12 topics with brief reviews: definitions, key facts, and seminar questions.
In this chapter, we examine how and why the thermoregulation system breaks down. You will study two fundamentally different typical pathological processes: fever (when the set-point is shifted by the action of pyrogens) and hyperthermia (when the body overheats in defiance of the thermoregulation center, including heatstroke and sunstroke). The section also covers the mechanisms of hypothermia, including controlled hypothermia used in major surgery.
In seminars and exams, students are most frequently asked to explain the fundamental differences between fever and hyperthermic reactions—this is a pathophysiology classic. Pay special attention to the stages of fever, reading temperature curves, and systemic changes in the patient's body.
A special emphasis is placed on pediatric practice (characteristics of fever in children) and the biological significance of the process. You will understand the basic principles of therapy: in which cases temperature must be reduced, and when it acts as a protective and adaptive reaction.
What is the effect of various agents on heat balance?
It can lead to a shift in the heat balance and the development of two main conditions (or two main syndromes): hyperthermic and hypothermic.
Why does the skin become dry in severe hyperthermia?
Dry skin is a sign of transition to the decompensation stage. Due to the exhaustion of thermoregulation mechanisms and critical fluid loss, sweating stops completely.
What is the main difference in the pathogenesis of sunstroke versus heatstroke?
In sunstroke, the brain (including the thermoregulation center) is primarily affected due to the deep penetration of infrared rays, whereas heatstroke begins with general overheating of the body by external heat.
Which homeostasis parameters are disrupted first during hyperthermia?
A shift in hydrogen ion concentration (pH) occurs, osmotic and oncotic pressure change, and the circulating blood volume (CBV) critically decreases with a simultaneous increase in its viscosity.
Why does shivering occur during fever?
This is a mechanism of shivering thermogenesis. The hypothalamus sends signals to skeletal muscles, whose involuntary contractions generate energy exclusively as heat, helping the body warm up rapidly to the new set point.
How does a lytic temperature drop differ from a critical one?
Lysis is a gradual drop in temperature over several days, which is favorable for the patient. Crisis is a sharp decrease within a couple of hours, capable of provoking vascular collapse due to arteriolar dilation and profuse sweating.
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