Cardiovascular System Part 2 Flashcards
Cardiac output
Total blood flow, the volume of blood that circulates through the blood vessels each minute
Cardiac output equation
CO = heart rate x stroke volume
How the cardiac output becomes distributes into circulatory routes that serve various body tissues depends on two more factors:
1) The pressure difference that drives the blood flow through a tissue
2) the resistance to blood flow in specific blood vessels
Frank-Starling law of the heart
The law states that the stroke volume of the left ventricle will increase as the left ventricular volume increases due to myocyte stretch cause a more forceful systolic contraction
Preload
The amount of sarcomere stretch experienced by cardiac muscle cells, called cardiomyocytes, at the end of the ventricular filling during diastole
Contractility
The inherent strength and vigor of the heart, contraction during systole.
According to Starling’s law, the heart will eject a greater stroke volume at greater filling pressures.
Afterload
The pressure against which the heart must work to eject blood during systole (systolic pressure). The lower the afterload, the more blood the heart will eject with each contraction.
Stroke volume =
End diastolic volume - end systolic volume
Average stroke volume at rest:
70ml -> amount of blood being pumped out per cardiac cycle
Stroke volume is regulated by:
Preload, contractility, and afterload
Cardiac reserve
Is the heart’s ability to increase cardiac output to meet the metabolic requirements during exercise
The difference between resting level and max we can achieve
Contractility (Inotropy)
Contractility is important for the balance between the left and right sides of the heart
Positive inotropy agents:
Increase forcefulness of a contraction (Ca2+)
Negative inotropy agents:
Reduce forcefulness of contraction (K+)
In blood plasma, key components that drive contractility are:
Na+, Ca2+, and K+
Factors that affect inotropy (contractility) of the heart include:
Heart rate
afterload
sympathetic activation
parasympathetic activation
At very high rates, stroke volume is _______, this can result in a ________ of cardiac output.
Decreased
Decrease
Increasing heart rate ______ ventricular filling time.
The heart compensates by being more efficient at relaxation.
Stroke volume is ______
_______ cardiac output and efficiency of contraction.
reduces
decreased
decreases
Ejection fraction: pumping efficiency usually between __-__%
60-70%
Ejection fraction goes ___ with high BP/hypertension (140/90mmHG), extra _____, can lead to heart failure.
down
afterload
What does the heart’s conducting system consist of?
Cardiac muscle cells and conducting fibers that are specialized for initiating impulses and conducting them rapidly through the heart.
The sequence of contraction:
1) The SA node signals the atria to contract
2) The signal travels to the AV node, through the bundle of His, down the bundle branches, and through the Purkinje fibers
3) Causing the ventricles to contract
The AP will be fired when the _______ reaches about ___mV (the threshold)
depolarisation
-55
ECG: P-wave
depolarisation of atrial contractile fibers produces P-wave
ECG: QRS complex
the onset of ventricular depolarisation
depolarisation of ventricular contractile fibers produces QRS complex
ECG: T wave
ventricular repolarisation
repolarization of ventricular contractile fibers produces T wave
ECG
A summation of the action/electrical potentials
ECG: After P-wave
atrial systole (contraction)
ECG: S-T segment
Ventricular systole (contraction)
ECG: After T wave
Ventricular diastole (relaxation)
Parasympathetic system on the heart
- affects the heart via the vagus nerves
- if reduced increases heart rate
- relaxation, slows the heart
- can change heart rate very quickly
Sympathetic system on the heart
- increase in the rate of spontaneous SA node depolarisation
- affects the heart via cardiac accelerator nerves
- sympathetic nerves run down the spinal cord and to the heart
- increases heart rate
chronotropic:
the heart rate
contractility/inotropy:
The force of energy of heart muscular contraction
Vagus nerve
Innervates the SA node to slow the rate of spontaneous depolarization, decreasing heart rate. It does not have any fibers that innervate and relax cardiac myocytes
Sympathetic nerves
Innervate both the SA node (accelerating spontaneous depolarization and therefore heart rate) and the cardiac myocytes (increasing contractility and stroke volume)
Time length of cardiac AP
300ms
Time for nerve AP
1-2ms
Phases of cardiac action potential
1) Rapid depolarization
2) Early repolarization
3) Plateau
4) Repolarization
5) Restoration of the resting membrane potential
Rapid depolarization:
Na+ channels open in the cell membranes -> rapid influx of Na+ ions into the cell
The membrane potential changes from -90mV - 30mV within 1-2ms
Early repolarization:
Na+ channels closed -> membraine potential stops esculating -> some K+ channels are activates -> produces small outward possitive current
Plateau:
- Inward and outward currents are equal
- producing constant MP at 0mV
- Inward current due to influx of Ca2+
- Balances by the outward current due to small efflux of K+
- This phase lasts 200ms
Repolarization:
- K+ flows down a concentration gradient and out of cell -> decreasing the MP towards a resting value of -90mV
- Slower than depolarisation
Restoration of resting membrane potential:
- Inward and outward currents are balanced
- MP sits at -90mV till the next wave of depolarisation
- Na+/K+ATPase is important in resetting concentration gradients across the cell.
