embryology exam 1

• The female ovarian cycle is controlled by the hypothalamus by the production of gonadotropin-releasing hormone (GnRH).
• GnRH acts on the anterior lobe of the pituitary gland to secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
• FSH and LH stimulate and control cyclic changes in the ovary.
• At the beginning of each ovarian cycle, 15 to 20 primary-stage follicles are stimulated to grow under the influence of FSH.
• One follicle reaches full maturity, while the others degenerate and become atretic, forming a corpus atreticum.
• FSH stimulates maturation of follicular cells surrounding the oocyte.
• Granulosa cells produce estrogens, including estrone and 17 B-estradiol, in cooperation with theca interna cells.
• Estrogens cause the uterine endometrium to enter the follicular or proliferative phase.
• Estrogens causes thinning of the cervical mucus and stimulation of the anterior lobe of the pituitary gland to secrete LH.
• The LH surge at midcycle elevates concentrations of maturation-promoting factor.
• Oocytes complete meiosis 1 and initiate meiosis II due to the concentrations of maturation-promoting factor.
• Follicular stromal cells production of progesterone is intitiated by The LH surge.
• Follicular rupture and ovulation is caused by The LH surge.
• Under the influence of FSH and LH, the vesicular follicle grows rapidly to become a mature vesicular follicle.
• The primary oocyte completes meiosis I and initiates meiosis II but is arrested in metaphase about 3 hours before ovulation.
• After which the follicle ruptures and ovulation occurs under the influence of FSH and LH.
• High concentration of LH increases collagenase activity, resulting in digestion of collagen fibers surrounding the follicle.
• Prostaglandin levels increase, causing local muscular contractions in the ovarian wall, ultimately leading to ovulation.
• The process of ovulation begins with the development of a primordial follicle, which consists of a primary oocyte surrounded by granulosa cells.
• Cycle progresses and some of these follicles develop into growing follicles and eventually into vesicular follicles under the influence of FSH and LH.
• The vesicular follicle produces estrogens, stimulating LH production, causing the follicle to mature and complete meiosis I, then enter meiosis II, where it is arrested in metaphase.
• Until ovulation occurs, at which point the oophorus breaks free and floats out of the ovary.
• Granulosa cells and cells from the theca interna form the corpus luteum which secretes estrogens and progesterone after ovulation.
• Granulosa and theca interna secretion prepare the uterine mucosa for embryo implantation.
• Some women may experience a slight pain near the middle of the menstrual cycle, accompanied by a rise in basal temperature, known as mittelschmerz.
• The oocyte is transported into the uterine tube by the sweeping movements of the fimbriae and by motion of cilia on the epithelial lining.
• Once in the tube, it is propelled by peristaltic muscular contractions and by cilia in the tubal mucosa.
• Rate of transport is regulated by the endocrine status during and after ovulation.
• The fertilized oocyte reaches the uterine lumen in approximately 3 to 4 days.
• In cases where women fail to ovulate due to low gonadotropin levels, administration of an agent to stimulate gonadotropin release can be employed.
• Administration of an agent to stimulate gonadotropin release may lead to multiple ovulations and increased likelihood of multiple pregnancies.

Follicular Development and Corpus Luteum Formation

• Follicle development is characterized by distinct stages, including primordial follicle, growing follicle, and vesicular follicle, with each with specific cellular components.
• Zona pellucida, granulosa cells and theca cells play a crucial role in the ovulation process and preparation for implantation.
• The corpus luteum reaches its maximum development approximately 9 days after ovulation.
• Corpus luteum can be recognized as a yellowish projection on the surface of the ovary.
• If Fertilisation does not occur, the corpus shrinks and forms a mass of fibrotic scar tissue known as the corpus albicans due to degeneration of lutein cells.
• The corpus albicans results from degeneration of the corpus luteum.
• Menstrual bleeding is precipitated by a decrease in progesterone production during degeneration of the corpus luteum.
• Human chorionic gonadotropin prevents the corpus luteum from degenerating if the oocyte is fertilized.
• The corpus luteum of pregnancy, also known as the corpus luteum graviditatis, is formed when the corpus luteum continues to grow after fertilisation.
• Corpus luteum of pregnancy secretes progesterone which plays a crucial role in maintaining pregnancy until the end of the fourth month.

