Presentation on theme: "The Physiology of Shock"— Presentation transcript:
1The Physiology of Shock Unit 8 / week 1R.E.B, 4MedStudents.com, 2003
2What 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.
3Symptoms 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
4Symptoms of shock3. 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
5Classification of Shock Shock is classified according to the causes to three classes:Hypovolemic shockDistributive shockCardiogenic shock
6Causes 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. HemorrhageInternal blood loss: ex. Ruptured spleen caused by blunt trauma.Severe dehydration as a result of:VomitingDiarrheaThis is a typical condition in cholera.Burns
7Causes of Shock2. 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
8Causes of ShockCardiogenic shock ( heart does not pump enough blood) is caused by:A) Myocardial infarction weak cardiacmuscle contraction IschemiaB) Arrhythmia ( such as ventricular fibrillation, which will stop the heart pump and that will decrease BPNote: Supraventricular (Atria) fibrillation will not cause shock because 75% of the blood transfer from the atrium to the ventricles by passive transport.Lead toAs a result of
9Causes of ShockC) 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.
10Compensatory system - At arterial end: - At venous end: Blood CapillaryVenous BloodHydrostatic Pressure = 30 mmHgHydrostatic Pressure = 20 mmHgColloid Osmotic Pressure= 25 mmHgArterial BloodInterstitial FluidHydrostatic Pressure= 0 mmHgNFP = +5 mmHgNFP = - 5 mmHgIn the normal microcirculation - At arterial end:water moves out of the capillary with a NFP of +5 mmHgHydrostatic 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 mmHgOncotic pressure dominates at the venous end and net fluid will flow into the bloodstream
11The 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”