Embryology Chapter 9

First pharyngeal pouch

a. The ______ pouch expands into a tubotympanic recess. 1. The distal part of this recess contacts the first pharyngeal groove and later contributes to formation of tympanic membrane. 2. The middle part-tympanic cavity and mastoid antrum b. Pharyngotympanic tube

4th pouch

a. also forms solid dorsal and hollow elongated ventral parts. b. connection with pharynx is reduced to a narrow duct that soon degenerates.

3rd pouch

a. expands and develops a solid , dorsal part and a hollow, elongated ventral part b. its connection with the pharynx is reduced to a narrow duct that degenerates c. by 6th week, epithelium of each dorsal part begins to differentiate into an inferior parathyroid gland

Second pouch

a. the ______pouch is largely obliterated as palatine tonsil develops b. part of pouch remains as tonsillar sinus

Aortic arch

becomes arterial pattern of head and neck-described in cardiovascular system. ________ arise from truncus arteriosus of primordial heart and enter the dorsal aorta.

foramen cecum

between tubercular impair and cupola, there is a ____________ - median pit on dorm of the tongue and represents the origin of the thyroid

4th pouch; hollow elongated ventral

calcitonin cells of thyroid ultimopharyngeal body

parathyroid hormone

elevate serum calcium levels

single frontonasal prominence

facial prominence a. Surrounds the ventrolateral part of forebrain which gives rise to optic vesicles that form the eyes. b. Frontal part forms forehead c. Nasal part forms rostral boundary of stomodeum and nose.

paired mandibular prominences

facial prominence a. derivative of 1st pair of pharyngeal arches b. forms caudal boundary of stomodeum c. Lower jaw and lower lip are first to form. They result from merging of the medial ends of the mandibular prominences in medial plane.

paired maxillary prominences

facial prominence a. derivative of 1st pair of pharyngeal arches b. form lateral boundaries of stomodeum

neural crest

facial prominences are produced by expansion of _________ populations that originate from the mesencephalic and rostral rhombencephalic neural folds. Cells are major source of CT components, including cartilage, bone and ligaments in facial and oral regions.

1st pharyngeal pouch

formation of tympanic membrane (eardrum) tympanic cavity (middle ear) mastoid antrum (opening) pharyngotympanic tube (eustachian tube or auditory tube)

Mandibular promience

forms mandible (Ventral part) and squamous part of temporal bone 3. Muscles of mastication 4. Trigeminal nerve (CNV) -sensory to face and motor to muscles of mastication.

Maxillary prominence

gives rise to maxilla, zygomatic bone and part of vomer bone a. Dorsal end of 1st arch cartilage (Meckel's cartilage) give rise to i. Incus ii. malleous

3rd aortic arch

i. Common carotid arteries ii. Internal carotid arteries

1st aortic arch

i. Maxillary arteries ii. May contribute to external carotid arterie

6th aortic arch

i. Part of R and L pulmonary arteries ii. Ductus arteriosus ( shunts blood from pulmonary trunk to aorta bypassing the lungs in fetus)

4th aortic arch

i. Proximal part of right subclavian artery ii. Part of arch of aorta

2nd aortic arch

i. Stapedial arteries ii. Hyoid artery

3rd pouch; solid, dorsal

inferior parathyroid gland

calcitonin

lowers serum calcium levels **neural crest cells migrate into ultimo pharyngeal body and gives rise to secreted cells

2nd pouch

obliterated; tonsilar sinus

trigeminal nerve

pain is carried by the _____ nerve. On the anterior 2/3 of the tongue

tongue muscles

postotic somites become

eye muscles

preotic somitomeres forms

glossopharyngeal (CNIX)

sensory and taste carried by the ______, on the posterior 2/3 of the tongue

trigeminal

sensory is carried by the ____ nerve. On the anterior 2/3 of the tongue

superior parathyroid gland-

solid dorsal part 1. early in 5 th week, the rudiments of the superior parathyroid glands form in fourth pouch. 2. The detach from the pharynx and migrate inferiorly and medially, coming to rest by seventh week in a position slightly superior to the inferior parathyroid glands 3. Thus, the superior parathyroids arise more inferiorly on the pharynx than the inferior parathyroids. 4. Their names reflect their final position.

