Lecture 30/Lab XXVI - Female Reproductive System III

Explain the difference in the type of cells that make up the amnion vs the chorion laeve.

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Are the following statements about the amnion true or false? 1) The amnion is very thin. 2) The amnion is the innermost of the maternal membranes. 3) The amnion encloses the amniotic cavity and covers the surface of the placenta (fetal side) and umbilical cord. 4) The epithelium of the amnion is not exposed to the amniotic fluid 5) The amnion consists of simple epithelium with underlying mesenchyme (connective tissue). 6) The amnion is derived from the outer cell mass 7) The amnion is vascular 8) The amnion is responsible for tensile strength of the membranes.

1) True 2) False - innermost of the reflected FETAL membranes 3) True 4) False 5) True 6) False 7) False 8) True

What are three critical exchange functions of the placenta?

1) uptake of nutrients 2) removal of metabolic waste products 3) gas exchange: oxygen and carbon dioxide

What are two major maternal vascular adaptations to pregnancy?

1. High input of maternal blood into placenta is required. 2. Changes occur in the spiral arteries to render them less reactive to vasoactive mediators.

What are two important anatomical requirements for proper functioning of the placenta?

1. Maternal and fetal circulations must be brought into close proximity. 2. Separate circulations must be maintained.

The human placenta is discoid in shape, averaging ____ cm in diameter and 2 cm in thickness. Average weight is 500 gm, generally one-_____ that of the fetus. Contains _____-_____ ml of maternal blood.

20, fifth, 150-200

Where are villous structures found? What are villi lined by? What bathes the surface of the villi? What do the villi contain?

5. Villous structure a. Villi lined by trophoblast, the specialized, fetal-derived epithelium. b. Maternal blood bathes the surface of the villi. c. Villi contain branching fetal vessels derived from chorionic vessels

What are the first three steps of implantation and the early placenta?

A. Blastocyst attaches to uterine epithelium in middle of secretory phase of cycle. B. Trophoblast erodes epithelium and invades endometrium C. Primitive villi form and the mother's blood vessels are tapped.

How can terminal villi be described? What important exchange occurs in them?

Arborization of smaller and smaller branches, both of the villi and the vessels inside; ultimately generates many terminal villi containing abundant capillaries filled with fetal blood. Fetal-maternal exchange occurs in these villi.

What do anchoring villi do?

Attach placenta to mother's decidual tissue.

Where does chorion laeve attach? What does amnion cover?

Chorion laeve attaches to edge of placenta. Amnion continues on, to cover the placental surface and umbilical cord.

What are the last three steps of implantation and early placenta?

D. Villous development initially occurs all the way around the conceptus. E. One-fourth of the interface continues to develop into the discoid placenta. F. Remainder of interface undergoes villous degeneration, leaving only multiple layers of cytotrophoblast, forming the chorion laeve of the reflected membranes.

How is surface area of the syncytium increased?

Expression of many branching microvilli on syncytial plasma membrane creates a huge surface area for exchange.

T/F: Only certain material passes through the syncytium.

False - everything must go through the syncytium

T/F: The placenta remains separate from maternal tissue (decidua).

False - it attaches to the maternal tissue

T/F: The placental barrier between maternal blood and fetal blood does not change significantly as gestation progresses.

False - it does change

T/F: Viruses cannot cross the placenta, although drugs can.

False: Viruses, drugs, and potentially harmful maternal antibodies can all cross into the fetus

Describe blood flow from the fetus to the mother.

Fetal blood: Umbilical arteries → chorionic arteries → stem villus arteries → branching arterial vessels → capillaries → merging venous vessels → stem villus veins → chorionic veins → umbilical vein

What features can be found in a cross section of the placenta on the fetal and maternal sides?

Fetal side: chorionic plate containing large fetal vessels derived from umbilical vessels. Maternal side: basal plate is region of maternal decidua where attachment occurs.

What in the placenta is the internal structure composed of? Where do they extend from?

Internal structure is composed of projections, called villi, extending from chorionic plate; branch dramatically, hence the term villous tree.

What is the intervillous space in the placenta filled with? From where does the blood come? From where does it drain out?

Intervillous space (space between villi) is filled with maternal blood. a. Blood squirts in from the spiral arteries of the decidua b. Drains out the veins of the decidua.

What is decidua?

It is the maternal tissue at both placental and non-placental interfaces.

Describe blood flow from the mother to the fetus.

Maternal blood: Enters through spiral arteries, bathes trophoblast lining the villi, exits through maternal veins.

Does the placenta contain both maternal and fetal blood or only one of these? Where does the outer aspect of the placenta attach to? What is the inner aspect of the placenta called and what does it contain?

Placenta contains both maternal blood and fetal blood in separate compartments. Outer aspect attaches to maternal decidua; inner aspect is the chorionic plate, which contains large vessels and is attached to fetus via the umbilical cord.

What are the three kinds of villi?

Stem villi, terminal villi, anchoring villi

The trophoblast lining of villi contains two cell types. What are they?

Syncytiotrophoblast (syncytial trophoblast) is outermost, facing maternal blood; no cell boundaries over entire surface. Formed by fusion of underlying cytotrophoblast cells. Cytotrophoblasts, innermost, are individual cells that are proliferative; considered to be the stem cells of this lining.

What four structures can be found in the placenta in the third trimester?

Syncytiotrophoblast and endothelial cells

What four structures can be found in the placenta in the first trimester?

