L9 Flashcards
what is the structure of a capillary wall
a basement membrane and a endothelial cell layer
what is the primary function of the capillaries
Primary function: exchange of nutrients and metabolic end products
do capillaries have smooth muscle associated with them
no but endothelial cells still contain actin/myosin
what % of total blood volume is in the capillaries
6%
how is capillary circulation adaptable
there are several routes between arterioles and venules.
the pathway that the RBC take is controlled by local metabolic factors
precapillary sphincters and metarterioles
main factor is metabolic demands
what are precapillary sphincters
bands of smooth muscle in the capillaries
what are metarterioles
i think they are the bits of capillary that blood can be shunted down
how big is the capillary network
it is very dense and is so big that in a adult they extend 40 000km
what is angiogenesis
increased capillary networks
it is a way that the body adapts to meet metabolic demands
what is the purpose of angiogenesis
increased capillaries = reduced diffusion distance
what is the relationship between angiogenesis and cancer cells
it enables the growth of cancer
this is because cancer cells have high metabolic demands. if the cancer cells are close to the capillaries then they send signals for more capillaries to be formed.
the increases capillary number means that the cancer cells have more nutrients for their metabolic demands allowing then to grow
A new therapy is working to try and stop the capillary growing to starve the cancer cells
what forces regulate fluid exchange across the capillary
starling’s forces
what are starling’s forces
capillary hydrostatic pressure (perfusion pressure)
interstitial hydrostatic pressure
capillary osmotic force due to plasma protein concentration (albumina)
intestinal osmotic force due to interstitial fluid protein concentration
which of starlings forces drive fluid out of the capillaries
capillary hydrostatic pressure (perfusion pressure)
and
osmotic force due to interstitial fluid protein concentration (interstitial osmotic force)
which of starlings forces drive fluid into of the capillaries
interstitial hydrostatic pressure
osmotic force due to plasma protein concentration (albumina) (osmotic capillary)
how d you find out what direction (the balance) fluid is moving in
ballance = out - in
capillary hydrostatic pressure and osmotic force due to interstitial fluid protein concentration
interstitial hydrostatic pressure and osmotic force due to plasma protein concentration
what are the most important determinants of fluid movement
capillary hydrostatic pressure and osmotic force due to plasma protein concentration
what is the resting value for capillary hydrostatic pressure in the arterioles
35 mmHg out
what is the resting value for interstitial hydrostatic pressure in the arterioles
0 mmHg
what is the resting value for osmotic force due to plasma protein concentration in the arterioles
cappilary osmotic pressure
28 mmHg into
what is the resting value for osmotic force due to interstitial fluid protein concentration in the arterioles
interstitial osmotic force
3 mmHg out
what is the balance of H2O in the arterioles
there is 10 mmHg pf pressure driving H2O out of the start of the capillaries
this is filtration
what are starlings forces in the venules
capillary hydrostatic pressure = 15 out
osmotic force due to plasma protein concentration = 28 in
interstitial hydrostatic pressure = 0
osmotic force due to interstitial fluid protein concentration = 3 out
what is the balance of H2O in the venioles
- 10 mmHg in
this is re(absorption)
why are there different pressures at the different ends of the capillaries
because pressure drops as you move through the ventricular system
what is the major determinant of capillary hydrostatic pressure
resistance in the small arterioles upstream
when they dilate there is a decrease in resistance therefore an increased in hydrostatic pressure causing a higher pressure for fluid to move out of the capillary
opposite for constriction
what is net filtration
the collection of fluid in the interstitial space
is fluid exchange equal
why
no
you need to have a balance otherwise we would become swollen
absorption and filtration are tissue specific
eg kidneys have net filtration and lungs are net absorption
what is it called when you have damaged or ineffective lymphatics
lymphedema
how do we not have pooling of the fluid
because of the lymphatic system
what is the lymphatic system
Drain excess interstitial fluid back into systemic circulation
It puts fluid back into the circulatory system just before the heart
what is the role of veins and venules
