Circulatory System 2 Flashcards
What is cardiac output
Volume of blood pumped per minute by each ventricle
What is heart rate
Number of heart beats (cardiac cycle) per minute
What is stroke volume
Volume of blood pumped per beat (per cardiac cycle) by each ventricle
How to calculate cardiac output CO
Heart rate x stroke volume
What is the average resting cardiac rate (heart rate)
70 beat/min
What is the average stroke volume
70-80 ml/beat
An average person with an average HR and SV would have an CO of ….?
HR = 70 beat/min
SV = 70 ml/beat
So… CO = HR x SV = 70 x 70 = 4900 ml/min or about 5 L/min
Unit of heart rate
Beat/min
Unit of stroke volume
ml/beat
Unit of cardiac output
ml/min
How many liters of blood does an average human have ?
5L of total body blood
For a person with 5L of blood and a CO of 5 L/min , this means that ….
The WHOLE total volume is circulated once around the body
What controls heart rate
Sympathetic and parasympathetic divisions of ANS
In the absence of any neural effects, does the heart stop beating?
No
The heart is still automatically controlled by the rate at which SA node fires action potential
How does sympatheitc activity increase heart rate ?
- increases the steepness of pacemaker potential
- threshold is reached sooner
- increases the rate of SA node firing
= increases heart rate
How does parasympathetic activity reduce heart rate
- Reduces the steepness of pacemaker potential
- Threshold is reached later
- Reduces rate of SA node firing
= decreases heart rate
What happens to cardiac output if heart rate increases ?
Increases
What controls stroke volume SV
- EDV (preload)
- Total peripheral resistance TPR (afterload)
- Contractility (inotropy)
What is EDV (preload)
Volume of blood in ventricles at the end of diastole
How does preload (EDV) affect SV
The more the ventricles are filled with blood during diastole, the greater EDV, and therefore the greater stroke volume

How does afterload (total peripheral resistance) affect stroke volume SV?
The greater the resistance to blood flow in the arteries, such as when there is vasoconstriction, the lower the stroke volume
What is total peripheral resistance TPR (afterload)
The resistance to blood flow offered by all the systemic vasculature, excluding the pulmonary vasculature
How does inotropy (contractility) affect stroke volume ?
The greater the inotropy, the greater the stroke volume
What is contractility (inotropy)
The intrinsic ability of the myocardium to contract independently of changes in preload or afterload
What is the relationship between SV and EDV (preload) and what is that relationship called
SV is directly proportional to EDV ; therefore if EDV increases, SV will increase too.
This is called Frank-Starling Law of the heart
What is Frank-Starling Law of the heart
Increased EDV stretches the myocardium, resulting in a more forceful contraction, therefore higher SV and CO
( high EDV = high SV = high CO)
The greater the volume of blood we start with (EDV), the greater the ejected volume
What law is this
Frank-starling law of the heart
How to calculate SV
SV= EDV - ESV
What is ejection fraction EF
The percentage of blood ejected by the ventricle each time it contracts
How to calculate ejection fraction EF
EF = SV/EDV x 100
Or
EF = (EDV-ESV)/EDV x 100
What happens to ejection fraction EF if EDV increases
Increases
High EDV = High SV = High EF = High CO
Normal EF is between ___% - ____%
50% to 70%
Calculate the EF of an individual if his ESV = 80 ml and EDV = 120 ml
EF = (EDV -ESV) / EDV x 100
EF = (120-80)/120 x 100
= 33%
EDV is controlled by factors that affect the ____________.
Venous return VR
What is venous return VR
The rate at which venous blood enters the right atrium
How does venous return affect EDV and SV and CO
The more venous blood returning to the heart, the higher the EDV and thus the higher the SV and CO
(High VR = High EDV = High SV = High EF = High CO)
What are some special mechanisms that INCREASE venous return VR
- Skeletal muscle pump
- Respiratory pump
- Venoconstriction
How does skeletal muscle pump increase venous return VR
NORMALLY, The low venous pressure is insufficient to push blood towards the heart, especially from the lower limbs
HOWEVER, Contraction of skeletal muscles of the lower limb such as during exercise, compresses the deep veins which facilitates venous blood flow to the heart. 
