UPSC-CMS 2009 — Physiology

Q: O2 (Oxygen) dissociation curve is shifted to right in the following except

Metabolic alkalosis. ***Metabolic alkalosis*** - A shift to the **right** on the oxygen dissociation curve indicates **decreased affinity** for oxygen, promoting oxygen release to tissues. - In **metabolic alkalosis**, the blood pH is elevated, which **increases hemoglobin's affinity for oxygen**, leading to a **left shift** in the curve. *Hypercapnia* - **Hypercapnia** (increased PCO2) decreases blood pH, reducing hemoglobin's affinity for oxygen via the **Bohr effect**, resulting in a **right shift**. - This facilitates oxygen release to tissues where CO2 production is high. *Rise in temperature* - An increase in **body temperature** weakens the binding of oxygen to hemoglobin, causing a **right shift** in the oxygen dissociation curve. - This is beneficial during exercise, when active tissues generate heat and require more oxygen. *Raised 2, 3 DPG level* - **2,3-bisphosphoglycerate (2,3-BPG)** binds to deoxygenated hemoglobin, stabilizing its T-state and **reducing its affinity for oxygen**, causing a **right shift**. - This is a key adaptation to chronic hypoxia, enhancing oxygen delivery to tissues. [Practice more Physiology PYQs on OnCourse]

Q: After how many hours of LH surge does the ovulation occur?

24-36 hours. ***24-36 hours*** - The **luteinizing hormone (LH) surge** triggers the final maturation of the oocyte and rupture of the dominant follicle. - Ovulation typically occurs **24-36 hours after the onset of the LH surge**, or approximately **10-18 hours after the LH peak**. - This is the **standard timeframe** taught in reproductive physiology and corresponds to the physiological cascade required for follicular rupture. *12-24 hours* - This timeframe is **too early** for ovulation to occur after the LH surge onset. - While some follicular changes begin during this period, the complete maturation and rupture process typically requires more time. - This might represent the interval from LH peak in some cases, but not from surge onset. *12-36 hours* - This range is **too broad** and includes both early (12h) and appropriate (24-36h) timeframes. - While the upper range is correct, the lower bound extends into a period when ovulation has typically not yet occurred. - Less precise than the 24-36 hour window. *24-48 hours* - While ovulation can occasionally occur up to 48 hours post-surge, this is **less common**. - The upper limit (48h) extends beyond the typical ovulation window. - Most ovulations are completed by 36 hours after the LH surge onset. [Practice more Physiology PYQs on OnCourse]

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O2 (Oxygen) dissociation curve is shifted to right in the following except

After how many hours of LH surge does the ovulation occur?