Chapter 14 Flashcards
What are the functions of the cardiovascular system?
transport materials throughout the body
- from external environment (entering body)
- materials between cells
- waste eliminated by cells (leaving body)
What are examples of external materials entering the body?
- nutrients
- water
- gases
What are examples of materials being moved between cells?
- hormones
- immune cells
- antibodies
What are examples of materials leaving the body?
- CO2
- heat
- metabolic waste
What 3 things does the cardiovascular system consist of?
1) blood vessels
2) heart
3) blood
Describe what blood vessels are + the structure/system of how they are organized.
- arteries vs. veins
- capillaries
- portal system joins 2 capillary beds in series
Describe the structure of the heart briefly and the main components.
- septum –> divides heart in 2 halves
- atrium –> receives blood returning to heart
- ventricle –> pumps blood out of heart
Describe what blood is made up of.
cells and plasma
Which side of the heart powers the pulmonary circuit?
the right side
Which side of the heart powers the systemic circuit?
the left side
Define pressure.
force exerted by fluid on its container
define hydrostatic/hydraulic pressure.
force fluid exerts on walls
How does blood flow?
from high to low pressure regions
define pressure gradient.
difference in pressure between 2 regions
When is the pressure the highest in the heart?
when blood flows out of the heart
When is the pressure the lowest in the heart?
when blood flows back to the heart via vena cavae
How is pressure continually lost?
due to friction
Contraction of the heart creates pressure without changing what?
the volume of blood
If blood vessels dilate, blood pressure _____
decreases
If blood vessels constrict, blood pressure _____
increases
Flow through a tube is directly proportional to what?
the pressure gradient
Flow through a tube is inversely proportional to what?
resistance
What does Poiseuille’s Law say?
- resistance is proportional to length of the tube
- resistance is proportional to viscosity (thickness) of the fluid (blood)
- resistance is inversely proportional to the tube radius to the 4th power
What does MAP mean?
mean arterial pressure
What is MAP/What does it do?
- primary driving force for blood flow
- pressure reserved in the arteries
What is MAP proportional to?
MAP = cardiac output (CO) x peripheral resistance (PR)
what is cardiac output?
the amount of blood that the heart is pumping out (volume / time)
What are the 2 types of myocardial cells?
- autorhythmic cells (pacemakers)
- contractile cells
What is the function of autorhythmic cells (pacemakers)?
signal for contraction –> APs
What are the characteristics/arrangements of the autorhythmic cells (pacemakers) or what are they made up of?
- have smaller + fewer contractile fibers compared to contractile cells
- do NOT have organized sarcomeres
What are the characteristics/arrangements of the contractile cells or what are they made up of?
striated fibers organized into sarcomeres
Describe cardiac muscle.
- smaller + have a single nucleus per fiber
- branch + join neighboring cells thru intercalated disks
- gap junctions
- T-tubules are larger + branch
- sarcoplasmic reticulum is smaller
- mitochondria occupy 1/3 of cell volume
Describe the membrane proteins and ion movement involved in myocardial excitation-contraction (EC) coupling and relaxation.
Contraction:
1) AP enters from adjacent cell
2) Voltage-gated Ca2+ channels open –> Ca2+ enters cell
3) Ca2+ induces Ca2+ release through RyR
4) Local release causes Ca2+ spark (increase in Ca2+)
5) Summed Ca2+ sparks create a Ca2+ signal
6) Ca2+ ions bind to troponin to initiate contraction
Relaxation:
7) Relaxation occurs when Ca2+ unbinds from troponin
8) Ca2+ is pumped back into the SR for storage
9) Ca2+ is exchanged with Na+ by the NCX antiporter
10) Na+ gradient is maintained by the Na-K-ATPase
What is the force generated proportional to?
the # of active cross-bridges –> determined by how much Ca2+ is bound to troponin
What does sarcomere length affect?
force of contraction
Compare and contrast APs of myocardial autorhythmic and contractile cells.
Autorhythmic cells:
- has a threshold at -40 mV
- has a graded potential
- RMP about -60 mV
- has a pacemaker potential –> Na+ influx and Ca2+ begins to flow in
- I(f) channels –> for Na+
- L-type Ca2+ channels
Contractile Cells:
- no graded potential
- RMP about -90 mV
- plateau –> Ca2+ channels are open and K+ channels close –> cancel out
- voltage gated Na+ channels
- L-type Ca2+ channels
What prevents tetanus in cardiac muscle?
long refractory periods
Describe the conduction of electrical signals through the heart.
1) SA node depolarizes
2) Electrical activity goes rapidly to AV node via internodal pathways
3) Depolarization spreads more slowly across atria (thru AV bundle) + conduction slows thru AV node
4) Depolarization moves rapidly thru ventricular conducting system of the apex (bundle branches) of the heart
5) Depolarization wave spreads upward from the apex (thru Purkinje fibers)
Describe the parts of an electrocardiogram.
