Placenta and Extraembryonic Membranes

Question 1

amnion summary

Answer 1

ectodermal derivative; forms a protective fluid-filled capsule around the embryo

Question 2

allantois summary

Answer 2

endodermal derivative; associated with removal of embryonic wastes

Question 3

extraembryonic mesoderm

Answer 3

bulk of umbilical cord

Question 4

amniotic fluid

Answer 4

buffer against mechanical injury; accommodates growth, allows normal fetal movements and protects the fetus from adhesions;

dilute transudate of maternal placenta

Question 5

two phases of amniotic fluid production

Answer 5

First 20 weeks of pregnancy: composition is quite similar to fetal fluids; fetal skin is unkeratinized and there is evidence that fluid and electrolytes are able to diffuse freely through embryonic ectoderm of skin; amniotic membrane secretes fluids

After first 20 weeks: increasing contributions from fetal urine, filtration from maternal blood vessels near the chorion leave; and filtration from fetal vessels in the umbilical cord and chorionic plate

fetal swallowing is important to turnover of amniotic fluid in the late pregnancy

Question 6

yolk sac

Answer 6

extraembryonic endoderm lining; formed ventral to the embryo

small and devoid of yolk; remains vital to embryo although not for nutritive purposes; may play role in prevention of neural tube defects

endoderm of yolk sac is lined on the outside by well-vascularized extraembryonic mesoderm

primordial germ cells which arise in extraembryonic mesoderm near the base of the allantois become visible in yolk sac

extraembryonic mesoderm becomes organized into blood islands and cells differentiate into primitive blood cells

Question 7

extraembryonic hematopoiesis

Answer 7

occurs in yolk sac until 6th week when blood forming activity moves to the intraembryonic sites like the liver

Question 8

Meckel’s diverticulum

Answer 8

attachment site of yolk stalk becomes less prominent, but in some adults, traces of the yolk duct persist as a fibrous cord or outpouching of small intestine

Question 9

allantois

Answer 9

hydramnios arises from pocketing of hindgut; in humans only retains secondary function;

blood vessels that differentiate fro the mesodermal wall of the allantois; form the umbilical circulatory arc

allantois is a cord of endodermal cells and is embedded in the umbilical cord

urachus=proximal part of allantois; continuous with forming urinary bladder; after birth is transformed into dense fibrous cord (median umbilical ligament) which runs from urinary bladder to the umbilical region

Question 10

hydramnios

Answer 10

excessive amount of amniotic fluid (>2000 mL)

associated with multiple pregnancies and esophageal atresia or anencephaly (congenital anomaly characterized by gross defects of the head and often the inability to swallow)

Question 11

oligohydramnios

Answer 11

too little amniotic fluid (

Question 12

amniocentesis

Answer 12

removing a small amount of amniotic fluid by inserting a needle through the mother’s abdomen into amniotic cavity

culture fetal cells present in amniotic fluid and examine for various chromosomal and metabolic defects

Question 13

alpha-fetoprotein

Answer 13

protein of central nervous system; high concentration in amniotic fluid is strong indicator of neural tube defects

Question 14

lecithin-to-sphingomyelin ratio

Answer 14

assess the fetal maturity by reflecting the maturity of the lungs

Question 15

erythroblastosis fetalis

Answer 15

Rh disease that can be assessed by examination of amniotic fluid

Question 16

early stages of implantation

Answer 16

original trophoblast surrounding embryo differentiates into cytotrophoblast and syncytiotrophoblast

lacunae in the rapidly expanding trophoblast have filled with maternal blood and connective tissue cells of endometrium have undergone the decidual reaction (containing increased amounts of glycogen and lipids)

Question 17

previllous embryo

Answer 17

trophoblastic tissues have no consistent gross morphological features

Question 18

primary villi

Answer 18

cytotrophoblastic projections

Question 19

secondary villus

Answer 19

mesenchymal core within the expanding villus; surrounding the core is complete layer of cytotrophoblastic cells and outside of that is the syncytiotrophoblast

