FORAMEN CECUM-pit of endoderm at the junction of the derivatives of the 1st and 2nd arch-this goes out into the mesenchyme to for, THYROID GLAND

Cephalization-this action pushes everything forwards-helps explain recurrent laryngeal nerve

•          In the case of the recurrent laryngeal, looks like it starts where 4^th branchial arch is, then cephalization pushes it forward such that it is tied to the aorta

UNDERSTAND: Things of the head and tongue get pushed forward with cephalization

•          Face starts as a series of paired branchial arhes-face is formed from 1^st arches along w/ area just above it

28 days-lower jaw has fused together from the branchial arches

31 days-nostrils start forming and eyes have appeared on sides of head; nostrils center two days later

35 days-nostrils closer together and more developed

40 days-baby has eyelids and more developed nose

48 days-nasal swelling joined in center of face; eyes moved to front of head

 

FACE FORMATION COMES FROM FIVE FACIAL PRIMORDIA

•          single frontal nasal prominence, paired maxillary, paired mandibular

NASAL PLACODES-form from ectodermal thickenings on front of front nasal process

•          Nasal placodes invaginate, forming nasal pits à become nasal sacs à becomes nasal cavity
•          Nasal placodes invaginate to form nasal pits which widen to form sacs which come close enough to the developing oral cavity to form the Oronasal Membrane
•          Oronasal membrane breaks down to form the primitive choane-bilateral connection b/t nasal and oral cavity
•          Frontal nasal prominence surrounding nasal pits invaginates to become medial & lateral nasal processes
•          nasal placodes invaginate, forming pits from the ectoderm of outside from the medial &lateral processes
•          Some cheek formation from the maxillary and mandibular processes-these processes fuse early to form the mandible
•          A groove remains where the frontal nasal and maxillary processes fuse-becomes NASOLACRIMAL GROOVE-this drains tears from the medial corner of the eye into the nose-EXIT FOR TEARS

CLINICAL: Nasolacrimal Duct Atresia-failure of this canal to form-no tear drainage

CLINICAL: Choanal Atresia-if the choane don’t form, kids do fine ‘til they get upper respiratory infection

Complete Choanal Atresia presents with cyclical respiratory distress-kid has to cry to breathe

CLINICAL: newborns can breathe and drink at the same time-useful for nursing-difference in the larynx and pharynx allows newborns to respire and drink.

 

TONGUE DEVELOPMENT-occurs on the floor of the branchial apparatus

•          At the time of development, there’s MEDIAN TONGUE BUD-rapidly overgrown by two DISTAL TONGUE BUDS
•          Distal Tongue Buds-grow out to form anterior 2/3 of the tongue-in adults, you see the median sulcus as a remnant
•          Development of the tongue is such that everything GROWS OUT-just stick your tongue out and there you have it
•          CUPOLA-small midline structure forming from the 2^nd arch
•          Cupola is overgrown by the HYPOBRANCHIAL EMINENCE from the 3^rd and 4^th arches
•          Hypobranchial eminence meets derivatives of distal tongue buds  at the persistent TERMINAL SULCUS
•          The eminence “melts” into the distal tongue buds
•          TERMINAL SULCUS divides the innervation of the tongue
•          anterior 2/3 tongue-facial nerve // posterior 1/3 tongue-glossopharyngeal
•          1^st Arch innervation = TRIGEMINAL-provides temp., touch, pain sensation to anterior 2/3 of tongue
•          2^nd Arch has no real structure for it’s innervation to hang on to-thus you it’s iinnervation-VII-goes out to tongue
•          2^nd Arch innervation = FACIAL-taste from the anterior 2/3 of the tongue
•          3^rd Arch innervation = GLOSSOPHARYNGEAL-provides all sensation, taste, temp., pain for posterior 1/3 of tongue

CLINICAL: Chorda tympani can be sacrificed-or one side of it-and patient can’t sense their unilateral analgesia(taste-loss)

INTERESTING: jalapenos are sensed by pain receptors of V and not by taste receptors on VII.

 

THYROID GLAND-starts as thickening of the endoderm b/t 1^st and 2^nd arch-the FORAMEN CECUM

THYROID GLAND STARTS AS THE FORAMEN CECUM

•          Pouch b/t 1^st and 2^nd invaginates and those endodermal cells migrate down trhough mesenchyme of head
•          Thyroid passes very close to the anterior part of the hyoid bone on its way down
•          It is hoped that a bilobed thyroid gland results and that its tract disappears

PYRIMIDAL LOBE-extra thyroid piece leftover from descent through anterior part of the neck

THYROGLOSSAL DUCT CYST-a MIDLINE abnormality originating from FORAMEN CECUM

•          often moves with tongue; can be removed so long as its not the only thyroid tissue in the body

BRANCHIAL CLEFT CYST-a LATERAL abnormality originating from 1^st branchial arch.

 

PALATE FORMATION-developed from two different processes

Medial Nasal Processes gives rise to the primary and secondary palates

•          Anterior part of palate forms from the fusion of the medial nasal processes

Medial & Lateral processes grow forward and together to form the INTERMAXILLARY SEGMENT

•          this segment is growing between other parts of the maxilla that are forming-hence the name

Intermaxillary segment-forming as the PALATINE SHELVES that form palate and roof of the mouth

Pre-maxillary Maxilla-part of the hard palate and the soft palate; holds your front four teeth; is closely border by the philtrum

•          Pre-maxillary Maxilla fuses with the two palatine shelves at the INCISIVE FORAMEN

Note-philtrum is the depression b/t nose and upper lip-formed from the medial nasal processes

Raphe-a rather narrow, low elevation in the center of the hard palate that extends from the incisive papilla posteriorly over the entire length of the mucosa of the hard palate.

•          the hard palate ends into the soft palate which moves due to muscle underlying-important in pHoNaTiOn
•          again, the secondary palate forms the hard and soft palate

Uvula-a conical projection from the posterior edge of the middle of the soft palate, composed of connective tissue containing a number of racemose glands, and some muscular fibers

Raphe and Uvula are unique to the secondary palate.

 

CLEFT PALATES

•          Anterior and Posterior Clefts can occur both unilaterally and bilaterally
•          Posterior Clefts usually occur at the back of the neck-they occur b/c of persistent separation of the secondary palate
•          Anterior Clefts result from failure of medial nasal processes to fuse and involve the lip & primary palate up to the incisive foramen
•          form primarily at the edge of where the philtrum would form
•          the median nasal processes need to fuse w/ the maxillary processes-if this is not filled in, then ANTERIOR CLEFT

Tags: branchial cleft cyst, cephalization, choanal atresia, cleft palate, cupula, distal tongue bud, facial primordia, foramen cecum, median tongue bud, nasal placodes, nasolacrimal duct, palate formation, philtrum, raphe, thyroglossal duct cyst, thyroid gland, uvula

This entry was posted on Sunday, January 11th, 2009 at 6:19 am and is filed under Embryology. You can follow any responses to this entry through the RSS 2.0 feed. Responses are currently closed, but you can trackback from your own site.