THE ENDOCRINE SYSTEM 209 



their secretion, and therefore with carbohydrate metabolism. 

 These results will be discussed in connection with the pancreas. 

 Since removal of the anterior pituitary lobe also causes atrophy 

 in the parathyroid glands, the presence of a parathyrotropic 

 hormone is indicated. 



Posterior Pituitary Gland. — Two substances, pitressin and pito- 

 cin, have been extracted from posterior lobe tissue, but since 

 neither has been obtained entirely free of the other, there is 

 some overlapping of the effects produced by them. Pitressin 

 has effects on the heart, blood vessels, respiration, kidneys, and 

 intestine. Pitocin causes the contraction of the muscles of the 

 uterus. Pitressin produces at first a fall and then a prolonged 

 rise in pulse rate, oxygen consumption, and heart output. An 

 irregular quickening of the respiratory rate is a secondary 

 effect of the circulatory disturbance. On the intestine, pitressin 

 produces a muscular constriction. Pitressin has an antidiuretic 

 effect, i.e., it decreases the volume of urine. This may be the 

 result of the resorption of water by the kidney tubules, or the 

 retention of water by the tissues. Such results are obtained with 

 patients having diabetes insipidus or with normal individuals, 

 who have previously taken water by mouth. On the other 

 hand, diuresis (secretion of urine) may be increased by pitressin 

 in animals with a low urine volume. Pitressin thus has both 

 a diuretic and antidiuretic action, depending upon the condition 

 of the subject. The action of pitocin on the musculature of the 

 uterus is more potent during the later stages of pregnancy and is 

 sometimes used to induce parturition. 



The Intermediate Lobe of the Pituitary. — A hormone called 

 intermedin obtained from the intermediate lobe of the pituitary 

 gland causes chromatophores (pigment-bearing cells) to expand. 

 This can be demonstrated by producing a darkening of the skin 

 of frogs as a result of injecting an extract of the intermediate 

 lobe. In man there is evidence that intermedin has an anti- 

 diuretic action on patients suffering from diabetes insipidus, 

 similar to the action of pitressin. 



Thyroid Gland. — The thyroid gland of the frog consists of two 

 lobes, completely separated, lying one on each side of the hyoid 

 apparatus between the posterolateral and thyrohyoid processes. 

 In man it consists of two lobes, joined usually by a narrow isth- 

 mus, the whole encircling the front and side of the trachea just 



