346 



THE INTERNAL ENVIRONMENT OF THE BODY 



Part III 



OVIDUCT 



HYMEN 



Fig. 18.10. Diagram of a section of the human female reproductive organs. 

 (Courtesy, Harbaugh and Goodrich, eds.: Fundamentals of Biology. New York, 

 The Blakiston Co., 1953.) 



From the surface of the ovary, the egg ordinarily enters the enlarged funnel- 

 shaped end of the oviduct which clasps the ovary in its soft ciliated folds 

 (Fig. 18.10). The ends of the oviducts contain smooth muscle and have 

 considerable range of position in cupping themselves about the ovaries. Even 

 if the egg is not discharged directly into the funnel, it is apt to be pulled 

 into it by the beat of the cilia always directed toward the uterus. If copulation 

 has recently occurred and sperm cells are present, they usually meet the egg 

 in the oviduct and fertilization results. Once in the oviduct whether fertilized 

 or not the egg is carried on to the uterus by peristaltic contractions of the walls 

 and the urging beat of the cilia. The second meiotic division occurs after the 

 sperm enters the egg. The nucleus of the egg is then ready to unite with the 

 nucleus of the sperm. At fertilization the addition of 24 chromosomes of the 

 nucleus of the egg and 24 of the nucleus of the sperm restores the regular 

 number of 48 in the human body cells. The sex of the individual is also deter- 

 mined at fertilization. 



In the ovary, the broken follicle soon enlarges. Influenced by the gonad- 

 stimulating hormones of the anterior pituitary its cells increase in size and 

 number and form an endocrine gland, the corpus luteum or "yellow body" 

 (Figs. 18.11, 18.12). This secretes progesterone which stimulates the further 

 growth of the uterus. If the egg has been fertilized, the embryo developing 

 from it may be gradually making its way into the uterine wall. If so, substances 

 will be produced by its outer membranes and taken by the blood through the 



