Chapter 3 Embryogenesis and Development Flashcards
Fertilization is
Fertilization is the joining of a sperm and an ovum
- It usually occurs in the ampulla of the fallopian tube.
- 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.
- When the first sperm penetrates it causes a release of calcium ions, which prevents additional sperm from fertilizing the egg and increases the meta-bolic rate of the resulting diploid zygote. This is called the cortical reaction.
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
after fertilization in the fallopian tube, the zygote(unicellular) must travel to the uterus for implantation. as it moves to the uterus for implantation, the zygote undergoes rapid mitotic cell division in a process called: cleavage!
- Cleavage refers to the early divisions of cells in the embryo. These mitotic divisions result 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.
- There are two types of cleavage:
- Indeterminate cleavage results in cells that are capable of becoming any cell in the organism. in fact monozygotic twins have identical genomes because they both originate from indeterminately cleaved cells of the same embryo.
- Determinate cleavage results in cells that are committed to differentiating into a specific cell type. these cells are committed to differentiating inot a certain type of cell.
The morula is a
the morula is a solid mass of cells seen in early development.
Blastulation and Implantation
Blastilation:
- once the morula is formed it undergoes blastulation to form the blastula(blastocyst) which is a hollow ball of cells with fluid-filled inner cavity known as a blastocoel and has two different structures: the trophoblast (which gives rise to the chorion and later the placental structures) and the inner cell mass (which becomes the developing organism).
Implantation:
- The blastula implants in the endometrial lining and forms the placenta. The blastula moves from fallopian tube to the uterus when it implants in the endometium.
- 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 (the allantois is involved in early fluid exchange b/t the embryo and the yolk sac) 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. ector attractor to physical things.
- The mesoderm becomes much of the musculoskeletal, circulatory, and excretory systems. Mesoderm also gives rise to the gonads and the muscular and connective tissue layers of the digestive and respiratory systems, as well as the adrenal cortex. means to how we get around
- 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. endo (internal)
Neurulation, or development of the nervous system, begins after the formation of the
- 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.
- The tip of each neural fold contains neural crest cells, which become the peripheral nervous system (sensory ganglia, autonomic ganglia, adrenal medulla, and Schwann cells), as well as specific cell types in other tissues (calcitonin-producing cells of the thyroid, melanocytes in the skin, and others).
- Remember: NS is dericed from the ectoderm.
Teratogens are
Teratogens are substances that interfere with development, causing defects or even death of the developing embryo. Teratogens include alcohol, certain pre-scription drugs, viruses, bacteria, and environmental chemicals.
Maternal conditions can affect what?
Maternal conditions can affect development, including diabetes (increased fetal size and hypoglycemia after birth) and folic acid deficiency (neural tube defects).
Cell specialization occurs as a result of
determination and differentiation.
- Determination is the commitment to a specific cell lineage, which may be accomplished by uneven segregation of cellular material during mitosis or with morphogens(may cause neighboring cells to follow a particular development pathway), which promote development down a specific cell line. To respond to a specific morphogen, a cell must have competency.
- Differentiation refers to the changes a cell undergoes due to selective transcription to take on characteristics appropriate to its cell line.
*When a cell is derermined, it is committed to a particular cell lineage. when the cell differentiates, it assumes the structure, function, and biochemestry of that cell type.
Stem cells are
Stem cells are cells that are capable of developing into various cell types. They can be classified by potency.
- Totipotent cells are able to differentiate into all cell types, including the three germ layers and placental structures.
- Pluripotent cells are able to differentiate into all three of the germ layers and their derivatives.
- Multipotent cells are able to differentiate only into a specific subset of cell types.
*stem cells are able to differentiate into different cell types. the totipotency of the stem cell determines how many different cell types a stem cell can become. As cells become more differentited, the potency of the cell decreases (from totipotent to pluripotent to multipotent)
___ signals act on cells in the local area.
Cell-cell communication
Paracrine signal
___act on the same cell that released the signal.
• Autocrine signals act on the same cell that released the signal.
Cells communicate through a number of
Cells communicate through a number of different signaling methods. An inducer releases factors to promote the differentiation of a competent responder.
- Autocrine signals act on the same cell that released the signal.
- Paracrine signals act on local cells.
- Juxtacrine signals act through direct stimulation of adjacent cells.
- Endocrine signals act on distant tissues after traveling through the bloodstream.
Cells may need to migrate to
arrive at their correct location.
Inducers are often what?
growth factors, which are peptides that promote differentiation and mitosis in certaint tissues.
Interestingly, induction is not always a one way pathway. To the end, differentiation of the lens then triggers the optic vesicle to form the optic cup, which ultimately becomes the retina. This is known as reciprocal development. Most tissues will be exposed to multiple inducers during the course of develpment.
Apoptosis is
Apoptosis is programmed cell death via the formation of apoptotic blebs that can subsequently be absorbed and digested by other cells. Apoptosis can be used for sculpting certain anatomical structures, such as removing the webbing between digits.
necrosis
which is a process of cell death in which a cell dies as a result of injury. In necrosis, internal substances can be leaked, causing irritation of nearly tissues or even an immune response.
Regenerative capacity is the
ability of an organism to regrow certain parts of the body. The liver has high regenerative capacity, while the heart has low regenerative capacity.
Senescence is the result of
multiple molecular and metabolic processes, most notably, the shortening of telomeres during cell division.
* some cells, including germ cells, fetal cells, and tumor cells, express an enzyme known as telomerase. This enzyme is a reverse transcriptase that is able to synthesize the ends of chromosomes, preventing senescence. *
Germ layer and organ: chart
Ectoderm (germ layer):
Organ: Integument (including the epidermis, hair, nails, and epithelia of the nose, mouth, and anal canal), lens of the eye, nervous system (including adrenal medulla), inner ear
Mesoderm(Germ layer):
Organ: Musculoskeletal system, circulatory system, excretory system, gonads, muscular and connective tissue layers of the digestive and respiratory systems, adrenal cortex
Endoderm (Germ layer):
Organ: Epithelial linings of digestive and respiratory tracts, and parts of the liver, pancreas, thyroid, bladder, and distal urinary and reproductive tracts
ectopic pregnancy
somwetimes the blastula implants itself outside the uterus, a situation known as an ectopic pregnancy.
over 95 % of ectopic pregnancies occur in the fallopian tube. these pregancies are generally not viable because the narrow fallopian tube is not an environment in which an embryo can properly grow. if the embryo does not spontaneously abort, the tube may rupture and a considerable amount of hemorrhaging may result. in fact, a suspected actopic pregnancy is often a surgical emergency.
