Physiology continued Flashcards
1
Q
What is the QRS complex?
A
Ventricular depolarisation (masks atrial repolarisation)
2
Q
What is T?
A
Ventricular repolarisation
3
Q
What is the ST segment?
A
Ventricular systole
4
Q
What is the TP interval?
A
Diastole
5
Q
Where does lead I go
.
A
Right arm - left arm
6
Q
Where does lead II go?
A
Right arm - left leg
7
Q
Where does lead III go?
A
Left arm - left leg
8
Q
In an ECG what is the right leg used for?
A
Earth
9
Q
What is the difference between positive and negative chronotropic effect?
A
Positive = increase in heart rate Negative = decrease in heart rate
10
Q
What are gap junctions?
A
Protein channels which form low resistance electrical communication pathways between neighbouring myocytes - ensure that electrical stimulation reaches all cardiac myocytes
11
Q
What adheres cardiac cells together?
A
Desmosomes
12
Q
What is the structure of striated muscle fibre?
A
Myofibrils - contractile units of muscle
- Actin (thin filaments) cause lighter appearance
- Myocjn (thick filaments) cause darker appearance
Within each mock rip actin and Myocjn are arranged in sarcomere so
13
Q
What causes muscle tension in the heart?
A
Sliding of actin filaments on myocin filaments
14
Q
What activates ventricular muscle contraction?
A
Ca2+ influx during plateau phase of AP
15
Q
What is the refractory period?
A
A period of time following an action potential in which it is not possible to produce another action potential
16
Q
What is tetany?
A
Spasm and twitching of cardiac muscle caused by reduced calcium influx
17
Q
How do you calculate stroke volume?
A
SV = EDV - ESV
18
Q
Intrinsic control of stroke volume
A
Changes in diastolic length of cardiac muscle fibres - EDV
19
Q
What is the EDV a determined by?
A
Venous return to the heart
20
Q
What is the frank starling law of the heart?
A
The more the ventricle is filed with blood during diastole (EDV) the greater volume of ejected blood during the resulting systolic contraction
21
Q
Why’s is afterload?
A
The resistance into which the heart is pumping
22
Q
Sympathetic influence on stroke volume
A
Noradrenaline acts on B1
Increases the force of contraction
Positive inotropic effect
23
Q
What is the effect of sympathetic stimulation on the frank starling curve?
A
Crude is shifted to the left
24
Q
Where does the left ventricle pump blood?
A
The aorta
25
Where does the RV pump blood?
Pulmonary artery
26
What drains into the RA?
SVC
| IVC
27
What drains into the LA?
Pulmonary veins
28
What are the stages of the cardiac cycle?
1) passive filling
2) atrial contraction
3) isovolumetric ventricular contraction
4) ventricular ejection
5) isovolumetric ventricular relaxation
29
What happens in passive filling?
Mitral & tricuspid valves open - venous return goes into ventricles
30
Which side of the heart is higher pressure?
Left
31
What happens in atrial contraction?
P wave - atrial depolarisation
| Atria contracts between P wave and QRS
32
What happens in isovolumetric ventricular contraction?
```
Starts after the QRS
Ventricular pressure rises
When ventricle pressure > atrial pressure AV VALVES SHUT
This produces the first heart sound
All valves are shut so pressure builds
```
33
What happens in ventricular ejection?
```
When ventricular pressure > aorta/pulmonary artery pressure
Valves open (silent)
Aortic pressure rises
T wave =!ventricular repolarisation
Ventricular pressure
```
34
What is P?
Atrial depolarisation
35
What happens in isovolumetric ventricular relaxation?
Ventricle is closed box again
When ventricular pressure falls below atrial pressure
AV valves open again (silent)
36
What causes the first heart sound?
Closure of mitral & tricuspid valve
| (beginning of systole!
37
What causes the second heart sound?
Closure of aortic & pulmonary valves
| end of systole, beginning of diastole
38
Where are the baroreceptors?
