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PREGNANCY & HUMAN DEVELOPMENT

PREGNANCY & HUMAN DEVELOPMENT. Fertilization. oocyte viable 12 - 24 after ovulation sperm retain fertilizing power within female reproductive tract 12 - 48 hours some “super sperm” viable for 72 hours about 5 days a month that pregnancy can occur. Sperm Transport.

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PREGNANCY & HUMAN DEVELOPMENT

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  1. PREGNANCY & HUMAN DEVELOPMENT

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

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

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

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

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

  7. Preembryonic Development fertilized egg is now called a zygote

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

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

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

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

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

  13. Events of Embryonic Development

  14. Formation & Roles of Embryonic Membranes • 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. yolk sac: blood cell formation & produce gonads • chorion: forms placenta • allantois: constructs umbilical cord • becomes part of bladder

  16. Gastrulation: Germ Layer Formation • Ectoderm • Mesoderm • Endoderm

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

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

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

  20. Effects of Pregnancy on Mother

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

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

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

  24. Respiratory System • lung volume decreases • nasal stuffiness

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

  26. Parturition Birth 280 days after conception

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

  28. Stages of Labor

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

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

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

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

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