Cardiovascular Flashcards
1
Q
What is the equation of stroke volume?
A
End Diastolic Volume (EDV) - End Systolic Volume (ESV)
2
Q
What is the equation for mean arterial pressure (MAP)
A
diastolic pressure +1/3 pulse pressure
3
Q
What is the equation for cardiac output?
A
Heart rate (HR) x Stroke volume (SR) Typically 5L/ minute
4
Q
What is the definition of cardiac output?
A
The volume of blood each ventricle pumps as a function of time (litres per minute)
5
Q
What is the equation for Ohm’s law and vessel resistance?
A
Flow = pressure gradient/ resistance
6
Q
What is the equation for Poiseuille and blood flow
A
Flow = radius to the power of 4
7
Q
What is the equation for pulse pressure?
A
systolic - diastolic pressure
8
Q
What is the definition of preload?
A
the volume of blood in the left ventricle which stretches the cardiac myocytes before left ventricular contraction
9
Q
What is the definition of after load?
A
the pressure the left ventricle must overcome to eject blood during contraction - dilate arteries = decrease in after load
10
Q
What is the definition of contractility?
A
Force of contraction and the change in fibre length - how hard the heart pumps. When muscle contracts myofibrils stay the same length but the sarcomere shortens - force of heart contraction that is independent of sarcomere length.
11
Q
What is the definition of elasticity?
A
myocardial ability to recover normal shape after systolic stress
12
Q
What is the definition of compliance?
A
how easily the heart chamber expands when filled with blood volume
13
Q
What is the definition of resistance?
A
Total peripheral resistance: the total resistance to flow in systemic blood vessels from beginning of aorta to vena cava - arterioles provide the most resistance.
14
Q
Starlings Law of the heart
A
force of contraction is proportional to the end diastolic length of cardiac muscle fibre - the more ventricle fills the harder it contracts.
15
Q
How long does systole last?
A
0.3 seconds. Ventricular contraction and blood ejection occurs.
16
Q
How long does diastole last?
A
0.5 seconds. Ventricular relaxation and blood filling occurs.
17
Q
What is isovolumetric contraction?
A
iso - equal/unchanging contraction of the ventricles. Increase in pressure but volume remain the same since valves remain closed.
18
Q
What are the parasympathetic fibres transmitted by?
A
vagus nerve (CN10)
19
Q
What is parasympathetic stimulation controlled by?
A
Acetylcholine which bind to muscarinic receptors
20
Q
What are the effects of parasympathetic stimulation?
A
- Decreases heart rate (negatively chronotropic)
decreases force of contraction (negatively inotropic)
decreases cardiac output (by up to 50%)
21
Q
What do sympathetic postganglionic fibres innervate?
A
The entire heart
22
Q
What is the sympathetic stimulation controlled by?
A
Adrenaline and noradrenaline
23
Q
What are the effects of sympathetic stimulation?
A
- Increases heart rate (positively chronotropic)
- increases the force of contraction (positively inotropic)
- increases cardiac output (by up to 200%)
24
Q
Explain the 5 phases of myocyte action potential
A
Phase 0: rapid depolarisation, inflow of Na+
Phase 1: partial depolarisation, inward Na+ current deactivated & outflow of K+
Phase 2: plateau, slow inward Ca2+ current
Phase 3: depolarisation K+ outflow, Ca2+ current deactivated
Phase 4: pacemaker potential, slow Na+ inflow, slowing of K = outflow
25
Isovolumetric ventricular relaxation
Ventricular volume is not changing. Decrease in pressure but volume remains the same
26
Name the effectors in the central circulation control
Blood vessels, heart and kidneys
27
What is the main aim of control of circulation?
It is maintain mean systemic arterial pressure (MAP) - the average blood pressure in the arteries during the cardiac cycle
28
Function and structure of circulatory system: arteries
- contain mainly elastic, collagen and smooth muscle.
- the intima is composed of an inner surface lining of endothelial cells and a very small amount of collagen.
- the adventitia shows mainly collagenous connective tissue
- there are 2 elastic laminae, one at the interface of the intima and media and the other on the outer edge of the media.
