Stages of Fetal Development PDF

Mrs. Zuwiana Aal-Khlaifin  1. Describe the fertilization and Objectives implantation process. 2. Explain the embryonic and fetal structures. 3. Discuss the fetal circulation  Fertilization Is the union o...

Mrs. Zuwiana Aal-Khlaifin  1. Describe the fertilization and Objectives implantation process. 2. Explain the embryonic and fetal structures. 3. Discuss the fetal circulation  Fertilization Is the union of an ovum and spermatozoon  Mature Sperm Mature Ovum (spermatozoon)  Released in semen with  Extruded by Graafian follicle of an ovary ejaculation (400 millions with ovulation each month. sperm/ejaculation).  Functional life span ( capable for  Functional life span: about 48-72 fertilization): about 24-48 hours. hours.  Surrounded by : 1. Zona pellucida. 2. Corona radiata  Carries 23 chromosomes.  Carries 23 chromosomes. Where does fertilization take place?  The Process of Fertilization https://youtu.be/_5OvgQW6FG4 Ovulation Fimbria pickup the ovum toward fallopian tube. Fimbria Ovum moves along the tube to the ampulla portion  cont… The Process of Fertilization Sexual relation. Spermatozoa deposit in vagina. Fimbria Spermatozoa move toward the cervix ( in 90 secs)  cont… The Process of Fertilization Spermatozoa move toward the Fallopian tube (in 5 min). Millions of spermatozoa Fimbria will die thought the journey, Only thousands are able reach the ovum.  cont… The Process of Fertilization Spermatozoa cluster around the ovum. Spermatozoa release proteolytic enzyme (hyaluronidase) to dissolve Fimbria the corona radiata. One sperm will enter the ovum  cont… The Process of Fertilization Cell membranes of ovum changes composition to become impervious to other spermatozoa. The chromosomes of both ovum Fimbria and spermatozoon fuse together to form zygote. Implantation Is the contact between growing structure of fertilized ovum and the uterine endometrium. It occur approximately 8-10 days after fertilization. Implantation process The zygote migrates toward the body of the uterus. During migration: Mitotic cell division (cleavage) occur. 3-4 days: Large cells collect at the periphery. (blastocyst)  Cont… Implantation process 8-10 days: blastocyst sheds the last residues of the corona radiata and zona pellucida, brushes against the rich uterine endometrium and settles down into its folds.  Cont… Implantation process Immediately, blastocyst burrows deeply into the endometrium and establish effective communication network with the blood system of the endometrium Occasionally, a small amount of vaginal spotting appears on the day of implantation.  Embryonic and fetal structure The decidua or uterine lining Chorionic villi The placenta The amniotic membranes The amniotic fluid The umbilical cord  The decidua or uterine lining Is the endometrium of uterus which increases in thickness and vascularity after ovulation in preparation for implantation. It will not slough off due to progesterone hormone produced by the corpus luteum early in pregnancy.  Chorionic Villi Start to form from the trophoblast cells at 11 or 12 day after fertilization.  cont Chorionic Villi They provide connection between fetal blood circulation and mother blood circulation.  Cont… Chorionic Villi It has central core, consisting of : Connective tissue Fetal capillaries ( surrounded by double layers of cells which produce placental hormones: HCG, hPL, estrogen, progesterone)  Cont… Chorionic Villi The middle layer (cytotrophoblast) have a second function: to protect the growing embryo and fetus from certain infectious organisms (e.g; syphilis) early in pregnancy. The middle layer disappears between 20 and 24 week of pregnancy.  The placenta Grows from trophoblast cells. Diameter: 15-20 cm. Depth: 2-3 cm. Weight: 400-600 gms (one-sixth the weight of the newborn) Covering about half surface of the internal uterus.  The placenta  Function: 1- Provide Oxygen and nutrients for the for the fetus. 2- It produce hormones 3- It produce proteins Placental Circulation  12 days of pregnancy: maternal blood begins to collect in the intervillous spaces surrounding the chorionic villi. 3rd wk: oxygen and other nutrients (e.g; Placental glucose, amnio acids, fatty acids, Circulation minerals, vitamins, water) osmose from maternal blood through the cell layers of the chorionic villi into the villi capillaries. Then nutrients are transported to embryo.  The rate of utero-placental blood flow increases from 50ml/min at 10 wks to 500-600 ml/min at term. Placental Circulation 12 wks of pregnancy: Braxton Hicks contractions will be present to aid in maintaining pressure in the intervillous spaces.  Placental Hormones 1- Human chorionic Gonadotropin (hCG) Endocrine function of 2- Progesterone placenta 3- Estrogen 4- Human Placental Lactogen (hPL) [Human chorionic somatomammotropin]  Human chorionic Gonadotropin (hCG) Endocrine function of Function: placenta 1- To ensure the corpus luteum continuous to produce progesterone and estrogen to maintain the integrity of endometrium. 