Fetal Development PDF

Introduction: Fetal development during pregnancy is measured in number of weeks after fertilization. An average human pregnancy lasts for about 280 days or 40 weeks from the date of the last menstrual period (LMP), estimated date of birth (EDB), sometimes referred to as the estimated date of deliv...

Introduction: Fetal development during pregnancy is measured in number of weeks after fertilization. An average human pregnancy lasts for about 280 days or 40 weeks from the date of the last menstrual period (LMP), estimated date of birth (EDB), sometimes referred to as the estimated date of delivery (EDD). pregnancy is calculated to last an average of 10 lunar months Fertilization The Process of Fertilization: is the process by which a sperm fuses with an ovum to form a new diploid cell, or zygote. The zygote begins life as a single cell with a complete set of genetic material, 23 chromosomes from the mother’s ovum and 23 chromosomes from the father’s sperm for a total of 46 chromosomes. Gestation Period The three stages of fetal development during pregnancy are the 1) Germinal Period – Pre-embryonic stage begins at fertilization and extends till the 2nd week. 2) Embryonic period – This extend from 3rd ~ 8th week, involving changes in shape and external appearance. 3) Fetal period – This extends from (9th wks) 3rd month up to termination of pregnancy. Development of supportive structures of fetus & Major Events  Pre-embryonic Development Fertilization takes place in ampulla of the fallopian tube. Union of sperm and ovum forms a zygote (46 chromosomes). Cleavage cell division continues to form a morula (mass of 16 cells). The inner cell mass is called a blastocyst, which forms the embryo and amnion. The outer cell mass is called a trophoblast, which forms the placenta and chorion. Implantation occurs 7 to 10 days after conception in the endometrium After Fertilization: Cleavage Division: The process of repeated mitotic division results in increase of number of cells known as Cleavage give rise to blastomere. Formation of morula and blastocyst: blastomere form compact ball called morula. The center of morula is inner cell mass. Blastocyst: The cells of morula continue to divide and forms blastocele. Implantation of blastocyst: Blastocyst attaches to endometrium and implantation takes place on 7th ~ 10th day after fertilization. Implantation: an event that occurs early in pregnancy th th (7 -10 days after fertilization) in which the human embryo(blastocyst) adheres to the wall of the uterus. The lining of the uterus thickens below the implanted trophoblast, and the cells of the trophoblast grow down into the thickened lining, forming processes called chorionic villi. After implantation, the endometrium is called the decidua. About 10 to 14 days after conception, the homogenous mass of blastocyst cells differentiates into the primary germ layers. These layers: the ectoderm, mesoderm, and endoderm  Three embryonic layers of cells formed are: 1. Ectoderm: forms the central nervous system, special senses, skin, and glands. 2. Mesoderm: forms the skeletal, urinary, circulatory, and reproductive organs 3. Endoderm: forms the respiratory system, liver, pancreas, and digestive system embryonic membranes begin to form at the time of implantation. these membranes protect and support the embryo as it grows and develops inside the uterus. chorion: first and outermost membrane amnion: is a thin protective membrane that contains amniotic fluid. Amniotic Fluid function: 1- Act as a cushion to protect the embryo against mechanical injury. 2- Help control the embryo’s temperature 3- Permit symmetric external growth and development of the embryo. 4- Act as an extension of fetal extracellular space (hydropic infants have increased amniotic fluid). 5- Prevent adherence of the embryo-fetus to the amnion. 6- Allow the umbilical cord to be relatively free of compression. 7- Act as a wedge during labor. 