Physiology Flashcards
(113 cards)
1
Q
what does the P wave signify
A
atrial depolarisation
2
Q
what does the QRS complex signify
A
ventricular depolarisation
3
Q
what does the T wave signify
A
ventricular repolarisation
4
Q
what does the PR interval signify
A
AV nodal delay
5
Q
what does the ST segment signify
A
ventricular systole
6
Q
what does the TP interval signify
A
diastole
7
Q
what system mainly influences HR
A
autonomic nervous system
8
Q
what effect does sympathetic stimulation have on HR
A
increase
9
Q
what effect does parasympathetic stimulation have on HR
A
decrease
10
Q
how does sympathetic stimulation increase HR
A
decreases AV nodal delay
11
Q
what chemical acts upon which cells during cardiac sympathetic stimulation
A
noradrenaline acting on B1 adrenoreceptors
12
Q
how does parasympathetic stimulation decrease HR
A
vagus nerves exerts a continous influence on SA node (vagal tone)
increases AV nodal delay
13
Q
what chemical acts upon which cells during cardiac parasympathetic stimulation
A
ACh acting on M2 receptors
14
Q
what is a competitive inhibitor of ACh
A
atropine
15
Q
when would atropine be used
A
during bradycardia to increase HR
16
Q
what is a resting HR
A
60-100bpm
17
Q
what HR is bradycardia
A
below 60bpm
18
Q
what Hr is tachycardia
A
above 100bpm
19
Q
where does the excitation of the heart originate
A
pacemaker cells in the SA node
20
Q
if the HR is driven by the SA node and is in regular rhythm it is said to be in what
A
sinus rhythm
21
Q
describe the route of excitation
A
spreads from SA node to AV node via gap junctions
then speeds down the bundle of his
then down the L and R bundle branches to the purkinje fibres
22
Q
what is the AV node
A
small bundle of specialised cardiac cells
23
Q
what is the only point of electrical contact between the atria and the ventricles
A
AV node
24
Q
where is the AV node located
A
at the base of the RA just above the junction of the atria and ventricles
25
what allows atrial systole to precede ventricular systole, why?
the AV node; is has a slow conduction velocity which delays conduction across the AV node
26
what is atrial systole also know as
contraction
27
outline the structure of cardiac muscle
striated fibres contains myofibrils
coupled via gap junctions
desmosome provide mechanical support
28
describe the structure of myofibrils
contain thick filaments (myosin) and thin filaments (actin) arranged into sarcomeres
29
what is stroke volume (SV)
the volume of blood ejected by each ventricle per heart beat
30
what is stroke volume equal to
end diastolic volume - end systolic volume
31
describe the intrinsic mechanisms that regulate SV
changes in the diastolic length of myocardial fibres, this is determined by EDV
32
what extrinsic mechanisms that regulate SV
hormones and nerves
33
what effect does sympathetic stimulation have on SV
increases
34
what effect does parasympathetic stimulation have on SV
no effect due to lack of innervation
35
what hormones effect SV
adrenaline and noradrenaline
36
what is the effect of adrenaline and noradrenaline on SV
increase
37
what is end diastolic volume (EDV)
the volume of blood within each ventricle at the end of diastole
38
what does EDV determine
preload
39
what is EDV determined by
venous return
40
what is end systolic volume (ESV)
the volume of blood in each ventricle at the end of systole
41
explain how changes to ventricular preload causes changes in SV
the more the ventricle is filled during diastole (EDV) the greater the volume of blood ejected during the resulting systolic contraction (SV)
42
how are the SV of the L & R ventricles matched
if venous return to the RA increases the EDV of the RA increases leading to an increased SV to the pulmonary artery. As a result venous return to the LA from the pulmonary vein increases causing to a increased EDV of the LV increasing SV to the aorta
43
what is afterload
the resistance into which the heart is pumping
44
what is the effect of prolonged increases afterload
ventricular hypertrophy
45
what is cardiac output (CO)
the volume of blood pumped by each ventricle per minute
46
what is cardiac output equal to
SV x HR
47
how does sympathetic stimulation affect ventricular contraction
increases force of contraction
| reduces duration of systole and diastole
48
how does parasympathetic stimulation affect ventricular contraction
little effect due to lack of innervation
49
what is BP
the outward pressure exerted by the blood on blood vessel walls
50
what is systolic BP
the outward pressure exerted by the blood on blood vessel walls of the aorta and systemic arteries when the heart CONTRACTS
51
what is diastolic BP
the outward pressure exerted by the blood on blood vessel walls of the aorta and systemic arteries when the heart when the heart RELAXES
52
what is normal systolic BP
<140
53
what is normal Diastolic BP
<90
54
what is normal BP
<140/90
55
what is pulse pressure
difference between the systolic and diastolic BP
56
what is normal pulse pressure
30-50
57
what is mean arterial BP (MAP)
average arterial BP during a single cardiac cycle
58
what is the normal range for MAP
70-105
59
what is the minimum MAP needed to perfuse vital organs
60
60
how do you calculate MAP
diastolic + (1/3 x pulse pressure)
[(2x diastolic) + systolic]/3
61
what is MAP equal to
MAP = CO x SVR so:
MAP = HR x HR x SVR
62
What are the main resistance vessels
arterioles
63
why are baroreceptors only involved in SHORT TERM regulation
sustained high BP will "re-set" baroreceptors
64
what effect does parasympathetic stimulation have on MAP
decrease
65
what effect does sympathetic stimulation have on MAP
increase
66
where are baroreceptors located
