Heart Flashcards
(138 cards)
1
Q
What happens in a heart attack?
A
A myocardial infarction is caused when the blood supply to the heart is disrupted hence the muscle does not get a good enough blood supply and therefore dies. It consequently causes a loss of blood supply to the body.
(An infarct is dead or dying tissue resulting from a lack of oxygen and nutrients).
2
Q
What are the functions of the cardiovascular system?
A
Delivery of oxygen and nutrients to cells, removal of CO2 and waste products from cells, temperature regulation, hydrodynamic device in sexual reproduction, communication between organs through transport of hormones.
3
Q
What can cardiovascular circulation be split into?
A
Systemic = entire body and pulmonary = lungs
4
Q
Whats the journey of blood in the body?
A
The aorta carries oxygenated blood from the heart to the systemic arteries, delivering it to cells and tissues around the body. Systemic veins then carry this deoxygenated blood back to the heart via the vena cava. The deoxygenated blood is then delivered to the lungs via the pulmonary trunk and arteries. At the lungs the blood is oxygenated and then transported back to the heart via the pulmonary vein.
5
Q
Whats the composition of blood if allowed to separate?
A
55% plasma which contains water, ions, proteins, nutrients, hormones, metabolic waste, gases etc.
5% leucocytes and platelets known as the buffy coat
45% erythrocytes (hematocrit) responsible for oxygen transport.
6
Q
At rest how is blood distributed around the body?
A
61% is in veins/venules of systemic circulation - this is a blood reservoir.
4% is in the heart, 20% in the kidneys and 24% in the abdominal organs.
7
Q
From the heart, whats the order of blood vessels that the blood enters?
A
Arteries - arterioles - capillaries - venules - veins.
8
Q
Whats the structure of the arteries and why?
A
The arteries contain a large lumen and a thick layer of smooth muscle and connective tissue. The thick layer of elastic smooth muscle acts as a pressure reservoir - the arteries are exposed to a lot of pressure from the heart pumping blood. At systole, when the blood is pumped into the arteries, the smooth muscle contracts hence absorbing pressure by stretching. Then at diastole, the muscle relaxes hence releasing the pressure by a passive recoil.
Without this mechanism blood would surge through the arteries and damage the capillaries.
9
Q
Whats the structure of the arterioles and why?
A
Arterioles contain a thin muscular wall and a small lumen. Contraction of the smooth muscle regulates the diameter of the lumen. This determines the blood flow to organs and is a major determinant of mean arterial pressure.
10
Q
Whats the structure of the capillaries and why?
A
Capillaries consist of just an endothelial cell wrapped round itself. The diameter of the capillaries allows just one erythrocyte at a time - this allows the exchange of nutrients, oxygen and waste accross the capillary wall, but not proteins. Intercellular clefts and fused vesicle channels in the endothelial cell assist the exchange. Exchange is also facilitated by the slow movement of blood and large surface area within the capillaries.
11
Q
Whats the structure of the venules and veins and why?
A
Venules and veins contain thin walls, large diameter lumen and valves. The large diameter allows storage of a high volume of blood as a reservoir.
The return of blood to the heart in veins is facilitated by valves and skeletal muscle pumps. Movement causes the skeletal muscle surrounding the veins to contract hence squeezing the blood up, towards the heart. The closed valves stop the backflow of blood - in varicose veins, broken valves allow the blood to flow backwards under gravity.
12
Q
Whats the structure of the heart?
A
Deoxygenated blood from body enters right atrium via vena cava, then enters right ventricle and goes to the lungs to be oxygenated. Oxygenated blood from the lungs then enters the left atrium then the left ventricle then gets transported around the body.
Right side supplies the lungs.
Left side supplies the body.
13
Q
How do the right and left sides of the heart vary?
A
Although the atria and ventricles are the same size, the left side of the heart has thicker muscle to allow it to pump blood all over the body.
14
Q
Wheres the right AV valve?
A
The tricuspid is on the vein entering the right atrium of the heart (vena cava). It is held in place by chordae tendinae attached to the papillary muscle. The chordae tendinae (heart strings) are fibrous cord of connective tissue.
