Circulatory system (CVS) Flashcards
Why is a circulatory system necessary?
to meet metabolic needs
- it allows fast convection system circulating fluids between surfaces
- unicellular organisms using simple diffusion & convection
Why is a circulatory system required (for intracellular vs extracellular)?
Maintains steep IC:EC concentration gradient to deliver nutrients/remove wastes from CENTRALLY LOCATED CELLS
What is the primary function of the circulatory system?
distribution of gases/molecules (nutrition, growth & repair)
What are the secondary functions of circulatory system (CVS)?
- fast chemical singalling - hormones
- dissipation of heat brings blood to the surface
- mediates inflammatory and host defence responses to invading microbes
What are the 3 functional parts of the CVS?
PUMP (heart) - maintains pressure
FLUID (blood) - dissolves substances
SET OF CONTAINERS (blood vessels)
What are the 3 types of blood vessels?
- arteries
- capillaries
- veins
What can lead to a change in demand which requires regulation?
- sleep/awake
- body position /intrathoracic pressure
- rest/exercise, acceleration/deceleration HR (heart rate)
- digestion - a lot of blood diverted towards gastrointestinal tract
- emotional stress, thermal stress
What % of blood goes constantly to the cerebrum?
15%
In what way is the heart is a dual pump?
the heart pump in two serial circuits
What type of circulation is the left heart?
systematic circulation
Where can capillary beds in series be found?
kidneys
Where can capillary beds be found in parallel & series?
spleen, intestine & liver
What type of circulation is the right heart?
pulmonary circulation
What is the name of the arterial system?
the distribution system (high pressure)
What is the name of the capillary system?
diffusion & filtration system
What is the name of the venal system?
collection system (reservoir) - low pressure
What is bifocation?
the separation of blood vessels (e.g. arteries in arterioles - microcirculation not just capillaries
How many capillaries are there?
40 billion
What is the cross-sectional area of aorta?
4cm^2
What is the cross-sectional area of capillaries?
2.8 x 10^-7 cm^2
What is the cross-sectional area of vena cava?
6cm^2
What is the aggregate cross sectional area of the aorta?
4cm^2
What is the aggregate cross sectional area of capillaries?
2827 cm^2
What is the aggregate cross sectional area of the vena cava?
6cm ^2
What is the mean velocity of the aorta?
21 cm/s
What is the mean velocity of capillaries?
0.03 cm/s
What is the mean velocity of the vena cava?
14 cm/s
What is the radius of the largest & smallest vessel?
1.1cm - 3um
What is the larger - combined cross-section area of daughter vessels or parent vessel?
combined cross-section area of daughter vessels
What are the 4 ‘building blocks’ in vascular wall?
- endothelial cells
- elastin fibres
- collagen fibres - tough protein - maintains integrity
- (vascular) Smooth-muscle cells (VSMC)
What are the 3 layers of blood vessel walls?
- intima (tunica interna)
- media (tunica media)
- adventitia (tunica externa)
What is the only intimal layer resting on a basement membrane?
capillaries
Why does an aorta have higher levels of elastic fibres?
allows aorta to accommodate for the high pressure generated from the heart
Why does the medium artery have higher levels of smooth muscle than the aorta?
smooth muscle is needed for contraction, which is needed more in the smaller vessels
Why does the aorta have high levels of collagen?
to maintain the integrity of the vessel
Why do veins have high collagen levels?
due to veins containing blood under low pressure, therefore loss of integrity could be fatal
Why is it useful for large arteries to have high compliance?
prevents tearing, and enables vessels to cope with peak ejection pressures. The recoil of elastic fibres forces blood to move even the ventricles relaxed - maintains pressure
Why is useful for medium-sized arteries to have lots of smooth muscle cells (VSMC)?
allows for greater vasoconstriction/dilation to adjust blood flow rate
- partial contraction always occurring (not either relaxed or contracting)
What are metaterioles?
Terminal regions (network shortcut)
Why are arterioles useful?
smooth muscle enables blood flow regulation to capillary networks - regulated microcirculation
What % of capillary beds are open at any one time?
10-25%
Why are postcapillary venules porous?
act as exchange sites for nutrients & waste
Why is useful for muscular venules to have a thin smooth muscle cell layer?
thin walls allow for expansion - excellent reservoirs for blood
What is the purpose of one-way valves?
prevent back flow of blood (facilitates the movement of blood towards the heart)
What condition can result from defective, leaky valves that allow back flow of blood?
varicose veins
Why can the expansion of a vein wall lead to varicose veins?
allows for blood accumulation in the pockets created, due to back-flow and pooling of the blood
What is the function of the CVS?
maintain sustainable environment for tissues
What is the principle site of exchange in the CVS?
principal exchange site
What substances are exchanged at capillaries?
- gases - e.g. oxygen
- water
- nutrients
- waste products
What additional functions can capillaries serve?
- glomerular filtrate
- skin temperature regulation
- hormone delivery
- platelet delivery
What 2 things are capillaries composed of?
endothelial cells & basement membrane
What are the 3 groups that capillaries could be, based on their leakiness?
- continuous capillary (not leaky)
- fenestrated capillary (partly leaky)
- sinusoidal (discontinuous) capillary (very leaky)
What influences the level of fenestration which capillaries have around the body?
The function of the capillaries in that area
What are the Starling forces which drives fluid transfer across capillary walls?
hydrostatic pressure & osmotic pressure
What makes up oncotic fluid?
colloid osmotic pressure (oncotic pressure), is due to serum proteins (albumin - protein most prevalent in blood)
What is the Starling’s forces equation?
Jv = Kf [Pc - Pi] - [pieC - pieI]
fluid movement = hydraulic conductance x [capillary hydrostatic pressure - interstitial hydrostatic pressure] - [ (pie x capillary oncotic pressure) - (pie x interstitial oncotic pressure)]
Why does capillary hydrostatic pressure decline along the length of capillary through fluid filtration?
As water is lost, there is less plasma, leading a reduction in pressure.
By how many litres does arteriole filtration exceed venular absorption in interstitium?
2-4L fluid/day
What is the role of the lymphatic system?
drains excess interstitial fluid
What can a blockage in lymphatic system lead to?
swelling
How does lymph return to the CVS?
via subclavian veins - vein under the clavicle
What are the other functions of the lymphatic system?
- transport of dietary lipids
- lymph nodes/organs (immunology)