Question 20

tertiary villus

Answer 20

when blood vessels penetrate the mesenchymal core and newly formed branches (individual villi undergo considerable branching but most of them retain the same basic structural plan throughout pregnancy)

near 3rd week of pregnancy

allow embryonic blood to come close to the maternal blood without actually touching it

Question 21

Msx2 and Dlx4

Answer 21

genes expressed at interface between the trophoblast and the underlying extraembryonic mesenchyme

often at sites of epitheliomesenchymal interactions

Question 22

Gem-1

Answer 22

TF which promotes an exist from the cell cycle; expressed at branching points on the villi;

cytotrophoblastic cells on either side of the region of Gem-1 expression continue to proliferate

Question 23

cytotrophoblastic cell column

Answer 23

terminal portion of the villus remains trophoblastic, consisting of a sold mass of cytotrophoblast; covered by relatively thin layer of syncytiotrophoblast

villus is bathed in maternal blood

Question 24

cytotrophoblastic shell

Answer 24

local hypoxic environment causes cytotrophoblastic cell column to expand distally and penetrate the syncytiotrophoblastic layer; abut directly on maternal decidual cells and spread over them to form complete cellular layer

Question 25

anchoring villi

Answer 25

villi that give off the cytotrophoblastic extensions; they represent the real attachment points between the embryo complex and the maternal tissues by means of cytotrophoblastic cell columns, it attaches the villus complex to the outer cytotrophoblastic shell

Question 26

overall relationships of the various embryonic and maternal tissues

Answer 26

embryo is attached to the body stalk (umbilical cord) and suspended in the chorionic cavity, which is bound to the chorionic plate (extraembryonic mesoderm overlaid with trophoblast) chorionic villi extend outward from the chorionic plate and their trophoblastic covering is continuous with that of the chorionic plate villi and outer surface of the chorionic plate are bathed in a sea of continually exchanging maternal blood human placenta is hemochorial type

Question 27

floating villi

Answer 27

unattached branches dangle freely in maternal blood that fills the space between the chorionic plate and he outer cytotrophoblastic shell

Question 28

what does the syncytiotrophoblast line continuously?

Answer 28

all surfaces of he villi, chorionic plate, and cytotrophoblastic shell that are in contact with maternal blood

Question 29

uteroplacental circulation

Answer 29

serves as the medium for bringing food and oxygen to and removing wastes from the embryo

Question 30

spiral arteries

Answer 30

walls are eroded and modified so that, as the embryo grows, these arteries can provide an increasing flow of blood at low pressure to bathe the syncytiotrophoblastic surface of the placenta

Question 31

invasive cytrophoblastic cells

Answer 31

migrate out from anchoring villi; invade the spiral arteries, but not the veins; cause major modifications of their walls by secreting a specialized ECM and displacing many of the normal cellular elements of the spiral arteries; arteries become wider but blood escaping from their open end leaves at much lower pressure than normal arterial pressure

Question 32

results of hypoxia on cytotrophoblastic cells

Answer 32

stimulates mitosis; explains the rapid growth of the cytotrophoblast during the early embryonic period after 12 weeks, switch from embryonic to fetal hemoglobin as oxygen content increases from maternal blood

Question 33

decidual reaction and decidual cells

Answer 33

stromal cells swell as the result of accumulation of glycogen and lipids in their cytoplasm spreads through stromal cells of he superficial layers of the endometrium

Question 34

decidua capsularis

Answer 34

decidual tissue that overlies the embryo and its chorionic vesicle

Question 35

decidua basalis

Answer 35

lies between the chorionic vesicle and the uterine wall becomes incorporated into the maternal component of the definitive placenta

Question 36

decidua parietalis

Answer 36

remaining decidua, decidualized endometrial tissue on the sides of the uterus not occupied by the embryo

Question 37

chorion

Answer 37

layer consisting of the trophoblast and the underlying exraembryonic mesoderm forms complete covering (chorionic vesicle) that surrounds the embryo, amnion, yolk sac, and body stalk villi at first project from the entire outer surface of the chorionic vesicle