15
Q
Wheres the pulmonary semilunar valve?
A
The pulmonary semilunar valve is on the artery carrying blood to the lungs from the right ventricle.
16
Q
How is atrium seperated?
A
By an interatrial septum.
17
Q
How are the ventricles separated?
A
By an interventricular septum.
18
Q
Wheres the left AV valve
A
The left atrioventricular valve is on the vein transporting blood from the lungs to the heart. It is also known as the bicuspid and is held in place by chordae tendinae, attached to pillary muscles.
19
Q
Wheres the aortic semilar valve?
A
The aortic semilunar valve is within the aorta.
20
Q
What are the layers of the heart?
A
The inner heart muscle is myocardium, its then a thin layer of epicardium then the pericardium.
21
Q
Explain the cycle of blood flow around the body.
A
Oxygenated blood leaves the heart in the aorta to be transported in the body by arteries. The blood then enters arterioles, then capillaries - this is where gas nutrient and waste exchange occurs. The now deoxygenated blood then begins its journey back to the heart through the venules, then the veins. It then enters the heart in the vena cava into the right atrium. It then goes through the right AV valve into the right ventricle. Next it goes through the pulmonary semilunar valve into the pulmonary trunk on its way to the lungs. It goes through pulmonary arteries to the capillaries of the lungs where it is oxygenated. It then returns to the heart via the pulmonary veins entering the left atrium of the heart and through the left AV valve into the left ventricle. It then goes through the aortic semilunar valve into the aorta, restarting its cycle around the body.
22
Q
Where does the blood supply to the heart come from?
A
The heart has an extensive network of blood vessels supplied with oxygenated blod via the coronary arteries. The coronary arteries branch off the aorta and split into right and left coronary arteries. Most deoxygenated blood drains back into the right atrium via a single vein (coronary sinus).
23
Q
What can cause coronary arterial disease?
A
Drugs, surgery, blood clots (coronary thrombosis) and atherosclerosis (thickening of the coronary arteries hence less blood can get through).
24
Q
Whats the treatment of coronary arterial disease?
A
Coronary arterial disease can be treated by balloon angioplasty - a procedure used to widen blocked or narrowed coronary arteries. This involves inserting a catheter into the artery then using a balloon to stretch the artery. It can also involve inserting a stent - a wire mesh tube which is left permanently to hold the blood vessel open so blood can flow more freely.
25
What are the meninges?
The meninges are tough finrosis membranes that surround the brain, below the skull. The meninges are the dura mater, arachnoid mater and pia mater. There is cerebrospinal fluid within the subarachnoid space (between the arachnoid and pia mater). A bacterial infection in the CSF is called meningitis - this causes increased pressure in the brain leading to seizures and loss of consciousness.
26
Where is the CSF produced?
CSF is produced by specialised epithelial cells called the choroid plexus of each ventricle.
27
Where does the CSF travel to?
The CSF flows through the ventricles into the subarachnoid space via the median and lateral apertures. Some CSF flows through the central canal of the spinal cord. CSF flows through the subarachnoid space. CSF is absorbed into the dural venous sinuses cia the arachnoid villi.
CSF passes into veins via valves at the top of the skull - arachnoid villus.
28
Whats the purpose of CSF?
The brain is floating in CSF hence it cushions the brain against damage.
29
What affects the changes in circulation of CSF around the brain?
The circulation of CSF around the brain is driven by changes in circulation, respiration and posture.
30
Whats the blood brain barrier?
Blood vessels dive deep into the brain - the capillaries contain very tight juctions which are impermeable to many substances. This protects the brain, but does mean its more difficult to get drugs and proteins into the brain. The exception is lipophilic molecules like alcohol and anaesthetics.
31
Why does the brain require a constant blood supply?
The brain has no stored glycogen and therefore requires a constant supply of oxygen and glucose - damage would occur within minutes without this.
32
Would happens if the blood supply is cut off?
A loss of blood supply would cause death of neurons - this is what happens in a stroke.
33
What are the 2 major fluid compartments of the body?
Intracellular = 28L
Extracellular:
- Interstitial = 11L
- Plasma = 3L
34
Whats the function of the interstitial fluid?
