Cardiovascular physiology Flashcards
1
Q
What is valve regurgitation
A
Blood leaks back into chambers; occurs when a valve does not close tightly
2
Q
How are the left and right atria separated
A
By fibromuscular wall - Atrial (interatrial) septum
3
Q
Where does the Left Atria receive blood from
A
Pulmonary vein
4
Q
Where does the right Atria receive blood from
A
Superior and Inferior Vena Cava
5
Q
Why does the left ventricle have a thicker muscular wall than the right ventricle
A
A high pressure is required to eject blood from the LV, through the aortic valve, into the aorta
6
Q
Which ventricle pumps deoxygenated blood
A
Right ventricle
7
Q
What is the cardiac afterload
A
The pressure the heart must eject blood against
-Left Ventricle
Afterload is relative to the aortic pressure
-Right Ventricle
Afterload is relative to that of the pulmonary artery pressure
8
Q
What allows blood to flow between right atria and right ventricle
A
Tricuspid valve
9
Q
How does blood flow from left atrium to left ventricle
A
Mitral (bicuspid) valve
10
Q
What are papillary muscles
A
Muscular projections of the ventricular walls connected to valve cusps by fibrous Chordae Tendineae
Function to prevent backflow of blood and limits valve cusp movements
11
Q
Why do valves not lift open when under pressure
A
When valves fill up with blood and close the valve, papillary muscles anchor the valve to chordae tendineae allowing the valves to remain closed under pressure preventing cusps from lifting open
12
Q
What are the semilunar valves of the heart called and where are they situated
A
Pulmonary valve - permits blood flow between right ventricle and pulmonary artery (right)
Aortic valve - permits blood to flow between the left ventricle and aorta (left)
13
Q
What forces the semilunar valves closed
A
The pressure difference between the artery and the ventricle
14
Q
How are the heart sounds generated
A
Sound one -AV vales closing (LUB)
Sound two - Semilunar valves closing (DUB)
15
Q
What is valve stenosis
A
Thickening/stiffening of valve cusps
Prevents the heart valve from opening fully; not enough blood can flow through
16
Q
When might a third heart sound be heard
A
Due to oscillation of blood flow into the ventricle or various disease states (e.g. heart valve defect)
17
Q
What are congenital heart defects
A
Often pulmonary / aortic valves that do not form properly during development
18
Q
What is the flow of blood during the cardiac cycle
A
Superior/inferior Vena Cava
Right Atrium
Tricuspid valve
Right Ventricle
Pulmonary valve
Pulmonary artery
Lungs
Pulmonary veins
Left Atrium
Mitral valve
Left Ventricle
Aortic valve
Aorta
Tissues of body systems
19
Q
What is systole
A
A phase of the cardiac cycle which involves contraction of the myocardium
ATRIAL SYSTOLE
-atrial contraction to eject blood into ventricles
VENTRICULAR SYSTOLE
-ventricular contraction to eject blood into aorta (LV) and pulmonary artery (RV)
20
Q
What is Diastole
A
Relaxation of the myocardium which facilitates re-filling of ventricles between contractions
ATRIAL DIASTOLE
-relaxation of atrial muscle, to allow refilling (masked by ventricular systole)
VENTRICULAR DISTOLE
-ventricular relaxation
21
Q
How does rapid ventricular ejection occur (blood leaves heart)
A
-Pressure in the ventricles exceeds pressure in the aorta and pulmonary artery
-Semi-lunar valves open and blood is ejected from LV into aorta and from RV into pulmonary artery
-Volume of blood ejected from ventricle during systole = stroke volume (SV)
22
Q
What is stroke volume
A
The volume of blood pumped from the left ventricle per contraction
23
Q
What is isovolumetric ventricular contraction
A
‘no change in volume’ contraction
when contracting is starting but not enough to force valves open to eject blood
24
Q
What is EDV end diastolic volume
A
Volume of blood in the ventricle prior to contraction
25
What does ESV end systolic volume refer to
Volume of blood remaining in ventricle after each ejection as ventricles are not fully emptied during systole
26
What is the ejection fraction
The volume of blood ejected by the ventricle with each contraction, as percentage of end diastolic volume (what systole begins with)
27
What is cardiac output and the equation
Volume of blood ejected in one minute
Cardiac Output (CO) = Stroke Volume (SV) x Heart Rate (HR)
28
What percentage ejection fraction indicates a severely impaired LV
<35%
29
How is heart rate determined
