Embryology - Branchial arches and pouches Flashcards
(114 cards)
1
Q
How are the branchial arches formed?
A
Mesodermal condensations develop in the side walls of the primitive pharynx.
2
Q
How do the branchial arches grow?
A
Around towards each other ventrally and they fuse in the midline.
3
Q
What happens when the branchial arches fuse in the midline?
A
Horse-shoe shaped arches (pharyngeal arches) will come and support the pharynx.
4
Q
What is the most cranial arch?
A
Mandibular arch.
5
Q
What does the mandibular arch do?
A
Separate the mouth pit from the pericardium.
6
Q
What happens when the mandibular arch moves caudally?
A
There is differential growth in the neck which causes the floor of the pharynx to elongate and there will now be 6 branchial arches.
7
Q
What are arches?
A
These are the outside that are covered in ectoderm.
8
Q
What is a cleft?
A
It is the space in between the pharyngeal arches that’s made with ectoderm.
9
Q
What is a pharyngeal pouch?
A
It is the inside that is covered in endoderm.
10
Q
What happens to the 4th and 5th pharyngeal pouches?
A
Open into the pharynx by a common groove on each side.
11
Q
What is the relationship with external aspect and internal aspect of the pharynx?
A
The four ectodermal depressions correspond in position with the four internal endodermal positions.
12
Q
What happens to the four thin parts between the arches?
A
The break down to form “gill clefts”.
13
Q
What separates the ectoderm and endoderm?
A
MEsoderm.
14
Q
What does the first pharyngeal arch develop into?
A
- Mandible.
- Maxilla.
15
Q
What does the second pharyngeal arch develop into?
A
Part of the hyoid bone.
16
Q
What does the third pharyngeal arch develop into?
A
Remainder of the hyoid bone.
17
Q
What do the 4th, 5th and 6th pharyngeal arch develop into?
A
Cartilages of the larynx.
18
Q
What forms in each arch?
A
- Central bar of cartilage forms.
- Muscle differentiates from the mesoderm around it.
19
Q
What supplies each arch?
A
- Artery.
- Vein.
- Nerves.
20
Q
What happens with the left and right half of the first arch?
A
They fuse ventrally in the midline.
21
Q
What produces meckels cartilage in the first arch?
A
Chondrification of the mesoderm.
22
Q
What happens cranially on each side of the arch?
A
A bump appears - maxillary process. This is not derived from cartilage.
23
Q
What do the two maxillary processes do on the first arch?
A
Grow towards the midline and meet each other as well as the medial and lateral nasal processes. This will then produce the upper jaw and palate.
24
Q
What does the dorsal end of meckel’s cartilage form?
A
- Incus and malleus.
- Anterior ligament of the malleus.
- Sphenomandibular ligament.
25
What is the sphenomandibular ligament?
It is the fibrous perichondrium of meckel’s cartilage, which remains after the cartilage has disappeared.
26
What is the lingula at the mandibular foramen?
Small persistent part of the cartilage.
27
What happens at the intervening part of meckel’s cartilage?
The mandible ossifying at the sixth week and extends into two symmetrical halves.
28
What happens to the meckel’s cartilage after birth?
It disappears.
29
What do derivatives of ectoderm and endoderm form in the first arch?
Mucous membranes and glands of the anterior 2/3 of the tongue.
30
What do mesoderm derivatives in the first arch form?
1. Muscles of mastication (mass enter, temporal, pterygoids).
2. Mylohoid and anterior belly of digastric.
3. Tensor muscles (tensor palate and tensor tympani).
31
What do all the muscles formed from the mesoderm of the first arch have in common?
All supplied by the mandibular nerve.
32
What supplies the taste buds of the anterior 2/3 of the tongue?
Chorda tympani branch of the facial nerve - this nerve normally supplies the second arch.
33
How does the chorda tympani branch of the facial nerve supply the anterior 2/3 of the tongue?
The nerve divides into pretrematic and post-thematic branches, so the pretrematic branch of the second arch nerve suppleis some sensory fibres to the first arch.
34
What artery supplies the first arch?
First aortic arch - maxillary artery.
35
What does the first arch (mandibular) also give rise to?
Maxillary process - own sensory nerve (maxillary branch of the tri germinal).
36
What is the second arch?
Hyoid arch.
37
What bones/ligament does the second arch form?
