Section 3: Cardiovascular System Flashcards
Human heart contains __ muscular pumps
2 muscular pumps, which each have a daily output of 7,000L of blood
Consequence of stoppage of heart’s muscular pumps
Unconsciousness in 10 seconds
Death in 4 minutes
Arteries vs veins
Arteries bring blood away from heart
Veins bring blood towards heart
Heart - circuits
Pulmonary circuit:
Only pumps to lungs
Medium resistance
Medium pressure
Systemic circuit:
Lots of systems involved
High resistance
High pressure
(Hepatic) portal veins
Veins don’t go straight back to heart
e.g. heptic portal vein - goes from gut to liver
Blood volume
9% pulmonary
7% pumps
84% systemic
Total 5L
Blood volume output
5L per minute for 1 pump
Can increase by 4 times if exercising, but trainable to up to 8x
Building a ventricular pump - phases
Filling phase:
Venous inlet on left side and arterial outlet on right
While ventricle is filling from venous end, an outlet valve is essential to prevent arterial blood from returning to the pump
Ejection phase:
Inlet valve necessary to prevent high-pressure blood in pumping chamber from returning to veins
Improvement #1:
An atrium is a reservoir upstream of the pump
During ejection phase, the atrium accumulates venous blood, which can enter the ventricle quickly during the filling phase
Improvement #2:
If inlet and outlet of pump are moved to lie close tgt, the walls of the pumping chamber can shorten in length and width
Adding an appendage = auricle also increases the capacity of the atrium
Auricle
An extension of the side of the atrium
Blood flow through heart - arrangements
Deoxygenated blood has a vertical arrangement
Oxygenated blood has a horizontal arrangement
Peak pressures (mmHg) - averages
Right atrium: 5 mmHg
Right ventricle: 27 mmHg
Left atrium: 8 mmHg
Left ventricle: 120 mmHg
Left higher as it must go through high resistance
Ventricular ejection - valves
Not actively opening valves - we’re actively preventing them from pushing too far
Ventricular inlet valves
AKA atrioventricular valves
Constructed from 2 or 3 flat flaps of fibrous CT
Free edge of each flap is tethered by tendinous cords - prevent it from bursting upwards into atrium during systole
Inlet valves
Tricuspid valve (right) Bicuspid/Mitral valve (left)
Left ventricle
Forms core of heart
Hollow cone with thick, muscular walls
Right ventricle
Sits on the side of left ventricle, much smaller
Open ends of ventricles are subdivided into…
An inlet and an outlet
Inlets and outlets - diameter
Inlets: large diameter to admit blood at low pressure
Outlets: small diameter because blood leaves ventricles at high pressure
Outlet valves
Pulmonary valve (right) Aortic valve (left)
Valves are essential for…
The operation of the pumps
Pathway taken by blood through ventricles
Approximately V-shaped
Ventricles in transverse section - peak pressure and wall thickness ratio
Peak pressure ratio (L:R) = 5:1
Wall thickness ratio (L:R) = 3:1 - main structural difference
Opening the pulmonary trunk
Shows three cusps of pulmonary valve
Shape = ‘semi-lunar’ - sometimes used to describe outlet valves
Outlet valves - number of cusps
Both outlet valves have three cusps, but unlike inlet valves, the cusps are each shaped like a pocket and lack cords
When inflated with blood, they gain strength from their 3D shape
Outlet valves - closed position
Ventricular filling
Pressure of blood trying to re-enter the ventricle forces the free edges of the cusps tightly together
Pressure in ventricle decreases
Pockets/cusps inflated
Where does the heart lie in our body
1/3 of mass of heart lies to right of mid-line of body and about 2/3 to the left
Apex of heart
Points inferiorly, anteriorly and to the left
So, heart is slightly rotated
Right border of heart
Formed mainly by right atrium
Inferior border of heart
Formed mainly by right ventricle
Left border of heart
Formed mainly by left ventricle (and in part, the left atrium/auricle)
Superior border of heart
Blood vessels = base
The heart is enclosed in a…
Double-walled bag
Pericardium - inner and outer walls is made of what?