The interstitial fluid acts as a reservoir that can supply or recieve fluid from the plasma.
35
Whats the characteristic of the capillary walls?
The capillary walls are highly permeable to water and most plasma solutes (not plasma proteins) allowing movement of molecules between the plasma and interstitial fluid.
36
Explain the process of filtration in the capillaries.
In the presence of a hydrostatic pressure, the capillary wall behaves like a porous filter, allowing protein free plasma to move by bulk flow from capillary plasma to interstitial fluid through water filled channels.
37
Explain the process of absorption in the capillaries.
The plasma proteins (colloids) are unable to move through capillary pores and have a low concentration in the interstitial fluid. This difference in protein concentration means the water concentration of plasma is slightly lower than interstitial fluid. This creates a colloidal osmotic pressure causing the flow of water from the interstitial fluid into the capillary.
38
If the body fails to regulate fluid compartments, whats the consequence?
Oedema - an abnormal accumulation of fluid in the interstitial fluid.
39
How can heart failure lead to oedema?
Heart failure causes increased venous pressure which reduces blood flow out of the capillaries, the increased capillary hydrostatic pressure causes excess filtration and accumulation of interstitial fluid.
40
Whats osmosis?
Osmosis is the net diffusion of water accross a selectively permeable membrane from a region of high water concentration to low water concentration. (low particle concentration to high particle concentration).
41
How is the total number of particles in a solution measured?
In terms of osmoles - 1 osmole = 1 mole of solute particles in 1L.
42
How is equilibrium reached accross a cell membrane for both a fully permeable and semi permeable membrane?
With a fully permeable membrane, both water and solute molecules will diffuse accross the membrane until equilibrium is reached - concentrations are balanced.
With a selectively permeable membrane, only water can diffuse hence it will move until equilibrium is reached - this will result in equal concentrations but different volumes.
43
Whats the permeability of cell membranes?
Cellular membranes are permeable to water but impermeable to solutes. Osmosis determines distribution of water - osmotic pressure is the pressure required to prevent osmosis.
44
How is the balance of ions maintained between fluid compartments?
There are differential levels of cations and anions in intracellular and extracellular compartments - the balance is maintained by active transport.
45
Whats the concentration of the intracellular and extracellular fluid?
300mM - the extracellular fluid is isotonic.
46
Why does the concentration of the extracellular media affect the cell size?
If there is a difference in concentration between extracellular and intracellular fluid, fluid will rapidly transfer accross cell membranes to establish osmotic equilibrium. If extracellular > 300mM - its hypertonic and cell will shrink.
If extracellular < 300mM - its hypotonic and cell will swell.
47
Whats colloidal osmotic pressure?
The concentration of plasma proteins is much higher in the capillaries then the interstitial fluid - this exerts a colloidal osmotic pressure, drawing water back into the plasma.
48
Whats hydrostatic pressure?
Hydrostatic pressure is the force exerted by the blood upon the capillary walls - it drives blood from plasma to interstitial fluid. Pressure drops as blood moves through the capillaries.
49
Whats the net filtration pressure (NFP)?
The overall movement accross the capillary membrane is determined by the capillary net filtration pressure.
50
How does NFP vary along the capillary?
In the arterial end of the capillary, hydrostatic pressure = 35, it therefore dominates and NFP = 10 meaning there is net filtration out of the capillary.
In the venous end of the capillary, hydrostatic pressure = 15, the colloidal osmotic pressure therefore dominates and NFP = -10 hence there is net filtration into the capillary.
51
The lymph system is a parallel vascular system - whats its two major functions?
Draining fluid from the tissues and returning it to the cardiovascular system.
Maintenance of the immune system.
52
Explain how the drainage of the lymphatic system works.
8L of fluid a day passes from the blood into the interstitial area, surrounding cells in tissues. Excess fluid passes into lymph capillaries through lymph nodes before passing back to the bloodstream at the neck (largest is thoracic duct that drains into subclavian vein).
Lymph vessels contain valves and fluid is forced along by action of muscles and breathing. Larger lymph vessels are surrounded by smooth muscle that contract spontaneously and are driven by pacemaker cells.
