STRUCTURE AND STRUCTURE AND FUNCTION FUNCTION

OF PLACENTA INCLUDING OF PLACENTA INCLUDING

PLACENTAL PLACENTAL INSUFFICIENCYINSUFFICIENCY

DEFINITIONDEFINITION: : • Placenta is a fleshy structure that

develops mostly from fetal chorionic tissue and maternal decidua during pregnancy. It lies implanted on the uterine wall. It is connected with fetus through umbilical cord in the amniotic cavity .It maintains pregnancy and carries vital fetal functions.

• The human placenta is discoid because of its shape; hemochorial, because of direct contact of chorion with the maternal blood

DEVELOPMENT OF THE DEVELOPMENT OF THE HUMAN PLACENTAHUMAN PLACENTA

Decidua : It is the name given to endometrium during pregnancy.

• Decidua basalis • Decidua capsularis • Decidua parietalis

Early Trophoblast • Syncitio trophoblast / Plasmodia

trophoblast • Cytotrophoblast / Langhan’s

layer • Extra embryonic mesoderm

Formation of chorionic villi

• The essential element of placenta are small finger like projection called villi.

• The villi are formed as offshoots from the surface of the trophoblast. As it along with the underlying extra-embryonic mesoderm, constitutes the chorion, the villi arising from it are called chorionic villi

• The villi related to the decidua capsularis are transitory and after some time they degenerate. This part of the chorion becomes smooth and is called the chorion laevae.

• The part of the chorion that helps form the placenta is called the chorion frondosum.

Stages in formation of chorionic villi

• Primary villi: consist of a central core of cytotrophoblast covered by a layer of syncitio trophoblast. Adjoining villi are separated by an intervillous space.

• Secondary villi: It shows 3 layers. Ouuter syncitiotrophoblast, an intermediate layer of cytotrophoblast and an inner layer of extra embryonic mesoderm.

• Tertiary villi: It is like secondary villi except that there are blood capillaries in the mesoderm.

Details of the process of villus formation

Placental ageing • Villi changes:

– Decreasing thickness of the syncitium and appearance of syncitial knots.

– Partial disappearance of Langhan’s cells.– Decrease in the stromal tissue including

Hofbauer cells.– Obliteration of some vessels and marked

dilatation of the capillaries.– Thickening of the basement layer of the fetal

endothelium and the cytotrophoblast.– Deposition of fibrin on the surface of the villi.

Decidual changes: Degeneration of Nitabuch’s layer (area where trophoblast cells meet the decidua)

• Intervillous space : -White infarcts -Rohr’s stria

STRUCTURE OF PLACENTA STRUCTURE OF PLACENTA AT FULLTIME PREGNANCYAT FULLTIME PREGNANCY

Naked Eye Anatomy:• It is disc like spongy fleshy

structure , thick at centre but thin at edge.

• It weighs 500gm.It measures from 15-20cm in diameter and 2.5cm at the centre.Its volume is 500 ml; surface area 243 sq.cm.

Fetal surface: covered with whitish smooth and glistening amniotic membrane and umbilical cord attached at or near the centre. Branches of umbilical vessels are visible on this surface radiating from umbilical cord. Amniotic membrane can be peeled of from underlying chorionic plate except at umbilical cord.

Maternal surface: looks dull red and shows 15-20 lobes or maternal cotyledons which are separated by sulci. Each sulcus corresponds to decidual septum. It is covered with a thin greyish layer of decidua-compact layer and spongy layer that comes away with basal plate at the time of separation .Numerous small greyish calcified white infarcts are visible on this surface.

• Margin : It is formed by fusion of basal and chorionic plates and is continuous with two membranes- chorion leave and amnion.

• Attachments: Placenta is attached to upper part of posterior or anterior wall of uterine cavity near fundus.

• Placental separation:It normally separates after birth of baby through spongy layer of decidua.

Micro anatomy At term 4/5th of placenta is of

fetal origin. Decidual plate and maternal sinus blood belong to mother. Structure of placenta from fetal to maternal are:

• Amniotic membrane: A thin layered cubical epithelium on a thin layer of avascular connective tissue.

• Chorionic plate: A sheet of connective tissue with branching umbilical vessels. Maternal surface is coated with anchoring and nutritive placental villi . Fetal surface is coated with amniotic membrane

• Basal plate: It consist of the following from outside inwards.– Part of the compact and spongy layer of

the deciduas basalis.– Nitabuch layer (area of fibrinoid

degeneration, wher trophoblast cells meet the deciduas.)

– Cytotrophoblastic shell.– Syncitiotrophoblast.

Intervillous space: It is lined on the inner side by the chorionic plate and outer side by the basal plate, limited on the periphery by the fusion of the two plates.It is lined internally on all sides by the syncitiotrophoblast and is filled with slow flowing maternal blood.

