Arteries, Arterioles, Veins Flashcards
What are the 2 patterns of blood flow?
Laminar: 0 velocity at walls, max velocity at centre.
Turbulent: Blood flows in whirlpools due to changes in velocity. Found in ventricles (mixing), aorta (peak flow), Atheroma (bruits)
Bolus (in capillaries) RBCs flow in single file. Uniform velocity, little internal friction so v low resistance
Describe how the compliance properties of the aorta regulate systolic and diastolic blood pressure
During LV ejection most SV stored in aorta and arteries as these structures stretch (compliance). Energy of blood out of the heart is stored in stretched elastin
During LV diastole, energy stored in elastin is returned to blood as aorta and artery walls recoil and contract.
This sustains diastolic BP and BF when heart is relaxed
What is pulse pressure?
Pulse pressure =usually around 40 mm Hg
Pulse Pressure tells you about SV and Large ARTERY COMPLIANCE (stretchiness)
Pulse pressure = stroke volume / compliance
What happens to pulse pressure when you exercise, or when a patient is elderly?
SV increases during exercise, which increases pulse pa. Higher SV increases stretch/compliance
If u stretch something more and more it gets less compliant – hence causing a systolic pa increase. This causes greater pulse pa
In an elderly patient, artierosclerosis means stiffer ateiries, thus decreased compliance and increased systolic BP. This means increased afterload on heart
Usually moving away from aorta leads to increased pulse pa due to tapering of vessels and increased stiffness of distal arteries
What is Darcy’s law?
The link between flow, arterial pressure and TPR is Darcy’s law:
How does TPR affect both blood flow and pressure? In which instances would you need to increase and decrease resistance?
Pa drops from large arteries to arterioles due to increased TPR. This is bc increased TPR means a smaller radius so holds less blood volume.
Also, blood flow= Arterial bp / TPR. So as TPR increases, blood flow decreases. Reduced resistance (dilate blood vessel) increases BF e.g. in skeletal muscle during exercise Increase resistance (constricted) reduces BF e.g. in GIT during exercise
What if you have excessive drop in TPR?
Excessive drop in TRP – excessive vasodilation eg due to sepsis.
Excessive dilation reduces BP upstream to an extent que será insufficient pressure drive for blood flow. Poor blood flow to end organs–> organ/tissue damage
What if you have excessive increase in TPR?
Excessive increase in TPR – excessive vasoconstriction eg in hypertension
Excessive constriction increases BP upstream and reduces blood flow downstream. Less blood flow to end organs –> end organ damage
What is Poiseuille’s law?
Blood Flow is directly proportional to Blood vessel radius to the power of 4. Blood flow is inversley proportional to viscosity.
Arteriole radius is controlled by symp nerves. This controls the large pa difference through the circulatory system
Complete this table to show Blood viscosity and clinical implications
Describe veins and venoconstriction
Veins= voluminous vessels, resovoir of blood. Contractile – contain smooth muscle
Increased venoconstriction: contraction of vessels which expels blood into central veins, stimulated by symp nerves
- Less volume in veins
- Blood is shifted back to heart
- Increased venous return
- Increased end-diastolic pressure and SV (Starling’s law)
How is venous return regulated by pressure gradients and a thoracic pump?
High venous pressure (90mmHg) creates a pa gradient to drive blood back to the heart in standing.
Thoracic pump: Inhalation expands the thoracic cavity, increasing abdominal pressure, forcing blood upward towards heart, increasing right ventricular SV. Blood flows faster with inhalation
How is venous return regulated by a skeletal muscle pump, why is this important?
Skeletal leg muscle contraction returns blood into RA. This reduces high local venous pa when in the upright position.
Also reduces swelling of feet and ankles – lower venous pressures, lower capillary pressure, less filtration
In contrast, standing still for long can lead to fainting due to pooling of blood volume in veins of lower limbs. SV and CO decreases
What best describes the equation for determining blood velocity?
Blood flow/ area
