Embryology Review KEY

  1. Define embryology: Branch of biology that studies the formation and early development of living things.
  1. There are four main processes to early embryonic development. Finish the statement about each process.

(a)Fertilization: This is the process when the __EGG___ and the sperm come together to form a _ZYGOTE_.

(b)Implantation: This is the process when the blastocyst implants into the wall of the ____UTERUS_. This implantation ensures that the baby will have a home for the next 9 months.

(c)Gastrulation: This is the process where the blastocyst folds in to become a ball of cells with __3___ layers. These layers are known as the germ layers.

(d)Cell differentiation: This is the process when the cells of the three germ layers are given specific ___JOBS/FUNCTIONS___. In other words, this is the time when stem cells become different from each other. They become nerve cells, blood cells, muscle cells, etc.

  1. When an embryo is going through the 4 processes from number 2, it takes on different shapes and looks along the way. For each of the following stages of an embryo, explain its structure and draw a picture of it.

(a)Zygote: Single Cell- Diploid

(b)Morula:Solid ball of cells (day 3)

(c)Blastocyst:Hollow ball of cells (day 5)

(d)Gastrula:Three distinct layers (after implantation)

  1. Gastrulation: Below is an image of a gastrula. For each arrow, state the name of the germ layer (endoderm, mesoderm, and ectoderm) and state the types of cells that that layer will become.
  1. Extraembryonic membranes are membranes around the growing embryo that do not become a part of the baby, but instead help to nourish and protect baby during development. Complete the statements about each extraembryonic membrane.

(a)Amnion: This membrane forms the ______Amniotic Sac______, which is a fluid filled sac that _____Cushions and protects_____ the embryo.

(b)Chorion: This is the outer-most membrane that combines with the uterine lining to for the _____Placenta______.

  1. What is the placenta?

Site of nutrient, waste, and gas exchange.

  1. What is in vitro fertilization (IVF)?

When fertilization happens outside of the organism. Once the embryo reaches the blastocyst stage it will be placed in the uterus with hopes of implantation.

  1. What are stem cells?

Unspecialized or undifferentiated cells that can give rise to various types of cells.

  1. What is the main goal of stem cell research?

To cure/treat diseases

Create a Venn diagram comparing oogenesis to spermatogenesis using the following statements:

Produces 1 viable gamete Involves millions of cells daily

Produces 1 cell per month (cycle) produces 4 viable gametes

Ends at menopause begins at puberty continues till death

Females Males

Fertilization to Implantation

The following pictures trace the development of an embryo from a zygote to a gastrula. Label each stage in the diagram below:

ZygoteMorula Blastula Gastrula

  1. How does the process of cleavage differ from a cell cycling through the normal cell cycle (MITOSIS)?

Cells undergoing cleavage do not grow before they divide. Because of this the cells decrease in size after each division.

  1. What is the difference between the following: morula, blastula, and gastrula?

Morula is a solid ball of cells, a blastula is hollow, and a gastrula has begun differentiation with 3 distinct germ layers.

  1. When and where does implantation take place (be specific)?

Implantation takes place at around day 7. The blastula (DAY 5) implants into the uterus.

Gastrulation

Gastrulation produces a three-layered embryo. Each of the three layers gives rise to particular structures. Label each of the body systems and parts with the germ layer from which they originated.

  1. Bladder
/ Endo- /
  1. Muscles
/ Meso-
  1. Heart
/ Meso- /
  1. Nerves
/ Ecto-
  1. Skin
/ Ecto- /
  1. Esophagus
/ Endo-
  1. Spinal Cord
/ Ecto- /
  1. Lungs
/ Meso-
  1. Nails
/ Ecto- /
  1. Hair
/ Ecto-
  1. Femur
/ Meso- /
  1. L Intestine
/ Endo-

Twinning

Twins are a natural phenomenon. Answer the following question in a complete sentence.

  1. What is the difference between fraternal and identical twins?

Fraternal twins come from 2 embryos while identical twins come from 1 embryo

  1. When identical twins split late in the embryonic development what can occur?

The later they split the more they share – they can share the placenta, amniotic sac, etc.

Conjoined twins