Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Fertilization and Development Fertilization Fertilization of the Ovum occurs in the oviduct – Only one sperm allowed • Electrical block • Surface of ovum altered • Binding sites for sperm altered Development Nuclei of sperm and ovum fuse to form the zygote – 1st division (mitosis) Occurs in oviduct 30 hrs after fertilization Development Cell division continues as mass moves through the oviduct to the uterus – a central hollow forms and fills with fluid – Now called a blastocyst • Cells on inside develop into embryo • Outer cells develop into supportive cells – Identical Twins Implantation On 6th day blastocyst breaks free of zona Implantation blastocyst in uterine wall on day 7- 8 Implantation Implantation Endometrium is maintained – Human corionic gonadotropic hormone (HCG) sectreted by outer cells (Chorion) of blastocyst to maintain corpus luteum • LH levels remain high • HCG used in pregnancy tests – Corpus luteum maintains levels of estrogen and progesterone to maintain endometrium The Embryo During implantation, the outer layer of cells of the blastocyst produces two membranes that surround, protect, and nourish the embryo – Chorion forms the placenta – Amnion forms amniotic sac Development Considered an embryo after implantation is complete – Approx. 2 weeks from fertilization Chorion Amnion Forms a fluid filled sac that insulates the embryo and fetus that protects from – – – – Infection Dehydration Impact Temperature changes Umbilical cord Contains one vein and two arteries – vein carries nutrient and oxygen rich blood to the fetus. – two arteries return blood containing waste from fetal circulation back to the placenta. • It takes about 30 seconds for a blood cell to make the round trip through the cord – cord can be as long as 4 feet at birth. Prenatal Development The in’s and then outs Prenatal development Pregnancy usually last for approximately nine months Divided into three trimesters First Trimester – Fertilization to the end of the 3rd month – by second week – germ layers form • Ectoderm, endoderm, and mesoderm – At one month – size is only 7mm Prenatal development First Trimester (Cont.) – Heart and brain have formed • heart rate can be heard at 10 weeks with a special instrument called a Doppler – – – – Limb buds with fingers and toes present Placenta begins developing Considered fetus after 8th week Movement occurs around 9th week • Sucking reflex st 1 Trimester 4 wks 8 wks 12 wks nd 2 Trimester Fetus is 57 mm – 350 mm long recognizable body form – Arms, hands, fingers, legs, feet and toes are fully formed • Bone begins to replace cartilage most of organs and tissues developed – Eyes are almost fully developed nd 2 Trimester 16 wks 20 wks nd 2 Trimester At the end of 16 wks: – Fetus is developing reflexes such as sucking and swallowing – Sex is identifiable – Skin is bright pink, transparent and covered with soft, downy hair At the end of 20 wks: – Mother begins to feel fetal movement – Internal organs are maturing – Eyebrows, eyelids and eyelashes appear Human Sex Determination Females have two XX chromosomes Males have the Xy chromosomes (the “y” chromosome is much smaller) The male and female fetuses do not differ until week 6 or 7 At this time, the presence of SRY gene (Sexdetermining Region of the Y chromosome) will stimulate the developing gonad to become a testis (in males) The hormones subsequently produced by the testis will lead to the development of male characteristics Testes develop in the abdomen (like the ovaries) and gradually descend The balance of hormones circulating in the maternal blood is crucial during fetal development (note that each sex produces a small quantity of the opposite sexes primary hormone) (eg) Too much estrogen could result in a genetic male showing outward female characteristics nd 2 Trimester At the end of 24 weeks: – Eyelids begin to part and eyes open occasionally for short periods of time – Skin is covered with protective coating called vernix – Fetus is able to hiccup rd 3 Trimester Rapid growth – Fetus is 350 mm – 530 mm long – Body mass increases from 0.68 kg to 3.4 kg – Organs are maturing rd 3 Trimester At the end of 7 months: – If born at this time, he/she will be considered a premature baby and require special care – Taste buds have developed – Fat layers are forming – Skin is still wrinkled and red rd 3 Trimester rd 3 Trimester At the end of 8 months: – Tremendous brain growth occurs at this time – Most body organs are now developed with the exception of the lungs • Movements or "kicks" are strong enough to be visible from the outside • Kidneys are mature • Skin is less wrinkled • Fingernails now extend beyond fingertips rd 3 Trimester At the end of 9 months: – The lungs are mature – Baby is now fully developed and can survive outside the mother's body • Skin is pink and smooth • Baby settles down lower in the abdomen in preparation for birth and may seem less active • labour Environmental Effects on Development A teratogen is any substance that might interfere with normal development of a fetus or embryo The first 9 weeks are especially critical because this is when organs of first differentiating and developing Some examples Cigarette smoke can constrict fetal blood vessels and prevent proper supply of O2 Babies tend to be underweight Chance of stillbirths and premature birth increases Possible behavioural or intellectual challenges Some examples Thalidomide Prescribed to treat morning sickness throughout the 50’s and 60’s Babies were born with missing or deformed limbs Thalidomide specifically blocks blood vessels that lead to the limbs Nutrition Proper nutrition is also very important during embryonic/fetal development (eg) A lack of folic acid may result in spina bifida (eg) over-consumption of vitamin C may lead to symptoms of vitamin C deficiency in the baby Parturition (Birth) Uterine contractions signal beginning of labor – Cervix thins and begins to dilate (max. 10 cm) – Labor starts when contractions are 10-15 min Amniotic membrane is forced into birth canal – Often bursts and amniotic fluid lubricates the canal (water breaking) – Usually ruptures during delivery but may occur before Contractions start moving baby through birth canal Parturition birth Hormones involved in birth Relaxin – Produced by placenta causes ligaments in pelvis to loosen Oxytocin – positive feedback loop enhances strength of contractions – Prostaglandins also involved Hormones involved in birth Milk Production – Prolactin • Levels increase dramatically after birth occurs • estrogen & progesterone levels drop • Stimulates glands in the breasts to produce fluids 1.5 L/day – Oxytocin • Stimulates contractions that move milk into ducts • Also causes contractions of sm. Muscle in uterus to return to normal size Contraception Any behavior or technology that prevents conception Abstinence Refraining from having sex If you don’t have sex you can’t get pregnant!!! Tubal Ligation Cutting of fallopian tubes Vasectomy Cutting of vas deferens Hormone Treatments Contain estrogen and progesterone Physical or chemical barriers Condoms (male and female) Diaphragms spermicide Natural Family Planning Uses natural functions of the body and menstrual cycle to calculate ovulation Record body temperatures Record changes in cervical mucus discharge Requires periodic abstinence (7-10days) during ovulation OR barrier/withdrawl method