Human Reproductive System

The functional layer of the human endometrium is a highly regenerative tissue undergoing monthly cycles of growth, differentiation, and shedding during a woman's reproductive years. Fluctuating levels of circulating estrogen and progesterone orchestrate this dramatic remodeling of human endometrium.

Ovulation is the biological process where a mature ovarian follicle ruptures and discharges a secondary oocyte, or ovum, from the ovary.

Sertoli cells are located within the seminiferous tubules and provide nourishment to the developing sperm cells.

Mammalian testes contain seminiferous tubules (where sperm are produced), Sertoli cells (nourishment), and Leydig cells (testosterone production). Graafian follicles are found in ovaries, not testes.

Vasa efferentia are fine ciliated ductules that arise from the seminiferous tubules of testis (where sperms are formed) and open into epididymis which is a mass of long narrow closely coiled tubule lying along the inner side of testis. Epididymis stores the sperms. Thus, if vasa efferentia get blocked, sperms will not be transposed from testes to epididymis.

Testes are the pair of oval organs, about the size of large olives that lie in the scrotum. The testes are responsible for making testosterone which is the primary male sex hormone, and for generating sperm. 

The primary reproductive organ of human male is testes, it produces male hormones  testosterone and sperm.

In mammals, sperm cells are produced in the seminiferous tubules of each testis. These sperm cells leave the testes and pass into a larger coiled tube known as the epididymis. The sperm cells attain maturity in the epididymis. The sperm cells are stored in this structure till they are ejaculated. During ejaculation, the sperms pass from the epididymis into the vas deferens and are ejaculated with the semen through the penis.

In males, testis are located in the scrotal sac and are extra abdominal in position. The temperature in the scrotum is 2$^o$ to 3$^o$ C less than the normal body temperature. This temperature is conducive for maturation of sperms. Thus the correct answer is option D.

Testes is the primary sex organ in human males. The testes are situated outside the abdominal cavity within a pouch called scortum. In adults, each testis is oval in shape, with a length of about 4 to 5 cm and width of about 2 to 3 cm. The testis is covered by a dense covering. They are enclosed in an outer tough capsule of collagenous connective tissue, the tunica albuginea. It is a protective layer.

Spermatogenesis is the process by which the formation of sperm which is the male gamete takes place and it is carried out in the tiny tubes like structure in seminiferous tubules of testes.

Testes are extra-abdominal in position. The testes are situated outside the abdominal cavity within a pouch called scrotum. The scrotum helps in maintaining the low temperature of the testes ($2 – 2.5^o$ C lower than the normal internal body temperature), which is necessary for spermatogenesis. The slightly cooler temperature of the scrotum is necessary for the development of normal sperm. So, the testes start their development in the abdominal cavity. But during the 7^th month of the foetal life, they descend into the scrotal sacs in presence of testosterone hormone.

To ensure the survival and growth of the sperms, testes have been placed outside the abdominal cavity within a pouch called scrotum so as to ensure the optimal temperature. The scrotum helps maintain the low temperature (by about 2-2.5 degrees than the normal body temperature) required for spermatogenesis. So, the correct option is '2.0−2.5o C lower than the normal body temperature'.