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68 Cards in this Set
- Front
- Back
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Describe how a baby get its genome.
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Egg and sperm each give 1 copy of each gene, arranged along 23 chromosomes.
Baby gets 2 copies of each gene, arranged along 46 chromosomes. |
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What is a karyotype made from?
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It's made from 'metaphase spreads' - the condesned, duplicated chromosomes from somatic cells during metaphase of mitosis.
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How do duplicate chromosomes from the mother and father know how to match up with each other?
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1) banded patterns
2) length of chromosome 3) Postion of centromere relative to arms of chromosome |
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How many autosomes and sex chromosomes are there?
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44 autosomes, 2 sex chromosomes
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What is the largest chromosome? smallest?
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largest - 1
smallest - 22 |
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What kinds of cells undergo mitosis?
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somatic cells (liver, skin, gut, etc)
germline stem cells (oogonium, spermatogenesis) |
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What are the steps of mitosis?
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1. S phase (synthesis) - DNA replication - generates 46 duplicated chromosomes
2. M - Prophase (chromosomes condense). Metaphase (chromosomes line up separately on the metaphase plate in center of cell. Microtubule spindles attach to centromeres of chromosomes). Anaphase/telophase/cytokinesis (centromeres split. 46 single chromosomes (chromatids) move to each of the 2 daughter cells. Cell membrane forms between daughter cells). 23 chromosomes --> 46 chromatids --> 46 chromosomes --> 46 single chromosomes (chromatids) in each of 2 daughter cells |
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What are the steps of meiosis?
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Each parent donates 23 chromatids (46 chromatids total)
1. S phase (like mitosis) - DNA replication, so 46 chromosomes 2. Synapsis/crossing over - each pair of duplicated chromosomes aligns. Large pieces of homologous DNA cross over between maternal and paternal chromosomes. 3. Metaphase: Linked chromosomes line up on metaphase plate. Each chromosome is attached to only 1 spindle pole 4. Pairs of duplicated chromsomse split. 23 single chromosomes move to each spindle pole/daughter cell. |
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Why does meiosis confer genetic differences among siblings?
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1. Crossing over between maternal and paternal homologous chromosomes
2. Random assortment of maternal/paternal chromosomes to daughter cells. |
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What are the steps of Meiosis II?
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- NO S PHASE!
- 23 chromosomes align on metaphase plate - sister chromatids split. - 23 single chromosomes move to each spindle pole. Result: 4 cells, each with 23 single chromosomes |
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Which of the following does NOT have an S phase: Mitosis, Meiosis I, Meiosis II?
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Meiosis II
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When does meiosis I begin/stop in males?
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It begins at puberty. It continues throughout adult life. (continuous spermatogenesis)
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For every 1 stem cell (spermatogonium), how many spermatids are made?
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5
(1 primary spermatocyte --> 2 secondary spermatocytes --> 5 spermatids) |
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When does meiosis I begin/stop in females? Meiosis II?
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It begins in the 5th month of fetal life, but arrests at synapsis/crossing-over at least until puberty (and some arrest through perimenopause)
Meiosis I is completed at the time of ovulation. It arrests again in metaphase of meiosis II. Completion of Meiosis II is triggered by fertilization. |
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In meiosis in males, is there symmetric or asymmetric cytokinesis? In females?
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Males: symmetric
Females: asymmetric |
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What are the products of Meiosis I and Meiosis II in females?
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Meiosis I - 1 large secondary oocyte (the egg that's ovulated), 1 inactive polar body
Meiosis II - mature ovum (fertilized secondary oocyte), a second polar body |
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What is aneuploidy?
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Incorrect number of chromosomes
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What is synapsis?
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Pairing of 2 homologous chromosomes during meiosis
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What is one of the main causes of aneuploidy? Define.
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Nondisjunction - failure of chromosome pairs to separate properly during cell division.
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Why is nondisjunction more common in female meiosis, especially with advancing maternal age?
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Because there is a prolonged female meiosis (5th month of fetal stage until puberty). They are especially susceptible to errors associated with synapsis.
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Give three causes of nondisjunction in meiosis.
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1. Premature resolution of crossovers - maternal and paternal homologues align separately on the metaphase plate.
