Exchange and the Lymphatic System Flashcards
What are capillaries specialised for?
Exchanging nutrients
Why are capillaries thin walled?
Presents a small diffusion barrier
What is the advantage of capillaries having a small diameter?
Large surface area:volume ratio
What does the ultrastructure of capillaries relate to?
Function

What are the 3 kinds of capillaries?
Continuous
Fenestrated
Discontinuous
What are the 2 different kinds of continuous capillaries?
No clefts or channels such as in the brain
Only clefts such as in muscle
What is present in fenestrated capillaries?
Clefts and channels
Where are fenestrated capillaries found?
Intestine
Where are continuous capillaries found?
Brain
Muscle
Where are discontinuous capillaries found?
Liver
What is present in discontinuous capillaries?
Clefts and massive channels
What is the difference between continuous and fenestrated capillaires?
Continuous have leaky junctions whereas fenestrated have large pores
What causes more of a nutrient to diffuse across a capillary?
If the cell uses more of it, it creates a larger concentration gradient and so more diffuses across

What are the 2 ways that nutrients can cross capillaries?
Diffusion
Carrier mediated transport
What is an example of carrier mediated transport?
Glucose transporter
How do polar substances diffuse across capillaries?
Through clefts/channels
How to non-polar substances diffuse across capillaries?
Across the membrane
What does hydrostatic pressure do?
Pushes fluid out of capillaries

What pushes fluid out of capillaries?
Hydrostatic pressure
What does osmotic (oncotic) pressure do?
Draws fluid back into capillaries

What causes osmotic pressure?
Hydrostatic pressure pushing fluid out of capillaries builds up an osmotic pressure
What is the balance between hydrostatic and osmotic pressures called?
Starling’s forces

What makes up Starling’s forces?
Capillary hydrostatic pressure vs interstitial fluid hydrostatic pressure
Plasma osmotic pressure vs interstitial fluid osmotic pressure
What formula describes net filtration pressure?
Net filreation pressure = (PC - PIF) - (πP - πIF)
Overall how much fluid is lost and gained from capillaries each day?
20L is lost
17L is gained
If 20L of fluid is lost from capillaries and 17L is gained each day, what happens to the remaining 3L?
Goes into the lymphatic system

What eventually happens to fluid that is drained into the lymphatic vessels?
Returned to venous circulation
What happens when the lymphatic system becomes overwhelmed?
Oedema
What is an oedema?
Accumulation of excess fluid
What is an accumulation of excess fluid called?
Oedema
What can an oedema be caused by?
Lymphatic obstruction
Raised hydrostatic pressure
Low osmotic pressure
What can cause a lymphatic obstruction?
Filariasis or surgery
What can cause a raised hydrostatic pressure?
Ventricular failure
What can cause low osmotic pressure?
Hypoproteinemia
Increased permeability
What can increased permeability be caused by?
Inflammation such as rheumatism
What can hypoproteinemia be caused by?
Nephrosis
Liver failure
Nutrition
What redirects blood?
Arterioles not capillaries
Why do capillaries not redirect blood?
They do not have any smooth muscle around them
What is varying the resistance of arterioles done by?
Altering the radius
What is Darcy’s Law?

What is Poiseuille’s Law?

What equation to you get by substituting Poiseuille’s Law back into Darcy’s Law?

What equation describes flow?

Why does varying the resistance of one set of vessels not only affect the flow through that region of the body?
Because it changes the total peripheral resistance so affects the mean arterial pressure

