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vamn3stlyq · 1 year

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twiainsurancegroup · 22 days

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top10buzz · 1 year

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Pourquoi l’ovule ne reçoit qu’un seul spermatozoïde ?

Car si deux spermatozoïdes arrivaient à entrer et à fusionner avec l’ovocyte, phénomène appelé polyspermie, la présence de deux matériaux génétiques mâles – et donc de 23 chromosomes excédentaires – stopperait précocement le développement de l’embryon ! Plusieurs mécanismes de protection existent donc afin d’empêcher l’ovule d’être assailli de spermatozoïdes, une fois une première fécondation…

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peertechz · 1 year

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Assisted hatching – should we keep doing it?

Assisted Zona Hatching (AZH) like most add-ons was introduced to In Vitro Fertilization and Embryo transfer (IVF/ET) in the early 1990s, when the live birth rate (LBR) in older women, age 35-39, was only 6%. This frustrating rate called for unusual measures including some add-ons like Assisted Hatching (AH) that were eagerly adopted, in conjunction with many theories, with the hope to increase the success rate. But today, due to various improvements in ovarian stimulation, culture media, and embryo selection, the LBR has tripled in 2019 in women aged 38-39 to about 19% (Human Fertilisation and Embryology Authority, http://www.hfea.gov.uk. [1]) and it is doubtful if any of the add-ons, which were never proven effective, including AH, is still needed in routine IVF. Despite hundreds of publications, and probably millions of AH procedures performed in over 30 years, no proof as to its efficacy in terms of LBR, was provided. In recent years all add-ons including AH came under crossfire in the professional and lay media for being redundant, costly, and inefficient [2,3]. Nevertheless, all add-ons including AH remain in very high usage.

Why assisted hatching?

Zona Pellucida is a glycoprotein produced by the growing oocyte that is responsible for sperm binding and acrosome reaction and in preventing polyspermy [4]. Before implantation, repeated expansion-contraction cycles help to thin out the zona [5,6], to facilitate embryo hatching and thereby implantation. Years before the ICSI (Intracytoplasmic Sperm Injection) era in the late 1980s, an intensive search to increase fertilization rate in male factor cases included a procedure named Partial Zona Dissection (PZD) that was used to allegedly facilitate the defective or low count sperm to fertilize the oocyte. This was later developed into AH in humans.

During the 1988 ASRM congress in Atlanta, at the hotel bar, I asked Jacques Cohen what message he would like to convey during the 1989 6th world IVF congress in Jerusalem, where I was in charge of the program. Enthusiastically he described his observation of a few patients that underwent PZD to treat low sperm count, in whom the pregnancy test of hCG (Human chorionic gonadotropin) turned positive one day earlier than non-PZD embryos [7]. His interpretation of the phenomena was that the embryos hatched earlier due to the breach in the zona. My question on why an embryo would choose to get out from an ‘artificial window’ if it supposedly possesses the key to the “front door” remained unanswered, but soon a new field in human IVF was born and named AH, along with the theory of a thick zona or zona hardening requiring AH emerged. The basis for the AH procedure is the presumed inability of the embryo to hatch out of the zona pellucida (ZP) due to zona hardening, a physiological change that increases the resistance to proteolytic digestion and hence the block to polyspermy [8]. It was suggested that zona hardening occurs because of in vitro culture conditions or maternal aging.

https://www.peertechzpublications.com/articles/JGRO-8-213.php

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emilyselberg · 3 years

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🦋The Gulf fritillary, Agraulis vanillae Has a life span of 14 to 27 days. In this species, male butterflies begin courtship by finding a female and engaging in “wing clap display". Pheromones are also involved in courtship and mating, as well as, nutritional offerings for the female. This will fertilize her eggs if she chooses. Her eggs can be fertilized by several males. As she does not have to lay all her eggs at once. 🦋An interesting term I've read while studying this topic in butterflies is physiological polyspermy. Read about it if you're interested! . . . . . . #paradise #learning #hike #insect #jungle #tinian #nature #naturephotography #instagood #islandlife #picoftheday #scenery #oceanlife #junglephotography #newplaces #traveldiary #newadventures #newjourney #travel #newbeginnings #lifeisgood #lifestyle #livinglife #science #photography #beachlife #sceneryphotography #outdoors #wildlife #butterfly (at Tinian) https://www.instagram.com/p/CR05RF-FB3Z/?utm_medium=tumblr