4th pouch; solid, dorsal

superior parathyroid gland

facial nerve or the chorda tympani

taste is carried by the ___ nerve. On the anterior 2/3 of the tongue

note

terminal sulcus --anterior 1/3 meets posterior 1/3

placodes

the ectoderm thickens in three locations to form olfactory, lens, and otic _____ that relate to the special sensory cranial nerves I, II, and VIII, respectively.

stomodeum

the surface ectoderm invaginates to form the _______

3rd pouch; hollow, elongated ventral

thymus

Nerve

(sensory and motor components) a. Each arch is supplied by its own cranial nerve. b. Neural crest migration bring own nerve fibers into the specific arch. c. SVE components supply muscles derived from pharyngeal arches d. sensory innervation of ventral side of face is supplied by the 3 divisions of the trigeminal nerve e. These nerves arise from neuroectoderm of the primordial brain (brainstem).

Ectodermal placodes (thickened regions of ectoderm)

1. Along with neural crest form some of the sensory ganglia

2nd//cervical sinus// 7th Fate of pharyngeal arches

1. During 5th week, ____ pharyngeal arch enlarges and overgrows 3rd and 4th arches 2. This forms the _______ 3. By end of ___ week, the 2nd-4th grooves and cervical sinus have disappeared

Paraxial mesoderm

1. Forms a large portion of the membranous and cartilaginous components of the neurocranium (skull) 2. All voluntary muscles of craniofacial region 3. Dermis and connective tissue in dorsal region of head

4th and 6th fuse to form laryngeal cartilages

1. Muscles of pharynx and larynx 2. Striated muscles of esophagus 3. Branches of vagus nerve (CNX)

Neural crest

1. Originate in neuroectoderm of forebrain, midbrain and hindbrain regions and migrate ventrally into pharyngeal arches 2. Migrate rostrally around the forebrain and optic cup into facial region 3. Gives rise to a. Viscerocranium (face) b. Parts of membranous and cartilaginous regions of neurocranium c. All other tissues in region including 1. Cartilage 2. Bone 3. Dentin 4. Tendon 5. Dermis 6. Pia and arachnoid 7. Sensory neurons 8. Glandular CT

3rd arch

1. Part of hyoid bone 2. Stylopharyngeus 3. Glossopharyngeal (CN IX)

note

1. Pharyngeal arches support the lateral walls of the primordial pharynx which is derived from cranial part of foregut. 2. The stomodeum initially appears as a slight depression on surface of ectoderm. 3. The oropharyngeal membrane separates them. Made of ectoderm and endoderm. 4. Ruptures at approximately 26 days. a. Ectodermal lining of first arch gives rise to oral epithelium

Second arch

1. Stapes 2. Styloid process of temporal bone 3. Stylohyoid ligament 4. Part of hyoid bone 5. Facial nerve (CNVII)-motor to muscles of facial expression, sensory to face teeth and mucous membranes. 6. Muscles a. Muscles of facial expression b. Stapedius c. Stylohyoid muscle

calcitonin cells of thyroid gland

1. The elongated ventral part of the 4th pouch develops into an ultimopharyngeal body. 2. This fuses with the thyroid gland and its cells disseminate within it, giving rise to the parafollicular cells of thyroid gland 3. Also called C cells 4. Produce calcitonin 5. C cells differentiate from neural crest that migrate from pharyngeal arches into the 4th pair of pouches.

3rd pouch thymus

1. The epithelium of the elongated ventral parts of the third pair of pouches proliferates, obliterating their cavity. 2. These bilateral primordial of the thymus come together in the median plane to form the thymus 3. between 4th and 7th week, the thymus glands lose their connections with the pharynx and migrate to the definitive location inferior and ventral to developing thyroid and just dorsal to sternum 4. they fuse to form a single gland 5. Soon they will become invested with neural crest -derived connective tissue which also forms septa among the endodermal epithelial cords and contributes to thymic vasculature. 6. Absence of neural crest cells, thymus fails to develop. 7. At about 9-10 weeks gestation, blood-borne thymoctye precursors called prothymocytes invade epithelial thymus.

Lateral plate mesoderm

1. laryngeal cartilages 2. connective tissue in region

CNX

A branch of the vagus nerve_____ of the 4th arch supplies a small area of the tongue anterior to the epiglottis.

