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Flashcards in Special Circulations Deck (49)
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1

Where do the right and left coronary artery arise from?

Base of aorta

2

How does most coronary venous blood drain?

Via the coronary sinus into the right atrium

3

Special adaptions of coronary circulation?

-High capillary density
-High basal blood flow (under resting conditions blood flow to heart is significantly higher than other tissues)
-High oxygen extraction under resting conditions
^Means extra O2 (when required) cannot be supplied by increasing O2 extraction
^Can only be supplied by increasing coronary blood flow

4

What is coronary blood flow controlled by?

Intrinsic and extrinsic mechanisms

5

What happens to coronary arterioles when there is decreased PO2?

Vasodilation

6

Coronary blood flow intrinsic mechanisms?

Decreased Po2= vasodilation of coronary arterioles
Metabolic hyperaemia (XS of blood in vessels) matches flow to demand
Adensine (from ATP) is potential vasodilator

7

Coronary blood flow extrinsic mechanisms?

-Coronary arterioles supplied by sympathetic vasoconstrictor nerves BUT are over ridden by metabolic hyperaemia (by increased HR and SV)
-Sympathetic stimulation of heart= coronary vasodilation
-Circulating adrenaline activates B2 adrenergic receptors which= vasodilation

8

What does circulating adrenaline activate as an intrinsic mechanism?

B2 Adrenergic receptors= vasodilation

9

When does peak left coronary blood flow occur?

Diastole

10

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

Diastole - when subendocardial vessels from the left coronary artery are not compressed**

11

What is the brain supplied by?

Internal carotid and vertebral arteries

12

What matter is very sensitive to hypoxia?

Grey matter

13

Where do major cerebral arteries arise from?

Circle of Willis

14

What would obstruction of a smaller branch of a main artery cause?

Deprive a region of the brain of its blood supply

15

What forms the circle of Willis?

Basilar and Carotid arteries
(Basilar is formed by two vertebral arteries)

16

What is stroke caused by?

Stroke is caused by interruption/cut-off
blood supply to a region of the brain

17

What happens if Mean arterial Blood pressure rises?

Resistance vessels automatically constrict to limit blood flow

18

What happens if MABP falls?

Resistance vessels automatically dilate to maintain blood flow

19

When does autoregulation fail?

If blood MABP is below 60mmHg or above 160mmHg

20

What MABP results in confusion, fainting and nbrain damage?

Below 50mmHg

21

Why can hyperventilation lead to fainting ?

Increased Po2 causes vasodilation
Decreased Po2 causes vasoconstriction

22

Why can hyperventilation lead to fainting ?

Increased Po2 causes vasodilation
Decreased Po2 causes vasoconstriction

23

Percentages of brain?

Brain 80%
Blood 12%
Cerebral spinal fluid 8%

24

Normal intracranial pressure within skull?

8-13mmHg

25

Cerebral perfusion pressure equation?

CPP=MAP- ICP (intercranial pressure)

26

What does increasing ICP cause? due to head injury/trauma

Decreased cerebral perfusion pressure and decreased cerebral blood flow

27

What can some conditions which increase ICP lead to?

Failure of autoregulation of cerebral Blood flow

28

Describe the blood brain barrier (BBB)?

Cerebral capillaries have very tight intercellular junctions

29

Cerebral capillaries are not permeable to O2 and CO2. True or false?

False. Highly permeable

30

How does glucose cross the BBB?

Facilitated diffusion using specific carrier molecules