Structure and Function of the Circulation Flashcards
What is haematocrit?
Ratio of volume of red blood cells to total volume of blood
What is the equation for resistance?
Blood viscosity x vessel length all over vessel radius ^4
What is the portal system?
Passing from one capillary bed to another capillary bed without passing through heart
Is the resistance higher or lower in the systemic system compared to the pulmonary system?
Higher- it is longer and more complex
Is the pressure higher or lower in the systemic system compared to the pulmonary system?
Higher
What is the major determinant of arterial blood pressure and blood flow?
Vessel resistance which is determined by vessel radius
The dicrotic notch shows what?
The aortic valve closing rapidly due to pressure
Where is the biggest pressure drop in the circulation?
Biggest pressure drop is in the arterioles (particularly to the organs), because of their small radius and therefore high resistance
Capacitance vessels are also known as what?
The veins- hold largest share of blood
Cardiac output
Amount of blood out of ventricles into cardiovascular system
The amount of blood the heart pumps through the circulatory system in a minute
What is the BP equation?
BP (mean arterial blood pressure)= CO x TPR (total peripheral resistance)
How is blood pressure regulated?
Name all the receptors
Neural Regulation:
Arterial baroreceptors- in carotid sinus + aortic arch
Chemoreceptors- in carotid body- check pH and CO2
Mechanoreceptors
What do baroreceptors do? how?
Regulate arterial pressure
Continuously send nerve impulses to cardiovascular centre in medulla.
The higher the arterial pressure the more impulses that go to the brain.
How do baroreceptors realise that the blood pressure too high?
They are mechanoreceptors
Realise if stretched and so increase firing rate to medulla oblongata
Which nerves send which baroreceptor signals to brain?
Baroreceptors in the aortic arch send through the vagus nerve
Baroreceptors in the carotid sinus send through the glossopharyngeal nerve to the medulla oblongata
What is the neural pathway to decrease heart rate with medulla oblongata?
Vagus nerve change frequency signal to medulla oblongata cause decrease HR
Which hormones help regulate blood volume and blood pressure?
Does it increase or decrease blood pressure?
Aldosterone - increases BP
ADH (Antidiuretic hormone;vasopressin)- increases BP
Type A and Type B Natriuretic Peptides- decreases BP
Angiotensin II
Adrenaline
Aldosterone is released from where? effect of the release?
Released from adrenal cortex
Increases sodium and water reabsorption from kidneys
ADH is released from where? Effect of the release?
Released from posterior pituitary in response to increased blood osmolality
Increases water reabsorption from kidneys and vasoconstriction
Type A and Type B Natriuretic Peptides releases in response to what? effect?
(ANP and BNP)
In response to high volume load (stretch) on atria and ventricles
Increases sodium and water excretion from kidneys (and vasodilation)
What effect does adrenaline have on blood pressure?
It can increase it or decrease it depending on which receptor it binds to
Adrenaline is released from where
Adrenal medulla in response to SNS (sympathetic nerve stimulation)
Alpha-1 adrenergic receptor causes what
Vasoconstriction- increases blood pressure
Beta-2 adrenergic receptor causes what?
Vasodilation- decreases blood pressure
Under normal physiological levels does adrenaline increase or decrease blood pressure?
Decrease due to its increased sensitivity for beta-2 compared to alpha-1 receptors
Under high dose of adrenaline, what effect does it have? why?
Increases blood pressure, alpha-1 receptors more numerous than beta-2 so overall effect is vasoconstriction
What does Angiotensin II do?
Vasoconstrictor activated by angiotensin converting enzyme (ACE) within blood vessels= increases blood pressure
What are the layers of the blood vessel?
Tunica interna/intima (inner most)
Tunica media- middle
Tunica externa-outer
When do arteries stretch and recoil?
Elastic artery walls stretch during systole
Inward elastic recoil during diastole propels blood and sustains high blood pressure
What is active hyperaemia?
Ability of arterioles to vasoconstrict/dilate rapidly and extensively allows them to adjust blood flow to tissues according to metabolic demand
What are the three types of capillary?
Continuous- most- allow only some water soluble molecules across
Fenestrated- fluid exchange
Discontinuous/sinusoid- allow proteins and entire cell to go across epithelial wall
How to calculate velocity of blood?
Blood flow/ cross sectional area
As the cross sectional area increases what happens to the velocity?
The velocity decreases
Net filtration pressure
Net sum of filtration and absorption across capillary bed
Fluid exchange between capillaries and surrounding fluid is determined by what
Hydrostatic pressure and osmotic pressure
When is osmotic pressure higher than hydrostatic and vice versa?
Hydrostatic pressure greater than osmotic pressure at arteriole end
Osmotic pressure greater than hydrostatic pressure at venule end
What aids venous return from lower half of body?
Skeletal muscle pump and respiratory pump
Respiratory pump- during inspiration increase abdominal pressure, decrease intrapleural pressure therefore help blood back to heart
What does venous return determine?
End- diastolic volume, therefore stroke volume, therefore cardiac output
What does venoconstrictino do?
Shunts blood from peripheral to central vessels, blood return to heart quicker, increase sttroke volume
Release of what hormone causes venoconstriction?
Alpha 1 receptors affected- norepinephrine from sympathetic neurones induces venoconstriction
What do elastic arteries do?
Conserve pressure and flow during diastole- convert intermittent flow to continuous flow - buffer systolic rise in pressure
What do muscular arteries do?
Distribute blood, adjust blood flow to tissues- conduit vessels
What do arterioles do?
Control arterial pressure and local blood flow- resistance vessels
What do capillaries do
Transfer of nutrients/waste products between cells
What do veins do?
Return blood to heart
