Fetal respiratory muscles develop early, and chest wall movements are detected sonographically as early as 11 weeks (Koos, 2014). From the beginning of the fourth month, the fetus engages in respiratory movement suiciently intense to move amnionic luid in and out of the respiratory tract. Some extrauterine events have efects on fetal breathing, for example, maternal exercise stimulates it (Sussman, 2016).
After its embryogenic formation from the yolk sac as the primordial gut, the digestive system forms the intestines and various appendages. The foregut gives rise to the pharynx, lower respiratory system, esophagus, stomach, proximal duodenum, liver, pancreas, and biliary tree. The midgut gives rise to the distal duodenum, jejunum, ileum, cecum, appendix, and the right colon. The hindgut develops into the left colon, rectum, and the superior portion of the anal canal. Numerous malformations develop in these structures from improper rotation, ixation, and partitioning.
Swallowing begins at 10 to 12 weeks, coincident with the ability of the small intestine to undergo peristalsis and actively transport glucose (Koldovsky, 1965). As a correlate, neo ..A:.A : 0 of immature gut motility (Singendonk, 2014). Much of the water in swallowed luid is absorbed, and unabsorbed matter o).
::) 0-0..
.-o i:S :.=. 0 is propelled to the lower colon. Gitlin (1974) demonstrated that late in pregnancy, approximately 800 mg of soluble pro tein is ingested daily by the fetus. he stimulus for swallow :.o)B : 0 ing is unclear, but the fetal neural analogue of thirst, gastric o : 0 :.=.=t ..A emptying, and change in the amnionic fluid composition are potential factors (Boyle, 1992). The fetal taste buds may play a role because saccharin injected into amnionic fluid increases ..At 40 swallowing, whereas injection of a noxious chemical inhibits it
Gestational age (weeks) (Liley, 1972).
Fetal swallowing appears to have little efect on amnionic
FIGURE 7-12 Relationship between the levels of lecithindipalmitoyl phosphatidylcholine (PC), phosphatidylinositol (PI), and fluid volume early in pregnancy because the volume swallowed phosphatidylglycerol (PG) in amnionic fluid. is small compared with the total. However, term fetuses swallow between 200 and 760 mL per day-an amount comparable to that of the term neonate (Pritchard, 1966). hus at term, amnionic fluid volume regulation can be substantially altered by fetal swallowing. For example, as discussed in Chapter 11 (p. 227), if swallowing is inhibited, hydramnios is common.
Hydrochloric acid and some digestive enzymes are pres ent in the stomach and small intestine in minimal amounts in the early fetus. Intrinsic factor is detectable by 11 weeks, and pepsinogen by 16 weeks. The preterm neonate, depending on its gestational age, may have transient deficiencies of these enzymes (Lebenthal, 1983).
Stomach emptying appears to be stimulated primarily by volume. Movement of amnionic luid through the gastroin testinal system may enhance growth and development of the alimentary canal. That said, other regulatory factors likely are involved. For example, anencephalic fetuses, in which swallow ing is limited, often have normal amnionic fluid volume and normal-appearing gastrointestinal tract.