Embryology

Question 0

Amniotic fluid Lecithin/sphingomyelin ratio (L/S ratio), Neonatal hyaline membrane disease.

Answer 0

Dipalmitoyl phosphatidylcholine (Lecithin, L) and phosphatidylglycerol are major constituents of lung surfactant. Fetal lung lecithin production increases sharply after 30 weeks gestation and phosphatidylglycerol production increases at 36 weeks gestation. The amniotic fluid sphingomyelin (S) level should remain approximately constant during the third trimester. An L/S ratio ≥ 2.0 indicates adequate surfactant production to avoid neonatal hyaline membrane disease.

Lecithin - component of pulmonary surfactant - increases throughout gestation in amniotic fluid

Sphingomyelin: common membrane phospholipid. increases slightly throughout gestation, decreasing abruptly before birth.

middle of the 3rd trimester, ratio is 1 since they equal. During midle of the 3rd, mature Type 2 pneumocytes begin secreting surfactant. Lecithin conecntration then increases sharply while sphingomyelin remains unchanged. By 35 weeks, L/S ratio is about 2:1, indicating lung maturity.

Phosphatidylglycerol is also component of surfactant that incresea after 36 weeks gestation in parallel with increased surfactant production by maturing fetal lung.

Amniotic fluid total protein and albumin concentrations decrease by abotu 50% from early gestation to term.

Question 1

O2 delivery to fetus in utero

Answer 1

Highly oxygenated blood from mother through placenta carried by umbilical vein –> inferior vena cava via the ductus venosus.

remnant of umbilical vein = ligamentum teres

blood from umbilical vein first delivered to liver, where it bypasses the hepatic ciruclation via the ductus venosus and enters the IVC.

from IVC, blood delivered to the heart where it’s either pumped into the pulmonary ciruclation or crosses directly from the right heart to the left heart via the foramen ovale. Fraction of hte blood pumped into the pulmonary circulation may bypass the lungs via teh ductus arteriosus and pass directly into descending aorta. Paired umbilical arteries carry deoxy blood back to placenta.

Question 2

Severe combined immunodeficiency

Answer 2

diorder marked by combined T- and B-cell dysfunction. Important features:
frequent fungal, viral and bacterial infections early in lifep marked hypogammaglobulinemiap thymic hypoplasia; persistent diarrhea; failure to thrive; severe lymphopenia; lack of clinically apprent involvment of any other organ systems.

Recurrent otitis media (bacterial, bronchiolitis (viral), candidiasis, and poor growth sugests primary defect in both cell mediated (T-cell) and humoral (B-cell) immunity. also Thymic hypoplasia.
Hypogammaglobulinemia and recurrent bacterial infections suggest concomitant B cell deficiency.

Question 3

X-linked Bruton’s aggammaglobulinemia

Answer 3

immunodeficiency syndrome caused by insufficient producntion fo mature B cells. T-cells not that affected.

Question 4

Common variable immunodeficiency

Answer 4

general deficiency of immunoglobulins secondary to failred B cell differentiation. Cell-mediated immunity not severely impaired.

Question 5

Wiskott-Aldrich syndrome

Answer 5

Both T and B cells impaired. Infants present with history of infections (viral, bacterial, fungal) but typically causes thrombocytopenic purpura and eczema too. Usually in WAS, only serum IgM levels are low.

Question 6

DiGeorge Syndrome

Answer 6

abnormal neural crest migration and development of 3rd and 4th pharyngeal pouches. Complete DiGeorge syndrome is a form of SCID and caharacterized by absence of thymic tissue.
occurs in less than 1% of patients with the typical 22q11.2 deletion.
patients usually have mild to moderate immune deficiency related to defects in T cell produnction and maturation. Patients have secondary humoral defects, including hypogammaglobulinemia, but this is not a universal feature. also facial abnormalities, hypoparathyroidism, cardiac defects.

Question 7

checking for fetal lung maturity

Answer 7

Amniocentesis checking for phospholipids, including dipalmitoyl phosphoatidylcholine (Lecithin) (major pulmonary surfactant.)
Lecithin to sphingomyelin ratio (L/S ratio) is a measure of fetal lung maturity. Fetal lungs are mature when they are producing adequate surfactant to yield L/S ≥ 2.
in premature labor, can give corticosteroids to induce fetal surfactant production.