Shock, Dehydration, and Volume Status - Anatomy and Physiology

1. What is shock, in physiological terms?

   A state of inadequate tissue perfusion, so oxygen delivery fails to meet cellular demand, regardless of the cause.

2. What is the basic problem in cardiogenic shock?

   Failure of the heart as a pump, for example after a large myocardial infarction, so cardiac output falls despite adequate volume.

3. After a major bleed, a patient has heart rate 125, cool clammy skin and low urine output. Which type of shock is most likely?

   Hypovolemic (hemorrhagic) shock. Volume loss triggers sympathetic tachycardia, skin vasoconstriction and reduced renal perfusion.

4. What is the basic problem in obstructive shock?

   A physical obstruction to blood flow, such as cardiac tamponade, tension pneumothorax or massive pulmonary embolism.

5. After a cervical spinal cord injury, a patient has blood pressure 80/50 mmHg, heart rate 50 and warm, dry skin. Which type of shock is this?

   Neurogenic shock. Loss of sympathetic tone causes vasodilation and bradycardia, unlike the tachycardia and cool skin of hypovolemia.

6. What is the basic problem in distributive shock?

   Widespread vasodilation lowers systemic vascular resistance, as in septic, anaphylactic or neurogenic shock.

7. A person loses much more water than sodium by sweating without drinking. How do plasma sodium and osmolality change?

   Both rise (hypernatremia and high osmolality), because water is lost in excess of solute.

8. How does urine change in a dehydrated person, and which hormones cause it?

   Urine becomes small in volume and highly concentrated, due to increased ADH and aldosterone.

9. Which reflex responses help maintain blood pressure early in hemorrhage?

   Baroreceptor-driven sympathetic activation: tachycardia, increased contractility, and vasoconstriction of skin, gut and kidney vessels.

10. A volume-depleted patient moves from lying to standing. How do blood pressure and heart rate typically change?

    Blood pressure falls and heart rate rises (orthostatic changes), because low volume limits venous return when standing.

11. Why does hematocrit rise in dehydration?

    Plasma volume falls while red cell mass stays the same, so the blood becomes more concentrated (hemoconcentration).

12. What is the basic problem in hypovolemic shock?

    Loss of blood or body fluid reduces venous return (preload), so stroke volume and cardiac output fall.

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