Health and Disease Week 25 Flashcards
What are the 4 main functions of the cardiovascular system (CVS)?
- delivery of oxygen to cells
- removal of CO2 and waste from cells
- communication between organs with hormones and other mediators
- temperature regulation - can move blood around
What is the main role of the CVS?
to create blood pressure that drives the movement of blood
Which 3 main factors is blood pressure determined by?
- cardiac output - pumping of the heart
- blood vessels or vasculature
- the fluid components
Which two circuits can the CVS be divided into?
- pulmonary circuit
- systemic circuit
Why do we need 2 different circuits in the CVS?
blood is pumped around the body (systemic circulation) at high pressure, and this would damage the lungs
What are the 3 main layers of the blood?
- plasma
- the ‘buffy layer’ - leucocytes and platelets
- erythrocytes
What is contained in the plasma?
water, ions, proteins, nutrients, hormones, metabolic waste, gases etc
At rest, where is most blood distributed?
in the veins and venules - they act as a reservoir
At rest, where is most blood flowing through?
the abdominal organs and the kidneys
Why is the majority of blood pumping through arteries in parallel, not a series circuit?
so if one organ’s blood supply gets cut off, it doesn’t affect the other organs in the body
Which 3 layers make up the blood vessels?
tunica adventitia, tunica media, tunica intima
What is the tunica intima layer made up of?
endothelial cells
What is the tunica media layer made up of?
smooth muscle cells
What is the tunica adventitia layer made up of?
connective tissues
What is the role of smooth muscle cells in the blood vessels?
they are involved in regulating the size of the lumen
What is the role of the connective tissue in the blood vessels?
they hold the blood vessels in place
Which layer do ALL blood vessels have?
endothelial layer - whether they have and the thickness of the smooth muscle and connective tissue varies
Which blood vessels are involved in transport AWAY from the heart?
- arteries
- arterioles
- capillaries
Which blood vessels are involved in the transport TOWARDS the heart?
- veins
- venules
- capillaries
What are features of the arteries?
- large lumen
- thick layer of smooth muscle and connective tissue
- very thick and elastic
How do the arteries act as a pressure reservoir?
during contraction of the heart, the arteries expand to absorb pressure, then squeeze blood down the rest of the body
Why is it important the arteries absorb pressure?
to avoid bursting the delicate capillaries further down the line
What are the features of arterioles?
- have a small lumen and thin smooth muscle layer
- contraction of the smooth muscle regulates the diameter of the lumen
Which blood vessels generate the most resistance in the body?
the arterioles - they contract or relax using smooth muscle to allow blood through or restrict blood flow
What are many drugs that control blood pressure aimed at?
smooth muscle cells in arterioles and these mainly control resistance
What are the features of capillaries?
- single layer of endothelial cells
- exchange of nutrients, oxygen and waste over walls
- NO protein diffusion
- intracellular clefts and fused vesicles assist exchange of proteins
What is exchange over the capillaries promoted by?
the slow movement of blood and a large surface area within the capillaries
What are features of the veins and venules?
- thin walls
- large lumen diameter
- contain valves to prevent backflow
How is blood moved through the veins and venules?
the veins run close to skeletal muscles and the movement of these aids movement through veins
What causes varicose veins?
broken valves means blood accumulates in the veins and leads to swelling of veins
What does the right side of the heart supply?
the lungs - vena cava and pulmonary artery
What does the left side the heart supply?
the body - aorta and pulmonary vein
Why is the muscle of the left side of the heart bigger?
left ventricle is pumping blood around the entire body, right ventricle is just to the lungs - chambers are equal size though!
What are the 2 septums within the heart?
- interatrial septum
- interventricular septum
What is the role of the atrioventricular valves?
prevent backflow of blood from the ventricles to the atria
What is each atrioventricular valve called?
left side - bicuspid or mitral
right side - tricuspid
What is the role of the semilunar valves?
they prevent backflow of blood from the major blood vessels back to the heart
What is the role of the chordae tendinae?
they are tendons that hold the atrioventricular valves in place so they do not flip
What supplies the heart muscle with oxygen and nutrients?
an extensive network of blood vessels from the coronary arteries
Where do the coronary arteries branch off from?
the aorta
Where does the deoxygenated blood delivered to the heart drain back to?
the right atrium via a single vein - the coronary sinus
What is ischemia?
insufficient blood flow to the heart muscle
What is ischemia associated with?
chest pains (angina) often radiating down the left arm
What is coronary arterial disease?
when the arteries that supply blood to the heart become narrowed or blocked, reducing blood flow and oxygen to the heart muscle
What are 4 main causes of coronary arterial disease?
