Unit 2.L2-Pharyngeal Apparatus, the Gut tube & Urogential System Flashcards
By Day 28, what is formed as paired structures and where can they be seen?
The Pharyngeal Apparatus/arches (or branchial arches) forms as paired structures, externally visible on the ventrolateral side of the early brain/head
What does the Pharyneal Apparatus comprise of? (7)
- Pharyngeal Arches
- Pharyngeal Grooves
- Pharyngeal Pouches (cannot be seen from the outside; endodermal side)
- Pharyngeal Membranes
- Pharyngeal Nerves
- Pharyngeal Muscles
- Pharyngeal Artery
What contributes to the formation of the Pharyngeal Apparatus?
All 3 germ layers, Ectoderm, Mesoderm & Endoderm contribute to the formation of the pharyngeal apparatus
How many arches form from the Pharyngeal Apparatus?
Five arches form (1,2,3,4, & 6)
NOTE: Humans only form 5 arches, Arch V is absent in humans
How many arches are externally visible and what are they? Which arches fuse?
- Only 4 are externally visible (1,2,3 & 4/6)
- 4 & 6 fused
What forms the skeleton of the arch?
A cartilaginous rod forms the skeleton of the arch.
What differentiates into the muscle of head/neck of the arch?
Mesoderm differentiates into muscles of head /neck.
What supplies blood/nutrition to each arch?
Each Aortic Arch Artery supplies blood/nutrition.
Sensory/motor nerves dervied from where, invade what in each arch?
Sensory/motor nerves derived from neuroectoderm of the brain invade the mucosa/muscles in each arch
When and how does the first pair of arches appear in the developing embryo?
By day 23 (3 weeks) the first pair of arches, the primordial jaw appears as surface elevations lateral to the developing pharynx (dorsal view)
During the emergence of the Pharyngeal Apparatus (Day 23-28) what develops by:
- Day 24
- Day 26
- Day 28
Week 3
- Day 24: 1st & 2nd Pharyngeal arch, 1st pharyngeal groove & optic placode
- Day 26: 1st, 2nd, & 3rd Pharyngeal arch, Optic pit
- Day 28: 1st, 2nd, 3rd & 4th Pharyngeal arch, 1st & 2nd pharyngeal groove
All lateral views
If you rotate the embryo to the Ventral/Facial view what is developing simultaneously to the Pharyngeal arches at Day 23, 26 & 28.
Week 3
- Day 23: Oropharyngeal membrane, maxillary prominence, mandibular prominence
- Day 26: Maxillary prominence, mandibular prominence, Ruptured Oropharyngeal membrane, heart prominence
- Day 28: Stomodeum, Nasal placode
- Which germ layer does the Pharyngeal arch originate form?
- Pharyngeal pouches?
- Pharyngeal membrane?
- Mesoderm→Arches
- Endoderm→Pouches
- Mesoderm,Endoderm & Ectoderm→Membrane
NOTE: Ectoderm→Clefts/Groove
What are the components of a developing Pharyngeal Apparatus? (8)
- Mesoderm→Arches
- Endoderm→Pouches
- Ectoderm→Clefts/Groove
- Pharyngeal Membrane
- An aortic arch artery, supplying blood
- A cartilaginous rod forming the skeleton
- Arch nerve to mucosa/muscles
- A muscular component (not seen)
By day 28, what develops along side the Pharyngeal arches? (2)
- The tongue buds (bilaterally)-gives rise to your tongue
- Laryngotracheal groove (between the arches)-gives rise to your larynx and trachea
What gives rise to the larynx and trachea?
Laryngotracheal groove (between the arches)
Between 4-8 weeks what is formed? What cells play an important role in the formation?
- The pouches/face forms
- Neural crest cells migrate into the pouches
When do the facial proportions develop?
9th wk-birth: The facial proportions develop in the fetal period
When does a definitive face form? And what causes it?
In childhood at puberty: After development of teeth & paranasal sinuses, a definitive face forms
What causes the change in your facial structures during puberty?
Paranasal sinuses
What is the origin of the core mesenchyme of the pharyngeal apparatus? What is the core mesenchyme covered by?
4.5 week (Day 32)
. Paraxial mesoderm→Core mesenchyme: Covered by ectoderm + endoderm
What is the origin of the Arch Endothelial cells and what do they eventually form?
