UNSW Embryology

Embryology for K12 Students

© Dr Mark Hill (2008)

Acknowledgements

Week 5 to 8

Introduction

In the fifth to eigth (5-8) week of embryo development, organs begin to form within the embryo. This period covers approximately the last stages of major embryonic development growth (Carnegie stages), after this time the embryo is described as a fetus.

Start by comparing at the outside (external) changes in what the embryo looks like from week 5 to week 8 in the pictures below. What new things can you see over this period?

Even though from the outside the embryo now looks very developed, if we were to look inside the embryo's head for a brain, we would find only a very thin layer of cells surrounding a large fluid-filled space. (almost like a water-filled balloon).

Then have a look at living embryos in the ultrasound movies below. The first 2 movies are at 7 weeks (the first a single embryo, the second twins). The next movie is one week later (week 8) where the limb buds and spine can now be clearly seen. At this early stage ultrasound shows the beating heart is the most obvious feature within the embryo. Ther is also another page covering this period looking at development of the arms and legs.

 

Embryo at 8 weeks

(Carnegie stage 23)

Facts

• ultrasound uses a beam of sound waves (frequency 3 to 10 MHz) reflecting back off diffferent structures and analysed by a computer this can then be shown as a picture on a screen.

(More? Year 7 -12 Detailed Embryology Notes - limb development)

Human Embryo development during week 5 to week 8

click the small picture to see a big picture.

Stage 15 (week 5)

Stage 16 (week 6)

Stage 18 (week 7)

Stage 19

Stage 20

Stage 21

Stage 22

Stage 23 (week 8)

Ultrasound

Movie of 7 week embryo ultrasound showing the head, heart and placental attachment.

Movie of 7 week twin embryos ultrasound showing the head, heart and placental attachment.

Movie of 8 week embryo ultrasound showing the limb buds, heart beating and spine.

Quicktime movie 1.3 Mb

Quicktime movie 1 Mb

Quicktime movie 1.8 Mb

Ultrasound uses a beam of sound waves (frequency 3 to 10 MHz) reflecting back off diffferent structures and analysed by a computer this can then be shown as a picture on a screen.

Inside the Embryo's Head

These are a series of slices through the embryo head showing areas where brain (dark red areas) is beginning to form. Notice that at this stage most of the brain is a thin layer of cells surrounding large liquid-filled space.

You can also look at a movie of the head being cut in slices from the top down to the neck.

Words Used

• brain- the thing inside your head that allows you to think, talk, see, hear and move. Even though it appears in the embryo very early, it is not fully made until many years after you are born. It is protected by the skull (not yet there).
• bone- the skeleton of the body. This gives your body a shape so that you are not a blob lying on the ground.
• embryo- the name given to the baby during the early time of growth.
• heart- the thing in your chest that pumps blood around your body.
• limb buds- these are the early arms and legs of the embryo. At this time they look like paddles either side ou the embryo.
• liver- this is below the heart and has an important role in blood and later for digesting food. It is an organ that works as part of the digestive system (stomach....) and part of the blood system (heart, blood vessels...).
• muscle- part of the body that moves the skeleton and allows you to stand up.
• organ- this is a name given to the different parts of our body. It saves you writing a long list: brain, spinal cord, heart, liver, eye, ear, nose.........
• placenta- all mammals provide support for the embryo growth through the placenta. It connects the embryo with the mother. It carries food and oxygen to the embryo and takes waste and carbon dioxide from the embryo.
• special sensory- parts of the eye ear and nose.
• spinal cord- part of the brain like a long rope running down your back. The spinal cord does what the brain tells it and allows you to move your muscles. The spinal cord is also the way you can to feel things with your skin (touch, hot, cold). It acts like a telephone cable passing messages from the brain to the body and from the body to the brain. If the spinal cord is damaged you cannot move your body.
• 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.

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