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253 Cards in this Set
- Front
- Back
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What are gametes?
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A reproductive cell having a single set of chromosomes, especially a mature sperm or egg.
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When do gametes first appear?
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Very early in the human cell embryo.
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When do the testis and ovary first appear?
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Around week 8
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Of what origin are the testis and ovaries?
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Of mesodermal origin
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What are gametes also referred as?
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Germ cells
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We know germ cells(gametes) appear very early in the embryo. But when does their differentiation begin?
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At puberty
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Differentiation can be subdivided into 3 periods. Name them.
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1.Multiplication period
2.Maturation period 3.Differentiation period |
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Where does spermatogenesis take place?
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In the seminiferous epithelium of the tubules of the testis.
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What happens in the multiplication period?
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Spermatogonia are proliferating by means of mitosis and form a stock of undifferentiated, very young cells.
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What happens in the maturation period?
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-Some of the spermatogonia enter the meiosis.
-At end of prophase I they are called primary spermatocytes (large + pale cells) -At the end of telophase I they are called secondary spermatocytes -At the end of meiosis, we get 4 haploid spermatids (small +rounded) |
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What happens in the differentiation period?
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Since spermatids are not motile, they have to differentiate and develop structures which allow cell movements. This period is called spermiogenesis and requires the help of the Sertoli cell.
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Describe Sertoli cells.
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Sertoli cells are tall, columnar cells, located close to spermatids.
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Describe the events in spermiogenesis.
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-the spermatids enter the cytoplasm of the sertoli cell and then become embedded into it
-inside the sertoli cell they develop a long, movable tail and some other morphological changes -the result of this process is a long cell, with very small and condensed cell nucleus in a head piece, followed by a neck, a middle piece and a long tail piece |
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What typical structure does the tail show?
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The typical structure of flagellum.
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What are the endocrine aspects (regulation) of spermatogenesis?
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hypothalamus
* anterior pituitary * leydig cell * sertoli cell * seminiferous epithelium |
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What is the process of differentiation of the female germ cell called? When does it commence?
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Oogenesis
It begins earlier than spermiogenesis- it begins in the 11th week of fetal life |
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1.How does the process of meiosis differ in oogenesis (as compared to spermiogenesis)?
2.How does the extremely long prophase affect the cells? 3.Are the steps in oogenesis similar to those of spermatogenesis? Explain. |
1.In oogenesis, meiosis stops in prophase I during fetal life, and the cells stay in prophase I until the beginning of puberty.
2.It makes the cells extremely vulnerable against environmental factors (radiation, drugs, etc..) 3.In principle, they are similar. However, oogenesis lacks the differentiation period. (i.e. oogenesis only has a multiplication and maturation period) |
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What are the functions of the ovary?
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Production of mature oocytes and secretion of sex hormones
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Do females continually produce oocytes like males continually produce sperm?
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NO. At birth, ovary contains 2 million immature ova which are the whole lifetime supply.
*Note: this occurs in the multiplication period. **Note: at the end of puberty, only 400,000 ova are left. |
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As the maturation period begins, what else commences?.
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Meiosis begins
-Cells that enter prophase I are called primary oocytes (they are surrounded by follicular cells) -At around puberty the primary oocyte continues through meiosis and at the end of telophase I, the cell is called secondary oocyte. Note: one of the two daughter cells forms a small insignificant cell termed the polar body (this is important to remember for later) |
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What are oocytes surrounded by?
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A single layer of granulosa cells, and a basement membrane (i.e. follicular cells)
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What occurs during metaphase I and anaphase I of meiosis? What is the first layer that grows around the oocyte?
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During metaphase I and anaphase I the germ cells grow, accumulates lipids and glycogen, and develops a thick outer coat.
This coat (the first layer that grows around the occyte) is called the Zona pellucida. |
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What are theca cells?
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Steroid producing cells that are formed from stroma surrounding the follicle differentiating.
They form an outermost cell layer around the whole structure. |
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The follicle develops in three different steps. Name them.
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1.Primary follicle
2.Secondary follicle 3.Graafian follicle |
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What is characteristic about the formation of primary follicles?
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The granulosa cells divide and increase in layer number
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What is the difference between a primary follicle and a secondary follicle?
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Secondary follicle has receptors for LH, FSH, and estrogen. It has an antrum which contrains the secretions of the granulosa cells
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What happens to form the preovulatory follicle?
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Granulosa cells elaborate follicular fluid. This is the mature follicle
Note: Mature follicle is also termed as Graafian follicle |
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When does the secondary oocyte complete meiosis?
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Only after fertilization
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What does the secondary oocyte give rise to?
What does the polar body give rise to? |
Secondary oocyte gives rise to the ovum(the egg cell).