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mcatmemoranda · 5 years

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Sperm go through the cervix and go through the uterine cavity. They need to undergo capacitation. During capacitation, the membrane dynamics change; cholesterol is removed, membrane potential changes, changes in calcium signaling. These allow the sperm to penetrate the surrounding cells of the egg and fertilize the egg. Calcium rises intracellularly in the sperm--> changes membrane potential. The uterine cavity helps propel the sperm towards the ampulla of the uterine tube, where the egg is waiting. The egg is in the ampulla, a section of the uterine tube. Myometrial contractions propel the sperm; channels form through the mucus and help propel the sperm. Capacitation also involves increased sperm motility, which helps guide them to where they need to go. Only one can get through the outer layer around the egg. The outer layer that gets expelled with the ovum is made of the cumulus, zona pellucida, and fusion cells. Cumulus cells = ECM, made of hyaluronic acid. The sperm secretes enzymes to digest the barrier. Zona pellucida is the next layer the sperm can breakdown and get through—the sperm use an acrosomal reaction. At the tip of the sperm is a compartment that opens and releases enzymes that break down the zona pellucida. Then the sperm will fuse with the egg. Acrosomal reaction exposes a part of the sperm that reacts with the egg membrane. The DNA and contents of the sperm then go inside the egg. The pronucleus of the sperm is the only part released into the egg that persists—the other elements in the sperm are degraded (so the mitochondria of the sperm are degraded and that’s why you only get mitochondria from your mom!); the fusion induces a calcium wave--> cortical reaction--> change properties of egg membrane to prevent other sperm from reaching the egg—cortical reaction prevents polyspermy.

#fertilization #zona pellucida #cumulus #cortical reaction #acrosomal reaction #capacitation

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jkxcomics · 7 years

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Today, JKX comics celebrates the outstanding work of Ernest Everett Just, an African American developmental biologist who discovered the importance of the cell surface during early embryonic development. His work helped explain why only one sperm can penetrate the egg, a process referred to as “fast block to polyspermy”. Just had to struggle with inequality during his time as a scientist in the early 20th century but was able to make significant discoveries that we still use today.

#black history month #blackscientists #stem #sciart #scicomm #jkxcomics #sciencerules #realizingdreams #diversity

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ibstudentaqua-blog · 5 years

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11 animal physiology

11.1 antibody production and vaccination

To know:

• Every organism has unique molecules on the surface of its cells.

• Pathogens can be species-specific although others can cross species barriers.

• B lymphocytes are activated by T lymphocytes in mammals.

• Activated B cells multiply to form clones of plasma cells and memory cells.

• Plasma cells secrete antibodies.

• Antibodies aid the destruction of pathogens.

• White cells release histamine in response to allergens.

• Histamines cause allergic symptoms.

• Immunity depends upon the persistence of memory cells.

• Vaccines contain antigens that trigger immunity but do not cause the disease.

• Fusion of a tumour cell with an antibody-producing plasma cell creates a

hybridoma cell.

• Monoclonal antibodies are produced by hybridoma cells.

To do:

• Application: Smallpox was the first infectious disease of humans to have been

eradicated by vaccination.

• Application: Monoclonal antibodies to HCG are used in pregnancy test kits.

• Application: Antigens on the surface of red blood cells stimulate antibody

production in a person with a different blood group.

• Skill: Analysis of epidemiological data related to vaccination programmes.

11.2 Movement

To know:

• Bones and exoskeletons provide anchorage for muscles and act as levers.

• Synovial joints allow certain movements but not others.

• Movement of the body requires muscles to work in antagonistic pairs.

• Skeletal muscle fibres are multinucleate and contain specialized endoplasmic reticulum.

• Muscle fibres contain many myofibrils.

• Each myofibril is made up of contractile sarcomeres.

• The contraction of the skeletal muscle is achieved by the sliding of actin and myosin filaments.

• ATP hydrolysis and cross bridge formation are necessary for the filaments to slide.

• Calcium ions and the proteins tropomyosin and troponin control muscle contractions.

To do:

• Application: Antagonistic pairs of muscles in an insect leg.

