Cardiovascular system Flashcards

Question

What are the volumes associated with the cardiac cycle?

Answer 1

- End-diastolic volume = 120ml (100ml [~80%] passive, 20ml [~20%] atrial systole). - End systolic volume = 40ml (~30% EDV). - Stroke volume = 80ml (~70% EDV). - The SV:ESV ratio is the ejection ratio.

Answer 2

- The "lubb" sound is caused by closing of the atrioventricular valves. - The "dubb" sound is caused by the closing of the semilunar valves.

Answer 3

Despite the aortic pressure being greater than the ventricular pressure, ventricular blood still possesses more overall mechanical energy than aortic blood (especially kinetic energy). This means that blood flows down mechanical energy gradient from ventricles into the aorta against pressure gradient.

Answer 4

1. Atrial systole occurs before ventricular systole and causes the a wave. 2. The c wave occurs immediately after the beginning of ventricular systole during isometric contraction of the ventricles, which compresses the atria and causes a transient increase in pressure. 3. The v wave begins to rise immediately after the isometric contraction phase, as the atria begin filling up with blood and the pressure increases as the AV valves are closed.

Answer 5

- As heart rate increases, ventricular systole shortens by small amounts. - Ventricular diastole shortens significantly, giving less time for the heart to fill, decreasing EDV and SV. - If heart rate > 180 bpm, cardiac output begins to decrease (although this is rarely physiological and main limit to CO is still VR).

Answer 6

Work done by the heart during each heart beat.

Answer 7

1. Fick's principle: Gold standard 2. Doppler effect: Use ultrasound to measure velocity of blood. 3. Bio-impedance: Blood vessel put in strong magnetic field. Flow of blood produces voltage proportional to rate of flow. 4. Thermodilution

Answer 8

- Fick's principle and thermodilution are more accurarte methods, but are also slow to respond to changes. They are also invasive so are usually only used to measure steady-state CO. - Doppler and bio-impedance are more responsive, but are less accurate, so are used to measure immediate CO.

Answer 9

- PRU = mmHg∙ml^-1∙s - 1 PRU is a vessel with resistance that results in a flow of 1 ml∙s^-1 (in ml∙s^-1) generated between 2 points with pressure difference of 1 mmHg.

Answer 10

1. Flow from the aorta to the foot: Aortic pressure ~90 mmHg while pressure in foot ~180 mmHg. 2. Flow out of the left ventricle into the aorta in the last 1/3 of ventricular systole is against pressure gradient. 3. Pressure is low at the stenosed vessel despite being high in the left ventricles.

Answer 11

Flow between point A and point B in the steady state is proportional to the difference in the fluid's mechanical energy.

Answer 12

- Pressure decreases as blood enters narrower vessels. - This is because flow needs to increase in narrower vessels to compensate for narrower diameter. - Velocity increases, so pressure energy converted to kinetic energy in order to increase velocity (GPE stays constant).

Answer 13

- As velocity of blood is increased, more turbulent flow occurs and more energy is lost as heat. - When the vessel widens again, the pressure energy is lost and cannot be recovered, resulting in a permanent drop in blood pressure.

Answer 14

- The blood in the aorta has more potential and pressure energy compared to blood in the aorta. - However, contraction of the heart gives ventricular blood more momentum, so it has more kinetic energy compared to aortic blood and more mechanical energy in total.

Answer 15

- Blood in the feet are lower down compared to aortic blood. A lot of its pressure energy comes from GPE being converted into pressure energy, so blood in the feet have much less GPE compared to aortic blood. - Aortic blood in total, has more mechanical energy than blood in feet, so blood flows from aorta to feet, even against pressure gradient.

Answer 16

- Shearing effect means that red blood cells are concentrated to the centre of the vessel. - This minimises the interactions between red blood cells and the vascular endothelium.

Answer 17

- Minimises friction between red blood cells and vascular endothelium, reducing amount of energy needed to drive blood flow through narrow vessels. - Minimises possibility of red blood cells sustaining damage while flowing through vessels, and decreasing the chance of thromboses forming.

Answer 18

Turbulent flow is proportional to square root of pressure gradient.

