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PLACENTAL FUNCTION

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PLACENTAL FUNCTION Powered By Docstoc
					PLACENTAL FUNCTION
Transfer of nutrients and waste
products b\n the mother & fetus.
             RESPIRATORY
             EXCRETORY
             NUTRITIVE
Produces or metabolizes the hormones
& enzymes necessary to maintain the
pregnancy.
PLACENTAL FUNCTION
BARRIER FUNCTION
IMMUNOLOGICAL FUNCTION
    Transfer function
   Transport is facilitated by the close
approximation of maternal and fetal
vascular systems within the placenta.
 It is important to recognize that there
normally is no mixing of fetal and
maternal blood within the placenta.
Respiratory function—Intake of o2 &
output of co2 takes place by simple
diffusion.o2 supply to fetus rate of
5ml/kg/min & this achieved with cord
flow of 165-330ml/min.
Excretory function—waste products
urea, uric acid,creatinine are excreted to
maternal blood by simple diffusion.
NUTRITIVE FUNCTION
Glucose is the major energy substrate
provided to the placenta and fetus. It is
transported across the placenta by facilitated
diffusion via hexose transporters
 Although the fetus receives large amounts of
intact glucose, a large amount is oxidized
within the placenta to lactate, which is used
for fetal energy production.
Amino acid concentrations in fetal blood are
higher than in maternal blood. Amino acids
are therefore transported to the fetus by
active transport .
LIPIDS—TG`s & FA directly transported from
mother to fetus in early pregnancy but
synthesised in fetus later in pregnancy.
Thus,fetal fat has got dual origin.
Water & electrolytes—Na,K+,Cl- by
simple diffusion.Ca,Ph,iron by active
transport.
BARRIER FUNCTION:-Protective
barrier to the fetus against noxious
agents circulating in maternal
blood.(High MW        >500daltons.
        IMMUNOLOGICAL
           FUNCTION
     Fetus & placenta contain paternally
     determined antigens,foreign to the mother .
     Inspite of this ,no evidence of graft rejection.
     Probably:
1.   Fibrinoid & sialomucin coating of
     trophoblast may suppress the troblastic
     antigen.
2.   Placental hormones ,steriods,HCG have got
     weak immunosuppressive effect,may be
     responsible for producing sialomucin.
3.Nitabuch`s layer which intervenes b\n decidua
    basalis &cytotrophoblast probably
    inactivates the antigenic property of tissue.
4.There is little HLA & blood group antigens on
    trophoblast surface.so antigenic stimulus is
    poor.
5. Production of block antibodies by mother
    ,protects fetus from rejection.
ENDOCRINE—hormones secreted
internally.
HORMONE--Any organic chemical that
is secreted by a gland into the
circulatory system and is transported to
some target organ. The target may be
either peripheral tissue (such as muscle
or other gland) or brain.
Fetal, placental & maternal compartments
    form an integrated hormonal unit

 The feto-placental-maternal (FPM) unit
               creates the
    Endocrine Environment
that maintains and drives the processes of
  pregnancy and pre-natal development.
PLACENTAL HORMONES
Human Chorionic              Estrogen (E)
Gonadotropin (hCG
Human Chorionic              Progesterone (P)
Somammotropin (hCS)          HYPOTHALAMIC-LIKE
or Placental Lactogen(hPL)   RELEASING HORMONES
 OTHER HORMONES              GnRH
Chorionic                    CRH
Adrenocorticotropin          cTRH
                             GH-RH
Chorionic thyrotropin
                             PLACENTAL PEPTIDE
Relaxin                      HORMONES
PTH-rP                       Neuropeptide-Y
                             Inhibin & Activin
hGH-V
                             ANP
 To understand the FPM one
          should know:
    1. The major hormones involved:
                  hCGn
              Progesterone
                Estrogen
Human Chorionic Somatomammotropin (hCS)
           (placental lactogen)

