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OBJECTIVES

OBJECTIVES

After studying this chapter, you should be able to:

  • Describe the development and structure of the pituitary gland and its relationship to the hypothalamus.

  • Identify the hormones secreted by the anterior and posterior lobes of the pituitary and their target organs, and how the numbers of the various cell types in the anterior pituitary are controlled in response to physiologic demands.

  • Understand the function of hormones derived from proopiomelanocortin (POMC) and how they are involved in regulating skin coloration.

  • Describe how growth hormone is secreted from the anterior pituitary and circulates and activates its receptors, and the stimuli that regulate growth hormone secretion with their underlying mechanisms.

  • Understand the role of growth hormone in growth and metabolic function, and how somatomedins (such as insulin-like growth factors) may mediate some of its actions in the periphery.

  • Define the normal timeline of growth in humans and identify factors in addition to growth hormone that contribute to its regulation.

  • Understand pituitary secretion of gonadotropins and prolactin, how these are regulated, and the actions of these hormones on reproductive tissues.

  • Understand the basis of conditions where pituitary function is abnormal, and how they can be treated.

INTRODUCTION

The pituitary gland, or hypophysis, lies in a pocket of the sphenoid bone at the base of the brain and is closely related to the hypothalamus (see Figure 17–2). It is a coordinating center for control of many downstream endocrine glands, some of which are discussed in subsequent chapters. In many ways, it can be considered to consist of two separate endocrine organs that contain a plethora of hormonally active substances. The anterior lobe of the pituitary secretes thyroid-stimulating hormone (TSH, thyrotropin), adrenocorticotropic hormone (ACTH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin, and growth hormone (see Figure 17–9), and receives almost all of its blood supply from the portal hypophysial vessels that pass initially through the median eminence, a structure immediately below the hypothalamus. This vascular arrangement positions the cells of the anterior pituitary to respond efficiently to regulatory factors released from the hypothalamus. Of the listed hormones, prolactin acts on the breast. The remaining five are, at least in part, tropic hormones; that is, they stimulate secretion of hormonally active substances by other endocrine glands or, in the case of growth hormone, the liver and other tissues (see below). The tropic hormones for some endocrine glands are discussed in the chapter on that gland: TSH in Chapter 19 and ACTH in Chapter 20. However, the gonadotropins FSH and LH, along with prolactin, are covered here. In some species, there is a well-developed intermediate lobe of the pituitary, which contains hormonally active derivatives of the proopiomelanocortin (POMC) molecule that regulate skin pigmentation, among other functions (see below). In humans, the intermediate lobe is rudimentary, and the cells that secrete derivatives of POMC are present in the anterior pituitary.

The posterior lobe of the pituitary consists ...

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