Extraembyronic Tissues And Placenta - Lectures 17 & 18

Question 1

What are the extraembryonic tissues?

Answer 1

Amnion (ICM - epiblast)
Yolk Sac (ICM hypoblast)
Chorion (fetal maternal interface)
Allantois (ICM)

Question 2

What are the fetal maternal interface tissues and where do they derive from?

Answer 2

Placenta and Chorion

Derive from trophoblast

Question 3

What are the functions of the amnion?

Answer 3

Buffer against mechanical injury
Accommadates growth
Allows normal movements
Protects fetus from adhesions

Question 4

Hydramnios

Answer 4

Condition is associated with esophageal atresia and anencephaly

excessive amount of amnionic fluid - more than 2000 ml

Question 5

Oligohydraminos

Answer 5

Too little amnionic fluid, less than 500ml

Renal agenesis - no kindeys, speaks to the importance of the fetus waste contribution to the fluid

Question 6

What can you learn from testing A-fetoprotein, creatine and lecithin-to-sphingomyelin ratio??

Answer 6

α-fetoprotein is a amniotic fluid indicator of a neural tube defect

Fetal maturity and lung development can be assessed with creatine concentration and the lecthin-to-sphingomyelin ratio

Question 7

What is phase I amnionic fluid and it’s source?

Answer 7

In the first 20 weeks of pregnancy

There’s free diffusion of electrolytes through fetal ectoderm

Maternal serum

Secreted by amionic membrane

Question 8

Phase II amnionic fluid

Answer 8

Fetus added urine

Filtrate from vessels associated with chorion laeve

Filtrate from fetal vessels in umbilical cord is another possible source

Turnover rate in late pregnancy is every 3 hours or 500ml/hour

Question 9

What are the possilbe functions of the yolk sac in mammals?

Answer 9

May concentrate: Folic acid and vitamins (A, B12 and E) - important source of nutrient for neuralation (histiotraphic nutrition)

Other functions: site of primordial germ cells and blood islands (origin of initial blood cells)
-extraembryonic hematopoesis

Meckels diverticulum - pouch of the ilium and represents the original attachment site of the yolk sac to the embryo

Question 10

Development of the allantois

Answer 10

Allantoic (umbillical) vessel develop in the mesoderm of the allantois

Proximal part of allantois - formation of urinary bladder and becomes the median umbilical ligament (runs from bladder to umbilical cord)

Question 11

4 Stages of Chorion Villi Development

Answer 11

previllous embryo - no villi have been formed on the trophoblast

primary villous stage - solid, cytotrophoblastic, ectodermal primary willi appear

secondary villous stage - mesodermal cores appears within the primary villi

tertiary villous stage - characterized by the appearance of blood vessels within the mesenchymal core of the secondary villi

Final Dev - cytotrophoblastic columns and shells and anchoring villi: villi achored to the cytotrohophoblastic shell

Question 12

What are Hofbauer cells?

Answer 12

Fetal macrophages

Question 13

Placental Development and Structure

Answer 13

Composed of two parts: fetal part and maternal part

Fetal part is chorionic plate and chorionic villi extended toward maternal.

Maternal part is the cytotrophoblastic shell, from the decidua basalis.

The intervillis space between the chorionic plate and cytotrophoblastic shell is filled with maternal blood

cytotrophoblastic columns are villus that extend from the chorionic plate to the cytotrophoblastic shell

if they connect to the shell then they are called anchoring villi, if they are unattached then- floating villi.

Question 14

why is the human placenta known as the hemochorial type?

Answer 14

Because the maternal blood directly interfaces with the fetal chorion

This in not seen in all animals

Question 15

What tissue in the mature placenta directly interfaces with the maternal uterine connective tissue?

Answer 15

the cytotrophoblast

Question 16

Decidual Reaction

Answer 16

The stroma cells of the endometrium swell full of lipids and glycogen

decidua capsularia -sorrounds the embryo and chorion

decidua basalis - is between chorion and the uterine wall, becomes part of the placenta

decidua parietalis - decidua (endometrium tissue that underwent the decidual reaction) on sides without the embryo

Question 17

What maternal tissues are lost at birth?

Answer 17

maternal decidua

Question 18

What is the fate of the decidua capsularis?

