NCERT Solutions for Biology Class 11 – Digestion in Stomach
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In this article, the following topic “Digestion in Stomach” from the unit 5 named ‘Human Physiology’ of NCERT Biology Class 11 syllabus is discussed. We have focused on various digestive glands present in the stomach.
DIGESTION IN STOMACH
The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals. After chewing (mastication) of food by teeth in the buccal cavity (mouth), the food is swallowed through the oesophagus and reaches the stomach for further digestion. In humans and many other animals, the stomach is located between the oesophagus and the small intestine.
The lining of the stomach(gastric mucosa) is pitted with the openings of about 35 million glands known as gastric glands. These glands secrete a fluid called digestive fluid /juice or gastric juice. The gastric juice contains digestive enzymes, gastric acid (Hydrochloric acid, abbreviated as HCl) that help in the digestion of food, and mucus that helps in lubricating the stomach wall hence protecting it from getting damaged.About 2-3 litres of gastric juice is secreted in a day in a normal human adult. Gastric juice is a thin, light colored transparent acidic fluid. It is acidic in nature due to the presence of HCl. The pH of the gastric juice is 1.5 to 2.5.
Let us discuss the Gastric Glands.
The gastric gland is the basic secretory unit of the stomach.Each gastric gland is a tubular structure opening by means of a narrow pore in the stomach. There are three types of gastric glands; they are distinguished from one another by their location. They are as listed below-
- Cardiac gastric glands- They are located at the very beginning of the stomach, in the cardiac portion into which the oesophagus opens.
- Fundic gastric glands – They are also known as intermediate or true gastric glands. They are present in the central stomach area.
- Pyloric gastric glands –They are present in the terminal portion of the stomach which opens into the first part of small intestine.
Watch the animated video on ‘Gastric glands’ by clicking NCERT Biology Class 11.
Both the cardiac and pyloric glands secrete mucus which coats the stomach and protects it from self-digestion by the HCl and digestive enzymes. The intermediate or fundic gastric glands produce most of the digestive substances secreted by the stomach. These glands have three types of cells (i) zymogenic / or chief cells (ii) parietal or oxyntic cells (iii) and mucus neck cells. The zymogenic cells produce the enzymes pepsin and renin (in some species). Pepsin is secreted as pepsinogen which is an inactive precursor or zymogen (of pepsin). The pepsinogen is converted into active pepsin, in the gastric juice by the presence of pepsin (known as aut-activation of pepsinogen). The enzyme pepsin digests the proteins and renin help in curdling of milk. The parietal cells or oxyntic cells occur throughout the length of the gland and are responsible for the production of HCl which is necessary to activate the other enzymes. The mucus neck cells secrete mucus.
Find animated videos and notes on ‘how gastric glands functions’ by clicking Biology notes Class 11.
There is usually a small, constant production of gastric juices, but their secretion can be enhanced due to several means. They can be stimulated by tasting, smelling or even by thinking of food. When we consume the food items, it provides the additional stimulus for the secretion of mucus. Entry of proteins into the stomach stimulates the gastric mucosa to secrete the hormone gastrin; this stimulates the release of hydrochloric acid by the parietal cells of the gastric glands and pepsinogen by the chief cells.
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