Physiology of Conception Lecture Notes PDF

Physiology of conception  Learning Objectives: At the end of this lecture, each student will be able to Define fertilization Identify the prerequisites for conception Explain the process of conception Recognize the development of the placenta and fetal membranes Out Line  Introduction...

Physiology of conception  Learning Objectives: At the end of this lecture, each student will be able to Define fertilization Identify the prerequisites for conception Explain the process of conception Recognize the development of the placenta and fetal membranes Out Line  Introduction  Define fertilization  The prerequisites for conception  The process of conception  The development of the placenta and fetal membranes Introduction: Every human cell contains 23 pairs of chromosome (homologous) except ovum &sperm, which contain 22 pairs of somatic chromosome and one pair of sex chromosome. In the female the sex chromosome are the same XX and in the male it different, the sperm may carry x or y. Definitions -Amniotic fluid : Is the Fluid contained in the amniotic sac, also called Liquor amnii and "waters". It is transparent or slightly yellow liquid and It protects the fetus from trauma; maintain body temperature& serves as source of oral fluid and waste repository -Oligo-hydramnios: Means the amount of amniotic fluid is less than the normal. -Polyhydramnios: Means the amount of amniotic fluid is greater than the normal. Fertilization Definition: It is the union of a sperm with an ovum in the fallopian tube. It takes place in the ampullary part of the fallopian tubes. 26 Prerequisites for conception: 1) Mature ovum 2) Mature spermatozoa 3) Capacitation and acrosome reaction of spermatozoa 4) Quality and quantity of spermatozoa 5) Meeting of sperm and ovum within 24 hrs. 27  Process of conception: Fertilization Divisions (cleavages) Implantation Development and formation of placenta a.Fertilization Each month one ovum matures, at the time of ovulation& considering fertile for about 24 hours after ovulation & remains viable for about 48 hours More than 100 million sperm\mL are contained in the ejaculated semen, The sperm swim with the flagellar movement of their tails. Some can reach to the ovum within 5 minutes.Sperm remain viable for about 2-3 days. 28 Only one is able to enter the ovum to fertilize it. With fertilization; (the nucleus from the ovum and the nucleus of the sperm make contact), this union restore the diploid number (46) of chromosomes and The resulting fertilized ovum called (Zygote).  The sex of the fetus is established depends on whether the ovum is fertilized by a Y- bearing sperm or an X- bearing sperm.  An XX zygote will become a female and an XY zygote will become a male 29  b.Divisions (Cleavages)  Cleavage refers to the rapid division of cells in the zygote following fertilization.  zygote continues its passage through the fallopian tube and reaches the uterus three days later to reach uterine cavity.  On its way to uterine cavity, cell division(Mitosis) takes place and the zygote divides into 2, 4, 8 then 16 cells. the 16 cells appear as solid ball of cells called morulla Within the morulla an fluid filled space appears, transforming it into a hollow ball of cells called a blastocyst. 32  The fluid filled cavity pushes some of the cells to one side and two layers are formed  The outer cells mass : This is the origin of the placenta (trophoblast)  The inner cell mass : becomes the fetus (embryoblast) Which of the following is the origin of the placenta? A. Inner cell mass B. Trophoblast C. Morula D. Blastomeres 33 34 c.Implantation  The blastocyst is the stage at which it embeds (implants)  At about the 7th day after fertilization or conception; the blastocyst settles on the endometrium to begin the process of implantation.  The endometrium after implantation is called the decidua  The decidua can be differentiated into 3 layers:  Decidua basalis is the area under the embedded ovum.  Decidua capsularis lies over the developing ovum.  Decidua Vera or true deciduas the reminder of the uterus. 35 36  After implantation, cell differentiation begins with in the inner cell mass  One cavity is known as the yolk sac that provides nourishment for the developing embryo for a brief time and then it disappears.  Another cavity is known as the amniotic sac and contains fluid that is later called amniotic fluid 37 In the embryonic area the following organization of germ cells occurs:  Ectoderm:mainly forms the skin, mucosa and nervous system.  Mesoderm: form bones, muscles, and heart blood vessels.  Endoderm: form mucous membranes, glands, and epithelium of the liver, pancreas, lungs & bladder. 38  d.Development and formation of the placenta  Three weeks after fertilization projections from the trophoblastic layer proliferate and branch forming the chorionic villi.  The villi become most profuse in the basal decidua where the blood supply is richest. This part is known as chorion frondosum and will develop into the placenta. The placenta is completely formed and functioning form 12 weeks after fertilization  Define fertilization List types of decidua List Prerequisites for conception List steps of conception process At what stage does the fertilized egg implant into the uterine lining? A. Zygote B. Morula C. Blastocyst D. Fetus Which event is the first step in conception? A. Implantation B. Ovulation C. Fertilization D. Cleavage An fluid filled space appears with in the morulla, transforming it into…….. A. Zygote B. blastomeres C. Blastocyst D. Fetus True or false question 1. The Inner cells mass is the origin of the placenta ( ) 2. Decidua basalis lies over the developing ovum ( ) 3. The fertilized ovum is called zygote ( )