- P wave –> depolarization of the atria
- QRS complex –> wave of ventricular depolarization (atrial repolarization is also part of QRS)
- T wave –> repolarization of the ventricle
The SA node sets the pace of the heartbeat at _____ bpm.
70
AV node (50 bpm) and Purkinje fibers (25-40 bpm) can act as _____ under some conditions.
pacemakers
Explain how the electrical events in an electrocardiogram are related to the mechanical events of the cardiac cycle.
1) SA node depolarizes –> P wave –> atrial depolarization
2) P-Q or P-R segment –> conduction thru AV node and AV bundle (some contraction begins)
3) Q wave –> depolarization spreads down septum
4) R wave –> depolarization moves up the walls of the ventricles (atrial repolarization)
5) S wave
6) S-T segment –> ventricles contract
7) T wave –> ventricular repolarization
8) end
What does an electrocardiogram (ECG) show?
show the summed electrical activity generated by all the cells of the heart –> not an AP
What are the stages/steps in the autorhythmic cell AP?
1) During Pacemaker potential: I(f) channels open + Na goes into cell
2) During Pacemaker potential: Some Ca2+ channels open + I(f) channels close
3) during AP: lots of Ca2+ channels open
4) during AP: Ca2+ channels close + K channels open
5) during AP: K+ channels close
6) during AP: I(f) channels open
What are the stages/steps in the contractile cell AP?
1) Na+ voltage gated channels open
2) Na+ voltage gated channels close + K+ fast channels open
3) (L-type) Ca2+ channels open + fast K+ channels close –> the opening/closing cancels each other out –> plateau
4) (L-type) Ca2+ channels close + slow K+ channels open
5) slow K+ channels close
6) resting potential
What is the formula for cardiac output?
stroke volume x heart rate
what is the relationship between preload and stroke volume?
direct relationship
what causes preload?
- the load a muscle is subject to before contraction
- stretch before contraction
what helps with venous return?
- skeletal muscle pump
- respiratory pump
- sympathetic innervation of the veins
what is the relationship between venous return and preload?
direct relationship
If we increase contractility, what happens to stroke volume?
increase –> more cross bridges formed
how is contractility increased?
- sympathetic –> by acting on the contractile cells
- more Ca2+
how does sympathetic increase preload?
by causing vasoconstriction
In contractile cells, what do sympathetic neurons do?
- release NE onto B1
- causes phosphorylation of L-type Ca2+ channels, RyR, and phospholambin
what does diastole mean?
relaxation of heart
what does systole mean?
contraction of heart
List the steps of the heart contracting and relaxing in a cardiac cycle.
- late diastole – both sets of chambers are relaxed and ventricles fill passively
- atrial systole – atrial contraction forces a small amount of additional blood onto ventricles
- isovolumic ventricular contraction – pushes AV valves closed but does not create enough pressure to open semilunar valves
- max blood volume in ventricles = EDV - ventricular ejection – as ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood is ejected
- isovolumic ventricular relaxation – as ventricles relax, pressure in ventricles falls; blood flows back into cusps of semilunar valves and snaps them closed
- min blood volume in ventricles = ESV
What is the equation for stroke volume?
SV = EDV - ESV
(volume of blood before contraction - volume of blood after contraction)
what is the average stroke volume?
70 mL
what is the average cardiac output?
5 L/min
Explain the role of the parasympathetic system in control of heart rate at the cellular and molecular level.
- decreases heart rate
- K+ permeability increases –> pacemaker potential begins at a lower value
- Ca2+ permeability decreases –> slows rate of pacemaker depolarization
- tonic control
Explain the role of the sympathetic system in control of heart rate at the cellular and molecular level.
- increases heart rate
- B1-adrenergic receptors on the autorhythmic cells
- Na+ and Ca2+ permeability increases –> increases rate of pacemaker depolarization
How does the parasympathetic system slow the heart rate down?
parasympathetic stimulation hyperpolarizes the membrane potential of the autorhythmic cell and slows depolarization –> slowing the heart rate
How does the sympathetic system increase heart rate?
sympathetic stimulation and epinephrine depolarize the autorhythmic cell and speed up the pacemaker potential –> increasing HR
what are length-tension relationships determined by?
volume of blood at beginning of contraction
what is the Frank-Starling law of the heart?
- SV is proportional to EDV
- the heart pumps all the blood that is returned to it
what is an inotropic effect?
any chemical that affects contractility is an inotropic agent
what do positive inotropes do?
increase contractility
what do negative inotropes do?
decrease contractility
what determine afterload?
EDV and arterial blood pressure
what is afterload?
combined load of EDV and arterial resistance during ventricular contraction
what is ejection fraction?
percentage of EDV ejected with one contraction (SV / EDV)