Answer 18

it starts to degrade within the decidua parietalis, l

Question 19

Layers of the womb

Answer 19

embryo 
amnion 
chorion - extraembryonic mesoderm 
synchtiotrophoblast 
cytotrophoblastic shell decidua capsularis

Question 20

Maternal blood flow

Answer 20

Maternal blood flow - from spiral arteries into trophoblastic lacunae, the intervillus space of the placenta

Exchange in the the villi

back to maternal blood

Question 21

Fetal Blood Flow

Answer 21

entirely enclosed in vessels

travels to capillary beds within placenta by umbilical arteries

Returns by umbilical vein

Question 22

Erythroblastosis fetalis

Answer 22

Rh incompatibility between maternal and fetal blood. Mother is Rh- and baby is Rh+, mother makes antibodies against the Ph antigen and in all subsequent pregnancy those antibodies will attack and lyse fetal erythrocytes

Hydrops

Question 23

How does hydrops fatalis relate to erthroblastosis fetalis?

Answer 23

hydrops fetalis: water accumulation in fetus

the bilirubin released from the lysed erthyocytes causes hydrops fetalis where the fetus takes on water, jaundice, brain damage and anemia

Question 24

hydatiform mole

Answer 24

placenta villi swell into grape like appearance and fetus is either absent or not viable.

Happens from paternal imprinting causes the female pronucleus to sit the whole process out, or by duplication of the sperm dna, or two sperms.

Question 25

Placenta previa

Answer 25

abnormal site for the placenta (ectopic pregnancy)

Question 26

Functions of the Placenta

Answer 26

diffusion of oxygen and carbon dioxide

diffusion of foodstuff

excretion of waste

Question 27

what’s the difference between the early placenta and the late placenta

Answer 27

early placenta is thick, has low permeability, small surface area with small diffusion conductance

the late placenta is thin, permeability, large surface area and great placental diffusion

Question 28

THere’s a low pressure gradient between the mother and fetus at the end of pregnancy, why does adequate oxyengation occur?

Answer 28

fetal hemoglobin has a higher affinity for oxygen

fetal blood hemoglobin concentration is 50% greater than maternal

bohr effect - lower CO2 means more O

Question 29

what is the double bohr effect?

Answer 29

the bohr effect is happening in both the fetus and mother but opposite

Question 30

Human chorionic gonadotropin

Answer 30

Secreted by syncytial trophoblast cells into maternal fluids, measurable 8-9 days after ovulation, maximum secretion 10th-12th week of pregnancy

Prevent involutionof corpus luteum
Induces release of progestrone and estrogens by the corpus luteum
Corpus luteum growth
Has an interstitial cell-stimulating effect on the testes of male fetus

Question 31

Estrogens

Answer 31

Secreted by syncytiotrophoblast cells of the placenta
At end of pregnancy secretion level is 30 times normal

Formed from androgenic steriod compounds, adrenal glands, and converted by trophoblast cells

Functions: 
Unterine enlargement 
Breast enlargement 
Growth of breast ductal structures 
Enlargement of maternal external genitalia 
Relaxation of pelvic ligaments 
Maybe affects fetal development 

Higher in later pregnancy

Question 32

Progestrone

Answer 32

Secreted in small amounts early in pregnancy by corpus luteum

In large amounts by placenta

Functions:

• caused decidual cells to develop
• decrease contractablility of the uterus
• increases secretion of fallopian tubes and uterus
• may help prepare breast for lactation

Higher in later pregnancy

Question 33

Human Chorionic Somatomammotropin

Answer 33

Secreted by placenta in 5th week

Functions:

• decreased insulin sensitivity andd decreased utilization of glucose by mother
• general metabolic hormone

Secretion levels off on end of pregnancy

Question 34

What are the theory’s on why the mother’s immune system doesn’t attack the fetus?

Answer 34

Placenta (syncytiotrophoblast and cytotrophoblast) don’t express MHC

Paralysis of mother’s immune system during preegnancy

Decidual immune barrier

Inactivation of mother’s immune system components by molecules formed on fetal placental surface

Question 35

Fetal Alcohol Syndrome

Answer 35

Poor growth rate 
Microcephaly
Mental retardation 
Heart defects 
Hypoplasia of facial features