By the rate which the cardiac pacemaker (sino-atrial node) fired action potentials to stimulate contraction of the cardiac muscle
30
What is the resting heart rate
60-100 bpm
31
What determines the rate of action potential firing and heart rate
Activity of the Autonomic nervous system
32
What do these terms mean:
A-Chronotropy
B-Inotropy
C-Lusitropy
D-Dromotropy
A-Increases heart rate
B-Strength of myocardial contraction
C-Rate of myocardial relaxation
D-Conduction speed in AV node
33
What cardiac effects does the sympathetic nervous system have
Positive chronotropy
Positive inotropy
Positive lusitropy
Positive dromotropy
34
What cardiac effects does the parasympathetic nervous system have
Negative Chronotropy
Negative inotropy
Negative lusitropy in atria
Negative dromotropy
35
Why does the parasympathetic system have these effects
Cholinergic nerves derived from the vagus nerve
Release neurotransmitter Acetylcholine (Ach)
Binds to M2 muscarinic receptors in cardiac muscle, particularly at the SA & AV nodes
Activates inhibitory G-protein
Blocking cAMP pathway and allows K+ efflux from cell
36
what is the membrane potential
-Potential difference between intra and extra cellular sides of the membrane
-Generated by ion gradients across the cell membrane
-Dependent on ionic gradients across membrane and ionic permeability
37
What is depolarisation
Potential (electrical) difference across the cell membrane becomes 'less negative'
38
What is repolarisation
Potential difference across sarcolemma returns to resting Vm following depolarisation (becomes 'more negative')
39
What happens during contraction of a cardiomyocyte
-T tubules takes signal deep into cell
-Calcium induced calcium released, small influx triggers greater release of calcium
-Falls during diastole
-Calcium is removed by sodium channel or by ATPsse
-Action potential triggers the calcium induced calcium release allowing calcium to bind to contractile apparatus
40
What does an increase in calcium within cardiac myocyte cytosol do
Increase the force of myocardial contraction of the cell due to excitation - contraction coupling
41
How can the force of cardiac contraction be influenced
By the length of the heart muscle cell
Level of calcium within the cardiac myocyte cytosol
42
What is Starling's Law
The force of muscle contraction increases as the muscle is stretched in response to an increased filling of the heart’s chambers.
-Heart muscle must respond to stretching in this way
-As otherwise circulation of blood would fail.
-This response is intrinsic to the heart
43
What is Cardiac preload
Initial stretching of cardiac myocytes to contraction indicated by ventricular end - diastolic volume because stretching of cardiac myocytes cannot be determined in intact heart muscles
The magnitude of the stretch (preload) predicts the strength of contraction
44
What is an echocardiogram
A type of ultrasound scan used to assess structure and function of heart at high temporal resolution (2D)
45
What can an echocardiogram aid detection of
Impaired cardiac contractility e.g as a results of myocardial infarction (heart attack)
Congenital heart disease; birth defects that impact cardiac function
Cardiomyopathy: enlargement of ventricular walls
Endocarditis: infection of endocardium that damages heart valves
Heart Failure: heart is unable to adequately pump blood to meet metabolic demands of the body
46
What is myocardial infarction
Heart attack
47
What is endocarditis
Infection of endocardium that damages heart valves
48
What happens in a doppler echocardiogram
Erythrocytes reflect ultrasound waves which are used to meassure the blood flow through the heart
49
What does ECG stand for
Electrocardiogram
50
What is the purpose of an ECG
Detects phasic change in potential difference between two electrodes
51
Where are the electrodes placed in an electrocardiogram
On limbs and the surface of the chest
52
What does bradycardia mean
Slow heart rate
53
What does tachycardia mean
Fast heart rate
54
What rhythms are detected by an ECG
Sinus rhythm
Sinus bradycardia
Atrial fibrillation
STEMI (S-T Elevated myocardial infarction)
55
What is the driving force for blood flow through organs
Mean arterial blood pressure
56
When is the arterial blood pressure greatest and lowest
On waking and sleeping
57
How is the arterial blood pressure measured
With a Sphygmomanometer
58
What is a result of the difference between systole and diastole
Pulse pressure
59
What is the systolic blood pressure
