In metazoans, these proteins evolved into thousands different molecular transducers capable to translate the presence of extracellular molecules into intracellular cascades of messages amplified by different G-proteins, which in turn enforce a myriad of different cellular processes via secondary messengers ( Different receptors, expressed by the same cell type or tissue, can trigger the same molecular cascade
Chan JCN, Lim LL, Wareham NJ, et al
Muscarinic acetylcholine receptors for psychotic disorders: bench-side to clinic
Urva et al., The novel GIP, GLP- 1 and glucagon receptor agonist retatrutide delays gastric emptying, Diabetes Obes
The lower bioavailability means the effective dose reaching your system is lower than the equivalent injection dose