Physiology Flashcards
1
Q
Where in the heart does excitation normally originate?
A
pacemaker cells in the SA node
2
Q
Where is the SA node located?
A
In the upper right atrium close to where the superior vena cava enters the right atrium
3
Q
A heart controlled by the SA node is said to be in ….?
A
Sinus Rhythm
4
Q
Cells in the SA node have a stable resting potential T/F?
A
False
they have no resting potential
5
Q
How does cardiac excitation normally originate?
A
- cells in the SA node generate regular spontaneous pacemaker potentials
- which takes the membrane potential to a threshold
- over time the threshold is reached and an AP is generated
- resulting in the generation of regular spontaneous APs
6
Q
What causes the pacemaker potential?
A
- Decrease in K+ efflux
- NA+ influx (funny current)
- transient Ca++ influx
7
Q
What happens to the pacemaker AP when the threshold is reached?
A
- depolarisation
- caused by the activation of long lasting (L-type Ca++ channels)
- which results in Ca++ influx
8
Q
What causes the depolarisation phase of the pacemaker AP?
A
- inactivation of L-type Ca++ channels
- activation of K+ channels resulting in K+ efflux
9
Q
How does cardiac excitation spread across the heart?
A
- cell to cell current flow via gap junctions
10
Q
Where is the AV node located?
A
At the base of the right atrium; just above the auction of the atria and ventricles
11
Q
What is the only point of electrical contact between the atria and ventricles?
A
The AV node
12
Q
Describe the characteristics of AV node cells
A
- small in diameter
- slow conduction velocity
13
Q
Why is conduction to the AV node delayed?
A
- allows atrial systole to precede ventricular systole
14
Q
How is excitation spread to the ventricles?
A
- through the bundle of His and the network of purkinje fibres
15
Q
What is the resting membrane potential of atrial and ventricular myocytes?
A
- 90 mV
16
Q
What happens in phase 0 of a myocyte AP
A
- fast NA+ influx
- leading to depolarisation (+20mV)
17
Q
What happens in phase 1 of the myocyte AP?
A
- closure of Na+ channels and transient K+ efflux
18
Q
What happens in phase 2 of the myocyte AP?
A
- mainly Ca++ influx
- plateau phase
19
Q
What happens in phase 3 of the myocyte AP?
A
- closure of Ca++ channels and K+ efflux
- repolarisation
20
Q
What happens in phase 4 of the myocyte AP?
A
return to resting membrane potential
21
Q
sympathetic stimulation ……… HR
A
Increases
22
Q
parasympathetic stimulation ………. HR
A
Decreases
23
Q
Describe parasympathetic innervation of the heart?
A
- vagus nerve exerts a continuous influence on the SA node under resting conditions
- vagal tone dominates under normal resting conditions, slowing HR
24
Q
What is normal resting HR?
A
60-100 bpm
25
Parasympathetic stimulation ....... AV node delay
increases
26
What is the NT for the parasympathetic supply of the heart?
- acetylcholine acting through M2 receptors
27
sympathetic stimulation ..... AV node delay?
decreases
28
Which parts of the heart are supple by cardiac sympathetic nerves?
- SA node
- AV node
- myocardium
29
What is the NT for the sympathetic supply of the heart?
- noradrenaline acting through beta1 adrenoceptors
30
What does the P wave on an ECG represent?
atrial depolarisation
31
What does the QRS complex on an ECG represent?
- ventricular depolarisation
32
what does the T wave represent?
- ventricular repolarisation
33
What does the PR interval represent?
- AV node delay
34
What does the ST segment represent?
ventricular systole
35
What does the TP interval represent?
diastole
36
What is the role of desmosomes in the heart?
provide mechanical adhesion between adjacent cardiac cells
| insure that the tension developed by one cell is transmitted to the next
37
What are myofibrils?
contractile units of muscle
38
Actin is the ..... filament and causes the ..... appearance in myofibrils and fibres
thin/light
39
Myosin is the ..... and causes the ....... appearance
thick/dark
40
how are actin and myosin arranged in each myofibril?
into sarcomeres
41
How is muscle tension produced?
by sliding of actin filaments on myosin filaments
42
force generation is ATP independent T/F?
F, it depends upon an ATP dependent interaction between thick an thin filaments
43
What molecule is required to switch on cross bridge formation?
Ca2+ binding to troponin
44
Where is the Ca2+ released from?
