Peripheral Circulation Flashcards
How are capillaries specialised for exchange?
Numerous - nearby to all tissues.
Thin-walled - small diffusion barrier.
Small diameter - big SA:Vol.
What are the different types of capillaries?
Continuous - no clefts or pores (brain), or only clefts (muscle). Most capillaries.
Fenestrated - clefts and pores (kidney, intestine).
Discontinuous - clefts and massive pores (liver).
What are the differences between clefts and pores?
Clefts - between epithelial cells.
Pores - across capillaries.
How does exchange occur in capillaries?
Diffusion - self-regulated and non-saturable.
Non-polar - PLBL.
Polar - through clefts and pores.
Carrier-mediated - glucose transporters (brain).
What determines bulk flow?
Starling’s forces - capillary hydrostatic pressure and plasma osmotic pressure.
Varies between capillary beds.
An overall loss of fluid occurs from the capillaries, with the excess becoming lymph.
What are the causes of oedema?
An accumulation of excess fluid. Caused by -
Raised CVP (ventricular failure).
Lymphatic obstruction (surgery).
Increased capillary permeability (inflammation).
Hypoproteinaemia (liver failure).
What is Poiseuille’s Law?
Varying the radius of resistance vessels controls flow and redirects blood. It also controls TPR and regulates MAP. MAP = CO x TPR.
Low TPR = high flow = low MAP.
Why is controlling arteriolar radius important?
Affects flow through individual vascular beds and MAP (both affected together).
What is active hyperaemia?
Local control of flow and MAP.
Increased metabolic activity increases [metabolites], triggering the release of NO - this causes arteriolar dilation.
Flow increases to decrease [metabolites].
Blood supply is matched with the metabolic needs of that tissue.
What is pressure autoregulation?
Local control of flow and MAP.
High MAP = low flow, metabolites accumulate.
Triggers NO release, causing arteriolar dilation.
Flow increases and is restored to normal.
Ensures that a tissue maintains its blood supply despite changes in MAP.
What is reactive hyperaemia?
Local control of flow and MAP.
Triggered by an occlusion of blood supply.
Causes an increase in blood flow.
What is the injury response?
Mast cells release histamines, with cause arteriolar dilation, increased flow and permeability (aids delivery of leukocytes to the site or injury).
What is the role of the SNS in the control of MAP and flow?
Sympathetic nerves release noradrenaline.
Adrenal medulla releases adrenaline.
Binds to A1 receptors.
Arteriolar constriction occurs.
Flow decreases through that tissue, and tends to increase TPR and MAP.
What is the role of the PNS in the control of MAP and flow?
No effect.
Genitalia and salivary glands increase flow.
What is the role of skeletal and cardiac muscle in the control of MAP and flow?
Activates B2 receptors.
Arteriolar dilation occurs.
Flow increased through that tissue, and tends to decrease TPR and MAP.
Significant during exercise.