2. Premature degradation of cohesins (which hold together sister chromatids) 3. Poor functioning of spindle tensional checkpoint in meiosis (esp female meiosis) - anaphase begins even if chromosomes are not aligned properly on metaphase plate with proper microtubule tension. |
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Is nondisjunction in male meiosis more common in sex chromosomes or in autosomes? Why?
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Sex (X and Y) chromosomes
Because of the limited region of homology that supports synapsis of X and Y. |
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What is the rate of sex chromosome aneuploidies in gametes derived from men vs. women? How about autosomal aneuploidies?
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sex chromosome aneuploidies: 50/50 (equal)
autosomal aneuploidies: 80% egg, 20% sperm |
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What are two examples of chromosomal diseases (other than nondisjunction)?
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1. Deletions of parts of chromosomes
2. Translocations of part of one chromosome onto another due to complete loss or mis-attachment during crossing over |
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Name and describe 4 parts of sperm.
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1. Acrosome - sac of digestive enzymes. Bores through zona pellucida.
2. Nucleus - Tightly condensed, compact. 3. Mitochondrial sheath - provides energy to drive flagellum. 4. Flagellum - Microtubule, motor, makes sperm swim. |
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What is the zona pellucida? What are its 3 main functions?
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matrix layer around oocyte. Sperm recognition/binding site. Block to polyspermy. Barrier to premature/ectopic implantation.
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How does the zona pellucida prevent polyspermy? List both the major and minor blocks.
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Cortical reaction: cortical granules in egg release cross-linking enzymes. This causes rapid cross linking, such that the zona pellucida is impermeable to further sperm entry.
Minor: rapid, temporary depolarization of egg membrane upon sperm fusion |
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How does the zona pellucida prevent ectopic implantation?
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The blastocyst must hatch from the zona pellucida in order for it to implant.
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Where is the embryo located? Where does it get nutrients from?
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It is encased inside the zona pellucida. It gets nutrients from the egg.
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What happens to the sperm when the sperm hits the egg?
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Sperm binds to zona pellucida (Sperm-egg fusion). This triggers the acrosomal reaction (release of acrosomal enzymes). The sperm penetrates the ZP, and the two cell membranes fuse. The ENTIRE sperm enters the egg. The mitochondria and tial degenerate. The paternal centrosome is preserved and used in offspring. The sperm nucleus decondenses, and is called "male pronucleus"
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What happens to the egg when the sperm and egg fuse?
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Temporary depolarization of egg membrane.
Egg nucleus is now termed "female pronuclus" Release from metaphase arrest, completion of meiosis II. |
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What is the product of fusion of male and female pronuclei called?
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zygote
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What are the three stages of the zygote before implantation? Each stage has increasingly small ______.
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Zygote
Morula Blastocyst -- Blastomeres |
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Describe the morula. - When does it form, how
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Forms after 3 days.
Compaction occurs - cell-cell adhesions (adherens junctions) form between cells, especially in the outermost layer. The adhesion protein "E-catherin" helps. Thus, the morula becomes a smooth ball of cells. |
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What forms the blastocyst?
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Fluid secretion into the ball to form a blastocyst cavity.
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What are the outer cells of a blastocyst called? What are they the precursors to?
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trophoblast cells. They develop into the fetal chorion (placenta).
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What is the inner cell mass? What does it develop into?
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A ball of cells at the embryonic pole of the blastocyst. It subdivides into the epiblast (embryo proper and amniotic sac) and hypoblast (yolk sac)
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What does the blastocyst hatch from?
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Zona pellucida (through release of proteolytic enzymes)
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How are dizygotic/fraternal twins made? What do they share?
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2 eggs are ovulated and separately fertilized.
They share a uterus, but no membranes. |
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Describe two ways that monozygotic twins are formed.
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1. (25%) splitting of zygote in first few cleavage divisions. --> formation of two blastocysts with 1 ZP --> implant separately after blastocysts hatch. Share no membranes (Chorion or amnion).
2. (75%) complete splitting of inner cell mass. blastocyst implants as one unit, share a chorion/placenta but have separate amniotic sacs. |
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How do conjoined twins form?
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Incomplete splitting of inner cell mass. Twins share chorion, amniotic sac, and various tissue connections.
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Where does normal implantation occur?
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Trophoblast (over inner cell mass) binds to uterine endometrium. Usually occurs in a posterior position in the uterus.
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What is placenta previa? What causes it?
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It is when the placenta grows over the cervix, preventing safe vaginal delivery. It occurs because implantation is too close to the cervix (though still in the uterus).
