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LECTURE4: CONCEPTION AND PATURITION Objectives ofstudy 1. Todescribe the process ofconception 2. Todescribe the endocrine function of the placenta 3. Todescribethe mechanism of parturition 1. CONCEPTION/FERTILIZATION Fertilization: the process by which spermatozoa (unites with the ovum, it — ey ihe activities of multiple sperm; approximately 200 of the 2-6million sperm ejaculate reat n vicinity of the ovum in humans. Movement of sperm in female tract is governed by jagella movement of sperm tail, prostaglandin secretion from both mate and oxytocin secretion. Ovum penetration # Multiple sperms are necessary for disruption of the cumulus oophorus and corona radiate. Acrosomal hyaluronidase is essential in this disruption step. Then the sperm binds to human- specific glycoprotein spermreceptors on the zona pellucida and proteolytically cleaves a narrow path through the zona pellucida. The acrosomal enzyme acrosin is important for zona pellucid penetration. Sperm penetration into zona pellucida and then into vitelline membrane, increases ovum calcium uptake and enzyme‘containing cortical granules are extruded from the ovum into the vitelline space; where proteolytic enzymes alter the zona pellucida so that further sperm * penetration cannot occur, these changes are called the zona reaction, which prevents polyspermia. Ovum penetration is the stimulus for completion of the 24 meiotic division and the appearance of the 2°4 polar body in the perivitelline space is an index of fertilization. N.B: the period of fertilization is limited because the ovum remains viable for only about 24hours and sperm in the female reproductive tract have a maximal survival of 2-3 cas The fertilized ovum = zygote + ———+ morula ——>+ blastocyst Zygote divides mitotically to form a ball of cells called a morula, within the zona pellucid and remains in the ampulla‘of the fallopian tube for 3-4 da ys nourished by fallopian tube secretions. The movement of morula in the fallopian tube is hormonally regulated; estrogen accelerates development of the fallopian tube cilia and increases their beating, which draw the ovum into the fallopian tube. The morula then moves into the uterus and secrete fluid into a cavity called the blastocyst cavity. On formation of this cavity, the morula becomes a blastocyst. Ped ae contains two types of cells. There is an asymmetrically located inner cel! mass wil become the embryo and an outer concentric layer of trophoblast cells. The trophoblast will form the chorion. The portion of the i trophoblast adjacent to the inner f cell the chorion frondosum, and the remainder of the trophoblast forms the chorion ees ee 
