Blood pressure Flashcards
Blood pressure measurements
- mm Hg: amount of pressure required to push 1 mm of mercury.
- kPa: 1 kPa= 1000 newton units/ m2
Normal blood pressure measurements
120/75 mm Hg
16/10 kPa
Pulse pressure
The difference between the maximum diastolic pressure and the minimum systolic pressure, in a given time.
Pulse pressure= Systolic max - Diastolic min
Blood flow circuits
In series: Blood flow goes through two paths in the same row. The pressure at the start of the row is higher that at the end- energy is lost.
In parallel- Branching of paths from one row into multiple rows. At the point of branching, the pressure is the same. If the resistance in each path is the same, the pressure at the end will also be the same.
Portal system
A type of in series blood vessel circuit where there are capillary beds in series.
A capillary bed converge into a venule/ arteriole before diverging into another capillary bed.
This allows conservation of the material in the blood and prevents diluting caused by mixing with other blood.
Example: Hepatic portal system.
Hepatic portal system- blood circuit
In series circuit:
Blood receives nutrients in the gut through the capillary beds.
Blood assembles into portal vein when it is carried to the liver.
Blood then diverges into another capillary bed whilst in the liver.
Allows nutritional content of the blood to be conserved.
Mean arterial pressure
Mean arterial pressure= Min diastole pressure + ( Pulse pressure/ 3)
A method of calculating blood pressure.
End diastolic volume
The volume of blood in the ventricle after filling, in diastole.
Greater volume = Ventricle is more stretched ( Starling’s law)
The average EDV is 120 ml.
End systolic volume
Volume of blood left in the ventricles after contraction. during systole.
The average ESV is 50 ml.
Stroke volume
The volume of blood pumped out of the ventricle after one heartbeat.
SV= EDV- ESV
Average SV is 70 ml.
Ejection fraction
Percentage of ventricular volume of blood pumped out during one heartbeat.
EF= SV/ EDV
Average ejection fraction is between 55-70%.
Heart failure occurs when EJ is too low.
Average HR and CO of an adult.
70 bpm
4.9L/min
What main factors cause an increase in blood pressure?
An increase in peripheral resistance.
An increase in cardiac output.
An increase in blood volume.
The vessel radius and blood pressure.
A decrease in the radius (vasoconstriction), causes more resistance and less flow= increased blood pressure.
What factors affect the size of the vessel radius.
Nervous control:
Autonomic control, CNS.
Hormonal control- endocrine
Local pressure regulation
Immune response
Haemostasis
Local vasomotor control
Release of NO- endothelial cells release NO which allows vasodilation, increasing vessel radius.
Blood flow- laminar flow allows shear force, which is atheroprotective. Sheer force is the stress on endothelial walls in the direction of blood flow.
Hydrostatic pressure pushes blood vessel walls outwards.
Factors that control systemic blood pressure.
Locally- endothelial cells and release of NO.
Nervous control- autonomic NS
Release of noradrenaline causes vasoconstriction
Humoral (blood volume)- renal, pituitary and adrenal gland.
Baroreceptors
Receptors that detects blood pressure.
Located:
Transverse aortic arch
Carotid sinuses
When pressure is high, receptors send impulses to the brain, to stimulate a decrease in pressure (parasympathetic system).
Low pressure= stimulation of sympathetic nervous system.
Chemoreceptors
Receptors that detect mainly low O2, also high levels of CO2 and H+.
Location:
Aortic bodies
Carotid bodies
When O2 levels are low, impulses are sent to the brain to stimulate sympathetic nervous system.
Nucleus tractus solitarius
Centre in the medulla oblongata that detects action potentials from baroreceptors,
Causes changes to cardiac output and systemic vascular resistance.
Frank-Starling mechanism (Starling’s law)
This states that an increase in stroke volume arises from the increase in pressure of the ventricles.
The more cardiomyocytes are stretched, the greater they will contract.
Preload
The initial stretching of cardiomyocytes before contraction.
The greater the venous return, the greater the preload.
Factors that increase preload
- Decrease in heart rate:
The gives more time for the ventricles to fill with blood. - Increased aortic pressure:
This increases background pressure, increasing the venous return. Therefore more blood fills ventricles. - Increased central venous pressure:
Increases venous return, thus increasing preload. - Decreased venous compliance:
Lower blood volume in the veins, thus decreasing central venous pressure. - Increased thoracic venous blood volume:
Increased venous return and total blood volume. - Increase atrial contractility:
More blood pumped into ventricle, cardiomyocytes stretch more. - Increase ventricular compliance:
The ventricles are more stretchy, more blood can fill ventricles.
Autonomic control of blood pressure
- Medulla oblongata receives signals from receptors, saying that blood pressure is too low.
- This triggers the sympathetic system, via the
Effects: Vasoconstriction Increased heart rate Increased peripheral resistance Increased cardiac output Ultimately increases blood pressure.