The sarcoplasmic reticulum
45
In cardiac muscle what is the release of Ca2+ dependent on?
the presence of extra cellular Ca2+
46
What happens to the Ca2+ when the AP has passed?
the influx ceases and Ca2+ is re-sequestered in SR by Ca2+ ATPase and the heart muscle relaxes
47
What is the importance of the long cardiac refractory period?
prevents tetanic contraction
48
Why is it not possible to produce another AP during the refractory period of the ventricular AP?
- during the plateau phase the Na+ channels are in a closed state
- during the descending phase the K+ channels are open and the membrane cannot be depolarised
49
What is stroke volume and how is it calculated?
- the volume of blood ejected by each ventricle per heart beat
- SV = end diastolic volume (EDV) - End systolic volume (ESV)
50
What is the end diastolic volume (EDV)
the volume of blood within each ventricle at the end of diastole
51
how is EDV determined?
it is determined by the venous return to the heart
52
What causes changes in stroke volume?
diastolic length/diastolic stretch of muscle fibres
53
What does starlings law of the heart state?
the more the ventricle is filled with blood during diastole (EDV) the greater the volume of ejected blood will be during the resulting systolic contraction (stroke volume)
54
How can the affinity of Ca2+ for troponin be increased?
by stretching the muscle
55
What is after load?
the resistance into which the heart is pumping
56
the ventricular muscle is supplied by .......... nerve fibres and the NT is ......
sympathetic/noradrenaline
57
What is the positive inotropic effect
stimulation of sympathetic nerves increases the force of contraction
58
describe the effect of sympathetic stimulation of ventricular contraction?
- force of contraction increases (greater Ca2+ influx)
- cAMP mediated
- peak ventricular pressure rises
- rate of pressure change during systole increases
- thus reducing the duration of systole
- rate of ventricular relaxation increases
- reducing the duration of diastole
59
How does sympathetic nerve stimulation effect the frank starling curve?
shifts to the left
60
What is cardiac output, how is it calculated and what is the average for a resting adult ?
- the volume of blood pumped by each ventricle per minute
- CO = SV x HR
- 5L per minute
61
What is diastole?
- the heart ventricles are relaxed and filled with blood
62
What is systole?
- the heart ventricles contract and pump blood into the aorta and pulmonary artery
63
What events occur during the cardiac cycle?
1. passive filling
2. atrial contraction
3. Isovolumetric ventricular contraction
4. ventricular ejection
5. Isovolumetric ventricular relaxation
64
Describe passive filling?
AV valves open so venous return flows into ventricles
65
Describe Atrial contraction?
- the P wave in the ECG signals depolarisation and the atria contracts between the P wave ad QRS complex
- atrial contraction complete the END diastolic volume
66
describe Isovolumetric ventricular contraction
- ventricular pressure rises\
- when ventricular pressure exceeds atrial pressure the AV valves shut
- producing first heart sound
- ventricular pressure rises very steeply
67
describe ventricular ejection?
when ventricular pressure exceeds aorta/pulmonary pressure aortic/pulmonary valves open
- Stroke volume is ejected
- aortic pressure rises
- ventricular pressure starts to fall
- aortic/pulmonary valves close and second heart sound is produced
68
describe isovolumetric ventricular relaxation
the tension falls around a closed volume
| when the ventricular pressure fallows below atrial pressure the AV valves open and a new cycle begins
69
When do the first and second heart sounds take place?
1st: during isovolumetric ventricular contraction
2nd: during ventricular ejection
70
What causes the first heart sound?
- closure of mitral and tricuspid valves
71
What causes the second heart sound?
closure of aortic and pulmonary valves
72
The first heart sound signals the beginning of ......... and the second heart sound signals the beginning of .........
systole/ diastole
73
What is BP?
The outward hydrostatic pressure exerted by the blood on the blood vessel walls
74
what is systolic arterial BP?
the pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart contracts
75
What is diastolic arterial BP?
the pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart relaxes
76
What is hypertension?
clinic BP of 140/90 mmHg or higher
| day time average of 135/85 mmHg or higher
77
what is pulse pressure and what is it normally?
the difference between systolic and diastolic blood pressures
- normally between 30-50mmHg
78
When does the blood flow in an artery become turbulent?
when the pressure exerted on the artery is between systolic and diastolic
79
laminar flow is audible through a stethoscope T/F?
false
| turbulent flow
80
When is diastolic pressure recorded?
at the 5th Korotkoff sound
81
What is the main driver of the flow around the systemic circulation?
- a pressure gradient between the aorta and the right atrium
- pressure gradient = MAP - central venous pressure (CVP)
82
What is MAP and how is it calculated?
