Game To Genesis

GAMETOGENESIS SPERMATOGENESIS Spermatogensis berlangsung pada dinding Tubulus seminiferus pada testis. Proses pembentukan sperma mempunyai 3 periode : 1) Periode perbanyakan sel : Bakal sel kelamin jantan memperbanyak diri secara mitosis dan menghasilkan spermatogonium yang bersifat diploid (2n). 2) Periode tumbuh : Di dalam testis spermatogonium akan tumbuh menjadi bertambah besar. Dan dinamakan spermatosit primer atau spermatosit I (2n). 3) Perode pematangan: Di dalam Tubulus seminiferus dari testis, spermatosit primer (2n) mengalami pembelahan meiosis I dan menghasilkan spermatosit sekunder yang bersifat haploid (n). Spermatosit sekunder akan mengalami pembelahan meiosis II dan menghasilkan spermatid (n). Kemudian spermatid akan berdifernsiasi dan berubah bentuk mnjadi spermtozoid

The Male Reproductive System

Testes are suspended outside the abdominal cavity by the scrotum, a pouch of skin that keeps the testes close or far from the body at an optimal temperature for sperm development. Seminiferous tubules are inside each testis, and are where sperm are produced by meiosis. About 250 meters (850 feet) of tubules are packed into each testis. Spermatocytes inside the tubules divide by meiosis to produce spermatids that in turn develop into mature sperm.

The Road the Sperm Take: Spermatogenesis

Spermatogenesis, or sperm production, begins around puberty and continues for the remainder of a man's life. The life of a single sperm begins in the seminiferous tubules, inside the testicles. In the walls of the seminiferous tubules, primordial germ cells turn into spermatogonia, diploid cells (with 46 chromosomes each) that are the precursors to actual sperm. The spermatogonia divide repeatedly, via mitotic division to produce cells called primary spermatocytes, still with 46 chromosomes. These divide again to produce secondary spermatocytes, now with 23 chromosomes each. The next cell division produces spermatids, which then develop into spermatozoa, or sperm cells. These sperm cells have 23 chromosomes each, half the number needed to initiate human development. The other 23 chromosomes needed are contributed by the egg of a woman. When a sperm joins with an egg, the conceptus (result of conception) will have 46 chromosomes. Spermatogenesis occurs continuously in a man's testicles from the onset of puberty to the end life. A young healthy man produces several hundred million sperm per day. Once produced, the sperm move their way up into the epididymis by traveling through a network of tiny ducts called rete testes. These rete testes are c-shaped structures that converge from the back, to the epididymis, which is located on the upper part of the testes. The coiled up, crescent-shaped epididymis is a maturation chamber where the sperm take on nutrients and grow for several weeks before moving on. The final road for the sperm is the vas deferens. The vas deferens begins at the epididymis and winds up past the pubic bone and urinary bladder. There are two vas deferens, one coming from each testicle, and they join at the back of the bladder. Each vas deferens joins with one seminal vesicle, which contains fluids needed at the time of ejaculation. Fluids from the vas deferens and seminal vesicles will be released into the ejaculatory ducts, located within the prostate gland. The prostate gland also secretes some of the fluids found in the ejaculation. The fluid secreted is a milky alkaline substance that provides a suitable living environment for sperm and allows them to survive in the acidity of the vagina. The ejaculatory ducts then connect to the urethra, where the sperm will be ejaculated during orgasm by sexual intercourse, masturbation, or even a wet dream.

The Female Reproductive System The female gonads, ovaries, are located within the lower abdominal cavity.

The female reporoductive system. Images from Purves et al., Lif

e: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission.

The ovary contains many follicles composed of a developing egg surrounded by an outer layer of follicle cells. Each egg begins oogenesis as a primary oocyte. At birth each female carries a lifetime supply of developing oocytes, each of which is in Prophase I. A developing egg (secondary oocyte) is released each month from puberty until menopause, a total of 400-500 eggs.