2- To Suppress the maternal immunologic response so placental tissue is not detected and rejected as a foreign substance. 3- If fetus is male, hCG exerts an effect on fetal testes to begin testosterone production and maturation of male reproductive tract. Endocrine Cont…. function of placenta Human chorionic Gonadotropin (hCG) By 8-16wks: The placenta begins to produce progesterone , making the corpus luteum no longer necessary. So, the production of hCG which sustain the corpus luteum begins to decrease at this point.  Progesterone: Function: 1- To maintain endometrial lining of the uterus Endocrine during pregnancy. function of placenta 2- To reduce the contractility of the uterus during pregnancy; preventing preterm labor. Endocrine Estrogen function of Referred as the hormone of women placenta Function: 1- It contributes to mammary gland development in preparation for lactation. 2- It stimulate uterine growth to accommodate the developing fetus  Human Placental Lactogen (hPL) Production begins at 6 wks. Endocrine Function: 1- It promotes mammary gland (breast) growth in function of preparation for lactation in the mother. placenta 2- It promote breast milk production. 3- It regulates maternal glucose , protein, and fat levels, so adequate amount of these nutrients are always available to the fetus.  Function: Placental 1- Decrease the immunologic impact of the growing placenta. proteins 2- Help prevent hypertension of pregnancy.  The Amniotic membranes  They are two membranes: 1- Chorion 2- Amnion Chorionic membrane form from the medial surface of chorionic villi of the trophoblast. Amniotic membrane form beneath the chorion. They have no nerve supply.  The Amniotic membranes Function: 1- Offer support to amniotic fluid. 2- Produces the amniotic fluid. 3- Produces phospholipid that initiate formation of prostaglandins to trigger the initiation of labor  The Amniotic Fluid  Produced by: 1- Fetal side of placenta 2- Fetal urine  Absorbed by: 1- Fetal side of placenta 2- Fetal swallowing  Cont… The Amniotic Fluid  Problems affecting fluid production: esophageal atresia 1- Diabetes ( in woman ) more fluid 2- Kidney problem ( in fetus) less fluid  Problems affecting fluid absorption: 1- Fetus is unable to swallow(e.g, in esophageal atresia, anencephaly) more fluid anencephaly  Cont… The Amniotic Fluid  Normal amount : 800-1200ml  Problems related to the amount of amniotic Fluid: Polyhydramnios (hydramnios): > 2000ml or AFI > 24 cm Oligohydramnios: AFI< 5cm Is amniotic fluid alkaline or acidic?  Cont… The Amniotic Fluid  Function: 1- It shield the fetus against pressure or a blow to mother’s abdomen. 2- It protect fetus from change in temperature. 3- It aid in muscular development for fetus. 4- It protects the umbilical cord from pressure, thus protecting the fetal oxygen supply.  The umbilical cord Formed from amniotic membranes ( amnion & chorion). It provides a circulatory pathway that connects the embryo to the chorionic villi of the placenta.  Cont… The umbilical cord Length at term: 52 cm (21 in). Thickness: 2cm (0.75 in) Bulk of the cord: is a gelatinous mucopolysaccharide (Wharton jelly)  Cont… The umbilical cord Blood vessels in the cord: One vein: carrying oxygenated blood from the placenta villi to the fetus. Two arteries: carrying unoxygenated blood from the fetus back to placental villi. Abnormalities in blood vessels : one vein and one artery this may indicate chromosomal disorders or congenital anomalies (particularly in kidney and heart)  Cont… The umbilical cord Rate of blood flow at term: 350 ml/min Function: 1- Transport oxygen and nutrients to the fetus from the placenta and return waste production from the fetus to the placenta  Cont… The umbilical cord  The abnormalities with the cord coiling: Hypercoiling Respiratory distress in newborn Hypocoiling Maternal hypertension. Fetal circulation  Fetal circulation Oxygenated blood Placenta Umbilical vein liver Ductus venosus Inferior vena cava Rt atrium  Fetal circulation Foramen ovale Lt atrium Lt ventricle Aorta Body parts  Fetal circulation  Small amount of blood that return to the heart via vena cava does leave rt atrium by adult circulatory route (RT atrium, RT ventricle, Pulmonary artery, Lungs, LT atrium, Lt ventricle, Aorta, Body part) However larger portion of even this blood, is shunted away from lungs through an additional structure, the ductus arteriosus, directly into the descending aorta.  Terms Used to Describe Fetal Growth Ovum: From Ovulation to fertilization. Zygote: From fertilization to implantation. Embryo: From implantation to 5-8 weeks. Fetus: From 5-8 weeks until term. Conceptus: Developing embryo and placental structure throughout pregnancy. Age of variability: The earliest age at which fetuses survive if they are born is generally accepted as 24 weeks or at the point a fetus weighs more than 500-600gm. Reference Silbert-Flagg and Pillitteri A (2018) Maternal & Child Health Nursing: Care of the Childbearing & childrearing family (8th edn) Philadelphia: Lippincott Williams and Wilkins. Page 526- 560