1. Fetal development organ system develop from the 3 primary germ layers

2. Cardiovascular System Is the first system to function Blood vessels formation begins early in the 3 rd week. Heart starts to beat by the end of the 3 rd week.

3. Fetal Circulation

4. Systems development Hematopoietic System – Formation of RBCs starts at 3 weeks in yolk sac, then in liver at 6 weeks, then in spleen, lymph nodes, & bone marrow. Respiratory system – Fetal lungs don’t function until after delivery – Production of surfactant starts at 24 weeks.

5. Systems development Renal system – kidneys appear in the 5 th week. Urine is excreted into and mixes with the amniotic fluid Neurologic System – Start to develop from ectoderm at week 3 – Continue to develop after birth – Affected by maternal anemia and nutrition and other factors (disease, trauma)

6. Systems development Gastrointestinal system – forms during the 4 th week – fetus begins to swallow amniotic fluid during second trimester. – Receives nutrients from mother. – Secretes his own insulin and synthesize glycogen. – Meconium: is a sterile, dark greenish brown, semisolid residue of bile and embryonic secretions plus cellular waste (epithelial tissue) and hair swallowed in utero. presence of meconium in amniotic fluid before delivery usually indicates fetal hypoxia

7. Systems development Hepatic system – begins to function around 4 th week – Hematopoiesis starts at about the 6 th week – Metabolic and glycogen store organ, secretes bile. – Full liver function is not achieved well until after delivery

8. Systems development Endocrine system – The fetal adrenal cortex produces cortisol, which may be important in the initiation of labor. – The thyroid gland develops by the 4 th week, it can synthesize thyroxin. – Island of Langerhans are developed by the 12 th week, and insulin can be extracted from the pancreas by week 20.

9. Systems development Reproductive system – By the end of the 9 th week, male and female external genitalia appear somewhat similar. At the 12 th week, the external genitalia are well developed enough to be easily distinguished. – The fetal ovary has many primordial follicles and produces small but increasing amounts of estrogen. – Withdrawal bleeding follows rapid drop of maternal estrogen following birth. – Estrogen passed to fetus causes enlargement of breast in both male and female infants

10. Systems development Musculoskeletal system – Bones and muscles are developed from mesoderm by 4 th week. Muscle contract spontaneously by 7 th week. Integumentary system – Skin derives from ectoderm at 4 th week. By 16 th week, hand and foot prints are formed. Lanugo hair appears at 12 week on the eye brows and upper lip and covers the body by 20 th week. Immunologic system – During third trimester, albumin and globulin are present in the fetus. The only immunoglobulin that crosses the placenta is IgG (passive acquired immunity). The fetus produces IgM by the end of first trimester. IgA is not produced by the fetus, but it is gained from colostrums.