carotid bifurcation
| aortic arch
67
how does the baroreceptors signal the medulla
carotid bifurcation = IXth CN
| aortic arch = Xth CN
68
where do the signals from the baroreceptors go
medulla
69
describe the baroreceptor response when the BP decreases
rate of firing will decrease
medulla send signals to increase sympathetic tone and decrease vagal tone (increase HR and SV)
sympathetic constrictor tone is increased (increase SVR)
MAP INCREASES
70
describe the baroreceptor response when the BP increases
rate of firing will increase
medulla send signals to decrease sympathetic tone and increase vagal tone (decrease HR and SV)
sympathetic constrictor tone is decreased (decrease SVR)
MAP DECREASES
71
what is postural hypotension
failure of baroreceptor responses to gravitational shifts in gravity
72
what happens to HR and BP when you suddenly stand up
venous return decreases due to gravity = decrease BP
baroreceptor firing decreases
medulla send signals to increase sympathetic tone and decrease vagal tone (increase HR and SV)
sympathetic constrictor tone is increased (increase SVR)
rapid correction of transient fall in MAP
73
what is the main driving force for blood flow
MAP
74
what does the 1st korotkoff sound signal
peak systolic
75
what does the 4th korotkoff sound signal
minimum diastolic
76
what does the 5th korotkoff sound signal
diastolic (recorded)
77
what does the LONG TERM control of BP involve
hormones
78
what 2 factors must be controlled to control ECF volume
Na+
| water
79
what must be controlled to control MAP and BP
ECF volume
80
which 3 hormones effect MAP
```
renin angiotensin aldosterone system (RAAS)
Natriuretic peptide (NP)
antidiuretic hormone (ADH)
```
81
what is the rate limiting step in RAAS
renin secretion
82
what does the RAAS system regulate
plasma volume and SVR
83
where is renin released from
kidneys
84
what does renin do
stimulate formation of angiotensin 1 in the blood from angiotensinogen
85
where is angiotensionogen located
liver
86
what is angiotensionogen converted to
angiotensin 1
87
what converts angiotensionogen to angiotensin 1
renin
88
what is angiotensin 1 converted to
angiotensin 2
89
what converts angiotensin 1 to angiotensin 2
angiotensin converting enzyme (ACE)
90
where is angiotensin converting enzyme (ACE) located
pulmonary vascular endothelium
91
what does angiotensin 2 do (4)
stimulates release of aldosterone from adrenal cortex
causes systemic vasoconstriction = Increased SVR & BP
stimulates thirst
stimulates ADH release
92
what stimulates the release of aldosterone
angiotensin 2
93
where is aldosterone released from
adrenal cortex
94
what does aldosterone act on
kidneys
95
what does aldosterone do
increases Na+ and water retention to increase plasma volume = increased BP
96
what is aldosterone
steroid hormone
97
what is renin secretion controlled by
renal artery hypotension
stimulation of renal sympathetic nerves
decreased [Na+] in renal tubular fluid
98
what is the cardiac cycle
all events that occur from the beginning of one heart beat to the beginning of the next
99
what happens during diastole
the heart ventricles are relaxed and fill with blood
100
what happens during systole
the heart ventricles contract and pump blood into the aorta (LV) and the pulmonary artery (RV)
101
what are the 5 different phases of the cardiac cycle
1. passive filling
2. atrial contraction
3. isovolumetric contraction
4. ventricular ejection
5. isovolumetric relaxation
102
what happens during passive filling
pressure in atria and ventricles are close to 0
AV valves open and venous return flows into the ventricles
Ventricles become 80% full by passive filling
103
what happens during atrial contraction
P-wave signals atrial depolarization
The atria contracts between the P-wave and the QRS complex
Atrial contraction completes the end diastolic volume (EDV) = 130ml
104
what happens during isovolumetric contraction
starts after the QRS complex
ventricular pressure rises, once the pressure exceeds the atrial pressure the AV valves shut producing the 1st heart sound (LUB)
the aortic valve is still shut so no blood can enter or leave the ventricles and the ventricular pressure rises very steeply
tension rises around the enclosed volume – ‘isovolumetric contraction’
105
what happens during ventricular ejection
when the ventricular pressure exceeds aorta/pulmonary artery pressure the aortic and pulmonary valves open
SV is ejected by each ventricle leaving behind the end systolic volume (ESV)
Aortic pressure rises
The T-wave signals ventricular repolarization
The ventricles relax and the ventricular pressure starts to fall
When the ventricular pressure falls below the aortic/pulmonary pressure the aortic and pulmonary valves shut producing the 2nd heart sound (DUB)
106
what produces the dicrotic notch
valve vibration during ventricular ejection
107
what happens during isovolumetric relaxation
closure of aortic and pulmonary valves signals the start of isovolumetric ventricular relaxation
the tension falls around the enclosed volume – ‘isovolumetric relaxation’
when the ventricular pressure falls below atrial pressure the AV valves open and a new heart cycle begins
108
what causes normal heart sounds
shutting of valves
109
what causes the 1st heart sound
closure of the mitral and tricuspid valves
110
what does the 1st heart sound signify
beginning of systole
111
what causes the 2nd heart sound
closure of the aortic and pulmonary valves
112
what does the 2nd heart sound signify
end of systole
| beginning of diastole
113
how is pressure maintained in blood vessels during ventricular diastole
vessels contract from being stretched during systole