Answer 19

Single-file flow

Answer 20

% RBC content in blood

Answer 21

- Turbulent flow damages the vascular endothelium. | - This can lead to formation of plaque, which increases the chance of clots forming via positive feedback mechanism.

Answer 22

1. Plasma proteins. | 2. Red blood cells (haematocrit) - Main determinant.

Answer 23

- Higher pressure needed in order to drive same flow rate. | - More work needs to be done by the heart, which increases the chance of having heart attack.

Answer 24

- Fall in total peripheral resistance, which decreases the mean arterial pressure. - This could result in shock. - More work needs to be done by the heart in order to maintain adequate MAP to perfuse tissues and prevent shock by producing higher CO.

Answer 25

- Blood in blood vessels with diameters

Answer 26

- Single file flow requires that red blood cells become slightly deformed. - Conditions that prevent this from happening, e.g. sickle-cell anaemia, disrupt blood flow in capillaries.

Answer 27

1. Lots of them in parallel. | 2. Fåhraeus-Lindqvist effect reduces viscosity of blood flowing though capillaries.

Answer 28

1. It shows that for a given pressure, the tension that needs to be withstood by arterial walls increase as the radius increases. This means that larger vessels (e.g. aorta) needs to have thicker walls compared to smaller vessels in order to withstand same pressure. 2. Under La Place's law, even a slight contraction of the arteriole smooth muscles would lead to positive feedback mechanism causing total collapse of the vessel. This is only avoided by the fact that the vessels are resistant to collapse.

Answer 29

- Inertia left from blood being ejected from the heart during ventricular systole. - Muscle pump: Blood being 'squeezed' back to the heart from the lower parts of the body. Valves in the veins prevent backflow of blood. - Respiratory pump: Contraction of the diaphragm during respiration decreases intra-thoracic pressure and increases intra-abdominal pressure.

Answer 30

- The veins have very high compliance. - High blood pressure in the lower parts of the body means that the walls of the veins expand and blood pools in the lower parts of the body, which effectively removes it from the circulation and decreases VR. - This is countered by venoconstriction and the muscle pumps. - Absence of muscle pumping when standing still for extended periods of time causes a drop in CO, leading to drop in MAP and loss of consciousness.

Answer 31

- Preload: Blood reservoir was raised/lowered physically in order to in increase/decrease preload. - Afterload: Windkessel was used. This was an air chamber surrounding a rubber tubing. Pressure could be changed in the chamber in order to change the diameter of the rubber tubing and thus vary the resistance to blood flow out of the heart.

Answer 32

The Frank-Starling mechanism states that the greater the preload on the heart, the greater the stroke volume and thus the greater the cardiac output.

Answer 33

The stretching force (wall tension) experienced by cardiac myocytes in the walls of the heart (mainly left ventricle) prior to contraction. This is proportional to the end diastolic pressure via La Place's law.

Answer 34

↑ Venous return → ↑ End-diastolic pressure → ↑ End-diastolic volume → ↑ Preload → ↑Contractility → ↑ Stroke volume → ↑ CO

Answer 35

- Key mechanism is still the sliding filament model used to describe the length-tension relationship in skeletal muscles. That is, when cardiac muscle is not stretched, the actin filaments overlap with each other and disrupt cross-bridge cycling. When the muscle is stretched, there is a better overlap between actin and myosin, resulting in more cross-bridges formed and thus more tension generated.

Answer 36

- The length-tension relationship in cardiac muscle is much steeper than skeletal muscles. - Additional mechanisms are responsible for this steepness, including the lattice spacing and Ca2+ sensitivity increase.

Answer 37

- Intrinsic mechanism to ensure that VR is matched with CO, preventing a build-up of blood in the venous system which may otherwise result in oedema. - It is also responsible for maintaining constant CO despite variations in TPR.

Answer 38

- When TPR increases, afterload increases, which increases the force the heart needs to pump blood against. - Initially, this decreases the stroke volume, which increases end-systolic volume and thus increases end-diastolic volume in the next stroke (assuming VR is constant). - By the FSM, this increases the stroke volume and thus increases the contractility of the heart, allowing more blood to be pumped out of the heart despite increased resistance, thus maintaining a constant CO.

