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1 PREGNANCY & HUMAN DEVELOPMENT. 2 Fertilization l oocyte viable 12 - 24 after ovulation l sperm retain fertilizing power within female reproductive tract.

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Presentation on theme: "1 PREGNANCY & HUMAN DEVELOPMENT. 2 Fertilization l oocyte viable 12 - 24 after ovulation l sperm retain fertilizing power within female reproductive tract."— Presentation transcript:


2 2 Fertilization l oocyte viable 12 - 24 after ovulation l sperm retain fertilizing power within female reproductive tract 12 - 48 hours l some “super sperm” viable for 72 hours l about 5 days a month that pregnancy can occur

3 3 Sperm Transport l acidity within the vagina is hostile to sperm & some leak from vagina or die almost immediately l many cannot penetrate cervical mucus l in uterus thousands are killed by leukocytes l only a few thousand finally reach uterine tubes

4 4 Capacitation l membranes must become fragile so that hydrolytic enzymes in their acrosomes can be released

5 5 Acrosomal Reaction l acrosomal reaction: release of acrosomal enzymes that occurs in immediate vicinity of oocyte l hundreds of acrosomes must rupture to break down intercellular cement of oocyte l single sperm makes contact with oocyte

6 6 Sperm Penetration l nucleus is pulled into oocyte cytoplasm l only one sperm is allowed to penetrate l Fusion of nuclear material occurs to complete fertilization

7 7 Preembryonic Development fertilized egg is now called a zygote

8 8 1. Cleavage & Blastocyst Formation l cleavage: period of rapid mitotic divisions following fertilization l daughter cells become smaller & smaller l results in a high surface-to-volume ratio for greater uptake of oxygen & nutrients

9 9 l blastomeres: –2 identical cells by 36 hours –4 identical cells by 60 hours –8 identical cells by 72 hours l morula: berry-shaped –100 cell 4-5 days

10 10 Implantation l 6 days after ovulation implantation begins l completed by 14 day

11 11 Placentation Placentation l formation of placenta l highly vascular l fully functional as nutritive, respiratory, excretory, & endocrine organ by end of 2nd month of pregnancy l some harmful substances can pass placental barriers

12 12 l teratogens: may cause severe congenital abnormalities or even fetal death –alcohol, nicotine, drugs, infections

13 13 Events of Embryonic Development Events of Embryonic Development

14 14 Formation & Roles of Embryonic Membranes l amnion: sac that becomes filled with amniotic fluid which bathes cells –provides buoyant environment & protection against physical trauma –helps maintain temperature –as kidneys develop urine is added to fluid –water portion is exchanged 3 hours

15 15 l yolk sac: blood cell formation & produce gonads l chorion: forms placenta l allantois: constructs umbilical cord –becomes part of bladder

16 16 Gastrulation: Germ Layer Formation l Ectoderm l Mesoderm l Endoderm

17 17 Ectoderm Ectoderm l all nervous tissue l skin, hairs, sebaceous & sweat glands, & nails l tooth enamel l epithelium of: oral & nasal cavities, anal canal, pineal & pituitary glands

18 18 Mesoderm Mesoderm l skeletal, smooth, & cardiac muscle l cartilage, bone & other CT l blood, bone marrow, lymph tissue l ureters, kidneys, gonads

19 19 Endoderm l epithelium of digestive tract l liver, pancreas l thyroid, parathyroid, & thymus glands

20 20 Effects of Pregnancy on Mother Effects of Pregnancy on Mother

21 21 Anatomical Changes l breasts enlarge & areolae darken l “mask of pregnancy” pigmentation of facial skin l uterus enlarges l lordosis l placenta produces the hormone relaxin, that causes ligaments to relax & become flexible for child birth l weight gain about 25 lbs

22 22 Gastrointestinal System l excessive salivation l morning sickness: increase of hormones l heartburn: esophagus & stomach is crowded l constipation: motility of digestive tract declines

23 23 Urinary System Urinary System l urination more frequent & sometimes uncontrollable l uterus compresses bladder l kidneys also have to dispose of fetal wastes

24 24 Respiratory System l lung volume decreases l nasal stuffiness

25 25 Cardiovascular System l total body water rises as safeguard against blood lose during birth l blood volume increases 25 - 40 % l blood pressure & pulse rise l uterus presses on pelvic blood vessels, venous return from lower limbs may be impaired & result in varicose veins

26 26 Parturition Birth 280 days after conception

27 27 I nitiation of Labor l last few weeks of pregnancy estrogen reaches highest levels l myometrium becomes increasingly irritable & weak which may cause Braxton Hicks contractions or false labor l oxytocin is released by posterior pituitary which causes expulsive contraction of true labor

28 28 Stages of Labor

29 29 Dilation l time from labor’s onset until cervix is fully dilated (10 cm) l contractions begin in upper part of uterus & move downward toward vagina l contractions 15 - 30 minutes apart & last for 10 - 30 sec. l contractions become more vigorous & rapid

30 30 l infant’s head is forced against cervix causing it to soften & become thinner l amniotic fluid breaks l lasts 6-12 hours

31 31 Expulsion l from full dilation to delivery l contraction every 2 - 3 minutes & lasting 1 minute l lasts 20 minutes to 2 hours l crowning l episiotomy may be performed to reduce tearing l umbilical cord is clamped & cut

32 32 Placental l delivery of placenta within 15 minutes of birth l important that all placental fragments be removed l called afterbirth

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