Both inner and outer pericardium are made of a single layer of squamous mesothelial cells
Walls are continuous where the great vessels enter and leave the heart
Pericardium - inner and outer wall - where
Inner wall (visceral pericardium) adheres to heart and forms heart's outer surface (epicardium) Outer wall (parietal pericardium) lines the fibrous pericardium
Fibrous pericardium
A tough fibrous sac
Outermost layer
Composed of collagen - doesn’t like to stretch
Parietal and visceral pericardium are made of…
Serous membrane
Pericardial space
Space between the visceral and parietal layers
Contains serous fluid, secreted by serous membrane
Allows parietal and visceral surfaces to slide without friction as the heart beats
What is ‘inside’ the pericardial space
Heart is NOT inside the pericardial space - excluded by visceral pericardium
Only pericardial fluid is inside the pericardial space
Fat
Good electrical insulator between atria and ventricles
Inlets and outlets - plane
Inlets and outlets on same plane with each other
Attach to fibrous skeleton - doesn’t allow inlet and outlet to stretch
Fibrous skeleton of heart
Fibres forming tricuspid ring are incomplete
Pulmonary ring is absent
Fatty CT present in areas where fibrous skeleton is incomplete
Sinoatrial (SA) node
Can depolarise and repolarise themselves (autonomic)
Pacemaker - determines heart rate
Influenced by hormones and nerve impulses
Atrioventricular (AV) node
Can depolarise and repolarise themselves, but not as fast as SA node
Purkinje fibres
Made of purkinje cells, which conduct APs very quickly and aren’t branched
Conduction system of heart: SA node –> Atrial muscle - speed and result
Speed - slow
Result - atrial contraction
Conduction system of heart: Atrioventricular node - speed and result
Speed - very slow
Result - 100ms delay in AP getting to ventricles
Conduction system of heart: AV bundle –> Purkinje fibres - speed and result
Speed - fast
Result - complete and even ventricular contraction, known as systole
The cardiac cycle
Ventricular filling:
Commences as pressure in ventricle drops below that of atrium
Mitral valve opens quietly and blood enters ventricle
Ventricle fills to ~80% of its capacity
Atrial contraction:
Left atrium contracts to complete filling of ventricle
Rise in atrial pressure is small for 2 reasons;
- atrial muscle layer is thin
- no valves where pulmonary veins enter atrium (so nothing to prevent backflow into veins)
Isovolumetric ventricular contraction (systole):
~0.05s
Ventricle starts to contract
Blood within it lifts backwards towards atrium and mitral valve closes (first heart sound)
Ventricular pressure still below aorta’s so aortic valve remains closed
Atrial P < ventral P (increasing) < arterial P
Ventricle is isolated from rest of circulation (inlet and outlet closed)
Ventricular ejection:
Systole continues, but ventricular pressure now exceeds aortic pressure and aortic valve cusps open quietly
Blood leaves ventricle
Since blood is ejected into aorta faster than it can run-off into distributing arteries, the pressure in ventricle and aorta continues to rise steeply
Later in this phase, rate of ejection falls below rate of run-off and aortic and ventricular pressures level-off, then decrease
Isovolumetric ventricular relaxation:
As ventricle relaxes, ventricular pressure drops suddenly, flow reverses in aorta and aortic valve closes (second heart sound) as blood tries to re-enter ventricle
Mitral valve is closed because ventricular pressure still exceeds atrial pressure
Atrial P < ventral P (increasing) < arterial P
Ventricle is isolated from rest of circulation (inlet and outlet closed)
Once ventricular pressure drops below pressure in atrium, cycle repeats
Heart sounds
First heart sound: lub
Second heart sound: dub
Do we need atria to survive
No, we don’t need atria for the last 20% filling
Can fill up some without it
Classes of blood vessels