• Stem villi: • These arise from the chorionic plate and extends

to the basal plate. Functional unit of the placenta is called a fetal cotyledon or placentome, which is derived from a major primary stem villus. Functional subunit is called a lobule which is derived from a tertiary stem villi. About 60 stem villi persist in human placenta. Thus each cotyledon (totalling 15-29) contains 3-4 major stem villi. The fetal capillary system within the villi is almost 50 km long. Thus, while some of the villi are anchoring the placenta to the deciduas, the majority are free within the intervillous space and are called nutritive villi

• Structure of a terminal villus: It has got following structure from outside inwards:– Outer syncitiotrophoblast– Cytotrophoblast– Basement membrane– Central stroma containing fetal capillaries,

primitive mesenchymal cells, connective tissue and a few phagocytic (hofbauer cells that can trap maternal antibodies crossing through the placenta) cells.

•  

PLACENTAL CIRCULATIONPLACENTAL CIRCULATION

The fetal circulation system • Fetal blood comes via the two umbilical arteries, arteria

umbilicales in the villi and leaves the placenta through a single navel vein, the vena umbilicalis .

• The pressure in the fetal vessels and their villus branches always lies over that of the intervillous space. This protects the fetal vessels from collapse.

• arterial pressure: 50mm of Hg• venous pressure: 20mm of Hg

1 Umbilical arteries

2 Umbilical vein

3 Fetal capillaries

The maternal circulation system• Via the spiral arteries (80 -100 mm Hg) that come

from the uterine arteries (Aa. uterinae), maternal blood gets into the intervillous spaces.

• Subsequently the blood leaves the intervillous spaces via the uterine veins that are arranged in the periphery of the intervillous space.

• The flow of the placental blood amounts to 600 cm3/min and the pressure in the spiral arteries to 70 mm Hg. In the intervillous spaces the pressure falls to only 10 mm Hg .The blood in the intervillous space is exchanged 2-3 times per minute.

 

1 Spiral arteries2 Uterine veins3 Intervillous spaces A Basal plate

The placental The placental membrane(barrier) membrane(barrier)

• In the first trimester it consists of the syncytiotrophoblast, the cytotrophoblast (Langhans' cells), the villus mesenchyma (in which numerous ovoid Hofbauer cells that exhibit macrophage properties are found) and the fetal capillary walls.

  

  •  

1 Intervillous space2 syncitiotrophoblast3 cytotrophoblast4 villus mesenchyma5 fetal capillaries 6 Hofbauer macrophage

• During the 4th month the cytotrophoblast disappears from the villus wall and the thickness of the barrier decreases while the surface area increases (roughly 12 m2 towards the end of the pregnancy). In the 5th month the fetal vessels have multiplied their branches and gotten closer to the villus surface.

•  

1 Intervillous space2 Syncytiotrophoblast3 Cytotrophoblast4 Villus mesenchyma5 Fetal capillaries6 Hofbauer macrophages

• During the 6th month the nuclei of the syncytiotrophoblast group together in the so-called proliferation knots. The other zones of the syncytiotrophoblast lack nuclei and are adjacent to the capillaries (exchange zones).

 

1 Intervillous space (with maternal blood)2 Placental barrier of a terminal villus3 Fetal capillaries4 Merged basal membranes of the fetal capillary and of the syncythiothrophoblast5 Endothelial cells6 Rare cytotrophoblast cells7 Basal membrane of the capillaries8 Basal membrane of the trophoblast portion9 Syncytiotrophoblast with proliferation knots (nuclei rich region)

PLACENTAL FUNCTIONSPLACENTAL FUNCTIONS

TRANSPORT FUNCTION: The placental membranes actively control the transfer of a wide range of substances by 5 major mechanisms

• Simple diffusion • Facilitated transport • Active transport • Pinocytosis• Bulk flow of water and some solutes result

from hydrostatic and osmotic pressures

• Respiratory function• Excretory function• Nutritive function Glucose Lipids Amino Acids Water and electrolytes Hormones

• ENZYMATIC FUNCTION• STORAGE FUNCTION• BARRIER FUNCTION• IMMUNOLOGICAL FUNCTION• ENDOCRINE FUNCTIONS: The placenta

produces hormones that are vital to the survival of fetus. It includes following.

• Protein hormones: hCG, hPL PS β-1G• Steroid hormones: Estrogen

(estriol,estradiol,estrone) , Progesterone. 

Human chorionic gonadotrophinHuman chorionic gonadotrophin (hCG)(hCG)

• Functions:• It stimulates the secretion of estrogen and progesterone by

the corpus luteum and prevents involution of the corpus luteum at end of menstrual cycle thereby preventing spontaneous abortion.

• It stimulates Leydig cells of the male fetus to produce testosterones that causes male sex organs to grow.

• It has got immuno-suppressive activity which may inhibit the maternal process of immunorejection of the fetus as a homograft.

• It is also used as basis for pregnancy test.

Human placental lactogen (hPL) / Human Human placental lactogen (hPL) / Human chorionic somatomammotrophin (hCS):chorionic somatomammotrophin (hCS):

• Functions:• Proteolysis and lipolysis in mother and

promotes transfer of glucose and amino acids to the fetus.

