Table 29.3 Fetal Stage of Development Time Period Major Events Primary ossification centers appear in most bones Reproductive organs begin to develop Wooks 9-12 Coordination between nerves and muscles for movement of limbs occurs Brain enlarges Body elongates Epidermis and dermis of the skin become more fully devekoped Permanent kidneys develop Palate (roof of mouth) develops CRL: 9 cm Average head circumference at 12 weeks: 68 millimeters (mm) Average crown-rump length at 12 weeks: 9 centimeters (em) Average weight: 28 grams (g) Woeks 13-16 Body grows rapidly Ossification in the skeleton continues Limbs become more propartionate in length to body Brain and skull eontinue to enlarge Average head circumference at 16 weeks: 123 mm (12.3 cm) Average crown unp length at 16 weeks 14 em Average weight: 170g CRL: 14 cm Wooks 17-2O Muscle movements become stronger and more frequent Lanugo covers skin Vernix caseosa covers skin Limhs near final proportions Brain and skull contimue to enlarge Average head circumference at 20 weeks: 174.5 mm (17.45 cm) Average crown-rump length at 20 weeks: 19 cm Average weight: 454 g CRL: 19 cm Wooks 21-38 Body gains major amount of weight Subcutancous fat is deposited Eyebrown and eyelashes appear Eyelids open Testes descend into scrotum (month 9) Blood cells form in marrow only Average head circumference at 38 wocks: 335 mm (33.5 cm) Average crown-rump length at 38 weeks 36 cm Average tolal length at 38 weeks: 53 cm Average weight: 2.5-4.5 kilograms (kg) CHL: 36 cm

Human Anatomy & Physiology (11th Edition)

11th Edition

ISBN:9780134580999

Author:Elaine N. Marieb, Katja N. Hoehn

Publisher:Elaine N. Marieb, Katja N. Hoehn

Chapter1: The Human Body: An Orientation

Section: Chapter Questions

Problem 1RQ: The correct sequence of levels forming the structural hierarchy is A. (a) organ, organ system,...

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Question

The physician determines that Ashley is in her twentieth week of pregnancy. Which of the following best describes the development of the fetus at this time (refer to table 29.3)? a. The crown–rump length is 19 centimeters. b. The heart and lungs have fully developed, but the GI tract has yet to form. c. The testes have descended into the scrotum. d. The average weight of the fetus at this time is about 2.5 kilograms.