UNSW Embryology

Embryology for K12 Students

© Dr Mark Hill (2008)

Acknowledgements

Week 1

The first week of human development begins with fertilization of the egg by sperm forming the zygote.

Zygote with 2 pronuclei
Dr S. J. DiMarzo

The zygote is the first cell of the new embryo containing a new combination of genes from mother and father. The zygote is a large single cell still floating free inside the uterus, it then begins to divide 2, 4, 8, 32, 64, 128 cells and so on. This cell division occurs initially without growth, so each division results in more smaller and smaller cells.

This process of fertilization occurs in all animals and plants that have a male and female. (Plants cannot move, how do they fertilize their eggs?)

More? Year 7-12 Detailed Embryology Notes- week 1

Cells in the embryo have different names from those in the adult.

This is because they are special cells that only occur in the embryo, they divide and gradually change into different types of cells with new names.

Next

   Click here to Go to Week 2 Lets see what happens to this ball of cells.

Facts

• This process of fertilization occurs in all animals and plants that have a male and female.
• A fertilized egg does not mean it will go on to form an embryo. Many fertilized eggs do not develop into embryos.
• In humans, usually only 1 egg is released at a time each month.
• A women will release between 300-400 eggs during their adult life.
• In cats, dogs and other animals several eggs can be released at once. This is one reason why these animals have many babies at once.

Words Used

• egg- the cell from the mother that contributes half the genes of the embryo.
• fertilization- A process where a single male (father) and female (mother) cell are joined together.
• genes- information in the cell that gives it rules on how to grow and what type of cell to become. This information is stored in DNA in the cell nucleus. (more? see Advanced note)
• sperm- the cell from the father that contributes half the genes of the embryo.
• uterus- the space within the mother where the embryo grows. It also grows when the embryo does and has lots of blood to feed the embryo and strong muscles in its walls for childbirth.
• zygote- The first cell formed after fertilization.

Advanced note - a few genes are also located in each cell outside the nucleus, in mitochondria (mitochondrial DNA) which are involved in cellular respiration. These mitochondrial genes are always inherited from your mother (the egg) not your father (sperm).

Quick Movie Links

Movie of Human Embryo Growth (this shows a human embryo growing, all images are to scale)

Movie of Limb Growth(this shows development of the human arm from bud to paddle, to hand with arm)

Movie of Mouse Embryo Growth (this shows a mouse embryo growing)

Movie of Rotating Embryo(this shows an early embryo from all angles)

All Moviesthis shows many different ways of looking in at changes in different embryos.

Quick Links

Week 1 | Week 2 | Week 3 | Week 4 | Week 5 to 8 | Week 9 to 12 | Week 13 to 15 | Week 16 to 20 |

Development Notes ----------------- Menstrual Cycle Week 1 Week 2 Week 3 Week 4 Placenta Serial Images Genes/DNA Molecular Dev Abnormal Dev Postnatal Dev Notes Index

System Notes ----------------- Heart/Cardiovascular Respiratory Coelomic cavity Gastrointestinal Tract Head and Neck Neural Neural Crest Eye Ear Nose Endocrine Urogenital Musculoskeletal Integumentary

Movies ----------------- Embryo Growth Ultrasound Week 1 Week 2 Week 3 Week 4 Stage 13/14 Stage 22 Neural Head and Neck Heart Vasculature Gastrointestinal Urogenital Other Embryos Larsen Internet

Other Embryos ----------------- Chicken Fly Frog Mouse Rabbit Rat Worm Zebrafish Guinea Pig

UNSW Embryology ISBN: 978 0 7334 2609 4

UNSW CRICOS Provider Code No. 00098G