Chapter 14: Cardiovascular Physiology Flashcards
- the heart
- blood vessels
- blood
cardiovascular system
what does the cardiovascular system transport?
- oxygen & nutrients to cells
- wastes from cells
- hormones, immune cells, and clotting proteins to specific target cells
what is the flow of blood through the cardiovascular system?
heart–> arteries–> arterioles—> capillaries –> venules–> veins–> heart
large, branching vessels taking blood away from the heart
arteries
small branching vessels with high resistance
arterioles
site of exchange between blood and tissue
capillaries
small converging vessels
venules
relatively large converging vessels that conduct blood to the heart
veins
is the cardiovascular system open or closed?
closed system
what does the blood consist of?
- erthyrocytes (RBC)
- leukocytes (WBC)
- platelets
- plasma
- red blood cells
- transport oxygen and carbon dioxide
erythrocytes
- white blood cells
- defend body against pathogens
leukocytes
- cell fragments
- important in blood clotting
platelets
fluid and solutes
plasma
- supplied by right heart
- blood vessels from heart to lungs, and from lungs to heart
- oxygen diffuses from tissues to blood
pulmonary circuit
- supplied by left heart
- blood vessels from heart to systemic tissues, and from tissues to heart
- oxygen diffuses from blood to tissues
systemic circuit
how is the flow of blood through systemic and pulmonary circuits?
its in series
what is the path of blood in the circuits?
Left ventricle → aorta → systemic circuit → vena cavae → right atrium right ventricle → pulmonary artery → pulmonary circuit → pulmonary veins → left atrium → left ventricle
- located in thoracic cavity
- weighs 250-350 grams
heart
separates the abdominal cavity from the thoracic cavity
diaphragm
- Membranous fluid-filled sac surrounding the heart
- Lubricates the heart and decreases friction
pericardium
what are the 3 layers of the heart wall?
- epicadium
- myocardium
- endothelium
external membrane of heart wall
epicardium
- middle layer of heart wall
- cardiac muscle
myocardium
- inner layer of heart wall
- layer of endothelial cells
endothelium
drives blood flow
pressure difference (high pressure to low pressure)
what is the normal direction of blood flow?
- atria to ventricles
- ventricles to arteries
- prevent backward flow of blood
- open passively based on pressure gradient
valves
what are the two main valves of the heart?
- Atrioventricular (AV) valves
- semilunar valves
tricuspid valve
Right AV valve
bicuspid valve = mitral valve
Left AV valve
Keep AV valves from being pushed back into atrium
Papillary muscles and chordae tendineae
- aortic valve
- pulmonary valve
semilunar valves
what happens when the ventricles are relaxed?
AV valves
blood enters the atria, pushing the atrioventricular valve cusps down into the ventricles, opening the valves
what happens when the ventricles contract?
AV valves
blood presses up against the atrioventricular valve cusps, forcing the valves closed
what happens when papillary muscles contract?
tightens the chordae tendineae, preventing the
valve cusps from being pushed into the atria
are the AV valves open or closed during ventricular contraction?
AV valves remain closed
to prevent blood flow
backward into the atria.
what happens when the ventricles contract?
semilunar valves
blood presses up against the semilunar valve cusps, forcing the valves open and allowing blood to flow into the aorta and pulmonary
artery
what happens when the ventricles relax?
semilunar valves
blood in the aorta and pulmonary artery presses down against the valve cusps, forcing them to close
prevent blood that has entered the arteries from flowing back into the ventricles during
ventricular relaxation.
semilunar valves
ensured by the two sets of valves
one-way flow of blood through the heart
drive blood flow from high pressure to low pressure
pressure gradients
flow due to pressure gradients
bulk flow
creates a pressure gradient for bulk flow of blood
the heart
what must exist in the circulatory system to maintain blood flow?
a gradient
the force exerted by blood
pressure
in which direction does blood flow occur?
from high pressure to low pressure
the force pushing blood against the various factors resisting the flow of liquid in a pipe
ΔP
what is flow proportional to?
