Human Conception PDF

**Human Conception** 1. ​After ejaculation, spermatozoon enters the vagina to unite with the ovum in the Ampulla (outer third fallopian tube) for fertilization. 2. ​Only one sperm can penetrate the ovum. The ovum automatically changes its composition to become impervious to other sperms....

**Human Conception** 1. ​After ejaculation, spermatozoon enters the vagina to unite with the ovum in the Ampulla (outer third fallopian tube) for fertilization. 2. ​Only one sperm can penetrate the ovum. The ovum automatically changes its composition to become impervious to other sperms. Sperms release an enzyme to penetrate the ovum. (Hyaluronidase) 3. ​After the union of sperm and ovum, a zygote is formed. For male, we have X and Y. On the other hand for female, we have X and X. 4. ​The zygote then travel for 3-4 days through muscle contraction of the fallopian tube until it reaches the body of the uterus. 5. ​The zygote then becomes a morula through cell division or "cleavage". (mulberry or clusters of cell formed through cell division). Morula is made out of 16-50 cells. (From Latin word *morus.)* 6. ​Implantation happens when morula then becomes blastocysts and is attached or burrowed to the uterine endometrium via enzymes. 7. ​Once the blastocysts is attached in the uterine endometrium, **(implantation)** the cells in the outer ring is called **Trophoblast cells.** 8. ​Trophoblast becomes placenta and membrane and the inner cell mass becomes the embryo. - Pre embryonic -- first 2 weeks, begins with fertilization - Embryonic -- week 3 through week 8 - Fetal- from week 8 through birth **Fertilization** - ​Beginning of pregnancy - ​Conception, impregnation, fecundation - ​Union of ovum and spermatozoon - ​Occur in the outer third fallopian tube - ​Sperm is functional until 3 days or 72 hours - ​Ovum can be fertilized until 2 days or 48 hour - Ovum is extruded from the Graafian follicle with an ovulation **Ejaculation** - ​Semen averages 2.5 ml of fluid containing 50 to 200 million spermatozoa per milliliter or an average of 400 million sperm per ejaculation. **Ovum** - Zona pellucida- rin of mucopolysacharide - Corona radiate- circle of cells - Ovum is propelled into the fallopian tube through combination of [peristaltic action] of the tube and the movement of the tube [cilia] **Sperm** - Spermatozoa deposited in vagina reach the cervix within 90 seconds - Reach the fallopian tube within 5 minute after depositon - Move by flagella (tails) and [uterine contractions] - **Hyaluronidase**- proteolytic [enzyme] released by sperm to penetrate the zona pellucida **Hyatidiform mole- [ ]**[multiple sperms] enter the ovum and leads to abnormal zygote formation **Factors for fertilization not to occur:** 1. ​Equal maturation of sperm and ovum 2. ​Ability of sperm to reach ovum 3. ​Ability of sperm to penetrate the zona pellucida 4. ​And cell membrane to achieve fertilization. **Terms used to denote fetal growth** - ​Ovum- from ovulation to fertilization - ​Zygote- from fertilization to implantation - ​Embryo- from implantation to 5-8 weeks - ​Fetus- from 5-8 weeks to term - ​Conceptus- developing embryo/ fetus and placental structures throughout pregnancy - ​[Age of viability]- earliest age of which fetus could survive if they were born at the time, generally accepted at 24 weeks for fetus weighing more than 400 grams. **Capacitation** - final phase process that sperm must undergo to be ready for fertilization - ​Sperm moves toward ovum, consist of changes in plasma membrane of the sperm head that reveals the [sperm- binding receptors.] **Implantation** - Occurs 8-10 days after fertilization - also referred to as "Nidation" - ​Zygote is called embryo (5-8 weeks) - ​Spotting on early pregnancy- due to the capillaries being ruptured by implanting trophoblast cells. - Once implanted, the zygote is called an embryo **Phases of Implantation** 1. ​[Apposition]- brushing of the blastocysts against uterine endometrium. 2. ​[Adhesion]- attaching to the surface (with the help of enzymes) 3. ​[Invasion]- settling down into its soft tissue folds **3 seperate parts of Decidua** - Decidua- Latin word meaning "falling off" - HCG- growth and thickness of endometrium 1. ​*Decidua basalis*- part of endometrium that lies under the embryo 2. ​*Decidua capsularis*- portion of endometrium that stretches and encapsulates the surface of trophoblast 3. ​*Decidua Vera*- remaining portion of uterine lining **Chorionic Villi** - ​As early as **11^th^ and 12^th^** day, miniature villi reach out from the single layer of cells into the uterine endometrium [to begin the formation of placenta.] - ​Begin the formation of placenta - ​All Chorionic Villi has **[central core]**. It contains **connective tissues and capillaries**. A [double layer of