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UPSC-CMS 2012 — Physiology

Q: The central venous pressure (CVP) is low in

Tension pneumothorax. ***Tension pneumothorax*** - A **tension pneumothorax** causes compression of the **superior and inferior vena cava** due to increased intrathoracic pressure and mediastinal shift. - This compression **impairs venous return** to the right atrium, leading to **decreased central venous pressure (CVP)**. - Despite elevated intrathoracic pressure, the net effect is **reduced venous return and low CVP**, along with hypotension and cardiac compromise. - This is a life-threatening emergency requiring immediate needle decompression. *Acute left ventricular failure* - In **acute left ventricular failure**, the left ventricle fails to pump blood effectively, causing backup into the pulmonary circulation. - However, the **right ventricle continues to pump** blood into the pulmonary circulation, leading to **increased right atrial pressure and elevated CVP**. - Patients typically present with **elevated CVP** along with pulmonary edema and dyspnea. *Massive pulmonary embolism* - A **massive pulmonary embolism** causes acute increase in **pulmonary vascular resistance** and right ventricular afterload. - The right ventricle becomes acutely strained and dilated, leading to **elevated right atrial pressure and increased CVP**. - Clinical features include hypotension, tachycardia, and jugular venous distension indicating high CVP. *Pericardial effusion* - A **pericardial effusion** causing **cardiac tamponade** compresses all cardiac chambers and restricts ventricular filling. - This leads to **equalization of diastolic pressures** in all chambers and **markedly elevated CVP**. - Classic Beck's triad includes hypotension, muffled heart sounds, and **jugular venous distension** (elevated CVP). [Practice more Physiology PYQs on OnCourse]

Q: Iron is absorbed predominantly in the

Duodenum. ***Duodenum*** - The **duodenum** is the primary site for iron absorption, with maximum absorption occurring in the **duodenum and proximal jejunum**. - Iron is absorbed in both **heme** and **non-heme** forms through specific transporters like **DMT1** (divalent metal transporter 1) and **ferroportin**. - The acidic pH from gastric secretions helps maintain iron in the soluble **ferrous (Fe²⁺) form**, which is readily absorbed in the duodenum. - The duodenal enterocytes have the highest concentration of iron transport proteins, making this the most efficient site for iron absorption. *Jejunum* - Some iron absorption can occur in the **proximal jejunum**, but it decreases progressively in the distal parts. - The jejunum primarily absorbs **carbohydrates**, **proteins**, **amino acids**, and **fats**. - While it contributes to iron absorption, it is not the predominant site. *Ileum* - The ileum is specialized for absorption of **vitamin B12** (via intrinsic factor), **bile salts**, and fat-soluble vitamins. - Iron absorption in the ileum is minimal compared to the duodenum. - By the time chyme reaches the ileum, most iron has already been absorbed in the proximal small intestine. *Stomach* - The stomach does not absorb iron but plays an important preparatory role. - Gastric **hydrochloric acid** (HCl) helps solubilize iron and convert ferric iron (Fe³⁺) to ferrous iron (Fe²⁺), which is the absorbable form. - **Intrinsic factor** is secreted here for vitamin B12 absorption, not iron. [Practice more Physiology PYQs on OnCourse]

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The central venous pressure (CVP) is low in

Iron is absorbed predominantly in the