Pharyngeal membranes

A. Appear in floor of pharyngeal grooves B. Form where epithelia of the grooves and pouches approach each other. C. The endoderm of the pouches and ectoderm of grooves are soon separated by mesenchyme D. Only one pair of _______ contribute to adult structures E. The first pharyngeal __________, along with intervening layer of mesenchyme, becomes the tympanic ______.

Pharyngeal arches

A. Contribute to formation of neck and face. B. Begin to develop early in fourth week as neural crest cells migrate into the future head and neck regions.

pharyngeal pouches

A. Primordial pharynx derived from foregut widens cranially-joins stomodeum B. Narrows caudally and joins esophagus C. Endoderm of pharynx lines internal aspects of pharyngeal arches and passes into a balloon-like diverticula—Pharyngeal pouches D. Form between pharyngeal arches E. One pouch is found between 1st and 2nd arch F. There are 4 pairs-5 th pair is absent or very small G. Separated from pharyngeal grooves by pharyngeal membrane.

Pharyngeal grooves

A. ______ separate the arches externally B. Only one pair of ______ contribute to postnatal structures-the first pair persists as the external acoustic meatus C. The other ______ live in cervical sinus and are normally obliterated

hypoglossal nerve (CNXII)

All muscles of tongue are supplied by ______ of the 4th arch except for one muscle which is supplied by branch of vagus nerve

chorda tympani branch

Although the facial nerve is the nerve of the 2nd pharyngeal arch, its ______ supplies the taste buds in the anterior 2/3s of the tongue.

Typical pharyngeal arches consists of

Aortic arch Cartilaginous rod Muscular component Nerve

aortic arches

Arises from truncus arteriosus of primordial heart and terminates in dorsal aortae.

hyoid bone and laryngeal cartilages// (larynx)

As embryo and tongue grow, the developing thyroid gland descends in neck, passing ventral to developing hyoid bone and laryngeal cartilages.

isthmus

At first the thyroid primordium is hollow but it soon becomes solid and divides into right and left lobes which are connected by the _____ of the thyroid gland. The _______ is lies anterior to developing 2nd and 3rd tracheal rings.

note about salivary glands

B. Clubbed shaped ends of epithelial buds grow into underlying mesenchyme. C. Connective tissue is derived from neural crest cells. All secretory tissue arise by proliferation of oral epithelium.

note

By 7 weeks the thyroid has assumed its definite shape and has usually reached its final site in the neck. By this time the thyroglossal duct has degenerated. In 50% of people the distal portion of the thyroglossal duct persists as the pyramidal lobe.

epiglottis

Caudal to copula is another swelling that represents the________.

salivary glands

During 6th and 7th weeks, _____ begin as solid epithelial buds from the pirmoridal oral cavity. (9-7C)

central rod

Each also contains a __________ or precartilaginous mesenchyme, which is transformed into characteristic adult skeletal derivative.

4th

Facial primordia appear early in the __ week around the large primordial stomodeum

Maxillary prominence and Mandibular prominence

First arch separates into two prominences

note

First pair is the primordium of the jaws and appears as surface elevations lateral to developing pharynx.

thyroglossal duct

For a short time, the thyroid gland in connected to the tongue by a narrow tube called the _________________.

fourth week

G. By end of ______ week, four pairs of pharyngeal arches are visible H. The 5th and 6th arches are rudimentary and are not visible on surface

lateral lingual swelling

Growth of the body of the tongue is accomplished by a great expansion of _____________ with a minor contribution by the tuberculum impar. As the lateral swellings increase in size, they overgrow the tuberculum impar and merge forming the anterior 2/3 of tongue-body **merge in midline- form median sulcus

first

In a 5-week old embryo, the tongue is represented by a pair of lateral lingual swellings in the ventral regions of the ___pharyngeal arches and two median unpaired swellings.

artery/cranial

In addition to being packed with mesenchyme (mainly of neural crest origin except for the premuscle mesoderm, which migrates from somitomeres), each pharyngeal arch is associated with a major ______ (aortic arch) and a ________ nerve

mesenchyme/neural crest cells

Originally ___________ is derived the third week from mesoderm. During 4th weeks, most is derived from _______________ that migrate into pharyngeal arches.

pharyngeal groove/craniocaudal

Pharyngeal arches are separated by ___________________ and are numbered in _____________ sequence

Parotid

Salivary Gland a. First to appear b. Arise from oral ectoderm at angles of stomodeum. c. Secretions start at 18 weeks

Submandibular glands

Salivary Gland a. develop late in 6th week. b. Develop from endodermal buds in floor of stomodeum.

