410 - Multicellular Animals, Especially Man 



mately at tlie center of the head, attached to 

 the base of the brain by a stalk, the infundi- 

 bulum (Fig. 22-8). Moreover, the pituitary is 

 a double gland, consisting of two main parts 

 — the anterior lobe and posterior lobe — al- 

 though part of the posterior lobe appears to 

 be different from the main mass, constituting 

 what is called the intermediary tissue (Fig. 

 22-8). The anterior lobe arises in the embryo 

 as a pouchlike upgrowth from the roof of the 

 pharynx; whereas the posterior lobe is a solid 

 downgrowth from the floor of the brain. 

 These parts of the embryonic pituitary make 

 contact, but the anterior lobe grows more 

 rapidly, partially encompassing the posterior 

 lobe. In the adult, all connection between 

 the anterior lobe and the oral cavity is lost, 

 except in rare anomalous cases, but the con- 

 nection of the posterior lobe with the brain 

 persists as the infundibulum. 



Pituitary research has been very active for 

 many years, but it still presents a number of 

 unsolved problems. The work is very diffi- 

 cult, because the gland lies in a relatively 

 inaccessible position and because most, if not 

 all, of the pituitary hormones are protein 

 compounds, which are difficult to isolate and 

 identify. 



Deficiency and Overdosage Experiments. 

 Rats are excellent specimens for pituitary 

 research, because the pituitary of the rat 

 is relatively easy to remove bv operating 

 through the roof of the mouth. When this 

 operation is successful, no damage is done 

 to the overlying brain; and there is seldom 

 any infection even in the absence of aseptic 

 precautions. 



Deprived of the pituitary, the animal dis- 

 plays a number of characteristic symptoms. 

 Young specimens stop growing and never 

 reach sexual maturity. In adults, the males 

 suffer a distinct retrogression of the testes 

 and accessory reproductive structures, and 

 females display a degeneration of the ovaries, 

 uterus and vagina. Both sexes are prone to 

 show an atrophy of the adrenal cortex and of 

 the thyroid glands. 



Consistent results are also obtained by 



overdosage with pituitary material, either in 

 the form of injected extracts, or from the 

 implantation of extra glands. Characteristi- 

 cally young animals grow prodigiously, reach- 

 ing a state of gigantism, with a very early 

 onset of sexual maturity. Also adult speci- 

 mens display hypertrophy and hyperactivity 

 of the primary and secondary sex organs, as 

 well as of the thyroid and adrenal cortex. 



Hormones of the Anterior Pituitary. On 

 the basis of these and many other experi- 

 ments, several separate anterior lobe hor- 

 mones have now been demonstrated. These 

 include somatotrophin, which is better 

 known as the growth hormone; the gonado- 

 trophins, a group of hormones that act 

 primarily on the sex organs; and also thvro- 

 trophin anil cortkotrophin, which act re- 

 spectively on the thyroid and adrenal cortex. 

 Other anterior pituitary hormones are also 

 indicated, but these will not be included in 

 the present account. 



The Growth Hormone. Human cases of gi- 

 gantism, with statures greater than 9 feet, 

 were recorded by the Greeks and Romans, 

 but it was not until about 1860 that the con- 

 dition was related to an overactive pituitary. 

 More recently, the work of separating the 

 growth-promoting substance from crude 

 pituitary extracts finally culminated in 1944 

 with the isolation of a simple protein, soma- 

 totrophin. This hormone is exceedingly po- 

 tent in restoring growth to hvpophvsectom- 

 ized animals. 



The pituitary giant is a well-proportioned 

 individual, although the overgrowth of the 

 limbs exceeds that of the other bodv parts. 

 Likewise the pituitary midget may be quite 

 normal, except for extremely diminutive legs 

 and arms. Apparently hyperactivity or hypo- 

 activity of the pituitary may be restricted 

 largely to the tissue that secretes the growth 

 hormone. 



Acromegaly is another human ailment in 

 which an excess of somatrophin appears to 

 be the major factor. In acromegaly the hyper- 

 activity of the pituitary is usually due to a 

 tumorous condition, which develops after an 



