exchange in and control of peripheral circulation Flashcards
Identify the processes involved in transport between capillaries and tissues.
Specialised for exchange. There are lots of them and every tissue is close to a capillary. Very thin wall so a small diffusion barrier
Explain the significance of the blood-brain barrier.
Protect against circulating toxins or pathogens that could cause brain infections, while at the same time allowing vital nutrients to reach the brain.
Explain the significance of Starling forces and the lymphatic system in relation to oedema.
bulk flow results on 3 L of fluid remaining which need to be drained by the lymphatic system.
Justify the importance of Poiseuille’s Law in relation to the control of resistance and blood flow.
varying radius of resistance vessels can be used to control flow and redirect blood.
reducing resistance of vascular bed increases flow through vascular bed but reducing TPR also reduces mean arterial pressure. you cannot effect one without the other.
- Define active hyperaemia, pressure autoregulation and reactive hyperaemia.
Explain the basis of the injury response.
c fibres are triggered by external stimuli. Results in arteriolar dilation which increases blood low and increases permeability. Aids delivery of blood front leucocytes to injured area
- Identify the various neural tone, affecting arteriolar tone.
sympathetic nerves release noradrenaline and binds to alpha one receptors causing arteriolar constriction therefore a decreased blood flow though the tissues and tends ti increase TPR and increases MAP
- Describe the dominant factors controlling blood flow in cardiac, cerebral, pulmonary and renal vascular beds.
cardiac- blood supply Is interrupted by systole. expresses beta 2 receptors which swamp any sympathetic arteriolar constriction
cerebral- needs to be kept stable. shows excellent pressure auto regulation
pulmonary- decreased O2 causes arteriolar constriction and entrees blood is directed to best ventilated parts of lung
renal- main job is filtration, kept constant during fluncuations in MAP due to pressure auto regulation
describe continuous capillaires
Tight junctions as endothelial cells are pressed really tightly together. No clefts or pores e.g brain
describe fenestrated capillaries
large pores and clefts making them specialised for fluid exchange
describe transcytosis
brings proteins and macromolecules across the endothelium and some vesicles fuse to create temporary channels
discontinous capillaires
clefts and massive pores e.g liver large proteins can move across
exchange of gases in capillaries
via diffusion. self regulating, non saturable- does’nt need transporter proteins
no polar substances can cross through membrane and polar substances through clefts and pores
active metabolic hyperaemia (local)
Trigger is an increase in local metabolism
During exercise (increase in metabolism) you will get an increase in skeletal muscle and increased porduciton in medabolites which increases concentration and trigger a local chemical signal called endothelial derived relaxing factor
When it is released from the endothelium it will diffuse into smooth muscle and surround arteriole. Arteriole will dilate, radius increase and resistance will go down and increased blood flow. Increased blood flow will remove metabolites and return to steady flow.
Only benefits this tissue
Pressure flow auto regulation
Triggered by decrease in perfusion pressure. Increases mean arterial pressure decreased blood flow. Metabloites increase. Releases EDRF. arterioles dilate and flow is rested to normal.
