Final Reproduction

Can fertilize the egg capacitation wave whip like

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Unformatted text preview: sperm is inside woman The plasma membrane of the sperm becomes capable of fusing with the egg membrane Why all the sperm don’t make it • • Only Hundreds of the millions make it into ovary The vagina is acidic • • Although, the prostate gland in males adds a buffer to semen to help lower the acidity of the vagina It takes a lot of energy What happens when the sperm reach the egg • Many sperm make it through the granulosa cells and bind to the zona pellucida • • • This triggers an acrosomal reaction The sperm membrane changes and the acrosomal enzymes are exposed These enzymes chew through the zona pellucida – Tail pushes the sperm forward – First one to reach egg membrane binds to it Why only one makes it • • Polyspermy is prevented because once one sperm binds to the egg membrane, the egg membrane changes potential and this prevents additional sperm from binging Cortical Reaction: secretory vesicles around the edge of the membrane inactivate the sperm binding sites and harden the zona pellucida so that no other sperm can bind Post Fertilization • • • After the second meiotic division (secondary oocyte divides), a second polar body is extruded (the first was extruded when the primary oocyte divided into the secondary oocyte) This second polar body disintegrates 23 chromosomes from the egg and 23 chromosomes from the sperm migrate to the center of the egg Ectopic Pregnancy • • Egg is fertilized before it binds to the uterus (aka while its still in the fallopian tube) This pregnancy doesn’t last because not enough nutrients Implantation • As the zygote travels down the fallopian tube, cleavage occurs – – • • • No change in size All cells are totipotent Once in the ovary, morula floats free for about 3 days Differentiation begins in the ovary and a blastocyst is forms The blastocyst is implanted into the More on implantation • • The zygote develops into both the embryo and its surrounding tissues Enzymes enable the blastocyst to bury itself in the endometrium – • Trophoblast invades Interaction of the blastocyst and endometrium results in the release of several chemical messengers Corpus Luteum • • • • If the egg IS fertilized, the corpus luteum still eventually degenerates, it just takes longer Human chorionic gonadotropin (hCG) hormone rescues the corpus luteum hCG is what is detected by pregnancy tests hCG is released from trophoblast cells Nutrients • • The endometrium provides nutrients for the embryo for the first few weeks Then the placenta takes over – • • The outer ring of the trophoblast (called chorion cells) make up the placenta The placenta is what interlocks the fetal and maternal tissue Chorionic villi extend from the chorion cells into the endometrium (tree like) Amniotic Sac • Amniotic fluid is similar to fetal extracellular fluid – Buffers mechanical disturbances – Buffers temperature variations Hormone Regulation • • • hCG (from trophoblasts in the zy...
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This note was uploaded on 09/27/2013 for the course ZOO 305 taught by Professor Schaeffer during the Spring '08 term at Miami University.

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