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Prenatal Form and Function – The Making of an Earth Suit

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Unit 9: 8 to 9 Weeks

Fetal Period Begins | Sighing, Sucking, Swallowing, Stretching, Tongue Motion | Sense of Touch | Uterus | Vocal Cords

Closer Look:

Applying the Science:

Movie 9.1 - 8 to 9 Weeks

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Movie 9.2 - Fetal Period Begins

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Pacifiers sometimes work well after birth, however, in the womb the embryo often discovers a thumb works best.

By the beginning of the fetal period, synapses, or connections between nerve cells, are found within the cerebral cortex.1 The fetal period continues until birth.

Movie 9.3 - Sucking and Swallowing

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A soft kiss on the face evokes the slightest smile from this newborn whose ability to sense light touch over her arms and legs began just 9 weeks after fertilization.

By 9 weeks thumb sucking2 begins and the fetus may swallow amniotic fluid.3 The fetus can also grasp an object,4 move the head forward and back, open and close the jaw, move the tongue, sigh,5 and stretch.6

By 9 weeks the fetus will grasp an object, an action we continue to see in newborns and small children exploring the world about them.

Movie 9.4 - Motion and Sensation

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By 9 weeks, the nerve receptors in the face, palms of the hands, and soles of the feet can sense and respond to light touch.7 Following a light touch on the sole of the foot, the fetus will bend the hip and knee and may curl the toes.8

Similar to a child having his foot tickled, the 9-week fetus will withdraw if the sole of the foot is lightly touched.

Figure 9.1 - Foot

The Biology of Prenatal Development DVD
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Long before birth, the female fetus is already developing reproductive cells which may one day help form yet another generation.

The eyelids fuse completely shut by 9 weeks.9

The peristalsis previously restricted to the large intestine begins in the small intestine.10

In female fetuses the uterus is identifiable by 9 weeks11 and, within the fetal ovary, immature germ cells called oogonia, are replicating via mitosis.12 Outside the body, the genitalia begin to differentiate as either male or female.13

In the larynx, the appearance of vocal ligaments signals the onset of vocal cord development.14

Movie 9.5 - Live Long and Prosper

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Movie 9.6 - Vocal Cord Development

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8 to 9
Weeks

Footnotes


1	Molliver et al., 1973. 404, 406.
2	Liley, 1986. 13; Liley, 1972. 103.
3	Campbell, 2004. 24; Cunningham FG et al., 2001. 149; de Vries et al., 1982. 311; Petrikovsky et al., 1995. 605.
4	Robinson and Tizard, 1966. 52; Valman and Pearson, 1980. 234.
5	de Vries et al., 1982. 305-307.
6	de Vries et al., 1982. 311.
7	Humphrey, 1970. 16-17; Humphrey, 1964. 96; Humphrey and Hooker, 1959. 77-78; Reinis and Goldman, 1980. 232.
8	Robinson and Tizard, 1966. 52; Valman and Pearson, 1980. 234.
9	Andersen et al., 1965. 648-649; Moore et al., 2000. 53-54; O'Rahilly and Müller, 2001. 465; Pearson, 1980. 39-41.
10	Cunningham et al., 1997. 169.
11	O'Rahilly, 1977a. 128; O'Rahilly, 1977b. 53; O'Rahilly and Müller, 2001. 327.
12	Blackburn, 2003. 7; O'Rahilly and Müller, 2001. 25, 322.
13	Campbell, 2004. 28, 35; Moore and Persaud, 2003. 315; O'Rahilly and Müller, 2001. 336.
14	Campbell, 2004. 29; O'Rahilly and Müller, 1984. 425.