Leads to the formation and organization of all the diverse cell types in the body.
Ensures that new individuals are produced from generation to generation.
The study of events occurring prior to birth.
First 38 weeks of human development that begin wither fertilization of the secondary oocyte and end with birth.
First 2 weeks of development, when the single cell produced by fertilization (the zygote) becomes spherical, mulicellular structure (a blastocyst). This period ends when the blastocyst implants in the lining of the uterus.
Includes the third through eighth weeks of development. It is a remarkably active time during which rudimentary versions of the major organ systems appear in the body, which is now called an embryo.
The remaining 30 weeks of development prior to birth, when the organism called a fetus. The fetus continues to grow, and its organs increase in complexity.
The zygote divides by mitosis to form a multicellular structure called a blastocyst.
The blastocyst cells form three primary germ layers, which are the basic cellular structures from which all body tissues develop.
The three primary germ layers arrange themselves in ways that give rise to all organs in the body.
Process that produces gametes (sex cells).
Contain genetic information for most human characteristics, such as eye color, hair color, height, and skin pigmentation.
A pair of autosomes.
Primarily determines whether an individual is female or male.
23 pairs of chromosomes.
Type of sex cell division that starts off with a diploid parent cell and produces haploid daughter cells.
Occurs in Prophase I. Genetic material is exchanged between homologous chromosomes.
Replicated chromosomes composed of two identical sister chromatids.
Each containsan identical copy of DNA.
Where the sister chromatids are attached.
Process by which homologous chromosomes pair up.
The actual pair of homologous chromosomes.
Process by whereby maternal and paternal chromosome pairs are separated and move to opposite ends of the cell.
Sex cell produced (in females).
Process of oocyte developement.
Parent cells, stem cells, that produce oocytes.
Arrested in prophase I and remain this way until the female reaches puberty.
Nonfunctional cell that eventually degenerates.
Expelled from the ovary into the uterine tube.
Cuboidal cells. Surrounds the oocyte.
Thin rings of proteins and glycoproteins that surrounds the oocyte.
The cell that receives the majority of the cytoplasm.
Male sex cell produced.
The process of sperm development.
Parent or stem cells that produce sperm. Diploid cells that reside in the make gonads, the testes.
Separation fails during Meiosis.
47 chromosomes. 3 copies of a chromosome.
45 chromosomes. One cope of a chromosome.
The exact copy of spermatogonium when it first divides by mitosis.
Haploid cells produced when primary spermatocytes undergo meiosis.
Spermatids lose much of their cytoplasm and grow a long tail called a flagellum.
The single diploid cell a male's sperm and a female's secondary oocyte form.
Formed within the first 2 weeks when the zygote undergoes mitotic cell divisions, and the number of cells increases.
Chronology of events in Pre-embryonic development
Fertilization, Zygote, Cleavage (30 hours to day 3 post-fertilization), Morula (days 3-4 post-fertilization), Blastocyst (days 4-5), Implantation (begins last first week and is complete by end of second week).
The process whereby two sex cells fuse to form a new cell containing genetic material derived from both parents. Occurs in the ampulla.
Period of conditioning that takes place in the female reproductive tract and usually takes several hours. Must be done so the sperm can fertilize the secondary oocyte.
Membranous cap at the head of the sperm containing digestive enzymes that can break down the protective layers around the secondary oocyte. The enzymes are released when the sperm comes into contact with the secondary oocyte.
Substances that mark and target the sperm for destruction by the immune system.
The release of enzymes from the acrosome by exocytosis. The enzymes are primarily hyaluronidase and acrosin and they eat away a portion of the zona pellucida.
More than one sperm nuclei entering the secondary oocyte. Immediately fatal because it causes the fertilized oocyte to have 23 triplets (if two sperm enter) of chromosomes instead of the normal 23 pairs.
What the nucleus of the sperm and the nucleus of the ovum are called after meiosis because they have a haploid number of chromosomes. The pronuclei then come together and fuse, forming a single nucleus that contains a diploid (23 pairs) of chromosomes. This is the zygote.
Series of mitotic divisions that happen after the zygote divides once and reaches the 2-cell stage. Results in an increase in cell number but not an increase in the overall size of the structure.
Process by which contact between cells is increased to the maximum.
Fluid-filled cavity develops within the morula after the morula enters the space (called the lumen) of the uterus.
Pre-embryo that has two distinct components: trophoblast and the embryoblast.
Outer ring of cells surrounding the fluid-filled cavity. These cells will form the chorion, one of the extraembroyonic membranes.
Inner cell mass. Tightly packed group of cells located only within one side of the blastocyst. Embryoblast will form the embryo proper.
Early cells, have the power to differentiate into any cell or tissue type in the body.
Inner lining of the uterine wall.
Within the endometrium. Deep.
Within the endometrium. Superficial.
Process by which the blastocyst burrows into and embeds within the endometrium.