Fertilization and Sperm Transport

• Fertilization occurs in the ampullary region of the uterine tube, which is the widest part of the tube and is close to the ovary.
• Fertilization involves the fusion of male and female gametes, with spermatozoa passing through the corona radiata barrier, penetrating the zona pellucida, and finally fusing with the oocyte cell membrane.
• Fertilisation process involves three phases:
  • Spermatozoa pass through the corona radiata barrier(Phase 1)
  • One or more spermatozoa penetrate the zona pellucida(Phase 2)
  • One spermatozoon penetrates the oocyte membrane while losing its own plasma membrane(Phase 3)
• Spermatozoa may remain viable in the female reproductive tract for several days, but only 1% of sperm deposited in the vagina enter the cervix.
• Movement from the cervix to the uterine tube occurs by muscular contractions of the uterus and uterine tube.
• The journey of a sperm from the cervix to the oviduct can take anywhere from 30 minutes to 6 days.
• Fertilization typically occurs in the ampulla, becomes motile again due to chemoattractants produced by cumulus cells surrounding the egg.
• Sperm must undergo two processes to acquire the capability to fertilize an oocyte
  • Capacitation, : a 7-hour period of conditioning in the female reproductive tract
  • Acrosome reaction: Induced by zona proteins after binding to the zona pellucida
• The acrosome reaction releases acrosin and trypsin-like substances to penetrate the zona pellucida.
• Only capacitated sperm can pass through the corona cells and undergo this reaction.
• Phases of fertilization include:
  • Penetration of the corona radiata
  • Penetration of the zona pellucida
  • Fusion of the oocyte and sperm cell membranes
• One sperm fertilizes egg successfully of the 200 to 300 million deposited in the female genital tract.
• Zona pellucida is a glycoprotein shell surrounding the egg.
• Zona pellucida facilitates and maintains sperm binding and induces the acrosome reaction.
• Permeability changes when the head of the sperm comes in contact with the oocyte surface, resulting in the release of lysosomal enzymes from cortical granules and the zona reaction.
• Fusion of oocyte and sperm cell membranes is mediated by the interaction of integrins on the oocyte and their ligands, disintegrins, on sperm.
• Plasma membranes of the sperm and egg fuse, with the sperm's plasma membrane covering the acrosomal head cap disappearing during the acrosome reaction.

Fusion of Gametes and Oocyte Activation

• Fertilisation process involves the spermatozoon entering the oocyte and responds in three ways:
  • The cortical and zona reactions
  • Resumption of the second meiotic division
  • Metabolic activation of the egg.
• All reactions are crucial for preventing polyspermy and initiating embryogenesis.
• Cortical and zona reactions involve the release of cortical oocyte granules which contain lysosomal enzymes.
• Lysosomal enzymes make the oocyte membrane impenetrable to other spermatozoa and altering the zona pellucida to prevent sperm binding and penetration.
• Resumption of the second meiotic division results in the formation of the second polar body and the definitive oocyte.
• Chromosomes arrange themselves in a vesicular nucleus known as the female pronucleus, which contains 22 plus X chromosomes.
• Spermatozoon after entering the oocyte, moves forward and its nucleus becomes swollen, forming the male pronucleus, while its tail detaches and degenerates.
• Male and female pronuclei eventually come into close contact and lose their nuclear envelopes.
• Male and female pronuclei(both haploid) must replicate their DNA and after DNA synthesis, chromosomes organize on the spindle in preparation for a normal mitotic division.
• A normal mitotic division results in the restoration of the diploid number of chromosomes, half from the father and half from the mother.
• Determination of the sex of the new individual is determined at fertilization.
• An X-carrying sperm produces a female (XX) embryo.
• A Y-carrying sperm produces a male (XY) embryo.
• Results of Fertilisation include:
  • Restoration of the diploid number of chromosomes
  • Formation of a zygote with a new combination of chromosomes different from both parents
  • Initiation of embryogenesis.