4.5 week (Day 32)
Lateral mesoderm→Arch Endothelial cells→Invasive angioblasts, forming the vasculature (gets attached to the aortic arches)
Arch endothelial cells surround the heart
By day 32, Neural crest migrate and largely form what? (2)
- Arch mesenchyme
- Connective tissue (cartilage, bone, muscles, ligaments & dermis) in 1,2,3,4 arch
Ventrally where does the blood supply to the pharyngeal apparatus arise from? Where does it pass?
Ventrally: Arteries arises from the Truncus arteriosus of the primordial heart & passes around the primordial pharynx, supplying blood to the pharyngeal apparatus
Dorsally, where does the blood supply to the pharyngeal apparatus arise from? Where does it enter?
Dorsally: Aortic Arch Arteries connects & enters the Dorsal Aorta on the other side
The Pharyngeal arch cartilage derivates of the 1st Arch gives rise to which structures? (ventrally and dorsally)
- Ventrally: Meckel’s cartilage→Ossified (membranous bone)→maxillary/mandibular prominences
- Dorsally: Middle ear bones (malleus, incus)
The Pharyngeal arch cartilage derivates of the 2nd Arch gives rise to which structures? (4)
- Stapes
- Styloid process
- Lesser cornu/horn of hyoid bone
- Superior body of hyoid bone
The Pharyngeal arch cartilage derivates of the 3rd Arch gives rise to which structures? (2)
- Greater cornu/horn of hyoid
- Inferior body of hyoid bone
The Pharyngeal arch cartilage derivates of the 4th Arch gives rise to which structures?
“Too Come And Count Cute Things”
- Neck Cartilages: Thyroid, Cricoid, Arytenoid, Corniculate, Cuneiform & Triticeal
NOTE: Thymus, thyroid, parathyroid comes from the 3rd apparatus but Thyroid cartllage comes from the 4th
By Week 4, the 1st Pharyngeal Arch has what type of depression and what does it form?
A ventral depression →stomodeum (future mouth) is contagious with the gut tube
The 1st Arches flank the stomedum (future mouth) and divides into what?
Flank the stomodeum & divide: dorsal maxillary process & ventral mandibular process
Ventrally, the Mandibular process of the 1st Arch becomes what? And what is it eventually replaced with?
Ventrally: Mandibular process→Meckel’s cartilage (NCC origin), which is replaced by intramembranous bony mandible
Dorsally, the Mandible process of the 1st Arch forms what?
Dorsally: Mandible forms incus & malleus (middle ear bones)
List the structures derived from the 1st pharyngeal arch:
- Bones
- Ligaments
- Muscles
- Nerve
- Blood supply
- Bones: Incus, mallelus, maxilla, mandible (also squamous part of the temporal lobe, zygomatic bone, palatine bones)
- Ligaments: Sphenomandibular ligaments,anterior ligament of malleus
- Muscles: Muscles of mastication (temporalis, masseter,ptyerygoids), anterior belly of diagastrc, mylehyoid, tensor vali palatini and tensor tympani
- Nerve: Trigemenal nerve (CN V) (Maxillary and mandibular branches-V2 & V3)
- Blood supply: Maxillary artery (first branch from the first aortic arch)
By week 5, the 1st Pharyngeal groove forms what part of the ear?
Week 5: 1st groove starts forming the external auditory meatus of the ear
Reminder the groove is of ectodermal origin
By week 5, what happens to the 2nd, 3rd, & 4th Pharyngeal groove and why?
Grooves 2,3 & 4 fuse and disapper because the growth in the mesodern is so fast
Fusing grooves causes a lacunae remaining in the mesoderm
When the 1st Pharyngeal Pouch forms a lengthy ingrown what does it become?
Endodermal origin
Forms a lengthy ingrowth→tubotympanic recess (endodermal origin)
Remember: The pharyngeal pouch has an endodermal surface so the ingrowth of tubotympanic recess is endodermal
What does the Tubotympanic recess (of the 1st Pharyngeal pouch) fuse with? And what does it form?
Tubotympanic recess ,which proximally fuses with pharyngeal structures to form the Pharyngotympanic tube (Middle ear cavity + Eustachian tube) & connects to the nasopharynx
The junction of the External acoustic meatus + tubotympanic recess forms what? And include it’s function?
