Cardiovascular Physiology Flashcards
What determines blood flow in the vascular system?
A net change in pressure.
What is hydrostatic pressure
The pressure exerted by a fluid
What is viscosity?
Friction between molecules of a flowing fluid
How do the length and diameter of a vessel affect viscosity??
Increase in viscosity due to increased interaction between blood cells and the stationary vessel wall.
What is hematocrit? How does it affect blood flow?
The number of blood cells in the vessel; increases viscosity and decreases blood flow.
What is Poiseuille’s equation?
R= 8nL/pi r^4
When can Poiseuille’s equation be used?
In laminar blood flow only.
What are the four functions of the cardiovascular system?
- Delivering nutrients and removal of waste.
- Chemical signalling delivery (hormones and NT)
- Thermoregulation.
- Mediation of inflammatory and immunity response.
What are the three components of the cardiovascular system?
The heart (pump), the vessels (pipes), and the blood (fluid).
What are the components of the vessels?
Arterioles, capillaries, arteries, and veins
Arterioles
Small branching vessels with high resistance, extend off arteries.
What are capillaries?
The smallest vessel unit that extends off arterioles, facilitates diffusion in nutrients from the blood to tissue and waste from tissue to blood.
Arteries
Vessels that push blood away from the heart
Veins
Vessels that bring blood to the heart.
What are the four chambers of the heart
Right atrium, right ventricle, left atrium, left ventricle
Which chambers contain the lowest pressure?
Atria, because they receive blood returning to the heart from the body or lungs.
What is the function of the septa? What are its divisions?
The function: separate oxygenated blood from deoxygenated blood.
Divisions: Interatrial septum
Interventricular septum.
What are the two serial circuits of the cardiovascular system?
Pulmonary circulation, system circulation
Describe pulmonary circulation:
Blood enters lungs from a pulmonary branch of the right ventricle, thin tissue allows oxygen to diffuse back into blood. Enters the heart through the left atrium through the pulmonary veins.
Describe systematic circulation:
Oxygenated blood leaves the heart through the aorta and travels through arteries to various tissue and organs. Oxygen diffuses through capillaries and blood takes up waste from tissue cells. Deoxygenated blood then circulates back to the heart through veins, where it enters the right atrium through the superior or inferior vena cava.
When does series flow occur in systematic circulation?
The liver; blood is supplied by the gastrointestinal tract.
What is the function of the pericardium?
Stabilization of the heart, protection of the heart, lubrication of the heart, and limitation of the heart filling (disaster prevention).
Pericardium
The fibrous sac surrounding the heart and roots of the great vessels consists of three layers.
What are the three layers of pericardium?
Fibrous pericardium, Parietal layer, Visceral layer.
Where is the pericardial fluid found?
In the pericardial cavity
Which layers make up the serous pericardium?
Parietal and visceral layers.
Which pericardial layer is a part of the heart wall?
Visceral layer (epicardium when attached to the wall)
Why is the left ventricle larger than the right?
Must pump blood to the entire body, has to create a large pressure.
What are the layers of the heart wall?
The endocardium, myocardium, and epicardium.
What is the epicardium?
Also the visceral layer of the pericardium covers the outer surface of the heart and secreted pericardial fluid.
What is the Myocardium?
The muscular wall of the heart containing the myocytes, nerves, and blood vessels.
What is the endocardium?
The innermost layer of the heart wall. Smoothest layer to decrease resistance; covers all inner surfaces of the ventricles and atria.
Myocyte
Cardiac muscle cell
Describe the appearance and connectivity of cardiac muscle cells:
Y-branched, connect to many different myocytes. Striated in appearance, contain only one nucleus. Contain intercalated disks.
Intercalated disk
Junctions between myocytes; desmosomes or gap junctions
Desmosomes
Mechanical connections between myocytes
Gap junctions
Electrical synapses between myocytes
Valves
Thin flaps of flexible endothelium-covered fibrous tissue attached at valve rings. Made up of collagen.
What are the four valves of the heart?
Pulmonary valve
Aortic valve
Tricuspid valve
Bicuspid valve
What are valve rings
A part of the cardiac skeleton; act as structural support to anchor valves to the myocardium.
Describe the unidirectional flow of blood through the heart
Valves open and close passively due to pressure changes and not by ATP or muscular contraction. When pressure is greater behind valve, it opens. When pressure is greater in front of valve, it closes.
