Parietal cells within the stomach lining secrete hydrochloric acid that lowers the pH of the stomach. A low pH (1.5 to 2) activates pepsin. Acetylcholine, gastrin, and histamine stimulate the proton pump in parietal cells to release hydrogen ions and decrease pH.
<span>Metamorphic rocks form by existing rocks join together under high heat and pressure. Examples of metamorphic rocks are marble, schist, slate, and quartzite. Metamorphic rocks formed when the minerals are chemically changed due to heat and pressure. They are often seen near magma but they do not melt like igneous rock.</span>
epidermis, dermis, subcutaneous fat
<span>Within a more biodiverse ecosystem, there is a higher chance that species will be able to adapt to change. For example, even with the eradication or migration of any one particular food group, consumers higher up in the food chain will remain able to survive due to alternative sources of energy.</span>