What formula describes the mean arterial pressure?
MAP = CO x TPR

What does MAP stand for?
Mean arterial pressure
What does TPR stand for?
Total peripheral resistance
Why is mean artieral pressure very important?
It provides the driving force that pushes blood through useful places like the brain, so a system must monitor and regulate in by controlling the state of construction in arterioles
What are the 2 levels of control over smooth muscle surrounding the arterioles?
Intrinsic mechanisms
Extrinsic mechanisms
What are intrinsic mechanisms concerned with?
Meeting the needs of each individual tissue
What are extrinsic mechanisms concerned with?
Ensuring that the total peripheral resistance (and so mean arterial pressure) of the whole body stays at the right levels
What is extrinsic control achieved by?
Neural
Hormonal
Angiotensin II
Vasopressin
Atrial natriuretic factor
How is the autonomic system used for extrinsic control?
Sympathetic nerves release noradrenaline which binds to A1 receptors causing arteriolar constriction and decreases flow through that tissue, increase total peripheral resistance
Parasympathetic system has no effect
What receptors does the sympathetic nervous system act on arterioles?
A1
What effect does parasympathetic nerves have on arterioles?
Usually no effect
What is a hormone that achieves extrinsic control?
Adrenaline
Where is adrenaline released from?
Adrenal medulla
What receptor on arterioles does adrenaline act on?
A1
How do hormones achieve extrinsic control?
Adrenaline causes arteriolar constriction so decrease flow through that tissue and increase total peripheral resistance
What is a complication with using adrenaline to achieve extrinsic control?
In some tissues (such as skeletal and cardiac muscle) as well as A1 it also binds to B2 receptors which cause arteriolar dilation, increasing flow and decreasing total peripheral resistance
What is angiotensis II produced in response to?
Low blood pressure
What effect does angiotensin II have?
Causes arteriolar constriction so increases total peripheral resistance
What is vasopressin released in response to?
Low blood volume
What effect does vasopressin have?
Causes arteriolar constriction so increases total peripheral resistance
What is atrial natriuretic factor released in response to?
High blood volume
What impact does atrial natriuretic factor have?
Causes arteriolar dilation so decreases total peripheral resistance
What is the important effect of B2 receptors in blood vessels?
Only in some places of the body so redirects blood to heart and skeletal muscles during fight or flight reaction
What is local (intrinsic) control achieved by?
Active (metabolic) hyperaemia
Pressure (flow) autoregulation
Reactive hyperaemia
The injury response
How does active (metabolic) hyperaemia achieve intrinsic control?
1) Increased metabolic activity causes increase in the concentration of metabolites
2) Triggers release of EDRF/NO (paracrines)
3) Causes arteriolar dilation
4) Increased flow to wash out metabolites
5) An adaptation to match blood supply to the metabolic needs of that tissue
How is pressure (flow) autoregulation used to achieve intrinsic control?
1) Decreased mean arteriolar pressure causes decrease in flow
2) Metabolites accumulate
3) Arterioles dilate and flow is restored to normal
4) An adaptation to ensure that a tissue maintains its blood supply despite changes to mean arterial pressure
How is reactive hyperaemia used to achieve intrinsic control?
Occlusion (the blockage or closing of a blood vessel) of blood supply causes a subsequent increase in blood flow
An extreme version of pressure autoregulation
How is the injury response used to achieve intrinsic control?
1) Substance P acts on mast cells which release histamine
2) Histamine causes arteriolar dilation which increases blood flow and permeability
3) Aids delivery of blood born leukocytes to injured area
What are areas that are ‘special’ (in terms of pressure)?
Coronary circulation
Cerebral circulation
Pulmonary circulation
Renal circulation
How is coronary circulation special?
Blood flow is interupted by systole
But still has to cope with increased demand during exercise
Does so by showing excellent active hyperaemia
Expressed many B2 receptors
These swamp any sympathetic arteriolar constriction
How is cerebral circulation special?
Needs to be kept stable whatever the circumstances
Shows excellent pressure autoregulation
How is pulmonary circulation special?
Decrease in O2 causes arteriolar constriction
The opposite reaction to most tissues
Ensures that blood is directed to the best ventilated parts of the lungs
How is renal circulation special?
Main function is filtration which depends on pressure
Changes in mean arteriolar pressure would have a big effect on blood volume
Shows excellent pressure autoregulation