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Flashcards in Circulation Deck (13):
1

resistance vessels

- are arterioles (have ability to dilate and contract)
- thick SM (tunica media) of A → due to A subjected to high pressure

2

capacitance vessels

- veins, acts as collectors and reservoirs
- have valves and prevent backflow

3

exchange vessels

capillaries
- carries blood from arterioles to venules
- allows delivery and exchange of substance
- thin SM (tunica media)

4

principles of circulation

1) fluid does not flow when pressure is the same in all parts
2) fluid flows from high→low pressure
3) BF b/w 2 points can be predicted by pressure gradient

5

what is the chief determinant of blood flow

vol of blood in arteries

6

factors affecting SV

- length of myocardial fibres before contraction
- determined by starling's law (increase preload stretch → increases contraction)

7

factors affecting HR

- ANS
- baroreflex - via CN9
(aortic, carotid baroR)

8

factors affecting CO

preload - vol of blood in vent at the end of diastole
- affected by BV and posture

afterload - res vent contracts against
- affected by A elasticity, blood viscosity

contractility
- affected by SNS, amount of viable muscles

9

peripheral resistance

- A resistance (accounts for half of TPR in systemic circulation)
- characterised by viscosity or diameter of arterioles

10

vasomotor pressoreflex (baroreflex)

inc BP → inc baroR firing → inhibit vasomotor centres in medulla → dec SNS + inc PNS

11

chemoR and chemoreflexes

sensitive to changes in pH
- excess CO2 → stimulates inc ventilation
- acidosis
- dec blood O2 (less sensitive)
all stimulates vasomotor centres → inc HR and SV

12

medullary ischaemic response

a last ditch effect
- BF to brain severely compromise (i.e. from trauma)
- dec O2 deficiency, inc CO2
- stimulates vasoconstrictor centres

13

venous return to heart

from vein constrictions
- skeletal muscle pumps → force blood flow through veins
- resp pump → create pressure gradient b/w ab and thorax