Collect blood from capillaries and take back to the heart
what is the structure of the veins
The veins have a little bit of fibrotic tissue around the outside
As you get to the larger ones then you start to get that elastic tissues back
The thickness if the walls in the veins are very thin
what % of TBV resides in the veins
40%
what are the characteristics of the veins
they are low pressure and low resistance system
they are the compliant vessels therefore they are the volume reservoir
explain why the veins are so compliant
The thin walls of the veins are really stretchy therefore highly compliant
Small increases in pressure lead to big changes in volume therefore they are able to accommodate for lots of blood
what is the plateau phase in vascular compliance
Large increase in pressure = small increase volume
near max volume therefore they cant stretch anymore
the arteries are also complaint vessels. why are they not know as the compliance vessels
because the veins are more compliant
the arteries need very high pressures to stretch i the same way that veins do
veins are 10x more compliant
what % of blood is in the venous system
60% in the venous system
40% in the veins and 20% in the venioles
what is the determinant of pressure i the venous system
we know that the pressure from the heart decreases over distance
the pressure in the venous system is from the amount of volume that is in that system (60%)
the sympathetic nervous system also has an effect
what is the effect of the sympathetic nervous system on venous pressure
SNS release noradrenaline which acts on a1 adrenergic receptors which causes venoconstriction
In the veins with vENoconstriction you get an increase in flow above the vASoconstriction whereas in the arteries you get a decrease in flow below the constriction
what effect does venous pressure have on the heart
venous pressure determines venous return
the more blood going into the heart = more blood coming out of the heart
therefore increase in venous pressure increases CO
this is starlings law
what is an external factor that has a major effect on determining venous pressure
posture
when you are lying down the effect of gravity is balanced across the body therefore venous pressure is balanced
when you are standing up the different parts of the body are at different heights therefore the effect of gravity is different therefore venous pressure increases below the heart
how do we overcome venous pooling
Unidirectional valves in veins and the skeletal muscle pump and the respiratory pump
how to the valves help us to overcome gravity
the ensure that the blood flows towards the heart as they split the veins into mini columns which reduce the effect of gravity
how does the skeletal muscle pump work
The veins are compressible and they run through the muscles
When the muscles contract they squeeze the veins which push the blood back up the the heart
valves prevent backflow
what overrules the skeletal muscle pump
thermoregulation
this changes the blood distribution as the cutaneous veins in the extremities dilate and blood is redirected to the skin
explain the respiratory pump
You can increase venous return by taking deep breaths
when you inhale the diaphragm contracts which decreases intrathoracic pressure and increases intra abdominal pressure.
this pulls blood in the thoracic vena cava and compresses abdominal vena cava therefore increasing venous return
this is the opposite for exhalation
this is important during exercise
Venoconstriction causes:
A: no change in venous return
B: an increase in venous return
C: a decrease in venous return
D: a increase in arterial pressure
B
The movement of water across the capillary wall is determined by the balance between capillary hydrostatic pressure and capillary colloid osmotic pressure
BECAUSE
a major determinant of
capillary pressure is the amount of resistance in the small arterioles.
both statements are true but not causal
NOTE they are related but because the question does not say anything about the direction they are not causal (it would also depend on what they said about the direction)
The walls of the capillaries are made of:
A: endothelium
B: endothelium and smooth muscle cells
C: endothelium, smooth muscle and elastic connective tissue
D: endothelium and fibrous connective tissue
A
future hayley- is it not D??
The skeletal muscle pump increases venous return
BECAUSE
sympathetic nerve activity induces contraction of the smooth muscle cells to constrict the veins.
both statements are true but not causal
Vasodilation of arterioles facilitates fluid reabsorption from the capillaries
BECAUSE
increased arteriole resistance decreases capillary hydrostatic pressure.
the first is false and the 2nd is true