Nervous system regulation of heart rate originates in the cardiovascular center of the _____ ______
medulla oblongata
____ input is a major stimulus that accounts for the rapid rise in heart rate at the onset of physical activity
Proprioceptor
Hormones from the _____ ______ and the _____ gland can increase heart rate
adrenal medulla
thyroid gland
Blood pressure
the pressure of circulating blood against vessel walls
Blood colloid osmotic pressure
a form of osmotic pressure induced by the proteins in the blood which draws fluid into the bloodstream
Total peripheral resistance
the amount of force affecting resistance to blood flow throughout the circulatory system
Capillary exchange
exchange of material between blood and capillary tissue
Blood hydrostatic pressure
the pressure that water in blood plasma exerts on the vessel walls. Drives filtration into the interstitial fluid
Interstitial fluid osmotic pressure
A form of pressure which is produced in the interstitial spaces and draws fluid out of the bloodstream
Interstitial fluid hydrostatic pressure
the oppositional force which “pushes” fluid from the interstitial spaces back in the capillaries
Hypertension:
High blood pressure
Bradycardia:
Slow heart rate
Tachycardia:
fast heart rate
Baroreceptors:
Sensors detect blood pressue
Poiseuille’s law:
flow is related to factors such as viscosity and the radius of a vessel
Angiotensin II:
A peptide that produces vasoconstriction
Hemorrhage:
loss of blood from a broken blood vessel
Starling’s law:
the force of contraction is related to how much stretch occurs
If a patient suddenly loses 15% of his blood volume and there was no adequate compensation, the end-diastolic volume would _____ and preload would _____. As a result, stroke volume would also _____
decrease
decrease
decrease
Name the law that described the relationship between end-diastolic volume and stroke volume:
Frank-Starling’s law
Decrease in blood volume leads to _____ in blood pressure
decrease
Pressure is sensed by the baroreceptors in the:
carotid sinus and aortic arch
In response to a decrease in arterial pressure, sympathetic nerve activity to the heart would increase (resulting in an increase in heart rate) and parasympathetic nerve activity to the heart would ___.
The sympathetic nerve would also _____ contractility of the cardiac myocytes.
decrease
increase
What does increased sympathetic activity due to peripheral resistance?
The resulting increase in the frequency of sympathetic nerve activity causes _______ (of smooth muscle fibers) in systemic blood vessels. This reduces the ____ of the lumen of the vessel, _______ resistance to blood flow, _____ total peripheral resistance
increases it
vasoconstriction
radius
increasing
increasing
Is there direct vagal (parasympathetic) innervation of the blood vessels?
No, the reduction in parasympathetic activity would increase the heart rate.
There is no direct parasympathetic nervous input to the blood vessels, total peripheral resistance is controlled by sympathetic nerve activity, as well as hormones and local metabolites.
If cardiac output falls by 20% but means arterial pressure remains constant, what must have happened?
TPR compensated:
- mean arterial pressure is a product of cardiac output and TPR, MAP = CO x TPR
- if MAP is constant, but CO is reduced by 20%, then TPR must have increased to compensate
- this is achieved by sympathetic stimulation of the smooth muscles of smaller arteries and arterioles, reducing their diameter and therefore, increasing their resistance.