29
Function and structure of circulatory system: arterioles
- may have an obvious media and adventitia
- smaller arterioles show only a few medial cells with a poorly defined elastic lamina
- a thin adventitia and normal intima also exist
30
Function and structure of circulatory system: endothelium
- single layer of spindle/pavement cells with tight adhesions between adjacent cells
- little cytoplasm and intra-cellular organelles-bit gap/adheren junctions are prominent
- they may be fenestrated (have pores in them for rapid diffusion) in the liver, kidney, glomeruli and endocrine tissue
- in some areas they may be very thin (lung) to enable rapid fluid and gas transfer
31
Function and structure of circulatory system: Capillaries
- tubes of endothelial cells (one cell thick wall - for rapid diffusion) bound to a basement membrane with co-existing pericytes.
- pericytes have muscle fibres and may regulate blood flow
32
Function and structure of circulatory system: Venules and veins
- show variable thickness
- veins generally have collagen and little muscle and elastic with the wall and a single internal elastic lamina
- veins contain valves for one way flow of the heart - prevent back flow
Some veins are surrounded by skeletal muscle which contracts to increase vein pressure and ensure blood flows back to the heart.
33
What is the pulmonary circulation?
Blood leaves the right ventricle via a single large artery, the pulmonary trunk, which divides into the two pulmonary arteries, one supplying the right and one supply the left lung. In the lungs the arteries continue to branch and connect to arterioles, leading to capillaries that unite into venules and then veins. The blood leaves the lungs via four pulmonary veins, which empty into the left atrium
34
What is the systemic circulation?
Blood leaves the left ventricle via single large artery, the aorta. The arteries of the systemic circulation branch off the aorta, dividing into progressively smaller vessels. The smallest arteries branch into arterioles, which branch into roughly 10 billion very small vessels, the capillaries, which unite to form larger-diameter vessels known as venules. The arterioles, capillaries & venules are collectively referred to as the MICROCIRCULATION. The venules then unite to form larger vessels, veins. The veins from the various peripheral organs and tissues unite to produce two large veins, the inferior and superior vena cava which drain into the right atrium
35
What are the two phases of the blood?
Cellular component (45%); Red cells (form 99% of blood cells), white cells &platelets
Fluid component (55%); plasma
36
What is haematocrit?
the volume of red blood cells i.e. haemoglobin in the blood, normal haematocrit is 0.45
37
What is haeopoiesis?
The process of the production of blood cells and platelets which continues throughout life.
38
Where does haemopoiesis occur in adults?
It is confined to the bone marrow
39
Where does haemopoiesis occur in embryonic life and early infancy?
It can occur at other sites.
40
What is the red blood cell lifetime?
120 days
41
What is the lifetime of a platelet?
7-10 days
42
What is the lifetime of a white blood cell?
6 hours
43
Do red blood cells and platelets have a nucleus?
No they are anucleate (have no nucleus)
44
Where are the precursor cells of RBCs located?
In the bone marrow
45
RBCs precursor cells: Where is this in adults?
In the axial skeleton: skull, ribs, spine, pelvis and long bones
46
RBCs precursor cells: where is this in children?
In all bones
47
RBCs precursor cells: where is this in utero?
yolk sac, then liver and spleen
48
Are precursor cells found in the blood?
No this is a sign of leukaemia
49
What is anaemia?
Reduction in haemoglobin in the blood
50
What are some examples of soluble plasma proteins?
Albumin, carrier proteins, immunoglobulins
51
What is the physiological function of platelets?
(organised anucleate particles) responsible for primary haemostasis = bleeding time: PT (prothrombin time), they adhere to damaged endothelium and aggregate to form platelet plug that blocks hole in vessel
52
Describe the structure of platelets
Small cytoplasmic anucleate cells that block up holes in blood vessels
• Made in bone marrow from cells called megakaryocytes
• Spherical, enucleate - cannot repair itself
• Lifespan: 5-10 days
• Normal number: 140-400 x 109/l
53
Name the types of white blood cells
- Neutrophils
| - lymphocytes: B cells and T cells
54
How long does each cardiac cycle usually last?
