Special Circulations Flashcards
What are the 2 circulations to the lungs?
Bronchial circulation
Pulmonary circulation
What is Bronchial circulation?
Part of systemic circulation which supplies Oxygen to the parts of the lungs NOT CLOSE to thee alveoli
It meets the metabolic requirements of the lungs
What is the pulmonary circulation to the lungs?
Blood supplied to the alveoli for gas exchange
What is the normal cardiac output for the typical 70kg male at rest?
5 L/min
What physiological situation does Cardiac Output increase with?
Exercise
What chamber of the heart is the pressure of the pulmonary artery equal to during SYSTOLE?
Right Ventricle
(Pulmonary artery pressure = Right ventricular pressure in diastole)
Is the pressure of the pulmonary artery less than, equal to or greater than the right ventricle in DIASTOLE?
Why?
Pulmonary artery pressure > RV pressure
Elastic recoil of artery makes it greater
What is the relative pressure of the right atrium compared to the right atrium during DIASTOLE?
Pressures equal
What chamber of the heart is the pressure of the aorta equal to during SYSTOLE?
Left ventricle
Is the pressure of the aorta less than, equal to or greater than the Left ventricle in DIASTOLE?
Why?
Aorta pressure greater than LV in diastole
Elastic recoil or aorta makes it a greater pressure
In terms of pressures, how are the atrial and ventricular pressures related in DIASTOLE?
Pressure of ATRIA = Pressure of Ventricles
What relative pressure and resistance does the pulmonary circulation/right side of the heart work at?
Low pressure
Low resistance
What relative pressure and resistance does the systemic circulation/left side of the heart work at?
High pressure
Higher resistance
What contributes to the low pressure of the pulmonary circulation?
Low Mean Arterial Pressure
Low Mean Capillary Pressure
Low Mean Venous Pressure
What contributes to the low resistance of the pulmonary circulation?
Short + wide vessels
Lots of capillaries (lots of parallel elements)
Arterioles have relatively little smooth muscle
What contributes to the High pressure of systemic circulation?
High Mean Arterial Pressure
HighMean Capillary Pressure
High Mean Venous Pressure
What contributes to the High resistance of systemic circulation?
Long + Narrow vessels
Variable blood flow to capillaries
Arterioles have relatively thick smooth muscle walls
What are the 2 adaptations to promote efficient gas exchange at the lungs?
High capillary density in Alveolar wall(Large SA)
Short diffusion distance
What needs to match the rate of ventilation of alveoli for efficient gas exchange?
Ventilation of alveoli = Perfusion of alveoli
Ventilation must match perfusion
What is the optimal perfusion ratio (V/Q ratio)?
V/Q = 0.8
How may mucus build up affect Perfusion ratio (V/Q ratio)?
Mucus prevents ventilation so means any perfused blood is not oxygenated
How is blood diverted away from alveoli that are not well ventilated to maintain an optimal V/Q ratio?
Hypoxic pulmonary vasoconstriction
What is hypoxic pulmonary vasoconstriction?
When the pulmonary blood vessels constrict in a response to hypoxia
Ensures that perfusion matches ventilation so that poorly ventilated alveoli get less perfused (maximising gas exchange)
How is hypoxic pulmonary vasoconstriction different to the response of hypoxia in the systemic circulation?
Response is opposite
In systemic vasodilation happens to maximise blood flow to area
In pulmonary vasoconstriction happens to keep blood away from areas that it wont get oxygenated
What negative effects can happen as a result of Chronic hypoxic vasoconstriction?
Chronic increase in vascular resistance causing Chronic Pulmonary Hypertension
High AFTERLOAD on RV, leads to RV Hypertrophy and eventually RV HEART FAILURE (this is called cor pulmonale)
How does gravity effect the lower pressure blood vessels of the pulmonary circulation?
Strongly
How does pressure affect the status of the vessels in the lungs during diastole at the Apex of the lungs, level of the heart and base of the lungs?
Apex vessels - Collapse during diastole, open in systole
Level of Heart vessels - Continuously open
Base of lung vessels - Vessels constantly distended/swollen
How does hydrostatic pressure in blood vessels change as you go down the body?
Increased pressure
More fluid above
What happens to pulmonary blood flow in exercise?
Inc Cardiac output
In Pulmonary arterial pressure opening apical capillaries
Inc O2 uptake by lungs
Capillary transit time reduces
What 2 types of pressure contribute to formation of tissue fluid
Hydrostatic pressure of blood in capillary
Oncotic pressure
What is oncotic pressure?
Pressure exerted by plasma proteins in the capillary drawing fluid back into the blood
What influences capillary hydrostatic pressure more, venous pressure or arterial pressure in the systemic circulation?
Venous pressure
What increase in pressure leads to peripheral oedema ?
Inc Central Venous Pressure
Hypertension doesn’t usually result in peripheral oedema
What factor causes a low amount of lymph/tissue fluid produced in the lungs?
LOW capillary hydrostatic pressure of capillaries in lungs
What is the primary cause of oedema causing capillary pressure to increase?
Increased Venous pressure
What may lead to Venous pressure increasing leading to pulmonary oedema?
Mitral valve stenosis
Left ventricular failure
How can Mitral valve stenosis lead to pulmonary oedema?
Pressure builds up in Left Atrium
Leads to pressure build up in the pulmonary veins leading to the left atria
Increased pulmonary venous pressure leads to increased capillary/hydrostatic pressure leading too more tissue fluid being filtered out than reabsorbed
How can left ventricular failure lead to peripheral oedema?
Pressure builds up in the Left Ventricle
Leads to increased pressure in the Left Atrium
Leads to increases pressure in the pulmonary veins
Increased Pulmonary Venous Pressure leads to pulmonary oedema
How does Pulmonary Oedema affect gas exchange?