A patient presents to the hospital with a heart rate of 37 beats per minute and a BP of 100/50mmHG. What is their condition?
Bradycardiac, hypotensive
- typically bradycardia is defined as HR < 50bpm and typically hypotension is defined as BP less than ideal pressure of 100/80mmHg
- these values can be normal for a young fit person
Fluid exits the capillaries because capillary hydrostatic pressure is _____ than blood colloidal osmotic pressure
greater
- remember that hydrostatic pressures force fluid out, which osmotic pressure pills back in
On what side of the capillary does reabsorption occur?
Venous
- Fluid re-enters capillary because the capillary hydrostatic pressure is less than the blood colloidal osmotic pressure
You stand up suddenly and feel faint for a few seconds. What would occur to restore homeostasis?
Decreased blood pressure -> decreased firing of baroreceptors -> increased cardiac output and vasoconstriction -> homeostasis restored
Arterioles are the major resistance vessels due to a big ____ in pressure
decrease
The opposition to blood flow due to friction between blood and the walls of blood vessels
vascular resistance
Vascular resistance is determined by three factors:
- Size (diameter) of lumen
- Blood viscosity
- Total blood vessel length
Stenosis
The abnormal narrowing of a passage in the body
Input to cardiovascular center from sensory receptors comes from:
- propioreceptors
- chemoreceptors
- barorecptors
Which sensory receptors monitor blood chemistry (blood acidity H+, CO2, and O2)
Chemoreceptors
____ arterial blood pressure during diastole leads to ___ afterload which leads to semilunar valves opening sooner when the blood pressure in the aorta and pulmonary artery is lower which leads to ____ stroke volume and therefore, ___ cardiac output.
decreased
decreased
increased
increased
Chemicals such as ___ or ____ hormones in the blood lead to a moderate increase in extracellular ___ which leads to increased ___ ___ and therefore, increased cardiac output
catecholamine
thyroid
Ca2+
heart rate
____ sympathetic stimulation and ____ parasympathetic stimulation leads to increased ___ ___
Increased
decreased
heart rate
In an ECG, a larger P wave could signal ___ ___
Atrial hypertophy
In an ECG, a very large R could signal ____ ___
ventricular hypertrophy
Cardiac accelerator nerves (sympathetic nervous system) affect which two things
Heart rate and stroke volume
The vagus nerve (parasympathetic NS) only affects ____ ____
heart rate
What is it called when vasomotor nerves (sympathetic) cause blood vessels to constrict?
vasoconstriction
The sympathetic nervous system ____ contractility, thus cause an ______ in stroke volume
increase
increase
The term that describes a change in HR
Chronotrophy
The term that describes a change in contractility
Inotropy
Blood distribution in the cardiovascular system:
- Pulmonary vessels _%
- Heart _%
- Systemic arteries and arterioles _%
- Systemic capillaries _%
- Systemic veins and venules (blood reservoirs) _%
- Pulmonary vessels 9%
- Heart 7%
- Systemic arteries and arterioles 13%
- Systemic capillaries 7%
- Systemic veins and venules (blood reservoirs) 64%
Mean arterial pressure
The average blood pressure in the arteries, roughly 1/3 between the systolic and diastolic blood pressures
diastolic BP + 1/3(systolic BP - diastolic BP)
Systolic blood pressure
the highest pressure attained in arteries during systole
Diastolic blood pressure
The lowest arterial pressure during diastole
Blood hydrostatic pressure at the arterial end is:
35 mmHg
Blood hydrostatic pressure at the venous end is:
16 mmHg
Blood colloid osmotic pressure at the arterial end is:
26 mmHg
Blood colloid osmotic pressure at the venous end is:
26 mmHg
Net filtration at the arterial end of capillaries is ___ per day
20 litres
Net reabsorption at the venous end of capillaries is ___ per day
17 liters
What are the pressures promoting filtration?
BHP
IFOP
What are the pressures promoting reabsorption
BCOP
IFHP
