Karnataka PGET Obstetrics MCQ Answer 10

The correct answer is D

Amniotic fluid is 98-99% water.The chemical composition of its substances
varies with gestational age. When fetal urine begins to enter the amniotic sac, amniotic osmolarity decreases slightly compared with fetal blood. After keratinization of the fetal skin, amniotic fluid osmolarity decreases further with advancing gestational age.The low amniotic fluid osmolarity, which is produced by the inflow of markedly hypotonic fetal urine, provides a large potential osmotic force for the outward flow of water across the intramembranous and transmembranous pathways.

• It is a clear pale, slightly alkaline ( pH 7.2) fluid.
• It is about 400 ml at mid pregnancy, reaches about 1000 ml at 36-38 weeks then decreases later on to be scanty in post-term pregnancy.
  

Composition:

• Water (98-99%),
• carbohydrates ( glucose and fructose), proteins ( albumin and globulins), lipids, hormones (oestrogen and progesterone), enzymes ( alkaline phosphatase),
• minerals (sodium, potassium and chloride),
• suspended materials as vernix caseosa, lanugo hair, desquamated epithelial cells and meconium.

Circulation of amniotic Fluid:

The amniotic fluid is not in a static state but is in a continuous turn over, 500 ml of it are replaced each hour.

Origin:

(1) Foetal:

a. Active secretion from the amniotic epithelium.

b. Transudation from the foetal circulation.

c. Foetal urine.

(2) Maternal :

• Transudation from maternal circulation.
• The foetal origin contributes more in the production of the amniotic fluid.

Category: Karnataka PGET 2007 MCQs