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What happens to the trophoblast after it binds to the endometrium?
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- trophoblast proliferates
- Cytotrophoblast (single layer of cells) is maintained - Formation of invasive syncytiotrophoblast |
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What does 'syncytio' mean?
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syncytio = many nuclei in the cell with no membranes separating them
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What does the syncytioblast do?
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Secrete enzymes that degrade the uterine wall, pull the entire blastocyst into the uterine wall.
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Give an example of the enzymes that the syncytioblast secretes
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matrix metalloproteinases
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How does the uterine wall respond to syncytioblast invasion? (2) What is the purpose of these responses?
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1. Decidual reaction - accumulation of glycogen and lipids, which are then engulfed by trophoblast to nourish the embryo.
2. Angiogenesis (new blood vessel formation) and endometrial gland secretion - also to nourish the embryo. |
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What is the rate of ectopic implantation?
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1 in 150 pregnancies
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Where do over 95% of ectopic pregnancies occur? Give 3 other sites as well.
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- in the ovuduct
(less frequently: ovary surface, abdominal cavity - esp rectouterine pouch, cervix) |
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Why is ectopic pregnancy a problem? (2)
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1. Not enough space for fetus to develop.
2. Despite angiogenesis, cannot form stable vascular network. |
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An ectopic pregnancy, in a location with unstable vessels, can lead to what?
What are some symptoms of ectopic pregnancy? |
hemorrhage, rupture of oviduct
Abdominal pain, vaginal bleeding, missed periods, slower rise in placental hCG (so may not get a positive pregnancy test immediately) |
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What does the bilaminar embryonic disk consist of?
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Hypoblast and epiblast (closest to embryonic pole and trophoblast), separated by a basement membrane
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What is the bilaminar embryonic disk?
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forms from inner cell mass
epiblast and hypoblast |
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What does the epiblast eventually form?
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Germ layers (ectoderm, mesoderm, endoderm)
extraembryonic mesoderm primordial germ cells |
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What does the hypoblast form?
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primary and secondary yolk sacs
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What is the amniotic cavity/sac? Where is it? What is its purpose?
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Forms from inner cell mass at same time as bilaminar embryonic disk
amniotic cavity + amniotic membrane = amnion Eventually encircles the embryo, cushions it |
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how does the primary yolk sac form?
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hypoblast cells migrate over cytotrophoblast surrounding the blastocyst cavity. this lining is called "Heuser's membrane." Blastocyst cavity is now the primary yolk sac.
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What is the extraembryonic mesoderm?
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extraembryonic mesoderm cells migrate out from epiblast, lie btwn trophoblast and yolk sac.
extraembryonic membrane splits so that it lines the inside of the trophoblast and outside of yolk sac with a cavity (chorionic cavity) Differentiates into connective tissue, blood vessels of the chorion. Forms blood vessels of the yolk sac and the connecting stalk. |
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What is the chorion?
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fetal side of the placenta.
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What is the connecting stalk?
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joins the embryonic disk/amnion to chorion. Where the umbilical chord is
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What is the secondary yolk sac?
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displaces the primary yolk sac
The initial hypoblast derived lining is eventually displaced by epiblast derived endoderm. This endoderm turns into the gut. |
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What is notable about the extraembryonic mesoderm?
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First site of hematopoiesis.
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Where are primordial germ cells?
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In the yolk sac
migrate out during gastrulation..organogenesis |
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What are the 3 cell types/layers in the chorion/
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synctiotrophoblast
cytotrophoblast extraembryonic mesoderm |
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What is primitive uteroplacental circulation?
What is its purpose? |
As the synctiotrophoblast penetrates the uterine wall, its lacunae spaces fill with maternal blood and glandular secretions
maternal capillary network also forms sinusoids around the lacunar network when synctiotrophoblast invades uterine wall. To get nutrients/oxygen to the early embryo (initially) |
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What are prrimary chorionic villi?
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extensions from the cytotrophoblast into the synctiotrophoblast, and eventually into the blood-filled lacunar network.
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How are secondary chorionic villi formed? Tertiary?
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week 3: somatic extraembryonic mesoderm will invade the core of the primary chorionic villi, transform them into secondary chorionic villi..
Fetal blood cells differentiate within this mesoderm layer, converting them into tertiary chorionic villi |
