MEC322: Cardiovascular System Flashcards
What are the three general functions of blood?
Transportation- of oxygen, carbon dioxide, nutrients, hormones, heat and waste
Regulation- of pH, body temperature and water contents of cells
Protection- against blood loss through clotting, disease through phagocytic white blood cells and proteins such as antibodies, interferons, and complement.
What are the components of whole blood?
Blood plasma – a liquid extracellular matrix that contains dissolved substances.
Formed elements – which are cells (red blood cells or erythrocytes, white blood cells or leukocytes, and platelets) and cell fragments.
What amount of blood loss causes weakness?
15-30%
What amount of blood loss causes shock?
over 30%
shock can be fatal
What are blood transfusions used to treat?
substantial blood loss, severe anaemia or thrombocytopenia (not enough platelets)
What are antigens?
Contained on the surface of red blood cells made up of glycolipids and glycoproteins
What is the ABO blood group?
Based on two antigens A&B these determine blood type
What are anti-A antibodies and anti-B antibodies?
Blood plasma contains antibodies that react with the A or B antigens if mixed.
What is an erythrocyte?
a red blood cell
How is the Rh blood group classified?
People whose erythrocytes have Rh antigens (the Rh factor) are classified as Rh+. Those who lack the antigen are Rh–.
What happens when Anti-B antibody and B antigen mix?
Clotting- adverse affect
What are some characteristics of blood?
Temperature of 38°C
Five times more viscous than water (more viscous due to plasma proteins and formed elements)
pH slightly alkaline 7.35-7.45
What is venipuncture?
Blood collected from veins (as they are more superficial, thinner and lower blood pressure than arteries)
common site- median cubital vein
What are other blood collection methods?
Collected from peripheral capillaries - fingertip or earlobe
Collected from arterial puncture - Required to evaluate efficiency of gas exchange at the lungs
Describe blood in terms of it biomechanics?
Blood is a heterogeneous multi-phase mixture of solid corpuscles suspended in a liquid plasma —> non-Newtonian fluid
What is a Newtonian fluid?
a fluid in which the viscous stresses arising from its flow, at every point, are linearly correlated to the local strain rate- the rate of change of deformation over time
What is the viscosity of blood determined by?
- viscosity of plasma
- The haematocrit level (volume of red blood cells in total volume of blood)
- the mechanical properties of blood cells
- Applied deformation forces (extensional and shearing)
- Ambient physical conditions
Compare plasma to red blood cells
Plasma- Newtonian Red blood cells - Vary in concentration Are elastic Aggregate in 3D structures (rouleaux) at low deformation rates
What is blood modelled as in computational models?
Newtonian fluid
What will blood flow effect?
The mechanical stress on the blood vessel walls and the surrounding tissues
- especially in cases of irregular lumen (inside space of tubular structure) geometry like stenosed (narrowing) arteries
- seems to have the most significant role in facilitating blood flow through stenotic vessels
What is the basic pattern of blood flow?
–> right side of heart –> lungs –> left side of heart –> sytemic cells –>
heart –> arteries –> arterioles –> capillaries–>venules–>veins–>
What does the right atrium do?
- receives and holds deoxygenated blood from the superior vena cava, inferior vena cava and coronary sinus
- sends down to the right ventricle
What does the left atrium do?
- receives the oxygenated blood from the left and right pulmonary veins
- pumps to the left ventricle
Do atria have valves at their inlets?
No
What does the right ventricle do?
- receives blood from the right atrium
- pumps it into the lungs via the pulmonary artery
What does the left ventricle do?
- receives blood from the left atrium
- pumps it into the circulation system via the aorta
What is the myocardium made of?
myocytes, cardiac extracellular matrix, and the capillaries
Heart wall
What does the cardiac extracellular matrix primarily consist of?
fibrillar collagens, type I (85%) and III (11%)
Why is type I and III collagen essential to the heart wall?
Maintaining the size and shape of the heart, wile only consisting of 1-4% of total heart protein
What changes the extra cellular matrix especially fibrillar collagen? and what are the changes?
Normal aging, hypertension and diabetes mellitus
- change in the collagen content
- conformational change in the type of fibrillar collagen (amount of type III collagen decreases and type I increases)
- increase in collagen cross-linking
What are ventricles?
3D thick-walled pressure vessels with changes in wall thickness and principal curvatures both locally and temporally through the cardiac cycle.
