Chapter 3 biology Flashcards
VIP NOTES:
A secondary oocyte is ovulated from the follicle on approximately day 14 of the menstrual cycle.
The secondary oocyte travels into the fallopian tube, where it can be fertilized up to 24 hours after ovulation.
Where does fertilization occurs ?
It occurs in the widest part of the fallopian tube, called the ampulla.
Explain the full pathway of fertilization (9 BIGS STEPS)?
1) SPERM TRAVEL: Sperm swim to the fallopian tube, specifically the ampulla.
2) CAPACITATION OF THE SPERM: The head of the sperm has different types of proteins (like glycoproteins) molecules and cholesterol. So, capacitation is basically “ the cleaning off the head of the sperm, so after the capacitation it will only have modified glycoproteins left over” + “ increases the motility of the sperm=being hypermotile”
3) MOVING THROUGH THE CORONA RADIATA: When it reaches the egg, it has to push through the corona radiata, which contain the granulosa cells that produces hyaluronic acid. Because of the sperm is now hypermotile it will help the sperm to move through the corona radiata. (NOTE: Sperm move faster in alkaline environments than in acidic environements, accordingly the hypermotility will try to resist that hyaluronic acid environment.)
4) SPERM BINDING: Now that the zona plucida is available to the sperm, it then binds onto the sperm receptors (zona pallucida type 3 protein; ZP3 receptors) on the zona pellucida, recognized by specific proteins on the sperm that can recongize these ZP3 receptors.
5) ACROSOMAL REACTION: once a sperm attach to the sperm recetors on the zona pellucida it intiate the Acrosomal Reaction, where calcium ions start getting the sperm cells and causes the sperm to fuses its acrosome vesicles and releases acrosomal enzymes/digestive enzymes/ hydrolytic enzymes (acrasin and proteases) that helps to break/digest away the glycoprotein in the membrane of the zona pellucida and, thus, allow the sperm to get deeper and expose the egg’s cell membrane to the sperm. NOTE: THE FIRST EGG TO MAKE CONTACT WITH THE EGG’S CELL MEMBRANE WILL BE THE ‘WINNER’ AND FERTILIZE THE EGG.
6) FAST BLOCK TO POLYSPERMY: The egg’s cell membrane also has specific proteins where the sperm can bind to it. The sperm also have 2 types of proteins (beta and alpha) that will bind to the proteins on the egg’s cell membrane. Once the beta protein interacts with the proteins on the egg’s cell membrane, it opens specific sodium ion channels on the membrane and allow sodium ions to follow into the egg= deplorization of the egg. This deplorization inhibits the following sperms (like the ones still in the acrosomal reaction) from binding onto the egg’s cell membrane.
7) FORMATION OF ACROSOMAL APPARATUS + TRANSFER OF GENETIC MATERIAL: Alpha protein binds to the proteins on the egg’s cell membrane and allows the sperm’s and egg’s cell membrane to fuse. The first sperm to come into direct contact/touch with the egg’s cell membrane forms a tube-like structure known as the acrosomal apparatus, which helps to penetrate the cell membrane and allow the cell membrane of the sperm to fuse with cell membrane of the egg and, thus, transfer the pronucleus (sperm’s nuclear material) into egg once meosis II is complete.
—— The now depolarized and impenetrable membrane is called the fertilization membrane
8) CORTICAL REACTION (ONE MORE BLOCK TO PLOLYSPERM): once penetration of the sperm through the egg’s cell membrane and transfer of genetic material is complete, it causes the Smooth ER in the egg to be activated and start releasing calcium ions. The increased concentration of calcium ions in the egg’s cytoplasm causes the cortical granule (lysosomes) to be released into the zona pellucida (by exocytosis through the cell membrane) and releases its hydrolytic enzymes, which also help to digest the glycoprotein and the sperm receptors (ZP3) + hardens the cell membrane = it sets a slow block of polyspermy so no other following/incoming sperms can bind and once they hit the zona pellucida, they just bounce off.
9) FORMATION OF ZYGOTE: The increased calcium concentration also increases the metabolic rate of the newly formed diploid zgyote ( IE: it tells the egg that in metaphase 2 to finish meiosis and, thus produce two habloid ovum cells: definitive and polar body; the definitive then fuses with the male pronucleus cell and form a zygote.)