0.8 seconds
55
What does systole involve?
Ventricular contraction and blood ejection
56
What does diastole involve?
Ventricular relaxation and blood filling
57
What happens during systole?
Isovolumetric contraction occurs and then once the pressure in the ventricles exceeds that in the aorta and pulmonary trance the aortic and pulmonary valves open and maximal ejection from ventricles into the arteries occur.
58
Do the ventricles empty during contraction?
No
59
What happens during diastole?
1. reduced ejection
2. ventricles begin to relax and aortic and pulmonary valves close
3. rapid left ventricle filling and ventricle suction.
4. slow ventricular filling
5. Atrial booster
60
When is the only time when all valves of the heart are closed?
isovolumetric contraction and relaxation
61
What are myofibrils?
Contractile proteins (actin and myosin) are arranged in a regular array of thick (myosin) and thin (actin) filaments
62
What forms the majority of the thick filament?
Myosin
63
What is myosin composed of?
Two large polypeptide heavy chains and 4 smaller light chains.
64
What is the thin filament composed of?
Mainly composed of actin, but also of troponin and tropomyosin (play important roles in regulating contraction)
65
Describe the structure of actin
- globular protein
- composed of a single polypeptide (a monomer) that polymerises with other actin monomers to form a polymer made up of two intertwined, helical chains.
- these chains make up the core of the thin filament.
- each actin molecule contains a binding site for myosin
66
Describe the structure of tropomyosin.
Elongated molecule that occupies the grooves between the two actin strands, overlies MYOSIN binding sites on actin
67
Describe the structure of troponin
Protein that changes shape when Ca+ binds to it, when it does it changes shape in doing so pushes the tropomyosin EXPOSING myosin binding sites on actin enabling contraction to occur
68
What is the A band of a sarcomere?
the region of the sarcomere occupied by thick and a few overlapping thin filaments - overall there are twice as many thin as thick filaments in the region of filament overlap.
69
What is the I band of a sarcomere?
Occupied only by thin filaments that extend to the centre of the sarcomere from the Z-lines. It also contains tropomyosin and troponin (the actin filament?)
70
What defines the limits of one sarcomere?
two successive Z lines
71
What is the H zone of a sarcomere?
Contains only thick filaments (myosin)
72
What is the M-line of a sarcomere?
It is in the centre of a H-zone, comprised entirely of thick filament myosin. Corresponds to proteins that link together the central region of adjacent thick filaments.
73
What is titin in a sarcomere?
Elastic protein filaments, extend from the Z-line to the M-line, linked to both the M-line proteins and the thick filaments.
74
What does the M-line linkage between the thick filaments and the titin filaments act to do?
Maintain the alignment of the thick filaments in the middle of each sarcomere.
75
What does one sarcomere contain?
2 half I-bands, 1 A-band, 1 H-zone, 1 M-line and 2 Z-lines
76
What is the sarcoplasmic reticulum?
Membrane network that surrounds the contractile proteins. Releases Ca2+ when Ca2+ binds to its ryanodine receptor.
77
Where are coagulation proteins (enzymes) produced?
In the liver
78
What is the key coagulation enzyme?
thrombin as it makes the platelet plug
79
What is vitamin K essential for?
The correct synthesis of coagulation factors II, VII, IX and X (2,7,9, and 10) - remember 1972.
80
What do coagulation factors 2,7,9 and 10 do?
They circulate in inactive form, and their function is to make a blood clot. Converts soluble fibrinogen into insoluble fibrin polymer.
Overactivity = thrombosis
Failure = bleeding
81
What are the steps of the conduction pathway in the heart?
1. Action potential at SAN
2. Wave of excitation spreads across the atria = contraction
3. Upon reaching AVN signal is delayed
4. Bundle of His (Interventricular septum)
5. Purkinje fibres
Bundle of His and Purkinje fibres spread the wave of impulses along the ventricles = contraction
82
Control of circulation. What is the role of arteries?