ΔP
- the pressure exerted on the walls of the container by the fluid within the container
- proportional to the height of the water column
hydrostatic pressure
- depends on the pressure gradient
- only if there is a positive pressure gradient (ΔP)
fluid flow through a tube
depends on the pressure gradient (ΔP), not the absolute pressure (P)
blood/fluid flow
is the pressure gradient greater in the systemic circuit or the pulmonary circuit?
it is much greater in the systemic circuit
is the flow greater in the systemic or pulmonary circuit?
flow is equal in both circuits
=ΔP/R
flow
is resistance less in the pulmonary or systemic circuit?
resistance through the pulmonary circuit is much less than resistance through the systemic circuit
inversely proportional to resistance
flow through a tube
what happens if resistance increases?
flow decreases
what happens if resistance decreases?
flow increases
- Resistance is proportional to length (L) of the tube (blood vessel)
- Resistance is proportional to viscosity (), or thickness, of the fluid (blood)
- Resistance is inversely proportional to tube radius to the (coffee straw)
Poiseuille’s Law
proportional to length (L) of the tube (blood vessel)
resistance
-Resistance increases as
length increases (long
straw)
proportional to viscosity (), or thickness, of the fluid (blood)
resistance
-Resistance increases as
viscosity increases
(milkshake)
inversely proportional to tube radius to the (coffee straw)
resistance
-Resistance decreases
as radius increases
has a large effect on resistance to blood flow (flow rate)
small change in radius of blood vessel
- decrease in blood vessel diameter/radius
- decreases blood flow
vasoconstriction
- increase in blood vessel diameter/radius
- increases blood flow
vasodilation
the volume of blood that passes a given point in the system per unit time (how much)
flow rate
the distance a fixed volume of blood travels in a given period of time (how fast)
velocity of flow
when is velocity directly related to flow rate?
when the tube has a fixed diameter
when does the velocity varies inversely with diameter?
when the tube has a variable diameter
faster in narrow sections
velocity of blood flow
slower in wider sections
velocity of blood flow
what does cardiac muscle consist of ?
- contractile cells
- autorhythmic cells (pacemakers)
Striated fibers organized into sarcomeres
contractile cells
- Signal for contraction
- Do not have organized sarcomeres
Autorhythmic cells, or pacemakers
branched, have a single nucleus, and are attached to each other by specialized junctions known as intercalated disks.
myocardial muscle
contain desmosomes
that transfer force from cell to cell, and gap junctions that allow electrical signals to pass rapidly from cell to cell
intercalated discs
- Spontaneously depolarizing membrane potentials generate action potentials
- Coordinate and provide rhythm to heartbeat
pacemaker cells
- Rapidly conduct action potentials initiated by pacemaker cells to myocardium
- Conduction velocity = 4 meters/second
conduction fibers
- Sinoatrial node
* Pacemaker of the heart - Atrioventricular node
pacemaker cells of the myocardium
what are the conduction fibers of the myocardium?
- Internodal pathways
- Bundle of His
- Purkinje fibers
- Sets the pace of the heartbeat at 70 bpm
- AV node (50 bpm) and Purkinje fibers (25–40 bpm)
sinoatrial (SA) node
Routes the direction of electrical signals so the heart contracts from apex to base
Internodal pathway from SA to atrioventricular (AV) node
- SA node → right atrium → left atrium
- rapid
- Simultaneous contraction of right and left atria
interatrial pathway
-SA node → AV node
internodal pathway
- Only pathway from atria to ventricles
- Slow conduction: AV nodal delay = 0.1 sec
- Atria contract before ventricles
AV node transmission
how does ventricular excitation occur?
- Down bundle of His
- Up Purkinje fibers
- Purkinje fibers contact ventricle contractile cells
- Ventricle contracts from apex up
what is the conduction system of the heart?
SA node–>internodal pathways–> AV node–>AV bundle–> bundle branchea–>purkinje fibers
how do pacemakers control the heartbeat?
- autorhythmic cells
- spontaneous depolarization
- depolarize to threshold
- repolarization
have pacemaker potentials
autorhythmic cells
**caused by closing K+ channels and opening two types of channels
-Na+ funny channels (If):
net depolarization
-Ca2+ channels (T-type):
further depolarization
spontaneous depolarizations
how is the heart depolarized to threshold?
