| Term | Definition |
|---|
| Embryology | The study of the development of a unicellular zygote into a complete multicellular organism. |
| Cleavage | Early development is marked by a series of rapid mitotic divisions. These divisions result in more cells, but without cell growth, the total volume remains the same. |
| Indeterminate Cleavage | When the cells maintain the ability to develop into complete organisms after division. |
| Determinate Cleavage | When cells whose future differentiation pathways are determined early on in development. |
| Differentiation | The specialization of cells that occurs during development. |
| First Cleavage | This occurs approximately 32 hours after fertilization. |
| Second Cleavage | This occurs 60 hours after fertilization. |
| Third Cleavage | This occurs 72 hours after fertilization. |
| Eight | Once the embryo reaches the uterus, it has this many cells. |
| Morula | A solid ball of embryonic cells. |
| Blastulation | Begins when the morula develops a blastocoel. |
| Blastocoel | A fluid-filled cavity in the early embryo. |
| Blastocyst | By the fourth day, the mammalian embryo is called... It contains two cell groups, the inner cell mass and trophoblast. |
| Inner Cell Mass | A clump of cells that protrudes into the blastocoel. |
| Trophoblast | This surrounds the blastocoel and gives rise to the chorion. |
| Endometrium | The site of implantation around five to eight days after fertilization. It undergoes proliferation due to the hormone progesterone. |
| Gastrulation | The process by which the three primary germ layers are formed. (See Pg120) |
| Gastrula | Three layered structure that is formed by gastrulation. |
| Archentron | The cavity that is formed during gastrulation. This later becomes the gut. |
| Blastopore | The opening into Archentron. |
| Deuterostomes | Organisms such as humans where the blastopore becomes the anus. |
| Protostomes | Organisms where the blastopore becomes the mouth. |
| Ectoderm | One of the three primary germ layers, this layer gives rise to the skin, eye lens, hair, nails, etc. |
| Endoderm | One of the three primary germ layers, this layer gives rise to the epithelial lining of the lungs, respiratory tracts, parts of the liver, pancreas, etc. |
| Mesoderm | One of the three primary germ layers, this layer gives rise to the musculoskeletal system, circulatory system, gonads, etc. |
| Selective Transcription | Through this process, cells can be differentiated as the embryo develops. |
| Induction | The process by which cells (organizers) influence other cells to differentiate. |
| Inducers | Induction occurs due to the organizers releasing these chemical substances. |
| Neurulation | After gastrulation, the nervous system begins to develop in a process called...(See Pg122) |
| Notochord | A rod of mesodermal cells, which develop on the longitudinal axis just under the dorsal layer of the ectoderm. |
| Neural Folds | These are the beginning of the neural tube which eventually grow to form the tube. |
| Neural Tube | This gives rise to the brain and spinal chord. |
| Neural Crest Cells | These are found at the tip of the neural folds and micrate laterally to give rise to components of the peripheral nervous system. |
| Fetus | Embryo is referred to as this after eight weeks of gestation. |
| Amnion | A fluid filled membrane which acts as a shock absorber and protects the fetus from harm. It also helps to create pressure during labor. |
| Chorion | A membrane that surrounds the amnion, which later forms the placenta. |
| Chorionic Villi | Two weeks after fertilization, the chorion extends these into the uterine wall. They associate with endometrial cells to form the placenta. |
| Allantois | This develops as an outpocketing of the gut and later joins with the yolk sac and surrounded by the amnion to become the umbilical cord. |
| Umbilical Cord | Connects the fetus to the placenta. |
| Placenta | The site of nutrition, respiration, and waster disposal for the fetus. |
| Fetal Hemoglobin (Hb-F) | Has a greater affinity for oxygen than the adult version so that oxygen flows into the fetal blood. |
| Human Chorionic Gonadotropin (HCG) | This is produced by the placenta and the presence of this in the blood indicates pregnancy. |
| Umbilical Veins | Carry oxygenated blood from placenta to the fetus. |
| Ductus Venosus | Blood is diverted around the liver by a shunt called the... |
| Foramen Ovale | Most blood entering right atrium bypasses pulmonary circuit and enters left atrium directly by the shunt called the... |
| Ductus Arteriosus | Blood that manages to get into the right ventricle, gets pumped into the pulmonary artery, where most of this gets diverted directly to the aorta through the... |
| Umbilical Arteries | Deoxygenated blood is returned to placenta via... |
| Trimesters | The 9 month gestation period is divided into three... (See pg 127) |
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