BIO 436 Lecture 8 & Lab 9
Flow of blood through the heart
- all blood returning to right atrium comes from superior/inferior vena cava - goes into right atrium - goes down to right ventricle - goes out to pulmonary arteries to lungs - picked up oxygen through pulmonary veins - bring blood back to left atrium - goes down to left ventricle pumped out through aorta to the entire body
What is cardiac output?
- amount of blood pumped out by each ventricle in 1 minute - directly related to HR and SV
What is the length-tension relationship of cardiac muscle?
- at rest, cardiac muscles are at a less than optimum overlap length for maximum tension production in healthy heart - when heart experiences an increase in stretch with an increase in venous return and EDV, it can respond by increasing force of contraction, yielding a corresponding increase in stroke volume
What is afterload?
- back pressure generated by blood in aorta and pulmonary trunk - threshold that must be overcome for aortic and pulmonary semilunar valves to open
Frank-Starling Law of the Heart
- before myocardial sarcomeres fill, actins overlap, actin-myosin interactions are reduced & contraction would be weak - as tension increases, there is increasing interaction of actin and myosin allowing more force to be developed
What are physical laws describing blood flow?
- blood flows through vascular system when there's pressure difference at its two ends - flow rate is directly proportional to difference - flow rate is inversely proportional to resistance - resistance is directly proportional to length of vessel and viscosity of blood - inversely proportional to 4th power of radius, diameter of vessel very important for resistance
What is venous return dependent on?
- blood volume and venous pressure - vasoconstriction of VEINS caused by Symp - skeletal muscle pumps - pressure drop during inhalation
What about small arteries and arterioles?
- both muscular - provide most resistance in circulatory system - arterioles cause greatest pressure drop
What is vasodilation caused by?
- decreased myogenic activity and O2 - increased CO2 & other metabolites - decreased symp. stimulation, histamine release, heat
What is vascular resistance to blood flow?
- determines how much blood flows through tissue or organ - vasodilation decreases resistance, increases blood flow - vasoconstriction does opposite
How does elasticity of blood vessels affect diameter?
- elasticity of large arteries serve as a "shock absorber" to reduce sudden sharp increase in systolic pressure - elastic recoil of vessel then serves to maintain continued flow during diastole - within arteriosclerosis, arteries can't expand and create more resistance and higher pressures
What are viscosity changes in blood?
- hct affects blood viscosity and resistance to flow - more viscous the blood (during dehydration), greater resistance it encounters and higher BP - viscosity is much lower in capillaries than rest of system
What is the cardiovascular system?
- heart - blood vessels that distribute blood containing oxygen and nutrients to every cell of the body
What is vasoconstriction caused by?
- increased myogenic activity - increased O2 - decreased CO2 - increased sympathetic stimulation, vasopressin, angiotensin II, cold
One-way valves
- one way into the right side, one way out - one way into the left side, one way out - work on a pressure gradient
Pulmonary arteries and veins
- pulmonary arteries have deoxygenated blood - pulmonary veins have oxygenated blood - artery: any vessel that is bringing blood away from the heart - vein: any vessel that is bringing back to the heart
What is venous return?
- return of blood to heart via veins - controls end-diastolic volume and thus systolic volume and cardiac output
Heart valves
- seal off blood into two ventricles - as we start contracting ventricle cells, their force is going to be transferred to the blood - transferred as force that we measure is pressure - if these vessels weren't able to seal off, we couldn't transfer force from cardiac myocytes to the blood - right AV valve (tricuspid) in between right atrium and right ventricle - left AV valve (bicuspid) in between left atrium and left ventricle - (right) pulmonary semilunar valve going out to pulmonary trunk and lungs - (left) aortic semilunar valve going up to the aorta through the body
What increases contractility?
- sympathetic activity - epi and norepi inactivates NCX proteins, pump Ca2+ into SR, next time cell is triggered, Ca2+ is going to flood out very quickly, cross-bridging is faster and contraction is stronger - after epi and norepi are gone, alleviates inhibition of NCX proteins and go back to normal, distribute Ca2+ back outside the cell and return to normal levels of Ca2+ in Sr
What are veins?
- veins hold most of blood in body (70%) and are thus called capacitance vessels - have thin walls and stretch easily to accommodate more blood w/o increased pressure (=higher compliance) - have only 0-10 mm Hg pressure - blood is moved toward heart by contraction of surrounding skeletal muscles (skeletal muscle pump) - and pressure drops in chest during breathing - one-way venous valves ensure blood moves only toward heart
What are 3 main sources of peripheral resistance?
- vessel diameter: smaller diameter > more fluid in contact with wall > greater resistance > greater pressure - blood viscosity - total vessel length
When do blood cells and plasma encounter resistance?
- when they contact blood vessel walls - if resistance increases, more pressure is needed to keep blood moving
What are the 3 main factors that affect resistance?
1. blood vessel radius 2. blood vessel length 3. blood viscosity
What are the 3 variables that determine stroke volume?