1. Stapes.
2. Styloid process.
3. Stylohoid ligament.
4. LEsser horn and upper part of the body of hyoid bone.
38
What muscles does the second arch form?
1. Muscles of facial expression - buccinator, platysma.
2. Stapedius.
3. Stylohoid.
4. Posterior belly of digastric.
39
What supplies the muscles that are formed from the second arch?
Facial nerve.
40
What bones/ligaments does the third arch form?
1. Greater horn and caudal part of body of hyoid bone.
41
What muscles does the third arch form?
1. Style-harangues.
42
What supplies the muscles that are formed from the third arch?
Glossopharyngeal nerve.
43
What bones does the 4th and 6th arch form?
1. Thyroid.
2. Cricoid.
3. Epiglottis and artenoid cartilages.
44
What muscles does the 4th and 6th arch form?
1. Intrinsic muscles of larynx.
2. Muscles of pharynx.
3. Levator palate.
45
What supplies the muscles of the 4th and 6th arch?
Laryngeal and pharyngeal branches of the vagus nerve.
46
What does each pouch grow into?
Except the first arch - grows into a dorsal and ventral diverticulum.
47
What is the relationship of ectoderm and endoderm in the first pharyngeal pouch?
Close apposition, particularly at the tympanic membrane.
48
What happens to the endoderm of the first pouch?
It is prolonged laterally via the auditory tube to form the middle ear and mastoid antrum.
49
What does the external branchial groove become?
It deepens and forms the external acoustic meatus.
50
How does the second pharyngeal pouch help form the middle ear?
The dorsal diverticulum helps the first pouch by taking its pretrematic nerve (tympanic branch of the glossopharyngeal nerve) with it.
51
What does the ventral diverticulum of the second pouch form?
1. Tonsillary crypts.
2. Supratonsillar fossa - from the endoderm.
52
What does the surrounding mesoderm of the 2nd pharyngeal pouch form?
Contributes lymphatic tissue of the palatine tonsil.
53
What supplies the derivatives of the second pouch?
Glossopharyngeal. Overlapped in part by the facial nerve.
54
What grows dorsally from the third pouch?
Parathyroid gland.
55
What grows ventrally from the third pouch?
Thymic rudiment.
56
What happens to the thymic rudiment?
It progresses caudally and joins with the thymic rudiment from the other side to produce the bi-lobed thymus gland.
57
What happens in the descent of the thymic bud?
It brings with it the parathyroid gland (parathyroid 3) so eventually it lies inferior to parathyroid 4 (derived from fourth pouch).
58
What overlies the third pouch externally?
Cervical sinus.
59
What does the thymic bud form?
1. Medulla of the thymic lobule.
2. Thymic (Hassall’s) corpuscles.
60
Where does the thymus get its lymphocytes from?
They originally migrated from bone marrow.
61
What grows dorsally from the fourth pouch?
Superior parathyroid glands (parathyroid 4) are from the endodermal lining of the pouch.
62
What is attached ventrally to the pouch?
Thyroid gland.
63
How does the thyroid gland attached ventrally to the 4th pouch affect the superior parathyroid gland?
The thyroid prevents the superior parathyroid from descending.
64
What happens to the fifth pharyngeal pouch?
Undergoes regression and forms the ultimobranchial body.
65
What is formed from the ultimobranchial body?
Parafollicular (C) cells of the thyroid gland - these produce calcitonin.
66
What happens to the second arch ectoderm?
Increases in thickness and grows caudally, it then covers the 3rd, 4th, 6th arch and meets skin caudally to these. Deep groove is formed.
67
When the deep groove is formed on the external side what does it become?
Deep pit - cervical sinus.
68
What happens with the pit?
The lips of the pit meet and fuse and the ectoderm disappears.
69
What causes a branchial cyst?
Persistence of the ectoderm - basically it doesn’t disappear.
70
What causes a branchial fistula?
The ectoderm breaks inwards, this causes the track (normally of the second pouch) to run from the region of the tonsils (between external and internal carotid arteries) and reaches the skin anterior to the lower end of the sternocleoidomastoid.
71
What causes the skin over the mandible to join with skin of the neck?
Formation of the cervical sinus and subsequent obliteration of the ectoderm.
72
What supplies the ectoderm?
1. Facial nerve.
2. Glossopharyngeal nerve.
3. Vagus nerve.
73
What lines the cervical sinus?
C1.
74
What forms from the floor of the mouth and pharynx?
