Circulation Flashcards
Name the 3 parts of the circulation
- Resistance part (Arteries)
- Exchange area (Capillaires)
- Reservoir (Veins)
Location of resistance part of the circulation
Left ventricle → Capillary bed
Location of the exchange area of the circulation
Locations of bidirectional transport of material
Location of the reservoir system of the circulation
Venules → Right atrium
Under normal conditions, the largest part of blood volume is located in…
The reservoir system
Describe the structure of an artery
- Muscular
- Elastic
- Thick walled
Describe the structure of an arteriole
- Muscular
- Little connective tissue
Describe the structure of a capillary
- Endothelial layer
- No muscle
Describe the structure of a venule
- Thin walls
- Some smooth muscle
Describe the structure of a vein
- Thin-walled
- Smooth muscle
- Flacid
The resistance part is composed of…
- Elastic arteries
- Muscular arteries
- Arterioles
Elastic arteries
- Aorta & large arteries
- Loaction of passive contraction (due to elastic elements)
Muscular arteries are the sites of…
- Regulated resistance
- Smooth muscle → active contraction
Arterioles
- Most important part of regulated resistance
During diastole, the aorta…
Passively contracts
‘Windkessel’ function of the aorta
- A simple pump with a closed air buffer
- Storage of pressure in the Windkessel
- Results in a near-constant pressure
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What is the location of capillary exchange?
Area of microcirculation
List the types of capillary
- Continuous
- Fenestrated
- Porous
- Sinusoid
Location of continuous capillaries
- Muscle
- Skin
- CNS
- Lung
Location of the fenestrated capillaries
- Intestinal mucosa
- Endocrine glands
Location of the porous capillaries
Glomeruli of the kidney
Describe the structure of continuous capillaries
- Endothelium (Inside layer)
- Lamin basalis
- Pericytes (Outside layer)
Sinusoid capillaries lack…
Pericytes
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Disse-space
Location of sinusoid capillaries
- Liver
- Haemopoietic organs
What limits the enlargement of veins?
Collagen
List the types of Venule
- Postcapillary venule
- Collecting venule
- Muscular venule
The function of venules is determined by…
The structure of the wall and valves
Potential energy
The pressure exerted onto the wall of the container (vessels)
Kinetic energy =
1/2 m x v2
Cause of energy loss in circulation
Flow friction
Resistance is determined by…
Flow rate
Kinetic energy =
Total energy - Potential energy
- Pitot-system
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Narrowing of blood vessels causes….
- A increase of kinetic energy
- A decrease of potential energy
Viscosity is higher in…
Larger vessels
(Fahraeus-Lindquist effect)
The viscosity of blood is a function of…
The hematocrit value
Factors maintaining the BP in Arteries
- Work of heart
- Total peripheral resistance (TPR)
- Distribution of blood
- Types of blood flow
Runoff (Qr)
Volume of blood which moves from:
Arterial part → Venous part
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The artificial increase in work of the heart is by…
Pacemakers
The natural increase in work of the heart is by…
Sympathetic activation
Increase in TPR causes…
Increase of blood pressure
What allows arteries to distend?
- Elastic elements
- Myogenic elements
Critical closing pressure
Pressure where vessels are collapsing
Arterial distensibility
- Volume change related to pressure change related to the original volume
- D = dV / dP x Va
What is compliance?
Volume change per unit pressure change
When is distensibility used for blood pressure?
If different circulations are compared
When is compliance used for blood pressure?