The pressure in the arteries (aorta) during myocardial contraction (systole)
60
What is the diastolic blood pressure
The pressure in arteries (aorta) during myocardial relaxation (diastole)
-when ventricles are refilling
61
How does control and regulation of blood pressure occur
Through rapid regulation of blood pressure
-nerves
-hormones
Long term regulation
-Blood volume
62
What are Baroreceptors
Mechanoreceptors that detect the degree of stretch of blood vessel walls and monitor blood pressure
63
Where are baroreceptors most abundant
In the aortic arch and carotid sinus
64
Why does mechanical stretch (circumferential stress) in arteries arise
Due to pulsatile blood flow
-directly related to blood pressure
-Increases during systole
-Gradually reducing during diastole
65
Where are baroreceptors found
Carotid sinus
Aortic arch
BOTH REQUIRED
66
How are the carotid sinus baroreceptors innervated
By the sinus nerve of Hering
67
How are the aortic arch baroreceptors innervated
By the aortic nerve (combines with vagus nerve)
68
Why are aortic arch baroreceptors less sensitive to changes in stretch than carotid sinus baroreceptors
They have a higher threshold pressure
69
How to identify the carotid sinus
The artery wall is thinner and contains a large number of branching nerve endings
70
Which cranial nerve is the sinus of Herring a branch of
IX - Glossopharyngeal nerve
71
What happens when baroreceptors detect a decrease in arterial pressure
There is a reduction in the action potential firing from baroreceptors
Stimulation travels along afferent neurons
To the medullary Cardiovascular Centre
Increased stimulation of sympathetic neurons to heart/arterioles/veins
Decreased stimulation of parasympathetic neurons (vagus nerve) to heart
72
Where is the Medullary Cardiovascular centre
In Medulla Oblongata
73
When the baroreceptors detect an increase in arterial pressure what occurs
Increased action potential firing from baroreceptors
Stimulation travels along afferent neurons
To the medullary Cardiovascular Centre
Decreased stimulation of sympathetic sympathetic neurons to heart/arterioles/veins
Increased stimulation of Parasympathetic neuros to heart/arterioles/veins
74
What is the Valsalva manoeuvre
The attempt to expire against a closed glottis
(exhaling when mouth & nose are closed)
75
What is the physiological response to the Valsalva manoeuvre
-Increased intrathoracic pressure
-Raising blood pressure; normal LV contraction + (1): increased baroreceptor firing
-Heart rate falls transiently - impending return of blood to heart
-Fall in CO and MAP
-As MAP decreases, HR rises and (w/TPR), stabilises blood pressure
76
What occurs when the glottis is re-opened after the Valsalva manoeuvre
slows fast heart rate
-Intrathoracic pressure falls
-BP falls initially
-Venous return is rapidly restored
-EDV & CO increase, raising BP
-Increased BP is sensed by baroreceptors results in reflex bradycardia (slowing of HR)
77
Within blood pressure regulation what does blood volume influence
Venous pressure
Venous return
End - diastolic volume
Stroke volume
Cardiac output
An increased blood volume increases arterial pressure
78
How does an increased arterial pressure reduce blood plasma volume
Via increasing renal excretion of salt & water
79
What are arterioles
Small diameter muscular walled blood vessels
80
What causes capillary fluid shift
Occurs due to venous dilators
Caused by reduced proximal capillary hydrostatic pressure
Most vasodilators have effects on both arteries and veins
81
Mechanisms that locally regulate long term blood pressure originate via:
- Renin - Angiotensin - Aldosterone System (RAAS)
-Blood vessels (myogenic or endothelial factors)
- Maintenance of constant blood flow
- Blood volume and fluid regulation
82
What is hypertension
Clinic blood pressure of 140mmHg systolic and 90mmHg diastolic (140/90) or higher
83
Risk of hypertension is raised by what
Age
Cigarette smoking
High salt intake
Lack of exercise
Being overweight
Regularly drinking excess alcohol
Stress
Genetic predisposition
Family history
84
How common is hypertension the result of an underlying health condition or medication
1 in 20 cases
85
What is secondary hypertension
Hypertension as the result of an underlying health condition or taking certain medicine
86
What therapeutics (medication) can increase Hypertension risk
Contraceptive pill
Non-steroidal anti-inflammatory drugs (NSAIDS)
Recreational drugs
87
Which health conditions can raise Hypertension risk
