Biology of Man 513 



13. Liver. — Composed of four lobes located just beneath the dia- 

 phragm; an unknown hormone may stimulate the bone marrow to form 

 erythrocytes. 



The great complexity and interdependence of the various parts of the 

 endocrine system may be observed from the following summary in which 

 some of the more important functions are given with some of the par- 

 ticipating hormones listed: 



Digestion — Gastrin (stomach) ; secretin, enterocrinin, enterogasterone, cholecys- 

 tokinin (intestine); gastroscopic, pancreotropic (pituitary) 



Sugar metabolism — Insulin (pancreas) ; adrenalin, cortin (adrenals) ; diabetogenic 

 (pituitary) 



Fat metabolism — Ketogenic (pituitary) ; lipocaic (pancreas) 



Calcium and phosphorus metabolism — Parathormone (parathyroids) 



Sodium and potassium metabolism — Cortin (adrenal) 



General metabolism — Thyroxin (thyroid) ; cortin (adrenal) 



Excretion — Cortin (adrenal) ; antidiuretic (pituitary) 



Growth regulation — Thyroxin (thyroid) ; growth-promoting (pituitary) ; cortin 

 (adrenal) ; possibly thymus and pineal? 



Sexual characters and reproduction — Testosterone, androsterone (testes) ; estrone, 

 progesterone, relaxin (ovaries) ; follicle-stimulating, luteinizing, prolactin, 

 galactogenic (pituitary) ; estrogen, emmenin, anterior pituitary-like (placenta) ; 

 cortin (adrenals) 



X. HUMAN REPRODUCTION AND DEVELOPMENT 



The stages in human reproduction and development are somewhat 

 similar to those of other higher vertebrates but, as might be expected, 

 there are differences depending upon the species (Figs. 363 to 366). 

 Many of the early stages of various vertebrates are so similar that it is 

 difficult to distinguish them (Fig. 363). The stages in the embryologic 

 development of a frog and of man are described somewhat in detail in 

 Chapter 24. 



The human male reproductive system (Fig. 254) consists of (1) a 

 pair of testes suspended in the scrotum, (2) numerous vasa efferentia 

 which lead into a single, highly convoluted collecting tubule, the two con- 

 stituting the epididymis which is attached to each testis, (3) the pair 

 of vasa deferentia (singular, vas deferens) or sperm ducts which lead 

 from the collecting tubules to the pair of saclike seminal vesicles, just 

 behind the bladder; (4) the small prostate gland surrounding the urethra 

 and ejaculatory ducts, (5) the ejaculatory ducts leading from the semi- 

 nal vesicles to the single tubular urethra which leads to the outside, and 

 (6) the pair of small Cow per' s glands posterior to the urethra and con- 

 nected to it by a pair of small ducts. 