- atherosclerosis
- blood clots
- drugs
- surgery
What is atherosclerosis?
thickening of the coronary arteries due to plaque build up from fat
What are coronary artery blood clots called scientifically?
coronary thrombosis
What are 2 common treatments for coronary arterial disease?
- balloon angioplasty
- stents
What are the steps of balloon angioplasty?
- a balloon-like structure is inserted into the coronary artery and inflated
- inflation pushes the plaque outwards to open up the artery
- the balloon is removed again
How do stents work?
a mesh tube-like structure is inserted into the blocked coronary artery and stays there to keep it open
Where is the cerebrospinal fluid located?
in the subarachnoid space, between the pia mater and dura mater
What does the cerebrospinal fluid contain?
the blood vessels that supply the brain with oxygenated blood
What do the capillaries in the cerebrospinal fluid contain? What does this mean?
tight junctions, which make up the blood-brain barrier - it is difficult to get drugs and proteins into the brain
Why is glucose and oxygen cut off to the brain so serious?
the brain has no stored glycogen - so cut off causes damage within minutes
What are the 2 major fluid compartments in the body?
- intracellular fluid
- extracellular fluid
Which 2 subdivisions is extracellular fluid divided into?
- the plasma
- interstitial fluid
By which 3 forces are the volumes in the plasma, interstitial and intracellular fluid maintained?
- osmosis
- colloid osmotic pressure
- hydrostatic pressure
Which 2 compartments does osmosis occur between?
intracellular fluid and the interstitium
Which 2 compartments does colloid osmotic pressure occur between?
the interstitium and the plasma
Which 2 compartments does hydrostatic pressure occur between?
the interstitium and the plasma
What does colloid osmotic pressure do?
pulls fluid back into the plasma from the interstitium
What does hydrostatic pressure do?
pushes fluid out from the interstitium into the plasma
Where do colloid osmotic pressure and hydrostatic pressure movements occur?
ONLY in the capillaries, NOT the venules, veins, arteries etc
What does failure to regulate fluid movements lead to?
fluid build-up
define osmosis
the net diffusion of water across a semipermeable membrane from a region of high water concentration to low water concentration
What is the total number of particles in a solution measure in?
osmoles
What is 1 osmole equal to?
1 mole of any SOLUTE particles in 1L
How many osmoles is 1 mole of NaCl?
2 osmoles - Na+ and Cl- are both solutes
How do molecular weight and osmolarity relate?
osmolarity is independent of molecular weight - for example, 1 molecule of albumin has an osmolarity the same as 1 molecule of glucose and 1/2 a molecule of NaCl
What can move across a fully permeable membrane?
BOTH solute and water
What happens to solute and water across a fully permeable membrane?
BOTH particles move in opposite directions to form an equilibrium
What does movement of solute and water across a fully permeable membrane result in?
- equal volumes
- equal water molecules
- equal osmolarity
What can cross a semipermeable membrane?
ONLY water molecules - not solute
How do water molecules move across a semipermeable membrane?
they move towards to more ion-concentrated side
What are the results of water movement across a semipermeable membrane?
- equal osmolarities
- equal water molecules
- DIFFERENT volumes
define osmotic pressure
the pressure required to prevent osmosis
How does water move as a result of osmotic pressure?
water moves through the semipermeable membrane and the level of water increases to the pressure of gravity
What is osmotic pressure proportional to?
the concentration of osmotically active particles in a solution
What is osmolarity like in intracellular and extracellular compartments?
it is equal on both sides of the semipermeable membrane (300mM inside and outside) - there are an equal number of ions on each side so water should not move across the membrane and this maintains a fluid balance
What happens if you put a cell into isotonic solution?
no transfer of fluid - the intracellular and extracellular are both 300 mOsm/L
What happens if you put a cell into hypotonic solution?
the osmolarity of the extracellular solution is lower than intracellular - so water will move in and the cell swells
What happens if you put a cell into hypertonic solution?
the osmolarity is higher in the extracellular solution than intracellular - so water moves out and the cell shrinks
What does colloid osmotic pressure control?
water movement between the interstitium and the capillaries
How does colloid osmotic pressure move water back into the capillaries (plasma)?