Contraceptive Methods and Infertility

• Contraceptive methods include:
  • Barrier methods: Male condom, female condom, diaphragm, cervical cap, contraceptive sponge
  • Hormonal methods: Birth control pills, skin patches, vaginal rings, injections, and implants
• Hormonal and barrier methods can prevent fertilization and pregnancy.
• The intrauterine device (IUD) is another form of contraception, available in hormonal and copper types.
• A male "pill" has been developed and tested in clinical trials and contains a synthetic androgen :prevents LH and Follicle-stimulating hormone secretion and either stops sperm production or reduces it to a level of infertility.
• The hormonal device releases progestin
  • Thickens cervical mucus to prevent sperm from entering the uterus
  • Makes sperm less active
  • Reduces the viability of both eggs and sperm
• Copper type: Releases copper into the uterus to prevent Fertilisation or inhibit attachment of the fertilized egg to the uterine wall.
• Emergency contraceptive pills (ECPs): Plan B, Mifepristone (RU-486), and ulipristal acetate (Ella) can be taken up to 120 hours after sexual intercourse to prevent pregnancy.
• Another form of birth control is sterilization.
• Vasectomy prevents release of sperm by blocking the ductus deferens.
• Tubal sterilization blocks or ligates the uterine tubes.
• Both procedures can be reversed in some cases
• Infertility: Affects 14% to 15% of couples.
  • Male : Insufficient numbers of sperm or poor motility
  • Female: Occluded uterine tubes, hostile cervical mucus, and absence of ovulation
• Clomiphene citrate (Clomid) is a drug used to
  • Increase FSH concentrations
  • Stimulate ovulation in women who do not ovulate or ovulate irregularly
  • Stimulate egg development for use in in vitro fertilization (IVF) procedures.
• Assisted reproductive technology (ART): Used in 1% to 2% of all pregnancies in the United States
• ART includes
  • IVF
  • Intracytoplasmic sperm injection (ICSI).
• ART can increase the risk of prematurity, low birth weight, and birth defects, particularly in multiple births.
• In vitro fertilization (IVF) involves:
  • Stimulating follicle growth in the ovary
  • Recovering oocytes by laparoscopy
  • Fertilizing the eggs with sperm in a culture medium.
• Intracytoplasmic sperm injection (ICSI)injecting a single sperm involves injecting a single sperm into an egg's cytoplasm to produce fertilization.

Cleavage and Blastocyst Formation

• The zygote reaches two-cell stage and undergoes a series of mitotic divisions called as cleavage.
• Cleavage increases number of cells and cells( blastomeres) become smaller with each division.
• Blastomeres form a compact ball of cells held together by tight junctions.
• Success Rate: 30% of woman(younger than 35 years of age) conceive after one attempt.
• Less than 5% of woman over 40 years of age conceive after one attempt.
• Natural fertilization techniques associated with a higher rate of birth defects.
• To increase success chance, multiple ova are collected fertilized and placed in uterus which can lead to multiple births and higher rates of morbidity and mortality.
• Severe male infertility : Oligozoospermia or azoospermia can be overcome using intracytoplasmic sperm injection (ICSI) involves injecting single sperm into cytoplasm to cause fertilization.
• Technique has increased risk of Y chromosome deletions and birth defects.
• Zygote undergoes several stages
  • Two-cell stage
  • Four-cell stage
  • Morula stage
• These stages take place before forming blastocyst.
• Blastocyst is characterized by:
  • Presence of an inner cell mass
  • Outer cell mass
• Inner cell mass gives rise to the tissues of the embryo proper and outer mass form trophoblast
• Blastocyst formation: Fluid penetrates the zona pellucida and allows embryo to implant where trophoblastic cells penetrating between epithelial cells of the uterine mucosa and initiation the process of implantation.
• Initial attachment: mediated by selectin on trophoblast cells and its carbohydrate receptors on the uterine epithelium which results the the promotion of successful implantation of the embryo.
• Implantation is result of mutual trophoblastic and endometrial action, with molecules interacting along signal transduction pathways to regulate trophoblast differentiation.
• End of the first week:
  • Human zygote has passed through morula and blastocyst stages -Begun implantation in the uterine mucosa
• The human blastocyst: - Forms around 4.5 days of development - Consists: Inner cell mass(embryoblast) and trophoblast cells
• Inner cell mass differentiates into epiblast and hypoblast cells under the influence of fibroblast growth factors
• Initially: Epiblast and hypoblast cells scatter in embryoblast.
• Time of implantation: segregate to form a layer of epiblast cells dorsally and hypoblast cells ventrally, establishing a dorsal-ventral polarity in the embryo.
• Some hypoblast cells specified to form anterior visceral endoderm (AVE)
• AVE cells: Migrate to the future cranial end of the embryo and secrete nodal homolog antagonists(cerberus and leftyl).
• In absence of inhibitors: nodal establishes the primitive streak at the caudal end of the embryo, establishing the cranial-caudal embryonic axis.

Stem Cells and Abnormal Zygotes

• Embryonic stem cell (ES cells):
  • Derived from the inner cell mass of the embryo
  • Potential to form virtually any cell or tissue type
  • Promising area of research for curing a variety of diseases, including diabetes, Alzheimer's and Parkinson's diseases, anemias, and spinal cord injurie.
• Reproduction cloning after in vitro Fertilisation(IVF):Process of embryonic stem cells(ES cells) has disadvantages of potential immune rejection due to genetic difference between cells and their hosts.
• This issue can be addressed through cell modification.
• Therapeutic cloning/Somatic nuclear transfer: Another approach of obtaining ES cells where nuclei from adult cells are introduced into enucleated oocytes, stimulated to differentiate into blastocysts and then harvested, resulting in genetically compatible cells that are less controversial since they do not involve fertilisation.
• Adult Stem Cells; Find in adult tissues
• Multipotent
• Treat diseases
• Limitations:
  • Slow cell division rates
  • Scarcity
• Abnormal zygotes can be formed due to chromosomal abnormalities.
• 50% of pregnancies result in spontaneous abortion and are often lost within 2-3 weeks of fertilization and half of these losses resulting from chromosome abnormalities.
• Chromosome abnormalities serve as a natural means of screening embryos for defects.

