Anatomy: Chap 3 Embryology
Compaction
At about day 3 after fertilization, the cells of the pre-embryo adhere tightly to each other and increase their surface contact
What are the four major events that occur in the generation of form during development?
Embryogenesis includes: cleavage, gastrulation, organogenesis, and maturation.
Abortion
Termination of pregnancy by premature removal of the embryo or fetus from the uterus. May be spontaneous or induced.
What is the name of the core of cells at one end of the blastocyst that will form the embryo proper?
Embryoblast
Draw a blastocyst and label the different regions of the cells. Which of these cell types is most important in the process of implantation?
Embryoblast (inner cell mass) Blastocyst cavity (blastocoele) Trophoblast (cavity walls) Degenerating zona pellucida (surrounds trophoblast) Endometrium (uterine lining) trophoblast cells, which subdivides into cytotrophoblast and syncytiotrophoblast cells
Describe the differences between the embryonic period and the fetal period.
Embryonic: focus is on rudimentary organ system formation Fetal: growth and and organ complexity is focus
What important event occurs with the formation of the primitive streak?
Gastrulation
What is crossing over, and during what phase of meiosis does it occur?
In Prophase I, homologous strands of chromosomes are paired up. maternal and paternal chromosomes cross over to create genetic diversity.
What are the main functions of the placenta?
Interchange of gases, nutrients, and waste between mother and fetal blood streams. Transmission of maternal antibodies Production of hormones for maintaining and building uterine lining.
A secondary oocyte is arrested in what phase of meiosis?
Metaphase II
List the five regions of the mesoderm, and identify some major body parts derived from each region.
Midline Group: forms notochord (neural tube) Paraxial Mesoderm: found on both sides of the neural tube. Forms somites (axial skeleton, muscles, cartilage, dermis, connective tissue) Intermediate Mesoderm: lateral to the paraxial mesoderm, form urinary system and reproductive system. Lateral Plate Mesoderm: Most lateral layers on both sides of the neural tube remain thin. Become most of the cardiovascular system, lining of the body cavities, thoracic and abdominal body walls and limb connective tissue. Head Mesenchyme: Forms connective tissue and musculature of the face.
What are two ways in which meiosis differs from mitosis?
Mitosis produces two daughter cells identical to the parent, 23 pairs of chromosomes. Meiosis produces four daughter cells that are not identical to the parent or eachother, 23 chromosomes.
Do cells that differ from one another in terms of structure and function contain different genes from one another?
No, but they read different parts of the coding.
Is development simply a process of cell division from zygote to adult?
No, it is a series of progressive changes that accomplishes two major functions: differentiation and reproduction.
What are the three phases of fertilization?
Phase 1: sperm penetrates corona radiata Phase 2: sperm undergoes acrosome reaction and penetrates zona pellucida Phase 3: sperm and oocyte plasma membranes fuse
Summarize the four stages of mitosis
Prophase: Metaphase: Anaphase: Telophase:
Identify three structures that originate from ectoderm.
Skin/nails/hair, nervous system, tooth enamel, sensory organs
Mitosis
Somatic cell division that results in two daughter cells each the same as the parent nucleus, typical of ordinary tissue growth.
How do cells differ in terms of when and how often they are capable of dividing?
Some cells, including nerve/muscle/fat cells, arrest division at the G1 stage. Others, such as liver/RBCs are continuously dividing.
What structures in the embryo are derived from the somites?
Somites (block-like masses) form the axial skeleton, most muscle/cartilage/connective tissue.
What is the name of the stem cells that form mature sperm?
Spermatogonia
Neurulation
The beginning of brain and spinal cord formation through inductive action that transforms a flat layer of ectodermal cells into a hollow nervous system tube.
Describe the implantation of the blastocyst into the uterine wall.
The blastocyst enters the lumen of the uterus and secretes an enzyme that digests a hole in the zona pellucida, allowing the blastocyst to burrow into the inner lining of the uterine wall (endometrium)
Explain why teratogens are especially harmful to the developing organism during the embryonic period. What events occur during this period?
The embryonic period includes organogenesis. Because rudimentary versions of most organs develop during the embryonic phase, and the most damage is done during early development, the most damage overall is sustained during the embryonic stage
Distinguish between the embryonic and fetal periods of development in terms of the kinds of cellular activity occurring in each. Which is more critical to normal development?
The embryonic period includes the 3rd-8th weeks of development. Beginning with 3 primary germ layers, cells rearrange to begin forming specific tissues, organs, and the major features of the external body form. The fetal period extends from week 8 to birth. It is characterized by maturation of tissues and organs and rapid growth of the body. Embryonic. If cells don't differentiate properly, organs, etc won't ever form properly. Toxins cause the most damage in this period.
What is the function of the chorion?
The membrane covering the fetus blends with the functional layer of the endometrium to form the placenta to become the site of exchange between mother and fetus (placenta).
What structure induces the process of neurulation?
The notochord induces the ectoderm to begin forming nervous tissue. The inductive action that transforms a flat layer of ectodermal cells into a hollow nervous system tube is "neurulation"
How is a secondary oocyte different from an ovum?
The secondary oocyte is released from the ovary, pre-fertilization. Once the secondary oocyte is fertilized, it completes meiosis. Two new cells are formed, but the division of cytoplasm is unequal. The cell that receives the bulk of the cytoplasm becomes the ovum, while the other becomes a polar body that degenerates.
