WBR0878
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| Author | [[PageAuthor::Serge Korjian M.D. (Reviewed by Serge Korjian)]] |
|---|---|
| Exam Type | USMLE Step 1 |
| Main Category | Physiology |
| Sub Category | Neurology |
| Prompt | A researcher is studying the various functions of the hypothalamus in rats. He selectively stimulates 4 different areas of the hypothalamus numbered 1 till 4 by local application of 250 nl of 1 M solution of glutamate and then monitors the bodily responses in the anesthetized rats. After repetitive stimulation of area 3, the researcher notices a sharp but transient increase in interscapular brown fat thermogenesis and core temperature. Which nucleus of the hypothalamus is most likely represented by area 3? |
| Answer A | Dorsomedial nucleus |
| Answer A Explanation | The dorsomedial nucleus of the hypothalamus in an important player in thermogenesis by increasing sympathetic activity. |
| Answer B | Anterior nucleus |
| Answer B Explanation | The anterior nucleus of the hypothalamus in an important player in inhibiting thermogenesis by parasympathetic activation. It's stimulation would lead to a decrease in core body temperature. |
| Answer C | Supraoptic nucleus |
| Answer C Explanation | The supraoptic nucleus is involved in ADH synthesis. It is not a main player in thermogenesis. |
| Answer D | Lateral nucleus |
| Answer D Explanation | The lateral nucleus in involved in hunger. It is not a main player in thermogenesis. |
| Answer E | Paraventricular nucleus |
| Answer E Explanation | The paraventricular nucleus is involved in oxytocin synthesis. It is not a main player in thermogenesis. |
| Right Answer | A |
| Explanation | The hypothalamus is the main player in thermoregulation in mammals. It is involved in metabolic regulation, shivering, and sympathetic overdrive all important in maintaining a relatively constant body temperature. The most important nucleus involved in thermogenesis and regulation is the dorsomedial hypothalamic nucleus located in the posterior hypothalamus. The posterior hypothalamus acts mostly by provoking heat generation via sympathetic activation. It is important for non-shivering thermogenesis. Its ablation would lead to hypothermia in rats exposed to cold temperatures, a occurrence usually seen in cold-blooded organisms. The ventromedial nucleus, also involved in satiety, is an important player in thermogenesis. Educational Objective: The dorsomedial hypothalamus in an important control center for thermogenesis. |
| Approved | Yes |
| Keyword | Dorsomedial nucleus, Posterior hypothalamus, Thermogenesis, Hypothalamus |
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