UNSW Embryology

Beginnings, Growth and Development

© Dr Mark Hill (2007)

Acknowledgements

Laboratory Embryology of the Face and Ear

Aim:  To introduce students to the practical embryology of the face and ear.

Human Embryo Face (Carnegie stage 16 to 18, Kyoto collection)

Face Development cartoon (More? on a new page)

Page Links: Introduction | Specific Objectives | Key Reading | Learning Activities | UNSW Embryology Notes | Serial Images | Computer Activities | Questions | Glossary |

Specific Objectives

1. To understand the formation and contribution of the pharyngeal arches to face and neck development.
2. To know the main structures derived from components of the pharyngeal arches (groove, pouch and arch connective tissue).
3. To know the 3 major parts (external, middle and inner) of hearing development and their embryonic origins.
4. To briefly understand some abnormalities associated with face and hearing development.

Key Reading

BGD Lecture: Development of the Face and Ear (17 May 2007)

Human Embryology (3rd ed), WJ. Larsen Chapter 12 Development of the Head, the Neck, the Eyes, and the Ears pp349 - 418.

The Developing Human: Clinically Oriented Embryology (7th ed) Moore & Persaud Chapter Chapter 10 The Pharyngeal Apparatus pp201 - 240; Chapter 19 The Eye and Ear pp465 - 483.

Learning Activities

In preparation for this class, revise the information from the GIT development practical related to the foregut. The following internal and external linked materials will be worked through in today's class. Note that there are currently no back links from the pages listed below, you will need to return to the current page to work through each section.

1. Begin

by looking at the stages in development of the external appearance of the head from week 3.

Week 3

In the third week, gastrulation establishes the 3 germ cell layers, endoderm, mesodern and ectoderm. All 3 layers will later contribute specific components to development of the face and ear.

Also present from these early weeks is the buccopharyngeal membrane or oral membrane. The membrane forms in the midline towards the cranial end of of the trilaminar embryo. Initially as a small circular region during gastrulation where ectoderm and endoderm associate closely together, without mesoderm between the layers (like the cloacal membrane at the other end of the disc).

Human Embryonic Disc (stage 7, 15 - 17 days)

The primitive streak extends from the primitive node towards the connecting stalk end of the disc. The primitive node (Hensen's node) is also the beginning of an axial process that extends in the opposite direction within the mesoderm layer. The axial process can extend cranially only as far as the buccopharyngeal membrane an differentiates to form then notochord. The notochord regulates development, both differentiation and folding, in the surrounding tissues. The regulation is initially physical, as a dense column of cells (folding) and then by secretion of developmental factors (differentiation) that pattern the surrounding ectoderm, mesoderm and endoderm.

Human Embryo (stage 11, Week 4, 23 - 26 days)

The following processes are occuring simultaneously around the developing pharyngeal arches: 1. rapid growth of the brainfold above, 2. rapidly growing heart below, 3. migration of neural crest into the arches, 4. development of arteries within the arch mesenchyme.

Now look through the embryonic stages that follow from week 4 onward.

2. Then

look at the specific notes and images on face and ear development. These notes give both an overview of development and cross-sectional images at specific times.

Face: Head | Embryo Images - Head | Stage 13/14 | Stage 22 | Face | Tongue

Hearing: Hearing | Embryo Images - Hearing | Stage 13/14 | Stage 22 | Stage 22 selected

Pharyngeal Arch Cartilages

3. Finally

look at the abnormalities associated with face and ear development.

Face and Hearing Abnormalities: Head | Face | Hearing | Critical Periods of Development

Unilateral cleft lip and palate	Bilateral cleft lip and palate	Cleft palate

Postscript

The above materials will more than occupy your 2 hours in the practical class, though it will be obvious by the end that there are other developmental systems that relate to the face and ear. These will not be covered in today's class, but I have included these links for you to follow for further information: Senses Development | Eye Development | Cardiovascular - Ventricles into the Aortic System | Musculoskeletal Development - Skull Development | Endocrine Development - Pituitary | Endocrine Development - Thyroid | Abnormal Development - Fetal Alcohol Syndrome

Background (2005)

• First obtain an overview of the external features of the developing head, face, and external ear by studying the Carnegie stages of human embryos in the Background at http://embryology.med.unsw.edu.au/Medicine/BGDlab4_1.htm
• Then work though the development of the pharyngeal folds, face, and ear from Carnegie Stage 10 through to Carnegie Stage 23 using the links to Practical Class 4 and Practical Class 11 in the left-hand pane.  BGD Cycle A (2004) Lecture 6 by Dr. Mark Hill also provides important information for this exercise
• Note the intact mouth membrane (buccopharyngeal membrane) is seen in the longitudinal section of the Carnegie Stage 11 embryo (under ‘Folding’).
• Using the Serial Images link at http://embryology.med.unsw.edu.au/ study ear development under Organs of Senses in the two panels for Stage 13/14 Embryo (Pig) Systems and Stage 22 Embryo (Human) Systems.  These images are taken from sections through the head of the embryos and sometimes it is difficult to visual the whole section when looking at a part of it.  In order to orientate yourself to the whole section, you may find it easier to study the features of ear development in the individual sections (listed below).