- The average arterial BP during a single cardiac cycle which involves contraction and relaxation of the heart
- ((2xdiastolic) + systolic)/3
- normally between 70-105 mmHg
- MAP = SV x HR x SVR
83
What is cardiac output and how is it calculated?
- the volume of blood pumped by each ventricle of the heart per minute
- CO = SV x HR
84
What are the major resistance vessels?
the arterioles
85
Where are the baroreceptors mainly found?
in the aortic arch and the bifurcation of the carotid artery
86
What is postural hypotension?
The failure of baroreceptor responses to gravitational shifts in blood, when moving from horizontal to vertical position
87
How is postural hypotension indicated?
- positive result indicted by a drop within 3 minutes of standing from lying position
- systolic drop of at least 20mmHg
- diastolic drop of at least 0 mmHg
88
What are the 2 main factors that affect extracellular fluid volume
1. water excess or deficit
| 2. Na+ excess or deficit
89
What are the hormones that regulate extracellular fluid volume?
1. The Renin-Angiotensin Aldosterone system RAAS
2. Natriuretic peptides
3. Antidiuretic Hormone ADH
90
Describe the Renin Angiotensin aldosterone system
- renin is released from kidneys and stimulates formation of angiotensin I in the blood from angiotensinogen
- Angiotensin I is converted to angiotensin II by angiotensin converting enzyme ACE
- angiotensin II stimulates the release of aldosterone from the adrenal cortex - causes systemic vasoconstriction
- aldosterone acts on the kidneys to increases sodium and water retention - increasing plasma vol
91
What causes renin to be released from the juxtaglomerular apparatus in the kidneys?
1. renal artery hypotension (caused by systemic hypotension)
2. stimulation of renal sympathetic nerves
3. decreased Na+ in renal tubular fluid - sensed by macula dense
92
What are natriuretic peptides and how do they work?
- peptide hormones synthesised by the heart
- released in response to cardiac distension or neurohormonal stimuli
- cause exertion of salt and water - reducing blood vol and BP
- decrease renin release
- act as vasodilators
93
Describe atrial natriuretic peptide?
- 28 amino acid synthesised and stored by atrial muscle cells
- released in response to atrial distension
94
describe brain type natriuretic peptide?
- 32 amino acid peptide synthesised by heart ventricles and brain
- can be measured in patients with suspected HF
95
How is BNP formed?
- first synthesised as prepro-BNP which is then cleaved to pro-BNP
-
96
Describe ADH?
- synthesised by the hypothalamus and stored in the posterior pituitary
97
What is secretion of ADH stimulated by?
1. reduced extracellular fluid volume
| 2. increased extracellular osmolarity (main stimulus)
98
What does ADH do?
- acts in the kidney tubules to increase the reabsorbtion of water
- increases extracellular and plasma volume and hence cardiac output and BP
- causes vasoconstriction - increases BP
99
resistance to blood flow is directly proportional to ........ and ............ It is inversely proportional to ............
blood viscosity
length of blood vessel
radius of blood vessel
100
The vascular smooth muscles are supplied by ........ nerve fibres. The NT is ....... acting on ........ receptors
sympathetic
noradrenaline
alpha
101
What is the vasomotor tone and what causes it?
The vascular smooth muscles are partially constricted at rest.
It is caused by tonic discharge of sympathetic nerves and continuous release of noradrenaline
102
increased ........ discharge will .......... vasomotor tone leading to ............
sympathetic
increased
vasoconstriction
103
adrenaline acting on alpha receptors causes vasoconstriction T/F
True
| adrenaline acting on B2 receptors causes vasodilation
104
Where are alpha receptors mainly found?
in the skin, gut and kidney arterioles
105
Where are B2 receptors mainly found?
cardiac and skeletal muscle arterioles
106
name 2 hormones other than adrenaline that cause vasoconstriction?
```
angiotensin II
antidiuretic hormone (ADH)
```
107
describe some factors that cause relaxation of arteriolar smooth muscle resulting in vasodilation and metabolic hyperaemia?
- decreased local PO2
- increased local PCO2
- increased local [H+]
- increased extracellular [K+] (decreased pH)
- increased osmolarity
- adenosine release
108
name some humoral agents which result in vasodilation?
- histamine
- bradykinin
- nitric Oxide
109
How is NO produced?
- continuously produced by vascular epithelium from the amino acid L-arginine through enzymatic action of NOS
110
How does NO cause smooth muscle relaxation?
diffuses from the vascular endothelium into adjacent smooth muscle cells where it activates the formation of cGMP that serves as a 2nd messenger for smooth muscle relaxation
111
Give examples of humeral agents that cause vasoconstriction?
serotonin
thromboxane A
Leukotrienes
endothelin
112
give examples of physical things that cause vasoconstriction?
