cells?
Because stretching the sarcomeres toward optimum length decreases spacing between thick/thin filaments (allows more crossbridge binding), and increases sensitivity of troponin for Ca and increases Ca release from the SR
What is the significance of the FS mechanism?
At any given heart rate, venous return increase forces an increase in cardiac output by increasing EDV and thus SV
How do epi/norepi increase contractility?
Act on beta-adrenergic receptors
What is ejection fraction?
SV/EDV = EF
What is standard EF?
Between 50% and 75%
What are the cellular mechanisms that regulate sympathetic myocardial contractility?
Adrenergic receptors activate G-protein coupled cascades (to produce cAMP and activate a protein kinase), which phosphorylates proteins to enhance contracility (L-type Ca channels, ryanodine receptors and proteins in the SR membrane, thin filament proteins (troponin), thick filament proteins, and Ca pump proteins)
Does parasympathetic NS activity affect ventricular contraction?
Not really: little parasympathetic innervation of ventricles
How does afterload affect stroke volume?
Greater load (increased arterial pressure) reduces stroke volume, because it’s harder to push blood through against the pressure
What is echocardiography?
Beaming ultrasonic waves at the heart and electronically plotting the echoes
What is cardiac angiography?
Requires temporary threading of a thin flexible tube (catheter) through an artery/vein into the heart and injecting a radio-opaque contrast material for tracking
What is the formula for compliance?
Compliace = delta V / delta P
What is systolic pressure?
The maximum arterial pressure reached during peak ventricular ejection
What is diastolic pressure?
The minimum arterial pressure that occurs just before ventricular ejection begins
What is pulse pressure?
The difference between systolic and diastolic pressures
What are the three most important factors in determining pulse pressure?
Stroke volume, speed of ejection of stroke volume, and arterial compliance
How does SV affect pulse pressure?
Greater SV increases pulse pressure
How does speed of ejection affect pulse pressure?
Greater speed of ejection increases pulse pressure
How does arterial compliance affect pulse pressure?
Greater compliance decreases pulse pressure