Final answer:
A preprohormone is synthesized in the endoplasmic reticulum, processed in the Golgi apparatus into a prohormone, and eventually cleaved into an active hormone that is secreted into the bloodstream. Through degradation and excretion, the active hormone's levels are regulated to maintain homeostasis.
Step-by-step explanation:
A preprohormone is a precursor to a hormone, generally synthesized within endocrine cells and requiring several modifications before becoming an active hormone that can exert physiological effects on target cells. One of the key locations for this process is the endoplasmic reticulum (ER), where the preprohormone is initially synthesized. Following synthesis, the preprohormone enters the Golgi apparatus for further processing, which often includes cleavage into a prohormone.
Afterwards, the prohormone is typically packaged into secretory vesicles and is transported to the cell membrane. Here, in response to specific signals, it is secreted into the bloodstream. During or after secretion, the prohormone is cleaved by enzymes to produce the mature, active hormone. This active hormone can then bind to receptors on target cells, eliciting biological responses. Throughout its life cycle, a hormone can also undergo degradation and excretion, typically via enzymatic modification in the liver and/or kidneys, ensuring that hormone levels can be tightly regulated.