Question

What are the functions of the placenta, vernix caseosa and surfactant? How does fetal circulation differ from post delivery circulation?

Answer 1

Placenta - The placenta is attached to the uterine wall and establishes connection between the mother and the foetus through the umbilical cord.

The placenta begins to grow at 6th week and is completed by 12th week.

Placental Functions:-

• Transfer of nutrients and waste products between the mother and the foetus. In this respect it attributes to the following functions: respiratory, excretory and nutritive

✓Respiratory function - Although the fetal respiratory movements are observed as early as 11 weeks. There is no gaseous exchange. Intake of Oxygen and output of carbon dioxide takes place by simple diffusion across the fetal membrane.

✓Excretory function - waste products from the fetussuch as urea, uric acid and creatinine are excreted to the maternal blood by simple diffusion.

✓Nutritive function - The fetus obtain its nutrients ( Glucose, lipids, amino acids, water & electrolytes) from the maternal blood.

•Endocrine functions - placenta is an endocrine gland. It produces both steroid (estrogen & progesterone) and peptide (human chorionic gonadotropin hCG) hormones to maintain pregnancy.

• Barrier function - Foetal membrane has long been considered as protective barrier to the foetus against noxious agents circulating in the maternal blood.

•Immunological function - the placenta and fetal tissue come direct contact with mother, which are foreign to the mother but there is no evidence of graft rejection. Placenta probably offers immunological protection against rejection.

Vernix caseosa - it is a white, creamy, naturally occurring biofilm covering the skin of the foetus during the last trimester of pregnancy.

Functions-

• It protect a newborn from infections after birth because the coating contains antioxidants as well as anti infection and anti-inflammatory properties.

• Because of its lipid content, vernix is hydrophobic and protect skin from excessive water exposure during the development of stratum corneum.

• It lubricates the birth canal and reduces friction as the baby passes through the birth canal during delivery.

• It helps to regulate baby's body temperature.

• It is a natural moisturizer for babies, protecting their skin from dryness and cracking.

Pulmonary surfactant - It is a complex mixture of phospholipids and proteins.

It is synthesized and secreted by type II alveolar epithelial cells, also called pneumocytes.

Function -

• It reduce surface tension at the air liquid interface of the alveolus, thus preventing its collapse during end exhalation.

• It also participate in innate host defense against inhaled pathogens.

Difference between fetal circulation and post delivery circulation:

We can observe these differences through the changes of the fetal circulation at birth, which are as follows:-

1. Closure of the umbilical arteries - Functional closer is almost instantaneous preventing even slight amount of the fetal blood to drain out.

2. Closer of the umbilical vein - The obliteration occurs a little later than the arteries, allowing few extra volume of blood to be received by the foetus from the placenta. The ductus venosus( ductus venosus shunts a portion of umbilical vein blood flow directly to the inferior vena cava. Thus, it allows oxygenated blood from the placenta to bypass the liver.) collapses and the venous pressure of the inferior vena cava falls and so also the right atrial pressure.

3. Closure of the ductus arteriosus - the functional closure of the ductus arteriosus ( it is a blood vessel in the developing foetus connecting the trunk of the pulmonary artery to the proximal descending aorta. It allows most of the blood from the right ventricle to bypass the fetus's fluid filled non-functioning lungs) may occur soon after the establishment of pulmonary circulation.

4. Closer of the foramen ovale - This is caused by an increased pressure of the left atrium combined with a decreased pressure on the right atrium. Functional closer occurs soon after birth but anatomical closer occurs in about 1 year time.

Foramen ovale is a normal opening between the atrium of fetus.