Blood Pressure Flashcards
where is blood pressure measured
at the brachial artery
units of blood pressure
`mmHg (or KPa – metric pressure)
what is a series path
two paths in a row (flow in both parts is the same), pressure is higher in the first path than the second one as energy is lost as blood experiences friction/resistance
what is a parallel path
branching paths so flow is split between two, pressure is the same at the start of both paths (identical resistance so have same pressure)
what is a portal system
a capillary bed reassembles to a blood vessel that splits into another capillary bed
what does a portal system enable
Allows transport of chemicals from one tissue to another without dilution by mixing with blood at the heart.
what is an example of a portal system
Hepatic Portal system – food us absorbed in gut capillaries, assemble into the portal veins, goes to liver and breaks into capillaries. liver- nutrients in blood (and dietary toxins eg alcohol) at high conc before distribution to the body
what are arterial pressures
low in diastole and high in systole, vary over time
what is pulse pressure
difference between diastolic and systolic pressure
how is mean pressure calculated
Mean = diastolic + (systolic-diastolic/3)
what is stroke volume
volume of blood pumped out of the ventricle during a single heartbeat
what is heart rate
BPM
What is the reciprocal of heart rate
RR interval which is 60/HR
what is cardiac output
Cardiac Output is the volume of blood pumped from a ventricle per minute
CO= HR X SV
what does atrial systole do
adds final 20-25% of blood to fill ventricles
what is end diastolic volume
volume of blood in a ventricle at the end of filling (diastole). Associated with preload (how stretched the muscle is)
what is end systolic volume
vol of blood remaining in a ventricle at the end of contraction (systole)
how is stroke volume calculated
SV=EDV-ESV
what is ejection fraction
percentage of filled ventricular volume pumped out during a heartbeat
SV/EDV
how does radius effect blood flow
Vasoconstriction = smaller radios so higher resistance and lower flow rate
how is conductance calculated
Conductance (g) = 1/Resistance (R)
what happens to flow and resistance when radius increases
Flow increases (to power of 4 assuming pressure stays the same) resistance decreases (power of 4 too)
what causes dilation and constriction of individual blood vessels
Central regulation: CNS, autonomic and endocrine
Local regulation of pressure
Immune
Haemostasis
how does exercise effect blood flow
Peripheral dilation (muscle/skin)
Vasoconstriction (splanchnic circulation)
BP systolic increases, diastolic decreases
HR increases vastly
what happens to blood pressure when standing
Initial drop in BP (compensatory recovery) Peripheral vasoconstriction (Arterial and Venous and increased HR) BP no change in systolic but diastolic increases as does HR
how is systemic blood pressure controlled
Local decisions related to endothelial cells, make NO to relax blood vessels
Neurological control via ANS (sympathetic – noradrenaline)
Humoral (HORMONAL) – renal/pituitary/adrenal (kidney central to BP)
what is local vasomotor control
Endothelial cells release vasodilator compounds eg NO
what happens in local vasomotor control
Controlled by local blood flow conditions (hydrostatic pressure, shear force)
how is BP controlled autonomically
Higher centres (eg eyes), hypothalamus, medullary centres, Vagal (parasympathetic) and Sympathetic balance out for appropriate effect on BP.
How does the sympathetic nervous system effect blood vessels
Sympathetic constricts blood vessels (increase PR, pressure, HR, cardiac output)
what do baroreceptors do
detect pressure and feed back to the brain
Activity decreases BP (maintain homeostasis)
where are baroreceptors located
Located in transverse aortic arch and carotid sinuses of L and R internal carotid arteries
what do chemoreceptors do
Detect when O2 levels are low and feedback to brain
where are chemoreceptors located
Located in carotid bodies and aortic bodies
what does the frank-starling mechanism explain
How the heart always pumps the right amount of blood (same enters as leaves)
what is the frank starling mechanism
Left ventricle end diastolic pressure is higher, the more blood is pumped out as more is pushed in so cant overfill.
what is venous return
the rate of blood flowing back to heart by the veins
what is preload
is the initial stretching of cardiac myocytes during diastoles
what is the pathological state when preload is too large
Volume overload is a pathological state (too large for the heart to pump out)
what factors effect preload
Atrial contractility (increases it)
Ventricular Compliance (more ventricle stretches, increases)
HR (decreases)
Aortic Pressure (leads to back pressure so ventricle cant evacuate itself, increases)
Central venous pressures (increases)
what is after load
resistance the chambers must overcome to eject blood (resistance during systole)
what increases after load
Increased by back pressure (aorta or PA)
Increases if exit valve fails to open completely
Pressure overload (elevated afterload)
how does the thoracic pump lead to venous return
Pulls blood towards right atrium during inspiration
why does the thoracic pump work
Intrathoracic pressure is negative (abdominal pressure, compression of organs by diaphragm) is positive) so pressure gradient to drive blood to the heart
how does the muscle pump lead to venous returns
Rhythmical contraction of limb muscles as occurs during normal locomotor activities
Squeezes blood from nearby veins and valves ensure one way flow to heart
what is pulmonary circulation
High capillary density so low vascular resistance to act as a blood reservoir
Acts a filter
what controls pulmonary circulation
Endocrine control of BP (ACE, an enzyme)
why is pulmonary circulation special
O2, CO2 and pH effects opposite compared to systemic system
Low O2 in lungs causes arterioles to constrict (CO2 and H+ high = vasoconstriction)
Poor ventilation = reduced perfusion
Minimises amount of blood poorly oxygenated
why is coronary circulation special
Cardiac muscle has a high demand
More flow happens in diastole (squeezed shut in systole)
Obtains blood almost before aorta
what is hypertension
High blood pressure (eg high diastolic pressure)
Often asymptomatic
May result in coronary artery disease and MI
what causes hypertension
Caused by mismatch between blood volume and circulatory capacity
Most cases are idiopathic (partly due to hormones (ANG II) and brain medulla (NTS))
Secondary to kidney disease
what can chronic hypertension lead to
Aneurysm or stroke
MI
Kidney/ heart failure
Cardiac hypertrophy
why is orthostatic hypotension
Low BP on standing (decrease in venous return)
Dizziness or syncope
what causes orthostatic hypovalaemia
drugs, hypovalaemia and age
what is cardiogenic shock
Tachycardia or Tachypnoea (compensatory mechanisms)
Low er urine output, hypotension, confusion, syncope, acidosis (failure to compensate)
