At  the  time  of  ejaculation,  the  contents  of  the seminal vesicles are emptied into the ejaculatory ducts. This action greatly increases the volume of fluid that is discharged by the vas deferens. Urethra The  urethra  is  an  important  organ  of  both  the urinary  and  reproductive  systems.  The  role  of  the urethra,  in  the  reproductive  system,  is  to  transport sperm through the penis to outside the body. See “The Urinary  System”  section  for  information  on  the structure of the urethra. Prostate Gland The  prostate  gland,  made  of  smooth  muscle  and glandular tissue, surrounds the first part of the urethra. It resembles a chestnut in shape and size, and  secretes an alkaline fluid to keep the sperm mobile, protecting it from  the  acid  secretions  of  the  female  vagina.  This substance is discharged into the urethra as part of the ejaculate, or semen, during the sexual act. Bulbourethral Glands Bulbourethral  glands,  also  known  as  Cowper's glands,  are  two  pea-sized  bodies  located  below  the prostate gland and lateral to the membranous urethra. These  glands  are  enclosed  by  fibers  of  the  external urethral sphincter. They release a mucous-like fluid in response to sexual stimulation and provide lubrication to  the  end  of  the  penis  in  preparation  for  sexual intercourse. Semen Semen is composed of sperm and secretions from the  seminal  vesicles,  prostate,  and  bulbourethral glands. It is discharged as the ejaculate during sexual intercourse.  There  are  millions  of  sperm  cells  in  the semen of each ejaculation, but only one is needed to fertilize  the  ovum.  It  is  generally  considered  that fertilization of the ovum occurs while it is still in the fallopian  tubes.  Therefore,  it  is  apparent  that  sperm cells can move actively in the seminal fluid deposited in the vagina and through the layers of the secretion lining the uterus and fallopian tubes. EXTERNAL ACCESSORY ORGANS The   external   accessory   organs   of   the   male reproductive  system  include  the  scrotum  and  penis (fig. 1-60). Scrotum The scrotum is a cutaneous pouch containing the testes  and  part  of  the  spermatic  cord.  Immediately beneath the skin is a thin layer of muscular fibers (the cremaster),  which  is  controlled  by  temperature  and contracts  or  relaxes  to  lower  or  raise  the  testes  in relation  to  the  body.  This  muscular  activity  of  the scrotum is necessary to regulate the temperature of the testes, which is important in the maturation of sperm cells. Penis The penis is a cylindrical organ that conveys urine and semen through the urethra to the outside. The penis is  composed  of  three  columns  of  spongy  cavernous tissue, bound together by connective tissue and loosely covered  by  a  layer  of  skin.  Two  of  the  columns,  the corpora  cavernosa,  lie  superiorly  side  by  side;  the third column, the corpus spongiosum, lies below the other two columns. The urethra is located in the corpus spongiosum.  The  dilated  distal  end  of  the  corpus spongiosum is known as the  glans penis  (fig. 1-60). The urethra terminates at the glans penis. The  cavernous  tissue  becomes  greatly  distended with  blood  during  sexual  excitement,  causing  an erection of the penis. The loose skin of the penis folds back on itself at the distal end (forming the prepuce, or foreskin)  and  covers  the  glans.  The  prepuce  is sometimes removed by a surgical procedure called a circumcision. FEMALE REPRODUCTIVE SYSTEM LEARNING OBJECTIVE:  Recall  the  parts of   the   female   reproductive   system   and   their function(s). The organs of the female reproductive system are specialized  to  produce  and  maintain  the  female  sex cells, or egg cells; to transport these cells to the site of fertilization;   to   provide   an   environment   for   a developing offspring; to move the offspring outside; and  to  produce  female  sex  hormones.  The  primary female reproductive organs are the ovaries. The other structures   of   the   female   reproductive   system   are considered   accessory   reproductive   organs.   The 1-59