Anatomy Lecture 2 Embryo Development PDF

1.Recognize the difference between germ cells and gametes and the role of meiosis in their development Germ Cells Definition: Germ cells are specialized cells that give rise to gametes. They are the precursors to gametes and are involved in the early stages of reproduction. Characteristic...

1.Recognize the difference between germ cells and gametes and the role of meiosis in their development Germ Cells Definition: Germ cells are specialized cells that give rise to gametes. They are the precursors to gametes and are involved in the early stages of reproduction. Characteristics: Chromosome Number: Germ cells are diploid (2n), meaning they have two sets of chromosomes, one from each parent. Location: In humans and many animals, germ cells are present in the gonads (testes in males, ovaries in females) and are set aside during early development. Function: They are not directly involved in reproduction until they undergo meiosis. Their primary role is to develop into gametes through the process of meiosis. Development: Germ cells divide by mitosis to produce more germ cells or to start the process of meiosis. During meiosis, they undergo two rounds of division to produce gametes. Gametes Definition: Gametes are the mature reproductive cells involved in sexual reproduction. In humans, these are spermatozoa (male) and oocyte (female). Characteristics: Chromosome Number: Gametes are haploid (n), meaning they contain one set of chromosomes. This is half the chromosome number of the parent diploid cells. Location: Gametes are released into the external environment (e.g., sperm is released into the female reproductive tract, and eggs are ovulated) or into the reproductive system for fertilization. Function: Their primary role is to fuse during fertilization to form a zygote, which will develop into a new organism. Development:  Gametes are produced through meiosis from germ cells. After meiosis, they mature and are ready for fertilization to become a zygote. Key Similarities and Differences Similarities: ○ Both are essential for sexual reproduction. ○ Both are involved in the transfer of genetic material from one generation to the next. ○ Both are derived from the same initial cell type (germ cells). Differences: ○ Chromosome Number: Germ cells are diploid (2n) with 46 chromosomes Gametes are haploid (n) with 23 chromosomes ○ Function: Germ cells are the precursors to gametes and are involved in meiosis Gametes are the cells that actually participate in fertilization. ○ Stage in Development: Germ cells undergo two cell divisions to create 4 haploid gametes ○ Flow Chart Germ Cells (2n) -> Meiosis -> Gametes (n) -> Fertilization -> Zygote (2n) -> Mitosis -> Diploid multicellular organism 2.Chart the development of oogonia to secondary oocytes, including developmental arrests, and explain the differences between cell and follicular stages Oogenesis Begins in the female fetus as a follicle ○ Follicle = oocyte + supporting cells ○ Primary Follicle = Follicular cells + primary oocyte ○ Secondary follicle = primary oocyte + follicular/granulosa cells + small antrum Completion of meiosis I ○ Secondary oocyte- receives majority of cytoplasm and will continue development ○ Polar body- second cell that degenerates Meiosis II begins in secondary oocyte ○ Mature follicle = secondary oocyte + antrum + zona pellucida + corona radiata + granulosa cells Stages of development ○ Meiosis -> Primary oocyte; Meiosis II -> Secondary oocyte  Development Chart Stage Cell and Phase Description Follicle Chromosome Developmental Number Arrest Before Birth and Childhood Oogonia Oogonia -> Early germ cells in the Diploid (2n) None Mitosis ovary. Undergo mitotic divisions. (one remains, the other progresses) Primary Primary Oocyte -> Oogonia that enter Primordial Diploid (2n) Arrested in Oocyte beings meiosis I prophase I of meiosis follicle prophase I until and begin the first puberty meiotic division Puberty/Ovulation Primary Primary oocyte -> Primordial follicle Primary Diploid (2n) none Oocyte ovulation begins matures in ovulation Follicle cycle Secondary Primary oocyte -> Primary oocyte Secondary none Oocyte completes completes meiosis I to follicle meiosis I -> produce a secondary oocyte and a polar body. Haploid (n) Arrested in Secondary oocyte Mature metaphase II of -> meiosis II Follicle meiosis II until begins fertilization. Fertilization Secondary Not Fertilized -> Ovulation, secondary Ovulated Oocyte Degenerate oocyte leaves ovary and is ovulated into uterine tubes Fertilized -> One cell receives most of Zygote Diploid (2n) completes cytoplasm (ovum) , meiosis II combines with sperm nuclei to become zygote 3.Chart the development of spermatogonia to spermatozoa, listing major events and defining related terminology Spermatogenesis Spermatogenesis occurs in the testes Spermatogonia: Germ cell ○ Progenitor cells that are diploid (2n) Spermatocytogenesis 1. Spermatogonia (Stem Cells) Definition: Spermatogonia are the undifferentiated germ cells located in the testes Major Events: ○ Mitosis: Undergo mitosis to create primary spermatocytes. 