53
Explain the role of the lymphatic system in immunity.
Lymph fluid contains white immune blood cells (lymphocytes, macrophages and dendritic cells).
The lymph system collects antigens (proteins produced by pathogens) - antigens are recognised by beta lymphocytes in lymph nodes leading to activation of immunity. Beta cells proliferate to produce antibodies - lymph nodes also contain multiple other immune cells.
54
How can heart failure lead to oedema?
Heart failure can lead to excessive water retention in the kidneys. This causes increased arteriolar resistance and high venous pressure which increases filtration and therefore leads to excess interstitial fluid.
55
What else can cause oedema?
A reduction in plasma proteins decreases colloidal osmotic pressure hence increasing the volume of interstitial fluid causing oedema. This can be caused by:
- loss of proteins in urine due to kidney failure.
- loss of proteins in burns.
- malnutrition.
56
If the lymph nodes get blocked the interstitial fluid can also build up causing oedema. What could cause this blockage?
Cancer, surgery, infection.
57
Whats intracellular oedema?
Intracellular oedema is when there is net movement of water into cells, causing the cell to swell.
58
How could intracellular metabolism occur?
Depression of metabolic systems of the tissues and lack of adequate nutrition to the cells.
For example, ischaemia - reduced activity of sodium pump leads to accumulation of sodium in cells causing osmosis of water into cells.
59
How is cardiac output calculated?
heart rate x stroke volume
60
What affects cardiac output?
Cardiac output = 5L/min, this decreases during sleep but is increased dues= to excitement, stress, pregnancy and excercise.
61
What drives heart rate?
Waves of electrical activity causing cardiac muscles to contract.
62
What are the two cells of the heart involved in heart rate?
Cardiomyocytes are the cardiac muscle cells which contract.
Pacemaker cells control the heart rate by producing electrical impulses know as action potentials - there are two pacemaker cells in the heart: the sinoatrial node and the atrioventricular node.
63
Describe the sequence of cardiac excitation.
The sinoatrial nde produces an action potential causing atrial excitation and activating the atrioventricular node. The action potential then spreads down the bundle of his (down the interventricular septum), then to the purkinje fibres of the right and left ventricles to produce a coordinated contraction of the ventricles.
64
What triggers the action potential of the SA node?
The pacemaker cells of the SA node have a low resting membrane potential of around -60. Sodium leakage leads to depolarization hence creating an action potential.
65
What causes the spontaneous action potentials?
Sodium ions leaking in through the F-type (funny) channels and calcium ions moving in through the T-type (transient) channels cause a threshold graded depolarization.
The rapid opening of voltage gated calcium L-type channels is responsible for the rapid depolarization phase.
Reopening of potassium channels and closing of calcium channels are responsible for the repolarization phase.
66
Whats the overall driver of heart rate?
Many heart cells demonstrate intrinsic rhythm but the overall driver of heart rate is the SA node. The SA node works at roughly 100 beats per minute.
67
Whats the mechanism of contraction of ventricular cardiomyocytes?
The rapid opening of voltage gated sodium channels is responsible for the rapid depolarization phase. The prolonged plateau of depolarization (contraction) is due to the slow opening of voltage gated calcium channels and closure of potassium channels. Opening of the potassium channels results in the repolarization phase.
68
How does calcium produce contraction of the cardiac muscle?
Through excitation-contraction coupling in cardiac muscle.
69
Whats the refractory period?
The refractory period is the time required before it is possible to restimulate muscle contraction. Cardiac muscle has a prolonged refractory period to allow the ventricles to fill with blood prior to pumping.
70
Whats the influence of the autonomic nervous system on heart rate?
The parasympathetic nervous system regulates the heart rate as the vagus nerve connects to the SA node hence reducing heart rate.
The sympathetic nervous system also connects to the SA node via the sympathetic ganglia - it can therefore increase heart rate (and regulate force/stroke volume) if required.
Both the sympathetic and parasympathetic nerves are tonically active - at rest the parasympathetic nervous system dominates reducing heart rate from 100 to 70.
71
How does the parasympathetic nervous system lower heart rate?