Kidney conditions
-Chronic kidney disease
-Narrowing of arteries that supply blood to kidneys / renal hypertension
-Long-term kidney infections
-Glomerulonephritis
Diabetes
Obstructive sleep apnoea
Hormone problems
88
What is sleep apnoea and what does is increase the risk of
Stop breathing during sleep causing you to wake up increasing risk of hypertension
89
What does an under/over active thyroid cause
Hormone problems
90
Why are baroreceptors ineffective monitors of absolute pressure of blood in carotid arteries to the brains and only short term regulators of blood pressure
When the arterial blood pressure is elevated for prolonged periods the threshold for baroreceptor activity rises to a higher value and baroreceptor activity adapts over time and heart rate will increase at the same level
91
When does the resetting of baroreceptor sensitivity occur
During exercise - Maintains Cardiac output as heart rate does not fall in response to increase in BP accompanying exercise
Hypertension - Aids buffering of acute fluctuations in BP at new higher BP level
92
What are some damages caused by prolongs hypertension
Aneurysms in cerebral arteries
Left Ventricular hypertrophy (LVH)
Thickening of arteries
Atherosclerosis Deterioration
93
What is atherosclerosis deterioration
A condition where the arteries become narrowed and hardened due to build up of plaque (fats) in the artery wall.
94
What can atherosclerosis deterioration, Thickening of arteries and Left ventricular hypertrophy all lead to
Renal disease
Development of heart failure due to myocardial adaptation to compensate for LVH
Malignant Hypertension
Angina or myocardial infarction
Stroke
95
What does HMOD stand for
Hypertension-mediated organ damage
96
What does SCORE stand for
Systematic coronary risk evaluation
97
When are endogenous catecholamines released
Due to pain/stress
98
What is Hypotension
Systolic = 90mmHg
Diastolic = 60 mmHg
(90/60mmHg)
99
What is another name for postural hypotension
Orthostatic hypotension
100
What is postural/orthostatic hypotension
An abnormal drop in blood pressure when individuals stand up after sitting or lying down
101
What are the symptoms of postural hypotension
Dizziness
Light head
Fainting
Possible fall
102
Who is orthostatic hypotension most commonly found in
Older people and those with certain underlying conditions that affect the sympathetic or parasympathetic nervous systems ex Parkinson's disease or diabetes
103
What is the P-Q interval
The time for the impulse to travel from the sino-atrial node to the ventricular muscle
104
Why might the Q wave (slight decrease before upstroke) be hard so see
Baseline noise
105
What does the QRS section on an ECG show
The time requires for depolarisation to spread throughout the ventricles
106
What can the duration of ventricular systole be denoted as on an ECG
Q-T interval
107
What does the ECG record
Total electrical activity (action potentials) produced by the heart muscle
108
What can the ECG tell us about the strength of force of the heart's contraction
Nothing
109
How many electrode combinations will a full clinical ECG use
12
110
What causes the P wave on an ECG
Depolarisation of the atrial muscle
111
What does the T-wave represent
The repolarisation phase of the ventricular action potentials
112
How can the mean arterial pressure be calculated
Diastolic BP + 1/3 Pulse pressure
Cardiac Output x Total peripheral
resistance
113
What does the pulse pressure represent
The force the heart generates with each contraction to overcome arterial resistance
114
What is afterload
The force (pressure) against which the heart must contract to eject blood into the arteries
115
What factors can influence pulse pressure
Stroke Volume
Ejection velocity of stoke volume
Arterial compliance
116
What happens to stroke pressure if stroke volume or ejection velocity increases
Increases
117
What happens to stroke volume if the arteries are more compliant
Decrease
118
What are the major branches of the aorta
Subclavian
Common carotid
Iliac
119
What are some muscular arteries
Coronary and renal arteries (smaller branches of aorta)
120
What size would a small artery be
<2mm diameter
121
What is haematocrit
The proportion of red blood cell total volume
122
What does increase haematocrit indicate
Dehydration
123
When does skeletal muscle have a greater demand for O2
During exercise than at rest. Thus during exercise, blood flow to skeletal muscle must increase.
