blood pressure Flashcards
what is series blood flow?
- 2 paths in a row
- flow in both paths the same
- pressure is higher in the first path than the 2nd path because energy is lost as blood experiences friction/resistance
what is parallel blood flow?
- branching paths
- flow is split between both paths
- if paths have identical resistance then same pressure
what is a portal system?
when a capillary bed reassembles to a blood vessel that splits again into another capillary bed
what is the function of a portal system?
allow transport of chemicals from one tissue to another without being diluted by mixing with blood at the heart
what is stroke volume?
volume of blood pumped out of a ventricle during one beat of the heart
what is heart rate?
its reciprocal is the RR interval which is 60/HR
measured in beats per minute
what is cardiac output?
volume of blood pumped out of a ventricle per minute
what is the equation for cardiac output?
CO = HR x SV
what is the end-diastolic volume?
volume of blood in a ventricle at the end of diastole. it is associated with preload, how stretched the muscle is
what is the end-systolic volume?
volume of blood remaining in a ventricle at the end of systole
what is the equation for stroke volume?
SV = end diastolic volume - end systolic volume
what is the ejection fraction?
percentage of filled ventricular volume pumped out during a heart beat
what is the equation for ejection fraction?
ejection fraction = SV/EDV
what percentage of the total volume of the ventricles does arteriole systole add?
20-25%
what are the effects of changes in radius?
- smaller radius = higher resistance
- smaller radius = lower flow rate
- flow increases as radius increases to the power of 4
what are the causes of dilation and constriction of individual blood vessels?
- central regulation: CNS, autonomic, endocrine
- local regulation of pressure
- immune
- haemostasis
what happens during exercise?
- peripheral vasodilation: muscle/skin
- vasoconstriction: splanchnic circulation
- BP systolic increases and diastolic decreases
- heart rate increases
what happens during standing?
- initial drop in BP & then compensatory recovery
- peripheral vasoconstriction: arterial & venous & increased heart rate
- BP final: no change in systolic, increase in diastolic & increase in heart rate
what vasodilator compounds do endothelial cells release and what does it do?
- nitric oxide
- causes smooth muscle to relax leading to vasodilation
what conditions control local blood flow?
- hydrostatic pressure
- shear force made greater by laminar flow and shear force is atheroprotective
what are baroreceptors?
receptors that detect pressure and feedback to the brain
where are baroreceptors located?
in the transverse aortic arch and the carotid sinuses of the left and right internal carotid arteries
what does activity of the baroreceptors do to BP?
it decreases blood pressure
what do chemoreceptors do?
detect when oxygen levels are low and feedback to the brain
where are chemoreceptors found?
in the carotid bodies and aortic bodies
what is the frank-starling mechanism?
the stroke volume of the heart increases in response to an increase in the stretching of blood filling the heart ( the end diastolic pressure)
what is venous return?
the rate of blood flowing back to the heart through vein
what is preload?
the initial stretching of the cardiac myocyte during diastole (prior to contraction) but it depends on venous return
what causes volume overload?
results when preload becomes too large
what causes pressure overload?
results from elevated afterload
what is afterload?
the resistance that the chambers of the heart must overcome in order to eject blood out of the heart
what increases afterload?
- back pressure from aorta or pulmonary arteries
- if the exit valve fails to completely open
what are the 2 methods of venous return?
1) thoracic pump
2) muscle pump
how does the thoracic pump work?
- ‘pulls’ the blood toward the right atrium
- during inspiration
- intrathoracic pressure is negative
- abdominal pressure is positive
- creates a pressure difference
how does the muscle pump work?
- rhymical contraction of limb muscles
- as occurs during normal locomotor activity
- squeezes blood out of nearby veins
- venous valves assume one-way flow towards heart
describe some features of pulmonary circulation
- high capillary density
- low vascular resistance
- acts as blood reservoir
- endocrine control of BP (ACE)
- acts as filter
if carbon dioxide and H+ levels are high what happens?
vasoconstriction
what does poor ventilation lead to?
reduced perfusion
what process does most blood flow occur?
diastole
what is hypertension?
high blood pressure (especially high diastolic pressure)
describe some features of hypertension
- often asymptomatic
- may result in coronary artery disease & MI
- usually caused by mismatch between blood volume & circulatory capacity
- most causes are idiopathic
- secondary to kidney disease
what can hypertension lead to?
kidney failure, heart failure, cardiac hypertrophy, aneurysm or stroke or MI
what is orthostatic hypotension?
- low BP on standing
- dizziness or syncope
what causes orthostatic hypotension?
drugs, hypovolemia and age
what is cardiogenic shock?
- compensatory mechanism: tachycardia, tachypnoea
- failure to compensate: low urine output, hypotension, confusion, syncope
- acidosis
