Foundations Practical - Week 1 to 8

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

The Embryonic Period

Development of Organs and Tissues

You have now been through the earliest stages of embryonic development. From the original simple trilaminar embryo all the organs and tissues will now begin to develop, details of these processes require more time than we currently have available. What we will now look at are the changes in the external embryo appearance during this period.

Historically the embryonic period was also divided into 23 stages (I do not expect students to identify embryo stages).

Week:	1	2	3	4	5	6	7	8
Carnegie stage:	1 2 3 4	5 6	7 8 9	10 11 12 13	14 15	16 17	18 19	20 21 22 23

Key features to note are:

• changes in overall size (CRL)
• surface bulges that reflect organ development
• development of the upper and lower limbs
• development of the head

This page is about getting an overview of the external changes that occur during the embryonic period. In order to observe and understand the internal changes occuring in organ development is beyond the scope of this current practical.

Changes in Overall Size

In the first 8 weeks the embryo grows from 0.1 mm to about 3 cm in length.

Actual Size

Enlarged Size

During this time the embryo size is also measured from "crown" to "rump" or the Crown Rump Length (CRL).

Surface Bulges Reflect Organ Development

Surface of the Stage 13 Embryo showing surface features reflecting surface and internal development. Carnegie stage 13

Week 8 - End of Embryonic Period
				‎‎Embryo Surface Page | Play	‎‎Embryo CNS Page | Play

Placentation

During this period the parts of the conceptus not contributing to the embryo will contribute the fetal component of the placenta and the embryonic/fetal membranes.

This topic will also be covered in detail in BGD.

Timeline Overview

‎‎Human Timeline

Page | Play

Terms

• Bulge - A non-technical term describing a protruding part or an outward curve or swelling.
• CRL - Acronym for Crown Rump Length, a staging measurement of embryo and fetal size.
• Crown Rump Length - (CRL) A staging measurement of embryo and fetal size. Measures length from the top curvature (crown) to bottom curvature (rump) in mm. (More? Crown Rump Length)
• Gestational Age - GA Clinical age from first day of the last menstrual period (LMP) about 2 weeks before fertilization occurs. Gestational Age, not Fertilization Age is generally used clinically.
• Organ - A collection of tissues joined in a structural unit to serve a common function.
• Stage - Carnegie stage, a historic staging system for human embryonic period from fertilization, between week 1 to 8 (GA 3-10) of development. (More? Carnegie Stages)
• Tissue - A group of cells that perform a similar function.

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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

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Cite this page: Hill, M.A. (2024, April 19) Embryology Foundations Practical - Week 1 to 8. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Foundations_Practical_-_Week_1_to_8

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