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Human Reproductive Systems
Transcript of Human Reproductive Systems
The spermatogonia grow to form primary spermatocytes which have completed S-phase.
Diploid primary spermatocytes separate homologous pairs of chromosomes in meiosis I to form haploid secondary spermatocytes.
The spermatids are formed from the separation of the sister chromatids in meiosis II. The spermatids are found in association with the Sertoli cells, which nourish the spermatids as they differentiate into spermatozoa.
The rate of production of spermatozoa is high and continuous throughout the life on the sexually mature male. The average number of spermatozoa in ejaculated semen is 32 million per millilitre. Oogenesis Comparing Spermatogenesis & Oogenesis Differences:
Spermatogenesis occurs in the testes, while oogenesis occurs in the ovaries.
Spermatogenesis starts at puberty, while oogenesis starts during gestation (fetal development).
Spermatogenesis occurs until death, while oogenesis ceases at menopause.
Spermatogenesis occurs continuously, while oogenesis is cyclic (menstrual cycle).
Millions of sperm are created daily, while only one ovum (or two) is produced every 28 days.
Ejaculation of sperm can occur at any time, while ovulation only occurs once per menstrual cycle.
Sperm are produced by equal divisions, producing four spermatids, while unequal divisions in oogenesis result in the production of only one ovum.
Spermatogenesis doesn’t produce polar bodies, while oogenesis produces 2 or 3 polar bodies. Male Human
Reproduction Male vs Female
Systems & Gametes Penis &
Tissue The structure of a mature sperm: remember this is a single cell ~50 um long and 3 um wide at the 'head'.
The acrosome vesicle contains the enzymes required to digest its way though the ovum wall.
Haploid nuclei (n=23) containing the paternal chromosome set.
The 'mid-section' of the sperm contains many mitochondria which synthesis ATP to provide the energy for the movement of the tails structure.
Protein fibres add longitudinal rigidity and provide a mechanism of propulsion. Oogonia (2n) divide by mitosis to produce many oogonia. Each oogonium grows within a follicle.
Oogenesis begins during fetal development.
Meiosis begins but stops at prophase I. The oogonia are found within the primary follicles. There are approximately 400,000 primary follicles present in the ovary prior to puberty.
Primary follicles (prophase I) may develop to secondary follicles (metaphase II) under the influence of FSH as part of the menstrual cycle. Note that the first polar body does not progress beyond metaphase II. The oocyte does not progress to the end of meiosis unless fertilisation takes place. The image shows the structure of the egg (diameter ~100 um) at the point of fertilisation.
The haploid nucleus (arrested at metaphase II ) sits inside a cell with a large volume of cytoplasm (yolk).
During follicle development unequal division of the cytoplasm & organelles during meiosis produces the 1st polar body. This will not develop.
The Zona pellucida surrounds the structure and is composed of glycoproteins. With the cortical granules they will be involved in the acrosome reaction at fertilisation.
Around the outside are the follicular cells (Corona radiata). Similarities:
Both spermatogenesis & oogenesis involve mitosis and cell growth before undergoing meiosis.
The hormones LH and FSH are involved in regulation of both processes. Female Reproductive System Male Reproductive System