Answer 39

- Sympathetic: 1:10 | - Parasympathetic: 1:3

Answer 40

- α1 (NAd): Vasoconstriction - α2 (non-selective): Pre-synaptic receptors - β1 (non-selective): Heart and intestinal smooth muscle - β2 (adrenaline): Bronchi and vascular smooth muscle (dilation)

Answer 41

- Pre-ganglionic fibres are usually myelinated type-B fibres. - Post-ganglionic fibres are usually unmyelinated type-C fibres.

Answer 42

- Parasympathetic nerve terminals are similar to NMJs. | - Sympathetic nerve terminals are varicosities.

Answer 43

Continual basal firing rate in the nervous system.

Answer 44

There is usually less parasympathetic tone compared to sympathetic tone, except in the heart where it is required to depress heart rate.

Answer 45

- Re-uptake into pre-synaptic terminal and storage into vesicles until ready to be re-released. - Uptake into effector cells (e.g. smooth muscle) at post-synaptic terminal and breakdown by monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT).

Answer 46

- Sympathetic fibres innervate the whole of the heart while parasympathetic fibres mainly innervate the SAN and AVN. - Sympathetic stimulation has large effects on heart rate and stroke volume while parasympathetic stimulation mainly affects heart rate and not so much stroke volume.

Answer 47

- Intrinsic control mechanisms, like the FSM, are much slower to respond compared to ANS-mediated extrinsic control. - ANS coordinates feed-forwards control. - ANS coordinates whole body response, ensuring that intrinsic mechanisms (which are isolated) don't cause any adverse effects on the body as a whole.

Answer 48

CO = HR x SV

Answer 49

- The heart is not the limiting factor of CO, but is essential in maintaining it. - At rest, if the pumping capacity of the heart is increased, the CO remains fairly constant. - If the pumping capacity of heart is decreased, the CO drops substantially.

Answer 50

The pressure that would be present in the circulation if the pumping capacity of the heart were to be removed.

Answer 51

- The heart is unable to change the overall pressure in the system, so it does not affect MSFP. - Instead, it is able to 'shift' pressure from one area to another, creating high pressure in the arteries while maintaining low pressure in the veins. - The pressure in the veins cannot drop below 0 mmHg as that is lower than atmospheric pressure and would cause venous collapse. - When CO increases too much and causes venous pressure to drop below 0, the veins collapse and limits VR, thus limiting CO.

Answer 52

At rest, the pumping capacity of the heart is capable of producing much higher CO than it does. It is only being limited by the amount of VR capable.

Answer 53

1. Increasing TBV | 2. Decreasing volume of circulation (i.e. venoconstriction)

Answer 54

By filling the circulation beyond unstressed volume into the stressed volume.

Answer 55

Because the arteries are much less compliant than the veins, shifting a volume of blood from the veins into the arteries increases arterial pressure much more than it decreases venous pressure. Consequently, a much greater pressure gradient can be created between arterial and venous side before venous pressure drops below 0 mmHg.

Answer 56

They contain ~60% TBV.

Answer 57

Increasing TBV increases the amount of blood in the stressed volume, thus increasing MSFP.

Answer 58

Venoconstriction maintains constant TBV, but increases the proportion of stressed volume in comparison to the unstressed volume.

Answer 59

- Collective term reflecting all of the difficulties faced by venous blood in returning to the heart. - It can be decreased by the action of the muscle and respiratory pump.

Answer 60

- In cardiac failure, the pumping capacity of the heart decreases, which causes a decrease in MAP. - The body responds by venoconstriction, in an attempt to increase MSFP and thus CO. However, the heart is unable to accommodate for this increase in VR so RAP increases. - This increases capillary hydrostatic pressure, leading to oedema.

Answer 61

MAP is too low in order to maintain adequate perfusion of tissues in the body.