Sperm Sperm Production Sperm are constantly being produced in the testes in a process called spermatogenesis. During spermatogenesis, sperm stem cells, called spermatozoids, multiply inside the seminiferous tubules of the testes. After undergoing meiosis, a special division process for gamete cells (e.g. egg and sperm), the cells are called spermatozoa. Spermatozoa have 23 chromosomes; which is half the amount of chromosomes in a normal cell. The spermatozoa are then sent to the epididymis where they are stored allowed to mature. It is in the epididymis that sperm are given the ability to cause fertilization. During ejaculation sperm are combined with fluids from the seminal vesicles and the prostate to form the ejaculate. Sperm that are not used get old, die and are reabsorbed by the body. The body is constantly replenishing its supply of sperm, and each

ejaculation in a healthy man contains around a hundred million sperm, enough to cause a pregnancy. Sperm Anatomy

Sperm are specialized male gamete cells that serve as a carrier for genetic material. They contain special features and organelles that help them fertilize an egg and induce pregnancy.

the nucleus: Like most cells, the nucleus contains the DNA of the sperm. Unlike most cells, however

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spermatozoa contain a haploid amount of chromosomes. In humans, this means they have 23 chromosomes instead of the normal 46. When the sperm fuses with the egg in the process called fertilization the resulting in a conceptus. The sperm can be thought of as a transportation device for male's genetic material: The sperm cell's only purpose is to transport genetic material to the egg, so the nucleus is arguably the most important part of the sperm. The Acrosome: This part of the sperm allows the sperm to penetrate the external layers of the egg. The ovum, or egg, has a protective jelly layer that sperm must pass through. Upon meeting the egg's protective layer, the sperm releases digestive

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enzymes from its acrosome. The sperm's acrosomal enzymes eat through the protective layer, allowing the sperm to reach and fertilize the egg. Only capacitated sperm can produce the acrosomal reaction. Sperm enter the vagina de-capacitated by chemicals in the seminal fluids and slowly become re-capacitated by chemicals in the female's reproductive tract. The Centriole: This is a fibrous structure that is important in the mechanics of flagellar movement. Centrioles are composed of fused microtubules � special proteins important in cellular movement and structure. The centrioles extend out into the flagella as the axial filament.

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The Axial Filament: This structure is responsible for the whip-like motion of the sperm's tail. The centrioles contain a special arrangement of microtubules in the flagella. The fused microtubules slide past each other, making one microtubule longer than the second. This discrepancy in length curves the sperm tail, as can be seen in the images below. Rapid alterations in microtubule lengths create the vigorous whipping motion observed in activated sperm.

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The mitochondria: Mitochondria are often called the "powerhouse" of the cell. They convert glucose, a simple sugar, into ATP which cells can use to do all kinds of work. Sperm use ATP to power the movement of their microtubules and propel themselves forward. The Plasma Membrane: Like all cells, sperm have a plasma membrane. The plasma membrane is the cell's "skin" and separates the cell from the external environment and covers the whole sperm. The plasma membrane surrounding the acrosome plays an important role in sperm-egg recognition and in fertilization.

The Testis & Spermatogenesis The following diagram shows the organization of the events of spermatogenesis within the testis. The earliest stages are closest to the outer wall of the seminiferous tubule while the most mature stages are near its lumen.

Back to outline

The Sequence of Events in Spermatogenesis In the next lecture we will deal with the details of spermatogenesis. Here we simply want to introduce the subject and indicate how it is organized in a general way. Since the seminiferous tubules are, as their name specifies, small tubes, they appear like the cross-section of a pipe or hose. Instead of the wall being made up of copper (pipe) or rubber (hose), the wall is made up of cells and extracellular material or basement membrane as indicated above. The interstitial cells and extracellular matrix lies on the outside of the seminiferous tubule wall where it is in contact with non-reproductive supportive tissues, blood vessels and nerves. Spermatogenesis occurs on the inside of the wall where the stages of spermatogenesis are lined up with the earliest stages adjacent the basement membrane. Thus the spermatogonia (originally derived from the PGCs) that have now increased in number lie closest to the basement membrane. Spermatogenesis occurs in contact with special non-sexual, Sertoli Cells that also adhere to the basement membrane. Successive stages lie further and further away from the basement membrane in the following order: Primary spermatocytes, secondary spermatocytes, spermatids and spermatozoa. Some of these stages can also sub-divided into other sub-categories of cell types that don't concern us in this course.