ToB week10 Andra (T1 Med23)

The pre-embryonic

period and gastrulation

ToB

week 10

Quizz

.7 questions: SBA, MCQ, FITB

.min 30 seconds each => take your time

.PDF of the quiz will be uploaded into today's session (under Files)

​Plan of the quiz

Multiple Choice

(SBA) What is the pre-embryonic stage/phase?

• From Ovulation until Fertilisation

• From Fertilisation until Implantation

• From Fertilisation until Foetus

• From Fertilisation until Gastrulation

What is the pre-embryonic phase?

Is the first and shortest phase of embryonic development.

It lasts from fertilisation to the second week of the embryo's life.

Second week: when a fertilized egg develops into a blastocyst that implants into the uterine lining,

BUT BETTER:

until Gastrulation: is the process by which the bi-laminar embryonic disc is converted into a tri-laminar embryonic disc.

Fill in the Blanks

Zygote: a diploid cell resulting from the fusion of two haploid gametes; a fertilized ovum.

​Begins as a single cel but divides rapidly.

The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism.

Fertilisation vs Conception

In ToB Workbook: The fertilised ovum, now known as the zygote, is transported along the tube to the uterus. This takes about four days.

Websites: Conception and fertilization are two different parts (or steps) of the same process. Conception is the first step, where an egg and sperm join. Fertilization is another step, where the joined sperm and egg plant like a seed into your uterine lining.

Multiple Select

(MCQ) The most important processes that happen on days 13-14 are:

• Embryo converted from bi-laminar to tri-laminar

• Embryo converted from one-layered to three-layered

• Embryo becomes bilaterally symmetical

• Embryo is converted from two-layered to three-layered

​Day 13-14 of the embryonic development

After 14, a thickened band of cells in the embryo known as the "primitive streak" forms.

This streak marks the start of cells rearranging into an early body plan and specialising to eventually form tissues and organs.

Two crucial processes occur around days 13-14 of development. The embryo is converted from a bilaminar (two-layered) to a trilaminar (three-layered) disc. It also becomes bilaterally symmetrical, with well- defined anterior and posterior ends, and a midline. These processes end the pre-embryonic phase. The three germ layers formed give rise to all the structures found in the adult body (a very simplified table appears at the end of this synopsis).

Multiple Choice

(SBA) What percentage of zygotes FAIL to develop to the blastocyst stage?

• 3 %

• 13 %

• 30 %

• 70 %

In general, less than 70% of all fertilized eggs will even implant into the mother's womb causing pregnancy to continue.

From there, there is a 25-50% chance of aborting before you even know you are pregnant.

If, however, you make it to your first month, your odds go up to 75% chance of carrying to term.

Extra: Read more on RationalWiki about Spontaneous abortion in humans

Multiple Select

(MCQ) ECTODERM layer will generate: skin (& derivated) and ........

• Brain

• Connective tissue

• Retina

• Blood vessels

DERIVATIVES OF ECTODERM

• Ectoderm is the outer most layer of trilaminar disc. 

• It give rise to those organs and structures that maintain contact with the outside world.

• During neurulation some of the ectodermal cells form neuroectoderm and the rest form surface ectoderm.

​Ectoderm -

Mesoderm -

Endoderm

​NeuroEctoDerm

Multiple Choice

(SBA) What does term PROLIFERATION refers to?

• Cell movement from one segment to another

• Increase in size of cell (growth)

• Increase in cell numbers

rapid increase in the number or amount of something: cells

Definition of Proliferation

Multiple Choice

(SBA) Is the age of the embryo SAME as the age of the pregnancy? (weeks)

• YES

• NO

• Sometimes

• I do not know

Example:

8 weeks into pregnancy =

6 weeks after fertilisation/conception

​Pregnancy starts counting from the first day of the last period. That means that the female pt won't really be pregnant during the first two official weeks of pregnancy.

Thank you!

Plan for today's group work

10:30 - 11:30 PeerWise MED23 Revision Question Writing = see info in the WorkBook page 83

Course ID for Med23 is 25924 and their username will be their Bucks email address.

AND

1:30 - 13:00 MED23 Histology Atlas