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PREGNANCY & HUMAN PREGNANCY & HUMAN DEVELOPMENTDEVELOPMENT

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FertilizationFertilization

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

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Sperm TransportSperm 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

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CapacitationCapacitation

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

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Acrosomal Reaction 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

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Sperm PenetrationSperm Penetration

nucleus is pulled into oocyte cytoplasm

only one sperm is allowed to penetrate

Fusion of nuclear material occurs to complete fertilization

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Preembryonic Preembryonic DevelopmentDevelopment

fertilized egg is now called a zygote

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1. Cleavage & 1. Cleavage & Blastocyst FormationBlastocyst 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

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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

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ImplantationImplantation

6 days after ovulation implantation begins

completed by 14 day

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PlacentationPlacentation

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

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

infections

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Events of Embryonic Events of Embryonic DevelopmentDevelopment

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Formation & Roles of Formation & Roles of Embryonic MembranesEmbryonic 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

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yolk sac: blood cell formation & produce gonads

chorion: forms placenta allantois: constructs umbilical cord

– becomes part of bladder

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Gastrulation: Germ Gastrulation: Germ Layer FormationLayer Formation Ectoderm Mesoderm Endoderm

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EctodermEctoderm

all nervous tissue skin, hairs, sebaceous & sweat

glands, & nails tooth enamel epithelium of: oral & nasal

cavities, anal canal, pineal & pituitary glands

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MesodermMesoderm

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

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EndodermEndoderm

epithelium of digestive tract liver, pancreas thyroid, parathyroid, & thymus

glands

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Effects of Effects of Pregnancy on Pregnancy on

MotherMother

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Anatomical ChangesAnatomical 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

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Gastrointestinal Gastrointestinal SystemSystem excessive salivation morning sickness: increase of

hormones heartburn: esophagus & stomach

is crowded constipation: motility of digestive

tract declines

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Urinary SystemUrinary System

urination more frequent & sometimes uncontrollable

uterus compresses bladder kidneys also have to dispose of

fetal wastes

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Respiratory SystemRespiratory System

lung volume decreases nasal stuffiness

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Cardiovascular SystemCardiovascular 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

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Parturition Parturition

Birth 280 days after conception

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IInitiation of Labornitiation 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

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Stages of LaborStages of Labor

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DilationDilation

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

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infant’s head is forced against cervix causing it to soften & become thinner

amniotic fluid breaks lasts 6-12 hours

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ExpulsionExpulsion

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

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PlacentalPlacental

delivery of placenta within 15 minutes of birth

important that all placental fragments be removed

called afterbirth