Polar body gives rise to two other polar bodies. ***END RESULT: 4 daughter cells; one egg cell and three polar bodies It doesnt take long for the polar bodies to begin to disintegrate and disappear. |
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Describe the structure of the mature sperm cell (showing the ultrastructural details and the proportions of the cell parts). Drawing and labeling may help
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1.Head of the sperm with nucleus and acrosome
2.Neck containing two centrioles 3.Middle piece containing regularly arranged mitochondria 4.Tail: principle(thick) piece and end (thin) piece Note: In the axis of the middle piece and tail we find an axenome (9+2 MT's = flagellum) and a firm structural protein skeleton around the axoneme. Total length of cell is 70 um |
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Why doesn't oogenesis have a separate differentiation period like in spermiogenesis?
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The differentiation is going on during meiosis and it is related very closely to the proliferation and differentiation of the follicular and theca-cells. Both of them are highly specialized endocrine cells, which have great significance in the regulation of ovarian and uterine cycles.
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Describe the endocrine regulation of oogenesis.
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hypothalamus
* anterior pituitary * follicular cell * theca cell * graafian follicle and tissues of the genetilial organs |
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When does ovulation take place?
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On the 14th day of the menstrual cycle
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Describe what happens during ovulation.
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-the graafian follicle ruptures and discharges the secondary oocyte (surrounded by a thick zona pellucida and folicula cells) into the abdominal cavity
-the egg cell reaches the uterine tube and begins its journey to the cavity of the uterus |
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1.When can fertilization take place?
2.Where does fertilization take place? 3.Describe what happens during fertilization. |
1. Fertilization can only occur after ovulation (when a secondary oocyte reaches the ampulla of the uterine tube)
2.Fertilization takes place in the cavity of the tube 3.The spermatozoa reaches the egg cell and one of them penetrates the follicular cells and the zona pellucida. Two haploid cell nuclei fuse resulting in a diploid cell, called the zygote. The development of the new organism begins with a series of mitotic divisions. |
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What is the name of the daughter cells of the zygote?
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Blastomeres
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Briefly describe the events of early development.
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fertilization
* zygote * cleavage(mitotic divisions) * morula(12-16 blastomeres) * blastocyst(50-60 blastomeres) |
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What follows ovulation, fertilization and cleavage?
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Implantation
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What happens in the implantation?
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The blastocyst reaches the uterus and becomes embedded in the endometrium.
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What are the two different cell types in the blastocyst?
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Trophoblasts - outer shell
Embryoblasts - inner cell mass |
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What does the trophoblast give rise to?
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The placenta and some of the fetal membranes (chorion).
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What is chorion?
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The outer membrane enclosing the embryo in reptiles, birds, and mammals. In placental mammals it contributes to the development of the placenta.
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What does the embryoblast give rise to?
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-Germ layers
-Embryo -Fetus |
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What is extrauterine pregnancy and placental previa caused by?
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Extrauterine pregnancy and placental previa are caused by errors in the implantation process.
Note: these are serious complications which need urgent treatment and surgical intervention. |
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What is placenta previa?
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Placenta previa is a condition that occurs during pregnancy when the placenta is abnormally placed, and partially or totally covers the cervix.
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List the different events of development that occur in week 1.
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-fertilization
-cleavage -formation of the blastocyst -differentiation into the cytotrophoblast/syncytiotrophoblast |
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When can fertilization take place?
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Only after ovulation, when a secondary oocyte reaches the ampulla of the uterine tube.
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Where does implantation usually occur, following fertilization in the uterine tube?
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Implantation usually occurs in the posterior wall of the uterus, except in the event of an ectopic pregnancy.
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How long is the process of fertilization?
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Over 24 hours
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Describe the sequence of events that occurs in fertilization.
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-initial contact between the sperm and the oocyte
-joining of the male and female chromosomes on the metaphase plate at the first mytotic division to form the zygote -end result: a diploid cell is formed with a new genotype and its genetic sex determined, stimulated to undergo mitosis |
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What happens in "cleavage"?
How long after fertilization does cleavage commence? Q: Are both the male and female pronuclei are essential for normal development? |
After the male and female pronuclei complete mitosis, cleavage begins. Cleavage is just a series of cell divisions.
Cleavage beings 30 hours after fertilization. A: Yes. Evidence for this exists when one or the other is absent, as in the case of a hydatiform mole. |
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What is the zygote referred to after its first cell division? Are the first two blastomeres totipotent?
How many cell divisions does the zygote undergo? |
-blastomeres
-the first two blastomeres ARE totipotent (capable of forming its own organism) -it divides into 2 cells, then 4, then 8 Note: during this time, cells are still surrounded by the zona pellucida, which caps its growth. Thus, as the cells divide, they become smaller. |
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What happens about 3 days after fertilization? What is this stage called?
