Stomach Histology Overview
📌 The stomach is the most dilated part of the digestive tract, functioning as an extensible fibromuscular sac connecting the esophagus to the duodenum, with a capacity between 1.5 and 3 liters.
🎯 The primary objective of studying stomach histology is to understand its internal configuration, the function of each component, and the molecules it produces, which transform food into chyme.
🗺️ The stomach wall is composed of four tunics, from inner to outer: mucosa, submucosa, muscularis, and serosa.

Gastric Mucosa Structure and Regions
🔬 The gastric mucosa, lined by simple columnar prism epithelium, features invaginations forming gastric pits leading to deep, tubular gastric glands (approximately 15 million).
📏 The mucosal surface, along with pits and glands, secretes mucus, gastric acid, and digestive enzymes, covering an area of about 800 m².
➡️ The stomach is subdivided into three regions: cardia (75%), pyloric (15%), and the smaller fundic region (10%).

Cell Types within Gastric Glands (Fundic Region)
💧 Mucous neck cells are small, cuboidal, often found in the cell cycle (division), and secrete gastric mucus.
🧪 Parietal cells are large (20-35 $\mu$m diameter), rich in mitochondria, and secrete hydrochloric acid ($\text{HCl}$) and intrinsic factor (essential for Vitamin $\text{B}_{12}$ absorption).
💥 Chief (Zymogenic) cells are numerous, cylindrical, basophilic, and secrete pepsinogen (via exocytosis) and gastric lipase.
🧠 Endocrine (Enteroendocrine) cells are few, pyramid-shaped with inverted polarity (apical pole doesn't reach the lumen), secreting various hormones like serotonin and somatostatin.

Mucosal Differences and Secretions
🚫 Pyloric glands consist only of mucous cells and $\text{G}$ endocrine cells, which secrete gastrin to stimulate $\text{HCl}$ and pepsinogen secretion.
🛡️ The gastric mucus secreted by mucous cells is alkaline due to bicarbonate, protecting the surface from mechanical damage and the highly acidic gastric secretions.
📉 Gastric acid ($\text{HCl}$) maintains a highly acidic $\text{pH}$ between 1.5 and 3, necessary for preliminary digestion and pathogen destruction; excess can cause ulcers, while deficiency ($\text{achlorhydria}$) risks infection and impairs protein digestion.
⚙️ Pepsinogen (inactive) is activated into pepsin by $\text{HCl}$, initiating protein breakdown into peptides; gastric lipase hydrolyzes triglycerides optimally between $\text{pH}$ 3 and 5.

Key Points & Insights
➡️ The stomach wall layers include the lamina propria (connective tissue rich in lymphoid cells/capillaries), the muscularis mucosae (smooth muscle aiding secretion ejection), the dense submucosa (containing Meissner's plexus), and the muscularis externa (three layers: oblique, circular, longitudinal).
➡️ A key function of the muscular layer is to mix the bolus with gastric secretions and facilitate chyme transit to the duodenum.
➡️ Parietal cells are absent in the cardia and pylorus, meaning these regions lack significant $\text{HCl}$ secretion capability.
➡️ Gastrin, secreted by $\text{G}$ cells in the pylorus, stimulates the secretion of $\text{HCl}$ and pepsinogen.

📸 Video summarized with SummaryTube.com on Dec 03, 2025, 13:12 UTC