Human Placenta Function and Structure Quiz

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Questions and Answers

What is the main role of the intervillous spaces in the mature placenta?

Support fetal vessel development

Facilitate blood drainage into maternal circulation (correct)

Act as a physical barrier between maternal and fetal blood

Store nutrients for the fetus

Which layer of the placental membrane is in direct contact with maternal blood?

Connective tissue in the villus core

Endothelial lining of fetal vessels

Syncytium (correct)

Cytotrophoblastic layer

How much blood is typically contained in the intervillous spaces of a mature placenta?

200 mL

150 mL (correct)

50 mL

100 mL

What primarily determines the amount of oxygen reaching the fetus?

Rate of placental blood flow Signup and view all the answers

Which statement about the placental barrier is correct?

Many substances can pass through it freely Signup and view all the answers

During which month does the placental membrane start to thin significantly?

Fourth month Signup and view all the answers

What type of placenta does the human placenta represent?

Hemochorial Signup and view all the answers

What method facilitates the exchange of gases in the placenta?

Simple diffusion Signup and view all the answers

What primarily forms the surface of the villi?

Syncytium Signup and view all the answers

What transformation occurs in the spiral arteries due to cytotrophoblast invasion?

Increase in diameter Signup and view all the answers

What are the structures formed by large pieces of syncytium that may break off into the intervillous blood lakes called?

Syncytial knots Signup and view all the answers

Which layer is not involved in the exchange between maternal and fetal circulations?

Cytotrophoblastic cells Signup and view all the answers

Which structure develops from the core of the vascular mesoderm within the villous stems?

Capillary system Signup and view all the answers

What does endovascular invasion by cytotrophoblast cells accomplish?

Release of maternal blood into intervillous spaces Signup and view all the answers

At the beginning of the fourth month, what happens to the cytotrophoblastic cells?

They persist in all sizes of villi Signup and view all the answers

Which of the following best describes the villi's coverage during the early weeks of development?

Covering the entire surface of the chorion Signup and view all the answers

What characterizes the chorion laeve by the third month of pregnancy?

It becomes smooth due to degeneration of villi. Signup and view all the answers

Which layer of the endometrium is shed during parturition?

Decidua Signup and view all the answers

What is the primary role of the chorion frondosum?

To facilitate the exchange process in the placenta. Signup and view all the answers

What occurs as the chorion laeve comes into contact with the decidua parietalis?

It fuses, obliterating the uterine lumen. Signup and view all the answers

Which component primarily forms the maternal portion of the placenta?

Decidua basalis Signup and view all the answers

What happens to the cytotrophoblast cells as pregnancy progresses?

They degenerate significantly. Signup and view all the answers

What fills the intervillous spaces found between chorionic and decidual plates?

Maternal blood Signup and view all the answers

What significant event occurs when the amniochorionic membrane ruptures during labor?

The water breaks, signaling the onset of labor. Signup and view all the answers

What is the most common method for calculating the expected date of delivery for a pregnant woman?

Counting 280 days from the first day of the last menstrual period Signup and view all the answers

Why is it difficult to determine the exact day of fertilization for a pregnant woman?

The day of fertilization is often vague in memory Signup and view all the answers

What is categorized as premature birth?

Birth occurring before 37 weeks of gestation Signup and view all the answers

Which measurement is most accurate for determining fetal age during the 7th to 14th weeks of development?

Crown-rump length (CRL) Signup and view all the answers

What triggers major changes in the placenta around the ninth week of fetal development?

Increased demands from the fetus Signup and view all the answers

What is the main function of the placenta?

To facilitate nutrient and gas exchange between maternal and fetal compartments Signup and view all the answers

Which structure is derived from the trophoblast during placental development?

Chorionic plate Signup and view all the answers

What can ultrasound measure during pregnancy to help assess fetal development?

Crown-rump length (CRL) and biparietal diameter (BPD) Signup and view all the answers

What percentage of twins are usually dizygotic?

Approximately 66% Signup and view all the answers

What is the primary biological process that leads to the formation of dizygotic twins?

Simultaneous shedding of two oocytes Signup and view all the answers

Which characteristic is TRUE for monozygotic twins?