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A ball of 12-15 cells enters the uterus. This stage is called the morula (meaning "mulberry").
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As the circular ball of cells with an inner cell mass and an outer cell layer arrives in the uterine cavity, what happens to the zona pellucida?
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It begins to disintegrate.
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A blastocoele, or fluid-filled cavity, begins to form, dividing the blastomeres into two cell groups. What are they and what will they eventually form?
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-the outer cell layer forms the trophoblast, that will eventually form the placenta
--the inner cell mass will eventually form the embryo Note: the fluid-filled embryo is called the blastocyst. |
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What happens to the blastocyst after having floated around in the uterine cavity for 2 days?
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-the blastocyst completely loses its zona pellucida and begins to grow fast
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What happens on day 6, of week 1 of development?
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The blastocyst attaches onto the endometrial epithelium, with the side of the inner cells mass attached to the uterine wall.
Eventually the embryo will be attached by its dorsal side. |
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Early implantation induces the trophoblast to differentiate into two layers. Name these two layers.
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-cytotrophoblast
-syncytiotrophoblast |
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Describe the cytotrophoblast layer.
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The cellular cytrotrophoblast layer surrounds the embryo as a single layer.
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Describe the syncytiotrophoblast layer.
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The syncytiotrophoblast layer is a multinucleated layer with no cell boundaries, that invades the endometrial epithelium to begin the implantation process.
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What is the trophoblastic shell?
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A cell layer at the beginning that differentiates into 3 cell layers and proliferates and grows rapidly.
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What is the growth of the trophoblastic shell responsible for?
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The growth of the embryo during the first 2-3 weeks
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What are the names of the 3 cell layers?
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1. SYNCYTIOtrophoblast - outer
2. CYTOtrophoblast - middle layer 3. Extraembrionic mesoderm - inner |
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What do these 3 layers form? What is its significance?
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These 3 layers form the chorion, or chorionic shell.
The chorion/chorionic shell plays a major roll in the feeding of the embryo |
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What is the inner layer of the chorion, the extraembryonic mesoderm, sometimes called?
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The chorion mesoderm.
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Which is the thickest of the 3 layers?
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The outer (syncytio- ) layer.
It invades the endometrium quickly, disrupting the wall of the uterine blood vessels and the uterine glands. |
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What does the SYNCYTIOtrophoblast form?
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Small cavities - the lacunae - which are surrounded by syncytio-cells.
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What takes plays next?
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-the disrupted blood vessels and uterine glands are opening directly into these lacunae, filling them with maternal blood and the secreted products of glands
-this is the 1st form of the feeding of the embryo: blood-borne substances are reaching the inner cells of the embryo by means of diffusion -the lacunae persist and grow together with the chorion and they will be parts of the placenta |
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What is the decidual reaction?
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-changes of the endometrium induced by fertilization and implantation
-the decidual reaction causes the cells of the endometrium to become large and pale, containing large amounts of glycogen and lipids |
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What is the endometrium of the pregnant uterus called?
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Decidua
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The decidua can be subdivided into 3 categories.
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At the site of implantation :
-decidua basalis -decidua capsularis The rest of the endometrium: -decidua parietalis |
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What does the decidua basalis eventually form?
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The maternal part of the placenta
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DEVELOPMENT AND STRUCTURE OF THE PLACENTA
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From what does the human placenta develop from?
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-from embryonic structures(fetal part)
-from decidua basalis(maternal part) |
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Describe the structure of the decidua basalis.
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-it forms fences(septa) which divide the chamber-like compartments which contain the blood of the mother
-the uterine blood vessels (veins and arteries) open directly into these chambers -these compartments are developing from the lacunae of the syncytiotrophoblast and have the same function: they allow the blood of the mother to get in close contact with the trophoblastic surface. |
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Describe the structure of the trophoblast.
How is it the "most important interface and barrier between the fetal tissues and the maternal circulation"? |
-it covers the surface of the chambers and the septa
-it also covers the chorionic villus -it is the most important interface and barrier between the fetal tissues and the maternal circulation since the trophoblastic surface is "washed" by the blood of the mother continuously |
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Describe the structure of the chorion.
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-the chorion grows, proliferates and forms a lot of finger-like processes(villous chorion) which build up a tree-like structure
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What is this villus attached to?
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-to the chorionic plate and to the decidua basalis
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What is this villus covered by?
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Trophoblasts
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What is found inside the villus?
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-CT(the chorionic mesoderm) and blood vessels of the fetus
-these blood vessels are branches of the umbilical blood vessels |
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What happens to the location of the placenta + decidua basalis during the 2nd phase of childbirth?
