A 65-year-old homeless man is brought to the hospital after he is found wandering the streets during a cold winter day. The patient appears confused and has slurred speech. He has no chronic medical conditions and takes no medications. On examination, his temperature is 32 C (89.6 F). Cardiopulmonary examination is normal. No focal neurologic deficits are present. Toxicology screen is negative for any substances. Which of the following physiologic adaptations is most likely occurring in this patient to help maintain homeostasis?

Question

A 65-year-old homeless man is brought to the hospital after he is found wandering the streets during a cold winter day.  The patient appears confused and has slurred speech.  He has no chronic medical conditions and takes no medications.  On examination, his temperature is 32 C (89.6 F).  Cardiopulmonary examination is normal.  No focal neurologic deficits are present.  Toxicology screen is negative for any substances.  Which of the following physiologic adaptations is most likely occurring in this patient to help maintain homeostasis?

Quizplus · Accepted Answer

11ec160b_3cd6_204f_9249_b3f6477ca98b_MD0001_00 The body maintains its core temperature in a tightly controlled process known as thermoregulation. In a normal state, body temperature is maintained between 36.5-37.5 C (97.7-99.5 F) via anterior hypothalamic control. Afferent signals (from central and peripheral thermal receptors) are interpreted by the hypothalamus, which promotes temperature homeostasis through alterations in the autonomic nervous system as well as the thyroid and adrenal axes. Hypothermia, defined as a core body temperature <35 C, occurs when the body loses more heat than it generates. It most commonly occurs due to cold exposure but may also occur due to endocrine disorders (eg, hypothyroidism), skin disorders (eg, burns), abnormal autonomic function (eg, peripheral neuropathies, stroke, spinal cord injury), or drugs that promote vasodilation (eg, alcohol) or impair sympathetic response (eg, beta blockers). The following physiologic adaptations occur in patients with hypothermia: Increased sympathetic activity (catecholamine release): promotes peripheral vasoconstriction and results in shunting of blood away from the skin. It also increases muscle tone and brown fat metabolism (Choices A and C). Shivering: rapid involuntary muscle contractions that increase muscle metabolism, generating heat as a byproduct. Increased thyroid function: prolonged cold exposure leads to increased production of thyroid hormone, which increases basal metabolic rate. These actions promote normalization of body temperature by reducing heat loss and increasing metabolic rate (heat generation) (Choice B). (Choice D) The sympathetic, not the parasympathetic nervous system, is responsible for the physiologic adaptations in hypothermia. Most blood vessels do not have parasympathetic innervation; therefore, an increase in parasympathetic activity would not have significant effect on vascular tone. Educational objective: The hypothalamus controls thermoregulation by promoting alterations in the autonomic nervous system and the adrenal and thyroid axes. Physiologic adaptations in response to hypothermia include increased sympathetic activity and thyroid hormone release, shivering, and peripheral vasoconstriction. These actions normalize body temperature by reducing heat loss and increasing metabolic rate (promoting thermogenesis). __________ References: Regulation of body temperature by the nervous system. (http://www.ncbi.nlm.nih.gov/pubmed/29621489)

A 65-Year-Old Homeless Man Is Brought to the Hospital After