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Anatomy > Structure and function of the heart > Flashcards

Structure and function of the heart Flashcards

1
Q

what is the ratio of muscle in left to right of heart

A

4-6 times more pressure in left side

3:1 ratio in muscle mass between Left and right

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2
Q

what happens to blood pressure throughout the body?

A

drops once blood leaves the heart

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3
Q

what is capillary mean pressure?

A 
systemic = 17mmHg
Pulmonary = 7mmHg
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4
Q

Conduction of cardiac AP?

A 
intercalated disces
interconnected cardiac muscle cells
secured by desmosomes
linked by gap junctions
propagate action potentials
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5
Q

how are action potentials conducted in cardiac muscle?

A

local changes in currents cause passive depolarisation of adjacent muscle cells through gap junctions

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6
Q

excitation-contraction coupling

A

T tubule transfers action potential into cell
high concentration of calcium in T tubule
calcium moves intracellularly through L type calcium channels and increases intracellular concentration or once calcium has moved from extracellular to intracellular it
binds to ryanodine receptors on sarcoplasmic reticulum which causes release of calcium –> calcium induced calcium release

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7
Q

altering calcium release

A

anything that alters calcium release or storage alters contractility and relaxation

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8
Q

what impacts calcium release or storage?

A

calcium ion channel blockers - non-dihydropyridines
beta blockers - blocks effect of adrenaline and noradrenaline
caffeine

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9
Q

What are the basic mechanics of cardiac contraction?

A 
preload
afterload
contractility
heart rate 
PACE
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10
Q

How to calculate stroke volume?

A

SV = end diastolic volume - end systolic volume

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11
Q

what is end diastolic volume?

A

volume of blood in heart just before contraction

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12
Q

what is end systolic volume?

A

volume of blood after contraction - left over

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13
Q

what is isovolumetric contraction?

A

pressure is changing - contracting but volume is same

valves are closed

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14
Q

preload

A

increases in end diastolic volume leads to increases in myocardial performance/ contractility

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15
Q

why does an increase in EDV cause increased myocardial performance?

A

physical and activating factors

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16
Q

physical factors that increase myocardial performance

A

more optimum myofilament overlapping
decrease lattice spacing - decreased distance between myofilaments so increased probability of interaction between contractile components

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17
Q

activating factors that increase myocardial performance

A

increase in calcium ion sensitivity by multiple mechanisms
increased calcium release
increase calcium sensitivity

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18
Q

what happens if you increase end diastolic volume?

A

increases contractility and increases stroke volume as the volume in the heart increases due to increase in venous return

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19
Q

what is afterload?

A

what the heart has to pump against

higher the pressure in systemic/ pulmonary circulation = more force/ work required by the heart

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20
Q

what happens when there is an increase in end systolic volume?

A

needs to increase pressure in ventricle to meet that in aorta and so increases volume so thre is less opportunity for the muscle to shorten
shifts the pressure-volume loop to the right
stroke volume decreases

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21
Q

when is there an increase in end systolic volume?

A

chronic hypertension

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22
Q

when is there a fall in contractility?

A

MI
heart failure
weak, floppy ventricle

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23
Q

what impact does decreased contractility have?

A

reduced stroke volume

reduction in cardiac output

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24
Q

what happens when there is a fall in compliance?

A

stiff, fibrotic ventricle
more difficult to contract and recoil
decrease in stroke volume

