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Flashcards in test 9 Deck (34):
1

Control of blood flow to local tissues depends on maintaining constant

-pressure drop across the tissue
-constant MAP and CVP

2

Mechanisms For Controlling Blood Pressure

 Aldosterone (hormonal)
 Baroreceptors (nervous)
 Capillary fluid shift (physiologic)
 Chemoreceptors (nervous)
 CNS ischemic response (nervous)
 Renal-blood volume pressure control (kidneys)
 Renin-angiotensin-vasoconstriction (hormonal)
 Stress relaxation of vasculature (physiologic)

3

BP control Mechanisms characterized by

 Activation time
 Activation strength (gain)
 Length of activation

4

BP control Mechanisms that respond within seconds

-Baroreceptors
-chemoreceptors
-stress relaxation
-CNS ischemic response

5

BP control Mechanisms that respond within minutes

-capillary fluid shift
-renin-angiotensin-vasoconstriction

6

BP control Mechanisms that respond within hours

-aldosterone
-renal-blood volume pressure control

7

BP control Mechanisms with medium strength (max feedback of 4)

 Renin-angiotensin-vasoconstriction
 Stress relaxation of vasculature
 Capillary fluid shift
 Chemoreceptors
 Aldosterone

8

BP control Mechanisms with large strength (max feedback 7 & 11)

 Baroreceptors
 CNS ischemic response

9

BP control Mechanisms with infinite strength

 Renal-blood volume pressure control

10

vasomotor center efferent pathways (parasympathetic impulses)

-via vegus nerve

11

vasomotor center efferent pathways (sympathetic impulses)

-via spinal cord & peripheral sympathetic nerves to all arteries, arterioles, veins

12

Sympathetic nerve fibers exit spinal cord via

all thoracic spinal nerves & first two lumbar spinal nerves

13

Sympathetic nerve fibers enter sympathetic chains via

-either side of spinal cord

14

sympathetic nerve fibers go to circulation by (2)

1. Specific sympathetic nerves to vasculature of internal viscera & heart
2. Peripheral portions of spinal nerves to peripheral vasculature

15

Vasomotor center location

-located in the medulla and lower third of pons

16

vasomotor center has an effect on

amount of vascular constriction and cardiac activity (HR and contractility)

17

Vasoconstrictor area

 Bilateral -Anterolateral part of UPPER medulla
 Sends fibers to all areas of spinal cord
 Fibers excite vasoconstrictor neurons of sympathetic system

18

Sensory area

 Bilateral in tractus solitarus in posterolateral part of medulla & lower pons
 Receives sensory signals from circulatory system via vagus & glossopharynegeal nerves

19

vasomotor center cardiac control

 Lateral portions of vasomotor center which sends excitation impulses via sympathetic nerves to heart (increasing HR and contractility)
 Medial portion of vasomotor center which sends inhibitory impulses to vegus nerves which send parasympathetic impulses to the heart

20

Vasoconstrictor center normally sends

1.5 to 2 impulses per second resulting in partial constriction

21

vasomotor center control by CNS

 Reticular substance of pons, mesencephalon, diencephalon
 Hypothalamus
 Cerebral cortex

22

Reticular substance of pons, mesencephalon, diencephalon

 Lateral / superior portions excite vasomotor center
 Medial / inferior portions inhibit vasomotor center

23

Hypothalamus

 Posterolateral portions excite vasomotor center
 Anterior portion produces mild excitation or inhibition

24

Vasodilator area

 Bilateral -Anterolateral part of lower medulla
 Sends fibers to vasoconstrictor area
 Fibers inhibit activity of vasoconstrictor area

25

Cerebral cortex

 Motor cortex excites vasomotor center

26

General Effect of Central Nervous Control

-Able to produce rapid increase in blood pressure (double blood pressure within 5 to 10 seconds)
 Stimulate vasoconstrictor area (sympathetic)
 Stimulate increases cardiac activity (sympathetic)
 Inhibit parasympathetic vagal signals to heart

27

General Effect of Central Nervous Control physiologic response

 Constriction of most arterioles of systemic circulation
 Strong constriction of veins / some constriction of larger arteries
 Increased cardiac performance

28

Baroreceptor location

 Carotid baroreceptors send impulses via Hering’s nerves to glossopharyngeal nerves which carry impulses to sensory area of vasomotor center
 Aortic baroreceptors send impulses to vasomotor center via vagus nerves

29

Carotid baroreceptors lowest pressure

50 to 60 mmHg

30

aortic baroreceptors lowest pressure

80 to 90 mmHg

31

Chemoreceptors sensitive to

- lack of oxygen and excess carbon dioxide and
hydrogen ions
-Kick in when pressure falls below 80 mmHg

32

CNS ischemic response

 Initiated when BP falls below 60 mmHg
 Reaches greatest level of stimulation at 15 to 20 mmHg

33

Brainbridge reflex

 Increase in atrial pressure causes an increase in heart rate

34

Inspiration

 Pressure in thoracic cavity becomes more negative
 Blood vessels in chest expand
 Expansion of blood vessels decreases venous return which decreases cardiac output and arterial pressure