Explain how does dizygotic (fraternal) twins occur? What happens if the zgyotes implant close together?
It forms from fertilization of two different eggs, released during one ovulatory cycle, by two different sperms. Each zgyote will then implant into the uterine wall and each develops its own placenta, chorion, and amnion.
If the zgyotes implant close together, the placentas may grow onto each other.
Explain how does monozygotic (identical) twins occur? What happens if the division is incomplete?
it forms when a single zygote splits into two, where because the genetic material is identical the genomes of the offspring will be too.
If the division is incomplete, conjoined twins may results, where the two offsprings are physically attached.
Monozygotic twins can be classified by the number of structures they shared. Explain the 3 different types monzygotic twins can occur?
monochorionic/monoamniotic: twins share the same amnion and chorion.
Monochorionic/diamniotic: each have their own amnion, but share the same chorion.
dichorionic/diamniotic: each have their own amnions and chorions.
VIP NOTES:
Which type of twinnig occurs is a result of when the separation occured.
As more gestational structrues are shared, there are more risks as the fetuses grow and develop.
What happens at day 14 or 15 of the women’s ovulation cycle? (IE: how the egg becomes prepared for fertilization?)
During the 14 or 15 day of ovulation cycle, women start releasing a specific hormone called Luteinizing hormone (LH). This hornomes is released in the following pathway:
1. Hypothalamus release GnRH
2. GnRH triggers the anterior pituatory gland to release the LH. The anterior pituatory gland is also triggered by the increased concentration of the estrogen (positive feedback loop).
3. The LH hornomen then travels through the bloodstream and goes down to the ovaries. The LH hormone then tells the ovaries to produce lots of fluid to pressurize the graafian follicle (containing the secondary oocytes/egg) + other steps, which at the end helps to pop out the secondary oocyte and the fimbrae helps to move the secondary ooocyte to the ampulla. There fertilization takes place. NOTE: this secondary oocyte means that it underwent through miosis I and it is paused at mieosis II (particularly metaphase II). The reason for that pause is particularly because that secondary oocyte is waiting for a sperm cell to touch it (sperm attaching to the zp3 receptors) and once a sperm does, the oocyte can actually finish meiosis II to get itself ready for the pronucleus of the sperm to get into it. Then it fuses with it and finally form the diploid zygote cell.
After fertilization in the fallopian tubes, where does the zygote go next? What happens if it travels too late?
The zygote must travel to the uterus for implantation.
There will no longer be an endometrium capable of supporting the embryo.
What happens as the zygote moves to the uterus for implanatation?
As the zygote moves to the uterus for implanatation, the zygote undergoes rapid mitotic cell division (cell proliferation) in a process known as cleavage.
In this process, the diploid zygote cell undergo division 1 that produces 2 cells (2-cell stage). Then division 2 to produce 4 cells (4-cell stage). Then division 3 to produce 8 cells (8-cell stage). And lastly division 4 to produce 16 cells (16-cell stage).
What is the product after the first cleavage process?
The first cleavage officially creates an embryo, which nullifies the zygote primary characteristic: being unicellular.
Although several rounds of mitosis occur, the total size of the embryo remains unchanged during the first few divisions. BUT, by divising into progressively into smaller cells, the cells increase two ratios, what are they?
The nuclear-to-cytoplasm ration
AND
Surface area to volume ratio.
THUS, the cells achieve increased area for gas and nutrient exchange relative to overall volume.
What are the two types of cleavage? Explain each one.
Monozygotic twins orginate from which type of cleavage?
Indeterminate cleavage: results in cells that can develop into complete organisms
Determinate cleavage: results in cells with their fates, as the term implies, already determined. IE: these cells are committed to undergo the differentiation process to develop into a particular type of cell.
— Monozygotic twins orginate from the indeterminatly cleavaged cells of the same embryo.
What is Morula and Blastomeres?
A structure consisting of a hollow mass of cells. IE: it is anything from 16-cell stage until the blastocyst is called the morula.
The 16 or plus cells itself is called the blastomeres.
IE: Morula is a stage in embryonic development pathway consisting of blastomeres (16 or plus cells).
Once the morula is formed, it undergoes what process? Describe it.
