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Visible Embryo Worksheet Go to this site http://www.visembryo.com/baby/1.html and complete the following: Stage 1 Fertilization begins when a sperm penetrates an oocyte ____________ and it ends with the creation of the __________. The fertilization process takes about ______ hours. A sperm can survive for up to ______hours. The fusion of the oocyte and sperm nuclei marks the creation of the ___________ and the end of _________________________. Stage 2 The zygote now begins to _________________, with each division occurring into two cells called blastomeres. The zygote's first cell division begins a series of divisions, with each division occurring approximately every ____________ hours. Each blastomere within the zona pellucida becomes smaller and smaller with each subsequent division. When cell division generates about sixteen cells, the zygote becomes a ____________________(mulberry shaped). It leaves the fallopian tube and enters the uterine cavity ___________________ days after fertilization. Stage 3 About four days after fertilization, the morula enters the _____________ cavity. Cell division continues, and a cavity known as a blastocele forms in the center of the morula. Cells flatten and compact on the inside of the cavity while the zona pellucida remains the same size. With the appearance of the cavity in the center, the entire structure is now called a ______________________. Stage 4 The pressure of the blastocele expanding in the middle of the blastocyst against the rigid wall of the zona pellucida, creates "hatching" of the ___________________ from the zona around the sixth day after fertilization. As the ___________________ enters the uterus free from the zona, the outer layer of trophoblast cells secrete an __________________ to erode the epithelial lining of the uterus and allow the ___________________ to implant. Human chorionic gonadotropin (hCG) is also secreted by the trophoblast cells stimulating the corpus luteum to continue progesterone production. Progesterone maintains the ____________ lining of the uterus. Endometrial glands in the uterus had already begun to enlarge in response to the progesterone stimulated to release by the corpus luteum ("yellow body") which once surrounded the egg as it grew in the ovary almost six days prior. The ______________ is therefore swollen with new blood capillaries and the circulation between mother and ______________ begins, a process needed for the continuation of pregnancy. Stage 5 Trophoblast cells continue to engulf and destroy cells of the uterine lining creating blood pools and stimulating new capillaries to grow - beginning the growth of the __________________. The _________________ inner cell mass differentiates into two layers: EPIBLAST The top layer of cells (dark blue) which will become the embryo and amniotic cavity. HYPOBLAST Lower layer of cells (yellow) which become the yolk sac. _______________________ ___________________ - implantation sites not in the uterus - can occur at this time and may continue up to 16 weeks unnoticed. Quick diagnosis can pharmacologically treat without surgery preserving the site of the pregnancy. Stage 6 Placenta Formation Chorionic _____________ "fingers" form in the "placenta" anchoring the embryo to the __________________. Blood vessels begin appearing first in the "placenta" surrounding the embryo. The _________________ begins producing hematopoietic or non-nucleated blood cells. Stalk Formation By the end of stage 6a, the embryo is attached to the developing ___________________ by a stalk later to become part of the umbilical cord. Gastrulation In Carnegie Stage 1, the exit of the first polar body through the zona pellucida determined the gastrulation axis. Stage 6b begins as a narrow line of cells appear on the surface of the formerly 2 layered embryonic disc. This "primitive streak" marks bilateral symetry in the embryo and indicates ___________________ has begun - the migration of cells from the outer edges of the disc into the primitive streak and down creating a new third layer. The embryo now has endoderm, mesoderm and ectoderm layers. ECTODERM ___________________________________of the embryonic disc. Will later form: skin, hair, lenses of the eyes, lining of the internal and external ear, nose, sinues, mouth, anus, tooth enamel, pituitary and mammary glands, and all parts of the nervous system. MEDODERM ________________________________ of the embryonic disc and precursor to the muscles, bones, lymphatic tissue, spleen, blood cells, heart, lungs, reproductive and excretory systems. ENDODERM _________________________________ of the embryonic disc from which will form the lining of the lungs, the tongue, tonsils, urethra and associated glands, bladder and digestive tract. Stage 7 Neurulation In Stage 6, gastrulation began with the appearance of the primitive streak. In Stage 7, __________________________ continues with the formation of a new cell layer - the ectoderm - changing the ____________-layered disc into a ____________-layered disc. Neural crest cells originate at the top of the __________________ tube and migrate extensively, differentiating into many cell types such as ________________, glial cells, pigmented cells of the epidermis, epinephrine producing cells of the adrenal gland, and various skeletal and connective tissues of the head. It appears that the _____________ of a migrating cell is largely determined