Cardiovascular module Flashcards
End of semester exam
How is the CV system a distribution system?
- Nutrients/water/gases enter and are transported
- Hormones are transported
- Immune defense
- Waste
- Heat
- Homeostasis: BP and water and salt balance
Where does blood spend the most time?
the systemic veins
What is the heart encased with?
- Pericardium: a membranous fluid-filled sac
What is the heart mostly commposed of?
Myocardium
Describe the location and function of the atriventricular valves
- Between atria and ventricles
- Tricuspid valve on the right side
Bicuspid valve on left side
Describe the location and function of the semilunar valves
- Between ventricles and arteries
- Aortic valve
- Pulmonary valve
What are contractile cells?
striated fibers organized into sarcomeres
What are autorhythmic cells
Pacemaker cells
- signal for contraction
- smaller and fewer contractile fibers compared to contractile cells
- Do not have organized sarcomeres
How does resistance oppose flow
- Flow through a tube is inversely proportional to resistance
- Flow = 1/R
- If resistance increase, flow decreases
- If resistance decreases, flow increases
How does a change in radius effect resistance to blood flow?
Small changes have a large effect
- vasoconstriction
- vasodilation
What is mean arterial pressure?
= cardiac output x peripheral resistance
What is flow rate
= the volume of blood that passes a given point er unit time (mL/min)
Write the flow equation
delta P/R
- Flow of blood in the cardiovascular system is
- Directly proportional to the pressure gradient
- Inversely proportional to the resistance to flow
How does flow effect pressure gradient?
They are directly proportional.
The higher the pressure gradient, the greater the fluid flow.
Flow goes from higher pressure to lower pressure.
What is hydrostatic pressure?
The pressure exerted on the walls of the container by fluid within the container. Hydrostatic pressure is proportional to the height of the water column.
What is the major parameter controlled by the cardiovascular system?
Systemic mean arterial pressure.
What feedback loops act to regulate MAP
- short-term via neural pathways
- Long-term via the vasculature and kidneys.
What is the relative risk equation?
Risk of CVD with elevated BP/risk of CVD in control group
Fully explain the Pressure equation
Pressure = flow x resistance
Mean arterial pressure = cardiac output x total peripheral resistance
CO = stroke volume x heart rate
How to calculate mean arterial pressure?
MAP = diastolic pressure + 1/3 (P systolic - P diastolic)
Where are baroreceptors located and what are they?
Mechanically-sensitive receptors located in the carotid sinus and aortic arch
How does increasing and decreasing firing triggers affect efferent pathways?
Increases decrease SNS and increase PSNS activity.
Decreases increase SNS and decrease PSNS
Effect of PSNS stimulation on MAP
- The heart normally received tonic PSNS activity from the vagus nerve
- Increasing PSNS activity reduces heart rate and therefore blood pressure
- Veryy few blood vessels receive PSNS innervation, so the predominant effect is cardiac
Effect of SNS stimulation on MAP
- both the heart and vasculature receive SNS innervation
- An increase in SNS activity increases MAP via effects on both the heart and vasculature.
What are the 6 things which regulate decreased cardiac output and decreased arterial pressure
- arterial baroreceptor reflex (incr. HP, rapis response.
- Activation of autonomic response (^ SNS, dec. PSNS)
- Activation of renin/angiotensin system (vasoconstriction, inotrope, antidiuretic)
- Stimulation of aldosterone release (Ang II) (Na retention in kidney (salivary glands, sweat glands, colon)
- stimulation of vasopressin release (increased water resorption in the medullary collecting duct om kidney)
- Increased erythropoietin production (production of RBCs)
List the three long-term controllers of MAP
- Regulation of extracellular fluid volume
- EFV influenced by changes in input (thirst) or output (excretion of water and salt)
- Kidneys are the primary organ in this
List the five stages of mechanical events in the cardiac cycle
- late diastole
- Atrial systole
- Isovolumic ventricular contraction
- Ventricular ejection
- Isovolumic ventricular relaxation
What is diastole
cardiac muscle relaxes
what is systole
cardiac muscle contracts
What makes the first sound of the heart?
Vibrations following closure of the AV valves
What is the second heart sound?
Vibrations created by closing of semilunar valve
What is the formula for stroke volume
End Diastolic Volume - End Systolic Volume
Cardiac output formula
heart rate x stroke volume
How does SNS and PSNS effect stroke volume?
SNS speeds heart rate
- B - adrenergic receptors on the autorhythmic cells
PSNS activity slows heart rate
What is the Frank-Starling Law
Volume of blood returning back to the heart each minute
- increases EDV
- causes heart muscles to stretch
What three factors is venous return affected by
- skeletal muscle pump
- respiratory pump
- sympathetic innervation of veins
What is a chemical that affects contractility?