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25
when is there a fall in compliance?
ageing
26
contractility
noradrenaline/ adrenaline binds to beta 1 adrenoreceptor on GPCR causes adenyl cyclase to be activated, converting ATP to cAMP which ultimately causes an increase in calcium and increase contractility
27
what does dual innervation mean?
both sympathetic and parasympathetic innervations
28
SAN and AVN
are dual innervated
29
Innervation of atria
sympathetic and small amount of parasympathetic innervation
30
innervation of ventricles
only really have sympathetic innervation
31
what does caffeine do?
increases calcium | increases contractility
32
control of contractility
sympathetic drive to ventricular muscle fibres - noradrenaline at beta 1 receptors in cardiac muscle cells hormonal control by circulating adrenaline and noradrenaline
33
how to calculate the ejection fraction?
stroke volume/ end diastolic volume | expressed as a %
34
what is ejection fraction?
quantification of contractility | measure of the ability of the ventricle to contract
35
Ranges of ejection fraction
>75% could indicate hypertrophic cardiomyopathy 55-70% normal or heart failure with preserved ejection fraction 40-55% abnormal - maybe clinically insignificant <40% = heart failure, can be very low
36
importance of contractility
most important factor in mortality
37
heart rate regulation
neuronal and endocrine
38
positive ionotropic
increase in heart contractility
39
chronotropic
affect on heart rate positive = increase HR negative = decrease HR
40
which hormones affect HR?
adrenaline and noradrenaline = increase | acetylcholine = decrease
41
what happens to the heart at rest?
increase parasympathetic activity
42
bowditch effect
aka staircase phenomenon | increased heart rate causes increase contractility strength
43
atrial reflex
aka bainbridge reflex stretch receptors in right atrium tirgger increase in heart rate through sympathetic activity due to venous return increase
44
sympathetic activity
increases permeability of membrane to sodium ions increase so sodium moves into cell spontaneous depolarisation reduces time to initiate depolarisation
45
Parasympathetic activity
decreases permeability of the membrane to sodium and increases potassium leaving the cell decreases spontaneous depolarisation increases time to initiate depolarisation - causes hyperpolarisation
46
what does a selective beta 1 antagonist affect?
reduced contractility reduced heart rate reduced renin release
47
how does a beta 1 antagonist affect renin release?
reduced renin secretion via selective beta 1 inhibition at juxtaglomerular cells
48
what determines how blood travels through blood vessels?
flow pressure resistance
49
flow
volumber per unit of time | blood flow is determined by pressure change and resistance to flow
50
pressure
driving force behind blood flow, generated by heart. Blood flows from high to low pressure regions
51
resistance
an impediment to flow, high resistance means a higher pressure gradient is needed to achieve the same flow
52
what affects resistance to blood flow
blood viscosity vessel length vessel radius
53
blood viscosity
thicker the blood the higher the resistance to flow. Increase in RBC count, LDL, smoking etc.
54
vessel length
the longer the vessel, the higher the resistance to flow. Unlikely to change by much in an adult
55
vessel radius
the narrower a vessel is the higher the resistance to flow.
56
what is the most important variable affecting resistance to blood flow?
vessel radius
57
resistance to blood flow formula
8nL/Pi x r^4 n = blood viscosity L = vessel length r = vessel radius
58
flow equation
``` Q = change in pressure/R Q = flow ```
59
what are the functions of the CVS?
delivery of oxygen and nutrients to tissues and removal of waste products distributes hormones, fluids and electrolytes immune function thermoregulation
60
what are the 2 circulations?
pulmonary and systemic circuits
61
pulmonary circuit
is a specialised circulation that is relatively short, simple and operates at a lower pressure than the systemic circulation
62
specialised circulations
circulation is specialised within specific organs most tissues receive enough blood to meet metabolic needs, whilst other tissues receive more blood than they need - reconditioning organs
63
reconditioning organs
tissues that receive more blood than they need metabolically
64
cardiac output in pulmonary and systemic circulation
equal in both
65
resistance to flow in pulmonary and systemic circulation
low in pulmonary as short and simple and high in systemic as long and complex
66
pressure in pulmonary and systemic circulation
low in pulmonary - 25/10mmHg | high in systemic - 120/80mmHg
67
mean arterial pressure/ pulse pressure
approximates to diastolic pressure plus 1/3 of the difference between systolic and diastolic pressure because more time is spent in diastole
68
BP
refers to mean arterial blood pressure
69
what is the dicrotic notch?
when the aortic valve shuts causing a small dip in pressure
70
pressure changes in circulation
decreases from LV, aorta/ arteries, arterioles, capillaries and veins
71
pressure changes in LV
ranges from 120-0 mmHg
72
pressure changes in aorta and arteries
smaller pressure changes- pressure is maintained
73
when is the biggest pressure drop?
arterioles because of their small radius and so high resistance blood rubs against walls and loses energy
74
exchange vessels
capillaries - main interface with tissues
75
veins
hold the largest share of blood in the whole circulation = capacitance vessels
76
what determines mean arterial blood pressure?
cardiac output total peripheral resistance blood volume
77
what is total peripheral resistance?
can be controlled by constricting or dilating of muscular arteries and arterioles
78
another phrase for total peripheral resistance
systemic vascular resistance
79
what is the most important factor in BP?
total peripheral resistance
80
what regulates BP?
autonomic NS | humoral
81
autonomic NS regulation of BP
short-term | influences cardiac output and vascular resistance
82
humoral control of BP
``` aldosterone adrenaline ADH atrial natriuretic peptide angiotensin II short and long-term regulation influences vascular resistance and blood volume ```
83
what are arterial baroreceptors?
stretch receptors/ mechanoreceptors in aortic arch and carotid sinus continuously monitor BP by monitoring stretch of vessel walls
84
where are chemoreceptors found?
carotid body
85
baroreceptor neural pathway
input to the cardiovascular centre in medulla oblongata via glossopharyngeal nerve from carotid sinus or via vagus nerve from aortic arch causes an autonomic nervous system response
86
what do baroreceptors do?
responsible for rapid, short-term control of BP
87
firing rate for BP
increases firing rate when BP increases | decreases firing rate when BP decreases
88
Controlling high BP
increased firing to brain via glossopharyngeal and vagus nerves to medulla increased firing down vagus to reduce HR, acts on SAN and decreased down sympathetic innervation to SAN and muscles of heart via Beta 1 decreased sympathetic activity to arterioles and veins via alpha 1 causing vasodilation and decreased systemic vascular resistance so BP falls
89
controlling low BP
parasympathetic activity is decreased to the heart and sympathetic activity increases to heart and vascular smooth muscle

Anatomy (16 decks)

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