Gametogenesis

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Gametogenesis

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the process of development and maturation of sex cells

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Gametogenesis

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specialized cells undergo both mitotic and meiotic cell divisions

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Spermatogenesis

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gametogenesis in the male

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Oogenesis

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gametogenesis in the female

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Spermatogenesis

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production of the male gamete, spermatozoa

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Spermatogenesis

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process involves mitosis of spermatogonia to produce daughter spermatogonia

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Spermatogenesis

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daughter cells produced will either divide to produce more spermatogonia or undergo the growth phase to produce primary spermatocyte

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Spermatogenesis

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process takes place inside the seminiferous tubules of the testicles

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Tunica albuginea

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fibrous connective tissue covering the entire testicle

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Lobules

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pyramid shaped, separated by septae of connective tissue that extend inward from the capsule.

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Seminiferous tubules

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coiled tubes that comprise bulk of the testicles. Each tubule is enclosed by a basement membrane and its wall is composed of cells in various stages of spermatogenesis.

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Structures inside the Seminiferous Tubules

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Spermatogonia, Primary spermatocytes, Secondary spermatocytes, Spermatids, Spermatozoa, Sertoli (sustentacular) cells, Interstitial cells (of Leydig)

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Spermatogonia

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single layer of small cells with dark staining oval nucleus located at the periphery (against the basement membrane) of the seminiferous tubule;

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Primary spermatocytes

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largest cells within the seminiferous tubules located next to the spermatogonia. They have larger and darker nuclei than the spermatogonia. Dark compacted chromatin structures can be found in the nucleus.

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Secondary spermatocytes

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cells smaller than the primary spermatocytes located near the lumen of the seminiferous tubule. These cells result from the first maturation (meiotic division). The chromatin is lighter than in the primary spermatocyte.

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Spermatids

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small cells usually with short tails embedded in the cytoplasm of Sertoli cells. These cells metamorphose into mature sperm cells (spermatozoa) during spermiogenesis

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Spermatozoa

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mature sperm cells with condensed darkly stained heads and filamentous tails. They are located in the lumen of the seminiferous tubules.

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Sertoli (sustentacular) cells

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tall, irregular columnar cells. Its base sits on the basement membrane and its apex extends towards the lumen of the tubule. It has a large, pale nucleus and numerous spermatids embedded in its supranuclear cytoplasm.

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Interstitial cells (of Leydig)

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cells located outside/ between seminiferous tubules. They are responsible for the production of testosterone.

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SPERMIOGENESIS

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the transformation of the spermatids into spermatozoa. During this stage, the spermatids which resemble a typical cell undergo structural changes (streamlining) to become a spermatozoon consisting of a head, middle piece, neck and tail.

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Fate of the spermatids’ cellular components

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1. Golgi apparatus- becomes the acrosome2. Nucleus- becomes the head3. Centriole-(proximal) becomes the neck4. Mitochondria- becomes the middle piece5. Microtubules- becomes the tail

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becomes the acrosome

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Fate of the spermatids’ Golgi apparatus

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becomes the head

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Fate of the spermatids’ Nucleus

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(proximal) becomes the neck

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Fate of the spermatids’ Centriole

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becomes the middle piece

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Fate of the spermatids’ Mitochondria

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becomes the tail

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Fate of the spermatids’ Microtubules

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Species variation

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The sperm of all animal species are comprised of the same parts however, they differ in appearance due to the variations in the shape of the head. This is brought about by variations in the shape of the nucleus.

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Rat sperm

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the head of this is approximately 2.5µm long and resembles a hook

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Rat sperm

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contains a dense nucleus and has a less dense tip referred to as the acrosome

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Rat sperm

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mid-piece contains the centrioles and a spirally coiled sheath of mitochondrial material

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Rat sperm

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tail contains a long axial filament that becomes vibratile for a brief period when the spermatozoon is mature

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Rat sperm

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occasionally the centriole may be visible, and is seen approximately halfway along the tail and should not be noted as an abnormality

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Bull sperm

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this and human sperm have paddle-shaped heads

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Rooster sperm

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The body structures of poultry spermatozoa differ from those of mammals. Their membrane surfaces are wider, their cytoplasm is less, and their flagellum is longer (SANTIAGO-MORENO et al., 2016)

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Rooster sperm

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A vermiform sperm head morphology (long and narrow) is very apparent in galliformes (chicken, quail, and partridges)

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Pig sperm

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are (mostly) symmetrical about the anterior-posterior axis.

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Pig sperm

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The spermatozoon of the boar closely resembles that of other domestic ungulates.

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Stallion sperm

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The equine spermatozoon head is defined as spatulate-shaped, in contrast to the falciform-shaped spermatozoal heads characteristic of some species (e.g. the mouse, rat and hamster)

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OOGENESIS

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the production of female gametes from the oogonia in the ovary

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OOGENESIS

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During the animal’s embryonic life, the oogonia undergoes mitosis to produce many daughter oogonia. This process ceases after the fetus’ delivery resulting to a fixed number of oogonia during its entire life.

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OOGENESIS

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primary oocytes and follicular cells in the ovary both originate from the oogonium

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OOGENESIS

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Oogonia which has grown bigger and entered the prophase stage of meiosis become primary oocytes while those that failed to enter this stage become follicular cells

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OOGENESIS

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Follicular cells are the small cells that surround the primary oocyte

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OOGENESIS

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the primary oocyte together with the surrounding follicular cells are collectively called an ovarian follicle.

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OOGENESIS

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Upon sexual maturity, the suspended meiotic activity of the primary oocyte continues

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OOGENESIS

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after its completion, a secondary oocyte and a first polar body is produced.

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OOGENESIS

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Polar body will degenerate and the secondary oocyte will further divide to give rise to the ovum and a second polar body.

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OOGENESIS

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The second polar body will also degenerate while the ovum will be released for possible fertilization

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Primordial follicle

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small follicle composed of a primary oocyte surrounded by a single layer of small, flat follicular cells

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Primordial follicle

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located at the marginal area of the ovary.

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Primordial follicle

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composed of an oocyte covered with a single layer of cuboidal or columnar follicular cells thus relatively larger than the primordial follicle.

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Primordial follicle

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located in the same area with the primordial follicle.

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Growing follicle

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Mature(Graafian) follicle

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Parts of the Ovary

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Cortex, Medulla, Tunica albuginea

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Cortex

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peripheral region of the ovary containing ovarian follicles, primordial follicles and germinal epithelium

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Medulla

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central portion of the ovary containing blood vessels

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Tunica albuginea

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dense fibrous layer of connective tissue at the outer margin of the ovary

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Follicular cells

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these are the small cells that surround the primary oocyte

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oogonium

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primary oocytes and follicular cells in the ovary both originate from the _________

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ovarian follicle

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the primary oocyte together with the surrounding follicular cells are collectively called an _________.