124
When does the GI system have a greater demand for O2
Following ingestion of food and so following a meal, blood flow to GI system must increase.
125
How does altered blood flow to specific organs/tissues occur
By changing arteriolar resistance
126
What is intrinsic control
Local
-Matches blood flow to metabolic requirement of tissue system
-Direct action of metabolites on arteriolar resistance
127
What is extrinsic control
Neural/hormonal
-Action of sympathetic nervous system on vascular smooth muscle
-Action of vasoactive substances (histamine, bradykinin, prostaglandins)
128
What are the specific needs of the tissues for blood flow
Delivery of oxygen to tissues and nutrients (glucose, amino acids, fatty acids)
Removal of carbon dioxide and hydrogen ions
Maintenance of ion concentrations in tissues
Transport of hormones
129
What are the three mechanisms of intrinsic control
Autoregulation
Active hyperaemia
Reactive hyperaemia
130
What are factors that determine resistance to blood flow
Vessel diameter
Vessel length
Viscosity of blood
131
What is autoregulation
Maintenance of constant blood flow while arterial pressure changes
If coronary arterial pressure decreases, immediate compensatory vasodilatation of coronary arterioles to decrease coronary vasculature resistance, will attempt to maintain constant blood flow in this coronary artery.
132
What occurs during active hyperemia
Blood flow to tissues is
proportional to its metabolic
activity
Increased blood flow when metabolic activity increases (exercising skeletal muscle increased O2 consumption / ATP demand)
Increased arteriolar dilation.
133
What is reactive hyperemia
Increase in blood flow in response to a prior period of decreased blood flow
e.g., following period of arterial occlusion, an O2 dept accumulates – longer the arterial occlusion, greater O2 debt, greater the increase in blood flow (above pre-occlusion levels) until the O2 dept reversed.
134
When does the viscosity of blood not remain within a narrow range
During changes in haemocrit
135
What can cause increases in viscosity
Dehydration, immobility in which blood flow is reduced and there is a risk of deep vein thrombosis
136
What does Poiseuille's equation describe
How flow is related to perfusion pressure, radius, length and viscosity
137
What happens to velocity as viscosity increases
The velocity of flow increases to a maximum at the centre of the tube (blood vessel)
138
What happens to the velocity if flow in a vessel has a negligible resistance
It is the same across the tube
139
What does the venous system transport
Blood from tissues systems/ organs back to the heart
140
Why are venous valves orientated towards the heart
To maintain blood flow in one direction
141
How does exercise aid in venous return
During exercise, venous return is aided as intrathoracic pressure becomes more negative – deeper and more frequent respirations increase the pressure gradient between abdominal and thoracic veins.
142
What is preload
Venous return to the right ventricle
143
What occurs if preload increases
The heart will have to work harder to pump the blood out and this can be a problem in coronary artery disease and heart failure
144
What are the types of circulation
Coronary
skeletal muscle
Cerebral
145
What is coronary circulation
Facilitates perfusion of
myocardium
Maintains high basal rate of O2 supply to cardiac muscle
146
What percentage of cardiac output does the heart receive
5% (<0.5% of total body weight)
147
What supplies the entire myocardium
Right and left coronary arteries
148
Where do the coronary arteries originate
From root of aorta, behind cusps of the aortic valve
149
What does the left coronary artery divide into
Left coronary artery divides close to its origin into left circumflex artery – branching to the LA & LV and the left anterior descending artery, descending to the apex – branching to supply interventricular septum and portion of right and left ventricles.