2. How the FPM compartments work together
     to produce the steroid hormones

   3. The transfer of hormones between
         the FPM compartments.
          Human Chorionic
         Gonadotropin (hCG)
     PREGNANCY HORMONE---
     glycoprotein
     Half life –24hrsof hCG
     Levels peak at 60-70 days then remain at a
     low plateau for the rest of pregnancy.
     Placental GnRH have control of hCG.
     FUNCTIONS:
1.   RESCUE &MAINTENANCE of      function of
     corpus luteum.
    Prevents degeneration of corpus luteum
    Stimulates corpus luteum to secrete E + P
    which, in turn, stimulate continual growth of
    endometrium.
2.hCG stimulates leydig cells of male fetus to
    produce testosterone in conjunction with
    fetal pituitary gonadotrophins.Thus indirectly
    involed in development of external genitalia.
3. Suppresses maternal immune function
    & reduces possibility of fetus
    immunorejection
      Human Chorionic
    Somammotropin (hCS)
       or Placental Lactogen
Structure similar to growth hormone
Produced by the placenta

Levels   throughout pregnancy

Large amounts in maternal blood but
DO NOT reach the fetus
      Human Chorionic
    Somammotropin (hCS)
         or Placental Lactogen
Biological effects are reverse of those of
insulin:              utilization of lipids;
make glucose more readily available to
fetus, and for milk production.

hCS levels proportionate to placental size

       hCS levels                  placental
insuffiency
        Estrogen (E)
FORMS-estriol,estradiol &estrone .
Estriol most important .
Levels increase throughout pregnancy
90% produced by
placenta.(syncytiotrophoblast)
Placental production is transferred to
both maternal and fetal compartments
Two of the principle effects of placental
estrogens are:
Stimulate growth of the myometrium and
antagonize the myometrial-suppressing
activity of progesterone. In many species, the
high levels of estrogen in late gestation
induces myometrial oxytocin receptors,
thereby preparing the uterus for parturition.
Stimulate mammary gland development.
Estrogens are one in a battery of hormones
necessary for both ductal and alveolar growth
in the mammary gland.
    Progesterone (P)
Levels increase throughout pregnancy
80-90% is produced by placenta and
secreted to both fetus and mother
Progestins, including progesterone, have
two major roles during pregnancy:
Support of the endometrium to provide an
environment conducive to fetal survival. If the
endometrium is deprived of progestins, the
pregnancy will inevitably be terminated.
Suppression of contractility in uterine
smooth muscle, which, if unchecked, would
clearly be a disaster. This is often called the
"progesterone block" on the myometrium.
Toward the end of gestation, this myometrial-
quieting effect is antagonized by rising levels
of estrogens, thereby facilitating parturition.
Progesterone and other progestins also
potently inhibit secretion of the pituitary
gonadotropins luteinizing hormone and
follicle stimulating hormone. This effect
almost always prevents ovulation from
occuring during pregnancy
FETAL ADRENAL GLAND
          Adrenal Gland
          Development
Adrenal Cortex
   Vital to organism survival
   Begins to develop at 4th week of embryonic life
   Functional around 10th to 12th week of embryonic
    life
   Enzymes necessary for biosynthesis of
    adrenocortical hormones do not develop
    simultaneously
   hCG may have a role in stimulating Adrenocortical
    development
Adrenal Medulla
   Originates from nervous system
   Ganglia of Autonomic Nervous System
    Fetal Adrenal Cortex

                Function
    Adrenal Cortex
     Zona Glomerulosa
        Has enzymes to convert Pregnenalone to:

            Progesterone

            Deoxycorticosterone

            Corticosterone

            Aldosterone

     Zona Fasciculata

        Converts Pregnenalone and Progesterone
         to 17OH-Pre and 17OH-Pro
        17OH-Pro is converted to cortisol (major
         glucocorticoid)
     Zona Reticularis

        Converts 17OH-Pre into DHEA and
         Androstenedione (androgens)