What are the AV valves?
Atrioventricular valves: connect atria and ventricles and prevent backflow of blood. Contain the right AV valve (tricuspid) and the left AV valve (bicuspid).
What is the valve apparatus composed of?
Chordae tendinae, papillary muscles?
What are chordinae tendinae?
Tendinous-type tissue that extend from the edges of each leaflet to the papillary muscles.
What are the papillary muscles?
Cone-shaped muscles that contract to stabilize the closed conformation of valves and prevent backflow due to increased ventricular pressure. Only present at AV valves.
What are the arterial/semi-lunar valves?
Contain three cusps and situate between the ventricles and arteries. Contain the pulmonary valve (right) and the aortic valve (left). Do not contain valve apparatus.
What is the cardiac skeleton? What is its purpose?
The fibrous skeleton of the heart that consists of dense connective tissue and valve rings. Separates atria from ventricles, contributes to support of heart, prevents electrical conductance from atria to ventricles.
What is the arrangement of cardiac muscles called?
Syncytium.
What is a functional syncytium?
A set of cells that are connected so that when one cell is excited, the excitation spreads over all cells in connection.
How many syncytium make up the heart?
2; one for ventricles and one of atria.
Automaticity:
Cardiac muscle contraction in the absence of neural or hormonal stimulation, as a result of the action potential it generates itself.
What are the two types of cardiac muscle cells?
Conducting cells and contractile cells
Conducting cells
Autorhythmic cells: initiate and conduct action potentials responsible for heart contraction by the contractile myocytes.
How is the conductive system connected?
Through gap junctions
What are the components of the conducting system?
SA node, Internodal pathways, Bundle of His and AV node, bundle branches, Purkinje fibres.
What is the only electrical connection between atrium and ventricle?
Bundle of His and AV node
What is the sinoatrial node?
Pacemaker that sets heart rate; internodal pathways carry signal from SA to bundle of His and AV node to contract ventricles.
What is the atrioventricular node?
Node that depolarizes bundle branches and purkinje fibres to contract ventricles. Receives impulse from SA node via the bundle of His. Contains a delay to ensure atria can contract before ventricles.
What are the purkinje fibres?
Fast-conducting fibres that depolarize both ventricles simultaneously.
What is the order of the conducting system of the heart?
SA node, internodal pathways, Atrial myocardium, AV node, bundle of His, right and left bundle branches, Purkinje fibres, ventricular myocardium.
What are the two types of action potentials in the heart?
Fast action and slow action.
Where does fast action potential occur?
Atrial myocardium, Ventricular myocardium, bundle branches, Purkinje fibres, bundle of His.
Where does slow action potential occur?
Sinoatrial node, Atrioventricular node.
Describe SA node action potential
Consist of pacemaker potential, depolariztion, and repolarization.
Pacemaker potential: closing of potassium channels at -60mV, the opening of funny type sodium channels to slowly increase potential. Opening of transient calcium channels to reach threshold potential.
Depolarization: Long-term calcium channels open and cause slow depolarization. Transient channels close.
Repolarization: Potassium channels open, Funny type channels close, long-term calcium channels close. Cell reaches negative potential.
Describe fast voltage action potential
Resting phase, depolarization, notch, plateau, repolarization:
Resting phase: Potassium gates open, resting potential is negative.
Depolarization is caused by depol. in surrounding cell: influx of sodium due to opening of sodium channels.
Notch: transient opening of potassium channels causing slight decrease in potential.
Plateau: transient potassium gate closes, sodium gate closes, only potassium channel and long-term calcium channels remain open and keep membrane potential from shifting.
Repolarization: potassium channels open and calcium channels close.
What are the expected action potentials for the SA node, AV node, atrial myocardium, and ventricular myocardium?
SA node: slow AP.
AV node: slow AP, delayed pacemaker potential.
Atrial myocardium: fast AP with shorter plateau.
Ventricular myocardium: fast AP
P-wave
depolarization of atria
QRS complex
depolarization of ventricles (atria repolarization)
T-wave
ventricular repolarization
PR interval
atrial depol. and AV delay
QT interval
Ventricular contraction
ST-segment
isoelectric period of depol ventricles plateau phase
What is AV node block?
lack of synchrony between atrial and ventricular contractions and electrical events, shown in ECG, driven by slow Bundle of His
Describe relaxation in ECC cardiac muscles
Influx of calcium stops as long term calcium channels close. SR no longer stimulated to release calcium, Calcium is taken up by SR by calcium ATP-ase. Calcium removed by sodium calcium exchanger. Troponin free, tropomyosin blocks actin binding site.
