Foundations Practical - Week 1 and 2

From Embryology

Foundations Practical: Introduction | Week 1 and 2 | Week 3 and 4 | Week 1 to 8 | Week 9 to 36 | Neonatal | Critical Periods | Additional Resources | Quiz

Fertilization and Blastocyst Development

The menstrual cycle dictates timing of fertilization and implantation and therefore when life can begin.

Development starts before fertilization with the release of the egg (oocyte) from the ovary (ovulation). This process along with preparation of the uterus for implantation is an endocrine controlled cycle, the menstrual cycle.

This first page will give a brief overview of: menstrual cycle, fertilization, blastocyst and implantation. You are not expected to know everything about these processes, just keep track of the relative "timings" as to when specific processes occur.


<html5media height="400" width="500">File:Follicle_001.mp4</html5media>

Click Here to play on mobile device

This animation shows the ovarian follicle released at ovulation (Graafian follicle) developing within the ovary.

Follicle 001 icon.jpg
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Bovine uterine tube oocyte transport 1.jpg
 ‎‎Oocyte Transport
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Menstrual Facts

Menstrual cycle.png

  • The average menstrual cycle is 28 days with ovulation (egg release) occuring approximately the middle of the cycle.
  • The last menstrual period is used clinically in determining developmental ages.
  • Menstruation phase (period) is the loss of the uterus epithelial functional layer and occurs if fertilization and implantation has not occurred before the end of the current cycle.

Fertility Window

Menstrual cycle fertility probability 01.jpg

Probability of women with regular or irregular cycles being in their fertile window

Clinical guidelines have typically identified the "fertile window" between days 10 and 17 within the typical 28 day menstrual cycle.

Data from a large USA NIEHS (1982-86) identified the timing of the “fertile window” within a range of different menstrual cycles.

  • fertile window occurred during a broad range of days in the menstrual cycle.
  • between days 6 and 21 women had at minimum a 10% probability of being in their fertile window.
  • women cannot predict a sporadic late ovulation; 4 - 6% of women whose cycles had not yet resumed were potentially fertile in the fifth week of their cycle.
  • in about 30% of women is the fertile window entirely within the days of the menstrual cycle identified by clinical guidelines (between days 10 and 17)
  • women should be advised that the timing of their fertile window can be highly unpredictable, even if their cycles are usually regular.


Mouse-fertilization 01.jpg Early zygote.jpg
Mouse oocyte fertilisation Early human zygote
Human fertilization 1 icon.jpg
 ‎‎Fertilisation to
4 Blastomere
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Human fertilization 2 icon.jpg
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Week 1 and 2

Week1 summary.jpg

Week 1 Movies

Follicle 001 icon.jpg
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Fertilization 002 icon.jpg
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Pronuclear fusion 001 icon.jpg
 ‎‎Pronuclear Fusion
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Week1 001 icon.jpg
 ‎‎Week 1
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Spermatozoa motility icon 01.jpg
 ‎‎Spermatozoa Motility
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Fertilization 001 icon.jpg
 ‎‎Mouse Fertilisation
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Bovine uterine tube oocyte transport 1.jpg
 ‎‎Oocyte Transport
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 ‎‎Day 3 to 6
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Pregnancy Test

Pregnancy test.gif

Pregnancy Test

Ovary and Corpus Luteum Anatomy Ovary and Corpus Luteum Histology
Human ovary - corpus luteum 11.jpg Ovary corpus luteum.jpg

Additional Information

Mark Hill.jpg
Where I use the sub-heading "Additional Information" in class materials, it is just that, not part of the class but useful in helping your understanding of the class concepts. I generally include the disclaimer shown below on the class page.

Additional Information - Content shown under this heading is not part of the material covered in this class. It is provided for those students who would like to know about some concepts or current research in topics related to the current class page.

Take the Quiz

Open the table below, select your answers, click submit, then reopen the table to see your result.