Uterine Wall and Menstrual Cycle

• Uterus Wall consist three layers: -Endometrium -Myometrium -Perimetrium
• Endometrium undergoes changes in 28 day cycle under hormonal control under ovaries passing through three stages; follicular or proliferative phase, the secretory of progestational phase, and the menstrual phases.
• Use of in vitro Fertilisation (IVF) and polymerase chain reaction (PCR) allows molecular screening of where single blastomeres from embryonic genetic defects can be removed and their DNA amplified for analysis.
• More sequencing information through genome projects will enable genes detection linked with various syndromes.
• Secretory Phase of menstrual cycle begins 2 to 3 days after ovalation in response to progestrone production from the corpus lutem, when endometrium under go significant changes to prepare for potential implantation for fertility egg.
• Fertilization Typically occurs during the 12-24 hours post ovulation.
• Zygote Development happens several stages
  • Two-cell stage
  • Morula
  • Blastocyst
• Embryo implantation occur after zygote endometrium at least 6 days post ovulation.
• Uterine endometrium consist three layers;
  • Compact layer
  • Sponge layer
  • Basal Layer, plays implantation and placenta formation, from glands of pregnant corpus luteum

If fertilization occur or not endometrium shed markings begin menstrual during time in compacted spongy layers are expelled during only basil during time.

• Ovaries undergoes maturity during follicle stage and ovulation form in Corpus Luteam creates progesterone potential in fertilized stage.

Implantation and Placenta information:

• Place: Anterior or posterior wall of the uterus.
• Step: Blastocyst become embedded between openings in and placenta over time assume hormones produced by the degeneration of Corpus Luteum
• Acrosomo reaction: Acrosin is released to facilitate fertilization.
• When spermatozoon enter oocyte and become impenetrable where the sperm head separate becomes swelled and forms the male pronucleus.

Assisted reproductive technology can overcome these barriers and help.

• 3-day-old human embryo or a 13-day-old embryo

• A 16-cell morula, and as the morula enters the uterus, a cavity appears, and the blastocyst forms, consisting of an inner cell mass and an outer cell mass and then a 13 days old embryo.

• Second Week of Bilaminin Germ Disc

• Endometrial storm and the synctiotrophablast layer that connect with the embryo with trophoblastic area.

By the9th development the penetration deffect and and by a 13-day old blastocyst we have the surface defect in the endometrium has usually and a trophoblast and a cytotrophabaolst

• Second week of development that leads to the sac forming from the endoderm and a yolk sac.
• Second week: 2 layers form with two cavities

Immune System Changes and Ectopic Pregnancies

This section discusses pregnancy within uterine and outside including location of the abdominal area where can attached from the pouch . The tubal pregnancy and can rupture from tubular areas.

• By end of the second trimester the blastocyte is completely embed in the uterus and a bilaminar disc is form.
• Trophoblastic membranes developed from the amniotic system.
• Some cases in trophoblast can develop and from placental membrane forming Hydiform Moler that create benign hormones and or malignant tumors.
• The trophablast differentiate into the chorionic where embryonic circulation developed where they can invade tissues maternal membrane by the end of the second trimester by the end of the cytotrophablast and the syncitiotiotrophabs

Reporodcutve failure with 58% the blastocyst develops through time.

• And the mesoderm develops through the the trophoblast and amniotic sac We learn that the mesoderm of trophoblast will eventually form the connecting stalk and the third trimester: Third Week of Development and Gasturaltion starts by a three germ, a 17 day from the beginning

• the invagination occurs and the invagination.

• The extraembryonic and amniotic are in the eceaphlaic direction

• the cells in primitive node move forward and in this step is the cells in the trophoblast.

• The cloacal forms form amniotic sac and we learn about the 16th days of development.

• Third Week of Development, and a small pit for with yolk-sac, and the ecanphlaic

• The Nodal homolog

• And the body axis is in an ecanpaic to the end of the fourth week

• and finally the BRACHUYR gene, and chording genes by the nodes helps with development, with what is the not notochord.

• Finally, the serotonin can lead to laterality .