Explain how the walls of the stomach are protected against;
a) corrosion of hydrochloric acid
b) digestion by protein enzymes
a) The walls of the stomach are protected against corrosion of hydrochloric acid by a layer of mucus that coats the inner lining of the stomach. This mucus layer acts as a physical barrier between the stomach walls and the acidic environment inside the stomach. It prevents direct contact of the hydrochloric acid with the stomach lining and prevents corrosion or damage to the cells.
Additionally, the stomach lining contains specialized cells called goblet cells that produce and secrete bicarbonate ions. Bicarbonate ions act as a buffer and help neutralize the hydrochloric acid, reducing its corrosive effects on the stomach walls.
b) The walls of the stomach are protected against digestion by protein enzymes through the secretion of an enzyme called pepsinogen. Pepsinogen is secreted by specialized cells in the stomach lining called chief cells. When pepsinogen comes into contact with the acidic environment of the stomach, it is converted into its active form called pepsin.
Pepsin is a protein enzyme that is responsible for the digestion of proteins in the stomach. However, the stomach lining itself is made up of proteins, and if pepsin were to digest these proteins, it would lead to damage and erosion of the stomach walls. To prevent this, the stomach lining simultaneously secretes mucus and bicarbonate ions, which form a protective barrier against pepsin activity.
Furthermore, the stomach lining has a rapid turnover rate, meaning that its cells are constantly regenerating and replacing damaged cells. This continuous renewal of the stomach lining helps protect it from the potential damaging effects of pepsin.
a) The walls of the stomach are protected against the corrosion of hydrochloric acid primarily through the secretion of a thick layer of mucus. The mucus layer covers the inner lining of the stomach and acts as a physical barrier, preventing direct contact between the acid and the stomach wall. The mucus is also alkaline, which helps to neutralize the hydrochloric acid that may come into contact with the stomach lining.
In addition to the mucus layer, the stomach also contains a layer of cells called epithelial cells. These cells are impermeable to acid and play a vital role in the protection of the stomach lining. They act as a barrier, preventing the acid from penetrating into the underlying layers of the stomach wall.
b) The digestion of proteins in the stomach is facilitated by the enzyme called pepsin. However, to prevent the stomach wall from being digested by pepsin itself, a few protective mechanisms come into play.
Firstly, the cells that produce pepsin in the stomach, known as chief cells, release pepsinogen, an inactive precursor of pepsin. This is done to avoid any premature digestion of proteins within the stomach walls. Pepsinogen is only converted into active pepsin when it comes into contact with the acidic environment of the stomach, thereby limiting its activity to the stomach cavity.
Secondly, similar to the protection against hydrochloric acid, the mucus layer in the stomach also provides a physical barrier against proteins and pepsin. The mucus layer covers the stomach lining, preventing direct contact between pepsin and the stomach wall.
Overall, these protective mechanisms, consisting of the mucus layer, impermeable epithelial cells, and the controlled release of pepsinogen, work together to protect the stomach walls from the corrosive effects of hydrochloric acid and digestion by protein enzymes such as pepsin.