Dislipidemias

Introduction, 175 Physiology and Disorders of Pituitary Hormone Axes, 179 Developmental and Genetic Causes of Pituitary Failure, 211

CHAPTER 8 CHAPTER
Pituitary Physiology and Diagnostic Evaluation
SHLOMO MELMED • DAVID KLEINBERG • KEN HO

INTRODUCTION
The pituitary gland, situated within the sella turcica, derives its name from the Greek ptuo and Latin pituita, “phlegm,” reflectingits nasopharyngeal origin. Galen hypothesized that nasal phlegm originated from the brain and drained via the pituitary gland. It is now clear that the pituitary, together with the hypothalamus, orchestrates the structural integrity and function of endocrine glands including the thyroid, adrenal, and gonads, as well as target tissues including cartilage and breast. The pituitary stalk serves as ananatomic and functional connection to the hypothalamus. Preservation of the hypothalamopituitary unit is critical for integration of anterior pituitary control of sexual function and fertility, linear and organ growth, lactation, stress responses, energy, appetite, and temperature regulation, and it is secondarily important for carbohydrate and mineral metabolism. Integration of vital bodyfunctions by the brain was first proposed by Descartes in the 17th century. In 1733, Morgagni recorded the absence of adrenal glands in an

anencephalic neonate, providing early evidence for a developmental and functional connection between the brain and the adrenal glands. In 1849, Claude Bernard set the stage for later advances in neuroendocrinology by demonstrating that central lesions to the areaof the fourth ventricle resulted in polyuria.1 Subsequent studies resulted in the identification and chemical isolation of pituitary hormones, and astute clinical observations led to the realization that pituitary tumors were associated with functional hypersecretory syndromes, including acromegaly and Cushing’s disease.2-4 In 1948, Geoffrey Harris, the father of modern neuroendocrinology,reviewed the control of anterior pituitary gland hormones and proposed that they were regulated by the hypothalamus, predicting the discovery of specific hypothalamic regulating hormones.5

Pituitary Anatomy
The pituitary gland comprises the predominant anterior lobe, the posterior lobe, and a vestigial intermediate lobe (Fig. 8-1). The gland is situated within the bony sella 175

176Pituitary Physiology anD Diagnostic Evaluation
Supraoptico-hypophyseal tract Paraventriculo-hypophyseal tract Anterior branches of hypophyseal artery Tubero-hypophyseal tract

Optic chiasm Superior hypophyseal artery (branch intracranial portion of interior carotid artery) “Gomitoll” Short stalk arteries Trabecular artery (loral artery) Pars tuberalis Long portal vessels

Posterior branch ofsuperior hypophyseal artery Tuber cinereum, median eminence and infundibulum Hypothalamo-hypophyseal tract Long stalk arteries Artery of the fibrous core Short portal vessels Communicating artery

Vein

Ascending branch of inferior hypophyseal artery

Anterior lobe Pituitary sinusoids Vein Capsular artery

Vein Posterior (neural) lobe Inferior hypophyseal artery (branch of cavernous portion ofinterior carotid artery)

Descending branch of inferior hypophyseal artery

Figure 8-1 schematic representation of the blood supply of the hypothalamus and pituitary. (Reproduced from Scheithauer BW. The hypothalamus and neurohypophysis. In: Kovacs K, Asa SL, eds. Functional Endocrine Pathology. Oxford, UK: Blackwell Scientific; 1991.)

turcica and is overlain by the dural diaphragma sella,through which the stalk connects to the median eminence of the hypothalamus. The adult pituitary weighs approximately 600 mg (range, 400 to 900 mg) and measures approximately 13 mm in the longest transverse diameter, 6 to 9 mm in vertical height, and about 9 mm anteroposteriorly. Structural variation may occur in multiparous women, and gland volume also changes with the menstrual cycle. During...