trophoblast cells] surrounds this. - **[Syncytial layer]**- The **outer** of the two covering layer that surrounds the chorionic villi that [produces placental hormones.] - **Langhan's layer** a. The **middle layer** or the **[cytotrophoblast,]** is present as early as the [12 days gestation]. b. **[Protects the growing embryo]** from certain infectious organisms such as the **[spirochete of syphilis]**. **Placenta** - ​Trophoblast tissue will become the placenta or "pancake" - Placenta servers as fetal lungs, kidneys and gastrointestinal tract - The placenta is measured [10-15 centimetres] **Placental circulation** - As early as the [12^th^ day of pregnancy], materal blood begins to collect in the intervillous spaces of the endometrium. - By the [3^rd^ week], oxygen and other nutrients osmose from the maternal blood through the cell layers of villi into the villi capillaries. From there, nutrients are transported to the developing embryo. - Because almost all drugs are able to cross into the fetal circulation, **[woman should not take nonessential drugs (alcohol, nicotine).]** - Because the process of osmosis is so effective, there is **no direct exchange of blood between the embryo and the mother** during pregnancy - In a mature placenta, there are a many as 30 separate segments or *cotyledons.* - Placental circulation, is most efficient when the woman is **[lying on her left side]**. This position lifts the uterine away from the inferior vena cava, preventing blood from being trapped in the women's lower extremities. - At term, the placental circulatory network has grown so extensively. It weighs **[400-600g or (1lb).]** **Mechanisms by which nutrients cross the the placenta** - **Diffusion**- [oxygen, carbon dioxide, sodium, and chloride] cross the placenta by this method. - **Facilitated diffusion**- substance cross the placenta guided by carrier. [Glucose] is an example. - **Active transport**- requires enzyme. Essential [amino acids and water-soluble vitamins] cross the placenta through this method. - **Pinocytosis**- [gamma globulin, lipoproteins, and phospholipids] cross through this. Also, [viruses] can enter through this process. **Endocrine function** [Hormones produced by the syncytial layer:] 1. Human Chorionic Gonadotropin - ​First placental hormone produced - ​Found in maternal blood/urine and can be detected as early as the first missed menstruation throughout the 100^th^ day of pregnancy - ​Ensures that corpus luteum continues to produces estrogen and progesterone - ​Suppress immune system of of mother 2. Estrogen - Second product of syncytial cells - ​Mammary gland development; for lactation - ​Development of uterus or growth of uterus 3. Progesterone - ​Hormone of women/pregnancy/mother - Changes on physical appearance of mother - ​Maintain endometrium lining of pregnancy - ​Increase on remainder of pregnancy to birth - ​Low in progesterone is bad because it increases contraction which can lead to early delivery (premature birth) 4. Human Placenta Lactogen - ​Growth promotion for uterus - ​Focuses on milk production - Regulate maternal glucose, protein, and fat levels for the fetus. - ​[At early 6 weeks ] I. **Milestone of Fetal Growth Development \[&pl9\]** **End of 4^th^ week** - ​Numerous cells are formed not to get resembling a human - ​1 cm, 400 grams - ​Forming of spinal cord - ​Fused/bent - ​Bulging of anterior surface ​**End of 8^th^ week** - \`2.5cm. 1 inch - Heart, valves, beat - ​Facial features - ​External genitary slowly forms (sex not yet determined) **End of 12^th^ week** - ​8 cm - ​Nail beds - ​Movement - ​Heartbeat is detected by Doppler - ​Reactive to light - ​Tooth buds - ​Sex is distinguished - ​Urine secretion ​ **End of 16^th^ week** - ​FHT heard by ordinary stethoscope - ​Sex can be determined **End of 20^th^ week** - ​Spontaneous fetal movement can be felt my mother - ​Vernix Caseosa begins to form - ​Definite sleeping pattern are distinguishable ​ **End of 24^th^ week** - ​Passive antibody transfer from the mmothe - ​Survival - ​Beating demonstrated ​ **End of 28^th^ week** - ​Lung aveoli mature - ​Testes begins to descend into socratal sac from lower abdominal cavity ​ **End 32^nd^ week** - ​Movement of sounds - ​Reflexes, active - ​Fingernails continue to grow **End of 36^th^ week** - ​Subcutaneous builds - ​Lanugo deminished ​ **End of 40^th^ week** - ​7-7.5 pounds - ​37 cm - ​Kicks - ​Fetal hemoglobin - ​Vernix caseosa **Additional terminologies** - ​Age of Gestation- measured primarily through learning the last menstrual period of the woman (ovulation age) - ​Last Menstrual Period (LPM)- first day of the last menstruation (gestational age) - ​EDB- Estimated Date of Birth - ​Naegles Rule- Length of Pregnancy - ​**Mc Donalds Rule**- symphysis fundal measurement ​ ​ ​