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-Placenta comes into the world
-Decidua Basalis remains in the uterus (it plays an important role during the subsequent regeneration precess) |
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What are the 3 main functions of the human placenta?
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1. METABOLISM - synthesis of glycogen, fatty acids, etc..
2. TRANSFER - materials from the mother and from the fetus are transported through the placenta 3. ENDOCRINE SECRETION - the syncytiotrophoblast synthesizes several placental hormones which are absolutely necessary for the maintenance of the pregnancy. |
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What does the placental barrier consist of?
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-trophoblast cells + basal laminae
-the chorionic mesenchyme -the endothelium of the fetal blood capillary |
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Name the different events or structures formed during week 2 of development.
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-Late implantation/Uteroplacental circulation
-Bilaminar disk, amniotic cavity and primary yolk sac -Extra-embryonic mesoderm and coelom -Formation of the chorion and definitive yolk sac |
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By the end of week 2, the blastocyst has completed implantation. Was is it now thought as?
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-an organism of twos: a bilayered embryonic disk, with two cavities and two layers of trophoblast
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What are the extra-embryonic structures the blastocyst formed during the second week?
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-amniotic cavity and amnion
-yolk sac -connecting stalk -chorionic sac |
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During week 2, what does the syncytiotrophoblast continue to invade? What does this induce?
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The syncytiotrophoblast continues to invade the stroma of the endometrium, inducing the decidual reaction, in which the uterine cells around the implanted embryo accumulate glycogen and lipids and swell.
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What role does the syncytiotrophoblast play for the developing embryo?
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An immunological and nutritive role.
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What does the syncytiotrophoblast begin to produce at the end of the week? What role does it play?
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The syncytiotrophoblast begins to produce human chorionic gonadotrophin (hCG) at the end of the week.
This is the basis of the pregnancy test. |
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How is the amniotic cavity formed?
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While the embryo is implanting on the embryonic pole, a cavity begins to form in the inner cell mass - the amniotic cavity
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What layer forms around the amniotic cavity? Where is this layer derived from?
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- a layer of amnion
- it is derived from the epiblast layer of the embryonic disc |
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What does the remainder of the inner cell mass form? What layers make it up? What will these layers eventually become?
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-a flattened disc
-a thicker, columnar epiblast layer (on the amniotic side) -a smaller, cuboidal hypoblast layer (exocoelomic side). This layer will become the future endoderm. |
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What makes up the primary yolk sac? What role is the primary yolk sac thought to play?-
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-The exocoelomic cavity and membrane
-role in nutrition, despite the absence of a yolk |
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Where will cells from the primary ectoderm migrate, and what will they form?
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-Cells from the primary ectoderm will migrate to surround the amniotic cavity, bilaminar disk and yolk sac
-They will form the extraembryonic mesoderm. |
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What do lacunae, or spaces forming in the syncytiotrophoblast provide?
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they provide a means through which maternal blood can access the embryo to provide nutrients and oxygen
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The arterial and venous branches communicate with the lacunae, forming the beginning of a _____ _______.
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Uteroplacental circulation
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Around day 12, these lacunae link up to form networks. What appearence do they give the syncytiotrophoblast?
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"spongy" appearance
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Endometrial sinusoids are gradually eroded by the invasive syncytiotrophoblast. Why?
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so that maternal blood can flow freely into the embryonic space
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How is the extraembryonic coelom formed?
What does the extraembryonic coelom surround? |
The extraembryonic coelom is formed by the fluid filled spaces, which open up in the extraembryonic mesoderm, and link up.
The extraembryonic coelom surrounds the amnion and yolk sac (except at the connecting stalk) |
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At this time the primary yolk sac shrinks. What is it replaced by and how is it formed?
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It is replaced by a smaller secondary (definitive) yolk sac.
The secondary yolk sac is formed from extra-embryonic endodermal cells that migrated to the primary yolk sac from the hypoblast |
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At the end of week 2, what happens to the primary chorionic villi?
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It will create portrusions into the endometrium.
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What does the extraembryonic coelom)chorionic cavity do?
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It separates the extra-embryonic somatic mesoderm (lining the trophoblast layer and amnion, future gestational sac) from the extra-embryonic splanchnic mesoderm (surrounding the secondary yolk sac).
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What does the thickening of the hypoblast at one end indicate?
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This indicates the prechordal plate (future mouth) of the embryo
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The bilayer embryonic disk surrounded by the amniotic cavity and yolk sac is then suspended by the connecting stalk, completely surrounded by a large, fluid-filled extraembryonic coelom (primordium of chorionic cavity) which is surrounded by the chorion.
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...
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THE BILAMINAR EMBRYONIC DISC: FORMATION OF THE AMNION AND THE EMBRYONIC DISC
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During the second week of development 2 important changes take place in the inner cell mass(embryoblast cells). Name them.