150
What are the circulations with specialised local control
Pulmonary circulation
Skin circulation
Renal circulation
Coronary circulation
Skeletal muscle circulation
Cerebral circulation
151
Where do the epicardial veins transport blood to
Coronary sinus
152
What does the coronary sinus do
Empty blood into the right atrium
153
What does the thesbian veins do
Drain deoxygenated blood from capillary networks in ventricular wall directly into the cardiac chambers
154
When does perfusion of the myocardium from the coronary arteries occur
During early diastole
155
What percentage of left coronary blood flow occurs during diastole
80%
156
what is the maximal cardiac work
300-400ml/min/100g
157
Why does ventricular mass increase in exercise training
To meet physiological demands of prolonged exercise training
158
What is an athletic heart
Physiological adaptation of structural and functional remodelling in response to exercise training.
159
What is blood flow coupled to
Exercise intensity
160
How is blood flow regulated at rest
Sympathetic innervation
161
What are some local vasodilators in skeletal muscle
Lactate
Adenosine
Potassium ions
162
What does muscle capillary density depend on
Muscle function
163
What does Alpha 1 adrenoreceptor activation cause
Vasoconstriction: increased resistance, decreasing blood flow
164
Which vasoconstriction primarily dominates
Alpha-1 induced
165
What does Beta-2 adrenoreceptor activation cause
Vasodilation: decreased resistance, increased blood flow
166
Where is adrenaline released
Adrenal gland
167
What is a special adaption of skeletal muscle contraction
Adrenaline causes vasodilation
168
Where does tonic sympathetic vasoconstriction continue
In feed arteries and proximal resistance vessels
169
What arteries account for 50% of vascular resistance
Cerebral arteries
170
What forms the circle of Willis
Basilar and internal carotid arteries enter the cranial cavity and anastomose
171
What does the circle of Willis do
Can help to preserve cerebral perfusion if carotid artery obstruction occurs
172
What can lead to cerebral vasodilation
Local hypoxia
173
What is cerebral autoregulation
Cerebral resistance vessels dilate
to maintain perfusion when
arterial blood pressure falls below arterial blood pressure of -60mmHg, cerebral blood flow steeply declines
174
What can reduce cerebral perfusion (dizziness)
Hyperventilation
175
What is hypercapnia
Prescence of higher than normal level of carbon dioxide in the blood
176
What does hypercapnia cause
Cerebral vasodilation, mediated by endothelial NO
And cerebral vasoconstriction
177
What are cerebral resistance vessels highly sensitive to
Local hypoxia and arterial CO2
178
Why are capillary walls normally 1 cell thick
Allow optimal exchange between blood and tissues via fenestrations
179
What layer do capillaries lack
Tunica media
Tunica adventitia
180
What size are the veins lumens relative to arteries
Larger diameter and lumen with thinner vessel walls
181
At low blood pressure what percentage of total blood volume do veins contain
70%
182
What doe venous valves do
Prevent backflow of blood due to lower pressure flowing through vessels
183
What could occur if venous walls or valves lost their elasticity
Leads to weakening of these structures resulting in turbulent blood flow within the vessel and can result in development of varicose veins as the vessel wall becomes distended
184
What is the 3 layer wall structure that blood vessels share (aside from capillaries)
Tunica intima
Tunica media
Tunica Adventitia
185
What is the structure of the tunica intima
Consists of endothelial cells attached to a basement membrane
Underlying layer of extracellular matrix
Separated from media by internal elastic lamina
186
What is the structure of the tunica media
Layers of elastin fibres and smooth muscle cells - proportion dependent on vessel function e.g. whether elastic or muscular artery
High elastin content enables vessel wall expansion during systole and recoil during diastole
187
What is the external layer on blood vessels
Tunica adventitia
188
What is the structure of the tunica adventitia
Often separated from media by external elastic lamina
Thick connective tissue -elastic and collagen fibres
Contain network of nerve fibres, lymphatics and in larger arteries, vasa vasorum perfuse the outer media
189
What fibres does the tunica adventitia contain
Collagen and elastic
190
What do larger blood vessels contain in the tunica adventitia
