The fetus has lungs that are capable of breathing air, although medical help may be needed out of the womb. The baby might have a full head of hair. The fetus can open and close its eyes, suck its thumb and cry. Nearly all babies born now will survive if they receive intensive care services.
Almost all babies born now will live if they receive intensive care services. The skin is pink and smooth. The fetus is more round and plump. Other therapies may include corticosteroids, supplemental oxygen, and assisted ventilation. Supportive therapies, such as temperature regulation, nutritional support, and antibiotics, may be administered to the premature infant as well. The development of the respiratory system in the fetus begins at about 4 weeks and continues into childhood.
Ectodermal tissue in the anterior portion of the head region invaginates posteriorly, forming olfactory pits, which ultimately fuse with endodermal tissue of the early pharynx. At about this same time, an protrusion of endodermal tissue extends anteriorly from the foregut, producing a lung bud, which continues to elongate until it forms the laryngotracheal bud. The proximal portion of this structure will mature into the trachea, whereas the bulbous end will branch to form two bronchial buds.
These buds then branch repeatedly, so that at about week 16, all major airway structures are present. Development progresses after week 16 as respiratory bronchioles and alveolar ducts form, and extensive vascularization occurs. Alveolar type I cells also begin to take shape. Type II pulmonary cells develop and begin to produce small amounts of surfactant. As the fetus grows, the respiratory system continues to expand as more alveoli develop and more surfactant is produced. Beginning at about week 36 and lasting into childhood, alveolar precursors mature to become fully functional alveoli.
At birth, compression of the thoracic cavity forces much of the fluid in the lungs to be expelled. The first inhalation inflates the lungs. Fetal breathing movements begin around week 20 or 21, and occur when contractions of the respiratory muscles cause the fetus to inhale and exhale amniotic fluid. These movements continue until birth and may help to tone the muscles in preparation for breathing after birth and are a sign of good health.
Answer the question s below to see how well you understand the topics covered in the previous section. Skip to main content. Module 6: The Respiratory System.
Search for:. Embryonic Development of the Respiratory System Learning Objectives By the end of this section, you will be able to: Create a timeline of the phases of respiratory development in the fetus Propose reasons for fetal breathing movements Explain how the lungs become inflated after birth. Figure 1. Development of the Lower Respiratory System. Critical Thinking Questions During what timeframe does a fetus have enough mature structures to breathe on its own if born prematurely?
Now he or she has functioning organs, nerves and muscles. Find out what happens during the second trimester by checking out this weekly calendar of events. Keep in mind that measurements are approximate. Thirteen weeks into your pregnancy, or 11 weeks after conception, your baby is beginning to make urine and release it into the surrounding amniotic fluid. Your baby also swallows some amniotic fluid. Bones are beginning to harden in your baby's skeleton, especially in the skull and long bones.
Your baby's skin is still thin and transparent, but it will start to thicken soon. Fourteen weeks into your pregnancy, or 12 weeks after conception, your baby's neck has become more defined.
Red blood cells are forming in your baby's spleen. Fifteen weeks into your pregnancy, or 13 weeks after conception, your baby is growing rapidly. Bone development continues and will soon become visible on ultrasound images. Your baby's scalp hair pattern also is forming. By the end of the 16th week of pregnancy — 14 weeks after conception — your baby's limb movements are becoming more coordinated.
Sixteen weeks into your pregnancy, or 14 weeks after conception, your baby's head is erect. His or her eyes can slowly move. The ears are close to reaching their final position. Your baby's skin is getting thicker. Your baby's limb movements are becoming coordinated and can be detected during ultrasound exams. However, these movements are still too slight to be felt by you.
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