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1. The cells which are lying close to the blastocyst cavity become flat - form the HYPOBLAST layer
2.The cells inside become tall and columnar -form the EPIBLAST layer |
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Lying on each other, the epiblast and hypoblast form what structure?
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The bilaminar embryonic disc.
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What is the name of the small cavity that appears between the trophoblast and the epiblast, which grows and separates the bilaminar embryonic disc from the trophoblast shell?
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The amnion.
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The hypoblast grows into the blastocyst cavity and seperates another cavity inside. Name this cavity.
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The yolk sac.
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As a result, what are the 2 cavities that surround the embryonic disc?
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The amnion (above the epiblast) and the yolk sac (below the hypoblast).
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The embryo and the fetus will develop further inside the cavity of the amnion which is filled by a special fluid. What is this fluid called?
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The amniotic fluid.
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What does the wall of the amnion belong to?
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Fetal membranes.
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Name 3 extraembryonic membranes.
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-amnion
-chorion -yolk sac wall |
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Name the different layers of the amnion
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Bilayer:
amniotic epithelium + extraembryonic somatic mesoderm |
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Name the different layers of the chorion
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Trilayer:
extraembryonic somatic mesoderm + cytotrophoblast + syncytiotrophoblast |
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Name the different layers of the yolk sac wall
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Bilayer:
yolk sac endoderm + extra-embryonic splanchnic mesoderm |
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THE TRILIMINAR EMBRYONIC DISC: THE FORMATION OF THE GERM LAYERS
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...
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At the end of week 2, important changes to the bilaminar embryonic disc take place. Describe the changes.
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Two small sites appear on the edge of the disc where the epiblast and the hypoblast firmly stick together and the hypoblast becomes tall and columnar, too.
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Where are these 2 sites located?
What forms at these two sites? |
At the poles of the disc.
-oropharyngeal membrane (the site of the further mouth) -cloacal membrane(this will be the anus later) |
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What is the significance of the axis which connects the oropharyngeal and cloacal membrane?
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-the events during week #3 take place in this axis
-this axis will be the axis of the embryo |
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Name this structure. The epiblast proliferates rapidly and the new cells are pushed towards the axis where they form a tiny elevation and a groove.
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The primitive streak.
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Name this layer. The new cels are pushed into the cleft between the epiblast and the hypoblast where they fill the space quickly and form an intermediate layer.
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The mesoderm.
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What does the epiblast become?
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The ectoderm - the outer germ layer
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What does the hypoblast become?
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The endoderm - the inner germ layer
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Where is the mesoderm situated?
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Between the ectoderm and the endoderm.
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What structure do these 3 layers help to form?
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The triliminar embryonic disc.
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What do these 3 germ layers give rise to?
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Every tissue of the human body.
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What does the formation of the notochord give rise to?
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The cranial/cephalic pole of the embryonic disc.
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Describe some characteristics of the notochord.
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-it is a solid, rod-like process of the ectoderm which grows into the mesoderm according to the axis of the embryonic disc
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What does the notochord grow towards and when does it stop growing?
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-it grows towards the oropharyngeal membrane
-it stops growing when it reaches the oropharyngeal membrane |
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What do the structures lying in front of the tip of the notochord form?
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The head of the fetus.
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What does the notochord form?
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Some parts of the vertebral column.
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EARLY DIFFERENTIATION OF THE ECTODERM AND MESODERM
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...
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What else (besides the direction of the head) does the notochord give rise to?
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the neurulation process
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What is neurulation and what does it give rise to?
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Neurulation is the early differentiation of the ectoderm and gives rise to the neural tube.
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What develops from the neural tube?
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The brain and the spinal chord
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What happens to the ectoderm which lies above the notochord?
As a result, what happens? What becomes visible? |
-it thickens and deepens
- a groove becomes visible in the midline - the neural groove |
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What is the upper edge of the neural groove called?
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The neural crest.
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How does the neural groove form the neural tube?
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-the neural groove deepens and grows down in the mesoderm forming a thick-walled tube
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What happens to the neural groove and neural crest as they continue to grow?
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They dissapear under the ectoderm.
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At first, are the ends of the cranial and caudal nerves open or closed?
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Open.
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Once the cranial and caudal nerves close, this induces the beginning of the development of what?
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The CNS.
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How are the developing sensory ganglia formed?
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By the neural crest, that breaks into small pieces on the two sides of the neural tube.
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The mesoderm on the two sides of the notochord thickens. What does this form?
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Two elongated columns.
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By the end of week #3 what does the mesoderm divide into?
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The mesoderm divides into cuboidal pieces along the axis of the embryo and somites develop.
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Till when do the # of somites continue to increase?
At this time, how many pairs of somites exist? |
Till the first month.