The inner cellular layer of the trophoblast.
Outer, think layer of the trophoblast where no plasma membranes are visible.
Layer of small, cuboidal cells adjacent to the blastocyst cavity.
Layer of columnar cells adjacent to the amniotic cavity.
Bilaminar germinal disc
The hypoblast and the epiblast together. Flat disc.
Yolk, sac, amnion, and chorion. First appear during the second week of development and continue to develop during the embryonic and fetal periods. They assist the embryo in vital functions such as nutrition, gas exchange, and removal of waste materials. Protect the embryo by surrounding it with an aqueous environment.
First extraembryonic membrane to form, is formed from and continuous with the hypoblast layer. Important site for early blood cell and blood vessel formation.
Thin membrane that is formed from and continuous with the epiblast layer.
The amnion eventually encloses the entire embryo in a fluid-filled sac (amniotic cavity) to prevent the embryo's desiccation. Amniotic membrane is specialized to secrete the amniotic fluid that bathes the embryo.
Outermost extraembryonic membrane, is formed from the rapidly growing cytotrophoblast cells and syncytiotrophoblast. These cells blend with the functional layer of the endometrium and eventually form the placenta, the site of exchange between the embryo and the mother.
Connection between the embryo or fetus and the mother is the richly vascular placenta.
Connects the early organism to the placenta. Precursor to the future umbilical cord.
Forms when the connecting stalk contains the umbilical arteries and veins that distribute blood through the embryo or fetus.
Stalklike structures that form the chorion. Contain brances of the umbilical vessels.
Within the first 3 months, this produces the estrogen and progesterone that maintains and builds the uterine lining.
Occurs during the third week of development immediately after implantation, and is one of the most critical periods in the development of the embryo. Is the process by which the cells of the epiblast migrate and form the three primary germ layers.
Primary germ layers
The cells from which all body tissues develop. Three primary ones are called: ectoderm, mesoderm, and endoderm.
The trilaminar structure that forms once the three primary germ layers (ectoderm, mesoderm, and endoderm) form.
A thin depression on the surface of the epiblast. Gastrulation begins.
Cephalic (head) end of the streak. Consists of a slightly elevated area surround a small primitive pit.
Inward movement of cells. (Cells detach from the epiblast layer and migrate through the primitive streak between the epiblast and hypoblast layers).
Primary germ layer that forms between the epiblast and hypoblast.
Is formed when other migrating cells eventually displace the hypoblast.
Cells remaining in the epiblast.
The 3-week embryo is a flattened, disc shaped structure.
Occurs in the head and caudal (tail) regions on the embryo.
Lateral folding. Occurs when the left and right sides of the embryo curve and migrate toward the midline.
Cylindrical structure of mesoderm, forms immediately internal and parallel to the primitive streak.
Process where one structure influences another structure to change form. EX: The notochord influences some of the overlying ectoderm to begin to form nervous tissue.
Inductive action that transforms a flat layer of ectodermal cells into a hollow nervous system tube.
Thickened layer of cells that the ectoderm forms during the third week of development.
Lateral edges of the neural plate elevated making the neural folds.
Depression between the neural folds.
Cylindrical tube formed when the neural folds approach each other gradually in the midline and fuse.
Neural crest cells
Cells that dissociate from adjacent cells along the lateral border of the neural folds. They migrate throughout the body and give rise to a vast, heterogeneous array of structures.
Found on both sides of the neural tube.
Blocklike masses responsible for the formation of the axial skeleton, most musle (including limb musculature), and most of the cartilate, dermis, and connective tissues of the body.
Tightly packed group of mesodermal cells. Forms the notochord. The notochord serves as the basis for the central body axis and axial skeleton, and induces the formation of the neural tube.
Lateral to the paraxial mesoderm. Cords that form most of the uninary system and the reproductive system.
Lateral plate mesoderm
Most lateral layers of the mesoderm on both sides of the neural tube. Remain thin and they give rise to most of the components of the cardiovascular system, the lining ofthe body cavities, the thoracic and abdominal walls, and all the connective tissue components of the limbs.
Last region of mesoderm. Forms connective tissues and musculature of the face.
Becomes the innermost tissue when the embryo undergos transverse folding. Structures formed by endoderm: linings of the digestive, respirator, and urinary tracts. Also forms the thyroid gland, parathyroid glands, thymus, and portions of the palatine tonsils, as well as most of the liver, gallbladder, and pancreas.
Once the three primary germ layers have formed and the embryo as undergone cephalocaudal and transverse folding, organegensis can begin. Upper and lower limbs attain their adult shapes, and the rudimentary forms of most organ systems have developed by week 8 of development.
Substances that can cause birth defects or the death of he embryo. EX: alcohol, tobacco smoke, drugs, some viruses, and even some seeming benign medications, like aspirin. During the embryonic period, the embryo is particularly sensitive to these things.
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