Elastic artery Muscular artery Arteriole Capillary Venule (collecting part) Vein (collecting part) Coronary arteries
Blood vessels: Elastic artery - structure and function
Structure: Many thin sheets of elastin in middle tunic, quite big - can fit finger inside
Function:
During systole - expand to store blood leaving ventricle
During diastole - push blood out into arterial tree by elastic recoil
Smooth the pulsatile flow of blood leaving ventricles
Transition between elastic and muscular artery
Gradual
Blood vessels: Muscular artery - structure and function
Structure: many layers of circular smooth muscle wrapped around vessel in middle tunic, varies in size from pencil to pin
Function: distribute blood around body at high pressure and lungs at medium pressure
Rate of blood flow is adjusted by using smooth muscle to vary radius of vessel
Controls bulk flow of blood - go where needed
Blood vessels: Muscular artery - flow rate
Flow is proportional to fourth power of radius (Poiseuille’s law)
Small change in radius has a large effect on flow rate
Blood vessels: Muscular artery - parts
Inner tunic (tunica interna/intima) Middle tunic with smooth muscle (tunica media) Outer tunic (tunica externa/adventitia)
Blood vessels: Arteriole - structure and function
Structure: 1-3 layers of circular smooth muscle wrapped around vessel in middle tunic
Have a thicker muscular wall relative to their size than other blood vessels
Function: control blood flow into capillary beds
Where greatest pressure drop occurs and where there is greatest resistance to flow
Blood vessels: Degree of constriction of arterioles throughout body determines…
Total peripheral resistance, which in turn affects;
Mean arterial blood pressure - the more arterioles open, the more the heart has to pump blood into the big vessel to keep pressure up
Which blood vessels are endothelial cells found in
All blood vessels
Which blood vessels are the tunica interna found in
All blood vessels
Blood vessels: Capillary - structure and function
Structure: diameter just wide enough to admit one RBC
Wall is a single layer of endothelium with an external BM
No smooth muscle in wall and no CT –> can’t adjust diameter
Function: tiny vessels which are thin-walled to allow exchange of gases, nutrients and wastes between blood and surrounding tissue fluid
Blood flow is slow to allow time for exchange to occur
Leaky - plasma escapes, but most is immediately recovered due to osmosis
Blood vessels: Venule - structure and function
Structure: small venules have endothelium plus a little CT
Larger ones have a single layer of smooth muscle
Vary in size
Function: low-pressure vessels which drain capillary bed
During infection and inflammation, venules are the site where WBCs leave the blood circulation to attack bacteria
Very slow flow
Blood vessels: Vein - structure and function
Structure: similar to a muscular artery but much thinner-walled for their size (less muscle and CT) Larger veins (especially in legs) have valves which prevent backflow
Function: thin-walled, low-pressure, high V vessels which drain blood back to atria (except portal veins)
Walls are thin and soft –> stretch easily
Small change in venous BP causes large change in venous V
Act as a blood reservoir
Coronary arteries - location
Arise from the aorta just downstream from aortic valve
Underneath fibrous pericardium
What do coronary arteries supply
Muscles of the heart (myocardium), which is what makes them important
Reduction of coronary artery size
If narrows to ~20% its normal X-section by atheroma, significant obstruction to blood flow occurs
During exercise, the myocardium supplied by the diseased artery runs low on oxygen (ischemia) causing chest pain (angina) - may result in death of a local area of myocardium
Deoxygenated blood is drained from the ___ by ____
Myocardium
Cardiac veins, which return the blood to the right atrium
What function does the heart serve?
Demand –> Supply
Oxygen use –> Oxygen demand
More in –> More out
Cardiac output (CO) = ?