- protein is the plasma is about 6x higher (1.2 mOsm compared to 0.2 mOsm) than in the interstitium
- therefore, pressure is exerted by proteins in the plasma and osmolarity is higher, even though ion concentrations are very similar
- this means fluid is sucked back into the blood vessels by osmosis
define hydrostatic pressure
the force exerted by the blood upon the capillary walls - essentially the blood pressure
What does hydrostatic pressure do?
hydrostatic pressure drives fluid from the plasma into the interstitium
How do we end up with net outward filtration at the arterial end of a capillary and net inward filtration at the venous end?
- osmotic force due to plasma protein concentration is much higher on outside than inside and drives fluid back into the capillaries all along them with a pressure difference of 28mmHg
- hydrostatic pressure changes over the capillaries
- at the arterial end, we get a positive overall value
- at the venous end, we get a negative overall value due to a drop in hydrostatic pressure and net inward filtration
What % of the liquid leaving the capillaries at the arterial end returns to the capillaries at the venous end?
about 90%
How do we get rid of excess fluid in the interstitial fluid?
the lymphatic system picks up excess fluid from the interstitium and returns it to the blood
What are the 2 main roles of the lymphatic system?
- draining excess fluid from the interstitial fluid in tissues and returning it to the blood vessels
- maintaining the immune response
How is excess fluid from the interstitial fluid in the tissues drained?
- excess fluid drains into the lymph capillaries
- goes through the lymph nodes before passing back into the bloodstream at the neck
- the largest vessel is the thoracic duct and this drains into the subclavian vein in the chest
Why do lymph vessels contain valves?
to prevent backflow of lymph fluid
How does lymph fluid move through the lymph vessels?
by the action of skeletal muscle and breathing - the larger lymph vessels are surrounded by smooth muscle that contracts spontaneously and is driven by pacemaker cells in the heart
What else does the lymph system collect other than excess interstitial fluid?
fats from the intestines/liver and deposits them into the veins
How does the lymph system have a role in immunity?
- lymph fluid contains white blood cells
- the lymphatic system collects antigens, which are recognised by B cells in the lymph nodes leading to activation of immunity
- B cell proliferation occurs to produce antibodies and this causes swelling of lymph nodes
- when excess fluid drains through the lymph nodes with immune cells in, they can recognise pathogens
What are the 4 main types/causes of oedema?
- increase in hydrostatic pressure
- decrease in colloid osmotic pressure
- blockage of lymph nodes
- intracellular oedema
What happens if there is increased capillary hydrostatic pressure at both ends?
- the pressure across the entire capillary has increased leading to high venous pressure
- this causes too much fluid to leave the capillaries and enter the interstitial fluid
- this leads to swelling of tissues
How does heart failure cause oedema through increased capillary hydrostatic pressure at both ends?
- the body tries to keep water in the capillaries to raise blood pressure as the heart is not pumping blood hard enough or efficiently
- this leads to an increased hydrostatic pressure
- oedema
How does a decrease in colloid osmotic pressure lead to oedema?
- there is a reduction in plasma proteins due to kidney failure, malnutrition, burns etc
- less liquid is sucked back into the capillaries and stays in interstitial fluid
- this cause swelling in tissues - oedema
How does blockage of lymph nodes lead to oedema?