Parasympathetic neurons release acetylcholine which act on m2 muscarinic receptors on the SA node hence increasing K+ efflux and decreasing calcium influx. This hyperpolarizes the cell and decreases the rate of depolarisation hence decreasing heart rate.
Bradycardia = lower heart rate than normal.
72
How does the sympathetic nervous system increase heart rate?
Sympathetic neurons release noradrenaline which act on B1 adrenergic receptors of the SA node hence increasing calcium and sodium influx which increases the rate of depolarisation hence increasing heart rate.
Tachycardia = heart rate higher than usual.
73
Whats an ECG?
Electrocardiogram - an ECG measures thr electrical activity of the heart and can be used to identify a number of cardiovascular disorders from certain features.
ECG is a summation of the spread of action potentials through the various sections of the heart.
74
What are the electrical events of the cardiac cycle seen in an ECG?
P wave = atrial depolarization
PQ segment = conduction through AV node and AV bundle.
Q
R wave = action potential spreads through purkinje fibres.
S wave
ST segment = ventricles contract
T wave = ventricular repolarisation
75
Whats a sinus arrhythmia?
A sinus arrhythmia is when the heart rate changes with respiration.
Upon inspiration, activity of vagus nerve decreases hence heart rate increases - this can be noticed by quicker ECG.
Upon exhalation, activity of vagus nerve increases hence heart rate decreases - this can be seen by slower ECG.
76
Whats a ventricular ectopic beat?
This is caused by irregular firing of the myocytes in the ventricles hence it becomes ill synchronised and fails to eject blood - this is common after heart attacks.
77
Whats a heart block?
An abnormal heart rhythm where the electrical signals telling the heart to contract are partially or totally blocked - this can be caused by fibrosis or ischaemic heart disease. (some P waves wont be followed by the rest of the cycle).
78
Whats a third degree heart block?
When there is a complete failure of conduction from atria to ventricles hence they beat independently. In this case a pacemaker is required - a device which stimulates the heart muscle, regulating contractions.
79
Whats ventricular fibrillation?
This is when fibrillating ventricles cannot pump blood due to random firing of heart. It is caused by myocardial infarction, electric shock, drug intoxication and impaired cardiac metabolism. It is fatal and treated with CPR followed by electronic defibrillation.
80
Where are atrioventricular valves located?
AV valves separate the ventricles and the atrium.
81
Where are semilunar valves located?
Semilunar valves separate the ventricles from the arteries.
82
What causes the opening/closing of valves?
Pressure changes in the 4 compartments of the heart leads to the opening/closing of valves. (mainly pressure changes in ventricles rather than atria).
83
Whats systole?
Systole = ventricular contraction and blood ejection.
84
Whats diastole?
Diastole = ventricular relaxation and blood filling.
85
What do we measure when measuring blood pressure?
We measure blood pressure in the systemic arteries, expecting a reading of around 120/80.
86
Systole is part of the cardiac cycle in which ventricular contraction and blood ejection occurs. What are the 2 phases it occurs in?
Isovolumetric ventricular contraction - the ventricles are contracting but all the valves in the heart are closed so no blood is ejected - ventricular volume is constant. The ventricular walls are developing tension increasing the ventricular pressure.
Ventricular ejection - Once the increasing pressure in the ventricles exceeds that in the aorta and pulmonary trunk, the aortic and pulmonary valves open and blood is ejected out as the contracting ventricular muscle fibres shorten.. The volume of blood ejected from each ventricle during systole is called the stroke volume.
87
Diastole is part of the cardiac cycle where ventricular relaxation and blood filling occurs. What 2 stages does this occur in?
Isovolumetric ventricular relaxation - The ventricles begin to relax and the aortic and pulmonary valve closes. The AV valves are also closed so no blood is entering the ventricles.
Ventricular filling - The AV valve opens and ventricular filling occurs as blood flows in from the atria. After most of the ventricular filling has taken place, atrial contraction occurs at the end of diastole.
88
Heart sounds heard through a stethoscope are caused by the closure of heart valves. Whats the typical sound heard?
lub - closure of AV valves - onset of systole.
dub - closure of pulmonary and aortic valves - onset of diastole.
