Difference between revisions of "Respiratory System - Upper Respiratory Tract"

From Embryology
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* part of foregut development
* part of foregut development
* anatomically the nose, nasal cavity and the pharynx
* anatomically the nose, nasal cavity and the pharynx
* the pharynx forms a major arched cavity within the pharyngeal arches
* the pharynx forms a major arched cavity within the pharyngeal arches
{{Larynx Links}}
{{Larynx Links}}

Revision as of 13:17, 13 February 2014

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A personal message from Dr Mark Hill (May 2020)  
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I have decided to take early retirement in September 2020. During the many years online I have received wonderful feedback from many readers, researchers and students interested in human embryology. I especially thank my research collaborators and contributors to the site. The good news is Embryology will remain online and I will continue my association with UNSW Australia. I look forward to updating and including the many exciting new discoveries in Embryology!


Respiratory system overview (stage 13)

The respiratory system does not carry out its physiological function (of gas exchange) until after birth. The respiratory tract, diaphragm and lungs do form early in embryonic development. In the head/neck region, the pharynx forms a major arched cavity within the phrayngeal arches.

The respiratory tract is divided anatomically into 2 main parts:

  1. upper respiratory tract - consisting of the nose, nasal cavity and the pharynx.
  2. lower respiratory tract - consisting of the larynx, trachea, bronchi and the lungs.

See also related notes on Smell Development and Head Development.

Respiratory Links: respiratory | Science Lecture | Lecture Movie | Med Lecture | Stage 13 | Stage 22 | upper respiratory tract | diaphragm | Histology | Postnatal | respiratory abnormalities | Respiratory Quiz | Respiratory terms | Category:Respiratory
Historic Embryology - Respiratory 
1902 The Nasal Cavities and Olfactory Structures | 1906 Lung | 1912 Upper Respiratory Tract | 1912 Respiratory | 1913 Prenatal and Neonatal Lung | 1914 Phrenic Nerve | 1918 Respiratory images | 1921 Respiratory | 1922 Chick Pulmonary Vessels | 1934 Right Fetal Lung | 1936 Early Human Lung | 1937 Terminal Air Passages | 1938 Human Histology

Some Recent Findings

Human embryo (stage 22) nasal epithelium development.
  • Establishment of smooth muscle and cartilage juxtaposition in the developing mouse upper airways[1] "In the trachea and bronchi of the mouse, airway smooth muscle (SM) and cartilage are localized to complementary domains surrounding the airway epithelium. Proper juxtaposition of these tissues ensures a balance of elasticity and rigidity that is critical for effective air passage. It is unknown how this tissue complementation is established during development. Here we dissect the developmental relationship between these tissues by genetically disrupting SM formation (through Srf inactivation) or cartilage formation (through Sox9 inactivation) and assessing the impact on the remaining lineage. We found that, in the trachea and main bronchi, loss of SM or cartilage resulted in an increase in cell number of the remaining lineage, namely the cartilage or SM, respectively. However, only in the main bronchi, but not in the trachea, did the loss of SM or cartilage lead to a circumferential expansion of the remaining cartilage or SM domain, respectively. In addition to SM defects, cartilage-deficient tracheas displayed epithelial phenotypes, including decreased basal cell number, precocious club cell differentiation, and increased secretoglobin expression. These findings together delineate the mechanisms through which a cell-autonomous disruption of one structural tissue can have widespread consequences on upper airway function."


  • Human Embryology Larson Chapter 9 p229-260
  • The Developing Human: Clinically Oriented Embryology (6th ed.) Moore and Persaud Chapter 12 p271-302
  • Before We Are Born (5th ed.) Moore and Persaud Chapter 13 p255-287
  • Essentials of Human Embryology Larson Chapter 9 p123-146
  • Human Embryology Fitzgerald and Fitzgerald Chapter 19,20 p119-123
  • Anatomy of the Human Body 1918 Henry Gray 1. The Respiratory Apparatus

Nasal Olfactory and Respiratory Epithelium

Olfactory epithelium

Respiratory histology 13.jpg Respiratory histology 14.jpg
Olfactory Epithelium (overview) Olfactory Epithelium (detail)
  • Olfactory cells
  • Sustentacular cells - located mainly in the superficial cell layer of the epithelium (difficult to distinguish from olfactory cells).
  • Basal cells - identified by their location in the epithelium.


  • Cilia are not visible
  • goblet cells are absent from the olfactory epithelium.

Lamina Propria

  • olfactory axon bundles (lightly stained, rounded areas) connected to olfactory cells.
  • Bowman's glands - (small mucous glands, olfactory glands) function to moisturise the epithelium.
Nasal Olfactory Histology: overview image | detail image | Smell Development | Histology | Histology Stains

Respiratory epithelium

Respiratory histology 11.jpg Respiratory histology 12.jpg
Respiratory Epithelium (overview) Respiratory Epithelium (detail)

  • goblet cells
  • ciliated cells
  • basal cells

Lamina propria

  • connective tissue
  • cavernous sinusoids - large spaces (empty or filled with red blood cells)
  • glandular tissue - mucous glands (green) and muco-serous glands (brownish-green)


  • Lamellae and osteocytes in lacunae.
  • Haversian systems are rare or absent.
Nasal Respiratory Histology: overview image | detail image | Histology | Histology Stains
Respiratory Histology: Bronchiole | Alveolar Duct | Alveoli | EM Alveoli septum | Alveoli Elastin | Trachea 1 | Trachea 2 | labeled lung | unlabeled lung | Respiratory Bronchiole | Lung Reticular Fibres | Nasal Inferior Concha | Nasal Respiratory Epithelium | Olfactory Region overview | Olfactory Region Epithelium | Histology Stains

Paranasal Sinuses

frontal sinus

Paranasal sinuses are thought to develop as "pneumatisation" of bone and out-pocketing of the respiratory nasal epithelium. There are 4 paired sinuses, named by their anatomical location, and lined with respiratory epithelium. The sinuses begins to form at 10 weeks (GA) by primary pneumatisation, later in fetal development secondary pneumatisation occurs enlarging the existing spaces. These sinuses continue to enlarge postnatally.