They share a common placenta in all cases Signup and view all the answers

At what stage of development does the earliest separation of a zygote into monozygotic twins occur?

Two-cell stage Signup and view all the answers

What happens to the uterine myometrium during the last 2 to 4 weeks of pregnancy?

It undergoes a transitional phase in preparation for labor Signup and view all the answers

Which of the following is NOT a characteristic of dizygotic twins?

Share a common placenta Signup and view all the answers

What happens to the chorionic cavity as the amniotic cavity enlarges during development?

It diminishes in size. Signup and view all the answers

What is the typical rate of occurrence of monozygotic twins per 1000 births?

3 to 4 Signup and view all the answers

What generally occurs during the transitional phase leading to labor?

Increased blood supply to the cervix Signup and view all the answers

What is contained within the primitive umbilical cord?

Yolk sac stalk and umbilical vessels. Signup and view all the answers

What is the primary source of amniotic fluid during pregnancy?

Maternal blood. Signup and view all the answers

How much amniotic fluid is typically present at 37 weeks of gestation?

800 to 1000 mL. Signup and view all the answers

What role does Wharton's jelly play in relation to the umbilical vessels?

It acts as a protective layer. Signup and view all the answers

What change occurs in the placenta at the end of pregnancy regarding fetal capillaries?

Thickening of basement membranes. Signup and view all the answers

What is estimated to be the amount of amniotic fluid the fetus swallows daily from the fifth month onward?

400 mL. Signup and view all the answers

How does the amniochorionic membrane assist during childbirth?

By forming a hydrostatic wedge to dilate the cervical canal. Signup and view all the answers

Study Notes

Embryology L5-P1

The fetal period spans from the ninth week until birth
Characterized by accelerated tissue and organ maturation and rapid body growth
Fetal length is measured as crown-rump length (CRL) or crown-heel length (CHL). These measurements are related to fetal age in weeks/months.
Growth in length is most notable during the third, fourth, and fifth months. Weight gain is more significant during the last two months of gestation.
Typical pregnancy duration is 280 days (40 weeks) from the last menstrual period (LNMP) or 266 days (38 weeks) from fertilization.
The head comprises about half the crown-rump length (CRL) at the beginning of the third month, decreasing to one quarter of the crown-heel length (CHL) at birth.
Facial features become more distinct during the third month.
The eyes and ears develop as well.
Limb growth occurs steadily during this phase.
Primary ossification centers form in the long bones and skull in the 12th week.
At 11 weeks, fetal intestinal loops may be present, causing swelling in the umbilical cord.
Growth slows in the head relative to the body, but the body's growth accelerates.
By the 12th week, external genitalia become apparent.
By the end of the fifth month, the crown-heel length (CHL) is approximately 15 cm, and the average weight is under 500 g.
Fetal hair (lanugo) and eyebrows are visible by this stage.
Fetal movements can be detected by the mother during the fifth month.
Weight increases considerably during the last two and a half months of gestation, reaching about 3,200 g at full term.
By the end of gestation, the fetus' skin is covered by vernix caseosa—a whitish, fatty substance.

Fetal Membranes and Placenta

The placenta is crucial for nutrient and gas exchange.
Its surface area increases during the fetal development.
The fetal component is derived from the trophoblast and extraembryonic mesoderm.
The maternal component originates from the uterine endometrium.
By the second month, the trophoblast exhibits numerous secondary and tertiary villi.

Changes in the Trophoblast

Maternal blood is delivered by spiral arteries into the intervillous spaces.
Cytotrophoblast cells invade the terminal ends of spiral arteries, replacing maternal endothelial cells.
This transformation turns these vessels into low-resistance, larger-diameter vessels.
This improved maternal blood flow promotes intervillous exchanges and nutrient delivery.
The syncytium in the intervillous space becomes thin, while cytotrophoblastic cells decrease.
Syncytial knots may appear in the intervillous spaces during this process.

Chorion Frondosum and Decidua Basalis

Villi that are on the embryonic pole continue to grow and expand to develop into chorion frondosum (bushy chorion) during pregnancy.
The chorion laeve on the abembryonic pole has degenerated and is smooth.
The decidua basalis is a compact layer of decidual cells on the fetal side of the placenta, with high lipid and glycogen content.
The decidua capsularis is the layer opposite the developing fetus. It separates with the growth of the chorionic vesicle and gradually degenerates.

