Exchange in, and control of, the Peripheral Circulation Flashcards
What are the 3 types of capillaries
CONTINUOUS
- No clefts or pored eg brain
- Clefts only eg muscle
FENESTRATED
- clefts and pores eg intestines and kidney
DISCONTINOUS
- clefts and massive pores eg liver
What are the methods of substance exchange
DIFFUSION
- self regulating
- non-saturable
- non-polar substances across phospholipid membrane
- polar substances through clefts/pores
CARRIER-MEDIATED TRANSPORT
- glucose tranporters
What does Starling’s forces determine?
BULK FLOW which results in loss of ~3L of fluid per day which the lymphatic system drains
What is oedema? and what could it be due to?
accumulation of excess fluid (fault in lymphatic system)
Could be due to:
- Raised centralvenous pressure e.g. due to ventricular failure
- Lymphatic obstruction e.g. due to filariasis, surgery
- Hypoproteinaemia e.g. due to nephrotic syndrome, liver failure, malnutrition
- Increased capillary permeability
-Inflammation e.g. rheumatism
Justify the importance of Poiseuille’s Law in relation to the control of resistance and blood flow
Varying the radius of resistance vessels is used to control flow and redirect blood, control TPR (total peripheral resistance) which leads to regulation of Mean Arterial Pressure THEREFORE Poiseuille’s law is used to workout resistance
What does arteriolar radius affect flow through?
individual vascular beds, and it affects mean arterial pressure
YOU CANNOT EFFECT ONE WITHOUT THE OTHER
What mechanisms are in place to ensure blood flow to each vascular bed is sufficient and mean arterial pressure is in the right range
- Local (intrinsic) mechanisms - concerned with meeting the selfish needs of each individual tissue
- Central (extrinsic) mechanisms – concerned with ensuring that the total peripheral resistance (and therefore Mean Arteriol Pressure) of the whole body stays in the right ball park
CAUSED BY SMOOTH MUSCLE SURROUNDING THE ARTERIOLES
What are the 3 types of local (intrinsic) controls?
- Active (metabolic) hyperaemia
- Pressure (flow) autoregulation
- Reactive hyperaemia
Define ACTIVE (metabolic) HYPERAEMIA
TRIGGER IS AN INCREASE IN LOCAL METABOLISM
Define PRESSURE (flow) AUTOREGULATION
TRIGGER IS A DECEASE IN PERFUSION PRESSURE
Define REACTIVE HYPERAEMIA
TRIGGER IS OCCLUSION OF BLOOD SUPPLY
Explain the basis of the injury response
Aids delivery of blood born leucocytes etc to injured area
Mast cells release histamine causing blood flow and permeability of arteriolar dilation to increase.
Identify the neural factors affecting arteriolar tone
SYMPATHETIC NERVES
- Release noradrenaline
- Binds to α1 receptors
- Causes arteriolar constriction
- Therefore ↓ flow through that tissue and tends to ↑ TPR and ↑ MAP
PARASYMPATHETIC NERVES
- Usually no effect
- Genitalia and salivary glands are the exception (↑ flow)
Identify the hormonal factors affecting arteriolar tone
ADRENALINE
- Released from adrenal medulla
- Binds to α1 receptors
- Causes arteriolar constriction
- Therefore ↓ flow through that tissue and tends to ↑ TPR and ↑ MAP
Describe the dominant factors controlling blood flow in cardiac vascular beds
- But in some tissues, e.g. skeletal and cardiac muscle also activates β2 receptors as well as alpha1
- Causes arteriolar dilation
- Therefore ↑ flow through that tissue and tends to ↓ TPR
- Significant during exercise
