Q2-CB12/Cardiac Output 2 Flashcards
the amt of blood returning to the heart must equal the amt of blood __________
ejected
venous return = cardiac output (VR = CO)
Explain the Frank Starling law:
they found out that as the heart fills up with more blood during diastole, it contracts harder and pumps out more blood during systole.
___________________
When the ventricles are empty, there is nothing stretching the muscles of the ventricle walls, so the length of sacromeres would be rly short. The Z disks are super close and there isnt enough room for contraction. Also the actin filaments cross the M line and overlap.
The increased overlap between actin filaments and myosin filaments allows for more cross bridges to form. Ventricular force has a direct correlation to the amt of overlap and crossbridges formed.
If the muscle is stretched too much the number of cross bridges falls.
What is cardiac preload?
It describes end diastolic volume/pressure in the left ventricle
ventricular wall stress at the end of diastole
What things affect venticular filling?
presure in the atria, venous pressure, gravity, and volume of blood in circulation
How do veins act as storage for blood?
veins contain 60-70% of total blood volume at any given time
What does an increased blood volume result in with regards to preload?
increased central venous pressure -> increased preload
(low blood volume decreases preload)
Is venous return easier or harder when you are standing up?
harder
What happens to venous return when you are lying in the supine position?
venous return increases
Explain the muscle pump.
the muscle pump promotes venous return to the heart.
Veins have valves which prevent backflow and only permit blood to move towards the heart
When we walk, the muscles in our leg contract. this contraction presses on the veins and pumps the blood upwards towards the heart. when the muscle relaxes, the venous valves prevent the blood from flowing backward.
explain the thoracic pump.
when we inhale, the diaphragm lowers and flattens. this causes abominal pressure to increase and thoracic pressure to decrease. Blood moves from the abdomen to thorax or says below the abdomen in the legs.
when we exhale, the diaphragm balloons up. this causes abdominal pressure to decrease and thoracic pressure to increase. blood moves from the legs to abdomen.
the starling law of the heart inc. stroke volume by changing the _____________
orientation of the fibers
the inotopes increase contractility by changing __________
calcium signalling
an inotrope will inc. the _____ of contraction for any given preload
force
What is cardiac afterload?
the amount of resistance the heart must overcome to open the aortic valve and push the blood volume out into the systemic circulation.
when stroke volume drops, what happens to the end of systolic volume?
systolic volume rises when stroke volume drops
what happens to contraction and stretch on ventricles when end diastollic pressure increases?
the stretch on the ventricles increases which leads to a more forceful contraction
what are the respective body water compartments and their percentages?
1/9 = vascular extracellular
2/9= interstitial extracellular
6/9 = intracellular
What are the 3 physiological controls of blood volume?
renin angiotensin system, anti diuretic hormone, and atrial natriuretic peptide
Explain the renin-angiotensin system.
the liver secretes angiotensinogen into the bloodstream.
renin is then secreted (by SNS) and cleaves angiotensinogen to form inactive angiotensin I.
an enzyme called ACE converts inactive angiotensin I to active angiotensin II.
the angiotensin II can then stimulate aldosterone, which increases salt and water retention. its net effect is the expansion of blood volume and increase blood pressure, and it does this by vasocontriction.
Explain how anti-diuretic hormone controls blood volume.
it is released when osmolarity is high and/or blood volume is low. decreases diuresis by driving water reabsorption away from the kidneys
Explain how atrial natriuretic peptide controls blood volume.
it does the opposite of RAS and ADH, promotes salt and water loss (inhibit salt reabsorption)
What is heart failure?
it is the inability to maintain cardiac output (low cardiac output for whatever reason)
any decrease in cardiac output results in ________ blood pressure
decreased blood pressure
What happens when blood pressure decreases due to decreased cardiac output regarding the sympathetic nervous system?
activation of sympathetic NS via baroreceptor reflex AND sympathetic NS induced increase in RAS
Stroke volume can be maintained by what?
by volume expansion
what is decompensated heart failure?
there will come a point where no further volume expansion can maintain stroke volume
Explain what happens in the heart when there is an excess of blood volume.
The heart has stretch receptors in the atria. When there is an increase in blood volume, the atria stretches and these receptors are activated, sending sensory afferents to the medulla. These sensory afferent signals inhibit the cardiovascular center.
The decrease in the Sympathetic NS means less RAS and ADH. This means that kidney filtration will increase and blood volume expansion is limited.
The stretch also trigger the release of ANP and BNP which are markers of volume expansion and help with fluid loss.