Syncytiotrophoblast, cytotrophoblast, mesenchyme, fetal endothelial cells

What are the inner and outer reflected fetal membranes called?

The reflected fetal membranes are the amnion (inner), which lines the amniotic cavity, and chorion laeve (outer), which interdigitates with maternal decidua.

How can stem villi be described?

Thick projections from chorionic plate, containing medium-sized vessels surrounded by abundant mesenchyme.

Why is the length of the umbilical cord important?

Too short or too long can cause severe complications such as tearing, knotting, or strangulation

T/F: The placenta is an endocrine organ.

True - it secretes both steroid and protein hormones.

T/F: Many kinds of import and export mechanisms are used to transport substances.

True: passive diffusion, facilitated diffusion, active transport, receptor-mediated endocytosis

What vasculature is normally present in the umbilical cord?

Two arteries (branches from the fetal iliac arteries) and one vein are normally present; the vessels spiral within the cord, creating a barber pole appearance.

What makes umbilical vessels unusual?

Umbilical vessels are unusual in that arteries carry deoxygenated blood, while the vein carries oxygenated blood.

Are the fetal membranes and most of the placenta "fetal derived"? Explain why or why not.

Yes - they originate from the conceptus (blastocyst) - these tissues are usually called extraembryonic tissues

Describe the two changes that occur in the spiral arteries to render them less reactive to vasoactive mediators. What can a complication with these processes lead to?

a. Trophoblast cells invade the spiral arteries b. The muscle wall is significantly altered. c. Problems with this process are associated with a major pregnancy complication, pregnancy induced hypertension.

The fetus floats in ___________ _______, which cushions and protects it; connected by umbilical cord to __________. The __________ ________ __________ are two contiguous membranes that extend from the edge of the placenta all the way around. Both the placenta and reflected fetal membranes are attached to maternal __________ ________, transformed into specialized tissue called ________.

amniotic fluid, placenta, reflected fetal membranes, endometrial stroma, decidua

Transfer of __________ from the placenta provides transient protective immunity to the fetus/neonate.

antibodies

As pregnancy progresses: In _______ ______ region, there is extensive invasion of maternal tissue by cytotrophoblast, creating a shell of __________ within upper decidua as well as many extravillous ____________ deep in decidua and even myometrium. Function of these cells is unknown.

basal plate, trophoblast, cytotrophoblasts

_______ _______ is attached to decidua.

chorion laeve

________ _______, also called smooth chorion, is the inner or outer? reflected fetal membrane.

chorion laeve, outer

As the placenta grows, the _______________ layer decreases and many fetal capillaries move closer to the ___________ basement membrane.

cytotrophoblast, trophoblast

Regarding the maternal surface of the placenta: The placenta pulls away from _________ at delivery, with small amounts attached. It is dark red and lobulated in appearance. The lobules, called ___________ are divided by septa of decidua. What shape are the arteries that enter form the decidua to supply maternal blood?

decidua, cotyledons, spiral arteries

Parturition: During labor the placenta and membranes separate from the _______; they are delivered after the baby with small amounts of _______ attached.

decidua, decidua

As pregnancy progresses: The endometrial stroma begins transformation into ______ in late secretory phase; if pregnancy occurs, this change progresses to include most of the functional zone of the ___________.

decidua, endometrium

What is the villi core filled with?

filled with mesenchyme surrounding fetal blood vessels -also, large population of macrophages present, and fetal vessels lined by endothelial cells

What is the function of the syncytiotrophoblast?

it controls fetal-maternal exchange

How does the villi core fulfill a main anatomical objective?

maternal and fetal circulations in close proximity but separate

The placenta is an elaborate structure designed for essential ________-_________ exchange.

maternal-fetal

What two structures make up the chorionic tissues?

placenta and chorion laeve

What are some metabolic functions of the placenta?

synthesizes cholesterol, fatty acids, some amino acids, and has some detoxifying activities.

What is Wharton's jelly? It is high in what properties? Which cells can be found in this "jelly"? It is enclosed by what on the outside?

the specialized mesenchyme of the umbilical cord that surrounds the vessels a. Special extracellular matrix is especially important for protecting the vessels. b. High in hyaluronic acid and chondroitin sulfate. c. Cells include fibroblasts, myofibroblasts, and mesenchymal stem cells d. Enclosed by amnion on the outside.

Where does chorion laeve attach? Is it vascular? What kind of cells does it contain? What do the chorion laeve's outermost cells appose?

to the edge of placenta, no, it is thin and avascular, contains multiple layers of individual trophoblast cells (cytotrophoblast), they appose maternal decidua

The primary functional cell of the chorionic tissues is a specialized epithelial cell derived from the outer layer of blastocyst. What is its specific name?

trophoblast

Concerning the fetal surface of the placenta: It is shiny due to covering of amnion. What important structure inserts into the center of the fetal surface? Beneath amnion is the _________ plate, a layer of connective tissue containing the ___________ vessels, which are branches from the umbilical vessels. _________ usually course over the veins.

umbilical cord, chorionic, chorionic, arteries

As pregnancy progresses, the ________ lumen gets smaller; when the epithelia become apposed, they break down, and the ________ in opposing walls of the uterus fuse; there is no longer a uterine lumen.

uterine, decidua

Changes during placental growth dramatically increase the ________ surface area in contact with maternal blood: Extensive villous branching dramatically increases the number of villi and decreases villous __________.

villous, diameter