Open fast Ca2+ channels(L-type): action potential
how is the heart repolarized?
open K+ channels
gradually becomes less negative until it reaches threshold, triggering an action potential
pacemaker potential
- Depolarization due to Na+ entry
- Repolarization due to K+ exit
- Long action potential (plateau) due to Ca2+ entry in the cell prevents tetanus
myocardial contractile cells
lasts almost as long as the entire muscle twitch
refractory period in cardiac muscle fiber
prevents tetanus
long refraction period in cardiac muscle
refractory period is very short compared with the amount of time required for the development of tension
skeletal muscle fast-twitch fiber
if they are stimulated repeatedly, it will exhibit summation and tetanus
skeletal muscles
how does cardiac muscle compare to skeletal muscle?
- smaller & have single nucleus per fiber
- branch & join neighboring cells through intercalated disks (desmosomes & gap junctions)
- T-tubules are larger & branch
- sarcoplasmic reticulum is smaller
- mitochondria occupy 1/3 of cell volume
allow force to be transferred
desmosomes
provide electrical connection
gap junctions
how is excitation-contraction coupling in cardiac muscle similar to properties of skeletal muscle?
- T-tubules
- Sarcoplasmic reticulum Ca2+
- Troponin-tropomyosin regulation
how is excitation-contraction coupling in cardiac muscle similar to properties of smooth muscle?
- gap junctions
- Extracellular Ca2+
what are the steps of excitation-contraction coupling of the heart?
- Depolarization of cardiac contractile cell to threshold via gap junction
- Opening of calcium channels in plasma membrane
- AP travels down T tubules
- Calcium is released from sarcoplasmic reticulum
- Calcium binds to troponin, causing a shift in tropomyosin
- Binding sites for myosin on actin are exposed
- Crossbridge cycle occurs
how is calcium released from sarcoplasmic reticulum?
- calcium-induced calcium release
- action potentials in T tubules
- Provides information on heart rate and rhythm, conduction velocity, and even the condition of tissues in the heart.
- has waves and sements
electrocardiogram
what are the components of an electrocardiogram?
- P wave
- QRS complex
- T wave
- PR segmet
shows atrial depolarization
P wave
shows ventricular depolarization and atrial repolarization
QRS complex
shows ventricular repolarization
T wave
- shows AV nodal delay
- conduction through AV nodes and AV bundle
PR segment
what does an upward deflection on an ECG mean?
means the current flow vector is toward the positive electrode
what does a downward deflection on an ECG mean?
the current flow vector is toward the negative electrode
what does no deflection on an ECG mean?
the vector is perpendicular to the axis of the electrode
- lag behind electrical events
- contraction follows action potential
mechanical events
begins with atrial depolarization, atrial contraction at the end of P wave
ECG
goes through AV node and AV bundle
PR segment signal
ventricular contraction begins and continues through T wave
Q wave end
- loss of conduction through the AV node
- P wave becomes independent of QRS
- atrial and ventricular contractions are independent
third degree heart block
- loss of coordination of electrical activity of the heart
- death can ensue within minutes unless corrected
ventricular fibrillation
-Events associated with the flow of blood through the heart during a single complete heartbeat
cardiac cycle
what are the two main periods of the cardiac cycle?
- systole: ventricle contraction
- diastole: ventricle relaxation
open passively due to pressure gradients
valves
open when atrial pressure > ventricular pressure
AV valves
open when ventricular pressure > arterial pressure
semilunar valves
what are the phases of the cardiac cycle?
