Exchange and the lymphatic system Flashcards
What properties of the capillaries means they are efficient in exchange
Lots of them - short distance for exchange Small diameter therefore large surface area to volume ratio Thin walled (one cell thick)
What are the endothelia cell junctions called in the capillaries
clefts
What can be present within the walls of the endothelia
fenestrations - produce channel
What is the structure of continuous capillaries in the brain
No clefts or channels
What is the structure of fenestrated capillaries
Clefts and channels present
What is the structure of discontinuous capillaries
Clefts and massive channels present
Called - sinusoids
Where would continuous/fenestrated/discontinuous capillaries be found
Continous = muscle Fenestrated = Intestine Discontinuous = Liver
Why is sinusoids present in the liver
to allow the passage of big molecule e.g. protein
What is the structure of the continuous capillaries in muscle
Clefts only
Why is there no clefts and channels present in the brain
To maintain an tight blood brain barrier
What is the two processes occurring in clotting
formation of a platelet plug
formation of a fibrin clot
How is the platelet plug formed
Platelets recognise collagen
Therefore signal and attract more platelets
What enzyme is responsible for activating precursor fibrinogen
Thrombin converts to fibrin
What is the 6 mechanism of the epithelium to prevent clotting
Stops blood contacting collagen
Produces prostacyclin and NO
Produces tissue factor pathway inhibitor (TFPI)
Expresses thrombomodulin
Expresses heparin
Secretes tissue plasminogen activator (t-PA)
What two mechanisms of the epithelium prevent platelet aggregation
The Stoping of blood contacting collagen
The Production of prostacyclin and NO
What two mechanisms of the epithelium inactivate thrombin
Expresses thrombomodulin
Expresses heparin
How does thrombodulin inactivate thrombin
Bind to it
The epitheliums production of tissue factor pathway inhibitor (TFPI) prevents clotting by
Stoping thrombin production
What is the purpose of the tissue plasminogen activator secreted by the epithelium
Breaks the clot down
What is the main mechanism of exchange in the capillaries
Diffusion
What is the exception of another exchange present in the capillaries and why it this important
The carrier mediated transport of glucose needed by the brain, as the tight blood brain barriers prevents diffusion
Why is the diffusion in the capillaries a self regulating process
Increasing the oxygen levels, increases the diffusion rate of oxygen
Why is the diffusion in the capillaries a non saturable process
Increasing the concentration Oxygen, increases conentration gradient, and allows continually movement of oxygen across the capillaries as nothing can prevent the movement so cant be saturated
How do non polar substances cross the capillaries
across the membrane
How do polar substances cross the capillaries
Through the cleft/channels of capillary membrane
What causes the bulk flow movement on the capillaries
The hydrostatic pressure pulling fluid out of the capillaries opposed by the osmotic pressure pulling fluid into the capillaries
Where does the hydrostatic pressure decrease
from the arterioles to the venules
Where does the osmotic pressure increase
from the arterioles to the venules
How much fluid is lost due to bulk flow due to how much is gained
20L is lost in the capillaries due to hydrostatic pressure
17L is retained in the capillaries due to osmotic pressure
Where does the remaining 3L, due to bulk flow end up
In the lymphatic system
What two factors ensure lymph is pumped upwards towards the heart
Smooth muscle in the lymph periodically contracts pushing the fluid
and valves ensure the fluid is pushed up the way towards the heart
What pushes the fluid forward in the capillary system
valves
Define oedema
accumulation of excess fluid
What is four reasons that cause oedema
Lymphatic obstruction
Raised CVP
Hypoproteinemia
Increased capillary permeability
What are two factors that causes lympathic obstruction
filariasis - tropical disease caused by worms
surgery
What can cause an increase in central venous pressure
ventricular failure
What are the various factors that cause hypoproteinemia - low protein levels in the blood
nephrosis - kidney disease
liver failure,
nutrition
What is an example of an autoimmune disease causing increased capillary permeability due to inflammation
rheumatism - inflammation and pain in the joints
How does low protein levels result in oedema
Low protein levels reduces osmotic concentration therefore reducing reabsorption causing this accumulation of fluid
What is the differing structure of capillaries and lymph vessels
Lymph vessles have blind ends
Where does lymph return to in the heart
The low presure part of systemic circulation
