A 4-year-old boy (height 90 cm, –3 standard deviations [SD]; weight 14.5 kg, approximately 15th percentile) presents with short stature. Review of the past history and growth chart demonstrates normal birth weight and birth length, but a progressive decrease in height percentiles relative to age-matched normal ranges starting at 6 months of age, and orthostasis with febrile illnesses. Physical examination demonstrates short stature and mild generalized obesity. Genital examination reveals descended but small testes and a phallic length of –2 SD. Laboratory evaluations demonstrate growth hormone (GH) deficiency and a delayed bone age of 18 months. The patient is started on replacement with recombinant human GH at a dose of 40 mcg/kg per day subcutaneously. After 1 year of treatment, his height velocity has increased from 5 cm/y to 11 cm/y. How does GH stimulate growth in children? What other hormone deficiencies are suggested by the patient’s history and physical examination? What other hormone replacements is this patient likely to require?
The control of metabolism, growth, and reproduction is mediated by a combination of neural and endocrine systems located in the hypothalamus and pituitary gland. The pituitary weighs about 0.6 g and rests at the base of the brain in the bony sella turcica near the optic chiasm and the cavernous sinuses. The pituitary consists of an anterior lobe (adenohypophysis) and a posterior lobe (neurohypophysis) (Figure 37–1). It is connected to the overlying hypothalamus by a stalk of neurosecretory fibers and blood vessels, including a portal venous system that drains the hypothalamus and perfuses the anterior pituitary. The portal venous system carries small regulatory hormones (Figure 37–1, Table 37–1) from the hypothalamus to the anterior pituitary.
The posterior lobe hormones are synthesized in the hypothalamus and transported via the neurosecretory fibers in the stalk of the pituitary to the posterior lobe; from there they are released into the circulation.
The hypothalamic-pituitary endocrine system. Hormones released from the anterior pituitary stimulate the production of hormones by a peripheral endocrine gland, the liver, or other tissues, or act directly on target tissues. Prolactin and the hormones released from the posterior pituitary (vasopressin and oxytocin) act directly on target tissues. Hypothalamic factors regulate the release of anterior pituitary hormones. ACTH, adrenocorticotropin; ADH, antidiuretic hormone [vasopressin]; CRH, corticotropin-releasing hormone; DA, dopamine; FSH, follicle-stimulating hormone; GH, growth hormone; GHRH, growth hormone-releasing hormone; GnRH, gonadotropin-releasing hormone; LH, luteinizing hormone; PRL, prolactin; SST, somatostatin; TRH, thyrotropin-releasing hormone; TSH, thyroid-stimulating hormone.
TABLE 37–1Links between hypothalamic, anterior pituitary, and target organ hormone or mediator.1 |Favorite Table|Download (.pdf) TABLE 37–1 Links between hypothalamic, anterior pituitary, and target organ hormone or mediator.1
|Anterior Pituitary Hormone ||Hypothalamic Hormone ||Target Organ ||Primary Target Organ Hormone or Mediator |