Answer 62

- Hypovolaemic shock (↓MSFP → ↓CO) - Cardiogenic shock (↓SV → ↓CO) - Distributive shock (↓TPR → ↓CO) - Obstructive shock (inadequate local perfusion, e.g. emboli)

Answer 63

- Septic shock: Systematic vasodilation as a result of secretion of vasodilatory agents by pathogens in the blood. - Neurogenic shock: Systematic vasodilation as a result of loss of sympathetic innervation. - Anaphylactic shock: Systematic vasodilation as a result of secretion of vasodilatory agent in response to allergic reaction.

Answer 64

- Constant pressure/variable flow system. - This system ensures that despite not being able to directly measure flow, the body is able to vary local resistance in order to control flow.

Answer 65

1. High pressure baroreceptors 2. Low pressure baroreceptors 3. Chemoreceptors

Answer 66

- Aortic sinus (vagus nerve) | - Carotid sinus (glossopharyngeal nerve)

Answer 67

1. When MAP too high, there is increased stretch on the HPBs. 2. This causes an increase in firing rate of the HPBs, which stimulate afferent sensory fibres innervating them.. 3. Sensory fibres transmit signal into NTS (Nucleus Tractus Solitarius) in the medulla and stimulate inhibitory interneurones. 4. Inhibitory interneurones inhibit sympathetic neurones via vasomotor centre and decrease sympathetic tone. 5. Excitatory interneurones excite parasympathetic neurones via the cardioinhibitory centre and increases parasympathetic tone to the heart via the vagus nerve.

Answer 68

- Carotid sinus HPBs are more sensitive compared to aortic HPBs. - Aortic HPBs are sensitive over a wider range of blood pressures.

Answer 69

- Atria - Junction between atria and great veins - Ventricles - All LPBs are innervated by the vagus nerve

Answer 70

1. Increased RAP as a result of increased MSFP causes increased stretch and firing rates of LPBs, generating signals in afferent sensory fibres. 2. Signals carried to various centres of the medulla via the vagus nerve. 3. Causes a range of responses that all aim to decrease ECF volume by excreting more NaCl and water. 4. This decreases TBV, which decreases MSFP.

Answer 71

- Increased heart rate. - Decreased renal sympathetic tone causing vasodilation of renal vessels and increased rate of NaCl excretion. - Inhibits release of ADH from posterior pituitary. - Possibly inhibition of thirst and sodium appetite.

Answer 72

- Denervation of HPBs has no effect on mean MAP but does increase the variations in MAP values, which emphasises its short-term control over MAP. - The reference value of HPBs reset when exposed to 2+ days of chronic hypertension. This is evident as the firing rate steadily decreases over time until it reaches normal levels despite increased MAP.

Answer 73

- Exercise - Emotions - Pain

Answer 74

Via glutamateric bulbospinal neurones

Answer 75

- Vasoconstriction → ↑TPR → ↑MAP (α1) - Venoconstriction → ↑MSFP → ↑VR → ↑CO → ↑MAP (α1) - ↑HR → ↑CO (β1) - ↑SV → ↑CO (β1) - Adrenaline release (N2 ACh)

Answer 76

They contain higher proportion of β2 compared to α1, which are more responsive to adrenaline and are vasodilators. The balance of adrenaline and sympathetic NAd dictates the state of their vessels.

Answer 77

↑HR and ↑SV (Muscarinic ACh)

Answer 78

There is a positive correlation between blood flow and O2 demand, suggesting that local blood flow is matched to demand.

Answer 79

- The circulation is a constant pressure-variable flow system. - MAP is maintained by feedback systems, allowing local flow to be varied simply by changing the local resistance.

Answer 80

- Local control is usually used to cause vasodilation. | - Systemic control is usually used to cause vasoconstriction.

Answer 81

1. Regulating number of available myosin binding sites on actin. 2. Regulating rate of cross-bridge cycling.

Answer 82

The increase in blood flow to a respiring tissue in response to an increased rate of metabolism.

Answer 83

- PO2 - PCO2 - pH - [K+]e

Answer 84

NO and PGI2 (prostacyclin) released, which are both vasodilators.

Answer 85

Increased stretch on smooth muscles due to increased blood pressure (and thus local flow) increased VSM tone and thus causes vasoconstriction, reducing local flow. This is caused by activation of stretch-activated ion channels.