- Ventricular filling
- isovolumetric ventricular contraction
- ventricular ejection
- Isovolumetric ventricular relaxation
- Middle of ventricular diastole
- Venous return
- AV valve opens
- Blood moves from atria to ventricle
- Pulmonary and aortic valves are closed
- Passive until atrium contracts
ventricular filling
- start of systole
- ventricle contracts-increases pressure
- AV & semilunar valves closed
- no blood entering or exiting the ventricles
Isovolumetric ventricular contraction
- Remainder of systole
- Pressure in ventricles > pressure in arteries
- Semilunar valves open
- Ventricular pressure < aortic pressure
- Semilunar valves close
ventricular ejection
- Onset of diastole
- Ventricle relaxes—decreases pressure
- AV and semilunar valves closed
- No blood entering or exiting ventricle
Isovolumetric ventricular relaxation
- Atrial pressure rises slowly with filling of blood
- Ventricular pressure is low
- Small rise in VP at end due to atrial contraction
Phase 1
- Rapid rise in ventricular pressure
- Atrial pressure falls
Phase 2
- Ventricular pressure falls
- Atrial pressure falls further until late systole
Phase 3
- Aortic valve closes
- Blood is still leaving aorta, so pressure falls
- Lowest point = diastolic pressure
Diastole
- Aortic valve opens
- Pressure rises rapidly with ejection
- Highest point = systolic pressure
- Aortic valve closes
- Backflow of blood causes slight increase—dicrotic notch
systole
- maintains blood flow through the entire cardiac cycle
- continuous blood flow during cardiac cycle
aortic pressure
- elastic
- pressure reservoir
- stores energy during systole as walls expand
- releases energy during diastole as walls recoil inward
aorta (and large arteries)
Volume of blood in ventricle at the end of diastole
EDV: end-diastolic volume
Volume of blood in ventricle at the end of systole
ESV: end-systolic volume
-Volume of blood ejected from ventricle each cycle
=EDV-ESV
=130 mL-60 mL = 70 mL
SV: stroke volume
-fraction of end-diastolic volume ejected during a heartbeat
=stroke volume/end diastolic volume
=70 mL/130 mL = 0.54 (i.e. 54% at rest)
ejection fraction (EF)
-Volume of blood pumped by each ventricle per minute
=SV x HR
cardiac ouotput
- average= 5liters/min at rest
- 72 beats min x 0.07 L/beat = 5.0 L/min
cardiac output
average blood volume of cardiac output
5.5 liters
determined by SA node firing frequency
heart rate
SA node intrinsic firing rate
100/min
is there extrinsic control on the heart from the SA node?
no, HR=100
under control of ANS and hormones
SA node
- at rest
- HR=75
parasympathetic system dominates
- excitement
- HR increases
sympathetic system takes over
what does the Activity of sympathetic neurons projecting to SA node do to the HR?
raises HR
what does the Activity of parasympathetic neurons projecting to SA node do to the HR?
lowers HR
what do levels of circulating epinephrine do to the HR?
raises HR
what does stimulation by the parasympathetic nerves do to the heart rate?
decreases heart rate
what does stimulation by sympathetic nerves do to the heart rate?
increases heart rate
how does increased sympathetic activity come about?
nerves or epinephrine–> beta 1 receptors in SA node –> increase open state of I_f and Ca2+ channels–> increase rate of spontaneous depolarization–> increase heart rate
depolarize the autorythmic cell and speed up the pacemaker potential, increasing the heart
sympathetic stimulation
what does increased parasympathetic activity do?
vagus nerve–>muscarinic cholinergic receptors in SA node–>increase open state of K+ channels & closed sate of Ca2+ channels—> decrease rate of spontaneous depolarization & hyperpolarize cell —> decrease heart rate
hyperpolarizes the membrane potential of the autorhythmic cell & slows depolarization, slowing down the heart rate
parasympathetic stimulation
what are the primary factors affecting stroke volume?
- ventricular contractility
- end-diastolic volume
- afterload
how does ventricular contractility affect stroke volume?
-a more forceful contraction will expel more blood
what is involved in the sympathetic control of ventricular contraction?
- sympathetic innervation of muscle cells
- Norepinephrine → β1 adrenergic receptors → cAMP second-messenger system
what are the steps involved in norepinephrine leading to the CAMP second messenger system?
- Augment open Ca2+ channels
- Increase Ca2+ release from sarcoplasmic reticulum (SR)
- Increase myosin ATPase rate
- Enhance rate of Ca2+ -ATPase activity on SR
what is the influence of end-diastolic volume on stroke volume?
***starlings law
-Increased EDV
stretches muscle fibers
-Fibers closer to optimal
length
-Optimal length →
greater strength of
contraction
-Result → increased SV—
–> increase venous
return—–> increase
strength of contraction–
–> increase stroke
volume
what does an increase in EDV cause?
stroke volume to increase
what are the factors affecting end-diastolic volume?
- end diastolic pressure
- filling time
- atrial pressure
- central venous pressure
- afterload
preload
end-diastolic pressure
pressure in aorta during ejection
afterload