- cold temperatures
| - myogenic response to stretch (MAP increases)
113
give examples of physical things that cause vasodilation
- warm temperatures
- myogenic response to stretch (MAP falls)
- sheer stress
114
What are the factors that influence venous return to the heart?
- increased venomotor tone
- increased skeletal muscle 'pump'
- increased blood volume
- increased respiratory 'pump'
- increased atrial pressure
115
What does increased venomotor tone cause?
increased venous return, stroke volume and MAP
116
How can the respiratory pump be used to increase venous return?
By increased rate and depth of breathing
117
how can the skeletal muscle pump be used to increase venous return?
By increasing muscle activity
118
What is shock?
An abnormality of the circulatory system resulting in inadequate tissue perfusion and oxygenation
119
adequate tissue perfusion depends on ................ and ...................?
adequate BP and adequate CO
120
Describe the mechanism of hypovolaemic shock?
loss of blood vol > decreased blood vol > decreased venous return > decreased EDV > decreased SV > decreased CO and BP > inadequate tissue perfusion
121
What is cariogenic shock?
sustained hypotension causes by decreased cardiac contractility
122
describe the mechanism of cariogenic shock?
decreased cardiac contractility > decreased SV > decreased CO and BP > inadequate tissue perfusion
123
Give an example of something that may cause obstructive shock?
tension pneumothorax
124
describe the mechanism of obstructive shock?
inc intrathoracic pressure > dec venous return > dec EDV > dec SV > dec CO and BP > dec tissue perfusion
125
describe the mechanism of neurogenic shock?
loss of sympathetic tone to blood vessels and heart > massive venous + arterial vasodilation - effect on HR > dec venous return and SVR, dec HR > dec CO and BP > inadequate tissue perfusion
126
What causes neurogenic shock
injury to the spinal cord
127
Describe vasoactive shock?
release of vasoactive mediators > massive venous and arterial vasodilation - inc capillary permeability > dec venous return and SVR > dec CO and BP > inadequate tissue perfusion
128
outline the treatment of shock?
- ABCDE
- high flow oxygen
- vol replacement (not cardiogenic)
- immediate chest drain for pneumothorax
- adrenaline for anaphylactic shock
- vasopressors for septic shock
- treat cause
129
Why would volume replacement not be appropriate in cardiogenic shock?
- the heart muscle is damaged therefore increasing blood volume will make the heart work harder and cause further damage
130
other than haemorrhage what else can cause hypovolaemic shock?
- vomiting
- diarrhoea
- excessive sweating
131
compensatory mechanisms can maintain BP until ..... is lost
> 30%
132
Define transient loss of consciousness
A state of real or apparent loss of consciousness with loss of awareness, characterised by amnesia for the period of unconsciousness, loss of motor control, loss of responsiveness and a short duration
133
name some of conditions that can result in TLOC?
- head trauma
- syncope
- epileptic seizures
- TLOC mimics
- other causes
134
define syncope?
transient loss of consciousness due to cerebral hypoperfusion, characterised by rapid onset, short duration and spontaneous complete recovery
135
Describe a reflex syncope?
- all syncopes in which neural reflects modify heart rate and or vascular tone hence predisposing to a fall in MAP of sufficient severity to affect cerebral perfusion causing a transient period of cerebral hypo perfusion resulting in syncope or near syncope
136
Describe the vasovagal reflex syncope?
- most common type of syncope
- faint triggered by emotional distress
- associated with a typical prodrome
- main risk is injury when falling
- treatment: education, reassurance, avoidance of triggers, adequate hydration
137
describe the situational reflex syncope?
- faint during or immediately after a specific trigger eh cough, micturition
- treat the cause
138
describe the carotid sinus reflex syncope?
- triggered by mechanical manipulation of the neck, shaving, tight collar
- more common in elderly especially males
- may occur after head and neck surgery or radiation
139
Describe the cardiac syncope?
- caused by a cardiac event resulting in sudden drop in CO
| - can be caused by: arrhythmias, acute MI, structural cardiac disease, other cardio disease
140
describe the features that suggest a cardiac syncope/
- during exertion or when supine
- presence of structural cardiac abnormality or coronary heart disease
- family history of sudden death at young age
- sudden onset palpitations followed by syncope
- findings on ECG suggestive of arrhythmic syncope