Where are the ventricle walls thicker and why?
Thickest at the equator and base of theleft ventriclewhich needs to pump blood to most of the body while the right ventricle fills only the lungs
Where are the ventricle walls thinnest and why?
thinnest at the left ventricular apex and right ventricular free wall
Which is larger the pressure of the atria to fill the ventricles or the load on the ventricles required to pump blood throughout the body and lungs?
the load on the ventricles required to pump blood throughout the body and lungs
Are the ventricles equal in size in an adult?
Yes- contains about 85 mL
Mass of left ventricle averages 143±38.4g
What are the 5-stages of cardiac cycle?
Atrial systole Isovolumetric Contraction Ventricular Ejection Isovolumetric Relaxation Ventricular Filling
What happens during Atrial systole?
Atrial contraction forces blood into ventricles
- Mitral valve opens rapidly and semilunar valves is closed
- Atria contract and pump blood
- Ventricles, already partially filled from phase 5, receive last ~30% of blood, for a final resting volume of about 130mL.
What happens during Isovolumetric Contraction?
Ventricular contraction pushes AV valves closed
- The deceleration of flow reverses the pressure across the valve leaflets and causes them to close (mitral valve closure)
- semilunar valves is still closed.
- Ventricles begin to contract. Ventricular muscle initially shortens a little, but intraventricular pressure rises rapidly(about 50 msec in adult humans). Ventricular volume unchanged.
What happens during Ventricular Ejection?
Semilunar valves open and blood is ejected
- Atrioventricular valves close but semilunar valves open.
- Pressures in left and right Ventricle exceed pressures in Aorta (80mmHg) and Pulmonary Artery (10mmHg).
- Ejection is quick at first, slowing down as systole progresses.
- Amount ejected each ventricle per stroke at rest is 70-90mL.
- About 50mL of blood remains in each ventricle at the end of systole
What happens during Isovolumetric Relaxation?
Semilunar valves close and blood flows into atria
- All the valves close as ventricles relax
- pressure within Ventricles drops below 120mmHg
- This ends once Ventricular Pressure falls below Atrial pressure Atrioventricular valves open.
- The heart pump blood to rest of body.
What happens during Ventricular Filling?
Chambers relax and blood fills ventricles passively
- Atrioventricular valves open and semilunar valve close.
- Ventricles are relaxed.
- Ventricles passively fill with approximately 70% of their final volume.
- As the ventricles fill, rate of filling decreases and the AV valves drift towards closing.
- Atria expand and are filling.
How is blood supplied to the heart?
Coronary artery and vein system
Right and left coronary arteries branch off of aorta –>Branch into smaller vessels
Cardiac veins deliver blood to coronary sinus, and back to the right atrium
What is the cause of coronary artery disease?
When coronary arteries cannot deliver blood adequately- usual cause plaque in arterial wall
What causes pain in the cardiovascular system?
pain (angina pectoris) when the body is not receiving adequate oxygen
What is the cause of myocardial infraction?
(Heart attack) when blood supply to heart is completely blocked; muscle dies
How does the heart conduct electrical signals?
Heart contracts as a unit
Atrial and ventricular syncytia help conduct electrical signals through the heart
Sinoatrial (S-A) node is continuous with atrial syncytium
S-A node cells can initiate impulses on their own; activity is rhythmic
What is a syncytium?
cells interconnected by specialized membrane with gap junctions, as seen in the heart muscle cells and certain smooth muscle cells, which are synchronized electrically in an action potential.
What do heart valves do?
Control flow of blood from one chamber to another and prevent backflow
Describe the parasympathetic autonomic nervous system
From medulla oblongata (vagus nerve)
- Nerve branches to S-A and A-V nodes, and secretes acetylcholine (slows rate)
- Parasympathetic activity can increase (slow heart rate) or decrease (increase heart rate)
Describe the sympathetic autonomic nervous system
from celiac plexus to heart
- Secretes norepinephrine
- Increases force of contractions
What maintains the balance between the sympathetic and parasympathetic nervous systems?
Cardiac control centre in medulla oblongata
Normally both are at a steady background level
What does a baroreceptor detect?
changes in blood pressure- rising pressure stretches receptors
What does the Vagus nerve control?
Parasympathetic system is partially controlled by the vagus nerve and controls heart rate
increased temp increases heart rate
excess potassium decreases it
excess calcium increases it
What is blood flow affected by?
