Embryology 9/11/2017
despite the instructor constantly insisting we did not need to take notes today, a pretty sizable amount of information was covered. the instructor first informed us that Embryology in this course would be divided into two main sections. General Vs. Systemic. From what I understand, the areas kind of overlap, because general embryology will include all of the basic systemic embryology information. in other words, systemic embryology will be much more detailed information only involving a single body system, while general will focus on the big picture and the relationships between all of the body systems. the difference between the two still seems a bit unclear to me. the instructor began with a very basic but much-needed embryology overview. He began by defining Gamate (sex cells egg sperm oocyte). He revealed to us that he has a pet-peeve of an oocyte being called an ovum. he told us never to call it an ovum, only to call it an oocyte. but khan academy calls it an ovum and i like those guys. He explained to us that a fertilized egg is called a zygote. and eventually, the zygote develops to become an embryo. From there, he began talking about cell division. he outlined similarities and differences between mitosis and meiosis. His choice of wording was that: mitosis is cell division throughout the entire body that results with an increasing number of cells. And meiosis results in a decreased number of chromosomes and is for sexual reproduction. He reminded the class that the typical number of chromosome in somatic cells (cells not involved in sexual reproduction) is 46 pairs or 23 sets. because this was a general overview he bounced around back and forth a bit between sexual reproduction and cellular division, for the sake of following my notes i am going to follow the chronological order of presentation. He defined the process of the sperm meeting the egg as uniting. a khan academy video I watched earlier this morning mentioned that 2-3million sperm competes in uniting, so that is worth noting. The instructor said that ‘before uniting, the chromosomal number is decreased from 23 pairs to 23 halves. he also stated that meiosis only occurs in gametes. he continued ‘gametes have a preparation phase which is three steps.’ G1 - S - G2 ‘ where g stands for growth and s stands for synthesis. he said ‘sytnthesis makes a copy.’ following G2 is meiosis1 and then meiosis2. so g1-s-g2-m1-m2. Then he said meiosis has 4 stages: prophase, metaphase, anaphase, and telophase. and a subscript following the name of the sub stage will identify if its referring to m1 or m2. ie: prophase1. he made the next infomration seem to be very important.. M1 prophase has 4 substages (all of which i was unfamiliar with, I couldnt read the board or understand his accent, so I am watching khan academy to get that information more clearly explained to me after this). i believe the first letter of each substage was L Z P D. little zebras playing dominos :) but that could be wrong lettering so we will see. After that fairly indepth review of cellular division stages he goes back into more familiar territory and starts reviewing ‘chromosomes are tightly packed within the nucleus, during division, chromosomes unwind and spread out or uncoil. they become more ‘prominent (his words) and the nuclear membrane begins to degrade. centrioles align along the middle of the cell and the nuclear membrane degenerates the centrioles spread from 1 side to the other (seperating the halves of the chromosomes?) he defined the terminology for the center where the centrioles align, however it was a word I couldnt remember, or understand with his accent so I should look into that if Its not covered in khan academy. epitorial line? then he continued on by explaining the differences between meiosis 1 and meosis 2. meiosis 1 results with 2 daughter cells, and meosis 2 results with a total for 4 daughter cells. so it seems to be they are pretty much the same? it just happens twice. he defined spermatogensis (formation of sperm) and oogenesis (formation of oocyte). he explained that in spermatogenisis, at the end of meosis 2 had a total of 4 sperm cells. this leads me to deduce that spermatogenisis includes the g1-s-g2-m1-m2 that was discussed earlier. he explained that unlike in spermatogenisis, when discussing oogenesis, only 1 egg is produced (and 3 other cells of a different type???) then he said *the most important thing for us is stage 3 of the m1 prophase, and if my acronym about little zebras playing dominos is correct, then that would be the P word. he defined diploid and halploid, 23 pairs, 23 individual chromosomes respectivley. he said *the most important thing about substage 3 (dominos) of m1 prophase is that during this time, the 23 maternal and paternal halploids unite. he said this uniting process can either be called unite, synapse, or junction. so involving this most important topic, he said when no seperation occurs at this time when it should have it is called a nondisjunction. disjuntion is the seperation and this normally happens in M1 prophase substage 3. this is clearly a high yield area to focus on studying when it comes time to review for the exam, make sure to focus some extra time on this specific topic. when nondisjuntion occurs in this m1 prophase substage 3, the result may be downsyndrome, if the zygote? (not sure if its a zygote at this stage) if it has 21 chromosomes on one side, and 23 on the other, rather than 23 on each side. a similar complication is called ?Microdition? (couldnt understand accent) but this is when a small part of the chromosome goes from 1 side to the other. something related is a word like cribucha??? he said that the area he defined as the most important area to us is the most important BECAUSE, most chromosomal abnormalities occur during this stage 3 of m1 prophase. it seems that the cell is considered a zygote at this time because he said the following two terms were synomyms. zygote abormalitiy and chromosomal abnormality. the majority amount of chromosomal abnormalities do no survive, resulting in sponatneous abortion. and that the majority of spontaneous abortions are due to chromosomal abnormalities. thats about where he left off. Ill try to watch as many khan academy videos before class on the areas I was unclear in, and may leave a follow up post if I have time.