Answer 86

- Local feedback system involving myogenic and metabolic control. - Keeps local flow constant despite changes is MAP.

Answer 87

- Allows local flow to remain constant despite changes in MAP, matching supply to demand. This is especially important in the kidneys as flow determines GFR. - Counteracts increase in wall tension as a result of increases in MAP, which prevents damage to the arteriolar walls.

Answer 88

1. NO stimulates guanylyl cyclase, which converts GTP into cGMP. 2. cGMP stimulates PKA and PKG. 3. PKA phosphorylates MLCK, which inhibits it. 4. PKG has number of effects: - Promotes SERCA - Promotes K+ channels - Inhibits PM Ca2+ channels - Inhibits Ca2+-release channels

Answer 89

- ACh - Bradykinins - Shear-stress - Majority work by promoting NO synthase

Answer 90

- Metabolic - Myogenic - Paracrine (e.g. NO)

Answer 91

- Sympathetic | - Endocrine

Answer 92

IP3 pathway induces Ca2+ release from SR

Answer 93

cAMP pathway causes phosphorylation and inhibition of MLCK

Answer 94

- Thromboxane A2 is vasoconstrictor produced by platlets. - PGI2 is vasodilator produced by endothelial cells. - Aspirin inhibits COX-1 which is needed to synthesise both substances. - Endothelial cells have nuclei and synthesise more COX-1 and produce PGI2. - Platlets don't have nuclei and cannot synthesis more COX-1, so doesn't produce thromboxane A2. - Increase in [PGI2] and decrease in [thromboxane A2] causes anti-inflammatory effect of aspirin.

Answer 95

Causes vasodilation upstream from point of shear stress.

Answer 96

- O2, CO2 (transcellularly) - Water (trans-/paracellularly) - Solutes (paracellularly)

Answer 97

1. Continuous: Does not allow movement of plasma proteins. 2. Fenestrated: Has holes, or fenestrations, through which plasma proteins can be exchanged. 3. Sinusoidal: Extra wide interendothelial junctions as well as fenestrations allow unobstructed movement of plasma proteins.

Answer 98

1. Substantially increases surface area, maximising efficiency of diffusion. 2. Allows for movement of surrounding tissue without damaging capillaries.

Answer 99

Rate of diffusion = ([X]c-[X]if) x Area/Diffusion distance x diffusion coefficient

Answer 100

- [X]c depends on flow of blood and rate of diffusion. - [X]if depends on rate of diffusion and rate of uptake of X by the tissues. - Area and diffusion distance depends on number of capillaries perfused. - Diffusion coefficient depends on the permeability of the capillaries to X, which can be modified by substances such as cytokines and histamine.

Answer 101

- At the arteriolar end of the capillary, outwards hydrostatic pressure gradient is greater than inwards osmotic pressure gradient, resulting in net filtration of fluid out of capillaries into IF. - At the venous end of capillary, hydrostatic pressure decreases as a result of resistance. Inwards osmotic pressure gradient is greater than outwards hydrostatic pressure gradient, resulting in net reabsorption of fluid from IF into capillaries.

Answer 102

- Pc can be increases as a result of increasing CVP and RAP (e.g. in heart failure), increasing net filtration. - Pc can be decreased as a result of arteriolar vasoconstriction due to sympathetic stimulation.

Answer 103

Haemorrhage → ↓TBV → ↓MSFP → ↓RAP → ↓Pc → ↓Filtration → Net reabsorption of fluid from IF into bloodstream.

Answer 104

- As water is reabsorbed, colloid osmotic pressure in the subglycocalyx space increases and opposes reabsorption. - This results in far less reabsorption than predicted by the Starling equation. - Consequently, there is net filtration across capillaries in most tissues.

Answer 105

- Drains excess fluid filtered out of capillaries in tissues and prevents its accumulation. - Carries proteins lost from capillaries into tissues back into into circulation.

Answer 106

- Lymph vessels contain valves to prevent back flow of lymph. - This also allows lymph to drain back into the circulation via the muscle pump. - Larger lymph vessels have smooth muscles that contract to aid in lymphatic return.