UNSW Embryology Notes

The following are links to the first page of more detailed UNSW Embryology Notes on material covered in this laboratory. In each notes section: the first page introduces the topic, page two covers abnormalities, page three is the stage 13 embryo slices, page 4 is the stage 22 embryo slices and there are additional specific pages on related topics listed in the lefthand side menu of each notes section.

Head Notes | Face Notes | Ear Notes

Serial Images

Stage 13/14 Embryo (6 mm pig)

A1: Thin caudolateral walls of rhombencephalon.

A2: Otocyst (R).  Apex of otocyst (anlage of L endolymphatic sac)

A3: Otocyst; surrounding mesenchyme = otic capsule.  Note proximity of otocyst to wall of rhombencephalon.   Superior glossopharyngeal ganglion.  Vestibulo-cochlear-facial ganglion complex (R).  Trigeminal ganglion.

A4: Indentation in rostral margin of otocyst = anlage of utriculosaccular canal.  Note alignment of superior cardinal vein (LS) in relation to the nerve trunks (XS).  Trigeminal ganglion.  Dorsal end of 1st pharyngeal arch and groove.  Note variation in height of cells of L otocyst wall.

A5: Facial ganglion (R).  “Floor” of L otocyst. Note on R, the former position of the otocyst in relation to the 2nd pharyngeal arch.

A6: 1st, 2nd arches, grooves and pouches on R.  Inferior glossopharyngeal and facial ganglia on L.

Stage 22 Embryo (27 mm human)

B3: Rhombic lip (developing cerebellum).  IV ventricle.  Trigeminal ganglion.  Adenohypophysis. Sphenoid cartilage.

B4:  Cochlear duct and temporal cartilage.  Semicircular duct (ampulla on L).  precartilage of auricle (pinna).  Malleus (medial, L).  Incus (lateral, L).

B5: External auditory meatus.  Auricle.  Incus (dorsal).  Malleus (ventral).  Tubotympanic recess (auditory rube).  Tensor tympani m. (L).  Utricle.  Semicircular ducts.  Internal auditory meatus (R), containing vestibular and spiral ganglia.  Endolymphatic sac (L).  Note proximity of sac to choroid plexus of 4th ventricle.

B6: External auditory meatus.  Anlage of tympanic membrane (L).  Manubrium of malleus (L).  Basal turn of cochlea duct (L).  Endolymphatic sac (R).  Common crus (R).  Junction of utricle and saccule (R).  Meckel’s cartilage.  Stapes (R).  Auditory tube.

Stage 22 Embryo (27 mm human) High Power Images

B3, B5: Cochlear duct.  Spiral ganglion.  Tubotympanic recess (auditory tube).  Internal carotid artery.  Malleus and incus.  Meckel’s cartilage.  Tensor tympani muscle.  Crista ampullaris of a semicircular duct.  Semicircular duct.  Utricle with macula.  Saccule (cut tangentially) adjacent to utricle.  Otic capsule.

B6: Turns of cochlea duct.  Note changes in height of the wedge-shaped epithelial cells at different sites in wall of cochlear duct; the region of tallest cells is the anlage of organ of Corti and the clear luminal cytoplasm is the anlage of the tectorial membrane; the thickening on the outer wall of the cochlear duct is the anlage of the stria vascularis; the thinnest part of the wall is the anlage of the vestibular membrane.  Spiral ganglion in modiolus.  Vestibular ganglion (collectively VIII cranial nerve ganglion - both parts composed of bipolar neurones).  Saccule.  Cartilage of future temporal bone.  Internal auditory meatus.

Computer Activities

Embryo Images Unit: Embryo Images Online | Craniofacial Development | Cell Populations | Pharyngeal Arches | Nose and Upper Lip

Human Embryology Movies: Development of the Face (451Kb) | Development of the Tongue

Other Head and Neck Lectures: The following are links to provide background from earlier lecture materials from other courses: ANAT2300 Vertebrate Development- Head Development | ANAM1006 Head Development | ANAT1006 Medicine 2002- Head Development

Questions

These questions will not be specifically answered in this laboratory (so don't ask the Tutor) and are designed to make you think more about the topic.

1. Which of the pharyngeal arches contribute mainly to the face and which contribute mainly to the neck?
2. Which of the lips has the most common clefting during development and why?
3. Which is the more common clefting, cleft lip or cleft palate?
4. What developmental environmental factors may contribute to abnormalities of both the face and ear position?
5. What is the Eustachian tube and what is its function?
6. What are preauricular tags and what may they indicate?
7. At what age is hearing tested with Australian children?
8. What is otitis media and how does it occur?

Next

Link to next page in this Face Practical - Face Primordium

This provides a brief coverage of the early development of the pharyngeal Arches.

Glossary of Terms

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

UNSW Embryology ISBN: 978 0 7334 2436 6

UNSW CRICOS Provider Code No. 00098G