A&P 2                        Human development    (updated 11/10/05)         Intro Biology I

Be able to recognize all reproductive structures and know their functions. Also review the embryonic stages of development of male and female reproductive structures, and know homologous structures of each sex. Male reproductive organs (1) in midsagittal view.

Male reproductive organs (2) in midsagittal view.

Cross section of penis.

The ductus epididymis is about 20 feet in length, and is folded and coiled into a connective tissue sheath that is about 1 1/2 inch in length.

Note in this view that the "Germinal cells" are also called spermatogonia. Each spermatogonium divides by mitosis to produce another spermatogonium and a primary spermatocyte. Each primary spermatocyte will undergo two meiotic divisions to ultimately produce four spermatozoa.

Scanning e.m. of human seminiferous tubules.

Spermatogonia are actually the outer layer of small cells. The large cells labeled spermatogonia are actually primary spermatocytes, and the smaller cells are secondary spermatocytes.

Spermatogonia are rather small cells, while primary spermatocytes are nearly twice as large (see photo above). The sustentacular cells (Sertoli cells) separate the secondary spermatocytes from immune cells, which would destroy them, since they do not have a full complement of chromosomes. 

The diagram below illustrates how the chromosome number is reduced by one-half in the first meiotic division (also known as the reduction division).

In the second meiotic division, the individual sister chromatids are separated, so that 23 chromatids remain in each spermatid. This diagram illustrates both meiotic divisions in spermatogenesis.

Sperms mature in the epididymis after developing in the seminiferous tubules.

Hormonal control of sexual cycle in males.

Female internal reproductive organs in side view (1).

Female reproductive organs in side view (2).

Female internal reproductive organs in front view (1).

Female internal reproductive organs in front view (2).

Female external reproductive organs.

Notice that only one ovum normally develops completely during each menstrual cycle, and the polar bodies (which contain the extra chromosomes) degenerate.

Another view of oogenesis including development from primary follicles within an ovary.

Micrograph of secondary oocyte and first polar body.

Drawing of mature follicle within ovary containing secondary oocyte.

Photo of mature follicle within ovary containing secondary oocyte.

Be able to relate the events within the ovaries to the reproductive hormone changes and to changes in the uterus and stages of the menstrual cycle. Fertilization normally occurs in the infundibulum, where the secondary oocyte is shown below.

Photomicrograph and scanning electron micrograph of uterine tube.

Photomicrograph of uterine wall.

Scanning electron micrograph view of sperm cells surrounding ovulated secondary oocyte.

Once the sperm head has entered the secondary oocyte, the last meiotic division of the oocyte is completed, and then the sperm and egg nuclei fuse to form the zygote (fertilized egg), which is the beginning stage in embryonic development. Be sure to know the interactions of hormones at each stage of the menstrual cycle and pregnancy.

Hormonal control of female reproductive functions.

Hormonal control of female reproductive functions: ovarian and menstrual cycles.

Reproductive System Lab