Aortic arch
| Carotid sinus
39
What causes postural hypotension?
Failure of baroreceptor responses to gravitational shifts
40
Summary of baroreceptor reflex
```
Person stands up
Venous return to the heart decreases
MAP decreases
Reduces rate of firing of baroreceptors
VAGAL TONE to the heart DECREASES
SYMPATHETIC tone INCREASES
- Increases TPR
- increases HR
- increases SV
Increases venous return
```
41
Which 2 main factors affect extracellular fluid volume?
Water (excess or deficit)
| Na+ (excess or deficit)
42
Which hormones regulate extracellular fluid volume?
RAAS
ANP
ADH
43
What is renin and what does it do?
Renin is released from the kidneys and stimulates formation of angiotensin I in the blood from angiotensin produced in the liver
44
What is angiotensin I and what does it do?
Angiotensin I is converted to angiotensin II by ACE (produced by pulmonary vascular endothelium)
45
What is angiotensin II and what does it do?
Stimulates the release of aldosterone from the adrenal cortex - causes sysstemic vasoconstriction - increases TPR
Also stimulates thirst and ADH release
46
What is aldosterone and what does it do?
Steroid hormone that acts on the kidneys to increase sodium and water retention - increases plasma volume
47
How is renin secretion regulated?
1. Renal artery hypotension (systemic hypotension)
2. Stimulation of renal sympathetic nerves
3. Decreases NA in renal tubular fluid (sense by macula densa)
48
What is Atrial Natriuretic Peptide (ANP)?
28 amino acid peptide synthesised and stored by atrial muscle cells (atrial myocytes)
49
What causes the release of ANP?
Atrial distension
| Hypervolaemic states
50
What is hypervolaemia?
Increased volume of circulating blood
51
What are the actions of ANP?
Excretion of salt and water in the kidneys
Reducing BP & blood volume
Acts as vasodilator - decreases BP
Decreases renin release
52
What is ADH (vasopressin)?
Peptide hormone derived from a ore hormone receptor synthesised by the hypothalamus and stored in the posterior pituitary
53
What stimulates ADH secretion?
1. Reduced extracellular fluid volume
| 2. Increases extracellular fluid osmolarity (osmoreceptors)
54
How does ADH act in the kidneys?
Acts in the kidney tubules
Increases water reabsorption
Causes vasoconstriction
55
Where is the main site of TPR?
Arterioles
56
What is the sympathetic control of vascular smooth muscles?
Sympathetic nerve fibres
| Noradrenaline acting on aloha receptors
57
Parasympathetic innervation of arterial smooth muscles
No significant innervation except penis & clitoris
58
Where is adrenaline released from?
Adrenal medulla
59
How does adrenaline act on vascular smooth muscle?
Adrenaline -> Beta receptors -> vasodilation
| Adrenaline -> alpha receptors -> vasodilation
60
Where are alpha raptors predominantly found?
Skin, gut, & kidney arterioles
61
Where are beta receptors commonly found?
Cardiac & skeletal muscle
62
Which 3 hormones cause vasoconstriction?
Angiotensin II
ADH (vasopressin)
Adrenaline (on alpha receptors)
63
What chemical factors can cause vasodilation?
```
Decreased local PO2
Increased local PCO2
Decreased pH
Increased extracellular K+
Increased osmolarity of ECF
Adenosine release (from ATP)
```
64
What humoral agents cause vasodilation?
Histamine
Prostaglandins
Bradykinin
NO
65
What does NO do?
Potent vasodilator
Diffuses into adjacent smooth muscle where it activates a form of cGMP that serves as a second messages for signalling smooth muscle relaxation
66
What humoral agents can cause vasoconstriction?
Serotonin
Thromboxane A2
Leukotrienes
Endothelium (potent vasoconstrictor released from endothelium stimulated by angiotensin II and vasopressin)
67
Factors that influence increased venous return
Increased venomotor tone
Increased blood volume
Increased "skeletal muscle pump"
Increased "respiratory pump"
68
What is a 3rd heart sound?