Impairs gas exchange
How does pulmonary oedema change when standing up and lying down?
Changes with hydrostatic pressure (due to gravity)
Forms at bases when standing
Forms throughout lungs when lying down
What symptoms does pulmonary oedema cause?
Breathlessness
How can the symptoms of pulmonary oedema be relieved?
Diuretics to minimise fluid retention
How does the Cerebral circulation meet the high O2 demand for the brain?
High capillary density
High basal flow rate
High O2 extraction
Why is a secure blood supply to the brain vital?
Neurones very sensitive to hypoxia
Irreversible damage to neurones after 4 mins without oxygen
What is an anastomoses?
An alternate pathway for blood to flow through in case of a blockage in one of the vessels
Structurally how is a secure blood supply to the brain ensured?
Anastomoses between basilar and internal carotid arteries
What is the main anastomotic structure of the cerebral circulation?
Circle of Willis
Functionally how is a secure blood supply to the brain ensured?
Myogenic auto regulation maintains perfusion during hypotension
Metabolic factors
Brainstem regulating other circulations
What is hypercapnia and hypocapnia?
High or low partial pressure of CO2
How do metabolic factors help secure blood flow to the brain?
Cerebral vessels are very sensitive to changes in arterial partial pressure of CO2
What happens to cerebral blood vessels in hypercapnia?
Vasodilation
What happens to cerebral blood vessels in Hypocapnia?
Vasoconstriction
Why does panic hyperventilation lead to dizziness or fainting?
Can cause hypocapnia by expelling lots of CO2
Causes cerebral blood vessels to vasoconstriction reducing blood flow to brain
What is the myogenic auto regulated response of the cerebral blood vessels when blood pressure increases?
Vasoconstriction
Reduce the blood flow to the brain
What is the myogenic auto regulated response of the cerebral blood vessels when blood pressure decreases?
Vasodilation
Increase blood flow to brain
If there is high activity in the brain what affect does this have on blood flow?
Areas with increased neuronal activity = increased blood flow
What is metabolic hyperaemia?
Increased blood flow to a highly metabolically active area
What metabolites act as vasodilators?
Increased:
-Partial pressure of CO2
-[K+]
-Adenosine (From ATP breakdown)
Decreased:
-Partial pressure of O2
If intercranial pressure increases how is cerebral blood flow affected?
Impaired
What happens if blood flow to the vasomotor control regions of the brainstem is impaired?
Increased sympathetic vasomotor activity
Increases arterial BP
(This helps maintain cerebral blood flow)
What baroreceptor reflex is stimulated when blood pressure increases?
Reflex bradycardia
What does bradycardia + acute hypertension indicate and why?
Hall mark of space occupying lesion in brain
Cerebral tumour increases intracranial pressure. This impairs cerebral blood flow. Blood flow to vasomotor control region in brainstem impaired leading to vasoconstriction which increases the BP. This stimulates the bradycardic response
What are the 3 main coronary arteries?
Right Coronary artery
Left Coronary artery branches into 2:
-Circumflex (Posteriorly)
-Left Anterior Descending (Front) LAD
Where do the coronary arteries come from?
First branches of aorta
When does the left coronary artery mainly flow with blood, systole or diastole?
Diastole
Why does angina come on during exercise but is relieved by rest?
In exercise Diastole period decreases. Left coronary artery mainly has blood flow during diastole, so less blood supplied to heart in exercise causing hypoxia to heart muscle, transient ischaemia causing pain
How is the coronary circulation maximised for blood flow?
High capillary density (Facilitates efficient O2 delivery)
Very short diffusion distance
What factors of the coronary blood vessels help cope with increases myocardial O2 demand?
Increased coronary blood flow (proportional up until a point)
Small increase in amount of Oxygen extracted
What causes the vasodilation of coronary arteries when demand for oxygen by the heart is high?
Metabolic hyperaemia
Adenosine, increased [K+] and lower pH are vasodilators
What is a problem with the structure of the coronary arteries?
They are end arteries therefore have very few anastomoses
Means if theres a blockage any tissue downstream will die since no alternate route for blood flow
What is a problem with the structure of the coronary arteries?
They are end arteries therefore have very few anastomoses
Means if theres a blockage any tissue downstream will die since no alternate route for blood flow
How do narrowed coronary arteries lead to angina on exercise?
Blood flows mostly through coronaries during diastole
Diastole in exercise reduced
This combined with increased demand causes the pain due to hypoxic heart tissue
How is skeletal muscles circulation controlled?
Capillary density depends on muscle type
Very high vascular tone
Only 1/2 capillaries perfused at rest (means more can be recruited when needed)
What metabolites act as vasodilators in skeletal muscle causing metabolic hyperaemia?
Inc [K+]
Inc osmolarity
Inorganic phosphates
Adenosine
Inc [H+]
Adrenaline acts on B2 receptors
What it’s the special role of cutaneous circulation?
Temperature regulation
How does cutaneous circulation play a role in temperature regulation?
Skin = Main heat dissipating surface
Arterovenous anastomoses
What are arterovnous anastomoses?
Shunts/blood vessels that pass from arteries to veins to avoid blood flowing close to the surface of the skin
What is the main regulator of blood flow through thee cutaneous circulation?
Sympathetic stimulation NOT metabolites
Blood flows mainly through arteriovenous anastomoses
What happens in terms of sympathetic tone in arterovenous anastomoses when core body temperature decreases?
Increased sympathetic tone in arterovenous anastomoses
Decreases blood flow to apical skin
What happens in terms of sympathetic tone in arterovenous anastomoses when core body temperature increases?
Decreased sympathetic tone in arterovenous anastomoses
Opens the anastomoses allowing blood to divert near to veins near the skin
