720
UNIT 4
Maintenance of the Body
19
Blood pressure maintained;
if fluid volume continues to
decrease, BP ultimately
drops.
BP is a late sign.
Chemoreceptors activated
(by
in blood pH)
Baroreceptor firing reduced
(by
blood volume and pressure)
Hypothalamus activated
(by
blood pressure)
Respiratory centers
activated
Cardioacceleratory and
vasomotor centers activated
Sympathetic nervous
system activated
Intense vasoconstriction
(only heart and brain spared)
ADH
released
Neurons
depressed
by
pH
Central
nervous system
depressed
Major effect
Minor effect
Brain
Adrenal
cortex
Kidneys
Heart rate
Aldosterone
released
Kidneys retain
salt and water
Angiotensin II
produced in blood
Renin released
Renal blood flow
Water
retention
Urine output
Rate and
depth of
breathing
CO
2
blown
off; blood
pH rises
Tachycardia;
weak, thready
pulse
Skin becomes
cold, clammy,
and cyanotic
Thirst
Restlessness
(early sign)
Coma
(late sign)
Signs and symptoms
Acute bleeding (or other events that reduce
blood volume) leads to:
1. Inadequate tissue perfusion
resulting in
O
2
and nutrients to cells
2. Anaerobic metabolism by cells, so lactic
acid accumulates
3. Movement of interstitial fluid into blood,
so tissues dehydrate
Initial stimulus
Result
Physiological response
Figure 19.18
Events and signs of hypovolemic shock.
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