Systole
Ventricular contraction, atrium relaxation
Diastole
Ventricular relaxation, atrium contraction
Isovolumetric ventricular contraction
All heart valves are closed, blood volume in ventricles remains constant, muscle tension develops and pressure rises. VENTRICULAR SYSTOLE
Ventricular ejection
Ventricular pressure is greater than arterial pressure and semi-lunar valves open. Blood is ejected outward and muscle shortens as ventricles contract.
Stroke volume
Volume of blood ejected from ventricles during systole
Isovolumetric ventricular relaxation
DIASTOLE. All heart valves are closed and blood volume remains constant, but pressure in ventricles drop below atria and arteries.
Ventricular filling
AV valves open due to pressure difference and both atria and ventricles are relaxed, about 70% of blood enters ventricles.
Atrial kick
Atria contract to squeeze remaining blood into ventricles.
End-diastolic volume
Amount of blood in each ventricle at the end of ventricular diastole
End-systolic volume
Amount of blood in ventricle after end of ventricular systole
Calculation for stroke volume
EDV - ESV
What is the first heart sound
Lub, caused by closing of the bicuspid/tricuspid valves. Signals the onset of ventricular systole.
What is the second heart sound?
Dub, the closing of the semi-lunar valves. Signals the onset of diastole.
What is compliance
The ability for a vessel to stretch due to change in volume.
What does the sympathetic nervous system innervate?
Atria, ventricles, SA node, AV node
What does the parasympathetic nervous sytem innervate?
Atria, SA node, AV node
Effect of parasympathetic stimulation on heart
SA node: decreased rate of depol to threshold, decreased heart rate.
AV node: decreased conduction, increased nodal delay
Atrial muscle: decrease in contractility
Effect of sympathetic stimulation on heart
Increased HR, decreased AV nodal delay, increased contractility
Cardiac output
amount of blood pumped by each ventricle in one minute
What is the formula for cardiac output
HR x stroke volume
What factors effect stroke volume
end diastolic volume, contractility, afterload
Effect of EDV on stroke volume
Increase in venous volume increased ventricular stretching and end diastolic volume. Greater force during contraction.
Effect of contractility on stroke volume
increased propulsion and stroke volume (due to sympathetic stimulation)
Effect of afterload on stroke volume
Tension against contraction increased, decreasing stroke volume
Endothelium
layer of endotheial cells continuous with endocardium, blood cells do not adhere to
Elastic arteries
Closest to heart, do not contain muscles. Expand and recoil to act as pressure reservoires.
Muscular arteries
Branch off elastic arteries, control arterial pressure and distribute blood
Arterioles
Resistance vessels that slow flow of blood
Types of capillaries
Continuous, fenestrated, sinusodial
Continuous capillaries
exchange of water, small solutes, lipid-soluble material. In most tissues.
Fenestrated capillaries
Contain pores. Rapid exchange of water, solutes and small peptides. In endocrine organs, GI tract, and kidneys.
Sinusoids
discontinuous capillaries, free exchange of water and solutes. In bone marrow, liver, spleen.
Transcytosis
Use of vesicles to cross endothelial cells
Bulk flow
movement of protein-free plasma across capillary wall, distribution of extracellular fluid volume.
Colloid osmotic pressures
Favor fluid movement into capillaries
Mean arterial pressure formula
Diastolic pressure + pulse average/3 OR CO x total peripheral resistance
Pulse pressure calculation
systolic - diastolic
What does increase in MAP cause?
Increase in rate of firing of baroreceptors
Short term regulation of MAP
baroreceptor reflexes: adjust CO and TPR by ANS
Long term regulation of MAP
blood volume adjustment, salt and water balance
Medullary cardiovascular center
Medulla oblongata, alters vagal stimulation (vagas nerve) by parasympathetic pathway to heart and sympathetic innervation to arterioles and veins.
Factors that increase contractility
Positive inotropy: exercise
Factors that decrease contractility
heart failure Calcium decrease
ESPVR
end-systolic pressure volume relation: describes maximal pressure that can be developed by the ventricle at any given left ventricular volume.
