Topic overview

Start with the big picture

Negative feedback is the main mechanism governing endocrine output: hormones from target glands can suppress upstream hypothalamic and pituitary release. Positive feedback is uncommon, with oxytocin during labor as an example. The hypothalamus communicates with the anterior pituitary through the hypophyseal portal system, while the posterior pituitary stores and releases hormones made in hypothalamic nuclei. Hormone chemistry shapes signaling: lipophilic steroid hormones generally act through intracellular receptors, while many hydrophilic peptide hormones act at membrane receptors using second messengers. Thyroid hormones and catecholamines have distinct synthesis and signaling features. The lesson also introduces GPCR and kinase-linked pathways, signal termination, carrier-protein transport, clearance, and modulation of secretion.