Cardiovascular Physiology - Lecture 4 Flashcards
What are the components of the circulatory system?
Heart
Blood Vessels
Blood
What is the blood made up of?
Formed elements (cells and cell fragments) Liquid (plasma)
What is included in the plasma?
Water Ions Proteins Nutrients Hormones Waste
What percentage of the blood does plasma (usually) make up?
55%
What cells are in the blood?
RBCs
WBCs
Platelets
What is the hematocrit? What is its normal value?
The percent of the blood volume that is composed of RBCs
45%
What is the hematocrit of a person with a plasma volume of 3L and a total blood volume of 4.5L?
They have RBC volume of 1.5L
1.5/4.5 = 33%
What is the difference between the pulmonary and systemic circuits?
Pulmonary = heart and lungs Systemic = heart and body
Where do arteries and veins carry blood?
Arteries = away from the heart Veins = towards the heart
What makes up microcirculation?
Arterioles
Capillaries
Venules
Which side of the heart is larger? Why?
Left - because it has to generate more force for the systemic circuit
From the R atrium, trace the flow of blood through the body
R atrium –> R ventricle –> Pulmonary a. –> Lung –> Pulmonary v –> L atrium –> L ventricle –> Aorta –> Systemic aa –> Capillaries –> Systemic vv –> Vena Cava –> R. atrium
What two organs get the most blood at rest?
Kidneys and muscles
T/F - Bloodflow can have dynamic adjustments
True - Dynamic adjustments allow a person to respond to varying circumstance
What is flow? What is the equation for flow?
Volume of blood per unit of time
F = /\P/R
flow = change in pressure over resistance
/\P
Change in pressure
The pressure difference between the artery side and the vein side of an organ
R
Resistance
How difficult it is for blood to flow between two points
What factor provides the most potential change for the resistance of blood flow, and therefore the most efficient way of regulating blood flow
Radius of the blood vessel
What prevents backflow in the valves of the heart?
Chordae tendinae connected to the papillary muscle
What valve separates the R. ventricle and the pulmonary a.?
Pulmonary semilunar valve
What valve separates the L atrium and ventricle?
Left (bicuspid) AV valve
Interventricular septum
Separates the R and L ventricles
What valve separates the L ventricle and the aorta?
Aortic semilunar valve
What are the 3 layers of the heart from deep to superficial?
Myocardium (thickest)
Epicardium
Pericardium
What are the jobs of the heart valves?
Control bloodflow
Electrical insulation
Describe the electrical insulation job of the valves?
The fibrous skeleton of the valves electrically separate the atria and ventricles
What is the blood flow through the heart (include valves)?
R atrium –> R AV valve –> R ventricle –> Pulmonary valve –> pulmonary a –> lungs –> pulmonary v –> L atrium –> L AV valve –> L atrium –> Aortic valve –> Aorta
Describe cardiac muscle
Branched (unlike skeletal muscle)
Has intercalated discs
GAP junctions (so each cell is electrically coupled)
Striated (like skeletal muscle)
How does the parasympathetic ns system innervate the heart?
Through the vagus n.
Innervates the atria only
Secretes ACh on muscularinic receptors
How does the sympathetic ns system innervate the heart?
Releases norepinephrine through the thoracic spinal nerve OR epinephrine through the blood
Has a direct effect on atria and ventricles (controls HR in the atria)
Epi and NE bind to B-1 receptors on the atria and ventricles
What is the pacemaker of the heart?
Sinoatrial node (SA)
Describe how an electrical signal travels through the heart
Starts in the SA node
Through gap juncitons, the electricity spreads through the atria (atria contracts)
Electricity travels to the AV node - here, it slows to allow the ventricles to collect the blood
Once the electricity reaches the bundle of His, the signal speeds back up and flies down the Purkinje fibers - this allows the ventricles to contract at the same time
Where does the Bundle of His deliver the electrical signal? Why?
To the apex of the heart
This allows the ventricular contraction to occur in an upwards sweep
What does the p-wave represent?
Atrial depolarization
What does the QRS complex represent?
Ventricular depolarization
What does the t-wave represent?
Ventricular repolarization
Why isn’t there an electrical representation of atrial repolarization?
It get obliterated by the QRS complex
What causes the rapid depolarization phase?
The opening of voltage-gated Na channels
What causes the prolonged plateau phase of depolarization?
The slow, but prolonged opening of Ca channels
plus the closure of potassium channels
What causes the repolarization phase?
Opening of K channels
Why don’t SA nodal cells have a true resting potential?
Because of funny channels
funny channels
Channels that allow Na and Cl ions to leak into the cell until they create a threshold graded depolarization
What is the difference between Nodal cardiac cells and myocardial ventricular cells?
Nodal cells have funny channels to automatically cause depolarizaiton
Ventricular cells require something to depolarize them (it comes form nodal cells)
The rapid depolarizaiton in nodal cells is caused by Ca channels, and it takes a little bit longer
What does the action potential in a Purkinje fiber look like? Why is this important?
The actual AP looks like a ventricular cell
However, Purkinje cells have funny channels so they can depolarize on their own
This is important because if the SA node dies, the heart can still happen
Second degree block
Every other p-wave will not be followed by a QRS complex and t-wave
This is because atria and ventricles aren’t talking to each other - the AV node is in refractory and cannot depolarize
Third degree block
p-waves are going and QRS complexes are going, but not in pattern with each other
This is because the AV node is dead, so atria and ventricles are completely separate
Long QT Syndrome
Voltage gated K channels in ventricular muscle are delayed and reduced. This causes the muscle to take longer to repolarize. An ECG will show the the T-wave being longer from the QRS
Excitation Contraction Coupling
Links the cardiac muscle cell action potentials to contraction via control of calcium within the myocardium
Works through Ca-induced-Ca-release
Ca-induced-Ca release
Cells become excited/depolarize - during the plateau phase, Ca channels open and Ca comes into the cell
Ca binds to receptors on the sarcoplasmic reticulum - this leads the SR to release more Ca into the cytosol
How does Ca effect muscle fibers?
It binds to troponin C, so actin and myosin can interact
What are the two jobs of the plateau phase?
Release Ca
Create a refractory period that prevents tetanic contraction
Why is avoiding tetanic contraction important?
It allows time for ventricles to fill with blood prior to pumping