1. end diastolic volume: volume of blood in ventricles at end of diastole 2. total peripheral resistance: impedance to blood flow in arteries 3. contractility: strength of ventricular contraction
"Lub" "Dub" cycle
1. late diastole: both sets of chambers relaxed. pressure ventricular filling. 2. atrial systole: atrial contraction forces a small amount of additional blood into ventricles. 3. EDV = end diastolic volume. maximum amount of blood in ventricles occurs at end of ventricular relaxation (EDV = 135 mL) "LUB" 4. isovolumic ventricular contraction: first phase of ventricular contraction pushes AV valves closed but doesn't create enough pressure to open semilunar valves 5. ventricular ejection: as ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood is ejected 6. ESV = end systolic volume. or minimum amount of blood in ventricles (ESV = 65 mL) 7. isovolumic ventricular relaxation: as ventricles relax pressure in ventricles drops, blood flows back into cups of semilunar valves and snaps them closed "DUB"
What factors affect stroke volume?
1. preload 2. contractility 3. afterload
How many chambers does the human heart have?
4
_% of the blood contained within the heart is ejected from the heart during ventricular systole, leaving _% of the blood behind.
60%, 40%
What is the normal heart rate?
75 bpm, pumps 70 mL/beat
Calculate mean arterial pressure (MAP).
MAP = Diastolic pressure + 1/3 Pulse Pressure (PP) PP = systolic pressure - diastolic pressure ex. BP = 120/80 PP = 120-80 = 40 MAP = 80 + 1/3(40) = 93.33 mmHg
What is the stroke volume formula?
Stroke volume = end diastolic volume - end systolic volume
What is blood flow?
amount of blood moving through a body area or the entire cardiovascular system in a given amount of time
What is stroke volume?
amount of blood pumped by each ventricle with each heartbeat, averaging 70 mL per beat in adult at rest
How do blood vessel lengths increase?
as we grow to maturity
What is viscosity?
blood "thickness", determined by hematocrit (fractional contribution of RBCs to total blood volume)
What is aortic valve stenosis?
condition where there is a partial blockage of aortic semilunar valve, increasing resistance to blood flow and left ventricular afterload
What is vasoconstriction?
contraction of smooth muscle of blood vessel that results in decrease in blood vessel radius
How do you control blood flow?
controlling blood vessel radius, which is accomplished by contracting or relaxing smooth muscle within blood vessel walls
What is preload?
degree to which ventricles are stretched by the end diastolic volume
What is the pressure gradient?
difference between pressure in arteries and pressure in veins that results when blood is pumped into arteries
Blood flow is _ proportional to the pressure gradient.
directly
What increases venous return and EDV?
exercise
The higher the hematocrit, the _ the viscosity.
greater
The longer the vessel length, the _ the resistance.
greater, because of friction btwn blood and vessel walls
The smaller the blood vessel radius, the _ the resistance.
greater, because of frictional drag between blood and vessel walls
What is cardiac output formula and units?
heart rate x stroke volume CO = HR x SV units: millimeters/min, liters/min avg CO = 5.2 liters/min avg blood volume = 5 liters
Blood flow is _ proportional to resistance.
inversely
When pressure is greater in front of the valve,
it closes (does not open in opposite direction)
When pressure is greater behind the valve,
it opens
Valves during heart relaxation
left side of heart when heart is relaxed, semilunar valve is closed blood filling in from elft atrium to left ventricle valve is open
How does total vessel length affect resistance?
longer total vessel length, greater resistance, greater BP
What is resistance?
measure of degree to which blood vessel hinders, or resists, flow of blood
The more viscous a fluid, the _ resistance to flow.
more aka flow rate is slower for more viscous solution
What is the septum?
muscle that separates the two sides of the heart
What is heart rate?
number of times the heart beats in one minute, averaging 70-75 bpm in adult at rest
Heart and lungs are:
on the same gravitational plane
What causes an increased resistance?
plaques in arteries, known as atherosclerosis results in decreased flow rate
What is the viscosity of the blood due to?
presence of plasma proteins and formed elements (WBCs, RBCs, platelets)
Total blood flow is _ to cardiac output.
proportional
What do the 2 ventricles do?
pump blood from arteries right side to lungs (pulmonary system) left side to body (systemic system)
What do the 2 atria do?
receive blood from venous system
What is vasodilation?
relaxation of smooth muscle of blood vessel that causes an increase in blood vessel radius
Valves during heart contraction
right side of the heart - when heart starts to contract, as we build pressure, this actual pressure is gonna close up these valves - these valves balloon up but don't allow blood in to the atria - they don't invert because they are held in place by chordae tendinae and papillary muscles
What decreases venous return and EDV?
severe blood loss and dehydration
What is the contractility of the heart?
strength of cardiac muscle contraction and its ability to generate force
What is the Frank-Starling law of the heart?
when more than the normal volume of blood is returned to the heart by the venous system, the heart muscle will be stretched, resulting in a more forceful contraction of the ventricles
What is pulmonary systolic blood pressure?
~12-14 mm Hg right side of the heart only pumps blood to lungs and back so it doesn't need as much pressure
What is systemic (body) systolic blood pressure?
~120 mm Hg left side is generating 180-200 millimeters of pressure
What is Poiseuille's Law?
π ΔP r4 / 8 L η average value for ΔP is 100mmHg describes relationship btwn blood pressure, vessel radius, vessel length, and blood viscosity on laminar blood flow