heart rate (HR) x stroke volume (SV)
At rest CO is between 4-7 litres / min
What is stroke volume (SV)
The volume of blood ejected by the left ventricle for 1 cardiac cycle
What is venous return
The volume of blood returning to the heart from the vasculature every min and is linked to CO
What is cardiac output (CO)
The volume of blood ejected into the aorta (or ejected from the left ventricle) per min (mL / min)
Cardiovascular system - flow
High flow
The more blood that returns to the heart during diastole…
The more blood is ejected during the next systole
Regulation of SV: Intrinsic regulation of force of contraction
Governed by degree of stretch of myocardial fibre at end of diastole
Regulation of SV: Extrinsic regulation
Determined by activity of ANS and circulating levels of various hormones
Starling’s Law
The energy of contraction of the ventricle is a function of the initial length of the muscle fibres comprising its walls
i.e. a greater force of contraction can occur if the heart muscle is stretched first
SV and diastole
As blood returns to the heart in diastole, it begins to fill the ventricle –> pressure rises –> stretches myocardial fibres, placing them under a degree of tension (preload)
What 3 factors regulate SV
Preload on heart (mmHg) - stretch on left ventricle before it contracts
- increased V –> increased pressure –> increased preload –> increased SV –> increased force of contraction
Contractility - ability of nervous system to increase contractility
Afterload (mmHg) - the pressure the heart has to work at to eject left ventricle, through aortic valve, into aortic arch (work heart must do) to pump blood out
- refers to arterial pressure in left ventricle
What is inotrophy
Force of a contraction / contractility
Ejection fraction
SV/EDV
60-70%
i.e. 60-70% of blood that comes into left ventricle is pumped out per cardiac cycle
<25% = heart failure
Pressure-volume curve
Shows the work performed by the heart each time it beats
Contractility - intropic agent
The SV increase when a +ve inotropic agent is present
These agents often promote Ca2+ inflow during cardiac AP, which strengthens the force of the subsequent muscle fibre contraction
Contraction of left ventricle requires…
Co-ordination (electrical activity)
Positive inotropic agents
A slight increase in Ca2+ plasma promotes Ca2+ inflow in AP –> increased inotrophy
K+ slows heart rate
Na+, K+ and Ca2+ highly regulated
Causes of heart failure
Ejection fraction decrease:
High blood pressure
Viruses
Coronary artery disease
Responds by increasing heart rate
What is the rhythmic pulsation of heart maintained by
Excitatory signals generated within the heart
Heart electrical activity
1.5 mV
Intrinsic HR
90-100 bpm (higher than resting)
Generated by pacemaker cells (e.g. SA node) which self-discharge
Causes ventricular myocytes to contract
What does an ECG measure
Sum of all electrical activity spreading over heart walls
Why does heart require electrical activity
To get to the right myocytes at the right time to allow them to contract
Which part of the heart is the last to contract
Apex of heart (base)
If measuring electrical activity in myocyte, you are measuring the…
Cardiac AP
Steps in cardiac muscle contraction (basic)
Depolarisation
Plateau
Repolarisation
Steps in cardiac muscle contraction (detail)
Excitation is initiated by specialised cells in SA node which lies close to right atrium
A wave of depolarisation is conducted throughout the myocardium
MP between successive APs show a progressive depolarisation - this is the pacemaker
When threshold is reached, an AP is triggered
Myocytes of atria, ventricle and conducting system have APs with a fast initial depolarisation followed by a pleateau phase prior to repolarisation
Since muscle is refractory during and shortly after the passage of an AP, the long plateau phase ensures unidirectional excitation of myocardium
Repolarisation of myocardial cells occur when V-gated Ca2+ channels inactivate and additional V-gated K+ channels open
SA node - resting potential
Cells of SA node have an unstable resting potential
Cardiac muscle contraction - Ca2+
Responsible for plateau phase (inward movement of Ca2+, as well as some K+ channels opening)
- ensures the AP lasts almost as long as the contraction
Electrocardiogram (ECG)
P wave = atrial depolarisation (atrial contraction) QRS complex (R wave) = onset of ventricular depolarisation (ventricular contraction) T wave = ventricular repolarisation
ECG - ‘leads’
12 leads give diff views of atria and ventricles (L and R)
Fibrilation
If atria stops working –> atria fibrilation –> can still function / walk around
Ventricular fibrilation –> heart attack –> must reset / use defibrillator
ECG - steps