2. Primary Spermatocytes Definition: These are cells that result from the differentiation of Type spermatogonia and are diploid (2n). Major Events: ○ Meiotic Division (First Meiotic Division): Primary spermatocytes undergo meiosis I, which reduces the chromosome number by half, producing secondary spermatocytes. 3. Secondary Spermatocytes  Definition: Cells resulting from the first meiotic division of primary spermatocytes; they are haploid (n). Major Events: ○ Meiotic Division (Second Meiotic Division): Secondary spermatocytes undergo meiosis II, resulting in the formation of spermatids. Spermiogensis 4. Spermatids Definition: These are the haploid cells resulting from the second meiotic division of secondary spermatocytes. Major Events: ○ Spermiogenesis: The process where spermatids undergo a series of morphological changes to become mature sperm cells/spermatozoa. This includes: Acrosome Formation: head of sperm contains nucleus Tail Formation: Elongation of the cell and development of the flagellum (tail) with mitochondria Cytoplasmic Reduction: Excess cytoplasm is discarded, forming a streamlined spermatozoon. 5. Spermatozoa (Mature Sperm) Definition: The final, motile male gametes capable of fertilizing an ovum. Major Events: ○ Maturation: Spermatozoa acquire motility and the ability to fertilize an egg where they then enter the lumen of male reproductive tract. Summary of Terminology: Spermatogonia: Stem cells that give rise to sperm cells. Primary Spermatocytes: Diploid cells undergoing meiosis I. Secondary Spermatocytes: Haploid cells resulting from the first meiotic division. Spermatids: Haploid cells resulting from the second meiotic division, which undergo spermiogenesis. Spermatozoa: Mature sperm cells capable of fertilization. 4.Visually recognize major structures and follicular phases of oogenesis on selected histology slides 5.Explain how growth and complexity drives embryological development, linking them to the processes covered in weeks 1-4 What processes allow for development? - Growth shape density Growth & Complexity - Genetic plans in chromosomes interact with environment 1. Growth a. Mitosis and production of ECM 2. Morphogensis a. Change in shape 3. Differentiation a. Density of pluripotent cells driven by cell lineage AND response cues from enviornment 4. Induction a. Tissue development influences pathway, INTRAcelluar message that influences genetic activity 6.List or chart Week 1 of embryological development, by describing processes (e.g., ovulation), cellular stages (e.g., morula), and tissue differentiation To do this, you will need to be able to define the bolded terms Term Definition Relevant Stage Ovary Starting point for Ovulation fertilization, secondary Oocyte leaves ovary in Ovulation  secretes hormones such as estrogen and progesterone Fimbriae fimbriae are the fringed, Ovulation finger-like projections at the end of the uterine (fallopian) tubes. help to guide the oocyte into the uterine tube, facilitating its movement towards the ampulla. Infundibulum funnel-shaped end of Ovulation the uterine tube closest to the ovary, equipped with fimbriae to Transports captured oocye from ovary to uterine tube conduits through which Ovulation the oocyte travels from Cleavage Uterine/Fallopian Tube the ovary to the uterus. Morula travel Capacitation of sperm Ampullae widest portion of the Fertilization uterine tube, located between the infundibulum and the isthmus. It is the most common site for fertilization, where sperm meets the oocyte Fundus of Uterus uppermost, rounded Morula to Blastocyst portion of the uterus. Once implantation occurs, it provides a suitable environment for the developing embryo. The fundus is involved in the structural support and growth of the fetus during pregnancy Pre-Embryonic Period 1. Ovulation ○ Secondary oocyte arrested in metaphase II, leaves ovary and is ovulated into uterine tubes 2. Capacitation of sperm ○ Occurs in the uterine tube ○ Plasma membrane covering the acrosome on head break down, allowing penetration of the secondary oocyte 3. Fertilization ○ 1. Sperm penetrate corona radiata then zona pellucida of secondary oocyte ○ 2. Zona pellucida hardens To prevent other sperm from entering ○ 3. Plasma membrane of oocyte fuses Only sperm nucleus enters ○ 4. Secondary oocyte finishes meiosis II Becomes ovum ○ 5. Ovum and soerm nuclei fuse to create diploid zygote 4. Cleavage ○ Zygote undergoes mitosis Increase cell number, size stays constant In uterine tube 5. Morula Forms ○ Ball of cells/blastomeres ○ Travels through uterine tubes 6. Blastocyst Forms ○ Morula becomes a Blasocyst ○ Arrives in fundus of uterus ○ Contains Embryoblasts: inner cell cluster  Forms embryo Blastocyst cavity: fluid filled cavity Yok sac Trophoblasts: outer cellular lining Placenta 7. Implantation ○ End of first week in endometrium of uterine wall ○ Blastocyst adheres to endometrium Embryoblast -> epiblast and hypoblast Blastocystic cavity -> yok sac/exocoelomic cavity ○ Trophoblast Penetrate functional layer of endometrium (inner uterine lining) Syncytiotrophoblast Burrows into functional layer of uterus Cytotrophoblast Encapsulates