Inotropic agent
what have positive inotropic effects
epinephrine, norepinephrine and digitalis
What is the force of contraction affected by?
- length of muscle fiber
- contractility of heart
- as stretch of the ventricular wall increases, so does stroke volume
- Preload is the degree of myocardial stretch before contraction
What is afterload?
- the load that the heart must eject blood against
- closely related to the aortic pressure
What is the ejection fraction?
the percentage of EDV ejected with one contraction
- SV/EDV
Explain the 10 steps of EC coupling in cardiac muscle
- Action potential enters from adjacent cells
- Voltage-gated Ca2+ channels open. Ca2+ enters cell
- Ca2+ induces Ca2+ release through ryanodine receptor-channels (RyR)
- 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
- Ca2+ is exchanged with Na+ y the NCX antiporter
- Na+ gradient is maintained by the Na+-K+-ATPase
Explain action potential in the heart
starts with the pacemaker cells
- voltage-gated L-type Ca2+ channels in the cell membrane open (extra cellular calcium contributes 10%)
- Ryanodine receptors open in the sarcoplasmic reticulum (SR)
- calcium binds to troponin
Explain the ten steps of EC coupling in cardiac muscles
- AP enters from adjacent cell
- Voltage-gated Ca2+ channels open. Ca2+ enters cell
- Ca2+ induces Ca2+ release through ryanodine receptor-channels (RyR)
- 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
- Ca2+ is exchanged with Na+ by the NCX antiporter
- Na+ gradient is maintained by the Na+-K+-ATPase
What are the graded steps of cardiac muscle contraction (5)
- AP starts with the heart pacemaker cells
- Voltage-gated L-type Ca2+ channels in the cell membrane open (extra cellular calcium contributes 10%)
- Ryanodine receptors open in the sarcoplasmic reticulum (SR)
- Calcium binds to troponin
- crossbridge cycle as in skeletal muscle
- Relaxation: calcium removed from cytoplasm: back into the SR with Ca2+ ATPase and out of the cell through the Na+-Ca2+ exchanger (NC)
- Force generated is proportional to number of active crossbridges: determined by how much calcium is bound to troponin
- sarcomere length affects force of contraction
What are the 5 steps of the spread of action potential in the heart?
- AP originates at SA node
- AP spread throughout right and left atria
- AP can only pass from atria into ventricles via AV node, after a brief delay
- allows atrial contraction to complete ventricular contraction begins - AP travels rapidly down interventricular septum via Bundle of His, then rapidly throughout myocardium through Purkinje fibres - ventricle begin contracting from base upward
- Remainder of ventricular cells activated by APs moving through gap junctions
What does the sinoatrial node do?
- sets the pace of the heartbeat at 70 bpm
- AV node (50 bpm) and Purkinje fibers (25-40 bpm) can act as pacemakers under some conditions
What does the internodal pathway do and where does it go
Goes from the SA to atrioventricular node.
- routes the direction of electrical signals so the heart contracts from apex to base
- AV node delay is accomplished by slower conductional signals through nodal cells
What is an ECG?
ELECTROCARDIOGRAPHY
Trace of the average electrical activity of the heart - across multiple angles
Write the four steps of the action potential of a cardiac contractile cell
- resting membrane potential is 90mv
- Na+ passes through voltage gated channels
- Plateau results from decreased K+ and increased Ca++
- Plateau end when flux is reserved
What happen in myocardial contractile cells in action potentials
- depolarisation due to Na+ entry
- Repolarisation due to K+ exit
- Long AP due to Ca2+ entry in the cells
What happens in myocardial autorhythmic cells APs
- unstable membrane potential called pacemaker potential (called the funny current)
- Depolarization is due to Ca2+ channels opening
What are the 5 steps of the conducting system of the heart
- SA node depolarises
- Electrical activity goes rapidly to AV node via internodal pathways
- Depolarization speads more slowly across atria. Conduction slows through AV node
- Depolarisation moves rapidly through ventricular conducting system to the apex of the heart
- Depolarisation wave spread upward from the apex
How does parasympathetic stimulation control heart rate
It hyperpolarizes the membrane potential of the autorhythmic cell and slows depolarization, slowing down the heart rate
How does sympathetic stimulation control heart rate
Sympathetic stimulation and epinephrine depolarize the autorhythmic cell and speed up the pacemaker potential, increasing the heart rate
What are the three waves of an ECG
- P depolarization of the atria
- QRS comples: wave of ventricular depolarization
- T repolarization of the ventricle
- Atrial repolarization is part of QRS
How does electrical conduction occur in the heart?
- purkinje fibers transmit electric signals down the atrioventricular bundle (bundle of His) to left and right bundle branches