- Depolarisation of atrial contractile fibres produce P wave
- Atrial systole (contraction)
- Depolarisation of ventricular contractile fibres produce QRS complex
- Ventricular systole (contraction)
- Repolarisation of ventricular contractile fibres produce T wave
- Ventricular diastole (relaxation)
Autonomic Nervous System (ANS)
A branch of the CNS
Involves brainstem - helps regulate cardiovascular system
Components of ANS
Parasympathetic: Increased parasympathetic --> decreased HR Quick acting Neurotransmitter ACh e.g. vagus nerve - slows HR
Sympathetic: Increased sympathetic --> increased HR Increased sympathetic --> increased SV (also increased by parasympathetic but v little) Slower acting (5-10s to change HR) Neurotransmitter NE
ANS - goes to…
Every arteriole in the body
What is the apex formed by
The tip of the left ventricle and rests on the diaphragm
Layers of the heart wall
Epicardium (external)
Myocardium (middle)
Endocardium (inner)
Layers of heart wall - myocardium
Responsible for pumping action of heart
Composed of cardiac muscle tissue
Makes up approx 95% of heart wall
Layers of heart wall - endocardium
A thin layer of endothelium overlying a thin layer of CT
Provides a smooth lining for chambers of heart
Continuous with endothelial lining of large blood vessels attached to heart
Coronary sulcus
Encircles most of the heart
Marks the external boundary betwen the superior atria and inferior ventricles
Anterior interventricular sulcus
A shallow groove on the anterior surface of the heart that marks the external boundary between the right and left ventricles
Continuous with posterior interventricular sulfucs
Which veins does the right atrium receive blood from
Superior vena cava, inferior vena cava and coronary sinus
Right atrium - anterior and posterior walls
Very different
Inside of posterior wall is smooth
Inside of anterior wall is rought due to presence of muscular ridges
Valves of the heart are composed of…
Dense CT covered by endocardium
Chordae tendineae
Tendon-like cords connected to cusps of the inlet valves
Pathway of blood from right ventricle
Blood passes from right ventricle through the pulmonary valve into pulmonary trunk, which divides into right and left pulmonary arteries and carries blood to the lungs
How many veins does the left atrium receive blood from
4
Blood passes from the left atrium into the left ventricle through the…
Bicuspid (mitral) valve
How are the systemic and pulmonary circuits arranged
Arranged in series; output of one becomes the input of the other
What blood do venules carry
Venules carry deoxygenated blood away from tissues and merge to form larger systemic veins
What does blood pressure measure
Pressure in arteries (arterial pressure, i.e. pulsatile pressure)
BP = ?
BP = CO x TPR (total peripheral resistance) = MAP
High levels of BP for long periods of time can cause…
Weakness in blood vessels –> may burst or become occluded –> coronary or stroke
What does BP drive
Exchange
Where does exchange occur
Capillaries
The rest is just transport
What is the driving force pushing blood through
Pressure
Arterioles provide lots of…
Resistance
Are small vessels with lots of smooth muscle –> have a degree of tension/tone –> provides a shock absorption –> decreased pulsatility
Does pressure increase or decrease in capillaries
Pressure continues to decrease in capillaries (was initially decreasing in arterioles) because we’re taking fluid out
Venous pressure - level
Low
Cardiovascular system - flow and pressure
Flow rate is same even though pressure changing
5L in and 5L out
Capillary exchange - in and out?
At one end of capillary bed, we’re squeezing fluid out, but at other end we’re absorbing it back in
i.e. high V out and high V in
Capillary exchange - lymphatic system
A certain amount of fluid passes out from capillaries into lymphatic system and is transported away
Capillary exchange - BHP
Blood hydrostatic pressure
The driving force for exchange in arterial end of capillaries
Capillary exchange - IFHP
Interstitial fluid hydrostatic pressure
Opposing pressure of interstitial fluid
Close to zero
Capillary exchange - BCOP
Blood colloid osmotic pressure
Have proteins dissolved in plasma all the time but aren’t pushed out of capillaries –> act as a restraint for fluid going out - opposes BHP
Capillary exchange - IFOP
Interstitial fluid osmotic pressure
Some proteins dissolve in interstitial fluid that isn’t reabsorbed back into capillaries
Normally very small
Capillary exchange - NFP
Net filtration pressure
Edema
Where you are pushing out more fluid than you are reabsorbing
Interstitial spaces between cells have lots of fluid in there
Net filtration increases –> extrudes more fluid out of plasma
Tissue in legs and limbs get swollen
Arterioles - constriction?