Answer 107

Oedema caused by blockage of lymph vessel.

Answer 108

- ↑Pc (↑RAP, vasoconstriction...) - ↓πc (↓[albumin] due to starvation) - ↑σ (histamine, cytokines) - Disrupted lymphatics drainage

Answer 109

- Systemic oedema: Increases diffusion distance between cells and capillaries, decreasing nutrient/O2 exchange and may lead to ischaemia. - Pulmonary oedema: Causes alveoli to be flooded with IF, which prevents gas exchange and decreases efficiency of gas exchange.

Answer 110

- ↑TPR - Venoconstriction (↑MSFP) - ↑ Heart rate

Answer 111

- Pumping capacity of the heart cannot be increased. | - Treatment is based on counteracting paradoxical responses of body to heart failure.

Answer 112

- β-blockers - Diuretics - ACE inhinbitors

Answer 113

- Blood flow increases as muscle arteriolar resistance decreases in response to increased metabolic activity by vasodilation (functional hyperaemia). - TPR decreases and so there is a significant drop in MAP.

Answer 114

1. Phase 1: Sudden increase in blood flow following the beginning of exercise. 2. Phase 2: Gradual increase in blood flow levelling off at a constant value.

Answer 115

1. Feedforward 2. Functional hyperaemia 3. Endocrine (adrenaline)

Answer 116

1. ↑[K+]e | 2. Muscle pump (↓RvR)

Answer 117

- ↑[K+]e causes hyperpolarisation of smooth muscle PM. - This is due to 2 effects: 1. Less current flow through inward rectifying K+ channels. 2. Increased activity of electrogenic Na+/K+-ATPase. - Hyperpolarisation closes voltage-gated Ca2+ channels, decreasing [Ca2+]i and causing smooth muscle relaxation.

Answer 118

1. ↑[K+]e 2. ↓PO2 3. ↑NO 4. ↓pH 5. Adrenaline

Answer 119

- Cortex and other higher processing centres of the brain. - Coordinates feedforward responses reflecting a decision to exercise. - This may involve the medial pre-frontal cortex.

Answer 120

- Increased sympathetic tone to heart causes ↑HR and ↑SV. Leads to ↑CO. - Increased sympathetic tone to vascular smooth muscle causes vasoconstriction and reduced blood flow to renal and splanchnic circulation. Leads to ↑TPR. - Increased sympathetic tone causes venoconstriction, leading to ↑MSFP. - Stimulation of adrenaline release.

Answer 121

- Muscle pump leads to ↓RvR and thus ↑VR and ↑CO.

Answer 122

Moderate exercise: - During moderate exercise, feedforward mechanisms are so good that there is often no change in MAP, or even an increase in MAP at the onset of exercise. - This would normally cause baroreceptor response to decrease MAP. Central mechanisms ensure this does not occur by resetting the set-point of these baroreceptors. Intense exercise: - Vasodilation in muscles overwhelm the feedforward response and a drop in MAP is experienced. - Baroreceptors mediate the feedback mechanism to restore MAP.

Answer 123

Maximum power output when 2 legs are used is less than double the maximum power output compared to when only 1 leg is used.

Answer 124

1. ↓TBV 2. ↓MSFP 3. ↓VR 4. ↓CO 5. ↓MAP

Answer 125

- ↑HR and ↑SV → ↑CO - ↑ Sympathetic tone → Vasoconstriction in splanchnic/renal/skin → ↑TPR - Venoconstriction → ↑MSFP - Vasoconstriction of renal arterioles → ↓GFR → ↓Urine production - Transcapillary autotransfusion

Answer 126

1. Restore fluid 2. Restore colloid 3. Restore red blood cells

Answer 127

- Stimulation of thirst | - Stimulation of Na+ appetite

Answer 128

Synthesis by the liver

Answer 129

1. Decreased O2 carrying capacity of blood causes release of hypoxia-induced factors. 2. Kidneys stimulated to secrete erythropoetin. 3. Bone marrow stimulated to produce more RBCs.