2nd Lecture: Conception & Fetal Development PDF

Milestones of Fetal Growth and Development Periods of Prenatal Development Stages of Fetal Development Germinal Period (conception) Sex Determination Definition of fertilization Outlines 1. Define the conception, implantation and fetal development. 2. Describe the stages of fetal developmen...

Milestones of Fetal Growth and Development Periods of Prenatal Development Stages of Fetal Development Germinal Period (conception) Sex Determination Definition of fertilization Outlines 1. Define the conception, implantation and fetal development. 2. Describe the stages of fetal development. 3. Identify the stages of prenatal growth 4. Discuss the milestones of fetal growth and development At the end of the session, the students will be able to: Objectives: conception and impregnation. - Union of an ovum and spermatozoon. - Ovum capable for fertilization for only 24 hours while spermatozoon is 4872hours. - also known as At time of ovulation, the cervical mucous becomes less viscous and providing channels for sperms passage. The sperms ascent through the uterine cavity and Fallopian tubes to reach the site of fertilization in the ampulla The ovum leaves the ovary after rupture of the Graafian follicle, the ovum is picked up by the fimbrial end of the Fallopian tubes and moved towards the ampulla After penetration of the ovum by a sperm, resistant to penetration by another sperms occur Ovum usually fertilized within 12-24 hours of ovulation, however sperm remain alive for up to 72 hours within the female genital tract. The moment the sperm penetrates the egg is called conception, creating a new and separate cell called the Zygote. The mature ovum carries 22 autosomes and one X chromosome, while the mature sperm carries 22 autosomes and either an X or Y chromosome. If the fertilizing sperm is carrying X chromosome the baby will be a female (46 XX), if it is carrying Y chromosome the baby will be a male (46 XY). Fraternal (dizygotic) twins: Two separate ova fertilized by two different sperm Identical (monozygotic) twins: Single fertilized ovum Blastocyst (attached morula) sinks into endometrium for approximately 7 days, completing implantation. Oocyte (female germ cell) released from ovary and travels to uterine tube. Sperm fertilizes oocyte in uterine tube. Zygote travels up uterine tube, dividing continuously, creating blastomere (group of cells). Morula (minimum 12-15 cells) attaches to endometrium (posterior wall of uterus) after approximately 6 days. dr.Shaban dr.Shaban Contact between the growing structure and the uterine endometrium occurs approx. 8 to 10 days after fertilization. Occurs on posterior surface of uterus. Blastocyst burrows deeply into the endometrium and establish communication network with blood system. Once implanted, zygote is called an embryo. Trophoblast cells produce enzymes (HCG) that allow blastocyst to burrow into endometrium. IMPLANTATION This maintains endometrium, prevents menstruation Can be detected by week 3 with a home pregnancy test (Basis of pregnancy test). Maintains corpus luteum & causes it to continue producing progesterone in the absence of LH through first four months of pregnancy till placenta produces sufficient estrogen & progesterone to maintain the pregnancy Target & Functions: Corpus Luteum Source: Trophoblasts of blastocyst & Chorion (effects similar to LH). Human Chorionic Gonadotropin (HCG): Embryonic Period (from implantation to 5 8 weeks) Embryo forms different layers of cells Ectoderm outside layer; becomes nervous system, sensory receptors, and skin Mesoderm middle layer; becomes circulatory system (heart begins to beat at 4 weeks), muscles, bones, excretory system, and reproductive system Endoderm inner layer; becomes digestive system and respiratory system. High risk of congenital malformation All organ systems are complete, at least in a rudimentary form at 8 weeks gestation (organogenesis). Fetus Embryo 2 weeks Zygote& Pre embryonic period Fertilization Implantation Start of Placenta Key Events From 5-8 weeks until term Sex organs develop Arms, legs, face, organs, From muscles all develop implantation Heart begins beating to 5-8 weeks Length Period dr.Shaban Bone Formation Pre embryonic Development Rapid increase in size and increased maturation of structures and systems Growth and Integration (3rd trimester) Physiological structures begin to connect into systems and work together Integration (2nd trimester) Rudimentary organs and structures laid down Organogenesis (1st trimester) Remarkable organ originating from trophoblast layer of fertilized ovum. Functions: fetal respiration. transport, and nutrient function. storage, barrier function. hormone excretion and produces glycogen, cholesterol and fatty acids, and hormones Human Chorionic Gonadotropin (HCG), Human Placental Lactogen HPL estrogen and progesterone. Weight: 400-600g at full term Diameter: 16-20 cm Thickness: 1-3 cm thick in center and thin in margin Divided into sections or segments called Two sides: 1) Fetal side- shiny and smooth in appearance, the amniotic sac is attached to it. 2) Maternal side- dark red and rough in appearance. Maternal and Fetal blood do not mix Shape: discoid round dr.Shaban and return waste products from fetus to placenta Transports oxygen and nutrients to the fetus from placenta Function: it its body; prevents pressure on the veins and arteries Length 15-120 cm (average 50cm) Contains 3 vessels: 2 arteries and 1 vein The . no nerve supply The lifeline between mother and fetus made up mainly from fetal urine (99% water) , fluid from maternal blood, castoff cells, vernix, and fetal waste products. cushion fetus and protect from injury, to keep infant at stable 37 temperature, to allow room for fetal movement and growth. Normal volume- 800 to 1200 ml at term. Clear, oder, pale straw, yellow or greenish colored pH slightly alkaline (7.2). Checking the pH at time of rupture to differentiate from urine. End of 4-5th G/W End of 9th G/W End of 13th G/W (First Trimester) End of 17th G/W End of 21th G/W End of 25-26th G/W (Second Trimester) End of 30th G/W End of 34nd G/W End of 38-42th G/W (Third Trimester) Milestones of Fetal Growth and Development Heart begins to beat approximately 85 beats /minute Upper limb buds Lungs begin to form Parts of gastro intestinal tract can be identified. Placenta is forming by end of fourth week. Circulatory system through umbilical cord well established Organogenesis is complete) Abdomen appears large because the fetal intestine is growing rapidly. Sonogram shows a gestational sac, diagnostic of pregnancy Fetal circulation functioning Begins to produce urine Fetal heart can be heard by electronic devices Ossification of bones are forming the fetus has all its body parts growth is rapid Sex can be determined by ultrasonography Baby's first kick. Baby is covered with a layer of thick, downy hair called lanugo. Start to sleep A protective coating called vernix caseosa begins to form on baby's skin. If you talk or sing, he can hear you. .Eyebrows and eyelids are visible Baby's started breathing motions. Baby weighs about 1,200 gm and is about 35 cm long. His body is well-formed. Fingernails cover his fingertips. Lung alveoli begin to mature & surfactant can be demonstrated in amniotic fluid. Iron stores are beginning to be developed Turned head-down in preparation for birth. Baby is gaining about 125 gm per week, and layers of fat are piling on. Fetus kicks actively, hard enough to cause the mother considerable discomfort. Weight : 2.5-4 Kg Length: 48 to 52cm (crown to rump, 35 to 37 cm)