epiblast and yok sac 7.Trace Week 2 of embryological development by describing the contributing tissue and developmental trajectories of the following: Bilaminar embryonic disc - former embryoblast; forms all tissues and organs of embryo Amnion - forms amniotic sac that will encompass and protect fetus during development Umbilical vesicle - (yok sac, exocoelomic cavity) formed from blastocyst cavity and will nutritionally sustain embryo until placenta is formed Chorion - helps forms placenta 1. Bilaminar Embryonic Disc Contributing Tissue: The bilaminar embryonic disc is formed from the inner cell mass of the blastocyst. This inner cell mass differentiates into two layers: Epiblast: The upper layer adjacent to the future amniotic cavity, which is columnar in shape and will give rise to all three germ layers of the embryo. Hypoblast: The lower layer adjacent to the blastocyst cavity, which is cuboidal and contributes to the formation of the umbilical vesicle (yolk sac). Developmental Trajectory: Formation: ○ By the end of the first week and the beginning of the second week, the inner cell mass differentiates into the bilaminar disc. ○ The epiblast and hypoblast are situated above the cytotrophoblast layer of the trophoblast. Function: ○ The epiblast will eventually contribute to the formation of the three germ layers (ectoderm, mesoderm, and endoderm) through a process called gastrulation. ○ The hypoblast, meanwhile, helps to form the umbilical vesicle. 2. Amnion Contributing Tissue: The amnion is derived from the epiblast layer of the bilaminar disc. As the epiblast cells proliferate and migrate, they form the amniotic membrane. Developmental Trajectory: Formation: ○ During the second week, the amniotic cavity begins to form within the epiblast. ○ The epiblast cells surrounding this cavity separate to form the amniotic cavity or amnion. Amnion: a thin membrane formed from amnioblasts (amniotic fluid forming cells)- which encloses amniotic cavity ○ This membrane eventually surrounds the embryo, creating the amniotic sac. Amniotic Sac: a structure that encompasses and protects fetus during development and contains specialized cells that create amniotic fluid Function: ○ The amnion fills with amniotic fluid, which cushions and protects the developing embryo and fetus. ○ It also plays a role in the maintenance of a stable environment. 3. Umbilical Vesicle (Yolk Sac) Contributing Tissue: The umbilical vesicle (also known as the yolk sac) originates from the blastocyst cavity. Bilaminar embryonic disc is sandwiched between the amniotic cavity (lined by cells from epiblast) and the primary umbilical vesicle (lined by cells from hypoblast). It is surrounded by extraembryonic mesoderm, which provides additional support and nutrients. Developmental Trajectory: Formation: ○ Begins as blastocyst cavity, called exocoelomic cavity later during implantation, then yok sack/primary umbilical vesicle ○ Is lined by exocoelomic membrane, which migrated from hypoblast and becomes extraembryonic endoderm Function: ○ The yolk sac provides early nutritional support to the developing embryo before the placenta is fully functional. ○ It also plays a role in the formation of blood cells and the development of the embryo's germ cells or gut. 4. Chorion Contributing Tissue: The chorion is formed from the trophoblast layer of the blastocyst, specifically from the cytotrophoblast and syncytiotrophoblast layers. It also incorporates extraembryonic mesoderm. Developmental Trajectory: Formation: ○ Within extraembryonic mesoderm, small openings appear called extraembryonic coelomic spaces Will fuse to form extraembryonic coelom- a large fluid filled cavity that surrounds a.Amnionic cavity b.Bilaminar disc Secondary* umbilical vesicle ○ Cells lining extraembryonic coelom further defined as: Extraembryonic somatic mesoderm lines trophoblast and amniotic cavity ○ Extraembryonic splanchnic mesoderm surrounds umbilical vesicle Function: ○ The chorion surrounds the amniotic sac and the embryo, and it is critical for the formation of the placenta. ○ It facilitates the exchange of nutrients, gases, and wastes between the maternal blood and the developing embryo via the lacunae Lacunae  spaces in syncytiotrophoblasts filled with maternal blood from ruptured uterine capillaries and cellular debris will form maternal portion of placenta ○ Fetus and surrounding amniotic cavity will grow and expand to fill chorionic cavity over time connected to placenta via the developing connecting stalk ○ Chorion: - all components, extraembryonic somatic mesoderm and two layers of trophoblasts Chorionic sac: - trophoblasts and lacunar network Chorionic cavity: - formed from extraembryonic coelom; surrounds amniotic sac, embryo, and umbilical vesicle Connecting stalk: - connection between chorion and amniotic cavity, bilaminar disc, and umbilical vesicle; becomes umbilical cord Primary chorionic villi: - cellular extensions of cytotrophoblast that grow into overlying syncytiotrophoblasts - Will grow and divide to form future placenta Focus on changing structure names over development and what each structure will form