Note that during development, these are amniotic fluid fluid-filled spaces, therefore pneumatisation (USA, pneumatization) is a misnomer as only postnatally fluid loss forms the air-filled (pneumatic) spaces.

A study of fetal cleft lip and palate[2] showed that sphenoid sinus was still present with variability in morphology compared to normal fetus perhaps due to altered shape and size of the adjacent hypertrophic cartilaginous structures.

Computed tomography measurements from a study of 120 adult (age 18-65 years) maxillary and frontal sinuses.[3]

  • mean maxillary sinus volume 15.7±5.3 cm3
  • larger in males than in females.
  • no correlation between the volume of maxillary sinuses with either age or side.
  • mean bone thickness at the canine fossa was 1.1±0.4 mm.

Frontal Sinus

Ethmoid Sinus

A 1997 article[4] based upon study of coronal sections of the heads of 23 human fetuses from 18-mm CR length to 282-mm CR length. The study suggests that the ethmoid sinus forms by: "constriction of the nasal cavity by a pair of turbinal cushions, and evagination from the nasal cavity by proliferation and subsequent disintegration of the nasal epithelium".

Sphenoid Sinus

Sphenoid Sinus

Data quoted in a 1996 article[5] on the sphenoid sinus.

  • 4 month - sphenoid sinuses can be identified.
  • at birth - sinus remains small and is little more than an evagination of the sphenoethmoid recess.
  • year 3 - invasion of the sphenoid bone is more rapid
  • year 7 - sinus has extended posteriorly to the level of the sella turcica.
  • year 12 - sphenoid pneumatization reaches its final form and a size equivalent to the adult
  • adult - further enlargement into the basisphenoid may occur.

Maxillary Sinus

Developmentally, the maxillary sinus originates in the middle meatus and extends into the ethmoid cartilage.

The data below is from a recent microscopical study of 100 human fetuses from the 9th to the 37th week (GA).[6]

  • week 10 - maxillary sinus begins development.
  • week 37 - the anterior-posterior diameter has a mean of 4.36 mm; ossification of the medial wall was absent, and the floor was located below the attachment of the inferior turbinate. Septa and recesses were temporarily observed.
  • maxillary sinus osmium (opening) was located at the anterior third of the ethmoid infundibulum
    • final dimensions were 1.96 mm in length and 0.44 mm in width.
  • mean length between the ostium to the lamina papyracea and nasolacrimal duct was 1 mm.


The animations below allow a comparison of early and late embryonic lung development. Compare the size and relative position of the respiratory structures and their anatomical relationship to the developing gastrointestinal tract.

Stage13-GIT-icon.jpg Early embryo (stage 13)

3 dimensional reconstruction based upon a serial reconstruction from individual Carnegie stage 13 embryo slice images.

Stage22-GIT-icon.jpg Late embryo (stage 22)

3 dimensional reconstruction based upon a serial reconstruction from individual embryo slice images Carnegie stage 22, 27 mm Human embryo, approximate day 56.

Links: Movies


  1. <pubmed>24218621</pubmed>
  2. <pubmed>9431465</pubmed>
  3. <pubmed>21466703</pubmed>
  4. <pubmed>9294654</pubmed>
  5. <pubmed>8958546</pubmed>
  6. <pubmed>22267494</pubmed>


<pubmed>21944636</pubmed> <pubmed>16798587</pubmed> <pubmed>15222948</pubmed>


<pubmed>21147652</pubmed> <pubmed>20966466</pubmed> <pubmed>20490493</pubmed>

Search PubMed

Search Pubmed: Upper Respiratory Tract Development | Upper Respiratory Tract Embryology


  • nasal concha - (turbinate) Within the nasal cavity the narrow, long and curled bone shelf increasing the nasal surface area and partially separating into smaller cavities. (concha = resemble a shell)

Additional Images

Adult upper respiratory tract conducting system

  • part of foregut development
  • anatomically the nose, nasal cavity and the pharynx
  • the pharynx forms a major arched cavity within the pharyngeal arches

Larynx Image Links: All cartilages of the larynx | Epiglottis cartilage | Thyroid cartilage | Cricoid cartilage | Arytenoid cartilage | Larynx ligaments anterior | Larynx ligaments posterior | Larynx sagittal section | Larynx and upper trachea | Larynx entrance | Larynx interior | Larynx muscular attachments | Larynx muscles 1 | Larynx muscles 2 | Larynx muscles 3 | Cartilage Development | Respiratory System Development

External Links

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Glossary Links

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Cite this page: Hill, M.A. (2020, August 8) Embryology Respiratory System - Upper Respiratory Tract. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Respiratory_System_-_Upper_Respiratory_Tract

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© Dr Mark Hill 2020, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G