Pressure and resistance (generally equal to cardiac output)
flows from high to low pressure
Define blood pressure
The force exerted by blood against vessel walls
(contraction of the ventricles, mmHg)
depends partly on total volume of blood
When is blood pressure highest and lowest?
highest in large arteries, with ventricular systole
Lowest with ventricular diastole
Plus pressure is difference between two above
Where is resistance to blood flow highest?
depends on size of blood vessel and thickness (viscosity) of blood
Highest in capillaries
What regulates cardiac output?
- contraction strength
- heart rate
- venous return:
skeletal muscles
breathing rate
What is the S-A node?
Hearts natural pace marker
cluster of cells that are situated in the upper part of the wall of the right atrium where electrical impulses are generated
What performs long term regulation?
Hormones
Which hormone is released if blood pressure is too low?
ADH- antidiuretic hormone:
promotes water retention
What does Angiotensin II do?
Angiotensin II is a hormone that may act on the central nervous system to regulate renal sympathetic nerve activity, renal function, and, therefore, blood pressure.
Vasoconstriction effect on blood pressure?
ADH is secreted
Aldosterone is secreted
EPO (erythropoietin) secreted by kidneys if blood volume is too low
ANP secreted if blood pressure is too HIGH
What is hypertension?
Excessively high arterial pressure
Risks of developing hypertension
Sedentary lifestyle Smoking Obesity Diet (excess sodium; cholesterol; calories in general) Stress Arteriosclerosis Genetic factors
Consequences of hypertension
Higher required power output of heart, leading to enlargement of left ventricle
Atherosclerosis (plaque build up inside arteries) may affect coronary arteries as well (which have to work harder anyway)
Heart disease
Deficient blood supply to other parts of body
Damage accumulation in blood vessels
Heart failure
Treatment for hypertension
Life style changes
Drug therapies
What are different ways to treat hypertension with drugs?
- Reduce heart rate (Calcium channel blockers reduce calcium flow into heart muscle and therefore heart rate)
- relax smooth muscle lining coronary arteries (Beta blockers (reduce stimulation by sympathetic nervous system))
- reduce blood volume (Diuretics: ACE inhibitors interfere with renin–angiotensin pathway)
- reduce resistance (by opening up blood vessels) (Vasodilators (such as nitroglycerin))
- increase efficiency of heart muscles (Digitalis: if heart is actually failing)
CAN BE TAKEN IN COMBINATION
What effect does exercise have on the heart?
A trained heart is bigger
- Pumps blood more efficiently (at a lower rate)
- Stroke volume increases (due to stronger contractions, allowing for lower rate)
- Other benefits: higher aerobic capacity (contributing to efficiency)
What do arteries and arterioles do?
Carry blood away from the heart
What do capillaries do?
site of exchange btw cells and blood (nutrients and waste)
most permeable of all vessels especially so in liver, spleen and red marrow( so cells can enter and leave circulation)
connects arterioles to venules
What do venules and veins do?
return blood to the heart
In the vessel wall what is the function of the endothelium?
prevents platelet aggregation
secretes substances that control diameter of blood vessels
In the vessel wall what is the function of the Tunica media?
comprises smooth muscle and connective tissue
Innervated by sympathetic nerves (vasoconstriction)
Missing in smallest arteries
In the vessel wall what is the function of the Tunica externa?
comprises connective tissue; is vascularised
Why don’t blood components pass through arteries and arterioles spontaneously?
vessel walls are too think
blood is force through arteries and arterioles
How and what is transported out of capillaries?
oxygen and nutrients move out
co2 moves in vis lipid membrane channels by diffusion
How does blood pressure move molecules out?
filtration
What does plasma proteins maintain?
osmotic pressure of blood
Why do veins in limbs have valves?
to prevent back flow
varicose veins arise when pressure on valves is prolonged
The heart is a double pump. True or false?
True
What is the medulla oblongata?
a long stem-like structure which makes up part of the brainstem
cardia centre is inside the medulla oblongata
What are the two valves in the right heart?
Tricuspid and pulmonic
control blood flow returned from the body to the lungs for oxygenation
What are the two valves in the left heart?
Mitral and aortic
regulate the flow of oxygenated blood
When do all four valves close?
isovolumic contraction and relaxation
What are the two semilunar valves?
aortic valveandpulmonary valve
2nd heart sound it due to the closure of these valves
What is the chordae tendineae? and which valves have it?
tendon-resembling fibrous cords of connective tissue that connect the papillary muscles to the tricuspid valve and the bicuspid valve in the heart.