- low resistance conduits
- elastic
- cushion systole
- maintain blood flow to organs during diastole
83
Control of circulation. What is the role of arterioles?
- principal site of resistance to vascular flow
- therefore, TPR = total arteriolar resistance
- determined by local, neural and hormonal factors
- major role in determining arterial pressure
- major role in distributing flow to tissue/organs
84
What is total peripheral resistance?
Basically arteriolar resistance. Vascular smooth muscle determines the radius
85
What happens when the vascular smooth muscle contracts? (vasoconstriction)
There is a decrease in the radius = increase in resistance and decrease in flow
86
What happens when the vascular smooth muscle relaxes? (vasodilation)
There is an increase in the radius = decrease in resistance and increase in flow
87
What is myogenic tone?
The vascular smooth muscle is never completely relaxed
88
Control of circulation. What is the role of capillaries?
- 40,000km and large area = slow flow.
- Allows time for nutrient/waste exchange
- Plasma or interstitial fluid flow determines the distribution of ECF between these compartments
- Flow also determined by: arteriolar resistance and the number of open pre-capillary sphincters.
89
Control of circulation. What is the role of veins?
- compliant
- low resistance conduits
- capacitance vessels
- Up to 70% of blood volume but only 10mmHg
- Valves aid venous return against gravity
- Skeletal muscle/ respiratory pump aids return
- SNS mediated vasoconstriction maintains venous resistance/venous pressure
90
Control of circulation. What is the role of lymphatics?
- Fluid/ protein excess filtered from capillaries
| - Return of this interstitial fluid to CV system - thoracic duct, left subclavian artery
91
What is uni-directional flow aided by in the lymphatics?
- Smooth muscle in lymphatic vessels
- Skeletal muscle pump
- Respiratory pump
92
What is the equation for blood pressure?
Cardiac output x total peripheral resistance
93
What's Ohm's law?
Flow = pressure gradient/resistance
94
What is the goal of circulation?
- Maintain blood flow
| This needs pressure to push blood through peripheral resistance (MAP = CO X TPR)
95
What are the components of control?
- Autoregulation
- Local mediators
- Humoral factors
- Baroreceptors
- Central (neural) control
96
What is myogenic auto regulation?
When blood flow is increased and stretches vascular smooth muscle the muscle automatically constricts until the diameter is normalised or slightly reduced.
Also, when the smooth muscle isn't getting stretched as much due to low blood pressure, the muscle relaxes and dilates in response.
97
What is intrinsic control of blood pressure?
Brain and heart intrinsic control dominates to maintain blood flow to vital organs
98
What is skin blood flow important for?
General vasoconstriction response and also in responses to temperature (extrinsic) via hypothalamus
99
What are the effects of skeletal muscle?
It has dual effects: at rest, vasoconstrictor (extrinsic) tone is dominant; upon exercise, intrinsic mechanisms predominate
100
What are some examples of local humeral factors for vasoconstrictors?
- Endothelin-1
| - Internal blood pressure (myogenic contraction)
101
What are some examples of local humeral factors for vasodilators?
- Hypoxia
- Adenosine
- Bradykinin
- NO
- K+, CO2, H+
- Tissue breakdown products
- Prostacyclin
102
Endothelium: control functions
- Essential for control of the circulation
103
Give some examples of circulating (hormonal) factors for vasoconstrictors and vasodilators
Vasoconstrictors:
- Epinephrine
- Angiotensin II
- Vasopressin
Vasodilators:
- Epinephrine
- Atrial Natriuretic Peptide
104
What is the role of baroreceptors?
Pressure sensing
105
Where are primary (arterial) baroreceptors found?
Carotid sinus and aortic arch
106
Where are secondary baroreceptors found?
Veins, myocardium, pulmonary vessels
107
What is the afferent and efferent stimulation? for baroreceptors?
Afferent: glossopharyngeal (IX)
Efferent: sympathetic and vagus (X)
108
Explain the firing rate of baroreceptors
The firing rate is proportional to mean arterial pressure and pulse pressure, integrated in the medulla
109
What happens when there is an increase in blood pressure in terms of baroreceptors?