Quiz - Week 1 and 2  


1 Which of the following statements is most correct about the human menstrual cycle.

The menstrual cycle in all women is a 28 day reproductive cycle
Ovulation always occurs at the midpoint of the menstrual cycle
The menstrual cycle's main function is to regularly replace the lining of the uterus
A high body temperature indicates ovulation is occurring
The menstrual cycle is an endocrine cycle regulating reproductive physiological changes

2 Pregnancies can be detected by a pregnancy test 1 to 2 days after fertilization.


3 Which of the following statements is correct about the zona pellucida:

surrounds the oocyte in the ovary
protects oocyte in the uterine tube
is a specialized extracellular matrix
is important for fertilization
all of the above

4 Pregnancy urine tests can be based upon the detection in maternal urine of:

human Chorionic Somatommotropin
human Chorionic Gonadotrophin
human Chorionic Corticotropin

Gamete Formation

Oogenesis and Spermatogenesis are the processes of haploid gamete formation by meiosis. If you have some time in the Lab also have a look at these topics and the gonad structure. These topics will be revisited in detail in BGDA.

Movement in the Uterine Tube

<html5media height="280" width="600">File:Mouse trachea 01.mp4</html5media>
The oocyte, zygote, morula, blastocyst floats in uterine secretions and is moved by the ciliated epithelium, similar to the mechanism seen in the movement of mucus by the trachea ciliated epithelium.
Mouse trachea 01-icon.jpg
 ‎‎Trachea cilia
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Note - linked terms in the list below are external resources to the current class content.

  • azoospermia - (ICD-11 GB04.0) Any condition of the genital system affecting males, caused by obstruction of the reproductive tract, abnormal hormone levels, testicular failure, or inadequate production of spermatozoa. Characterized by the absence of a measurable level of sperm cells in semen, and very low levels of fertility. Confirmation is by the absence of spermatozoa in the sediment of a centrifuged sample of ejaculate.
  • blastocyst - (Greek, blastos = sprout + cystos = cavity) Term used to describe the hollow cellular mass taht forms in early development. In humans, this stage occurs in the first and second weeks after the zygote forms a solid cellular mass (morula stage) and before implantation. The blastocyst consists of cells forming an outer trophoblast layer, an inner cell mass (embryoblast) and a fluid-filled cavity. The blastocyst inner cell mass is the source of true embryonic stem cells capable of forming all cell types within the embryo.
  • cervix - (Latin, cervix = neck) The female anatomical region of the uterus forming a canal that opens and connects to the vagina.
  • conceptus - The entire product of conception, that is all the structures derived from the zygote and includes not only the embryo, but also the placental and membrane components.
  • fundus - top part of the uterus body formed by the region lying between the two uterine tubes. A common implantation site.
  • gonad - (Greek, gonos = seed) A gamete-producing (germ cell) organ. A non-sexual term which is used to describe both the female ovary and male testis.
  • hCG - An acronym for the hormone human Chorionic Gonadotrophin.
  • human Chorionic Gonadotrophin - (hCG) Placental hormone initially secreted by cells (syncitiotrophoblasts) from the implanting conceptus during week two, supporting the ovarian corpus luteum, which in turn supports the endometrial lining and therefore maintains pregnancy. Hormone can be detected in maternal blood and urine and is the basis of many pregnancy tests. Hormone also stimulates the onset of fetal gonadal steroidogenesis, high levels are teratogenic to fetal gonadal tissues.
  • implantation - The term used to describe process of attachment and invasion of the uterus endometrium by the blastocyst (conceptus). Abnormal implantation is where this process does not occur in the body of the uterus (ectopic) or where the placenta forms incorrectly.
  • pronuclei - The male spermatozoa and female oocyte haploid nuclei located in the early zygote before they fuse to form the diploid nucleus.
  • uterus - The female internal genital (reproductive) tract forming a hollow muscular walled organ, embryonically derived from the paramesonephric ducts. The human uterus has two uterine tubes or horns (fallopian tubes) where the first week of development occurs and a single hollow body where implantation of the blastocyst normally occurs. Following puberty, the non-pregnant uterus (epithelium and underlying stroma) undergoes cyclic changes under the influence of hormones, the menstrual cycle. This cycle of uterine changes ceases during pregnancy and it contributes the maternal component of the placenta.


Foundations Practical: Introduction | Week 1 and 2 | Week 3 and 4 | Week 1 to 8 | Week 9 to 36 | Neonatal | Critical Periods | Additional Resources | Quiz

Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers

Cite this page: Hill, M.A. (2024, April 22) Embryology Foundations Practical - Week 1 and 2. Retrieved from

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G