Vasa vasorum (small arterioles) which perfuse the outer media (are vessels of the vessels)
191
What is compliance in relation to blood vessels
The ability of a blood vessel wall to passively expand and recoil in response to changes in pressure
192
How is compliance calculated
Change in volume/ Change in pressure
193
What occurs during arterial compliance
Arterial wall will expand to accommodate the
ventricular stroke volume allowing large arteries to act as pressure reservoir
194
What does the decline in arterial compliance due to age affect
Can increase pulse pressure
195
What is arteriosclerosis
Age related arterial stiffness due to calcification of elastin, collagen and the extracellular matrix
196
Why are endothelial cells arranged along the axis of blood vessel walls
To minimise shear stress by providing a friction free surface for blood flow
197
What role to endothelial cells play in cardiovascular function
-Regulate platelet function and fibrinolysis
-Promote angiogenesis and vessel remodelling
-Regulate permeability of blood vessels (form a selective barrier between blood and tissues)
-Form inner lining of entire blood vessel (tunica intima) system and the heart
198
What is angiogenesis
Process of new capillaries forming out of pre-existing blood vessels
199
What do SMCs secrete
An extracellular matrix which gives cells their elastic properties
200
What is vasoconstriction
Contraction of vascular smooth muscle to narrow vessel lumen and reduce radius
201
What is vasodilation
Relaxation of vascular smooth muscle to widen vessel lumen and increase radius
202
What is the appearance of SMCs
Mononucleated spindle shaped non-striated myocytes
203
How is peripheral resistance determined
Autonomic activity
Pharmacologic agents
Blood viscosity
204
What does Local control refer to (BP)
The mechanism of altering small artery and arteriolar resistance in organs and tissues
-self regulation of blood flow
-regulation by autocrine and paracrine substances
205
How does adrenaline aid in local control
Released from adrenal medulla, circulates in blood and binds (mostly) to beta 2 adrenoreceptors leading to vasodilatation via increase in cAMP and reduced sensitivity for SMC contraction
206
When does adrenaline cause vasoconstriction
At high conc adrenaline binds to alpha 1 adrenoreceptors on arteriolar smooth muscle causing contraction
207
What does ANP stand for
Atrial Natriuretic Peptide
208
How does ANP influence BP
A potent vasodilator and influences BP due to regulation of Na+ balance and blood volume
209
What does Angiotensin II do
Constricts arterioles and is important as part of RAAS (renin - angiotensin - aldosterone system)
210
What is the RAAS
Reduced blood flow to kidney is sensed by receptors in juxta – glomerular apparatus in kidney, causing release of Renin from juxta – glomerular cells.
Renin acts on circulating Angiotensinogen (produced by liver) to convert it to Angiotensin I
Angiotensin I is converted by angiotensin converting enzyme (ACE) – released from endothelial cells – in the lungs and kidney to Angiotensin II
Angiotensin II is a potent vasoconstrictor
211
How does angiotensin II increase intravascular volume
Stimulates Na and water reabsorption and stimulates
release of aldosterone from
adrenal cortex
Aldosterone acts on distal convoluted tubule (DCT) and collecting duct (CD) of kidney to increase sodium and water retention therefore increasing intravascular volume.
212
What stimulates the release of aldosterone from the adrenal cortex
Angiotensin II
213
How does Angiotensin II increase water reabsorption
Angiotensin II stimulates antidiuretic hormone (ADH) release from posterior pituitary gland
ADH release causes increased water via aquaporin – 2 channels in DCT and CD of kidney and vasoconstriction of blood vessels via V1 receptors on vascular SMCs.
214
How do many drugs lower blood pressure
By acting on the RAAS pathway
215
Which nervous system does the RAAS pathway affect
Autonomic nervous system
(sympathetic)
216
What are some vasodilators
Nitric Oxide (NO)
-Produced by Nitric Oxide Synthase (NOS) from L – arginine in vascular endothelial cell
-NO diffuses into SMC and induces relaxation via cGMP activation of guanylate cyclase.
-NO release occurs in response to factors such as binding of endothelium dependent vasodilators (e.g. acetylcholine, ATP and bradykinin) to receptors on surface membrane of endothelial cells and shear stress.