Epigenesis
The theory that an individual is developed by successive differentiation of an unstructured egg rather than by a simple enlarging of a preformed entity.
determination vs. differentiation
They are progressive steps, with determination preceding differentiation. The determination of cell types (fates) involves progressive restrictions in their developmental potentials. The fate of determined cells does not change. Differentiation results in the presence of cell types that have clear-cut identities, such as muscle cells, nerve cells, and skin cells.
Nondisjunction
causes an abnormal number of chromosomes in a cell following meiosis.
What structures are formed from endoderm?
epithelial lining of respiratory tract, GI tract, bladder, urethra. Pancreus/thymus/thyroid gland/parathyroid glands/tonsils/gallbladder.
What are some factors or events that can prevent sperm from reaching the secondary oocyte?
leakage, incomplete motility, acid vaginal environment, , getting "lost", going up the wrong uterine tube, immune system response attacking sperm, .
What are somites? Where are they found? What do they become?
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Name the events that occur during the embryogenesis phase of development. What happens to the size of the embryo during cleavage? By the end of the cleavage stage, how many cell types are there?
Cleavage: zygote divides by mitosis to form a multicellular structure (blastocyst) Gastrulation: The blastocyst cells form three primary germ layers, which are the basic cellular structures from which all body tissues develop. Organogenesis: The 3 primary germ layers arrange themselves in ways that give rise to all organs in the body. The overall size of the embryo remains the same. One
What do each of the primary germ cell layers give rise to?
Ectoderm Mesoderm Endoderm: Epithelial layers of digestive tract, respiratory tract, pituitary, tonsils,
Gestation
Period of intrauterine development
What is gastrulation?
Process by which cells of the epiblast migrate and form the 3 primary germ layers, which are the cells from which all body tissues develop. (ectoderm, mesoderm, endoderm)
Trophoblast
The outer layer of the blastocyst that attaches to the wall of the uterus at implantation
Capacitation
a period of conditioning in which a glycoprotein coat and some other proteins are removed from the sperm plasma membrane over the acrosomal region of the sperm
Draw a 3-week old embryo complete with extra-embryonic membranes and describe the functional significance of each. The presence of of these signals the end of the pre-embryonic period:
amniotic cavity (ectodermal side of disc) amnion embryo (3 germ layers) placenta (chorion-syncytiotrophoblast layer, functional layer of uterus) connecting stalk (future umbilicus-pt of chorion, connected to primitive streak side) yolk sac (endoderm side) 3 primary germ layers, formed through gastrulation.
Gastrulation
cells from the ___ layer of the bilaminar germinal disc migrate and form the three primary germ layers.
karyokinesis vs. cytokinesis
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What is meant by the dichotomy of mitotic potential and differentiation? How does this explain the general view that infants have more stem cells than adults? How does this affect our view of tissue regeneration in adults?
*** If adults have few stem cells, they are less able to recreate damaged tissue zones, particularly where the coding has been damaged as in cancer.
Summarize the stages of of the cell cycle. What proportion of a cell's life is spent in mitosis? At what stage of the cycle are cells in when they are performing their specific functions for the body?
***Interphase (G1, S, G2) and Mitosis (prophase, metaphase, anaphase, telophase) It depends on the cell, but the majority of their time is spent in interphase, when they are completing their bodily functions. Interphase
Give an example of replaceable, expanding and irreplaceable cells.
***Replaceable, expanding: RBC, liver, epidermis Irreplaceable: nerve, muscle, lipid cells
What is a stem cell and why are they so important to our ability to develop, maintain healthy tissues, and live long lives?
***Stem cells are undifferentiated, totipotent cells. They have the potential to become any type of cell.
Describe how the embryonic disc undergoes folding in two dimensions to yield the head-to-tail, tube-within-a-tube body form. Can you already distinguish between the somatic and visceral parts of the body?
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Describe the events of organogenesis that lead to the formation of the nerve cord.
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Explain how the cylindrical body shape of the human embryo is derived from the flat embryonic disc.
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List the hierarchy of cell differentiation beginning with the fertilized egg and going all the way to terminally differentiated cells. Are these discrete steps or a continuum?
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The embryonic period begins with gastrulation. What kinds of events occur that lead to the formation of the three primary tissue layers? What makes these 3 layers of cells so special?
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What is meant by the trilaminar embryo?
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What is the principal developmental activity occurring during the fetal period?
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When is the embryo/fetus most susceptible to deformities? Why?
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Congenital Anomaly
A malformation or deformity present at birth
Ectopic Pregnancy
A pregnancy in which the embryo implants outside the uterus; commonly occurs in the uterine tube
What cells in the body undergo mitosis?
All somatic cells undergo mitosis. Reproductive cells undergo meiosis.
Extraembryonic Membranes
Amnion Chorion Yolk sac
Describe the formation of the primary germ layers.
At gastrulation (formation of primitive streak), cells detach from the epiblast layer and migrate through the primitive streak between the epiblast and hypoblast layers (invagination). The layer of cells that forms between the epi- and hypo- blast layers becomes the mesoderm. Other migrating cells displace the hypoblast, forming the endoderm,and the epiblast, forming the ectoderm.
