Arteries, veins and control of PVR Flashcards
What are the different types of blood vessel in the CVS?
- Large arteries
- Arterioles
- Capillaries
- Venules
- Veins
What are endothelial cells?
The thin layer of cells that line the interior surface of all blood vessels
- They line ALL vessels and the inside of the heart chambers
What are the functions of endothelial cells?
- Important for local blood pressure control
- Prevent platelet aggression and blood clot formation
- Angiogenesis and vessel remodelling
- Permeability barrier for nutrients/fluid between plasma and interstitial fluid
- Release constrictors
- Can influence proliferative state of smooth muscle cells - hypertension (can get changes in structure of blood)
- Can release free radicals which can oxidise LDL
- Can express molecules which tether inflammatory cells
What is platelet aggression?
The clumping together of platelets in the blood
What is angiogenesis?
The development of new blood vessels
Where is vascular smooth muscle present?
In all vessels with the exception of the smallest capillaries
What does vascular smooth muscle determine?
Determine vessels radius by contracting and relaxing
What does vascular smooth muscle secrete which gives the vessels their elastic properties?
An Extracellular matrix
Is which disease can vascular smooth muscle multiply?
Hypertension
What is arterial elasticity?
When heart ejects stroke volume of blood artery has to expand - pressure goes up to systolic blood pressure - if did not have elasticity then systolic blood pressure would be much higher
- Compliance is important to allow large arteries to act as a pressure reservoir (allows it to expand then the vessel can recoil after blood has passed through)
- This prevents the pressure falling to 0 as blood leaves the arteries during diastole
What is calcification in human arteries caused by and what can this cause?
- Caused by a healing response to the presence of ‘dead cells’
- Some cells are replaces regularly - smooth muscle cells last a long time but when they do start to die they can be replaces with calcified tissue which reduces elasticity
- Reduces the elasticity of the vessel - BP affected
- Increases the risk of coronary events
What is the basis of blood pressure?
- ‘Circulation of fluid contained within a space of definite volume’ (can change the volume by opening up capillary beds - increasing the volume for blood to flow in)
- Pressure falls as blood circulates from the left ventricle to the right ventricle (systemic circulation) and right ventricle to left ventricle (pulmonary circulation)
- Require a certain volume per minute to satisfy metabolic demands
What is the ‘normal’ blood pressure?
120/80 but varies with age, environment etc
What is mean arterial pressure?
The average pressure pushing blood round the system
How can you calculate the mean arterial pressure?
MAP = diastolic BP + 1/3 pulse pressure
*pulse pressure is the difference between systolic and diastolic pressure
What are the 2 ways of calculating MAP?
MAP = diastolic BP + 1/3 pulse pressure
MAP = CO x TPR
What is arterial blood pressure?
- Blood forcefully ejected into the arteries from the ventricles
- Blood leaves the aorta (or pulmonary artery) continuously through other branches, then arterioles etc
What is special about arteries that allows them to be able to withstand raised pressure?
- They have elastic muscular walls
What is the structure of major arteries and why?
- They have very thick walls which are elastic as they contain a small amount of blood at high pressure
What is the structure of arterioles and why?
- A variable resistance system which distributes the blood - dissipate most of the pressure
- They are much smaller in terms of diameter compared to arteries but still have a thick muscular wall
What is the structure of capillaries and why?
- walls are as little as one cell thick
- Have a vast surface area where the interchange of substances with the extracellular fluid of the tissues occurs
What is the structure of venules and veins and why?
- Very distensible
- They are a collecting reservoir system which contains most of the blood at low pressure
- They can expand to accommodate a lot of the blood
What is an erythrocyte?
A red blood cell
How much of the total blood volume is contained within capillaries?
About 5%