When absolute change is of interest
Compliance decreases with…
Age
Law of Laplace related to blood vessels
- In order to maintain BP
- There should be an increase in wall tension
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An increase in arterial volume causes…
An increase of blood pressure
Parallel attachment of organs is beneficial because…
Changes in perfusion of one organ don’t suddenly change the work of the heart
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Examples of serially coupled elements of the circulation
- Arteries
- Capillaries
- Veins
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Perfusion
- Flow of volume
- Determined by Ohm’s law
Reynolds number =
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Laminar blood flow
Re<2320
Turbulent flow
Re>2320
The physiological relevance of laminar flow
- Low resistance, less work of the heart
- Blood cells arranged in the axis of the flow
Capillary blood pressure is maintained by…
Microcirculation
Factors maintaining venous blood pressure
- Gravitation
- ‘Vis a tergo’ (work of the heart)
- Valves
- Skeletal muscle pump
- Central venous pressure (CVP)
Skeletal muscle pump
- Muscle tension pumps blood
- Valves cause centripetal flow
- Weak muscle tension → Blood accumulation → Increased pressure → Oedema
Pressure changes in chest and abdomen
- Inspiration → Intrathoracic pressure decreases (RA fills)
- Abdominal pressure → Transmural pressure of veins in abdomen
Peripheral blood pressure is maintained by…
Cardiovascular regulatory mechanism
Static pressure
- Blood pressure measured post mortem
- Approx 7mmHg
Blood pressure above and below the heart
- Higher below the heart
- Lower above the heart
Pulse pressure
Systolic pressure - Diastolic pressure
- e.g 120 - 80 = 40 mmHg
Mean arterial pressure
- Weighted average of the systolic and diastolic pressure
- Diastole 2 times longer than systole, therefore:
- (Psyst + (2xP diast)) /3
Relationship of blood pressure and body size
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Types of blood pressure measurement
- Direct method
- Indirect method
- Palpation
- Auscultation
Direct blood pressure measurement
- Glass catheter inserted into carotis
- Height of fluid volume measured
Palpation blood pressure measurement
- Closing a BP cuff
- Opening and recording Systolic BP when a pulse is felt
Cannot measure diastolic pressure
Auscultation blood pressure measurement
- Closing cuff around an arm
- Opening cuff and listening for first pulse (Systolic pressure)
- Continue opening, listening for the sound to stop (Diastolic pressure)
What is the diagram?
What is indicated?
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Pressure pulse
- Anacrotic limb
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Steepness
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Pulse pressure
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Dicrotic notch
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Catacrotic limb
Speed of a palpable pulse
7m/sec
Dicrotic notch of pressure pulse
- Effect of the reflected pressure wave
- Increases with distance from the aorta
Flow rate in the aorta
40cm/sec
Flow rate in capillaries
0.33mm/s
Pulse diagnosis is carried out with…
A sphygmograph
The sphygmograph shows which components?
- Frequency
- Rhythm
- Amplitude
- Steepness
- Tension
Which two kinds of substance exchange occur during microcirculation?
- Diffusion
- Filtration/resorption
What % of capillaries are open during rest?
5-10%
Filtration is blocked by…
The precapillary sphincter
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Components of microcirculation
- Arterioles
- Metarterioles
- Precapillary sphincters
- Capillaries
- Venules
The two types of capillary exchange
- Flow limited
- Diffusion-limited
What is exchanged by capillaries?
- Gas
- Ions
- Small substances
Transport of small molecules during diffusion is dependent on…
Blood flow
Flow limited needed
Transport of large molecules during diffusion required
Diffusion limited exchange
What are the determining factors of diffusion?
- Conc. gradient
- Permeability
- Surface area
The extent of gas diffusion is dependent on…
Partial pressure
The higher the O2 consumption, the faster the drop of…
pO2
(Partial pressure of oxygen)
The drop of pO2 leads to…
How is it mitigated?
- Hypoxia
- More capillaries open → Local autoregulation
Partial pressure of a gas
Measure of how much gas is present
Major/Starling forces of substance exchange
- Hydrostatic pressure difference (Ph)
- Permeability
- Oncotic pressure (Ponc)
- Pressure of tissue (Pinterst)
The direction of substance movement is determined by…
Effective filtration pressure
Peff =
Phydrostatic - Poncotic - Ptissue
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Net filtration
Phydrostatic > Poncotic
Net reabsorption
Phydrostatic < Poncotic
Phydrostatic at the arteriolar end of the capillary
35mmHg
Phydrostatic at the venule end of the capillary
15mmHg
Pressure profile of the capillary is…
Linear
Phydrostatic of ISF
5 mmHg
Colloid Oncotic pressure
- Sucking force
- Absorbing H2O from the ISF to the plasma
- Proportional with [protein]
Oncotic pressure of plasma
28mmHg
Oncotic pressure of ISF
3mmHg
Net oncotic pressure value
25mmHg
The balance of effective partial pressure can be altered by
- Changes in capillary pressure near arterioles or venules
- Alterations in oncotic pressure
Vasodilation
Increased BP at the capullaries
Characteristics of the venous system
- Capacitance system
- Redistribution
- Large distensibility
What % of blood is found in the veins?