Sublingual glands

Salivary Gland a. Appear late in 8th week. b. Develop from multiple endodermal epithelial buds in paralingual sulcus.

glossopharyngeal nerve

The (posterior 1/3) vallate papillae in the oral part of the tongue are innervated by the _____ (CN IX)-The mucosa of the posterior third is pulled slightly anteriorly as tongue develops.

tongue

The __ begins to take shape from a series of ventral swellings in the floor of the pharynx about the same time as the palate forms in the mouth. Major shifts in the positions of tissues of the ___ occur, making the characteristics of the adult form difficult to comprehend without knowledge of the basic elements of its embryonic development.

copula

The ___ unites the second and third arches. Formed by the fusion of the ventromedial parts of the 2nd pair of pharyngeal arches

thyroid gland/24

The _________ is the first endocrine gland to develop in embryo It begins to form about_________ days after fertilization.

papillae

The dorsal surface of the tongue is covered with a large number of _____ which appear toward the end of the 8th week. Some ______ will contain taste buds. 1. Develop during weeks 11-13 by inductive interaction between epithelial cells of tongue and invading gustatory nerve cells from chorda tympani, glosspharygneal and vagus nerves.

second arch

The epithelium of the ______ is overgrown by that of the 3rd arch so there is no general sensory innervations to tongue by facial nerve

A. Pharyngeal arches B. Pharyngeal pouches C. Pharyngeal grooves D. Pharyngeal membranes

The pharyngeal apparatus consists of

copula

The root of the tongue is derived from the ___ along with additional ventromedial tissue between the third and 4th pharyngeal arches (hypopharyngeal eminence)

trigeminal nerve

The sensory supply to mucosa of almost the entire anterior 2/3s of the tongue is from a branch of the _____________. The mucosa (epithelium) of anterior tongue originates from first arch. The trigeminal nerve is the nerve of the 1st pharyngeal arch. The lateral lingual swellings originate from 1st arch.

thyroid primordium

The thickening soon forms an outpocketing called the __________.

tuberculum impar

The______________ is located between the 1st and 2nd arches

3rd pouch Inferior parathyroid gland

They detach from pharyngeal wall and migrate inferiorly and medially, coming to rest by the seventh week on the dorsal side of the inferior ends of the thyroid lobes

myoblasts

Tongue muscles are derived from _______ from occipital myotomes. The hypoglossal nerve (CN12) accompanies migration of ________.

five/stomodeum

___ facial primordia appear as prominences around __

pharyngeal grooves

______ of ectoderm separate each pharyngeal arch on the surface

pharyngeal pouches

________ of foregut endoderm are their equivalent on the inside.

the foramen cecum

__________, which marks the original location of the thyroid primordium, serves as a convenient landmark delineating the border between the original tuberculum impar and copula

pharyngeal arch

___________ mesenchyme forms CT and vasculature of tongue.

myogenic mesoderm//Endothelial cells

4. ________________ from paraxial regions moves into each pharyngeal arch forming a central core of muscle primordium. 5. ________________ are derived from both lateral mesoderm and invasive angioblasts that move into pharyngeal arches.

laryngeal cartilages

4th and 6th arches fuse to form _____________

rudimentary and has no derivates.

5th pharyngeal arch is _________________.

mesenchyme/ectoderm/endoderm

Initially, each arch consists of ___________ derived from the intraembryonic mesoderm and is covered with __________ externally and __________ internally.

The development of the thyroid gland------endoderm/1st and 2nd

It begins as a thickening of ____________ caudal to median tongue bud in primordial pharynx. It forms along the ventral midline of the pharynx between ___________ pouches.

Paraxial mesoderm Lateral plate mesoderm Neural crest Ectodermal placodes (thickened regions of ectoderm)

Mesenchyme for the region of the head is derived from