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Fertilization and Development

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Presentation on theme: "Fertilization and Development"— Presentation transcript:

1 Fertilization and Development

2 Fertilization Fertilization of the Ovum occurs in the oviduct
Only one sperm allowed Electrical block Surface of ovum altered Binding sites for sperm altered


4 Development Nuclei of sperm and ovum fuse to form the zygote
1st division (mitosis) Occurs in oviduct 30 hrs after fertilization

5 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

6 Implantation On 6th day blastocyst breaks free of zona
Implantation blastocyst in uterine wall on day 7- 8

7 Implantation

8 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

9 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

10 Development Considered an embryo after implantation is complete
Approx. 2 weeks from fertilization

11 Chorion

12 Amnion Forms a fluid filled sac that insulates the embryo and fetus that protects from Infection Dehydration Impact Temperature changes


14 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.

15 Prenatal Development The in’s and then outs

16 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

17 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

18 1st Trimester

19 12 wks 4 wks 8 wks

20 2nd 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

21 2nd Trimester

22 16 wks 20 wks

23 2nd Trimester At the end of 16 wks: At the end of 20 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

24 2nd 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

25 3rd Trimester Rapid growth Fetus is 350 mm – 530 mm long
Body mass increases from 0.68 kg to 3.4 kg Organs are maturing

26 3rd 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

27 3rd Trimester

28 3rd 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

29 3rd 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

30 Parturition (Birth) Uterine contractions signal beginning of labor
Cervix thins and begins to dilate (max. 10 cm) Labor starts when contractions are 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


32 Parturition

33 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

34 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

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