55-75%
What sets the limit of distensibility of veins?
Collagen networks of vessels
Pressure goes…from veins to venules
Down
Local/intrinsic regulation of circulation
Dependent on oxygen and nutrient demand of organs
Central/Extrinsic regulation of circulation
Maintaining the optimal working condition of organs
List all forms of the regulatory systems
- Intrinsic short term
- Intrinsic long term
- Extrinsic short term
- Extrinsic long term
Intrinsic short term regulation
- Fast adjustment of perfusion rate
- Autoregulation & myogenic regulation
- Constant perfusion rate
- Endothel derived regulation
- Metabolites related regulation
- Autoregulation & myogenic regulation
Autoregulation by myogenic tone
- Microcirculation not influenced by BP (Myogenic adaptation)
- Bayliss effect
Bayliss effect
- Pressure changes → Metarteriole sphincter contraction/relaxation
- Stable pressure maintained
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Autoregulation of perfusion exists within which pressure range
40-140mmHg
Endothel-related humoral factors
- Endothelium-derived relaxing factor (EDRF)
- Endothelium-derived contracting factor (EDCF)
Describe detection during endothel-related regulation
- BP expressed on endothelium
- Deformation + plasma factors
- Humoral signals generated
- Contraction of smooth muscle
Causes of EDRF regulation
- Nitrogen monoxide
- Prostacyclin (PGI2 hormone)
- Endothelial-factor
Mechanism of nitrogen monoxide in endothelial related regulation
- NO → Smooth muscle
- cGMP increases
- Smooth muscle relaxes
Mechanism of Prostacyclin (PGI2 hormone) in endothelial related regulation
Increases production of NO
Mechanism of endothelial-factor in endothelial related regulation
- Hyperpolarisation by activating ATP dependent K-channels
- K is an indirect vasodilator
Causes of EDCF regulation
- Endothelins
- Cyclooxygenase dependent factors
- Angiotensins
Mechanism of Cyclooxygenase dependent factors in the Endothelial related regulation
- TXA2
- Stimulates NO degradation
Also a direct effect resulting in contraction
Mechanism of Endothelins in Endothelial related regulation
- Strong constrictors
- ET-1-3 (in tissues)
- ET-4 (In lung)
Mechanism of Angiotensin-II in Endothelial related regulation
Direct vasoconstrictor
- Stimulates endothelin production
- Increases sympathetic vasoconstriction
ET-1
- Binds to ET receptor
- Vasoconstriction of airways and lung
- Formation of new blood vessels
- Survival of specific cell types
Role of acetylcholine in endothelial related regulation
- Through nerve endings
- Direct stimulation
- Vasoconstriction
- From lumen of the blood vessel
- Increase NO production
- Vasodilation
During endothelial related regulation through metabolites, increased metabolic activity results in…
- Increased O2 consumption
- Increased [adenosine]
- Increased [H+]
- Increased [CO2]
- Increased [K<span>+</span>]
All stimulate EDRF stimulation
What is the response to EDRF stimulation through increased metabolic activity?
- NO production increases
- PGI2 released
- Hyperpolarising factors released
Lack of oxygen at a tissue level (hypoxia) causes…
- Automatic increase of perfusion
- Better O2 supply
Intrinsic long-term regulation
- Morphologic changes
- Stimulation of revascularisation
Hyperemia
Increased local perfusion
Give the types of hyperemia
- Active (functional) hyperemia
- Reactive hyperemia
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Active hyperemia
Caused by increased metabolic activity of the tissue
Reactive hyperemia
A secondary increase of perfusion
Compression of artery → hyperemia
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Causes of extrinsic short-term regulation of circulation
- Sympathetic effects
- Parasympathetic effects
- Humoral effects
- Vessel-related reflexes
Extrinsic regulation of circulation
- Compensation of organ perfusion differences
- via redistribution
- Balance of:
- Sympathetic-vasoconstrictor tone
- Sympathetic-vasodilator tone
- Results in permanent vasoconstriction
Location of the cardio-vasomotor centres
Medulla oblongata
(formatio reticularis)
List the cardio-vasomotor centres
- Pressor area
- Depressor area
- Cardioaccelerator area
Pressor area responsibilities
- Spontaneous activity of the heart
- General sympathetic vasoconstriction
- Increasing blood pressure
Depressor area responsibilities
- Blood pressure decrease
- Vasodilation
- Decrease chronotropic and dromotropic effects
- Direct inhibition of pressor centre
Effect of the depressor centre on heart rate
Inhibits cardiac activity via vagal stimulation