Prostaglandin I2 (Prostacyclin)
-Eicosanoid produced in endothelial cells
-Activates adenylate cyclase to increase cAMP production, activating protein kinase A (PKA)
-Leads to vasodilation
217
What are some vasoconstrictors
Endothelin – 1 (ET – 1)
-Belongs to endothelin family of peptide agents
-Secreted by endothelial cells in response to stimuli such as pulsatile stretch, sheer stress, neurohormones and cytokines
Acts on ETA receptor on vascular smooth muscle cells to initiate vasoconstriction
Thromboxane A2
-Eicosanoid
-Activated by tissue injury and inflammation
218
What is shear stress
Force that blood flow exerts on the vessel wall
219
Why does shear stress occur
Due to blood travelling at different velocities within a blood vessel
220
What can lead to physiologic adaptation of disease of the blood vessel wall
Alterations in the homeostatic conditions:
-exercise
-pregnancy
-growth
-hypertension
-flow reduction
-flow overload
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What is the primary site for exchange of fluid, electrolytes and gases
Capillary system
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What are the spaces separating endothelial cells of the capillary walls
Intercellular clefts
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What are the 3 structural classifications of capillaries
Continuous
Fenestrated
Discontinuous
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What are the properties of continuous capillaries
Continuous basement membrane with tight intercellular clefts
Continuous capillaries have the lowest permeability
225
Where are continuous capillaries found
Muscle
Skin
Pulmonary system
CNS
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Where are fenestrated capillaries found
Exocrine glands
Renal glomeruli
227
What are fenestrated capillaries
Possess perforations or fenestrations in endothelium
Enables relatively high permeability
228
Where can discontinuous capillaries be found
In liver
229
Which capillaries are the most permeable
Discontinuous due to large intercellular clefts and gaps in the basement membrane
230
What are metarterioles
Terminal arterioles that do not contain a continuous layer of smooth muscle, instead smooth muscle fibres encircle the vessel at intermittent points along its length
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What do metarterioles do
Connect arterioles and venules and branch off to capillaries
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Why is blood through capillaries not continuous
Vasomotion
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What is vasomotion
Spontaneous oscillation in tone of blood vessel walls, independent of heart beat, innervation or respiration
234
What is the ring of smooth muscle surrounding branch sites of capillaries
Pre-capillary sphincters which contract and relax in response to local metabolic factors.
235
Which are lower:
Pulmonary hydrostatic pressures or systemic hydrostatic pressures
Pulmonary hydrostatic pressures
236
What is pulmonary oedema
Excess fluid in the lungs that collects in the alveoli
237
How might pulmonary oedema be induced
-Heart failure
-Left side heart failure – capillary hydrostatic pressure is increased, particularly in extremities
-Right sided heart failure
-High altitude exposure
-Lung damage due to severe infection
-Adult respiratory distress syndrome
-Following major injury
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What does the lymphatic system play a role in controlling
Concentration of proteins in interstitial fluids
Volume of interstitial fluids
Interstitial fluid pressure
239
What does increasing the interstitial fluid pressure result in
Increase in the rate of lymph flow, which caries interstitial fluid volume and protein that accumulates in interstitial away
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What is the purpose of the lymphatic system
Acts as an overflow mechanism to return excess fluid volume from tissue spaces to the circulation
241
How does increasing colloid osmotic pressure in interstitial fluid promote fluid filtration
Shifts the balance of forces at the membrane of blood capillaries in favour of fluid filtration
242
What exists under normal conditions of most capillaries
A state of near equilibrium
243
What is a near state of equilibrium within capillaries
The amount of fluid filtering outward from arterial end
is almost exactly equal to fluid returned to the circulation by absorption
244
How does disequilibrium occur within capillaries
Fluid returned to the circulation via the lymphatic system
245
What is the structure of the lymphatic system
A network of small lymph nodes and lymphatic vessels through which lymph flows
246
What is lymph
A fluid derived from interstitial fluid
247
What does hydrostatic pressure do
Tends to force fluid and dissolved substances through capillary intercellular spaces to the interstitial spaces
248
What causes osmotic pressure
Plasma proteins
249
What forces fluid movement from interstitial space to the blood via capillary intercellular spaces
Osmotic pressure
250
What happens to hydrostatic pressure as blood pressure drops from arterial to venous system
Decreases
251
Why does fluid move out of capillaries at the arterial end and in at the venous end
Hydrostatic pressure drops from arterial to venous system and the colloid osmotic pressure remains constant forcing fluid out at the arterial end and providing an osmotic gradient at the venous end with a high conc of proteins which are too big to pass out of capillaries
