Human Reproduction

<body topmargin=0 leftmargin=0 marginheight=0 marginwidth=0> <table cellpadding=0 cellspacing=0 border=0><tr> <td valign="top" colspan=2 height=90 BGCOLOR="#006699" TEXT="#080000" bgproperties="fixed" background="02c285a1erlcgo.png"> <div> <FONT SIZE="5" COLOR="#FFCC66" FACE="Arial" ><B>Mr. Manning's Life Science Class</B></FONT><B>     |     </B><A HREF="index.htm" TARGET="_top" TITLE="Mr. Mannings Life Science Class"><B>home</B></A></div> <div>                                                   </div> <div> </div> </td> </tr><tr> <td valign="top" width=210 BGCOLOR="#FFCC66" TEXT="#080000" background="02ad2c00dkelyh.png"> <div> <A HREF="id138_m.htm#human_reproduction" TARGET="TRLX_Middle" TITLE="Human Reproduction">Human Reproduction</A></div> <div> <A HREF="id138_m.htm#production_of_gametes" TARGET="TRLX_Middle" TITLE="Human Reproduction">Production of Gametes</A></div> <div> <A HREF="id138_m.htm#testis_1" TARGET="TRLX_Middle" TITLE="Human Reproduction">Testis</A></div> <div> <A HREF="id138_m.htm#spermatogenesis" TARGET="TRLX_Middle" TITLE="Human Reproduction">Spermatogenesis</A></div> <div> <A HREF="id138_m.htm#role_of_hormones" TARGET="TRLX_Middle" TITLE="Human Reproduction">Role of Hormones</A></div> <div> <A HREF="id138_m.htm#structure_of_ovary" TARGET="TRLX_Middle" TITLE="Human Reproduction">Structure of Ovary</A></div> <div> <A HREF="id138_m.htm#oogenesis" TARGET="TRLX_Middle" TITLE="Human Reproduction">Oogenesis</A></div> <div> <A HREF="id138_m.htm#mature_sperm_and_egg" TARGET="TRLX_Middle" TITLE="Human Reproduction">Mature Sperm and Egg</A></div> <div> <A HREF="id138_m.htm#sperm" TARGET="TRLX_Middle" TITLE="Human Reproduction">Sperm</A></div> <div> <A HREF="id138_m.htm#egg" TARGET="TRLX_Middle" TITLE="Human Reproduction">Egg</A></div> <div> <A HREF="id138_m.htm#production_of_semen" TARGET="TRLX_Middle" TITLE="Human Reproduction">Production of Semen</A></div> <div> <A HREF="id138_m.htm#spematogenesis_vs__oogenesis" TARGET="TRLX_Middle" TITLE="Human Reproduction">Spematogenesis vs. Oogenesis</A></div> <div> <A HREF="id138_m.htm#fertilisation_and_pregnancy" TARGET="TRLX_Middle" TITLE="Human Reproduction">Fertilisation and Pregnancy</A></div> <div> <A HREF="id138_m.htm#fertilisation" TARGET="TRLX_Middle" TITLE="Human Reproduction">Fertilisation</A></div> <div> <A HREF="id138_m.htm#role_of_human_chorionic_gonadotropin" TARGET="TRLX_Middle" TITLE="Human Reproduction">Role of Human Chorionic Gonadotropin</A></div> <div> <A HREF="id138_m.htm#placenta" TARGET="TRLX_Middle" TITLE="Human Reproduction">Placenta</A></div> <bR> <bR> </td> <td valign="top" height=390 width="100%" BGCOLOR="#FFFFFF" TEXT="#080000"> <div> <I>Human Reproduction</I></div> <div> <I><B> <A NAME="human_reproduction"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A></B></I><I><B>Human Reproduction</B></I></div> <div> <I> <A NAME="production_of_gametes"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A></I><I><B>Production of Gametes</B></I></div> <div>  <A NAME="testis_1"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A><I><B>Testis</B></I></div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">consist of many seminiferous tubules </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">find interstitial cells and blood capillaries between them </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">have outer germ cell layer surrounded by “basement membrane” </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">developing spermatozoa nourished by Sertoli cells </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">eventually leave tubule via lumen </div> <div>  <A NAME="spermatogenesis"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A><I><B>Spermatogenesis</B></I></div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Primordial Germ Cells of the embryonic testes differentiate into Spermatogonia, which are Diploid Cells, and are a precursor to Sperm </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Near the outer wall of the Seminiferous Tubules, the Spermatogonia undergo REPEATED MITOSES. This ensures a large population of potential Sperm </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">About 3 million Spermatogonia per day differentiate into Primary Spermatocytes that are Diploid (2n) </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Primary Sprematocytes undergo the first division of Meiosis </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">This results in Secondary Sprematocytes that are Haploid (n) </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">They contain only 2 chromosomes </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">These 2 chromosomes are duplicated (each containing two identical chromatids) </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">The second Meiotic division produces four spermatids, each with 2 single chromosomes </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">These are known as Spermatids </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Spermatids differentiate into mature spermatozoa, also known as SPERM CELLS </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Differentiation is accomplished by associating the developing Sperm with large Sertoli Cells </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Sertoli Cells transfer nutrients to the Spermatids </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">During Spermatogenesis, developing Sperm are gradually pushed to the center of the seminiferous tubule and then the Epididymis where Motility is acquired </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Entire process takes 65 to 75 days </div> <div>  <A NAME="role_of_hormones"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A><I><B>Role of Hormones</B></I></div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">The pituitary, secretes two gonadotropic hormones which have effects on the Testes: </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Lutenizing Hormone (LH): Stimulates Androgen production (such as testosterone) by the Interstitial Cells </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Since Androgens are required for Sperm production, LH stimulates Spermatogenesis indirectly. </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">FollicleStimulating Hormone (FSH); acts on Seminiferous tubules to increase Spermatogenesis </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Gonadotropinreleasing Hormone (GnRH): controls the release of LH and FSH </div> <div>  <A NAME="structure_of_ovary"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A><I><B>Structure of Ovary</B></I></div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Ovaries contain follicles in different stages of development (which contain developing Oocytes) </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Developing follicles are known as Graafian follicles </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Developing Oocytes are surrounded by Zona Pellucida </div> <div> <I><B> <A NAME="oogenesis"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A></B></I><I><B>Oogenesis</B></I></div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Primordial Germ Cell (diploid) in Embryo undergo Mitosis, which results in Oogonia (Diploid) </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Each Oogonium develops into a Primary Oocyte (Diploid) </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Starting at puberty, a single primary Oocyte completes Meiosis I each month </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">The Meiotic divisions of Oogenesis involve unequal Cytokenisis </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Fist Meiotic division produces a large cell (called the Secondary Oocyte, a Haploid), and a small Polar body </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Second Meiotic division occurs only if a Sperm cell penetrates the Secondary Oocyte. If this occurs, this Meiosis will result in the Ovum, and another small Polar body </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Once Meiosis is complete, and the second Polar body separates from the Ovum, the Haploid nuclei of the Sperm and the mature Ovum fuse (this is fertilization) </div> <div>  <A NAME="mature_sperm_and_egg"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A><I><B>Mature Sperm and Egg</B></I></div> <div> <I><B> <A NAME="sperm"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A></B></I><I><B>Sperm</B></I>:</div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Head: Contains the Nucleus and the Acrosome </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Neck connects Head to the Middle Piece </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Middle Piece: Contains a Mitochondrion which is in a spiral </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Tail: Flagellum that propels the sperm, surrounded by Plasma Membrane </div> <div> <I><B> <A NAME="egg"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A></B></I><I><B>Egg</B></I>:</div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Contains a follicle and the Oocyte </div> <div>  <A NAME="production_of_semen"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A><I><B>Production of Semen</B></I></div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Sperm Cells are produced in the Seminiferous tubules, and travel to the head of the Epididymis </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Sperm matures </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Sperm becomes Motile </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Sperm is concentrated since fluid that was produced by the Sertoli cells in the Seminiferous Tubules and carried the Sperm to the Epididymis is reabsorbed </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Most of the fluid in the semen is produced by the Seminal Vesicles </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Contains Fructose (energy) </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Prostaglandins (cause contractions in female reproductive system and helps sperm move towards egg) </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Prostate produces fluid that forms part of the ejaculate </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Alkaline fluid which helps reduced the acidic environment (pH 6) of the female reproductive system to a pH of 4, which is the ideal pH for Sperm </div> <div>  <A NAME="spematogenesis_vs__oogenesis"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A><I><B>Spematogenesis vs. Oogenesis</B></I></div> <div> Three major differences between Oogenesis and Spermatogenesis:</div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Cytokinesis stage of Meiotic divisions in Oogenesis is unequal </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Almost all cytoplasm is taken in forming a single daughter cell, the Secondary Oocyte (which can go on to become the Ovum), whereas little is dedicated to the formation of a small Polar body (that degenerates) </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">In Spermatogenesis, all 4 products of Meiosis I and Meiosis II mature and develop into Sperm </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">In Spermatogenesis, the cells from which sperm develop divide continually through Mitosis throughout the male’s reproductive years </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">In females, the ovary already contains all the cells it will ever have that will develop into eggs </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Oogenesis undergoes long “resting” periods of inactivity </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Spermatogenesis produces mature sperm from precursor cells in an uninterrupted sequence </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Other differences: </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Spermatogenesis results in 4 sperm cells from 1 Primary Spermatocyte </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Oogenesis results in 1 Ovum from 1 primary Oocyte </div> <div> <I> <A NAME="fertilisation_and_pregnancy"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A></I><I><B>Fertilisation and Pregnancy</B></I></div> <div>  <A NAME="fertilisation"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A><I><B>Fertilisation</B></I></div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Acrosomal reaction: </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">The sperm cell contacts the egg’s jelly coat </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Acrosome in the head of the sperm releases Hydrolytic enzymes </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Enzymes excavate a hole in the jelly coat </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Actin polymerizes and creates an extension from the sperm head (this extension is known as the Acrosomal process) </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">The Acrosomal process extends through the jelly coat and binds to the Vitelline layer of the Egg </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Acrosomal process makes contact with the egg’s plasma membrane </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Penetration </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Plasma membranes of the sperm and egg fuse as a result of Acrosomal reaction </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Nucleus of the sperm enters the cytoplasm of the egg </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Fusion of the gamete membranes triggers: </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Electric change in the plasma membrane of the egg </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Ion channels open, which allow sodium ions to flow into the egg cell and change the membrane potential. The membrane depolarization takes place 13 seconds after the sperm cell binds to the Vitelline layer. This is also known as the <I><B>Fast Block to Polyspermy</B></I> since it prevents any other sperm cells from fusing with the egg’s plasma membrane </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Cortical reaction </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Cortical granules in egg fuse with the plasma membrane and discharge enzymes and macromolecules that raise and harden the Vitelline layer, effectively forming a spermproof fertilization membrane </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">When the sperm and egg fuse, there is a release of a G Protein that triggers the release of Calcium </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Calcium acts as a messenger and effects change in the Cortical Granules </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Cortical Granules fuse with plasma membrane and release their contents </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Vitelline layer separates from Plasma Membrane </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Osmotic difference draws water in, thereby swelling the Vitelline layer </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Other enzymes harden the Vitelline layer </div> <div>  <A NAME="role_of_human_chorionic_gonadotropin"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A><I><B>Role of Human Chorionic Gonadotropin</B></I></div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Following fertilization, and the fusion of the Blastocyst to the Endometrium, the outer cells of the Blastocyst secrete Human Chorionic Gonadotropin (HCG) </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">HCG sustains the Corpus Luteum, which in turn continues to produce Progesterone, thereby maintaining the Endometrium </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">HCG is excreted in the urine and can be detected by a pregnancy test </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Stick lined with HCG antibodies and pigment is dipped in urine </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">If HCG is present, antibodies bind to the HCG and this complex of HCGantibodiespigment travels to the other end of the stick where a second group of FIXED antibodies are found </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">HCGantibodiespigment attaches to second set of antibodies, and blue line of pigment appears </div> <div>  <A NAME="placenta"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A><I><B>Placenta</B></I></div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Placenta </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">A combination of maternal and embryonic tissues, transport nutrients, respitory gases, and wastes to and from the embryo or fetus </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Maternal blood enters the placenta in arterioles, flows through blood pools in the endometrium, and leaves via the venules </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Embryonic (or fetal) blood remains in vessels and enters the placenta through arteries and passes through the capillaries in fingerlike chorionic villi, where oxygen and nutrients are acquired </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Fetal (Embryonic) capillaries and villi project into the maternal portion of the placenta </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Embryonic (Fetal) blood laves the placenta through veins leading back to the embryo </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Materials are exchanged via diffusion, active transport, and selective absorption between the Embryonic capillary bed and the maternal blood cells </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Hormonal role </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.png" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Once the Corpus Luteum deteriorates, the Placenta begins releasing its own Progesterone, which maintains the pregnancy by sustaining the Endometrium and inhibiting the release of FSH </div> <bR> </td> </tr></table></body>