Control Of The Circulation Flashcards
What percentage of blood flow does each organ receive?
Liver - 27%
Kidneys 22%
Brain 14%
Skin 6%
Bone 5%
Heart 4%
Job of arteries?
Elastic to stretch and recoil to smooth pressures surges and hence maintain blood flow to organs during diastole.
What is the principle site of resistance to vascular flow?
Arterioles
As they are the Percival site of resistance total peripheral resistance = total arteriolar resistance.
They therefore play a major role in controlling pressure and distributing blood flow to organs.
This pressure is determined by local, neural and hormonal factors.
What is TPR and what does it show?
Total peripheral resistance
In arterioles smooth muscle can contract to alter the resistance to blood flow.
When it contracts the radius of the arterioles decrease and hence resistances increases and flow decreases.
When it relaxes - increase radius, decrease resistance and increase flow
Formula:
Cardiac output (CO)
Blood pressure
Pulse pressure (PP)
Mean arterial pressure
CO= heart rate x stroke volume
Blood pressure = CO x TPR
PP = systolic - diastolic pressure
Mean arteriole resistance = diastolic pressure + 1/3 pulse pressure
How is capillary flow determined and why does this matter?
Determined by arteriolar resistance and some pre capillary sphincters.
Important to slow flow to allow time for nutrient/waste exchange.
What is the job of the lymphatics?
Filters fluid protein excess from interstitial space in capillaries and returns this interstitial fluid to CV system via the thoracic duct and left subclavian vein.
Return aided by smooth muscle and skeletal muscle pumps.
Also contains valves.
What is the Frank Starling mechanism?
It is the ability of the heart to change its force of contraction and therefore stroke volume in response to changes in venous return.
As venous return increases so does the end diastolic volume. This results in a larger stoke volume (more stretch also leads to a stronger contraction) and hence a larger cardiac output.
End diastolic volume = volume of blood in the ventricles just before systole.
Name 2 systems that affect blood volume?
Osmoregulation - ADH
The Renin-Angiotensin -aldosterone system
When is systolic pressure highest?
When is diastolic pressure lowest and why never zero?
What is used to measure blood pressure?
Highest when ventricles contract - 100-150mmHg
Lowest when ventricles relax - 60-90mmHg
Never zero due to elasticity of aorta.
Measured using a sphygmomanometer
Using brachial artery
See YouTube of how do take blood pressure.
What is autoregulation?
It is defined as the intrinsic ability of an organ to maintain a constant blood flow despite changes in perfusion pressure.
Lead to the organ blood vessels dilating when too little blood flow and contraction when too much blood flow.
Intrinsic = heart and brain
Extrinsic control is when something else controls the blood flow to that organ. E.g the thermoregulatory centre in the hypothalamus fo the skin.
Skeletal muscle has both intrinsic and extrinsic control mechanisms.
What are 5 different components of blood pressure control?
Autoregulation Local mediators Humoral factors Barorecpetors Neural control
What are local humoral factors and what is their function in the control of blood pressure?
They are signalling molecules that do not circulate in the blood.
The most common are endothelin-1 = vasoconstrictor
And NO and prostacyclin = vasodilators
They are produced by the endothelium and are released into the blood causing dilation or constriction and hence play a role in blood pressure.
What are circulating humoral factors and give a few examples?
They are signalling molecules usually hormones that are transported in the blood.
Vasoconstrictors include Epinephrine - adrenaline
Angiotensin II
Vasopressin - ADH
They are all vasoconstrictors and some also effect the volume and hence pressure of the blood.
Vasodilators - epinephrine, atrial naturetic peptide (increases excretion of Na+)
What is the job of baroreceptors?
Where are they found?
Nerves involved?
What is the outcome?
They sense pressure changes in the arterial wall.
Primary baroreceptors are found in the coronary sinus and aortic arch.
Secondary can be found in veins, myocardium and pulmonary vessels.
The afferent nerve is the glossopharyngeal nerve (IX) it receives sensory info from the baroreceptors.
The efferent nerve is the vagus (X).
If there is an increase in blood pressure there will be an increase in firing via the afferent nerve leading to parasympathetic action such as decreasing CO and hence B.P.