What is the aortic valve composed of?
three semilunar cusps included within a connective tissue sleeve .
The cusp is a complicated and multi-layer with 300~700µm thickness.
What are the three layers of the semilunar cusp?
the fibrosa(~45%), collagen (unorganised in unstressed state) spongiosa(~35%) central part includes variable loose connective tissue and proteins ventricularis(~20%) covers the ventricular side of the valve and consists of collagen (unorganised in unstressed state) and elastin
What are the semilunar cusps lined with?
endothelial cells and has a dense collagenous core adjacent to the high pressure aortic side.
What happens when stress is applied to semilunar valves?
they become oriented mainly in the circumferential direction with a lower concentration of elastin and collagen in the radial direction
the aortic valve diameter is 23.2 ± 3.3 mm and pulmonic valve diameter is 24.3 ± 3.0 mm
What valves have atrioventricular valves?
mitral and tricuspid valves
they prevent backflow fro the ventricles into the atria during systole
They are anchored to the walls of the ventricles by chordae tendineae, which prevent the valves from inverting.
what is the mitral valve also called?
bicuspid valve because it contains two leaflets or cusps.
Describe the chordae tendineae
attached to papillary muscles (subvalvular apparatus) that cause tension to better hold the valve
Its function is to keep the valves from prolapsing into the atria when they close. It has no effect on the opening and closure of the valves (caused entirely by the pressure gradient across the valve).
The peculiar insertion of chords on the leaflet free margin, however, provides systolic stress sharing between chords according to their different thickness.
What happens in valvular stenosis?
the tissues forming the valve leaflets become stiffer, narrowing the valve opening and reducing the amount of blood that can flow through it. The valve can become so narrow (stenotic) that heart function is reduced, and the rest of the body may not receive adequate blood flow
What happens in valvular insufficiency?
(or regurgitation, incompetence, “leaky valve”), the leaflets do not close completely, letting blood leak backward across the valve. This backward flow is referred to as “regurgitant flow.
Why are disk-and-cage valves not implanted anymore?
Inferior haemodynamic characteristics
What design improvements were made to the tilting-disc valve?
Design improvements focus on the disc-retaining system, the disc tilting angles during open and closed phases and disc geometry.
What are the key innovative features of the bileaflet valve?
Length-to-diameter ratio close to native heart valves
Smoothed pivot recess that allows the leaflets to open at an angle of 90°
Two-point landing mechanism during valve closure
Breakthrough: pyrolytic carbon as a suitable valve material
Why is pyrolytic carbon the material of choice for mechanical heart valves?
superior biocompatible, thromboresistant and wear resistant properties
What do you know about bioprosthetic heart valves?
1967: use the patient’s own pulmonary valve to replace the aortic valve, followed by the use of a homograft to function as the pulmonary valve
1969: use glutaraldehyde to “fix” the valve (better stability, less degradation)
Most commonly: pig valves, followed by calf valves
What causes difference in flow for different valves?
Height of the valve
Material (porcine, pericardial etc.)
Stent characteristics (stentedvsstentless valves)
Disadvantages of mechanical and biological valves?
More thrombosis (clots) when mechanical valves are placed in right side (usually in the first 5-7 years) More degradation with the biological hear valves (steep increase after 7 years)
What causes bioprosthesis calcification?
due to chemical interaction between aldehyde groups’ phospholipids and circulating calcium ions.
What is the artifical heart used for?
Either used as a Bridge to Transplantation
Either used as a Ventricular Assist Device
What do 1st generation ventricular assist devices inculde?
A pulsatile volume displacement pump
Pumping chamber
Two valves (outflow and inflow valves) that fill and empty cyclically
Capable of generating a stroke volume of around 65–83 ml
Pumps are driven by either pneumatic or electrical drive
advantages and disadvantages of 2nd gen VAD?
Main advantages:
smaller size that reduces the risk of infections and simpler implantation
fewer moving parts
absence of valves to direct blood flow
smaller blood-contacting surfaces
reduced energy requirements that enhance simplicity and durability.
Major limitations:
Haemolysis
ventricular suction and thrombus formation
pump stoppage
What does a 2nd gen VAD include?