- blockage of lymph nodes means that fluid cannot get back from the interstitial fluid into the blood via the lymphatic system
- leads to swelling in tissues
What causes blockage of lymph nodes?
cancer, infections, surgery, parasitic infections (parasites often get stuck in lymph nodes and prevent fluid drainage)
define intracellular oedema
where fluid accumulates within the cells themselves
How does intracellular oedema occur?
friction burns:
- this causes depression of metabolic systems of the tissues and a lack of adequate nutrition to the cells
ischemia (reduced blood supply to a tissue or organ):
- a reduced activity of Na+ pumps due to reduced input of glucose and ATP
- leads to accmulation of Na+ in cells
- causes osmosis of water into cells
What is the equation for cardiac output?
heart rate x stroke volume
What is the heart rate driven by?
waves of electrical activity that induce the cardiac muscle to contract
What are the 2 nodes in the heart called?
the sinoatrial (SA) node and the atrioventricular node (AV)
Which type of cells make up the 2 nodes?
pacemaker cells
What is the function of the Bundle of His?
it runs down the middle of the heart into the Purkinje fibres and ensures the atria and ventricles are insulated from each other
What is the function of the Purkinje fibres?
to carry impulses from the AV node down to the apex of the ventricles to ensure the ventricles contract from the bottom
Why is there a delay in the spread of action potentials from the SA node and AV node?
there is delay after the excitation of the SA node before the AV node to allow the atria to contract and the ventricles to fill with blood
What are the stages of generating an SA node action potential (don’t need to remember this)?
- SA node pacemaker cells have a low resting membrane potential
- leaky (funny-type) sodium channels allow slow influx of sodium ions
- calcium ions move through the T-type calcium channels and eventually cause a threshold potential to be reached
- the rapid opening of voltage-gated calcium L-type channels causes rapid depolarisation
- the reopening of potassium channels and closing of calcium channels leads to repolarisation
Which node is the overall driver of the heart rate?
the SA node - the AV node and Purkinje fibres have their own intrinsic rhythms, but the SA node depolarises fastest, so takes over the rest of the heart
Why are there pacemaker cells in the AV node and Purkinje fibres?
only if there is damage to the SA node - then the AV node or Purkinje fibres can take over and keep the heart beating
What is heart block?
when there is a blockage from the top to the bottom of the heart so a failure of AV conduction
What are the steps of contraction of the ventricular cardiomyocytes?
- Electrical activity comes from the pacemaker cells
- This leads to the rapid opening of voltage-gated sodium channels – this causes rapid depolarisation
- The prolonged ‘plateau’ of depolarisation is due to the slow and prolonged opening of voltage-gated calcium channels (the calcium channels drive the contraction of the muscles) and closing of potassium channels
- The opening of potassium channels allows repolarisation
What are the steps of calcium’s effect on contraction of the ventricular cardiomyocytes?
- Voltage-gated calcium channels open and calcium floods in
- Calcium binds to ryanodine receptors on the sarcoplasmic reticulum, and this causes the release of even more calcium
- Calcium binds to actin and myosin leading to contraction
- Calcium is then pumped out of muscle cells by sodium channels
- Calcium also gets taken up by the mitochondria
define refractory period
the time required before it is possible to re-stimulate muscle contraction
Why is the refractory period longer in cardiac muscle than skeletal muscle?
the prolonged refractory period allows the ventricles to fill with blood again prior to pumping
What condition occurs if the cardiac muscle cell refractory period is too short?
tetanus - spasms of the heart heart
What is the SA node regulated by?
the autonomic nervous system
What does the sympathetic nervous system stimulate?
the WHOLE heart
What does the parasympathetic nervous system control?
ONLY the SA and AV nodes
What does stimulation of the vagus nerve do?
decrease the heart rate
What does stimulation through the sympathetic nervous system do?
increase the heart rate AND stroke volume
What are the steps of the effect of the sympathetic nervous system on the heart rate?
- sympathetic neurones release noradrenaline
- this binds to beta-1 adrenergic receptors on the SA node
- this causes an influx of sodium and calcium
- this increases the rate of depolarisation
- increases the heart rate
What is the name given to increased heart rate?
tachycardia
What is the name given to decreased heart rate?
bradycardia
What are the steps of the effect of the parasympathetic nervous system on the heart rate?
- the parasympathetic neurones release acetylcholine
- acetylcholine binds to muscarinic-2 receptors on the SA node
- this increase potassium efflux and decreases calcium influx, so delays depolarisation
- this hyperpolarises the cell and decreases the rate of depolarisation
- decreases heart rate
Which system dominates at rest?
the PARAsympathetic nervous system
What do ECGs measure?
the ELECTRICAL activity of the heart
define ECG
a summation of the spread of action potentials through the various sections of the heart - if you put all contractions together, you end up with an ECG
What does the P wave show?
atrial depolarisation
What does the QRS wave show?
ventricular depolarisation
What does the T wave show?
ventricular repolarisation
What does the PG segment show?
atrial contraction - gives the length of atrial contraction
What does the QT segment show?
ventricular contraction - gives the length of ventricular contraction
Which factors does an ECG give information on?
