(LESSON 2) Chapter 3-Embryology Flashcards
Embryology
The study of the origin and development of an individual person.
Prenatal Period
Before Birth. Time from conception to birth. Divided into two stages: Embryonic Period (8 weeks) and Fetal Period (30 weeks).
Oocyte (pg 52)
The egg a woman’s ovary releases each month.
Conception
When a sperm fertilizes an oocyte.
Zygote
The fertilized Oocyte. Moves toward the uterus as it begins to divide repeatedly. 2,4,8…
Blastomeres
The daughter cells of the dividing Zygote.
Cleavage
the early division sequence of the the zygote/blastomeres, providing the large number of cells needed as building blocks for the embryo.
Morula
the cluster of 12-16 blastomeres created approx. 72 hours after fertilization. Still multiplying. At day 4, consisting of about 60 cells, the morula enters the uterus.
Blastocyst
Upon entering the uterus, the structure begins to take up fluid that gathers into a central cavity. Two cell types form. This stage lasts about 3 days-Days 4-7.
Inner cell mass
cluster of cells on one side of the blastocyst cavity. Will form embryo.
Trophoblast
Layer of cells surrounding blastocyst cavity. Will help form the placenta.
Placenta
Structure that transfers nutrients from the mother to the fetus.
Implantation
From day 4 to day 6 the blastocyst is floating freely about the uterus. On day 6 blastocyst begins burrowing into the wall of the uterus. Trophoblast layer begins to erode inward until the entire blastocyst is embedded in the uterine wall. Takes about a week.
Monozygotic Twins (Identical)
From one zygote. When the inner cell mass of a single blastocyst splits into 2 during early stages of cleavage.
Inner cell mass division (pg 53)
Day 9 the inner cell mass divides into 2 sheets of cells. The epiblast and the hypoblast. Extensions of both sheets form fluid filled sacs with epiblast and hypoblast being point of contact.
Bilaminar embryonic disc
together the hypoblast and epiblast make this up..which will give rise to the whole body.
Amniotic Sac
Extension of the epiblast. Outer membrane is called the amnion and the cavity is filled with amniotic fluid which acts as a buffer until birth. (“water just broke” is the rupture of the amniotic sac and release of amniotic fluid near the start of labor)
Yolk Sac
Extension of the hypoblast. Hold very small amount of yolk. Forms part of digestive tube.. Tissue around sac give rise to earliest blood cells and vessels.
Gastrulation
During week 3 the embryo grows from a two layered disc to a three layered disc. Forms three primary germ layers: ectoderm, mesoderm, and endoderm-the layers from which all body tissues develop.
Primitive Streak
On day 14-15, this raised groove appears on the dorsal surface of the epiblast. Epiblast cells migrate inward at this streak.
Endoderm
The first cells that migrate through the primitive streak displace the cells of the underlying hypoblast to become the endoderm. Day 14-15.
Mesoderm
The cells following the endoderm cells through the primitive streak form a new layer between the epiblast and endoderm. Day 16
Ectoderm
The remaining epiblast cells on the embryo’s dorsal surface make this form. All three layers derived from epiblast cells.
Epithelial Tissue
Epithelia. Sheets of tightly joined cells. Endoderm, Ectoderm.
mesenchyme tissue
mesen=middle, chyme=fluid. Cells do not attach to one another but are free to migrate within the embryo. Mesoderm.