40-42 pairs of somites exist on both sides of the neural tube and notochord at the end of the first month. |
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What do somites give rise to?
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-some parts of the skull
-the vertebrae -muscles of the back -etc.. |
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Where is the intermediate mesoderm located. What does it resemble?What does it later give rise to?
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-located lateral from the somites
-the intermediate mesoderm resembles knot-like structures -later gives rise to the urogenital system |
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What does the lateral mesoderm form. What does it later give rise to?
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-it forms a slit-like cavity which opens first into the blastocystic cavity
-soon however, it loses this connection and eventually becomes the cavity of the embryo and the fetus |
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Of what is the cavity and the embryo proceeders of?
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The peritoneal, pleural and pericardiac cavities.
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Name the 2 sheets that the lateral mesoderm splits into.
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The parietal layer - somatopleura
The visceral layer - splanchnopleura |
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What do these 2 layers give rise to?
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The serous membranes - peritoneum, pleura and pericardium
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When does the development of the first blood vessels of the yolk sac take place?
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the 3rd week
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Towards where do these blood vessels grow?
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Towards the cranial part of the embryo
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With what do these blood vessels fuse with/?
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The primitive heart tubes
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From where do these primitive heart tubes develop?
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From the mesoderm in front of the oropharyngeal membrane.
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What is the name of the mesoderm in front of the oropharyngeal membrane?
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Cardiogenic area.
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Eventually, the blood vessels grow together and the tissue fluid starts to circulate. Of what does this mark the beginning of development of?
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The cardiovascular system ad blood.
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THE DERIVATIVE OF THE GERM LAYERS.
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....
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What are the different germ layers?
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-ectoderm
-neural tube (ecdoderm) -neural crest (ectoderm) -endoderm -mesoderm |
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What are the derivates of the ectoderm?
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-epidermis
-hair -nails -glands of the skin -mammary gland -enamel of the teeth -inner ear -lens -anterior pituitary gland - - |
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What are the derivates of the neural tube (ectoderm) ?
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-CNS
-retina -pineal gland -posterior pituitary |
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What are the derivates of the neural crest (ectoderm)?
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-sensory ganglia and peripheral nerves
-autonomic ganglia and nerves -medulla of the adrenal gland -pigment cells of the skin |
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What are the derivates of the endoderm?
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-epithelium and glands of the respiratory tract
-epithelium and glands of the alimentary tract -liver -pancreas -thyroid gland -parathyroid glands -thymus -tonsils -pharynx -tympanic cavity -auditory tube (the epithelium and the gland, only) -posterior part of the tongue |
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What are the derivates of the mesoderm?
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-skeletal systems (bones, joints, ligaments)
-muscle (skeletal, smooth and cardiac muscle) -CTs everywhere -dentin of the teeth -serous membranes(pleura, pericardium, peritoneum) -cardiovascular system(testicles, ovaries) -urogenital organs(the epithelium and the glands of these organs are mesodermal, too) |
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THE FOLDING OF THE EMBRYO - WEEK 4
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...
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What is the folding of the embryo?
In how many planes does the folding take place? |
It is the transformation of the flat embryonic disc into a cylindrical body.
Two- longitudinal and transverse |
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What does folding in the longitudinal plane give rise to?
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The head fold and the tail fold.
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What is the head fold due to?
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The fast growth of the brain.
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What does the cranial end of the neural tube form?
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The forebrain, which grows over and above the oropharyngeal membrane
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What happens to the oropharyngeal membrane?
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It turns upside-down and together with the cardiogenic area moves to the ventral surface of the embryo
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At the site of the oropharyngeal membrane, what does the ectoderm form?
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A pit - this is the primitive mouth.
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What is found posterior to the mouth? What is characteristic about its growth?
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The heart.
The heart develops very rapidly. |
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Does the embryo have a neck at this time?
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No
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What does the foregut form?
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The upper part of the alimentary tract (Gastrointestinal tract).
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What is the foregut?
Describe the process of formation of the foregut. |
The anterior alimentary canal in a vertebrate embryo, including those parts which will develop into the pharynx, esophagus, stomach, and anterior intestine.
During the folding of the head, the anterior segment of the yolk sac cavity becomes a narrow endodermal tube incorporated by the body of the embryo - this forms the foregut. |
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Do the tail fold and head fold develop similarly? Are there any difference?
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They do develop similarly, however the rate of growth of the tail fold is not so fast.
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Describe how the neural tube grows.
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The neural tube grows over and above the cloacal membrane, so the membrane is pushed to the ventral side and a small tail develops.
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Does the body stalk develop the same position as the neural tube?
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Yes, they both take on ventral positions.
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How does the body stalk attach to the belly of the embryo?
