chief cells
Summary
Chief cells are secretory cells found in the gastric fundic glands and in the parathyroid gland, though they serve distinct functions in each location. Gastric chief cells secrete pepsinogen and gastric lipase, while parathyroid chief cells secrete parathyroid hormone (PTH). Both are high-yield for Step 1 physiology and histology questions.
Detail
Gastric chief cells: Located primarily at the base of gastric glands in the fundus and body of the stomach, these cells synthesize and secrete pepsinogen, an inactive zymogen that is converted to pepsin by the acidic environment created by parietal cells (HCl) and by pepsin itself (autocatalysis). Pepsin is a protease that begins protein digestion in the stomach. Chief cells also secrete gastric lipase, contributing to fat digestion. They are stimulated by vagal input (ACh via M3 receptors), gastrin, and local acid (low pH) — importantly, secretin and CCK can also enhance pepsinogen secretion in response to acid in the duodenum. Histologically, chief cells appear basophilic due to abundant rough endoplasmic reticulum, reflecting their protein-secretory function; they release zymogen granules apically.
Parathyroid chief cells: These are the predominant cell type in the parathyroid glands and are responsible for synthesizing and secreting parathyroid hormone (PTH) in response to low serum calcium (sensed via the calcium-sensing receptor, CaSR). PTH increases serum calcium by: (1) stimulating osteoclastic bone resorption (indirectly via RANKL upregulation on osteoblasts), (2) increasing renal calcium reabsorption in the distal tubule, (3) decreasing renal phosphate reabsorption (phosphaturic effect), and (4) stimulating renal 1-alpha-hydroxylase to increase active vitamin D (calcitriol) production, which enhances intestinal calcium absorption. Chronic hypocalcemia (e.g., in chronic kidney disease) causes chief cell hyperplasia, leading to secondary hyperparathyroidism. Parathyroid adenomas, most commonly arising from chief cells, are the leading cause of primary hyperparathyroidism.
Clinical correlations: Gastric chief cell dysfunction is less clinically emphasized than parietal cell pathology, but understanding pepsinogen secretion is relevant to peptic ulcer disease pathophysiology. Parathyroid chief cell pathology (adenoma, hyperplasia, carcinoma) is highly tested in the context of hyperparathyroidism, hypercalcemia, and related bone/renal manifestations (e.g., 'stones, bones, groans, and psychiatric overtones').
Sources
- Guyton and Hall Textbook of Medical Physiology
- BRS Physiology
- First Aid for the USMLE Step 1
- Robbins and Cotran Pathologic Basis of Disease
- Junqueira's Basic Histology
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