Change in radius = big effect on resistance
Blood flow decrease = vasoconstriction
Renal blood flow
Renal blood flow can go from 1L/min to 50mL/min
What happens if pressure decreases
No longer drives exchange
What happens to blood vessels when you’re hot
Vasodilation (regulates temp)
How is the cardiovascular system arranged
Anatomically arranged in parallel (not series) –> all receive same amount of pressure
Cardiovascular system - arterioles in diff organs
Constriction of arterioles in diff organs helps redistribute blood flow to other organs
Blood pressure - main points
Exchange
Stability
General pathway for inputs and outputs
Input –> CNS (particularly ANS) –> Output
Why don’t you faint when you stand up
Input: senses BP using arterial baroreceptors –>
CNS/ANS –>
Output:
- decrease in parasympathetic NS –> increase HR
- increase in sympathetic NS –> increase HR and SV
–>
Increased CO
BP = CO x TPR
Both CO and TPR increase –> increase BP
Arterial baroreceptors
Y-shaped
Have afferent nerves entering which are stretch sensitive (stretch every heartbeat)
Increased BP activates more
Baroreceptors also found in aortic arch
Arterioles and sympathetic nerves
Arterioles have sympathetic nerves branching throughout the muscle
Sympathetic nerves have varicosities that release NE –> vasoconstriction
CNS: types of outputs
Neural and hormonal
CNS: Output - angiotensin II
Important hormone for vasoconstriction
Ace inhibitor if you have high BP –> decrease angiotensin II –> vasodilation
Related to renin (produced in kidneys)
Inputs to CNS
Multiple inputs which give rise to an output
Vasoconstriction/dilation of organs
Vessels in some organs will vasoconstrict and other vessels in other organs will vasodilate
i.e. tailored response
Cardiopulmonary receptors
Receptors found in major veins around the heart (especially SVC)
Respond to stretch of veins
Cardiopulmonary receptors - drinking fluid process
Drinking fluid increases venous pressure –> receptor is stretched and fires off –>
CNS –decreases renal SNS activity–>
Kidney:
- increase renal blood flow
- increase filtration
- increase urine flow rate
–>
Venous pressure returns to normal (homeostasis)
Slow / long-term process compared to arterial baroreceptors
CNS: Drinking fluid - hormonal response
Also slow activity
Antidiuretic hormone (ADH) decreases urine production
Decreased ADH –> allows you to excrete urine more
Stable BP is important for…
Exchange
When you almost get into an accident, you have elevated HR for a while (longer lasting) - why?
Increased sympathetic NS
CNS triggers adrenal gland via SNS
- secretes NE into bloodstream –> acts on α-receptor –> vasoconstriction –> increased HR and SV
Blood vessels: Tunica interna/intima
Forms inner lining of blood vessel
In direct contact with blood as it flows through the lumen
Contributes minimally to thickness
Blood vessels: Tunica media
Muscular and CT layer
Greatest variation among diff vessel types
In most vessels, relatively thick
Substantial amounts of elastic fibres
Blood vessels: What separates the tunica media from the tunica externa?
External elastic lamina
Blood vessels: Tunica externa
Consists of elastic and collagen fibres
Contains numerous nerves and tiny blood vessels
Helps anchor vessels to surrounding tissues
Elastic arteries - elastic lamellae
The thick tunica media, dominated by elastic fibres
Examples of elastic arteries
Aorta and pulmonary trunk
Elastic arteries - important function
Help propel blood onward while ventricles are relaxing
Elastic arteries AKA…
Conducting arteries
Muscular arteries are also called…
Distributing arteries - continue to branch and ultimately distribute blood to each of the various organs
Arterioles - metarteriole
Terminal end of arteriole
Tapers toward the capillary junction
Capillary bed
A network of 10-100 capillaries that arise from a single metarteriole
Cardiac conduction system
A network of specialised cardiac muscle fibres that provide a path for each cycle of cardiac excitation to progress through the heart
Where is the only site where APs can electrically conduct from atria to ventricles?