Venous blood flow from the lower limbs to large abdominal veins is facilitated by ________________. HOWEVER, movement of venous blood from abdominal to thoracic veins is aided by an additional mechanism which is _______________.
Skeletal muscle pump
Breathing
How does respiratory pump increase VR?
During inspiration,
Intra-thoracic pressure : reduced
Abdominal pressure: increased
- this pressure difference INCREASES the venous return by increasing the flow of venous blood from the abdominal viscera to the heart and lungs
How does venoconstriction increase venous return VR
Sympathetic activity increases VR by stimulating smooth muscle contraction in the venous walls:
- reducing their compliance and distensibility (⬇️C)
- increasing their pressure (⬆️P)
Venoconstriction increases VR by causing:
- lumen becomes more rounded (less surface area)
- decreases resistance
- increase venous return
Summary of factors that affect VR and EDV
TPR is mainly determine by the __________.
Arterioles
How does TPR reduce stroke volume ?
A greater TPR increases the afterload (arterial pressure) , thus reducing SV
(Unless there is compensation by increased inotropy)
True or false
The degree of constriction and relaxation of arterioles markedly affects TPR
True
Explain the effect or arteriolar vasoconstriction on blood pressure
- INCREASES the pressure upstream (arterial pressure)
- DECREASES the pressure downstream (capillary and venous pressure)
How does inotropy affect SV
The greater the inotropy, the greater the SV
Inotropy depends on ___________________.
Cytosolic calcium (Ca2+)
As the cytosolic calcium increases, what happens to inotropy
Increases
Agents that increase contractility are called ____________________. While agents that decrease contractility are called ________________.
Positive inotropes
Negative inotropes
What two things have a positive inotropic effect on the myocardium (increase contractility)
Stimulation of sympathetic nervous system
Circulating catecholamines
What two things have a negative inotropic effect MOSTLY ON THE ATRIA (decrease contractility)
Stimulation of parasympathetic nervous system
Acetylcholine
Quick summary revision
Notice that:
Heart rate
Preload
Afterload
Contractility
ALL affect cardiac output
Veins contain ____% to ____% of the blood volume in the body
60% to 70%
Which blood vessels are called capacitance vessels
Veins
Which blood vessels are called resistance vessels
Arteries
why are veins called capacitance vessels ?
- bigger lumen
- more distensible
Why are arteries called resistance vessels ?
- smaller lumen
- less distensible
Why are veins more distensible
Due to thinner, less muscular walls that contain less elastic tissue
Why are arteries less distensible
Due to thicker, highly muscular walls that contain more elastic tissue
Velocity of the blood flow is related to two things
-Total cross-sectional area of blood vessel (diameter)
- blood flow
How to calculate velocity of blood flow
V = F/A
F - blood flow
A - cross-sectional area
What’s the advantage of the low velocity of blood flow through the capillaries
To allow enough time for gas, nutrients, and waste exchange
Understand this fact:
👍🏻
Arterial blood pressure depends on:
- Stroke volume SV
- Heart Rate HR
- Total Peripheral Resistance TPR
How does stroke volume affect arterial blood pressure
The greater the stroke volume, the greater the blood pressure
How does heart rate affect arterial blood pressure
The greater the heart rate, the greater the blood pressure
How does total peripheral resistance affect arterial blood pressure
Vasoconstriction of the arteries increases peripheral resistance which increases the blood pressure
Physics law for flow
F = ΔP/R
ΔP - pressure difference
R - resistance
F - blood flow
What is the relationship between blood flow and pressure difference
Directly proportional
What is the relationship between blood flow and resistance
Inversely proportional
Physics law for resistance
Relationship between resistance and viscosity of blood
Directly proportional
Relationship between resistance and length of the vessel
Directly proportional
Relationship between resistance and radius of the vessel
Inversely proportional to the 4TH power of the radius of the vessel !