1. Tongue.
2. Thyroid gland.
3. Larynx.
75
What forms the glands and epithelium of the tongue?
Buds from the following arches:
1. First.
2. Third.
3. Fourth.
76
What forms the glands and epithelium of the tongue?
Buds from the following arches:
1. First.
2. Third.
3. Fourth.W
77
What forms the musculature of the tongue?
Occipital myotomes.
78
How does the thyroglobulin duct form?
1. It evaginates from the foramen caecum ventrally between 1st and 2nd arch.
2. It then passes caudally in front of the remaining arches.
79
How does the thyroid gland form?
It buds from the thyroglobulin ducts distal end, which may give rise to the pyramidal lobe.
80
What other remnants can the duct give rise to?
1. Cysts - commonly behind the hyoid bone. The cyst becomes stuck behind the bone.
81
Where does the laryngotracheal groove appear?
Ventral wall of the oesophagi.
82
What is the furcula?
Ridge in the shape of a wish-bone that lies in the caudal part of the floor of the pharynx.
83
What end of the laryngotracheal groove is limited by the furcula?
The cephalic end.
84
What happens in development of the furcula ridges?
They grow towards each other and fuse, which cause the conversion of the gutter/groove into a tube.
85
What is the tube?
Trachea.
86
What happens in development to the trachea?
Separates form the oesophageal and buds out into bronchi and lungs at the caudal end.
87
What happens to the furcula after fusion?
The furcula doesn’t fuse at the caudal end, thus creating the aperture of the larynx, whose cartilages include the epiglottis.
88
What arches does the larynx come from?
4th and 6th pharyngeal arch.
89
What end of the primitive heart tube is the ventral aorta formed?
Cephalic end.
90
What does the ventral aorta divide into?
Right and left - divide into two branches which curve back caudally as two dorsal aortae.
91
What happens to the two dorsal aortae?
THey continue into two umbilical arteries.
92
What happens in terms of vessels as each pharyngeal arch develops?
A vessel in each arch joins the ventral to the dorsal aortae. Therefore there are 6 aortic arches.
93
What happens to the first and second aortic arch?
They disappear early.
94
What are the only remnants of the first and second aortic arch?
Maxillary and stapedial arteries.
95
What happens to the fifth aortic arch?
Disappears entirely.
96
What happens to the third aortic arch?
It remains as part of the internal carotid artery.
97
What happens to the right fourth aortic arch?
It becomes the subclavian artery.
98
What happens to the left fourth aortic arch?
It becomes the arch of the aorta.
99
What happens by the time the 6th artery appears?
The upper bulbar part of the heart tube has been divided into aorta and pulmonary trunk.
100
How are the 6th aortic arch arteries connected to the pulmonary trunk?
Ventrally.
101
How do the 6th aortic arch arteries communicate with he dorsal aortae?
Dorsally.
102
What does the sixth arch become?
Pulmonary arteries.
103
What happens to the dorsal part of the sixth arch artery?
Disappears on the right side, but becomes the ductus arteriosus on the left side.
104
What does the ductus arteriosus do?
Connects the left pulmonary artery to the arch of the aorta.
105
What is a patent ductus arteriosus?
Ductus arteriosus fails to close in the immediate postnatal period.
106
What is coarctation of the aorta?
Narrowing of the aorta.
107
Why does coarctation of the aorta occur?
Defect of the tunica media, this will form a shelf-like projection into the lumen. This causes collateral circulation distal of the obstruction.
108
What supplies collateral circulation distal to coarctation of the aorta?
Internal thoracic and posterior intercostal arteries.
109
When does an abnormal origin of the right subclavian artery occur?
When the right fourth aortic arch disappears and the distal part of the right dorsal aorta persists.
110
What happens if the right subclavian artery’s origin is abnormal (just distal to left SCA)?
The artery will pass behind the oesophagus.
111
Why is it a hazard surgically if the right subclavian artery is not of good origin?
There is now no right subclavian arch, so the right recurrent laryngeal nerve doesn’t go underneath the branch and back up, instead it runs down the side of the larynx. Possible hazard in a thyroidectomy.
112
When does a right aortic arch occur?
When the left fourth arch and dorsal aorta disappear.
113
What occurs in interrupted arches?
When only the left fourth arch disappears, not the dorsal aorta.
114
What happens in a double arch?
The right dorsal aorta persists as well as the left, the trachea and oesopahgus will be in the middle of the two.
