EMBRYOLOGY lyi 



OVULATION AND SEMINATION 



The discharge of the ovum from its follicle (in the ovary) comprises 

 ovulation. In primates, ovulation is periodic, at intervals of about four weeks. 

 The human female begins to ovulate at puberty (about the fourteenth year) 

 and ends with the menopause (about the forty-seventh year). Generally 

 only one follicle and ovum mature each month, the ovaries alternating 

 with irregular and unpredictable sequence. Thus from the many thousands 

 of potential ova provided, only about 200 ripen in each ovary during the 

 thirty-odd years of sexual activity. 



Sometimes two or more follicles mature and expel their eggs simul- 

 taneously; this phenomenon is responsible for the common type of mul- 

 tiple births. The reason why only one follicle at a time ordinarily reaches 

 maturity is because of the nice balance maintained between the amount of 

 follicle-ripening hormone (prolan A) and the response of the ovary to it. 

 Hormone oversecretion brings about multiple ovulation, while under- 

 secretion is responsible for ovulatory failure. How long the human egg 

 retains its ability to receive a sperm and then start developing cannot be 

 stated with certainty. It is now generally believed that the fertilizable 

 period is not more than a day. 



For many years ovulation and menstruation were supposed to take 

 place synchronously. But when actual data was collected, it became ap- 

 parent that this assumption is untrue. In reality the time of ovulation is 

 about midway between two menstrual periods. 



The purpose of coitus is to introduce spermatic fluid into the vagina. 

 Spermatozoa gradually attain their full functional state, retain it for a 

 hmited period, and if not discharged, then slowly decHne in vigor until 

 death and resorption supervene. At the climax of coitus, ejaculation occurs; 

 involuntary muscular contractions forcibly eject the older spermatozoa, 

 along with the secretions of several accessory glands which discharge at 

 the same moment. The combined fluid mass is the seminal fluid, or semen. 

 The volume of the ejaculate is about 4 c.c. and in it swim some 300,000,- 

 000 spermatozoa. An acid environment, such as the vagina where the 

 seminal fluid is first deposited, is deleterious or fatal to spermatozoa; a 

 neutral medium, as furnished by the uterus and tubes, is more favorable. 



The outstanding functional feature of spermatozoa is their lashing 

 flagellate swimming which resembles that of a tadpole. Forward progress 

 of the human spermatozoon is at the rate of about 1.5 mm. a minute which, 

 in relation to their respective lengths, compares well with average swim- 

 ming ability for man. 



These innate activities, however play but little part in the transport of 

 sperm through the female genital tract. Passage from vagina to uterus 

 is the result of muscular movements of the cervix. The journey through 

 the uterus is similarly accomplished, in some animals at least, by muscular 