- heart rate
- heart rhythm
- conduction speed
- anatomical orientation of the heart
- relative chamber sizes
- condition of the tissue within the heart
- damage to the myocardium
- the influence of certain drugs
What is the name for a normal heart activity?
sinus arrythmia
What happens to the heart rate naturally?
- as you breathe in, the heart rate increases due to a drop in vagus nerve activity
- as you breathe out, the heart rate decreases due to an increase in vagus nerve activity
What happens in ventricular ectopic heartbeat?
- there is unusual firing of myocytes in the ventricles
- unsynchronised heart beats which fail to eject blood
- common after heart attack
- ECG shows a random jump in electrical activity, which is essentially the heart beating between beats
What is heart block caused by?
fibrosis or ischaemia heart disease
What does an ECG show for heart block?
you get a P wave, but no following QRST, so maybe 2 P waves in a row with no QRST in between
What happens in heart block?
the P wave is not being spread to the ventricles and damage is preventing the spread
What happens in third degree heart block?
complete failure of conduction from the atria to the ventricles - they will beat independently due to activity now from the AV node as well as the SA node
How is third degree heart block rectified?
a heart pacemaker will be fitted- the pacemaker kicks in when the heart stops beating
What is the different between heart attack and cardiac arrest?
heart attack - when the heart tissue dies due to a lack of blood supply
cardiac arrest - when the heart STOPS
What can ventricular fibrillation lead to?
cardiac arrest
What is the result of ventricular fibrillation?
- the heart is not producing a regular beat, so blood is not being pumped efficiently
- leads to random firing of impulses
- fatal after minutes
What is ventricular fibrillation caused by?
- myocardial infarction (heart attack)
- electrical shock
- drug intoxication
- impaired cardiac metabolism
What is the treatment for ventricular fibrillation?
CPR followed by electronic defibrillation
Why do animals or people with a larger heart have a slower heart rate?
a large heart means a stronger heart, so leads to a larger stroke volume, therefore a slower heart rate is efficient for the same cardiac output
What are the 2 sets of valves in the heart?
the atrioventricular valves and the semilunar valves
Which 2 phases can the cardiac cycle be divided into?
systole and diastole
define systole
ventricular contraction and blood ejection
define diastole
ventricular relaxation and blood filling
What is the average pressure in the systemic arteries?
systolic = 120 mmHg diastolic = 80 mmHg
What is the average pressure in the pulmonary arteries?
systolic = 28 mmHg diastolic = 8 mmHg
What leads to the opening and closing of valves?
changes in the pressure in the 4 compartments of the heart
What are the 2 main steps of systole?
- isovolumetric ventricular contraction
- ventricular ejection
What are the steps of isovolumetric ventricular contraction?
- ventricular walls contract
- NO change in volume yet as the valves are closed
- pressure in the aorta is currently around 80 mmHg
- as the ventricles contract, the pressure in the ventricles is higher than atria, so atrioventricular valves close
- the pressure in the ventricles is less than pressure in the arteries, so the semilunar valves are closed - we need pressure above 80 mmHg in the ventricles to open the aortic valve
What are the steps of ventricular ejection?
- the contraction of the ventricle walls eventually causes a reduction in volume of the ventricles
- the pressure in the ventricles now rises above the pressure in the arteries
- the aortic and pulmonary valves open
What are the 3 main steps of diastole?
- isovolumetric ventricular relaxation
- negative pressure in the ventricles
- atrial contraction
What are the steps of isovolumetric ventricular contraction?
- ventricular walls relaxing but NO change in volume yet as valves are closed
- pressure in the ventricles is higher than atria - AV valves closed
- pressure in the ventricles is lower than pressure in arteries (120mmHg and 28mmHg) - so SL valves closed
What are the steps of negative pressure in the ventricles?