Increase in blood pressure = increased firing = increased PNS/ decreased SNS = Decreased CO/TPR = decrease in blood pressure and vice versa
110
How do arterial baroreceptors affect central control?
Increase in arterial pressure = increase in arterial baroreceptors firing
- Decrease in sympathetic outflow to heart, arterioles and veins
- Increase to parasympathetic outflow to heart
111
Arterial baroreceptors: short and longer term
Key role in short-term regulation of BP; minute to minute control, response to exercise, haemorrhage
If arterial pressure deviates from ‘norm’ for more than a few days they ‘adapt’/’reset’ to new baseline pressure eg. in hypertension
The major factor in long-term BP control is blood volume
112
Where are cardiopulmonary baroreceptors found?
In the ratio, ventricles, pulmonary arteries
113
What happens when the cardiopulmonary baroreceptors are stimulated?
- Decreased vasoconstrictor centre in medulla = decrease blood pressure
- Also, decrease release angiotensin, aldosterone and vasopressin (ADH), leading to fluid loss
114
What do cardiopulmonary baroreceptors play an important role in?
Blood volume regulation
115
What are the main neural influences on the medulla?
- Baroreceptors
- Chemoreceptors
- Hypothalamus
- Cerebral cortex
- Skin
- Changes in blood [O2] and [CO2]
116
What are central chemoreceptors?
Chemosensitive regions in medulla
117
Central chemoreceptors: what happens when there is an increase/ decrease in PaCO2?
Increase: vasoconstriction , increase in peripheral, increase in blood pressure
Decrease: decrease in medullary tonic activity, decrease in blood pressure
Note there are similar changes with increase/decrease pH
118
What is the effect of PaO2 on the medulla?
Less effeCt, moderate decrease = vasoconstriction
| Severe decrease = general depression
119
What is the effects of PaO2 mainly via?
Peripheral chemoreceptors
120
Standard BP control: what happens in the short term?
Baroreceptors
Increase in blood pressure = increase in firing = increase PNS/ decrease SNS = decrease in CO/TPR = decrease in blood pressure
121
Standard BP control: what happens in the long term?
- Volume of blood
| - Na+, H2O, renin-angiotensin-aldosterone and ADH
122
Where are key central effectors?
Peripheral
123
What do the key central effectors effect?
- blood vessels (vasodilation and vasoconstriction: affects TPR)
- Heart (rate and contractility: CO = HR x SV
- kidney (fluid balance: longer term control)
124
Homeostasis: minute-by-minute feedback loop
Blood pressure - baroreceptor discharge - sympathetic and parasympathetic outflow - vasomotor tone and cardiac output - blood pressure
125
How many aortic arches are there?
6 + 7th segmental artery
126
What does the first aortic arch develop into?
Disappears early and forms the maxillary artery
127
What does the secondary aortic arch develop into?
Disappears early and develops into the stapedial artery
128
What does the third aortic arch develop into?
Commencement of internal carotid artery (ICA)
129
What does the fourth aortic arch develop into?
Right - right subclavian
| Left - aortic arch
130
What does the fifth aortic arch develop into?
Regresses and doesn't form anything
131
What does the sixth aortic arch form?
Right -proximal right pulmonary artery
| Left - left pulmonary artery and part of ductus arterioles
132
What does the seventh segmental artery form?
Left - left subclavian artery
| Right - part of the right subclavian artery
133
What are the parts of the primitive heart tube?
```
Truncus arteriosus
Bulbus cordus
Primitive ventricle
Primitive atrium
Sinus venosus
```
134
What does the trunks arteriosus develop into?
Ascending aorta and pulmonary trunk
135
What does the bulbs cordus develop into?
Smooth (outflow) parts of the left and right ventricles
136
What does the primitive ventricle form?
Forms majority of ventricles
137
What does the primitive atrium form?
- Both auricular appendages
- Entire left atrium
- Anterior part of right atrium
138
What does the sinus venosus form?
- Smooth part of right atrium
- Vena cavae
- Coronary sinus