We can combine these 2 formulas to give us a single formula which is
Understand this
As you can see in (b) …
When we doubled the size of the radius (2x),
The resistance reduced (1/16 of original resistance)
= blood flow increasing 16x
When we halved the radius (1/2),
The resistance increased (16x the original resistance)
= blood flow is reduced (1/16 of original flow)
Understand this
- Mean pressure is highest in aorta and large arteries
- mean pressure decreases progressively as blood flows from the arteries to the artieroles to the capillaries to the veins and back to the heart
- LARGEST PRESSURE DROP OCCURS IN THE ARTERIOLES !!
Why does the largest pressure drop occur in the arterioles
Due to their high resistance to flow
A sudden change in blood pressure will be sensed by the ______________.
Baroreceptors
where are baroreceptors located
Arch of aorta AND the carotid sinuses
What happens if baroreceptors detect an increase in blood pressure
- The parasympathetic system will be activated
- The sympathetic activity will decline
to restore blood pressure to normal level
What happens if baroreceptors detect a decrease in blood pressure
- The sympathetic system will be activated
- The parasympathetic activity will decline
to restore blood pressure to normal level
How is blood pressure regulated by the baroreceptor reflex
By regulation of:
- HR
- SV
- TPR
Understand this (read picture)
Note:
This reflex is a SHORT-term mechanism for BP regulation
The opposite will take place if BP was high
How to calculate arterial blood pressure
Hint: we already know that the factors that affect arterial blood pressure are : SV, HR, and TPR
An increase in ______, ______, or _______ will increase MAP
SV
HR
TPR
(Unless there is a compensation via a decrease in another factor )
Blood pressure is usually measured by __________________.
Sphygmomanometer
Unit of blood pressure
mmHg
How is blood pressure represented
BP = systolic BP / diastolic BP
Normal blood pressure is around :
120/80 mmHg
Explain how sphygmomanometer works
- Cuff pressure is increased to a value higher than systolic pressure SP (ex: 140 mmHg) to constrict the brachial artery closed and stop blood flow (NO SOUNDS)
- Cuff pressure is then reduced slowly. The reading at the FIRST turbulent sound is the SYSTOLIC pressure
- Cuff pressure is reduced even lower (< DP) , until NO SOUND is heard, which is DIASTOLIC pressure . (Laminar blood flow)
When the cup pressure is between SP and DP, blood flow stops at each diastole and resumes with every systole. The turbulent blood flow through the partially constricted artery at each soul produces sounds called ___________________.
Korotkoff sounds
What is pulse pressure ? calculation
Is the difference between the systolic pressure SP and diastolic pressure DP
PP = SP - DP
SP = 120 mmHg
DP = 80m mmHg
What is pulse pressure ?
PP = SP - DP = 120 - 80 = 40 mmHg
We know MAP = CO x TPR
But how can you just approximate MAP?
By adding 1/3 of PP to the diastolic pressure
So…
MAP = DP + 1/3PP
DP = 80 mmHg
PP = 40 mmHg
Estimate MAP
MAP = 80 + (1/3 x 40) = 93 mmHg
What is hypertension
Consistently high blood pressure
What is secondary hypertension
Hypertension that is caused by failure of another organ
What is essential or primary hypertension
Hypertension which is not related to any other organ
Two types of hypertension
Primary hypertension and secondary hypertension
What is elevated hypertension ?
SP = 120-129
DP = less than 80
What is stage 1 hypertension ?
SP = 130 - 139
DP = 80 - 89
What is stage 2 hypertension ?
SP = 140 or higher
DP = 90 or higher
What is hypertensive crisis?
SP = higher than 180
DP = higher than 120
Which type of hypertension accounts for 95% of cases
Primary hypertension
Essential (primary) hypertension might be due to:
- increased renin secretion
- increased sympathetic activity
- increases salt intake
True or false
Essential hypertension is multifactorial and doesn’t have one distinct cause
True
True or false
Hypertension is a silent killer
True
Hypertension may lead to complications such as:
- vascular damage
- organ failure
- congestive heart failure
- stroke (cerebral blood vessel damage)
Hypertension treatment includes:
Lifestyle changes + medication
