How Do Gastric Glands Help in Digestion?
The gastric glands are the tube-like, branched structures that are present at the inner lining of the stomach. These glands are the basic secretory unit of the digestive system and are composed of various cell components which perform certain specific functions. These glands originate at the opening of the stomach’s lumen, the gastric pits, which itself is present at the gastric mucosa of the stomach. The gastric pit has pale-staining mucous droplets due to the presence of mucous-secreting cells. The base consists of the isthmus and neck of the gland. The gastric glands are mostly known to be exocrine in nature and help in the synthesis and secretion of the gastric juices along with protective mucous.
Types of Gastric Glands
There are various types of gastric glands present in the digestive system and depending on the region in the stomach, these gastric glands are divided into 3 major parts:-
1. Cardiac Glands – These glands are located close to the cardiac orifice. They usually contain cardiac glands. Also, they are comparatively very few in number and are positioned in the mucosa shallowly. These are generally of two kinds, which are the simple tubular (like those of pyloric ends) and short ducted, and the compound racemose resembling the duodenal glands. Their main function in the digestive system is to secrete mucus.
2. Fundic Glands – These glands are located in the fundus or body of the stomach. They are straight, parallel, tube-like structures. It has been observed that two or more of such tubes open into a common duct. Also, these tubes are at most one-sixth the length of the entire gland. These glands are much shorter than the pyloric glands. These glands are lined by columnar epithelium. Their main function in the digestive system is to produce digestive enzymes.
3. Pyloric Glands – These glands are the endocrine glands located in the antrum, known as the pyloric portion of the stomach. They consist of two or three short, wavy closed tubes which open into a common duct. These tubes are generally half the length of the entire duct. The duct is usually lined by columnar cells and the tubes by short, granular cubical cells. The main function of these glands is to secrete gastrin (produced by G cells) and mucus.
The mucus which is produced by the Cardiac glands and the Pyloric glands coats the stomach, dilutes the acids and enzymes, and hence protects the oesophagus and the duodenum from self-digestion.
FAQs on Gastric Gland: Definition, Structure & Types
1. What are gastric glands and where are they located in the stomach?
Gastric glands are microscopic, tubular glands found in the inner lining (mucosa) of the stomach. They are located deep within the stomach wall at the base of small pits called gastric pits. Their primary role is to secrete gastric juice, which is essential for the chemical digestion of food.
2. What are the major types of cells found in gastric glands and what does each cell secrete?
Gastric glands are composed of several specialised cell types, each with a specific function:
- Mucous neck cells: Secrete mucus to protect the stomach lining from acid.
- Parietal cells (or Oxyntic cells): Secrete hydrochloric acid (HCl) and intrinsic factor (for vitamin B12 absorption).
- Chief cells (or Zymogenic cells): Secrete pepsinogen, the inactive form of the protein-digesting enzyme pepsin.
- Enteroendocrine cells (G-cells): Secrete hormones like gastrin, which regulates stomach acid secretion.
3. Which cells in the gastric glands produce hydrochloric acid (HCl), and why is it important for digestion?
Hydrochloric acid (HCl) is secreted by the parietal cells (or oxyntic cells) of the gastric glands. HCl is crucial for digestion for two main reasons: it converts inactive pepsinogen into the active enzyme pepsin, which breaks down proteins, and it creates a highly acidic environment (pH 1.5-3.5) that kills most harmful bacteria and pathogens ingested with food.
4. What are the main enzymes secreted by gastric glands?
The primary enzyme secreted by gastric glands is pepsin (in its inactive form, pepsinogen). Pepsin is a protease, meaning it begins the digestion of proteins into smaller polypeptides. Gastric glands also secrete a small amount of gastric lipase, which plays a minor role in digesting fats.
5. How do the different types of gastric glands (cardiac, fundic, and pyloric) differ in their function?
While all are gastric glands, their cellular composition and primary function differ based on their location in the stomach:
- Cardiac glands: Located near the oesophagus, these primarily secrete mucus to protect the oesophagus from stomach acid.
- Fundic glands (or Oxyntic glands): Found in the main body (fundus) of the stomach, they are the most numerous and contain all major cell types, producing most of the stomach's acid, enzymes, and intrinsic factor.
- Pyloric glands: Located in the lower part of the stomach (pylorus), they mainly secrete mucus and the hormone gastrin from their G-cells.
6. How does the stomach protect itself from being digested by its own acidic secretions?
The stomach protects itself through a thick layer of alkaline mucus secreted by mucous neck cells and surface mucous cells. This mucus-bicarbonate barrier coats the stomach lining, neutralising the hydrochloric acid at the cell surface. This prevents the acid and the enzyme pepsin from breaking down the stomach's own walls.
7. What are the phases that regulate the secretion of gastric juice from the glands?
The secretion of gastric juice is regulated by a combination of nerve and hormonal signals in three distinct phases:
- Cephalic Phase: Triggered by the sight, smell, or thought of food. Nerve signals from the brain stimulate the gastric glands to begin secretion in anticipation of eating.
- Gastric Phase: Begins when food enters the stomach. The stretching of the stomach wall and the presence of proteins stimulate the release of gastrin, which further increases the secretion of acid and pepsin.
- Intestinal Phase: Starts when partially digested food (chyme) enters the small intestine. This phase has an initial excitatory effect but then becomes inhibitory to slow down gastric secretion, allowing the intestine time to process the chyme.
8. How can a malfunction in gastric glands lead to a condition like pernicious anaemia?
Pernicious anaemia is caused by an inability to absorb vitamin B12. This occurs when the parietal cells of the gastric glands are damaged (often by an autoimmune condition) and fail to produce intrinsic factor. Intrinsic factor is a protein that binds to vitamin B12, allowing it to be absorbed in the small intestine. Without intrinsic factor, vitamin B12 cannot be absorbed, leading to a deficiency that impairs the production of healthy red blood cells, resulting in anaemia.