- n. vagus determines the work of the heart
Sympathetic effect on the circulation
- The depressed activity of the pressor area
- The decrease of sympathetic vasoconstrictor tone
- Vasodilation
Parasympathetic effects on the circulation
Decrease of sympathetic vasoconstrictor tone
(No parasympathetic effect is actually expressed)
Indirect parasympathetic vasodilation
Bradykinin release → Vasodilation
During exercise, redistribution of blood is mainly to the…
Skeletal muscles
Redistribution in regulation of circulation
- Resistance vessels
- (under influence of sympathetic postganglionic fibres)
Vasomotor effect of regulation of circulation
- Decreased sympathetic predominance → vasodilation
- Epinephrine release → Dilates vessels of skeletal muscle
- Increased perfusion to the skeletal muscle
- Increased Cardiac output
Humoral regulation of circulation effects
- Epinephrine
- Nor-epinephrine
- Other hormones
Small epinephrine dose causes…
- Skeletal muscle vasodilation
- Through ß-adrenergic receptors
- Skin/splanchnic muscle vasoconstriction
- Through α-adrenergic Receptors
High dose of epinephrine causes…
General α-adrenergic constriction
Effect of norepinephrine dose
Has only α-adrenergic vasoconstrictive effect
Humoral regulation of circulation effect
- Transport via blood (endocrine)
- Epinephrine + norepinephrine
List the blood vessel related reflex mechanisms
- Baroreceptors
- Volume receptors
- Bainbridge-reflex
- Effect of pO2 and pCO2
Location of baroreceptors
-
Arcus aortae
- Baroreceptors & Chemoreceptors
-
Sinus caroticus
- Baroreceptors & Chemoreceptors
Function of baroreceptors
Fast resetting of blood pressure
Describe Heimans’ crossed-dog experiment
- Dog B blood → Dog A (via carotis)
- Dog A BP changes reciprocally to dog B
What is the effective range of baroreceptors?
50-170mmHg
Volume receptors functions
- Atrial stretching → ADH release
- ANF (atrial natriuretic factor) release during hypervolaemia
Volume receptors
Regulate cardiovascular and renal volume
What does this figure show
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The Starling mechanism/Bainbridge effect on heart rate
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Intravenous infusion
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Atrial pressure increases
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CNS pressor response
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HR increase
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Transient increase in cardiac output
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- Baroreceptor reflex
- (Overrides the Bainbridge reflex)
- CNS depressor response
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HR decrease
Location of peripheral receptors of pO2 and pCO2
- Glomus caroticum
- Glomus aorticum
What stimulates peripheral differentiation?
Decrease of pO2
What stimulates central afferentation?
Increase of pCO2
What stimulates efferentation?
Sympathetic activation
Extrinsic long-term regulation
- CV system adapts to the needs of the organism
- Adaptation in climatic changes
- Long-term changes in oxygen supply
Organs with specialised circulations
- Heart
- Brain
- Skin
- Liver
- Fetus
Coronary circulation during systole
- Fast ejection:
- High pressure ensures coronary flow
- Slow ejection:
- Aortic pressure drops → slow coronary perfusion
Coronary circulation during diastole
Maximal coronary flow (More than when in systole)
What occurs in the coronary circulation during the beginning of systole?
- Blood pressed out from coronary vessels
- Reversed flow of blood
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What occurs in the coronary circulation during the end of systole?
- Fast ejection
- Slow ejection
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Describe the blood flow entering and leaving the brain
Both are of equal value
Blood pressure in the brain
Between 60-160 mmHg
- Blood flow doesn’t change when in this range
Splanchnic circulation
- Double, serially-attached capillary system
- Main regulator → Alpha-receptor (Sympathetic tone)
Blood entering the fetal circulation
- Via umbilical vein
- 85% spO2
- 35 mmHg pO2
- Travels to the liver and heart
Describe circulation at birth
- After delivery → Increase of pulmonary circulation
- The onset of breathing → Surfactant factors appear
- Pulmonary resistance decreases dramatically
- More blood passes through the lung
Which process closes the ductus arteriosus?
Prostaglandin liberation
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Placenta
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Liver