• Skill: Annotation of a diagram of the human elbow.

• Skill: Drawing labelled diagrams of the structure of a sarcomere.

• Skill: Analysis of electron micrographs to find the state of contraction of muscle fibres.

11.3 The kidney and osmoregulation

To know:

• Animals are either osmoregulators or osmoconformers.

• The Malpighian tubule system in insects and the kidney carry out osmoregulation and removal of nitrogenous wastes.

• The composition of blood in the renal artery is different from that in the renal vein.

• The ultrastructure of the glomerulus and Bowman’s capsule facilitate ultrafiltration.

• The proximal convoluted tubule selectively reabsorbs useful substances by active transport.

• The loop of Henle maintains hypertonic conditions in the medulla.

• ADH controls reabsorption of water in the collecting duct.

• The length of the loop of Henle is positively correlated with the need for water conservation in animals.

• The type of nitrogenous waste in animals is correlated with evolutionary history and habitat.

To do:

• Application: Consequences of dehydration and overhydration.

• Application: Treatment of kidney failure by hemodialysis or kidney transplant.

• Application: Blood cells, glucose, proteins and drugs are detected in urinary tests.

• Skill: Drawing and labelling a diagram of the human kidney.

• Skill: Annotation of diagrams of the nephron.

11.4 Sexual reproduction

To know:

• Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation.

• Processes in spermatogenesis and oogenesis result in different numbers of gametes with different amounts of cytoplasm.

• Fertilization in animals can be internal or external. • Fertilization involves mechanisms that prevent polyspermy.

• Implantation of the blastocyst in the endometrium is essential for the continuation of pregnancy.

• HCG stimulates the ovary to secrete progesterone during early pregnancy.

• The placenta facilitates the exchange of materials between the mother and fetus.

• Estrogen and progesterone are secreted by the placenta once it has formed.

• Birth is mediated by positive feedback involving estrogen and oxytocin.

To do:

• Application: The average 38-week pregnancy in humans can be positioned on a graph showing the correlation between animal size and the development of the young at birth for other mammals.

• Skill: Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis.

• Skill: Annotation of diagrams of mature sperm and egg to indicate functions.

#ib #ib student #studyblr

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tenorself34-blog · 5 years

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dark denim dress Secrets

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richard1lauritsen-blog · 6 years

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Schoenwolf et al.: Larsen's Human Embryology, 5th Edition

For Order This And Any Other Test

Banks And Solutions Manuals, Course,

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Contact us At: [email protected]

Test Bank Larsens Human Embryology 5th Edition

Chapter 1: Gametogenesis, Fertilization, and First Week

Test Bank

MULTIPLE CHOICE

1. A child with a large sacrococcygeal teratoma is delivered by cesarean section. The teratoma likely arose from which type of cells?

A. Neuroectodermal stem cells

B. Neural crest cells

C. Primitive streak cells

D. Primordial germ cells

E. Secondary oocyte cells

ANS: D

2. A baby is diagnosed with Down syndrome shortly after birth. Which of the following events occurred abnormally during prenatal development?

Anaphase of mitosis

Metaphase of mitosis

Telophase of mitosis

Anaphase of meiosis

Metaphase of spermatogenesis

ANS: D

3. The birth control pill acts by blocking which process?

Fertilization

Ovulation

Cleavage

Capacitation

Implantation

ANS: B

4. RU-486 is an effective abortifacient. It acts by which mechanism?

Blocking oogenesis

Causing menstruation

Blocking ovulation

Causing polyspermy

Blocking capacitation

ANS: B

5. A 36-year-old woman is unable to conceive a child because both her oviducts were severely scarred by pelvic inflammatory disease resulting from gonorrhea. Which type of assisted reproductive technology could be used to help her conceive?

Gamete intrafallopian transfer (GIFT)

Zygote intrafallopian transfer (ZIFT)

In vitro fertilization (IVF) and embryo transfer

ANS: C

6. A researcher knocks out expression of the POU domain transcription factor Oct4 in the early epiblast of a mouse embryo. Which cell type would you expect to be affected?

