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 Gonadotropin (hCGHuman Chorionic Somammotropin (hCS)or Placental Lactogen(hPL)

OTHER HORMONES

Chorionic AdrenocorticotropinChorionic thyrotropinRelaxinPTH-rPhGH-V

Estrogen (E)Progesterone (P)HYPOTHALAMIC-LIKE RELEASING HORMONESGnRHCRHcTRHGH-RHPLACENTAL PEPTIDE HORMONESNeuropeptide-YInhibin & ActivinANP

To understand the FPM one should know:

1. The major hormones involved:hCGn

ProgesteroneEstrogen

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---glycoproteinHalf life –24hrsof hCGLevels 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 luteumStimulates 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 LactogenStructure 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 LactogenBiological 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 CortexZona 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)