Early diastolic low frequency filling sound (passive filling of ventricle)
69
What is a 3rd heart sounds indicative of?
Can be normal finding
| Can indicate heart failure in a patient with evidence of heart failure, especially if the patient is older
70
What is a 4th heart sound?
Late diastolic low frequency sound which relate to the active filling of a stuff non-compliant ventricle by atrial contraction
71
What does a 4th heart sound indicate?
```
Ventricular stiffness (e.g. Left ventricular hypertrophy)
Almost always pathological
```
72
What intrinsic mechanisms control coronary blood flow?
Decreased PO2 causes vasodilation
Metabolic hyperaemia matches flow to demand
Adenosine (from ATP) is a potent vasodilator
73
Extrinsic mechanisms to control coronary blood flow
Sympathetic stimulation causes vasodilatation
| In exercise - circulating adrenaline activates B2 adrenergic receptors
74
What arteries supply the brain?
Carotid and vertebral arteries
75
What is the main adaptation of the cerebral circulation to prevent ischaemia?
Circle of Willis
76
What does MABP drop below to cause confusion, fainting and brain damage if not quickly corrected?
50mmHg
77
How does pCO2 affect cerebral circulation?
Increased PCO2 -> vasodilation
| Decreased PCO2 -> vasoconstriction
78
What is the normal range of intracranial pressure?
8-13mmHg
79
How do you calculate cerebral perfusion pressure?
COO = MAP - ICP
80
How does raised ICP affect cerebral blood flow?
Decreases cerebral blood flow
81
How does glucose cross the BBB?
By facilitated diffusion
82
What is the skeletal muscle pump?
Large veins in limbs lie between skeletal muscles
| Contraction of muscles aids venous return
83
What conditions can failure in the skeletal muscle pump cause?
Postural hypotension
| Fainting
84
What causes varicose veins?
Incompetence of venous valves
85
Why do varicose veins not lead to a reduction in cardiac output?
Chronic compensatory increase in BP
86
What are capillaries?
Kringle layer of endothelial cells
87
What is the function of capillaries?
Allow rapid exchange of gases, water and salutes with interstitial fluid
Delivery of nutrients and O2 to cells
Removal of metabolites from cells
88
What regulates blod flow to the capillary bed?
Terminal arterioles
89
When capillaries join together what do they form?
Venules
90
How do substances transport across the capillary wall?
Fluid - follows pressure gradient
Gas - Ficks law of diffusion (I.e. downhill)
Lipid soluble - go through endothelial cells
Water soluble - through water filled pores
Large molecules can generally not cross the capillary wall
91
What are the forces involved in transcript liars fluid flow called?
Starling forces
92
What forces favour filtration?
Pc - capillary hydrostatic pressure
| interstitial fluid osmotic pressure
93
What forces oppose filtration?
Capillary osmotic pressure
| Interstitial fluid hydrostatic pressure
94
Overall what do the starling forces do?
Favour filtration at arteriolar end
AND
Reabsorption at venular end
95
How is excess fluid returned to the circulation in capillaries?
Via the lymphatics as lymph
96
What role do the starling forces have in pulmonary capillaries?
Prevent oedema
97
What is oedema?
Accumulation of fluid in interstitial space
98
What causes oedema?
Reduced capillary pressure
Reduced plasma osmotic pressure
Lymphatic insufficiency
Changes in capillary permeability
99
How does raised capillary pressure cause pulmonary oedema?
```
Causes arteriolar dilatation
Raised venous pressure
LV failure - pulmonary oedema
RV failure - peripheral oedema
Prolonged standing - swollen ankles
```
100
What causes lymphatic insufficiency leading to oedema?
Lymph node damage
Filariasis
Elephantiasis
101
What causes changes in capillary permeability?
Inflammation
| Histamine - increases leakage of protein
102
Where can you get pitting oedema?
Ankles
| Sacrum
103
What does pulmonary oedema look like on a CXR?
Haziness in peri hilar region
