Lecture 8: Heart as a Pump; Blood Vessels and Blood Pressure Flashcards
Recap: What are the events during a cardiac cycle?
- Refilling
- Atrial contraction
- Isovolumic contraction
- Ventricular contraction
- Isovolumtric relaxation
What is cardiac output?
Cardio output = Heart Rate (how many contractions per min) x Stroke Volume (Volume of blood pushed at every contraction)
What factors affect the heart rate (Briefly in terms of the flow diagram)?
-Parasympathetic nerves (decrease heart rate)
-Sympathetic nerves (increase heart rate)
-Contraction strength
What factors impact stroke volume (in terms of the flow diagram)?
-Mean arterial pressure
-End-diastolic volume (EDV)
-Frank-starling
-Stretch
-Contraction strength
How is the heart rate regulated?
-pace follows the SA node intrinsic rhythm
-Main control = sympathetic/adrenal medulla and parasympathetic by modulating the length of potential drift in autorythmic cells
Sympathetic and
Adrenal medulla and
Parasympathetic all affect the heart rate
What is the equation for the volume of blood ejected per contraction?
=End-Diastolic Volume (EDV) - End-systolic Volume (ESV)
What are the primary determinants for the regulation of stroke volume?
EDV= Preload= Volume of blood packed into the ventricles at the end of diastole
-Linked to the work imposed on ventricles prior to contraction
ESV=Afterload= Residual volume of blood contained in ventricle after systole
-Depends on the impedance to ejection of blood from ventricles
How do you increase the EDV?
Increase EDV= increase in stroke volume
-alters cardiac performance via the Frank Starling Law of the Heart
-As preload is increased, the contractility of the heart is increased–>increased stroke volume
-Increase stretch of cardiac muscle fibers at the end of diastole induces increase in contractility by enhancing binding of Ca2+ to troponin-C
-Under resting cond. EDV stretches cardiac muscle to sub-optimal levels
What factors affect preload (EDV)?
Main factor is the VENOUS RETURN
-Increased venous return= increased EDV
-Decreased venous return= decreased EDV (blood will sit in the venous system)
What is the venous return dependant on?
Dependant on the pressure difference between the large veins and the right atrium.
- Skeletal muscle pump; muscle contraction squeezes veins = push blood towards heart (valves in veins prevent back flow)
- Respiratory activity (respiratory pump); inspiration (contraction of the diaphragm) increases abdominal pressure=transfer to abdominal veins
-Creates low pressure in the thoracic cavity, where the vena cava is - Blood volume; Increased blood volume= elevated venous return
- Autonomic nervous system; Veins contain smooth muscles innervated by sympathetic fibers
-Increase in AP’s in nerve fibers=contraction
-Increase pressure in vein
-Increase venous return
What are factors affecting after load (ESV)?
-Resistance the ventricles encounter during ejection
-During exercise, indirectly controlled by the heart contractility (higher contractility = lower ESV)
-During rest, main determinant is arterial vasomotor tome (atria vascular resistance) = Total Peripheral Resistance (TPR)
-Measure blood prose as surrogate indicator of after load (high ESV low cardiac output)
-Blood pressure =cardiac output x arterial resistance
What are the important factors for blood vessels?
-Diameter (bigger in aorta and decrease to capillary then increase to vena cava)
-Elasticity (same as diameter trend)
-Contractility
What is the equation for flow?
Flow=volume fluid transported per time unit
-Flow b/w 2 pts is dependant on pressure difference
-Flow b/w 2 pts is dependant on the resistance to fluid
Flow(Q)= Pressure diff (delta P) / Resistance (R)
-Pressure higher in arteries then veins
-Arterioles are the “bottleneck” of the circulation
What blood vessel has the most smooth muscle and how does impact flow?
Arterioles have the most smooth muscles and therefore are the main site of pressure/flow regulation
TRUE OR FALSE: its the pressure that is important when considering flow.
FALSE: its the delta P that is important which is the difference in pressure
What does resistance depend on?
-Length of vessel (constant in individual can’t change)
-Radius of vessel = most important factor; resistance decreases by the 4th power of the radius ex if radius increases 2 times, resistance decreases 16 times
-Viscosity of blood; varies with cells and proteins amount, not main control role
What is the arterial pressure during a cardiac cycle?
