Primary Endocrine Disease involves the thyroid, adrenal cortex, gonads, and liver. The negative feedback loops play a role in regulating hormone secretion in the hypothalamus-pituitary-peripheral gland axis. Various inputs, whether short-term (such as stress or infections) or long-term (like the onset of reproductive function at puberty), can affect the axis. The hypothalamus plays a crucial role in integrating information to set or change the set point of the axis, allowing for the influence of neurogenic states on pituitary function. An example of this is psychosocial dwarfism, where children experiencing abuse or intense emotional stress have lower growth rates due to decreased growth hormone secretion by the pituitary gland.

Abnormal levels of peripheral hormones, like thyroid hormone, can result from defects at the peripheral endocrine gland (e.g., thyroid), pituitary gland, or hypothalamus. These defects are classified as primary, secondary, and tertiary endocrine disorders, respectively. Understanding the feedback relationships within an axis helps determine the location of the defect. Primary endocrine deficiencies tend to be the most severe as they often involve the complete absence of the peripheral hormone.

The adenohypophysis consists of different endocrine cell types: corticotropes, thyrotropes, gonadotropes, somatotropes, and lactotropes. Corticotropes play a role in the hypothalamic-pituitary-adrenal (HPA) axis by stimulating the adrenal cortex. They produce ACTH (corticotropin), which stimulates two zones of the adrenal cortex. ACTH is synthesized as part of the prohormone proopiomelanocortin (POMC). Corticotropes are also known as POMC cells because they contain the peptide sequence for ACTH, as well as other fragments like melanocyte-stimulating hormone (MSH), endorphins, and enkephalins. However, in humans, corticotropes primarily produce ACTH as the active hormone. The N-terminal fragment and β-lipotropic hormone (β-LPH) cleaved from POMC do not have physiological roles in humans.
X Primary Endocrine Disease (Thyroid, adrenal cortex, gonads, liver) •Fig. 41.6 Negative-feedbackloopsregulatinghormonesecretioninatypicalhypothalamus-pituitaryperipheralglandaxis.X,peripheralglandhormone;XIH,hypothalamic-inhibitinghormone;XRH,hypothalamic-releasinghormone;XTH,pituitarytropichormone.
short-term (e.g., various stress/infections) or long-term (e.g., onset of reproductive function at puberty) inputs. Thus inclusion of the hypothalamus in an endocrine axis allows integration of a considerable amount of information for setting or changing the set point of that axis. Clinically this means a broad range of complex neurogenic states can alter pituitary function. Psychosocial dwarfism is a striking example in which children subject to abuse or intense emotional stress have lower growth rates as a result of decreased growth hormone secretion by the pituitary gland.
3. Abnormally low or high levels of a peripheral hormone (e.g., thyroid hormone) may be due to a defect at the level of the peripheral endocrine gland (e.g., thyroid), the pituitary gland, or the hypothalamus. Such lesions are referred to as primary, secondary, and tertiary endocrine disorders, respectively (see
Fig. 41.6 ). A thorough understanding of the feedback relationships within an axis allows the physician to determine where the defect lies. Primary endocrine deficiencies tend to be the most severe because they often involve complete absence of the peripheral hormone.
Endocrine Function of the Adenohypophysis
The adenohypophysis consists of the following endocrine cell types: corticotropes, thyrotropes, gonadotropes, somatotropes, and lactotropes (see
Table 41.1
Corticotropes stimulate the adrenal cortex as part of the hypothalamic-pituitary-adrenal (HPA) axis. Corticotropes produce the hormone ACTH (corticotropin), which stimulates two zones of the adrenal cortex (see ). ACTH is a 39–amino acid peptide that is synthesized as part of a larger prohormone called proopiomelanocortin (POMC). Thus corticotropes are also referred to as POMC cells. POMC harbors the peptide sequence for ACTH, two isoforms of melanocyte-stimulating hormone (MSH), endorphins (endogenous opioids), and enkephalins (
Fig.
41.8 ). However, the human corticotrope expresses only pro-hormone convertase-1, which produces ACTH as the sole active hormone secreted by these cells. The other fragments that are cleaved from POMC are the N-terminal fragment and β-lipotropic hormone (β-LPH), neither of which plays a physiological role in humans.