Special Circulations

Question 1

where do the right and left coronary arteries arise from?

Answer 1

arise from base of the aorta

Question 2

where does most of the coronary venous blood drain via and into what?

Answer 2

Drains via = coronary sinus

Drains into = right atrium

Question 3

what are 3 special adaptations does the coronary circulation have to deliver maximal O2 to myocardium?

Answer 3

1) high capillary density
2) high basal blood flow
3) high oxygen extraction (75% compared to 25% whole body average) under resting conditions

Question 4

what does the higher oxygen extraction, in the special adaptation of coronary circulation mean?

Answer 4

means extra O2 (when required) CANNOT be supplied by increasing O2 extraction

Question 5

how can extra O2 only be supplied to the myocardium ?

Answer 5

by increasing coronary blood flow
BECAUSE;
- the O2 extraction at the capillaries cannot be increased any further

Question 6

how is coronary blood flow controlled?

Answer 6

1) intrinsic mechanisms

2) extrinsic mechanisms

Question 7

in the intrinsic control of coronary blood flow, what happens to PO2 levels and what does this cause?

Answer 7

= Decreased PO2

= causing vasodilation of coronary arterioles

Question 8

what matches coronary bloods flow to demand in the intrinsic control?

Answer 8

metabolic hyperaemia

Question 9

what is hyperaemia?

Answer 9

increased blood flow to an organ

Question 10

what is an example of a potent vasodilator involved in the intrinsic mechanism of coronary blood flow?

Answer 10

Adenosine (from ATP).

Question 11

what are the coronary arterioles supplied by?

Answer 11

supplied by sympathetic vasoconstrictor nerves

Question 12

However, why is there no vasoconstriction in the coronary arterioles then?

Answer 12

1) as the sympathetic system is over-ridden by metabolic hyperaemia
(- due to increased HR & SV)

2) causes vasodilation so heart gets increased flow

Question 13

what is released from the adrenal gland that activates B2 adrenergic receptors causing vasodilation?

Answer 13

adrenaline

Question 14

when does peak left coronary flow happen and why?

Answer 14

= during diastole

• as its when the left ventricle contracts during systole the left coronary artery is also affected

Question 15

when does most of the coronary blood flow and myocardial perfusion occur?

Answer 15

occurs in diastole when the sub-endocardial vessels from the left coronary artery are not compressed

Question 16

which 2 main arteries supply the brain?

Answer 16

1) internal carotids

2) vertebral arteries

Question 17

what is grey matter?

Answer 17

darker tissue in CNS that consists of nerve cells bodies.

• consciousness is lost after a few seconds of ischaemia, irreversible cells damage within 3minutes

Question 18

what is grey matter very sensitive to?

Answer 18

sensitive to hypoxia

Question 19

when is consciousness of grey matter lost?

when is irreversible cell damage done?

Answer 19

Consciousness lost
= after few seconds of ischaemia

Irreversible cell damage
= within 3 minutes

Question 20

what forms the circle of willis?

Answer 20

= BASILAR (formed by 2 vertebral arteries) & CAROTID arteries anastomoses

Question 21

what arises from the circle of willis?

Answer 21

major cerebral arteries

Question 22

how does circle of willis maintain cerebral perfusion?

Answer 22

• even is one carotid artery gets obstructed, the others can redistribute their blood at the anastomosis

Question 23

what causes a stroke?

Answer 23

interruption/cut-off blood supply to a region of the brain

Question 24

what does auto regulation of cerebral blood flow do?

Answer 24

= gourds against changes in cerebral blood flow if MABP changes within a range (60-160mmHg)

i.e. stops flow changing even if there are changes in pressure;

Question 25

what happens to the resistance of the vessels if MABP rises?

Answer 25

vessels automatically constrict to limit blood flow.

Question 26

what happens to the resistance of the vessels if MABP falls?

Answer 26

vessels automatically dilate to maintain blood flow

Question 27

what happens if MABP falls below 50mmHg?

Answer 27

- confusion - fainting - brain damage if not quickly corrected

Question 28

what does an increase and decrease in PCO2 do to cerebral flow?

Answer 28

Increase = causes vasodilation Decrease = causes vasoconstriction

Question 29

what is normal intra-cranial pressure within the skull?

Answer 29

about 8-13mmHg

Question 30

what is the relationship between cerebral percussion pressure (CPP), MAP and ICP?

Answer 30

CPP = MAP - ICP

Question 31

what does increasing inter-cranial pressure, i.e. due to head injury or brain tumour, do to cerebral perfusion pressure and blood flow?

Answer 31

= decreases cerebral perfusion pressure and blood flow

Question 32

what is the blood brain barrier?

Answer 32

= very tight inter-cellular junctions at the cerebral capillaries

Question 33

what are the cerebral capillaries highly permeable to?

Answer 33

O2 and CO2

Question 34

how does glucose cross the BBB?

Answer 34

by facilitated diffusion using specific carrier molecules.

Question 35

what is the BBB impermeable to and why is this useful?

Answer 35

hydrophilic substances; e.g. ions, catecholamines, proteins - useful as it protects the brain neurones from fluctuating levels of ions in the blood

Question 36

where does the entire cardiac output flow from and into?

Answer 36

flows from right ventricle into pulmonary circulation

Question 37

is the pulmonary system a high or low pressure system?

Answer 37

low

Question 38

what type of force exceeds filtration forces and what does this protect from?

Answer 38

absorptive forces = protecting against pulmonary oedema

Question 39

does hypoxia constrict or dilate PULMONARY arterioles and why?

Answer 39

constricts them | = diverts blood away from poorly ventilated areas of lung

Question 40

True or false. | Resting blood low is low because of parasympathetic vasoconstrictor tone.

Answer 40

False. | - it is low due to SYMPATHETIC vasoconstrictor tone

Question 41

what happens during exercise in terms of vasoconstriction/dilation in skeletal muscles?

Answer 41

- local metabolic hyperaemia overcomes sympathetic activity causing vasodilation - adrenaline causes vasodilation (B2 adrenergic receptors) - increased CO increasing skeletal muscle blood flow

Question 42

where does the skeletal muscle pump originate from? and what does contraction of these muscles aid?

Answer 42

large veins in limbs lie between skeletal muscles = aids venous return

Question 43

what does the skeletal muscle pump reduce the chances for?

Answer 43

= postural hypotension & fainting

Question 44

what are varicose veins?

Answer 44

when valves in veins of lower limbs become incompetent and so blood pools form in them

Question 45

how does varicose veins not reduce cardiac output?

Answer 45

because there is a chronic compensatory increase in blood volume