Spermatogenesis & Oogenesis Wright Chapter 3 & 4

Meiosis

Anatomy of Sperm & Testis

Human Male Testis Anatomy

Mammalian Testis

Human Testis – Seminiferous Tubules

Seminiferous Tubules

Monkey Testis

Human Testis

Female Ovarian Anatomy & Oocyte

28-19 Oogenesis and Fertilization Oogenesis is the production of a secondary oocyte in ovaries Oogonia are cells from which oocytes develop. The oogonia divide by mitosis to produce other oogonia and primary oocytes. Five million primary oocytes (2n) produced by the 4 th month of prenatal life. About 2 million begin first meiotic division but stop at prophase (2n). All remain at this state until puberty. Primary oocytes (2n) are surrounded by granulosa cells and called a primordial follicle Primordial follicle becomes a primary follicle when oocyte and granular cells enlarge Primary follicle becomes secondary follicle and enlarges to form mature or Graafian follicle –Usually only one is ovulated, others degenerate Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Zona pellucida Mesovarium Blood vessels Secondary follicle Degenerating follicle Medulla Mature follicle Corpus albicans Corpus luteum Primary follicles Granulosa cells Theca Primary oocyte Antrum Primary oocyte Primordial follicles Cortex Visceral peritoneum Tunica albuginea Vesicles

Oogenesis and Fertilization Ovulation 1 Oogonia give rise to oocytes. Before birth, oogonia multiply by mitosis. During Development of the fetus, many oogonia begin meiosis, but stop in prophase I and are now called primary oocytes. They remain in this state until puberty. Before birth, the primary oocytes become surrounded by a single layer of granulosa cells, creating a primordial follicle. These are present until puberty. After puberty, primordial follicles develop into primary follicles when the granulosa cells enlarge and increase in number. Secondary follicles form when fluid-filled vesicles develop and thecal cells arise on the outside of the follicle Mature follicles form when the vesicles create a single antrum. Just before ovulation, the primary oocyte completes meiosisI, creating a secondary oocyte and a nonviable polarbody. The secondary oocyte begins meiosisII, but stops at metaphase II. During ovulation, the secondary oocyte is released from the ovary. The secondary oocyte only completes meiosis II if it is fertilized by as permcell. The completion of meiosis II forms an oocyte and a second polar body. Fertilization is complete when the oocyte nucleus and the sperm cell nucleus unite, creating a zygote. Following ovulation, the granulos a cells divide rapidly and enlarge to form the corpus luteum. The corpus luteum degenerates to form a scar, orcorpus albicans. Oocyte MaturationFollicle MaturationAge Oogonia Before birth Primordial follicle Mitotic division 46 Birth to puberty Puberty to menopause Daughter cell 46 Primary oocyte 46 Primary oocyte Granulosa cells Number of primary oocytes decreases to 300,000 Fluid-filled vesicles Primary oocyte Granulosa cells Zonapellucida First meiotic division begins And then stops 1 2 Primary oocyte Zona pellucida Granulosa cells Theca Zonapellucida Cumuluscells Antrum Theca Mature(Graafian) follicle First meiotic division completed just before ovulation Granulosa cells being converted to corpus luteum cells Corpus luteum Secondary oocyte Secondary oocyte Firstpolarbody (maydivideto formtwopolar bodies) 23 Corpus albicans Secondmeiotic division begins and then stops Secondary oocyte Spermcell unites with secondary oocyte Zona pellucida Cumulus cells Zygote Fertilization 3 4 Secondary follicle Second Polar body Second meiotic division completed after sperm cell unites with the secondary oocyte Primary follicles Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display

28-21 Ovulation, Fertilization, Follicle Fate Ovulation: release of a secondary oocyte from an ovary. Unlike spermatogenesis, division of cytoplasm during meiosis is uneven and polar bodies are very small, oocyte very large Graafian follicle become corpus luteum Fertilization: begins when a sperm cell binds the plasma membrane of secondary oocytes and penetrates into cytoplasm. Secondary oocyte completes meiosis II forming one polar body. Fertilized egg now a zygote Fate of corpus luteum –If fertilization occurs, corpus luteum persists –If no fertilization, becomes corpus albicans

28-23 Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at

Mammalian Ovary (Human)

Primary & Secondary Follicle

Graafian Follicle