Question 38

chorion frondosum

Answer 38

region that contains the flourishing chorionic villi and ultimately becomes placenta; extension and growth of villi that preferentially occurs nearest to the decidua basalis

Question 39

chorion laeve

Answer 39

ultimately becomes smooth; chorion villi that are located on the opposite side (the abembryonic pole) of the chorionic vesicle that fail to keep up and eventually atrophy as the growing embryo complex bulges into the uterine cavity oxidative stress may play a role

Question 40

fate of decidua capsularis

Answer 40

growth of chorionic vesicle pushes the decidua capsularis farther form the endometrial blood vessels; by the end of the first trimester, decidua capsularis undergoes pronounced atrophy and begins to disappear, leaving portions of the chorion leave in direct contact with decidua parietalis on the opposite side of the uterus decidua capsularis fuses with decidua parietalis by mid-pregnancy

Question 41

fetal component of the placenta

Answer 41

part of the chorionic vesicle represented by the chorion frondosum--wall of chorion (chorionic plate) and the chorionic villi that arise from that region

Question 42

maternal component of the placenta

Answer 42

decidua basalis;; covering of decidua basalis is fetally derived outer cytotrophoblastic shell

Question 43

intervillous space of placenta

Answer 43

occupied by freely circulating maternal blood

Question 44

structure of mature placenta

Answer 44

weights about 500 g; fetal side of the placenta is shiny because of the apposed amniotic membrane from the fetal side, attachment of umbilical cord to the chorionic plate and the large placental branches of the umbilical arteries and vein radiating from it are evident maternal side of placenta is dull and subdivided into as many as 35 lobes; placental septa between lobes arise from decidua basalis and extend toward the basal plate within placental lobe are several cotyledons = main stem villus and all of its branches intervillous space of each lobe is a nearly isolated compartment of the maternal circulation to the placenta

Question 45

umbilical cord

Answer 45

conduit for the umbilical vessels which are embedded in a mucoid connective tissue called Wharton's jelly 50-60cm at end of pregnancy; typically twisted many times; contains 2 arteries and 1 vein; occasionally will have 2 veins if the right umbilical vein doesn't undergo its normal degeneration

Question 46

placental circulation

Answer 46

both mother and fetus contribute to this; fetal blood reaches placenta through 2 umbilical arteries and break up into successively smaller branches which then consolidate into larger and larger venous branches ==> one vein back to fetus maternal circulation is free-flowing lake that is not bounded by vessel walls==> 80-100 spiral arteries open directly into intervillous space releasing about 150 mL of maternal blood maternal blood enters at reduced pressure due to cytotrophoblastic plugs placental barrier of mature placenta consists of the syncytiotrophoblast, basal lamina of the fetal capillaries; and capillary endothelium

Question 47

structure of mature chorionic villus Hofbauer cells

Answer 47

mass of interwoven branches; core of villus is blood vessels and mesenchyme that is similar in composition of the mesenchyme of the umbilical cord Hofbauer cells: function as fetal macrophages and are scattered among the mesenchymal cells villus core is covered by continuous syncytiotrophoblast, surface of which is covered by microvilli, increasing the total surface area of placenta;; size and density of microvilli are not constant trophoblastic surface contains areas that: contain numerous transport systems for substances ranging from ions to macromolecules, hormone and growth factor receptors, enzymes, numerous other proteins placental surface is deficient and lacking major histocompatibility antigens, the absence of which plays a role in protecting against maternal immune rejection of fetus and fetal membranes

Question 48

epithelial plates

Answer 48

scattered areas where the barrier between fetal and maternal blood is extremely thin; designed to facilitate diffusion of substances between the fetal and maternal circulations transfer goes both ways: mother gives oxygen and nutrients, baby gives carbon dioxide and fetal waste materials