Cardiac defects can be detected using a stethoscope.
89
Central venous pressure affects end diastolic volume which in turn will affect stroke volume.
What factors affect central venous pressure (CVP).
Respiration - inspiration increases CVP whilst expiration decreases CVP.
Sympathetic nerves produce noradrenaline which acts on beta-adrenergic receptors causing contraction of central and peripheral veins which increases CVP.
Gravity - when standing gravity leads to pooling o blood in legs and reduces volume and CVP.
Blood volume - Reduced blood volume leads to reduced CVP.
90
Whats the Frank Sterling mechanism?
The ventricles will contract with more force if it contains more blood - if end diastolic ventricular volume increases, stroke volume will increase. The Frank Sterling mechanism is determined by length tension relationship in the muscle - the greater the stretch the more tension will develop in the cardiac muscle.
91
Whats the purpose of the Frank sterling mechanism?
It maintains a balance between the right and left sides of the heart - this stops accumulation of blood in the lungs.
92
How is stroke volume regulated?
Sympathetic nerves regulate stroke volume - sympathetic neurotransmitter norepinephrine acts on beta-adrenergic receptors to increase ventricular contractility - the strength of contraction at eny given end diastolic volume.
Noradrenaline:
- Increases force and speed of cardiac muscle contraction.
- Increases ventricular contraction at any given end diastolic ventricular volume.
93
What can cause heart failure?
arterial pressure opposing ejection - hypertension makes it more difficult to open the valves and eject blood - this can cause heart failure.
94
Whats congestive heart failure?
Congestive heart failure is characterised by reduced cardiac output. Symptoms include tiredness, shortness of breath, fluid retention to increase cardiac output (venous return).
95
Whats chronic left ventricular failure? Both systolic dysfunction and diastolic dysfunction.
Systolic dysfunction - coronary artery disease leading to ischaemic heart disease and myocardial infarction. Following a heart attack heart muscle will be damaged so there will be reduced ventricular contractility and therefore a reduced stroke volume.
Dystolic dysfunction - hypertension. High blood pressure increases arterial pressure and cardiac resistance hence increasing ventricular muscle. This causes stiffening of ventricular wall which lowers the end diastolic ventricular volume hence decreasing the stroke volume.
96
What is Pouseuilles law?
The law describes the factors that determine the flow through a tube in terms of pressure, flow and resistance.
Flow is proportional to the pressure gradient and inversely proportional to resistance.
97
How can pouseuilles law be applied to blood flow?
Cardiac output = Blood pressure/peripheral resistance
98
How is blood flow measured?
From a region of high pressure t a region of low pressure so the change in pressure is always positive.
99
How is flow related to absolute pressure?
Flow is independent of the absolute pressure. A pressure difference is needed to allow blood flow.
100
How is flow related to length?
Flow is inversely proportional to the length - as length increases so does the resistance and theres therefore less flow. However in the body, the length remains constant and therefore does not affect flow.
101
How is flow related to viscosity?
Flow is inversely proportional to viscosity - the higher the viscosity, the more resistance and therefore the less flow.
102
What causes blood viscosity to change?
Viscosity is related to the hematocrit as erythrocytes make the blood thicker. This can occur from:
- Dehydration
- High altitude
- Erythropoietin - stimulates red blood cell production.
Viscosity remains constant under physiological conditions and therefore does not control blood flow.
103
How is flow affected by radius?
Flow is directly proportional to radius^4 hence increasing radius by two fold would increase flow by 16 fold. Therefore, the radius of the vessel is the most important factor in determining flow.
The radius of blood vessels can be regulated by smooth muscle.
104
Whats total peripheral resistance?
Total peripheral resistance is the sum of the resistance of all the blood vessels and determines blood pressure.
105
Briefly describe the different structures of the blood vessels.
Arteries have thick muscular walls which acts as a pressure reservoir.
Arterioles have thin muscular walls which regulate blood pressure and blood flow to organs.
Capillaries are comprised of a single layer of endothelial cells with a small diameter and large surface area allowing gas nutrient and waste exchange.
Venules and veins have thin compliant walls with a large diameter allowing them to hold a large volume with low resistance and valves to aid the return of blood to the heart.
