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Lecture 19

Fetal Development (Lecture 19)

by Anu J
3 Pages
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York University
Natural Science
NATS 1675
Barbara Czaban

Lecture 19 – Fetal Period - Fetal period is week 9 to birth - Main developments: o Continued differentiation and growth of tissues and organs o Increase in size and weight rd  Most weight increase in 3 trimester  Growth influenced by maternal hormones and later, by fetal hormones o Changes in structural form don’t occur anymore - Timeline of major events o End of 8 weeks (months 1-2)  Now called a fetus  All organ systems present  3 cm long  Heart beats since 4 week, pumps blood  Heart and liver are big  Head is nearly 50% of body mass o End of 16 weeks (months 3-4)  Hair  Bones replace cartilage rd  Distinguish between male and female (3 month)  SRY gene on Y-chromosome starts development of testes  Can hear heartbeat  6 inches, 6 ounces o End of 28 weeks (months 5-7)  Fetal movement felt by mother  Eyelids open  12 inches, 3 pounds o End of 36 weeks (months 8-9)  Massive weight gain (~1 pound each week)  Fetus rotates so head faces cervix  20.5 inches, 7.5 pounds - Fetal circulation through the placenta o Functions of the placenta  Source of pregnancy hormones, progesterone and estrogen  Prevent new eggs from maturing  Maintain endometrium (uterine lining)  Exchanges gases, nutrients, wastes between mother and fetus  Mother’s side: endometrium  Fetus’ side: amniotic fluid and amniochoironic membrane  Exchange occurs in: choiron o Blood vessels of mother and fetus mix  Separated by placental barrier  From fetus side:  Umbilical arteries (take away O-poor blood)  Umbilical veins (bring fresh O-rich blood)  Fetal capillaries (absorb oxygen)  From mother’s side:  Uterine veins (carry O-poor blood to mother’s heart)
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