Aortic valve opens during ventricular contraction
-Rapid flow of blood
-Increased arterial pressure
-Aorta elasticity absorbs some of the pressure (temporarily stores energy like a rubber elastic)
Aortic valves close during diastole
-No blood flowing from the ventricle
-Energy stored during the stretching of the aorta released
-Allows blood flow to continue in vessels-gradual decreased in article pressure
TRUE OR FALSE: arteries are compliant?
TRUE
-Elastic, large diameters = low pressure = high flow
-Recoil of wall limits the drop in pressure after systole (bc absorbs some p)
-Difference in arterial blood pressure can be observed b/w systole and diastole this is called PULSE PRESSURE (measure of pressure on artery wall during systole)
What are factors that influence arterial pressure?
-Elasticity of the artery (low elasticity = high pressure ie aging)
-Cardiac output; more blood from systole=increase pressure
-Respiration; low pressure in thoracic cavity where heart and major vessels are, high pressure in abdominal cavity which promotes Venus return
-Resistance to blood flow (MAIN FACTOR): total peripheral resistance (TPR) depends on vascoconstriction of arterioles. TPR increase = pressure increase
-Blood volume:Influences the cardiac output not huge affect only when under abnormal circumstance
What is the basal level of constriction?
= Myogenic tone (basal tone) makes it possible to decrease and increase vessels contraction thus diameter
Decrease diameter= increase resistance
What are the 2 levels of control of arteriolar resistance?
-Autoregulation (local mechanisms)
-Extrinsic control factor (neuro-hormonal)
Explain autoregulation (local) in detail.
-Within organ or tissue; overrides extrinsic regulation
-Controls flow to critical organs (heart coronary arteries, brain, liver, kidneys, working skeletal muscle)=protective mechanism
Metabolic regulation: Not impacting overall BP
-Response to changes in metabolisms thus blood requirement
-Results in increase in diameter (>CO2,<pH, >K+, >NO)
-Relative importance of factors depend on the organ
Myogenic (pressure) auto regulation:
-Vessels respond to changes in tone or stretch
-Maintain the blood supply virtually unchanged even when pressure changes
Explain the extrinsic regulation in detail.
-Regulates the peripheral pressure as a whole
-Vascoconstriction influences
*Sympathetic stimulation on alpha adrenergic receptors-trigger vascocontriction
*Angiotensin 2
*Arginin vasopressin
-Few vasodilatory influences
*Parasympathetic stimulation (vagus nerve, mainly in penis and clitoris
Explain how veins and venous pressure affect the body.
-Blood entering the venous system has low pressure as it travels towards the right atrium the delta p is sufficient
-Like said before- during inspiration P in thoracic cavity is lower then P in the abdominal cavity
-Veins have little resistance
-Heart acts as a pump after ejection almost acts as a suction bc low pressure after contraction sucks blood upward
-Skeltal muscle activity can help squeeze blood upward
-Veins possess smooth muscle, when pressure in veins too high=flow is reduced and fluid leaks out and accumulates in tissue (edema)
How does controlling blood pressure work?
main variables
-Heat rate (pressure at aorta)
-Stoke volume (pressure at aorta)
-TPR (Total peripheral resistance)
What are the 5 blood pressure reflex?
-Barareceptors: stretch receptors-Sense stretching of arterial wall
*Free of nerve endings
*Located in sensitive areas (aortic arch and carotid sinus)
-Sensory fibers
*Ascend via vagus nerve
*Stretch increases=increase in AP’s frequency
*Stretch decreases=decrease in AP’s frequency
-Integration center: Cardiovasular (vascomotor) Peter in the medulla oblongata/Brian stem
*compares info to reference value
-Motor fibers: Autonomic nervous system (both branches)
-Effectors
*Heart: rate and stoke volume = cardiac output
*Arterioles and vein=TPR
What are other mechanisms of BP control?
-Arterial volume receptor reflex
*strech receptors in wall of atria
*regulates blood volume via ANS and neural input that controls theirs and the section of hormones that alter renal handling of sodium and water