106
What is total peripheral resistance primarily regulated by?
The arterioles.
107
How can the arterioles determine blood flow to individual organs?
Arterioles can determine the blood flow to individual organs through radius/resistance of the arterioles. The smooth muscle can contract to allow less blood flow or relax to allow more blood flow to the organs.
108
How do the arteries change with systole/diastole?
Systole is when the ventricles contract and eject blood hence the arteries stretch to decrease pressure.
Diastole is when the ventricles relax and fill with blood so the arteries passive recoil (relax).
109
How can blood pressure be measured directly?
Blood pressure can be directly measured by cannulating an artery and measuring the pressure with a transducer. This is very accurate but not very convenient as its invasive.
110
How can blood pressure be measured using a stethoscope?
Cuff attached to arm and pumped up so pressure is greater than 120 - greater than systolic pressure hence artery is completely occluded so there is no sound.
Release pressure - once you begin hearing sounds the cuff pressure is below systolic - ttake measurement off sphygomanometer.
Once the noise stops it has reached diastole so take measurement from sphygomanometer - this is because vessel is now open hence theres no turbulence.
111
Whats the name of the noises heard between the systolic and diastolic blood pressures?
Korotkoff sounds - caused by opening and closing of artery.
112
What causes the pulse?
The pulse is caused by vibration of the arteries caused by ejection of blood from the heart into the systemic circulation.
113
Where can pulse be measured?
Radial artery or the carotid artery.
114
Whats the pulse pressure?
The difference between systolic and diastolic blood pressure. This is typically 120-80 hence its 40.
115
Whats the mean arterial pressure?
Average pressure over the cycle. As the diastole is twice as long as the systole, the MAP = diastole + 1/3 systole.
116
What factors affect pressure?
Height, density and gravity.
117
Blood pressure is affected by posture (gravity). How can this cause fainting?
When standing, theres an increased mean arterial presure in the legs leading to pooling of blood in the veins and lack of blood going to the brain. This is why you faint if your stood up for too long - its to make your head level with your heart (which is at zero pressure point) to allow flow of blood.
This is also why when you stand up you can initially feel faint.
118
How does gravity affect blood gradient?
The venous and arteriial blood is at the same height of the body hence the blood gradient is consant and blood flow continues.
119
What are the issues with having high blood pressure?
- Can cause a stroke if a blood vessel ruptures.
- Can cause a myocardial infarction if a coronary blood vessel ruptures.
- Heart failure
- Chronic kidney failure.
120
How is mean arterial pressure regulated?
By baroreceptors - baroreceptor neurons function as sensors in the homeostatic maintenance of mean arterial pressure - they are located in the aortic arch and carotid sinuses where they monitor pressure. They are located in thinner walls that can be stretched by pressure. Baroreceptor nerve endings are sensitive to stretch and pressure in the arteries.
The rate of baroreceptor nerve firing is proportional to magnitude and changes in the mean arterial pressure.
Baroreceptors can only act as a short term sensor of blood pressure.
121
Explain the biological process by which baroreceptors regulate blood pressure.
Afferent neurons travel from the baroreceptors to the brain stem where actions are coordinated by the medulla oblingata (medullary cardiovascular centre). The brain can then react to this information by altering heart rate, stroke volume or vessel diameter in order to change the blood pressure. The arterial baroreceptors act as part of a negative feedback system.
122
How is mean arterial pressure (MAP) affected by the autonomic nervous system?
The sympathetic nervous system increases MAP.
Sympathetic nerves are activatedby noradrenaline via B-adrenergic receptors and a-1-adrenergic receptors in arterioles. This increases cardiac output and peripheral resistance.
The parasympthetic nervous system decreases MAP. This is mediated by acetylcholine via muscarinic receptors, inhibiting heart rate.
123
How is the mean arterial pressure (MAP) affected by hormones?
Adrenaline increases MAP whilst angiotensin II and vasopressin increases MAP.
124
Hypotension is a reduction in arterial pressure. What can cause this?
- Loss of blood (hemorrage)
- Stress or emotions (leads to fainting)
- Loss of salts through burns, sweating, diarrhea and vomiting.