Once the morula is formed, it undergoes the process of blastulation.
This process forms the blastula, which is a hollow ball of cells with a fluid-filled inner cavity known as the blastocoal.
The mammalian blastula is known as the blastocyst and consists of two noteworthy types of cell groups:
* A bunch of blastomeres cells clump together towards one edge and form the **inner cell mass–> Embryo blast ** that protrudes into the blastocoal (not all of it but only toward one edge) and give rise to the organism itself.
* The surrouding circular blastomeres cells become the **outer cell mass–> Trophoblast cells ** surrouding the blastocoal and give rise to the chorion and later to the placenta.
Trophoblast cells then develop into what (2 things)? Embroblast then develop into what (1 thing)?
Trophoblast (chorion/placenta): Cytotrophoblast (differentriate into this first) and synetrophoblast (differentiate into this second)
Embroblast (the organism itself): Bilaminar disk.
Once the blastula is implanted into the endometrium (uterus cavity lining), explain how does the trophoblast differentiate into the cytotrophoblast? and then the synthiotrophoblast?
Blastula is currently implanted into the endometrium:
1. Some of trophoblast cells (cytotrophoblast) start profilerating alot and as they profilerate these cell start moving out of the zona plucida (by releasing particular enzymes that allows it to move beyond the zona plucida) and its cell membrane to disintegrate/break into smaller pieces to the point of an area (like fingers) where all the cytoplasm and nuclei of these disintegrated cells are located; this area is called the synthium pool–> syntiotrophoblast.
2. This basically means that the cytotrophoblast cells is line of distinct cells and the ‘finger areas’ with floating cytoplasm and nuclei is the syntiotroblast cells, where eventually the cytotrophoblast cells will also start profilerating and enterning a villi into the syntiotrophoblast.
3. Overtime, the syntiotrophoblast will release specific hydrolytic enzymes that allow it to move deeper into the uturus cavity lining and eventually becoming confluent with maternal blood vessels. By this way, the embryo can grow by recieving oxgyenated blood, nutrients, hormones, etc from the mother via the maternal blood vessels.
WATCH NINJA NERD FOR BETTER UNDERSTANDING (4:00-7:00)
NOTE:
NO PREGNANCY: Progestrone level drops = shedding of the endometrium lining
THERE IS PREGNANCY: Cytotrophoblast release a hornome called (B-HCG), it triggers the corpus letueum to release progestrone = prevent shedding of the endometrium lining along with the implanted embryo.
The blastula moves from the fallopian tube to the uterus, where it burrows into the endometrium (the blastula has specific types of proteins that allows it to hook into the endometrium; IE: the uturine cavity).
What does the trophoblastic cells give rise to?
The trophoblastic cells give rise to the chrion, which is an extraembroynic membrane that develips into the placenta. The chrion contain chorionic villi (also formed by trophoblast), which are microscopic finger-like projections that penetrate the endometrium and as the placenta forms, it help to support the maternal-fetal gas exchange.
What is the umbilical cord?
The embryo is connected to the placenta by the umbilical cord, which consists of two arteries and one vein encased in a gelatinous substance.
The vein carries freshly oxgyenated blood rich with nutrients from the placenta to the embryo.
The arteries carry deoxgyenated blood and waste from the embryo to the placenta.
In addition to the placenta, what else does the chorion form?
it also forms an outer membrane around the amnion for additional layer of protection.
What is yolk sac, allantois and amnion? Also mention what is umbilical cord formed from?
Until the placenta is functional, the embryo is supported by the yolk sac which is also the site of early blood cell development.
The allantois is involved in early fluid exchange between the embryo and the yolk sac. Later, the umbilical cord is formed the remnants of yolk sac and the allantois.
The allantois is surrounded by the amnion, which is thin and tough membrane filled with amnotic fluid which serve as a shock absorbed during pregnancy, as it helps in lessening the impact of maternal motion on the developing embryo.
GASTRULATION: What is the process that occurs after implantation (what happens after the formation of the blastocyst)?
Once the cell mass (blastocyst) is formed and implanted into the endometrium at the uterus undergo another developmental process known as the gastrulation process, which is the development of three distinct cell layers.
What does the blastopore develops into for deuterostomes? For Protostomes?
Deuterostomes: anus
Protostomes: mouth