Chorion Frondosum and Decidua Basalis (Continued)

Subsequently, the chorion laeve contacts the uterine wall causing the two to fuse and obliterate the uterine lumen.
The chorion frondosum and decidua basalis together make up the structure of the placenta.
The amniochorionic membrane forms by the fusion.
During childbirth, this membrane ruptures (breaking the water), allowing labor to take place.

Circulation of the Placenta

Cotyledons (compartments) receive blood through 80-100 spiral arteries.
Pressure forces blood deep into the intervillous spaces.
Blood flows back from the chorionic plate to the endometrial veins, eventually returning to the maternal circulation.
The intervillous spaces contain approximately 150 mL of maternal blood.

Fetal Membranes in Twins

Dizygotic twins develop from two separate ova.
Monozygotic twins originate from a single ovum, which splits during development.
The arrangements of fetal membranes for twin births depend on the type, and the time of separation of monozygotic twins.
The zygotes in dizygotic twins individually develop their own placenta, chorion, and amnion.
Occasionally, the placentas/chorions may fuse if closely positioned.

Parturition (Birth)

Before the onset of labor, uterine myometrium does not respond to parturition signals.
In preparation for labor, the uterine myometrium undergoes transitional changes, including thickening in certain regions and softening processes in others.
The cervical regions thin, while simultaneous dilatation of the cervix takes place.
Labor involves effacement (cervix thinning) and widening of the cervix, followed by delivery of the fetus, and finally, the placenta.

Placental Changes at the End of Pregnancy

Fibrous tissue increases in the core of the villi.
Capillaries of the villi thicken.
Obliteration of villi capillaries occurs.
Fibrinoid is deposited on the villi's surface in the junctional zone and chorionic plate.

Amniotic Fluid

Amniotic fluid is mainly produced by amniotic membranes and maternal blood.
Fluid volume increases from 30 mL at 10 weeks to 800-1000 mL at 37 weeks. (approx)
Acts as a cushioned environment for the fetus, accommodating its movement and preventing adherence to membranes.
The fetus swallows about half of the fluid (approx 400 mL per day), and urine is added to the remaining volume daily.
Amniotic fluid plays a role in cervical dilation during childbirth.

Function of the Placenta

Exchanges metabolic and gaseous products (oxygen, carbon dioxide, and carbon monoxide) between the mother and fetus.
Produces important hormones during pregnancy.

Exchange of Gases

Gas exchange (oxygen, carbon dioxide, and carbon monoxide) occurs by simple diffusion.
Placental blood flow is critical for oxygen supply.
An interruption in the oxygen supply is fatal to the fetus.

Exchange of Nutrients and Electrolytes

The transfer of nutrients such as amino acids, fatty acids, carbohydrates, and vitamins is rapid, increasing with advancing pregnancy.
An essential role for maternal-fetal exchange in preserving fetal development.

Transmission of Maternal Antibodies

Fetal immunological competence develops in the first trimester.
Maternal Immunoglobulin G (IgG) is transferred to the fetus beginning in the 14th week, giving passive immunity against certain infections.
Newborns start producing their own IgG; but full adult levels are generally attained later. (after 3 years).

Hormone Production

Placental production of hormones (progesterone and estrogen) is substantial enough to maintain a pregnancy even if corpus luteum functions fail.
Estrogen biosynthesis is predominantly estriol, increasing until late pregnancy, and regulating uterine growth and mammary gland development.
Human chorionic gonadotropin (hCG) maintains the corpus luteum during the first two months of pregnancy. Its presence in maternal urine is utilized for pregnancy detection.
Placental lactogen (somatomammotropin) is responsible for the fetus' priority on maternal glucose, promoting diabetogenic effects in the mother and influencing breast development and preparing for lactation in the mother.

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Description

Test your knowledge about the structure and function of the human placenta with this quiz. Explore key concepts such as intervillous spaces, placental membranes, and the placental barrier. Perfect for students studying human anatomy and physiology.