TESTES The testes, as stated earlier, are the primary male reproductive   organs.   They   produce   sperm   cells (spermatozoa) and male hormones, both necessary for reproduction. Structure The testes are oval glands suspended inside a sac (the  scrotum)  by  a   spermatic  cord.  The  spermatic cords are formed by the vas deferens, arteries, veins, lymphatics,   and   nerves,   all   bound   together   by connective tissue. Each   testis   is   encapsulated   by   a   tough,   white, fibrous tissue called the tunica albuginea. The interior of the testis is divided into 250 lobules (small lobes). Each lobule contains 1 to 4 highly coiled, convoluted tubules  called   seminiferous  tubules.  These  tubules unite to form a complex network of channels called the rete testis. The rete testis give rise to several ducts that join a tube called the  epididymis  (fig. 1-60). Functions The   testes   perform   two   functions:   to   produce sperm  cells  and  to  secrete  male  sex  hormones.  The process by which sperm cells are produced is called spermatogenesis.   Spermatogenesis   occurs   in   the seminiferous  tubules  of  the  testes.  Once  the  sperm cells  are  formed,  they  collect  in  the  lumen  of  each seminiferous tubule. When the sperm cells are ready, they  pass  through  the  rete  testis  to  the  epididymis, where they remain for a time to mature. The production of   sperm   cells   occurs   continually   throughout   the reproductive life of a male. The male hormone testosterone is produced in the testes.  This  hormone  is  initially  responsible  for  the formation  of  the  male  reproductive  organs.  During puberty, testosterone stimulates the enlargement of the testes   and   various   other   accessory   reproductive organs.  It  also  causes  the  development  of  the  male secondary sexual characteristics. Refer to the section titled   “The   Endocrine   System”   for   more   detailed discussion on male secondary sexual characteristics. Other  actions  of  testosterone  include  increasing the  production  of  red  blood  cells.  As  a  result,  the average number of red blood cells in blood is usually greater in males than in females. INTERNAL ACCESSORY ORGANS The   internal   accessory   organs   of   the   male reproductive   system   include   the   epididymis,   vas deferens,  ejaculatory  ducts,  seminal  vesicle,  urethra, prostate gland, bulbourethral glands, and semen (fig. 1-60). Epididymis Each  epididymis  is  a  tightly  coiled,  thread-like tube that is approximately 6 meters long. This tube is connected   to   the   ducts   within   the   testis.   The epididymis covers the top of the testis, runs down the testis'  posterior  surface,  and  then  courses  upward  to form the vas deferens. The  epididymis  secretes  the  hormone  glycogen, which helps sustain the lives of stored sperm cells and promotes   their   maturation.   When   immature   sperm cells   enter   the   epididymis,   they   are   not   mobile. However,   as   the   sperm   cells   travel   through   the epididymis, they mature and become mobile. Once the sperm cells are mature, they leave the epididymis and enter the vas deferens. Vas Deferens The vas deferens is a small tube that connects the epididymis and ejaculatory duct. It ascends as part of the  spermatic  cord  through  the  inguinal  canal  of  the lower   abdominal   wall   into   the   pelvic   cavity,   and transmits the sperm to the ejaculatory ducts. Ejaculatory Ducts The   vas   deferens   and   the   seminal   vesicles converge,   just   before   the   entrance   of   the   prostate gland,  to  form  the  ejaculatory  ducts  (fig.  1-60).  The ejaculatory  ducts  open  into  the  prostatic  urethra.  Its function is to convey sperm cells to the urethra. Seminal Vesicles The   seminal   vesicles   are   two   pouches   that   are attached to the vas deferens near the base of the urinary bladder. The lining of the inner walls of the seminal vesicles secrete a slightly alkaline fluid. This fluid is thought to help regulate the pH of the tubular contents as   sperm   cells   are   conveyed   to   the   outside.   The secretion   produced   by   the   seminal   vesicles   also contains a variety of nutrients, such as fructose (simple sugar), that provides the sperm cells an energy source. 1-58