by its final _____________________. Gastrulation Gastrulation in full force. Cells are ___________________ across the surface of the 2 layered embryonic disc and into the newly formed Primitive Streak. After migrating through the Primitive Streak, these new cells collect into a new 3rd layer - the _______________________. Stage 8 The embryonic area is now shaped like a pear, and the head region is broader than the tail end. The ectoderm has thickened to form the ____________ plate. The edges of this plate rise and form a concave area known as the neural __________________. This groove is the precursor of the embryo's ________________ system and it is one of the first organs to develop. By stage 8, the ______________ cells are already developed and begin to form channels along side of the epithelial cells forming at the same time. What is the Sonic Hedgehog (shh) gene and how did it get its name? Stage 9 Looking at the embryo from the top, the head end is wider than the tail end, with a slightly narrowed middle. _________________, which are composed of mesoderm, appear on either side of the neural groove. The first pair of somites appear at the tail and progress to the middle. One to three pairs of somites are present by Stage 9. Every ridge, bump and recess now indicates cellular differentiation. A _____________ fold rises on either side of the primitive streak. The primitive streak now runs between one-fourth to one-third of the length of the embryo. Secondary blood vessels now appear in the chorion/placenta. Hematopoietic cells appear on the _____________________ simultaneously with endothelial cells which will go on to form ______________ vessels for the newly emerging blood cells. Endocardial (muscle) cells begin to fuse and form into the early embryo's two _________________tubes. Stage 10 Rapid _________________ growth and change elongates the embryo and expands the yolk sac. On each side of the neural tube, between four and twelve pairs of somites can exist by the end of Stage 10. The cells which become the _____________ appear as thickened circles just off of the neural folds. The newly differentiated cells of the ears are also present. Neural folds are rising and fusing at several points along the length of the neural tube concomitant with the budding somites which appear to "zipper" the neural tube _______________. Neural crest cells will eventually contribute to the ___________ and ________________of the embryo. The two endocardial tubes formed in Stage 9 now fuse in Stage 10. Together they form one single tube generated from the cells of the "roof" of the nueral tube. The heart tube takes on an _________________establishing the asymetry of the heart. As the S-shape forms, _______________ muscle contraction begins. Stage 11 Thirteen to twenty pairs of ______________ are present and the embryo is shaped in a modified S curve. The embryo has a bulb-like tail and a connecting stalk to the developing placenta. A primitive S-shaped tubal _______________ is beating and peristalsis, the ______________muscle contractions propelling fluids throughout the body, begins. However, this is not true circulation because blood vessel development is still ____________________________. At this stage, the neural tube determines the form of the embryo. Although the primary blood vessels along the central nervous system are now connecting in Stage 11, the central ___________________ system appears to be the most ____________________ system. If twenty somites are present in the embryo, the forebrain is completely closed. Stage 12 The embryo curves into a C shape. The arches that form the ____________ and ___________ are now becoming evident under the enlarging _____________________. By the time the neural tube is closed, both the ___________ and ____________ will have begun to form. At this stage, the _________________ and _______________ cord together are the largest and most compact tissue of the embryo. Valves and septa may appear in the ______________ in Stage 12. The beginning cells of the ____________ form before the rest of the ______________ system. Stage 13 The ______________________ epithelium layer begins to differentiate into the future locations of the liver, _______________, stomach and _____________________. Stage 14 Head and Neck The _____________ and ___________ grow rapidly. The mandibular and hyoid arches are noticeable. Ridges demarcate the three sections of the brain (midbrain, forebrain and hindbrain). Thorax _____________________, the tube through which food is swallowed, forms from a groove of tissue that separates from the trachea, which is also visible. Semilunar ____________ begin to form in the heart. Four major subdivisions of the heart (the trabeculated left and right ventricles, the conus cords and the truncus arteriosus) are clearly defined. Two sprouts, a ventral one from the aortic sac and a dorsal one from the aorta, form the pulmonary (sixth aortic) arch. Right and left lung sacs lie on either side of the esophagus. Abdomen and Pelvic Regions Ureteric bud appear. Metanephros, which will eventually form the permanent _________________, is developing. Limbs Upper ____________ elongate into cylindrically-shaped buds, tapering at tip to eventually form hand plate. Nerve distribution process, i_______________________, begins in the upper limbs. There are more stages and other events that happen. We will cover them later but you should click ahead to see what they are.