Cardio 11 Flashcards
What happens when bleeding occurs?
-blood lost from CVS (particularly veins)
veins = blood reservoir of the body
>high capacitance/compliance
What happens to the blood with an intact compensatory VS without?
- Without:
-venous volume
-venous pressure
-atrial pressure = CVP
-ventricular preload
-EDV
-SV
-CO
-MAP
=Death - Normal animals can withstand 40% hemorrhage without death
-10% decrease in MAP
What is the first event in hemorrhage?
-loss of blood
-decreased blood volume
-decrease in amount of circulating blood
>decreases right atrial volume/pressure
>decreases EDV
>decrease CO
>decrease MAP
What are the immediate compensations for bleeding initiated by?
-baroreceptors (mechanoreceptors) located in arterial & venous side of the circulation located in carotid sinus & aortic arch
>arterial baroreflex
* arterial side of circulation = high pressure receptors
>arterial volume receptor reflex
* cardiopulmonary low pressure baroreceptors
—sense changes in blood volume
—located in venous side of circulation
[both reflexes take seconds]
What does the baroreflex activate during a hemorrhage?
-medullary cardiovascular control centers
-generate sympathetic response
>vasoconstrictor center
>cardiac accelerator center
Describe the baroreceptor reflex when there is a decrease in MAP.
Describe the contribution of atrial volume receptor reflex to hemorrhage.
Describe the immediate reflexes during hemorrhage.
-increase HR = brings CO back to 20% of normal level
-sympathetic vasoconstriction in non critical organs raises TPR & put MAP in 10% of its normal level
-SV is 25% below normal in 40% bleeding
baroreflex remains activated bc its responsive to MAP & pulse pressure
What happens to the abdominal veins & spleen during severe bleeding?
-sympathetic activation
-blood in spleen goes to abdominal veins & moves toward the heart
>dogs & horses mobilize 10% of total blood volume
>blood from spleen = higher # of RBCs
>helps offset the fall in hematocrit
What are the other compensations that come into play the minutes & hours after hemorrhage to restore the lost fluid volume?
-both venous & arterial pressure fall below normal
-capillary hydrostatic pressure falls
>favors reabsorption
>volume is reabsorbed in 1 hour = 10% of volume lost
>after 3 or 4h = opposes reabsorption
Describe what the interstitial reabsorbed fluid contains.
-neither plasma proteins nor blood cells
-dilution makes proteins & hematocrit decrease in circulation
-hematocrit blood test = percentage of RBCs in the blood
What does the complete restoration of blood volume after hemorrhage depend on?
-atrial volume receptor reflex & RAAS
>RAAS = hormonal mediated (slower)
>RAAS = activated by decrease in MAP = decrease in renal perfusion pressure
>activated baroreceptors = renin release by juxtaglomerular cells
Which component of RAAS is a vasoconstrictor of arterioles?
-angiotensin II
Describe the regulation of aldosterone secretion in the RAAS pathway.
Describe the effect of RAAS in MAP.
Describe how peripheral chemoreceptors interfere with BP.
Describe how central chemoreceptors interfere with BP?