Include implantable, continuous flow, rotary pumps with axial flow
What does a 3rd gen VAD include?
centrifugal continuous-flow pumps
Levitation systems
Suspend the moving impeller within the blood field without any mechanical contact
Eliminates frictional wear and reducing heat generation
Magnetic levitation devices are larger
Main challenges for VADs
Most cases, patient dies before the device
Implantation must be accompanied with lifelong anti-coagulant treatments
Fluid turbulence, protein adhesion on pump lead to clotting
Patients experience neurological events after implantation
Name the 5 main types of blood vessel?
Arteries – carry blood AWAY from the heart Arterioles Capillaries – site of exchange Venules Veins – carry blood TO the heart
Name the 3 main types of tissue layers?
Tunica interna (intima) Tunica media Tunica externa
What are the arteries two major properties?
elasticity and contractility
What is a decrease in the diameter of a blood vessel lumen?
Vasoconstriction
What is an increase in the diameter of a blood vessel lumen?
vasodilation
What are arterioles?
small arteries that deliver blood to capillaries
What do arterioles play a key role in?
Regulating blood flow from arteries into capillaries (through contraction and dilation)
What do precapillary sphincters do?
regulate blood flow through capillaries.
Describe venules?
Similar in structure to arterioles
thinner walls near capillary and thicker as they get closer to heart
How does the structure of a vein differ from an artery?
middle and inner layers are thinner
outer layer is thickest
lumen is wider
What forms valves in some veins?
inner layer folds inward
What does venous return refer to?
movement of blood from capillaries to venules to veins back tot the atria of the heart
aided by skeletal muscle pump and respiratory pump
Describe the skeletal muscle pump?
collection of skeletal muscles that aid the heart in the circulation of blood
What is the opposition of blood flow due to friction between blood and the walls of the blood vessel AND what three factors does it depend on?
Vascular resistance
size of the blood vessel lumen
blood viscosity
total blood vessel length
What is the velocity of blood proportional to?
the inverse of the cross-sectional area
When is the velocity of blood slowest?
when the total cross sectional area is greatest
and father from the heart
Blood flow is fastest in capillaries. TRUE or FALSE
FALSE its slowest in capillaries as this aids exchange
What is the circulatory time from blood to leave right atrium and return back to it?
1 min at rest
What is blood flow measured in?
cm/sec
Describe the history of coronary stents
1977- reopening vessel with balloon, 5-10% failure
1986- self-expanding stainless steel stent, complicated delivery removed from market 1991
1987- ballon-expendable stainless steel stent, a lot of variation in market
What are some of the initial challenges faced with stents?
high metallic density–>high incidences of sub-acute stent thrombosis (st)
bulky and technically challenging to use results in frequent failure
risk of in-stent restenosis
what is the evolution of stent material used?
Stainless steel –> cobalt chromium –> platinum-chromium alloy
What coatings can be put on a stent?
gold, carbon heparin: no effect
drugs w/ a polymer coated on the surface of BMS : slowly release over a few weeks after depolyment
What does BMS stand for?
Bare metal stent
What are the key requirements of stents?
resist a uniform radial force
offer structural scaffolding to the arterial wall
expand on a range of diameters
What do the properties of a stent rely on?
strut length
axial spacing of strut rings along stent
no. of struts w/in a ring
How many people have a ruptured brain aneurysm each year in England?
1 in 12500
How many people with a subarachnoid haemorrhage die within two weeks?
3 in 5
half who severe are left w/ sever brain damage
What are the treatment options for a subarachnoid haemorrhage?
endovascular coiling
microsurgical clipping
stent-supported coiling
flow-diverter therapy
What percentage of wall surface coverage are stents design to have?
30-50%
Where do cerebral aneurysm often occur?
bifurcation
something branches into two
What percentage of patient experience arteries closing or narrowing following insertion of flow diverters?
61%
43% of those cases lead to permanent neurological damages
The ratio between _____ is critical to stent outcome?
vessels diameter
What do flow diverters cause?
disruption of flow and difference in shear stress
What ration of D1/D2 will have a higher probability of narrowing of blood vessels?
<75
Describe a stent retriever
a cylindrical device consisting of a self-expanding stent mounted on a wire and deployed within a catheter, once at the site of the clot the stent is released and expands within the thrombus (clot) pushing the clot to the walls of the artery
when stent is retrieved the thrombus is pulled with it
Challenges to retrieving clots
damage to endothelial walls
break down clot or move further down vessel