Neural crest cells

Neural plate cells

Mesodermal cells

Primordial germ cells

Endodermal cells

ANS: D

7. Formation of haploid spermatozoa occurs during which developmental event?

Spermiation

Capacitation

Spermatogenesis

Spermiogenesis

Fertilization

ANS: C

8. Increase in the levels of which hormone prevents menstruation during a cycle in which fertilization occurs?

LH

FSH

GnRH

hCG

Estrogen

ANS: D

9. A newborn girl is suspected of having Turner syndrome. Which diagnostic procedure would be used to determine if this is indeed the case?

Karotyping

Spectral karotyping (SKY)

Comparative genomic hybridization (CGH)

Fluorescent in situ hybridization (FISH)

ANS: A

10. A researcher establishes mouse spermatozoa lacking one of the following two sperm-specific proteins: Izumo and CD9. Which developmental events will be perturbed in the absence of either of these proteins?

Spermatogenesis

Capacitation

Binding of spermatozoa to the zona pellucida

Fusion of the egg and spermatozoa membranes

Spermiogenesis

ANS: D

#Schoenwolf et al.: Larsen's Human Embryology 5th Edition

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leedsomics · 7 years

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Proteomics of phosphorylation and protein dynamics during fertilization and meiotic exit in the Xenopus egg

Fertilization triggers release from meiotic arrest and initiates events that prepare for the ensuing developmental program. Protein degradation and phosphorylation are known to regulate protein activity during this process. However, the full extent of protein loss and phospho-regulation is still unknown. We examined absolute protein and phospho-site dynamics after fertilization by mass spectrometry-based proteomics. To do this, we developed a new approach for calculating the stoichiometry of phospho-sites from multiplexed proteomics that is compatible with dynamic, stable and multi-site phosphorylation. Overall, the data suggest that degradation is limited to a few low abundance proteins. However, this degradation promotes extensive dephosphorylation that occurs over a wide range of abundances during meiotic exit. We also show that eggs release a large amount of protein into the medium just after fertilization, most likely related to the blocks to polyspermy. Concomitantly, there is a substantial increase in phosphorylation likely tied to calcium activated kinases. We identify putative degradation targets as well as new components of the block to polyspermy. The analytical approaches demonstrated here are broadly applicable to studies of dynamic biological systems. http://dlvr.it/PJqkCN

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eurekamag--com · 7 years

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Polyspermy-preventing mechanisms in the golden hamster egg

http://dlvr.it/Ny3lZr

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elevatedmindzinc · 7 years

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Happy Black History Month! We at Elevated Mindz Incorporated would like to share the accomplishments of some of the great pioneers of American and World History! Black History is our History! Your History! Black History is everyones #HISTORY #365! Ernest Everett Just (August 14, 1883 – October 27, 1941) was a pioneering African-American biologist, academic and science writer. Just's primary legacy is his recognition of the fundamental role of the cell surface in the development of organisms. In his work within marine biology, cytology and parthenogenesis, he advocated the study of whole cells under normal conditions, rather than simply breaking them apart in a laboratory setting. Just authored two books: "Basic Methods for Experiments on Eggs of Marine Animals (1939)" and "The Biology of the Cell Surface (1939)" along at least seventy papers published in the areas of cytology, fertilization and early embryonic development. He discovered what is known as the fast block to polyspermy; he further elucidated the slow block, which had been discovered by Fol in the 1870s; and he showed that the adhesive properties of the cells of the early embryo are surface phenomena exquisitely dependent on developmental stage. Just believed that the conditions used for experiments in the laboratory should closely match those in nature; in this sense he can be considered to have been an early ecological developmental biologist. Just was the subject of the 1983 biography Black Apollo of Science: The Life of Ernest Everett Just by Kenneth R. Manning. The book received the 1983 Pfizer Award and was a finalist for the 1984 Pulitzer Prize for Biography or Autobiography. Just has been featured in The Black Heritage Stamp series that began in 1978 honoring African Americans' greatest accomplishments. His stamp became available on February 1, 1996. In 1996, the U.S. Postal Service issued a commemorative stamp honoring Just. #BlackHistoryMonth #BlackGirlsRock #day #EMZ_INC #Science #blacklivesmatter #youth #Business #Inventors #Makers #USPatient #Fun #Machine #BlackBoysRock #Learning #Scholarship #Community #commentforcomment #YouthEmpowerment #change #Science #History #America #Facts (at Elevated Mindz Incorporated)

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