Blood pressure Flashcards
Measurements and units of pressure
Units: mmHg or kiloPascals
Series circuit
2 paths in a row
Flow in both parts is the same
Pressure is higher in the first than the second because energy is lost as blood experiences friction/ resistance
Parallel circuit
Branching paths
Flow is split between 2 paths
Pressure is the same at the start of both paths
If paths have identical resistance then they have the same pressure
Hepatic portal system
- Food is absorbed in capillaries of the gut
- Capillaries assemble into portal vein
- Portal vein goes to the liver and breaks inter capillaries
- Liver ‘sees’ nutrients in blood at high concentration before it’s distributed throughout the body
Causes of increased blood pressure (3)
Increased:
- peripheral resistance
- cardiac output
- blood volume
Pmean=
Pdiastolic + (Psystolic - Pdiastolic)/3
Stroke volume
Volume of blood pumped out of a ventricle during one beat of the heart
Heart rate
Measured in beats per minute
Its reciprocal is the RR interval
Cardiac output
Volume of blood pumped out of a ventricle per minute
=HRxSV
End diastolic volume
Volume of blood in a ventricle at the end of diastole
Associated with pre-load (how stretched the muscle is)
End systolic volume
Volume of blood remaining in a ventricle at the end of systole
SV=EDV-ESV
Ejection fraction
Percentage of ventricular volume pumped out during a heart beat
=SV/EDV
Conductance
=1/ resistance
Poiseuille’s law
The fall in pressure along the length of a cylindrical blood vessel is proportional to flow x resistance
Causes of dilation and constriction in individual blood vessels (4)
Central regulation: CNS, autonomic, endocrine
Local regulation of pressure
Immune
Haemostasis
Effect of exercise on blood distribution
Peripheral vasodilation Vasoconstriction of splanchnic circulation Increase in systolic pressure Decrease in diastolic pressure Increase in heart rate
Standing
BP initially drops then compensatory recovery Peripheral vasoconstriction Increased heart rate No change in systolic pressure Increase in diastolic pressure Increase in heart rate
Control of systemic blood pressure
Local: endothelial, nitric oxide
Neurological: ANS
Humoral: renal, pituitary, adrenal
Local vasomotor control
Endothelial cells release vasodilator compounds
- nitric oxide causes smooth muscle relaxation
- vasodilation
Controlled by local blood flow conditions
- hydrostatic pressure
- shear force
Shear force
The force on the endothelium in the direction of blood flow
Laminar flow
Flow without turbulence or eddies
Flow of all molecule is directly in the direction of the overall flow of all fluid
Baroreceptors
Detect pressure and feed back to the brain
Located in the transverse aortic arch and the carotid sinuses of the left and right internal carotid arteries
Chemoreceptors
Detect when O2 levels are low and feed back to the brain
Located in the carotid bodies and aortic arch
The Frank-Starling mechanism
The stroke volume of the heart increases in response to an increase in the volume of blood filling the heart
Venous return
The volume of blood flowing back to the heart through the veins
Preload
The initial stretching of the cardiac myocytes prior to contraction
Depends on venous return
Volume overload
Results when preload becomes too large
Chronic pathological stress on myocardial tissue
Contractility
The force of contraction with which muscle contracts
If heart contractility increases it will pump more blood per minute with greater force
Factors increasing ventricular preload
- Increase atrial compliance
- Increase ventricular compliance
- Increase aortic pressure
- Increase thoracic venous blood volume
- Decrease venous compliance
- Decrease heart rate
Afterload
The resistance that the chambers of the heart must overcome in order to eject blood out of the heart
Increased by back pressure from aorta or pulmonary arteries
Increases if the exit valve fails to open completely
Pressure overload
Pathological stress on the myocardial tissue that occurs during systole when myocardium generates force to contract but cannot contract
Thoracic pump
During inspiration, intrathoracic pressure is negative, abdominal pressure is positive
Pressure gradient pulls blood towards the right atrium
Muscle pump
Rhythmical contraction of limb muscle occurs during normal locomotor activity
Squeezes blood out of nearby veins
Venous valves assure one way flow toward the heart
Pulmonary circulation
High capillary density
Low vascular resistance
Acts as blood reservoir
Endocrine control of BP (conversion of Ang1 to Ang2 by ACE in endothelial cells)
Acts as filter
O2, CO2, pH effects are opposite to those in systemic circulation
Coronary circulation
Cardiac muscle has high demand
Most flow occurs during diastole
Obtains blood before aorta
Hypertension
High blood pressure
Often asymptomatic
May result in CAD or MI
Causes of hypertension
Mismatch between blood volume and circulatory capacity
Most cases idiopathic:
- hormones (Ang 2)
- brain medulla (NTS)
Secondary to kidney disease
Consequences of chronic hypertension (5)
Aneurysm of stroke Myocardial infarction Kidney failure Heart failure Cardiac hypertrophy
Orthostatic hypotension
Low BP on standing
- decreased venous return
Dizziness or syncope
Causes: drugs, hypovolaemia, age
Cardiogenic shock: signs and symptoms
Compensatory - Tachycardia - Tachypnoea Failure to compensate - Low urine output - Hypotension - Confusion - Syncope
