Prenatal Form and Function – The Making of an Earth Suit
Unit 12: 11 to 12 Weeks
Closer Look: 
Applying the Science: 
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Between 11 and 12 weeks, a second huge burst of growth occurs as weight increases by roughly 58 percent.1 12 weeks also marks the end of the first trimester of pregnancy.
The taste bud cells that appeared by 7 weeks have matured into discrete taste buds, but are still scattered throughout the mouth.2 By birth, the taste buds will be confined to the tongue and palate or roof of the mouth.3
Bowel movements begin as early as 12 weeks and continue until 18 weeks.4 The material first expelled from the fetal and newborn colon is called meconium (mĭ-kō'nē-ŭm).5 It is composed of digestive enzymes, proteins, and dead cells shed by the digestive tract.6
The bladder now contains cells organized in patterns and resembling smooth muscle.7
By 12 weeks, the arms have grown to approximate their final proportion relative to body size. As usual, leg development is slower than arm development and the legs still have not achieved their final proportion.8
The whole body surface, except the top of the head and the back, responds to light touch.9
| 1 | Brenner et al., 1976. 561. |
| 2 | Carmichael, 1970. 526; Miller, 1982. 169; Mistretta and Bradley, 1975. 80. |
| 3 | Lecanuet and Schaal, 1996. 3; Miller, 1982. 169; Mistretta and Bradley, 1975. 80. |
| 4 | Abramovich and Gray, 1982. 296; Ramón y Cajal and Martinez, 2003. 154-155. |
| 5 | Grand et al., 1976. 791; O'Rahilly and Müller, 2001. 257. |
| 6 | Grand et al., 1976. 806. |
| 7 | Konishi et al., 1984. 241. |
| 8 | Moore and Persaud, 2003. 105. |
| 9 | Carlson, 1994. 237; Lecanuet and Schaal, 1996. 2; Reinis and Goldman, 1980. 232. |