Bio Ch3

• Fertilization is the joining of a sperm and an ovum, usually occurring in the ampulla of the fallopian tube.
• The placenta and umbilical cord are expelled after birth.
• Uterine contractions, coordinated by prostaglandins and oxytocin, result in birth of the fetus.
• The sperm uses acrosomal enzymes to penetrate the corona radiata and zona pellucida.
• Once it contacts the oocyte’s plasma membrane, the sperm establishes the acrosomal apparatus and injects its pronucleus.
• The cortical reaction is a process where the first sperm penetrating the oocyte causes a release of calcium ions, preventing additional sperm from fertilizing the egg and increasing the metabolic rate of the resulting diploid zygote.
• Fraternal (dizygotic) twins result from the fertilization of two eggs by two different sperm.
• Identical (monozygotic) twins result from the splitting of a zygote in two.
• Monozygotic twins can be classified by the placental structures they share (mono- vs diamniotic, mono- vs dichorionic).
• Cleavage refers to the early divisions of cells in the embryo, resulting in a larger number of smaller cells, as the overall volume does not change.
• The zygote becomes an embryo after the first cleavage because it is no longer unicellular.
• Indeterminate cleavage results in cells that are capable of becoming any cell in the organism, while determinate cleavage results in cells that are committed to differentiating into a specific cell type.
• The morula is a solid mass of cells seen in early development.
• The blastula (blastocyst) has a fluid-filled center called a blastocoel and has two different structures: the trophoblast (which becomes placental structures) and the inner cell mass (which becomes the developing organism).
• The blastula implants in the endometrial lining and forms the placenta.
• The chorion contains chorionic villi, which penetrate the endometrium and create the interface between maternal and fetal blood.
• Before the placenta is established, the embryo is supported by the yolk sac.
• The allantois is involved in early fluid exchange between the embryo and the yolk sac.
• The amnion lies just inside the chorion and produces amniotic fluid.
• The developing organism is connected to the placenta via the umbilical cord.
• During gastrulation, the archenteron is formed with a blastopore at the end.
• As the archenteron grows through the blastocoel it contacts the opposite side, establishing three primary germ layers.
• The ectoderm becomes epidermis, hair, nails, and the epithelia of the nose, mouth, and anal canal, as well as the nervous system (including adrenal medulla) and lens of the eye.
• The mesoderm becomes much of the musculoskeletal, circulatory, and excretory systems, as well as the adrenal cortex.
• The endoderm becomes much of the epithelial linings of the respiratory and digestive tracts and parts of the pancreas, thyroid, bladder, and distal urinary tracts.
• Neurulation, or development of the nervous system, begins after the formation of the three germ layers.
• The notochord induces a group of overlying ectodermal cells to form neural folds surrounding a neural groove.
• The neural folds fuse to form the neural tube, which becomes the central nervous system.
• Multipotent cells are able to differentiate only into a specific subset of cell types.
• To respond to a specific morphogen, a cell must have competency.
• Stem cells are cells that are capable of developing into various cell types and can be classified by potency.
• Fetal hemoglobin (HbF) has a higher affinity for oxygen than adult hemoglobin (primarily HbA), assisting in the transfer (and retention) of oxygen into the fetal circulatory system.
• Determination is the commitment to a specific cell lineage, which may be accomplished by uneven segregation of cellular material during mitosis or with morphogens, which promote development down a specific cell line.
• The umbilical arteries carry deoxygenated blood from the fetus to the placenta, while the umbilical vein carries oxygenated blood from the placenta back to the fetus.
• Senescence is the result of multiple molecular and metabolic processes, most notably, the shortening of telomeres during cell division.
• Nutrient, gas, and waste exchange occurs at the placenta, with oxygen and carbon dioxide being passively exchanged due to concentration gradients.
• Regenerative capacity is the ability of an organism to regrow certain parts of the body.
• The placenta secretes estrogen, progesterone, and human chorionic gonadotropin (hCG).
• The liver has high regenerative capacity, while the heart has low regenerative capacity.
• Paracrine signals act on local cells.