Anatomy & Physiology

Anatomy & Physiology Study Guide In spermiogenesis, the last step of spermatogenesis, each spermatid matures into a single spermatozoon, or sperm. Developing spermatocytes undergoing meiosis and spermatids undergoing spermiogenesis are surrounded by the cytoplasm of the nurse cells. As spermiogenesis proceeds, the spermatids gradually develop the appearance of mature spermatozoa. At spermiation, a spermatozoon loses its attachment to the nurse cell and enters the lumen of the seminiferous tubule. In approximately nine weeks, the entire process, from spermatogonial division to spermiation, has taken place. The Anatomy of a Spermatozoon Each spermatozoon has three distinct regions: the head, the middle piece, and the tail. The head, which contains the densely packed chromosomes of the nucleus, resembles a flattened ellipse. At the tip of the head is the acrosomal cap , a membranous compartment containing enzymes essential to fertilization. A short neck attaches the head to the middle piece. The neck contains both centrioles of the original spermatid. The ATP required to move the tail is provided by high mitochondrial activity. The tail is the only flagellum in the human body. A flagellum, a whip-like organelle, moves a cell from one place to another. Whereas cilia beat in a predictable, wavelike fashion, the flagellum of a spermatozoon has a complex, corkscrew motion. The testes produce physically mature spermatozoa. The other portions of the male reproductive system are responsible for the functional maturation, nourishment, storage, and transport of spermatozoa. 25.3 The Male Reproductive Tract The Epididymis Late in their development, spermatozoa detach from the nurse cells and lie within the lumen of the seminiferous tubule. They have most of the physical characteristics of mature spermatozoa, but are functionally immature and incapable of coordinated locomotion or fertilization. Cilia lining the efferent ductules create fluid currents to transport the immobile gametes into the epididymis. The epididymis is a coiled tube bound to the posterior border of each testis. It has a head, a body, and a tail. The superior head is the portion of the epididymis proximal to the testis and receives spermatozoa from the efferent ductules. The epididymis has three functions. It monitors and adjusts the composition of the fluid produced by the seminiferous tubules. It protects and stores spermatozoa and facilitates their maturation, and it acts as a recycling center for damaged spermatozoa. Transport along the epididymis includes a sequence of fluid movement and peristaltic contractions of smooth muscle in the walls of the epididymis. After passing along the tail of the epididymis, the spermatozoa enter the ductus deferens. The Ductus Deferens Each ductus deferens, or vas deferens, begins at the tail of the epididymis and ascends through the inguinal canal. Before the ductus deferens reaches the seminal and prostate glands, its lumen enlarges. The ampulla of the ductus deferens is this expanded region. The wall of the ductus deferens Achieve Page 341 of 368 ©2018