8- Provide fluid for analysis to determine fetal health and maturity. Placenta an organ with blood vessels that nourishes the baby in the uterus. placenta is developing at the end of 2 wks and completed at 12 wks. Function of placenta: Metabolic and gas exchange. Hormone production. Protection. The placenta develops at the site where the developing embryo attaches to the uterine wall. development and circulation does not begin until the 3 week. At 40 weeks’ gestation, the placenta is about 15 to 20 cm in diameter and 2.5 to 3 cm in thickness. It weighs approximately 400 to 600 g. The placenta has two parts: the maternal portion and the fetal portion. the maternal portion consists of the decidua basalis and its circulation. Its surface is red and flesh like (often called dirty duncan). the fetal portion consists of the chorionic villi and their circulation. the fetal surface of the placenta is covered by the amnion, which gives it a shiny, gray appearance (often called shiny schultz) Yolk Sac In humans the yolk sac is small and functions only in early embryonic life. It develops as a in the blastocyst, about day 8 or 9 after conception and forms primitive red blood cells during the first 6 weeks of development. Umbilical cord: the cord that connects the fetus to the placenta. At term (38 to 42 weeks’ gestation), the average length of the cord is 55cm. ̵ consist of two umbilical arteries and one vein ̵ Arteries carry deoxygenated blood. ̵ The vein carries oxygenated blood.  Embryonic And Fetal Development WEEK 3 Beginning development of brain, spinal cord, and heart. Beginning development of the gastrointestinal tract Neural tube forms, which later becomes the spinal cord. Leg and arm buds appear and grow out from body. WEEK 4 Brain differentiates Limb buds grow and develop more  WEEK 5 ‣ Heart now beats at a regular rhythm. ‣ Beginning structures of eyes and ears. ‣ Some cranial nerves are visible. ‣ Muscles innervated.  WEEK 6 ⁃ Beginning formation of lungs. ⁃ Fetal circulation established. ⁃ Liver produces RBCs. ⁃ Further development of the brain. ⁃ Primitive skeleton forms. ⁃ Central nervous system forms.  WEEK 7 ‣ Straightening of trunk ‣ Nipples and hair follicles form ‣ Elbows and toes visible ‣ Arms and legs move ‣ Diaphragm formed ‣ Mouth with lips and early tooth buds 7 weeks 8 weeks WEEK 8 ⁃ Rotation of intestines ⁃ Facial features continue to develop ⁃ Heart development complete ⁃ Resembles a human being 6 Weeks 7 Weeks 8 Weeks WEEKS 9–12 Sexual differentiation continues Buds for all 20 temporary teeth laid down Digestive system shows activity Head makes up nearly half the fetus size Face and neck are well formed Urogenital tract completes development  Red blood cells are produced in the liver Urine begins to be produced and excreted Fetal gender can be determined by week 12 Limbs are long and thin.  WEEKS 13–16 A fine hair called lanugo develops on the head Fetal skin is almost transparent Bones become harder Fetus makes active movement Sucking motions are made with the mouth External genitalia are recognizable Fingernails and toenails present Weight quadruples Fetal movement detected by mother (quickening)  WEEKS 17–20 ̵ Rapid brain growth occurs ̵ Fetal heart tones can be heard with stethoscope ̵ Kidneys continue to secrete urine into amniotic fluid ̵ Vernix caseosa, a white greasy film, covers the fetus ̵ Eyebrows and head hair appear ̵ Brown fat deposited to help maintain temperature ̵ Nails are present on both fingers and toes ̵ Muscles are well developed WEEKS 21–24 ‣ Eyebrows and eyelashes are well formed ‣ Fetus has a hand grasp and startle reflex ‣ Alveoli forming in lungs ‣ Skin is translucent and red ‣ Eyelids remain sealed ‣ Lungs begin to produce surfactant  WEEKS 25–28 Rapid brain development Eyelids open and close Nervous system controls some functions Fingerprints are set Subcutaneous fat is visible under the skin Blood formation shifts from spleen to bone marrow Fetus usually assumes head-down position  WEEKS 29–32 Rapid increase in the amount of body fat Increased central nervous system control over body Functions Rhythmic breathing movements occur Lungs are not fully mature Pupillary light reflex is present Fetus stores iron, calcium, and phosphorus WEEKS 33–38 ✓ Testes are in scrotum of male fetus ✓ Lanugo begins to disappear ✓ Has strong hand grasp reflex ✓ Increase in body fat ✓ Earlobes formed and firm ✓ Fingernails reach the end of fingertips ✓ Small breast buds are present on both sexes ✓ Mother supplies fetus with antibodies against disease ✓ Fetus is considered full term at 38 weeks ✓ Fetus fills uterus 37 weeks Two Months 3 Months 4 months 15 Weeks 18 Weeks 16 Weeks Smallest baby in the world born At just 22 weeks Baby Saybie was 245 grams when born and 24 cm weighed the same as a large apple when she was born at 22 wks and three days in December 2018. 6 Months Seven Months Eight Month Thank you