- the ventricles relaxing creates a vacuum
- the pressure in the ventricles will eventually drop below that in air and this sucks blood in from the atria - the AV valves are now open as pressure in the atria is now higher than in the ventricles
What are the steps of atrial contraction?
eventually, the atria contract and it forces the final 10% of blood in them into the ventricles
What are the two sounds heard with a stethoscope ‘lub dub’?
‘lub’ = the closure of the AV valves and the start of systole
‘dub’ = the closure of the semilunar valves and the start of diastole
What are the 3 factors that regulate the stroke volume?
- filling pressure (preload)
- contractility
- arterial pressure opposing ejection (afterload)
define preload
the volume of blood returning to the heart from the body
How does preload affect stroke volume?
- increase blood coming back to the heart
- the larger the end diastolic ventricular volume
- the heart needs to pump harder to get all the blood around the body
- increased stroke volume
What is another name for preload?
end diastolic ventricular volume
What are the 5 factors that affect the end diastolic ventricular volume?
- sympathetic nerves
- gravity
- respiratory pump (breathing)
- blood volume in the veins
- skeletal muscle pump
What is the end diastolic volume determined by?
the central venous pressure (CVP)
How does the central venous pressure affect the end diastolic volume?
if the pressure in the vein coming back to the heart increases, it means more blood is coming back to the heart, so larger end diastolic volume and stroke volume
How do the sympathetic nerves affect end diastolic volume?
- the release of noradrenaline causes the smooth muscle in the veins to contract
- smooth muscle can contract to increase CVP
- there is more blood coming back to the heart - increases stroke volume
How does gravity affect the end diastolic volume?
- when standing, gravity leads to pooling of blood in the legs and feet
- pooling in the feet reduces central venous pressure as blood pressure is highest in the feet
How does the respiratory pump (breathing) affect the end diastolic volume?
- CVP increases as you breathe in due to pressure in the chest increasing
- as you breathe out CVP decreases
How does blood volume in the veins affect end diastolic volume?
- the volume of blood in the veins affects CVP
- for example, dehydration leads to a reduced blood volume and lower CVP
How does the skeletal muscle pump affect the end diastolic volume?
as you move around, skeletal muscle ‘squeezes’ blood in the veins back towards the heart
What does the Frank-Starling mechanism describe?
how the heart adjusts its force of contraction based on the volume of blood filling it to balance the right and left sides
What are the steps of the Frank-Starling mechanism?
- if more blood returns to the right ventricle through the vena cava, then there is stronger contraction
- more blood goes to the lungs
- if more blood returns to the left ventricle through the pulmonary vein, there is stronger contraction
- higher stroke volume
- ensures blood does not accumulate in the lungs and maintains a balance of blood volume pumped on both sides of the heart
Does the vagus nerve affect stroke volume?
NO it only affects the heart rate through acting on the AV and SA nodes
How do the sympathetic nerves increase stroke volume?
- cause the release of noreadrenaline
- acts on b1 adrenergic receptors
- increase force and speed of contraction of cardiac muscle
- you get the same end diastolic volume as the same amount of blood enters the ventricles, but an increase in stroke volume as the ventricles contract stronger
What is afterload?
- if a patient has hypertension the pressure in the arteries is higher
- the heart needs to pump harder to overcome this pressure and get blood into the blood vessels
- this puts stress on the heart
- can lead to heart failure
What is congestive heart failure (CHF)?
reduced cardiac output as the heart muscle is failing
What are the 2 main causes of heart failure?
- heart attack or chronic left ventricular failure (systolic dysfunction)
- high blood pressure (diastolic dysfunction)
What is chronic left ventricular failure caused by?
- coronary artery disease leading to ischaemic heart disease
- hypertension
- cardiomyopathy
How does heart failure due to systolic dysfunction (heart attack) occur?
- heart attack means there is damage to the heart muscle
- the ventricles cannot contract as strong
- the stroke volume decreases
How does heart failure due to diastolic dysfunction (high blood pressure) occur?
- higher arterial blood pressure means higher cardiac resistance (afterload)
- ventricles need to contract stronger (hypertrophy)
- this causes stiff ventricular walls and cannot pump effectively
- decreased end diastolic volume
- lower stroke volume