What does the body stalk develop into? |
-via the umbillicus
-the umbilical chord |
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What is the posterior part of the yolk sac become?
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It becomes the endodermal tube inside the body - the HINDGUT
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What does the hindgut later give rise to?
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-descending colon
-rectum -cloaca |
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FOLDING IN THE TRANSVERSE PLANE
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...
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How is the lateral body wall formed?
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By the right and left edges of the embryonic disc growing down.
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As a result of the lateral body wall formation, what happens?
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The middle part of the yolk sac becomes incorporated and forms the midgut and the endodermal.
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What do the visceral and parietal layers of the lateral mesoderm give rise to as they follow the movement?
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They give rise to the body cavity and the mesentery which is covering the midgut.
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What happens to the remainder of the yolk sac?
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It becomes a narrow duct connecting the midgut to the remnant of the yolk sac(which is the smallest part, excluded from the body)
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During the growth and development of the amnion, what happens to the duct and yolk sac remnants?
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They are compressed into the umbilical cord.
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What is the umbilical cord covered by?
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Epithelia of the amnion
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Describe the morphological changes that take place at the end of week 4 on both sides of the head.
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The mesoderm is proliferating and elevating the ectoderm in a crescent-like manner.
Four elevations and three grooves appear on the surface. |
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What are the elevations referred to as?
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Branchial arches.
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What do the branchial arches give rise to?
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The structures of the neck
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What does every arch contain?
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-an ectoderm, mesoderm and endoderm
-each has a cartilage, an artery and a nerve |
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What type of nerves are these?
What do these nerves innervate? |
-cranial nerves
-they will innervate the structures which develop from their corresponding arch. |
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What is the first (or mandibular) arch innervated by?
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Trigeminal nerve
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What is the second (or hyoid) arch innervated by?
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Facial nerve
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What is the third arch innervated by?
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Glosspharyngeal nerve
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What is the fourth arch innervated by?
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Vagus nerve
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What do the nerves which develop from the neural crest regulate?
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The development processes of the arches.
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During what week does the embryo develop a neck? What is this due to?
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-week 8
-due to the differentiation of the branchial arches |
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Name the skeletal elements of the mandibular arch.
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-incus
-malleus -sphenomandibular ligament -mandible |
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Name the muscles of the mandibular arch.
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-masticatory muscles
-mylohyoid muscles -ant. belly of digastricus -tensor veli palatini -tensor tympani |
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Name the organs (ectodermal and endodermal) of the mandibular arch.
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-external auditory meatus
-tympanic membrane -tympanic cavity -auditory tube -tongue |
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Name the skeletal elements of the hyoid arch.
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-stapes
-styloid process -stylohyoid ligament -part of the hyoid bone |
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Name the muscles of the hyoid arch.
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-muscles of facial expression
-post. belly of digastricus -stapedius -stylohyoideus |
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Name the organs (ectodermal and endodermal) of the hyoid arch.
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-palatine tonsil
-tongue |
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Name the skeletal elements of the third arch.
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-part of the hyoid bone
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Name the muscles of the third arch.
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-stylopharyngeus
-upper pharyngeal muscles |
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Name the organs (ectodermal and endodermal) of the third arch.
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-parathyroid glands
-thymus |
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Name the skeletal elements of the fourth arch.
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-cartilage of the larynx
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Name the muscles of the fourth arch.
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-pharyngeal and laryngeal muscles
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Name the organs (ectodermal and endodermal) of the fourth arch.
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-parathyroid glands
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SUMMARY OF EVENTS DURING THE EMBRYONIC PERIOD
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...
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Week 1 - Give a summary of the events.
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-ovulation
-fertilization -cleavage -blastocyst |
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Week 2 - Give a summary of the events.
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-implantation
-chorion -bilaminar embryonic disc - |
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Week 3 - Give a summary of the events.
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-trilaminar embryonic disc
-germ layers -neurulation |
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Week 4 - Give a summary of the events.
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-neural tube
-somites -intermediate and lateral mesoderm -folding begins |
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Week 5 - Give a summary of the events.
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-folding of the embryo
-primitive heart and circulation -branchial arches appear |
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Week 6 - Give a summary of the events.
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-appearance of limb buds
-differentiation of the branchial arches -oral and nasal cavities begin to develop |
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Week 7 - Give a summary of the events.
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-limbs are apparent
-face -eyes -ears -the placenta differentiates |
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Week 8 - Give a summary of the events.
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-external genital organs begin to develop
-end of embryonic age -CR: 3 cm note: CR = crown-rump Crown-rump is the length of an embryo, fetus, or newborn as measured from the crown of the head to the prominence of the buttocks. |
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How long is the embryonic period?
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8 weeks = 2 months
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What is the 7-month period following the embryonic period?
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The fetal period.
