Physiology of early pregnancy

The formation of the trophoblastic cells heralds the beginning of the production of hormones by the embryo through its membranes. Before the actual syncytiotrophoblast, outer cell mass begins to elaborate hCG which will become the most important source of gonadotropin during pregnancy as the pituitary ones loose their importance and are no longer produced. The hCG converts the corpus luteum of menstruation to the corpus luteum of pregnancy. With this conversion the ovarian steroids are maintained so that they do not reduce production until 16 weeks of gestation. At about the 12th week of gestation, placental steroids begin to be formed and they gradually take over from the ovarian source (corpus luteum). They become the main source of sex steroid production through out pregnancy.

Other hormones of less importance are produced by the placenta and they include human placental lactogen or human choronic somatotrophin (hCS) produced by the cytotrophoblasts. Also we have the so called posterior pituitary –like hormone being produced from the placenta. Certain embryos also produce some hormones such as blastocyst estrogen, prostaglandins etc.

Local hormones.

Certain hormones are produced by the uterine decidua. They include FS, LH, sex steroids etc. We are not quite sure what these hormones do to the process of early pregnancy except to perhaps stimulate and maintain the process of nidation

Paracrine hormones

The placenta produces the following mostly paracrine secretions for the maintenance of pregnancy.

  • Human chorionic gonadotropin (hCG)

  • Human chorionic somatotropin (hCS)

  • Human chorionic corticotropin (hCC)

  • Hypothalamic like hormone (β-endorphin, ACTH-like hormone)

  • SPI- pregnancy specific β-1 glycoprotein

  • SP4-pregnancy specific β-1 glycoprotein

  • Pregnancy-associated plasma proteins (PAPP)

    • PAPP-A

    • PAPP-B

    • PAPP-C

    • PAPP-D

  • Pregnancy associated B1 macroglobulin (B1 PAM)

  • Pregnancy associated α2 macroglobulin (α2 PAM)

  • Pregnancy associated major basic protein (pMBP)

  • Placental proteins (PP) 1 to 21

  • Placental membrane proteins  (MP) 1 to 7

    • MP1 also known as placental alkaline phosphatase (PLAP)

  • Progesterone

  • Estrone

  • Estriol

  • Estradiol

  • Relaxin from corpus luteum

Placental transport

Placenta primarily transports oxygen and nutrients to the fetus and also CO2, and also urea. Some, such as substances involved in new tissue formation are transported by active process. Large proteins may be transported to the fetus via pinocytosis while other means of transportation include- simple diffusion, facilitated diffusion, active transport, leakage and pinocytosis..

 

 

 

 

 

 

 

 

 

 

 


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