the peripheral circulation Flashcards
capillary properties
thin walled - small diffusion barrier
small diameter - big surface area:volume ratio
continous capillaries
no clefts or pores e.g. brain
clefts only e.g. muscle
fenestrated capillaries
clefts and pores e.g. intestine
discontinuous capillaries
clefts and massive pores e.g. liver
diffusion
self-regulating, non-saturable
non-polar surfaces across membrane, polar substances through clefts/channels
types of exchange at capillaries
diffusion
carrier-mediated transport
bulk flow
hydrostatic pressure
pushed water out - leaves behind solutes and so conc increases
osmotic (oncotic pressure)
pulls liquid in
starling’s forces
balance between hydrostatic and oncotic pressure
oedema
acculumation of excess fluid
causes of oedema
lymphatic obstruction
raised CVP
hypoproteinemia
inc capillary permeability
MAP =
CO x TPR
extrinsic control of ateriolar resistance
neural
hormonal
sympathetic effect on arteriolar resistance
noradrenaline acts on a-1 receptors to cause arteriolar constriction
increases TPR
hormonal effect on TPR - adrenaline
released from adrenal medulla, acts on a-1 receptors
inc TPR
in some tissues acts on B-2 receptors to cause dilation and dec TPR
hormonal effect on TPR - angiotensin
produced in response to low blood volume
causes arteriolar constriction and so inc TPR
hormonal effect on TPR - vasopressin
antidiuretic hormone
arteriolar constrictoin and so inc TPR
hormonal effect on TPR - ANP
arteriolar dilation and so dec TPR
local (intrinsic) controls of TPR
active hyperaemia
pressure flow autoregulation
reactive hyperaemia
injury response
effect on TPR - active hyperaemia
inc metabolic activity caused inc concentration of metabolites
release of EDRF/NO which causes ateriolar dilation - inc flow to wash out metabolites
effect on TPR - pressure flow autoregulation
decreased MAP causes decreased flow, metabolites accumulate - release of EDRF/NO
arterioles dilate and flow restored to normal
effect on TPR - reactive hyperaemia
occlusion of blood supply caused subsequent increase in blood flow
extreme version of pressure autoregulation
effect on TPR - injury response
substance P released and acts on mast cell
mast cell releases histamine - arteriolar dilation : inc blood flow and permeability