Week 2 Flashcards
What are the 3 basic principles of Circulatory Function
- Blood flow to most tissues is controlled according to tissue needs
- CO is the sum of all the local tissue blood flows
- Arterial pressure regulation is generally independent of either local blood flow control or cardiac output control
Def: Flow
The movement of substances or heat from one point to another, driven by energy gradients between those two points
What directly impacts the rate of flow
Magnitude of energy gradient
What energy gradient causes the flow of molecules
concentration
What energy gradient causes the flow of heat
temperature
what energy gradient causes the flow of gases
partial pressure
What energy gradient causes the flow of fluids
oneiric pressure or hydrostatic pressure
What energy gradients cause the flow of ions
Concentration and voltage (electrochemical)
Def: Blood Pressure
a hydrostatic pressure, which reflects the force exerted by blood against a unit area of vessel wall
Def: Resistance
the impediment to flow due to friction, both external (against vessel wall) and internal (due to viscosity)
Def: Conductance
1/resistance
Methods of measuring blood flow
Invasive: ultrasonic doppler flowmeter
Methods for measuring blood pressure
invasive: intravascular pressure transducer
noninvasive: blood pressure sphygmomanometer
Cardiac Output animal differences
Total blood flow through the aorta
Humans: 5 L/min
Giraffe: 60 L/min
Mouse: 0.02 L/min
Def: Change in pressure
The difference in mean blood pressure between the aorta and the right atrium
- Little variation between species
Def: total peripheral resistance
The resistance of the entire systemic circulation
Sum of resistances in series
Sum individual resistances to get total resistance
- Total resistance is greater than any individual resistance
Sum of resistances in parallel
Total resistance is equal to 1 over the sum of 1/rs
- total is less than any single resistance
Def: Laminar Flow
Blood usually flows smoothly in ‘streamlines’ through vessels, with reactively little mixing in a radial direction
Def: Turbulent Flow
Blood flow can become disorderly, whirling in a radial direction to form what are called ‘eddy currents’
- Usually occurs in largest vessels at highest flow rates, around obstacles or during vasodilation
-Increases the resistance to blood flow due to internal resistance
Determinants of resistance in laminar flow
- Small changes in vessel diameter have large effect on blood flow
- in larger vessels, more streamlines of blood are far from the vessel wall where flow is much slower, blood flows at a higher velocity
-Viscosity and vessel length also affect resistance but don’t change over short periods of time - reduction in vessel diameter reduces blood flow at a given pressure gradient (arterioles)
Poiseuille’s Law
F=(pi change in pressure r^4)/8nL
R= 8nL/pir^4
Changes in blood viscosity
Changes in hematocrit can alter blood viscosity
-more red blood vessels increases friction between adjacent cells and vessel wall
Decrease: anemia - can occur during menstrual cycle and/or in response to blood loss
increase: polycythemia - occurs at high elevation, in response to sleep apnea, pulmonary disease etc.
Pulmonary Circulation
- Picks up O2 at lungs
- Low pressure system (20mmHg)
- RV to Lungs to LA
Systemic Circulation
- Delivers O2 to other organs and tissues
- High pressure system (100mmHg)
- LV to tissues to RA
Layers of the Pericardium
- Epicardium
- Pericardial space
- Parietal Pericardium
- Fibrous Pericardium
Layers of the heart walls
- Endocardium
- Myocardium
- Pericardium
Heart muscle histology
Cardiomyocytes
- Striated
- Interconnected at intercalated disks
Heart Fiber Structure
- Subendocardial fibers run oblique to subepicardial fibers
- aids in left ventricle ejection and relaxation
- Shortening of fibers during contraction cause wringing motion that pulls the base towards the apex and reduces lumen diameter
- At the end of systole, the left ventricle is similar to a loaded spring that recoils during diastole and rapidly expands lumen diameter
How do heart valves help direct blood flow?
Open and closed passively in response to pressure gradients
What is the relationship between flow and the volume of blood in the ventricle
Amount of time blood is flowing
What causes blood flowrate to change?
change in pressure gradient
Can anything cause blood flow to stop entirely?
Valves
Ventricular Filling
- Begins when A-V valve opens
- Ends when A-V valve closes
- P atrium >P ventricle
- At end of stage atrial systole occurs resulting in a boast in pressure and volume
Isovolumetric Contraction
- Begins when A-V valve closes
- Ends when P ventricle > P aorta causing aortic valve to open
- P atrium < P ventricle < P aorta
- Increase in pressure due to increase force with decrease ventricle space
Ejection
- Begins when aortic valve opens
- P ventricle greater than P aorta
- Aortic valve takes time to close once pressure gradient shifts due to stiffness
- Ends when aortic valve closes
Isovolumic Relaxation
- Begins when Aortic valve closes
- Ends when P ventricle < P atrium causing A-V valve to open
- P aorta > P ventricle > P atrium
Atrioventricular Valves
- Very thin
- open/close very easily in response to forward/backward pressure gradients
Semilunar Valves
- Stronger and heavier
- do not open and close as easily
Pressure-Volume Loops
- Useful way of showing the changes in pressure and volume during the cardiac cycle
- The area of the loop represents the net external work of one cardiac cycle
