The Physiology of Shock

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The Physiology of Shock

• Unit 8 / week 1

R.E.B, 4MedStudents.com, 2003
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What is Shock?

• Shock is any condition in which the circulatory
  system is unable to provide adequate circulation
  to the vital body organs such as the brain,heart
  and lungs. As a result of a decrease in the blood
  pressure.
• Shock is usually accompanied by renal failure, as
  a normal compensatory mechanism, because the
  blood flow to the kidney is decreased to keep
  enough blood for the vital organs.

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Symptoms of shock

• Increase heart rate as a result of the
  baroreflex
• Shock will decrease the volume of blood pumped
  from the heart and the blood flow to the brain.
  That will activate the baroreceptors in the
  carotid bodies to increase HR trying to supply
  enough blood to the vital organs.
• Pale skin
• As a result of vasoconstriction of the peripheral
  vessels, because the skin is the least priority
  tissue for blood flow

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Symptoms of shock

• 3. Cold and clammy skin As a result of
  vasoconstriction.
• Shock decreases the skin surface temperature as a
  result of vasodilatation, which will increase the
  internal body temperature. Because the skin plays
  a major role in controlling body temperature, as
  it will help in exchanging heat with the external
  environment.
• There are two mechanisms to get red of the excess
  heat
• Hyperventilation ( Minimal effect in humans)
• Vasodilatation of the vessels Flush
  ( Increase blood flow to the skin)
  BP Real shock

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Classification of Shock

• Shock is classified according to the causes to
  three classes
• Hypovolemic shock
• Distributive shock
• Cardiogenic shock

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Causes of Shock

• Hypovolemic shock is caused by low blood volume.
• Normal blood volume is 5 L and by losing 1-2 L it
  can lead to shock.
• The Decrease in blood volume is caused by
• External blood loss ex. Hemorrhage
• Internal blood loss ex. Ruptured spleen caused
  by blunt trauma.
• Severe dehydration as a result of
• Vomiting
• Diarrhea
• This is a typical condition in cholera.
• Burns

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Causes of Shock

• 2. Distributive shock is caused by excess
  vasodilatation (ex. Anaphylactic shock and
  septicemia)
• Vasodilatation Arteriole resistance
  increase blood exchange from the
  vessels to the peripheral tissues decrease
  blood return to the heart BP
  shock

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Causes of Shock

• Cardiogenic shock ( heart does not pump enough
  blood) is caused by
• A) Myocardial infarction weak
  cardiac
• muscle contraction Ischemia
• B) Arrhythmia ( such as ventricular fibrillation,
  which will stop the heart pump and that will
  decrease BP
• Note Supraventricular (Atria) fibrillation will
  not cause shock because 75 of the blood transfer
  from the atrium to the ventricles by passive
  transport.

Lead to
As a result of
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Causes of Shock

• C) Valve problems, ex. Valvular stenosis which is
  narrowing of the valves, or leakage of blood
  through the valves ( Regurgitation).
• D) Problems in the A-V shunt.

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Compensatory system
In the normal microcirculation
  - At arterial end water moves out of the
capillary with a NFP of 5 mmHg Hydrostatic
pressure dominates at the arterial end and net
fluid flows out of the circulation. - At venous
end water moves into the capillary with a NFP
of -5 mmHg Oncotic pressure dominates at the
venous end and net fluid will flow into the
bloodstream
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The Compensatory system

• In shock, the hydrostatic pressure decreases and
  the oncotic pressure is constant, as a result
• The fluid exchange from the capillary to the
  extracellular space decreases.
• The fluid return from the extracellular space to
  the capillary increases.
• That will increase the blood volume, which will
  increase BP and will help to compensate shock
  situations.
• This system is known as the Fluid shift system

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In shock situations