Question 49

substances that readily cross placental barrier

Answer 49

gases (oxygen from mother; carbon dioxide from fetus) cross by diffusion; amount exchange limited by blood flow; carbon monoxide and inhalational anesthetics water and electrolytes are readily transferred across placenta fetal wastes (urea, creatinine, bilirubin) rapidly transferred across placenta highly permeable to glucose, amino acids, some free fatty acids, water-soluble vitamins steroid hormones cross barrier from maternal side (protein hormones in general are not transported) some proteins transferred slowly mostly by pinocytosis maternal antibodies (IgG)--increases throughout pregnancy beginning at 12 weeks transferrin (maternal protein that transfers iron to the fetus)

Question 50

erythroblastosis fetalis

Answer 50

small quantities of fetal blood cells escape into maternal circulation; if you have Rh+ fetus but Rh- mother, the mother will develop antibodies to Rh+ cells; first child is okay but subsequent pregnancies are attacked by maternal anti-Rh antibodies which make their way into fetal bloodstream antibody causes hemolysis of Rh-+ fetal erythrocytes

Question 51

human chorionic gonadotropin (HCG)

Answer 51

first protein hormone produced by placenta (syncytiotrophoblast); responsible for maintaining corpus luteum and its production of progesterone and estrogen synthesis begins even before implantation production peaks at ~8 weeks and then gradually declines

Question 52

progesterone and estrogen

Answer 52

produced by the placenta; pregnancy can be maintained even if corpus luteum is removed; progesterone from acetate or cholesterol precursors but doesn't contain machinery needed to make estrogens; placenta must operate in concert with fetal adrenal gland and possibly the liver to make estrogens

Question 53

chorionic somatomammotropin

Answer 53

human placental lactogen similar to HGH, influences growth, lactation, lipid and carbohydrate metabolism placenta also produces chorionic thyrotropin and chorionic corticotropin

Question 54

human placental growth hormone

Answer 54

produced by syncytiotrophoblast; influences growth of placenta by paracrine fashion exerts profound effect on mother; replaces maternal pituitary growth hormone; regulation of maternal blood glucose levels so that the fetus is ensured of an adequate nutrient supply

Question 55

placental immunology

Answer 55

thought that fetal tissues like placenta that interface with mother do not present foreign antigens to the mother's immune system --somewhat true because syncytiotrophoblast and cytotrophoblastic shell do not present antigens but they are found on cells of fetus and in stromal tissues of the placenta fetal RBCs and WBCs found circulating in the maternal blood possible that mothers immune system is paralyzed during pregnancy but mother is capable of mounting immune response to other invaders possible that local decidual barriers prevent either immune recognition of the fetus by the mother or the reaching of competent immune cells from the mother to the fetus molecules formed on the fetal placental surface might be able to inactivate the T cells or other immune cells locally

Question 56

placenta previa

Answer 56

abnormal implantation sites with the uterine cavity;; part of placenta may cover the cervical outlet of the uterine cavity, mechanical obstacle in the birth canal; may also result in fatal hemorrhage

Question 57

velamentous insertion

Answer 57

if umbilical cod attaches to the smooth membranes outside the boundaries of the placenta itself

Question 58

accessory lobes

Answer 58

placenta can be subdivided into accessory lobes or completely divided into two parts

Question 59

hydatidiform mole

Answer 59

noninvasive condition in which many of the chorionic villi are characterized by nodular swellings that give them an appearance similar to a bunch of grapes; embryo is either absent or not viable ; villi show no signs of vascularization result of paternal imprinting in which female pronucleus of the egg does not participate in development

Question 60

choriocarninomas

Answer 60

malignant tumors derived from embryonic cytotrophoblast and syncytiotrophoblast ; contain only paternally derived chromosomes and products of paternal imprinting

Question 61

twin-to-twin transfusion syndrome

Answer 61

when vascular systems are fused, one twin may receive a greater proportion of the placental blood flow; may result in mild to severe stunting of growth of the embryo that receives the lesser amount of blood; twin with less blood is misshapen and called acardiac monster