125
What happens when arterial baroreceptors detect a decrease in arterial pressure?
Heart rate will increase from decreased parasympathetic discharge to heart and increased sympathetic input.
Veins and arterioles will constrict due to increased sympathetic discharge.
Stroke volume, cardiac output and total peripheral resistance will all increase hence arterial pressure will return to normal.
126
How can standing for a long period of time lead to fainting?
Gravity leads to pooling of blood in the legs causing reduced blood volume and lowering of central venous pressure. There is reduced venous return, reduced end diastolic pressure, reduced stroke volume and reduced blood pressure. The baroreceptor reflex will then compensate.
127
Blood volume is an important long term regulator of mean arterial pressure. Baroreceptors can regulate short term changes in blood pressure, how is blood pressure regulated long term?
The kidneys will regulate blood volume through the renin-angiotensin system hence regulating MAP.
128
How is local flow regulated?
Local flow is regulated by both local, neuronal and hormonal factors - these influence the radius of the arteriole affecting resistance and flow.
129
How can local blood flow to organs be regulated?
Myogenic response - vasoconstriction of arterioles caused by smooth muscle - this occurs in brain, kidney and heart - not skin.
Vasodilation is induced by metabolites: decreased oxygen, increased co2, increased H+ adenosine K+ and osmolarity.
Autocoids - histamine, bradykinin, prostaglandins - released as a result of inflammation and bleeding.
Endothelial cells release paracrine factors: nitric oxide and prostacyclin causing vasodilation, endothelin - 1 causes vasoconstriction.
130
Whats active hyperemia?
Increased metabolic activity of organ/tissue decreases oxygen levels and increases metabolites in organ interstitial fluid causing arteriolar dilation in organ and increased blood flow to organ.
131
Whats flow autoregulation?
Reduced arterial pressure in organ causes reduced blood flow to organ which decreases oxygen and increases metabolites and decreases vessel wall stretch in organ. This causes arteriolar dilation in organ which restores blood flow to normal in the organ.
132
To summarise, what factors cause vasodilation?
CO", K+, H+, osmolarity, adenosine, eicosanoids, bradykinin, nitric oxide and decreased oxygen levels.
133
How are arterioles under neural control?
Sympathetic nerves release noradrenaline which acts on a1 adrenergic receptors causing vasoconstriction, and acts on b-adrenergic receptors in skeletal muscle to cause vasodilation.
134
How do arterioles in the skin change with temperature?
In the cold sympathetic discharge is increased and arterioles vasoconstrict to divert blood to essential organs.
In the heat, sympathetic discharge is reduced and arterioles vasodilate so there is increased blood flow to skin to facilitate cooling.
135
What hormones control arterioles?
Adrenal medulla can increase plasma adrenaline - this can act on a1 adrenergic receptors to cause vasoconstriction or b2 adrenergic receptors to cause vasodilation.
Angiotensin II causes vasoconstriction.
Vasopressin (ADH) from the posterior pituitary gland causes vasoconstriction.
Atrial natriuretic peptide from the cardiac atria causes vasodilation.
136
How does excercise affect the cardiovascular system?
During excercise the body needs to boost oxygen uptake and carbon dioxide removal hence there is increased cardiac output. This increases blood flow to muscle, heart and skin (affecting peripheral resistance). The body will try to stabilise arterial blood pressure despite these changes.
When you begin excercise your brain will activate these changes.
137
What happens during strenous excercise?
Your body will increase blood flow to skeletal muscle, skin and the heart via vasodilation of arterioles.
Your body will decrease blood flow to non-essential organs like the kidneys and abdominal organs through vasoconstriction of the arterioles.
138
Whats the valsalva manouvre?
Forced expiration against a closed or narrow airway leads to an increase in intrathoracic pressure which decreases central venous pressure and end diastolic ventricular volume this causes the frank sterling mechanism: stroke volume decreases, cardiac output decreases, MAP decreases, firing of baroreceptors decreases and then heart rate increases. This explains why some people have a heart attack when coughing etc.
(valsalva manouvre = way of breathing that increases pressure in chest)