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During the fetal period, the rate of growth is fast. When is it especially fast?
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Between week 9 and 20
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How is the fetus measured?
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Via the crown-rump (CR) length.
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What is the CR length at birth (at the end of the fetal period)?
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36 cm
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What is the CR length from week 9-12?
Describe the development of other features of the fetus that take place during these weeks. |
-CR length is 5 cm
-eyes are closed -head is large |
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What is the CR length from week 13-16?
Describe the development of other features of the fetus that take place during these weeks. |
-CR length is 14 cm
-ossification of the skeleton progresses rapidly |
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What is the CR length from week 17-20?
Describe the development of other features of the fetus that take place during these weeks. |
-CR length is 19 cm
-fetal movements are felt by the mother -body is covered with a fine hair, the LANUGO |
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What is the CR length from week 21-25?
Describe the development of other features of the fetus that take place during these weeks. |
-fetus gains weight
-skin is translucent -organs are well developed |
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What is the CR length from week 26-29?
Describe the development of other features of the fetus that take place during these weeks. |
-CR length s 26cm
-fetus may survive if born prematurely, because the lungs are able to breathe -subcutaneous fat is present |
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What is the CR length from week 30-34?
Describe the development of other features of the fetus that take place during these weeks. |
-skin is smooth and pink
-pupillary light reflex is present |
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What is the CR length from week 35-38?
Describe the development of other features of the fetus that take place during these weeks. |
-CR length is 36 cm
-fetus has a firm grasp -exhibits spontaneous orientation of light -circumference of the head and belly are approximately equal |
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ANATOMY AND PHYSIOLOGY OF PREGNANCY
|
...
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What is the gestational age?
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Time counted from the first day of the LMP (last menstrual period)
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What is the fertilization age?
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The gestational age - 2 weeks (14 days)
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Which of the two ages is more relevant to the fetus?
Why do we subtract 2 weeks from the gestational age to get the fertilization egg? |
The fertilization age is more relevant to the fetus.
Fertilization only happens on day 14 of the menstrual cycle, not on day 1. Day 1 marks the first day of the menstrual cycle, when women first begin to bleed. The gestational age is thus 2 weeks longer than the age of the child cuz fertilization could only occur around day 14 of the menstrual cycle. |
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There are many signs of pregnancy, most due to hormonal changes in the body. Name some of the consequences of hormonal actions.
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1. The presence of human chorionic gonadotropin (hCG) determines a positive pregnancy test
2. The cessation of the menses (the stopping of the bleeding) 3. Increased pigmentation in the skin (this only occurs later on) 4.abdominal striation(visible skin furrows on the belly) 5.growth of the breasts 6.Hegar's sign(softening of the uterus upon palpation) 7.abdominal enlargement(in second trimester) |
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When can the enlarged uterus be palpated above the symphysis?
|
Week 12
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During what weeks can a heart beat be detected, as well as the body of the fetus via ultrasonography?
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Around weeks 17-19
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Through what does the fetus come to the world?
|
through the perineum
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Often before birth (parturition), many women go into training in hope to ease the pain of pregnancy. Which muscles are they exercising in particular?
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The levator ani and the muscles of the urogenital diaphragm.
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What is episiotomy?
|
-it is a simple surgical procedure
-muscles such as the sphincter vaginae and the transverse perinei muscles are cut by obstetricians in order to help the delivery and prevent spontaneous rupture |
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CONGENITAL MALFORMATION
|
...
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Define teratology.
|
The study of birth defects.
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Define teratogens.
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The factors which cause these birth defects.
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What are human birth defects caused by?
|
1.genetic factors
2.infectious agents 3.drugs, hormones and chemical agents 4.ionizing radiation 5.other factors |
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What are genetic factors?
Give an example. |
Genetic factors are the numerical and structural aberrations of the chromosomes.
ex: down's syndrome |
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Describe how infectious agents act.
|
Infectious agents (viruses, bacteria and parasites) infect the mother primarily, then invade the fetus transplacentally.
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|
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What does the rubella (German measles) virus cause?
|
Serious heart defects
|
|
|
what does the genital herpes virus infection result in?
|
-mental retardation
-retinal dysplasia -hepatosplenomeglia (i.e. pathological enlargement of the liver and spleen) |
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|
Give examples of some harmful drugs, hormones and chemical agents.
|
-diazepam
-thalidomide -retinoic acid -methotrexate -oral cotraceptives -cigarette smoke -alcohol -illicit drugs(cocaine, LSD, etc..) -lead -organic mercury |
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What are some of these "other factors"?
|
-malnutrition
-diabetes -prenatal or perinatal hypoxia and asphyxia (i.e. pathological changes caused by reduction or lack of oxygen in the blood or in the respired air) |