• It antagonizes insulin action, high level of maternal insulin promotes protein synthesis.

• Stimulates breast development to prepare for lactation.

•  

Pregnancy specific -1 glycoprotein (PS β-1G

• Function: It is a potent immuno-suppressor of lymphocyte proliferation and prevents rejection of the conceptus.

 Human chorionic thyrotrophin (hCT) and Human chorionic corticotrophin (hCC

• Function: Accelerating the activity of thyroid, adrenal cortex and pancreas to meet the additional needs during pregnancy.

• Functions of steroid hormones :(estrogen and progesterone)

• Estrogen causes hypertrophy and hyperplasia of the uterine myometrium, thereby increasing the accommodation capacity and blood flow of the uterus.

• Progesterone in conjunction with estrogen stimulates growth of the uterus, causes decidual changes of the endometrium required for implantation and it inhibits myometrial contraction.

• Proliferation and hypertophy of the ducts in breast are due to estrogen while those of lobulo- alveolar system are due to combined action of estrogen and progesterone

• Both the steroids are required for the adaptation of the maternal organs to the constantly increasing demands of the growing fetus

• Progesterone maintains uterine quiescence, by stabilizing lysosomal membranes and inhibiting prostaglandins synthesis. Estrogen and progesterone are antagonistic in the process of labour.

• Estrogen sensitizes the myometrium to oxytocin and prostaglandins. It ripens the cervix.

• Progesterone along with hCG and decidual cortisol inhibits T- lymphocyte mediated tissue rejection and protects the conceptus.

• Together they cause inhibition of cyclic fluctuating activity of gonadotrphin-gonadal axis thereby preserving gonadal function.

 

PLACENTAL GRADINGPLACENTAL GRADING

• Grade 0: placental age 12-24 weeks • Grade 1: placental age 30-32 weeks• Grade 2: placental age 36 weeks• Grade 3: placental age 38 weeks

ABNORMALITIES OF ABNORMALITIES OF PLACENTA AND CORD PLACENTA AND CORD

• PLACENTA SUCCENTURIATA

PLACENTA EXTRACHORIALIS: PLACENTA EXTRACHORIALIS:

Circumvallate Placenta Circumvallate Placenta

• Placenta marginata

• PLACENTA MEMBRANECAE• BIPARTITE PLACENTA • TRIPARTITE PLACENTA• Placenta in multiple pregnancy

Abnormal placental attachment or Abnormal placental attachment or separationseparation

• Placenta accreta/percreta/increta• Placental abruption• Placenta praevia

CORD ABNORMALITIES CORD ABNORMALITIES

• BATTLEDORE PLACENTA

VELAMENTOUS PLACENTAVELAMENTOUS PLACENTA

• Abnormal length of cord long cord (>100 cm) short cord (<40 cm)

• Cord Knots• Cord Vessels• Thromboses

PLACENTAL INSUFFICIENCYPLACENTAL INSUFFICIENCY

• Definition: Placental insufficiency is a complication of pregnancy in which the placenta cannot bring enough oxygen and nutrients to a baby growing in the womb.

• Etiology• Effects

Risks to the fetus• 8-fold higher risk of death during delivery • 5-fold higher risk of poor oxygenation at birth that may lead

to cerebral palsy and other complications • Hypothermia, or low body temperature • Hypoglycemia, or low blood sugar • 30 to 40% chance of learning disabilities • Premature delivery • Poor tolerance of labor • Increased chance of cesarean birth • Increased chance of having birth defects • Increased chance of meconium aspiration, in which the

baby inhales some of the amniotic fluid during labor • Polycythemia, which is an excess of red blood cells • Hypocalcemia, which is too little calcium in the blood

• Treatment• Side effects of the treatment• Monitoring the condition• Preventing the condition

INTRA UTERINE GROWTH RETARDATIONINTRA UTERINE GROWTH RETARDATION

• Definition: Intrauterine growth restriction refers to a fetus whose weight is below the 10th percentile of the average for its gestational age.

Etiology:• Maternal:• Constitutional : Small women, maternal genetic

and racial background are associated with small babies.

• Poor maternal nutrition before and during the pregnancy

• Maternal diseases: Heart disease, preeclampsia or eclampsia, anemia, chronic renal disease etc.

• Toxins: Alcohol abuse, drug addiction, smoking • Fetal: • Structural anomalies: cardiovascular, renal or others • Chromosomal abnormality: Turner’s

syndrome ,trisomies (13.18,21)• Infection: TORCH agents• Multiple pregnancy: there is mechanical hindrance to

growth and excessive fetal demand. Placental: • Poor uterine blood flow to the placenta for along time.• Placental pathology: Placenta praevia , abruption,

infarction etc

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 • Jacob Annamma . A Comprehensive Textbook of Midwifery .

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• http: //www. ScienceDirect .com- Placenta Placental Findings Contributing to Fetal Death.

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