Atrioventricular (AV) bundle
Nervous system regulation of the heart originates in…
The cardiovascular centre in the medulla
Capillary exchange
The movement of substances between blood and interstitial fluid
3 basic mechanisms by which substances enter and leave capillaries
Diffusion
Transcytosis
Bulk flow
Bulk flow
A passive process where large numbers of ions, molecules, or particles in a fluid move tgt in the same direction
Move at faster rates than with diffusion alone
What is bulk flow more important for
Regulation of relative volumes of blood and interstitial fluid
Filtration vs reabsorption
Filtration: pressure-driven movement of fluid and solutes from blood capillaries into interstitial fluid
Reabsorption: pressure-driven movement from interstitial fluid into blood capillaries
What does net filtration pressure (NFP) determine
Whether volumes of blood and interstitial fluid remain steady or change
Within vessels, what is hydrostatic pressure due to
Pressure that water in blood plasma exerts against blood vessel walls
NFP (net filtration pressure) = ?
(BHP + IFOP) - (BCOP + IFHP)
i.e. pressures that promote filtration minus pressures that promote reabsorption
If +ve = net outward pressure (filtration)
If -ve = net inward pressure (reabsorption)
Systolic BP vs diastolic BP
Systolic: highest pressure attained in arteries during systole
Diastolic: lowest arterial pressure during diastole
Mean arterial pressure (MAP) is roughly…
1/3 of the way between diastolic and systolic pressures
Another way of calculating cardiac output = ?
CO = MAP / R
Vascular resistasnce depends on…
Size of lumen
Blood viscosity
Total blood vessel length
Total peripheral resistance
Refers to all vascular resistances offered by systemic blood vessels
Circulation time
The time required for a drop of blood to pass from the right atrium, through the pulmonary circulation, back to the left atrium, through the systemic circulation down to the foot, and back again to the right atrium
In a resting person, usually ~1 min
Proprioceptors
Monitor movements of joints and muscles and provide input to cardiovascular centre during physical activity
Baroreceptors
Monitor changes in blood pressure and stretch in walls of blood vessels
Chemoreceptors
Monitor conc of various chemicals in blood
Baroreceptors - when BP falls…
Baroreceptors are stretched less –> send nerve impulses at slower rate to cardiovascular centre, which decreases parasympathetic stimulation of heart and increases sympathetic stimulation
Where is the bicuspid valve located
Between the left atrium and the left ventricle
Where does deoxygenated blood returning from the systemic circulation flow into
Right atrium
Blood flows from the pulmonary veins into the..
Left atrium
The outlet valves lack chordae tendinae because…
When the valves close, the cusps remain stable because of their cup shape
Where the great arteries and veins attach at the base of the human heart, the aorta is…
Posterior to the pulmonary trunk
There is a semilunar valve between the..
Right ventricle and the pulmonary trunk
Does the left ventricle expel a greater volume of blood per beat than the right ventricle
No
When do the atrioventricular valves close
The ventricles contract
Where does blood flow into the coronary arteries from
The ascending aorta
What component of the conduction system provides the only electrical connection between the atria and the ventricles
AV bundle
A decrease in arterial blood pressure would most likely and immediately lead to…
Decreased afterload
Blood flow to muscles increase if _______ in arterioles supplying the muscles increase
Vasodilation
An increase in cardiac sympathetic activity would most likely and immediately…
Increase SV
Increased stimulation of the heart by cardiac accelerator nerves causes…
Stimulation by NE of the SA node and of the beta receptors on the cardiac muscle fibres of the ventricles
Where does blood flow most slowly through
Capillaries because their total cross-sectional area is the largest
In terms of the structural organisation of the cardiovascular system, what factor contributes most to BP
The parallel arrangement of the vascular beds
Stimulation of the heart by autonomic nerves fibres traveling with the vagus nerve causes…
Decreased HR but no change in ventricular contractility
What happens if heart rate increases to very high levels
End-diastolic volume drops because ventricular filling time is so short
Moderator band is part of..
