Heart Physiology Flashcards
What is an equation to calculate blood pressure?
Cardiac output x total peripheral resistance
What constitutes cardiac output?
Heart rate x stroke volume
What is total peripheral resistance?
Resistance to forward flow of blood from the left ventricle
What is systolic pressure?
Blood pressure during left ventricular contraction
What is diastolic pressure?
Blood pressure during left ventricular relaxation/elastic recoil of large arteries
Reason for regulating blood pressure
Maintain steady blood flow to tissues and organs
Avoid ischaemia, necrosis
Hagen-Poiseuille equation
Change in pressure = (8 x viscosity x length x flow)/(Pi x radius^4)
What is the main implication of Hagen-Poiseuille equation?
A small change in the radius of a blood vessel has a large effect on blood pressure (radius to the power of four)
Injections have a maximum output/unit time
Pulse pressure
Systolic - diastolic
Mean arterial pressure
Diastolic + 1/3 x pulse pressure
Features of the fast control system of blood pressure
Sensors are mainly stretch receptors in the aorta, carotid arteries
Neural linking to brainstem
Effectors are cardiac output, vasomotor tone
Features of the slow control system of blood pressure
Sensors in kidneys
Receptors detect stretch in blood vessels, diffusion of electrolytes
Respond with hormones that influence vasomotor tone, fluid/electrolyte balance
Sensors of the fast control system
Stretch receptors in the carotid sinus, aortic arch
Which nerves connect the carotid sinus, aortic arch stretch receptors to the brain stem?
Cranial nerves IX, X
What do cranial nerves IX and X do (related to blood pressure)?
Connect the carotid sinus and aortic arch stretch receptors (baroreceptors) to the brainstem
What occurs when the baroreceptors in the carotid sinus and aortic arch detect an increase in blood pressure?
Send more impulses to the inhibitory centres of the brainstem
Where is the vasomotor area located?
In the brainstem
Inputs to the vasomotor area 1) 2) 3) 4)
1) Baroreceptors
2) Chemoreceptors
3) Skeletal muscle proprioceptors
4) Hypothalamus (body temperature)
Afferents from the vasomotor area
Vagus nerve
Sympathetic nervous system
What does the vagus nerve afferent do?
Leads to the cardiac inhibitory function
Removed if higher heart rate is required
What is the effect of sepsis on blood pressure?
Decreases blood pressure (systemic vasodilation)
Effects of sympathetic activity on blood pressure 1) 2) 3) 4)
1) Increase heart rate, stroke volume
2) capacitance vessels - veins - change diameter
3) Resistance vessels - arterioles - change diameter
4) Adrenal gland secretes adrenaline
Effectors of blood pressure 1) 2) 3) 4)
1) Heart
2) Veins (capacitance vessels)
3) Arterioles (resistance vessels)
4) Adrenal gland
What does vasoconstriction of capacitance vessels do?
Emptying of blood in reservoirs into circulation
EG: Splanchnic bed
Example of abnormal CNS control of blood pressure
Harlequin syndrome
What is Harlequin syndrome?
Asymmetrical flushing and sweating of thorax, neck, face
How does the kidney respond to a decrease in blood pressure?
Secretes renin
What does the kidney detect, apropos of blood pressure?
Stretch receptors, electrolyte balance
What does angiotensin do?
Vasoconstriction
Secretion of aldosterone
What is renin converted to?
Vasopressin
What does aldosterone do?
Retain sodium and water in kidney.
Increases blood pressure
Potential dangers of faliure of fluid regulation: overload
Pulmonary oedema
Wound dehiscence
Local effects of exercise 1) 2) 3) 4) 5)
1) Blood flow to skeletal muscle increases 30x
2) Potassium, CO2, temperature rise, O2 fall
3) Temperature rise leads to vasodilation
4) Number of open capillaries increases 10-100-fold
5) up to 100-fold increase in O2 consumption
Systemic effets of exercise
1)
2)
3)
1) Arterial dilation
2) Vasodilation
3) Adrenaline secretion
Change in percentage of blood flow received by muscles at rest and during exercise
13% to 88%
Change in percentage of blood flow received by kidneys at rest and during exercise
19% to 1%
Change in percentage of blood flow received by stomach at rest and during exercise
21% to 1%
Change in percentage of blood flow received by brain at rest and during exercise
13% to 3%
Orthostatic hypertension 1) 2) 3) 4) 5) 6) 7)
1) Move from a lying to a standing position
2) Decrease in arterial pressure
3) Detected by baroreceptors (carotid, aortic)
4) Decrease in firing from arterial baroreceptors
5) Reflex via the medullary cardiovascular centre
6) Increase sympathetic/decrease parasympathetic signals to the heart
7) Increase heart rate, stroke volume, arteries and veins contract
When are chemoreceptors in the aorta stimulated?
Only when the heart is severely lacking in blood supply
How is blood redirected to different organs?
Constriction and dilation of arterioles
Response to significant blood loss
1) Reduced stretch in baroreceptors
2) Inhibition of vagal cardiac inhibition
3) Increase in heart rate, stroke volume
4) Sympathetic constriction of arterioles in skin, veins in splanchnic circulation
5) Juxtoglomerular apparatus in kidney stimulated by decrease in blood pressure, filtering in kidneys –> kidneys release renin
6) renin-angiotensin, aldosterone lead to increased fluid retention
