Medical brain notes 44

  Pituitary Gland and Its Relation to the Hypothalamus Pituitary Gland: Two Distinct Parts–The Anterior and Posterior Lobes.  The pituitary gland (Figure 75–1), alsocalled the  hypophysis,  is a small gland—about 1 cen-timeter in diameter and 0.5 to 1 gram in weight— that lies in the  sella turcica,  a bony cavity at the base of the brain, and is connected to the hypothalamus by the  pituitary  (or  hypophysial ) stalk. Physio-logically, the pituitary gland is divisible into two distinct portions: the  anteriorpituitary,  also known as the  adenohypophysis,  and the  posterior pituitary,  alsoknown as the neurohypophysis.  Between these is a small, relatively avascular zone called the  pars intermedia,  which is almost absent in the human being but is much larger and much more functional in some lower animals.         Embryologically, the two portions of the pitui...

  Hypothalamus Controls Pituitary Secretion Almost all secretion by the pituitary is controlled by either hormonal or nervous signals from the hypo-thalamus. Indeed, when the pituitary gland is removed from its normal position beneath the hypothalamus and transplanted to some other part of the body, its  rates of secretion of the different hormones (except for prolactin) fall to very low levels.      Secretion from the posterior pituitary is controlled by nerve signals that originate in the hypothalamus and terminate in the posterior pituitary. In contrast, secretion by the anterior pituitary is controlled by hor-mones called  hypothalamic releasing  and  hypothala-mic inhibitory hormones  (or  factors ) secreted withinthe hypothalamus itself and then conducted, as shown in Figure 75–4, to the anterior pituitary through minute blood vessels called  hypothalamic-hypophysialportal vessels.  In the anterior pituitary, these releas...

  Physiological Functions of Growth Hormone All the major anterior pituitary hormones, except for growth hormone, exert their principal effects by stimulating target glands, including thyroid gland, adrenal cortex, ovaries, testicles, and mammary glands. The functions of each of these pituitary hormones are so intimately concerned with the functions of the respec-tive target glands that, except for growth hormone, their functions are discussed in subsequent along with the target glands. Growth hormone, in  contrast to other hormones, does not function through a target gland but exerts its effects directly on all or almost all tissues of the body. Growth Hormone Promotes Growth of Many Body Tissues Growth hormone, also called  somatotropic hormone  or  somatotropin,  is a small protein molecule that con-tains 191 amino acids in a single chain and has a molecular weight of 22,005. It causes growth of almost all tissues of the body that are capable of growing....