The heart’s conduction system
With regard to resistance, the parameter with the largest effect is…
Radius / diameter
If plasma proteins are lost due to kidney disease, which of the following pressure changes occur as a direct result
Blood colloid osmotic pressure (BCOP) decreases
The vasomotor region of the cardiovascular centre directly controls…
Peripheral resistance by changing diameter of blood vessels
Where are baroreceptors located
In the walls of the aorta (aortic arch) and carotid arteries/sinus
End-systolic volume
The amount of blood remaining in the ventricle when the semilunar valve closes
What is angina pectoris
The pain accompanying myocardial ischemia
Pons - grey or white matter?
Both
Fibrous skeleton - function
Insulates the ventricular myocardium from electrical activity of the atria, so wave of electrical activation can only propagate between the 2 chambers via the AV node - prevents simultaneous contraction of atria and ventricles
Vital for coordination of mechanical contraction and thus ejection of blood
Mitral regurgitation
Blood regurgitation from LV into LA during ventricular systole due to failure of valves to close properly
As soon as pressure in ventricle exceeds that of the atria (isovolumetric ventricular contraction), regurgitation may occur
When does atrial diastole first occur
During isovolumetric ventricular contraction
Longest phase in cardiac cycle
Ventricular filling
~0.4s
What is the valve immediately upstream of the coronary arteries
Aortic semi-lunar valve
Cardiac reserve
The difference between the rate at which the heart pumps blood and its max capacity for pumping blood at any given time
Hypothermia ____ HR
Decreases
Hypertension
Abnormal higher BP
Bradycardia
Abnormally slow HR
Tachycardia
Abnormally rapid HR
Poiseuille’s law
States the velocity of a liquid flowing through a capillary is directly proportional to the pressure of the liquid and the fourth power of the radius of the capillary
Hemorrhage
Blood loss
Chronotropy
Heart rate
i.e. +ve chronotropic effect = increased HR
Starling’s Law of the Capillaries
States that the V of fluid reabsorbed at the venous end of a capillary is nearly equal to the V of fluid filtered out at the arterial end
Arterioles - nerves
Only contain sympathetic nerves (so there is a constant degree of tension)
Doesn’t contain parasympathetic nerves
Chordae tendineae when valves are open
Chords are relaxed and closer to the middle of the lumen of the ventricle
For no ventricular filling to occur…
Ventricular P must be higher than peak atrial pressures to keep inlet valves closed
Upstream vs downstream
Upstream = closer to heart Downstream = further from heart
Afterload and BP
Increased afterload = increased BP = hypertension
Decreased BP and baroreceptors
Decreased BP –> baroreceptors fire less and upregulate sympathetic nervous activity
Why is resting HR slower than intrinsic HR
Due to activity of parasympathetic NS
Most anterior structure at base of heart
Pulmonary trunk
Fibrous skeleton is made of…
CT
Pulmonary veins drain into the…
LA –> LV
Atria contract when initially stimulated by…
SA node
Initiation of heartbeat is the responsibility of…
SA node
Increase in venous return results in…
Increased end-diastolic volume –> increased preload
Alpha vs beta receptors
Alpha receptors affect skin
Beta receptors affect cardiac muscle
Vasomotor nerves
Activated by sympathetic activity –> vasoconstriction –> increased resistance
Arteries and veins - pressure
Arteries = high pressure Veins = low pressure
Standing still for long periods of time
Lack of skeletal muscle pumping of veins –> venous return decreases –> SV decreases –> CO decreases
What happens during diastole
Relaxes and fills with blood
End-systolic volume
The amount of blood remaining in the ventricle when the semi-lunar valve closes
