Fertilization and Fetal Development PDF

FERTILIZATION AND FETAL DEVELOPMENT PREPARED BY: TYSEER MARZOUK  FERTILIZATION & STAGES OF FETAL DEVELOPMENT 1.GAMETOGENESIS 2.CONCEPTION 3.PRE-EMBRYONIC PERIOD 4.EMBRYONIC PERIOD 5.FETAL PERIOD. 6.AUXILIARY STRUCTURES. 1. Gametogenesis Is the development of ova...

FERTILIZATION AND FETAL DEVELOPMENT PREPARED BY: TYSEER MARZOUK  FERTILIZATION & STAGES OF FETAL DEVELOPMENT 1.GAMETOGENESIS 2.CONCEPTION 3.PRE-EMBRYONIC PERIOD 4.EMBRYONIC PERIOD 5.FETAL PERIOD. 6.AUXILIARY STRUCTURES. 1. Gametogenesis Is the development of ova in the woman and sperm in the man. Oogenesis Defined as the formation of female gametes (ova) within the ovary. Oogenesis begins during prenatal life. By the 30th week of gestation, the female fetus has all the ova she will ever have. Spermatogenesis Defined as the formation of sperm, or male gametes, in the testes. It begins during puberty in the male and requires about 70 days to be completed. Spermatogenesis Defined as the formation of sperm, or male gametes, in the testes. It begins during puberty in the male and requires about 70 days to be completed. The gamete from a male determines the gender of the new baby because the ovum carries only an X chromosome. Each mature sperm contains 23 chromosomes: 22 autosomes and either an X or a Y chromosome. If an X bearing spermatozoon fertilizes the ovum, the baby is a girl. If a Y-bearing spermatozoon fertilizes the ovum, the baby is a boy. 2. Conception Natural conception is the interaction of many factors, including correct timing between release of a mature ovum at ovulation and ejaculation (semen expulsion) of enough healthy, mature, motile sperm into the vagina. a. Preparation for Conception in the Female This is attained by release of the ovum and ovum transport. Release of the Ovum Ovulation occurs approximately 14 days before a woman’s next menstrual period would begin. Ovum Transport The ovum is transported through the tube by the muscular action of the tube and movement of cilia within the tube. Fertilization normally occurs in the ampulla. b. Preparation for Conception in the Male This is attained by the following steps: 1. Ejaculation The male ejaculates during sexual intercourse, 35 to 200 millions sperms. Sperms are deposited in the upper vagina and over the cervix. The sperm are suspended in 2 to 5 milliliters (mL) of seminal fluid, which nourishes and protects the sperm from the acidic environment of the vagina. 2. Transport of Sperm in the Female Reproductive Tract The whip like movement of the tails of spermatozoa propels them through the cervix, uterus, and fallopian tubes. Uterine contractions induced by prostaglandins in the seminal fluid enhance movement of the sperm toward the ovum. 3. Preparation of Sperms for Fertilization The sperms undergo changes that enable one of them to penetrate the protective layers surrounding the ovum, a process called capacitation. During capacitation, a glycoprotein coat and seminal proteins are removed from the acrosome. After capacitation, the sperm are more active and can better penetrate the corona radiata and zona pellucida surrounding the ovum. The sperm that reach the ovum release hyaluronidase and acrosin to digest a pathway through the corona radiata and zona pellucida. Their tails beat harder to propel them toward the center of the ovum. Eventually, one spermatozoon penetrates the ovum. c. Fertilization Means entry of one spermatozoon into the ovum and the two nuclei containing the parents’ chromosomes merge. After entry of a spermatozoon into the ovum: 1. The zona pellucida surrounding the ovum prevent other sperm from entering. 2. The cell membranes of the ovum and sperm fuse and break down, allowing the contents of the sperm head to enter the cytoplasm of the ovum.  Fetal developmental stages 1. Preembryonic period The preembryonic period is the first 2 weeks after conception. Around the fourth day after conception, the fertilized ovum, called a zygote, enters the uterus. 2. Embryonic period The embryonic period of development extends from the beginning of the third week through the eighth week after conception. Basic structures of all major body organs are completed during the embryonic period. Differentiation of Cells The embryo (developing baby from the beginning of the third week through the eighth week after conception) progresses from undifferentiated cells with essentially identical functions to differentiated cells. By the end of the eighth week, all major organ systems are in place, and many are functioning, although in a simple way. 3. Fetal period The fetal period begins 9 weeks after conception and ends with birth. All major systems are present in their basic form. Further growth and refinement in the structure and function of all organ systems occur during the fetal period.  Auxiliary structures Three auxiliary structures sustain the pregnancy and permit normal prenatal development: 1. The placenta. 2. The umbilical cord. 3. Fetal membranes. 1.The Placenta The placenta is a thick, disc-shaped organ. The placenta has two components: maternal and fetal. It is involved in: 1. Metabolic functions 2. Transfer functions 3. Endocrine functions. 2. Fetal Membranes and Amniotic Fluid The two fetal membranes are the amnion (inner membrane) and the chorion (outer membrane). Sources of the amniotic fluid: (1) Fetal urine. (2) Fluid transported from the maternal blood across the amnion. Amniotic fluid functions 1. It protects the growing fetus and promotes normal prenatal development. Allowing symmetric development. Preventing the membranes from adhering to developing fetal parts. Allowing room for fetal movement. 2. Maintaining a stable temperature. The amniotic fluid volume Normally, it increases during pregnancy and is approximately 700 to 800 mL at 40 weeks. An abnormally decrease quantity of fluid (less than 50% of the amount expected for gestation, or under 400 mL at term) is called oligohydramnios and may be associated with the following: o Poor placental blood flow. o Preterm membranes rupture. o Failure of fetal kidney development. o Blocked urinary excretion. o Poor fetal lung development. An abnormally increase quantity of fluid is called Polyhydramnios, in which the quantity may exceed 2000 mL. Hydramnios may be associated with the following: Imbalanced water exchange between mother, fetus, and amniotic fluid that has no known cause. Poorly controlled maternal diabetes mellitus that results in large quantities of fetal urine excretion having an elevated glucose level. Malformations of the CNS, cardiovascular system, or gastrointestinal tract. Chromosomal abnormalities and multifetal gestation. 3. Umbilical Cord The fetal umbilical cord is the lifeline between the fetus and placenta. It has two arteries that carry deoxygenated blood and waste products away from the fetus to the placenta, where these substances are transferred to the mother’s circulation. The umbilical vein carries freshly oxygenated blood from the placenta back to the fetus.  The umbilical arteries and vein are coiled within the cord to allow them to stretch and prevent obstruction of blood flow through them. The entire cord is cushioned by a soft substance called Wharton’s jelly to prevent obstruction resulting from pressure. THANK YOU