Endocrine Secretory Control (Autocrine, Paracrine, and Endocrine Mediators)

Higher animals (i.e., mammalian vertebrates) have well-developed nervous systems for immediate physiologic responses. Although their endocrine systems are slower acting, the physiologic responses they provoke generally last longer. Mammalian vertebrates also have wellintegrated neural and endocrine regulatory systems, and in many cases these two systems are difficult to separate (e.g., the adrenal medulla, hypothalamic nuclei, the posterior pituitary, and neurocrine regulation of gut function). In contrast, invertebrates are more dependent on paracrine and autocrine regulation because they possess primitive nervous systems.