1st Pharyngeal pouch
Junction of External acoustic meatus + tubotympanic recess forms the “tympanic membrane (Ear drum)”; separates outer & middle ear
External acoustic meatus (ectodermal origin)
Tubotympanic recess (endodermal origin)
What is the function of the Eustachian tube?
1st Pharyngeal pouch
Part of the pharyngotympanic tube w/ middle ear cavity
Equalizes atmospheric pressure in the middle ear
How does the 2nd Pharyngeal Arch grow? And what does it cover? What does it form?
Arch II grows rapidly and inferiorly to cover the smaller arches (3&4) forming the operculum.
This growth forms a ‘lid’ over other arches and creates the smooth covering of the neck
What is formed from the 2nd Arch connective tissue? (6)
- Stapes bone/stapedius muscle (smallest bone & muscle; 1mm), are formed from the 2nd arch connective tissue.
- Bony styloid process, the lesser cornu (horn) of the hyoid bone & the stylohyoid ligament are formed by 2nd arch connective tissue
What is the nerve of the 2nd Arch and what does it innervate?
2nd arch facial nerve (CN VII) innervate the muscle and tongue mucosa
List the structures formed from the 2nd Pharyngeal Arch:
- Bones
- Ligaments
- Muscles
- Nerve
- Blood supply
- Bones: Stapes, styloid process of temporal bone, lesser horn and superior part of the body of the hyoid bone
- Ligaments: Stylohyoid ligament
- Muscles: Muscles of facial expression, stapediusm mylohyoid, posterior belly of diagastric, auricular, buccinator, platysma
- Nerve: Facial nerve (CN VII)
- Blood supply: Hyoid artery (foetal), stapedial artery (foetal)
How does the 2nd Pharyngeal Groove get isolated? What does the isolation form?
2nd Pharyngeal groove gets isolated by growth of the second arch, which forms the operculum (flap; evolutionarily conserved- gills or smooth neck)
2nd Pharyngeal Groove
What does the Operculum fuse with and what does it form?
Operculum formed by 2nd arch
Operculum fuses with 3rd & 4th grooves & forms the cervical sinus lined with ectodermal epithelia →Later forms glands
2nd Pharyngeal Groove
What is the Cervical sinus lined with and what does it later form?
Lined with ectodermal epithelia →Later forms glands
2nd Pharyngeal Groove
What happens to the Cervical sinus later on and what do the ectodermal cells lining it form?
Later, the Cervical sinus disappears & the Ectodermal cells → Hassall’s corpuscles found in the thymus gland
2nd Pharyngeal Groove
Where are Hassall’s corpsuscle found?
Thymus gland
The 2nd Pharyngeal Pouch endodermal epithelium proliferates and invades the mesenchyme to form what?
2nd Pharyngeal pouch endodermal epithelium proliferates and invades into the mesenchyme to form lymphoid tissue→Palatine tonsils
What forms the Palatine tonsils from the 2nd Pharyngeal Pouch?
Palatine tonsils form (mesodermal lymphoid tissue + crypts lined by endodermal epithelia)
- Lymphoid tissue form lymphocytes
- Endodermal Epithelium invades the mesoderm as crypts
What does the 2nd Pharyngeal Pouch endodermal epithelium form?
2nd Pharyngeal pouch endodermal epithelium proliferates and form Tonsillar crypts
2nd Pharyngeal Pouch
Where do the Tonsillar crypts invade and what do they form?
The Tonsillar crypts invade into the neck mesenchyme, which form lymphoid tissue
At Birth: Palatine tonsils are formed by two components: 1____________ +2________________
At Birth: Palatine tonsils are formed of two components: 1. Mesodermal lymphoid tissue + 2. Crypts lined by endodermal epithelia
What does the 3rd Pharyngeal connective tissue form?
3rd arch connective tissue forms: Greater horn (cornu) & inferior parts of the hyoid bone
What does the 3rd Pharyngeal mesoderm form?
3rd arch mesoderm forms the Stylopharyngeus muscle
What is the 3rd Arch innvervate by? And what does the nerve innervate?
- 3rd Arch innervated by the glossopharyngeal nerve (CN IX)
- CN IX, also innervates pharyngeal plexus in the Palate + Pharynx
What are the 3rd Aortic Arch ateries?
3rd aortic arch artery→ Adult common & internal carotid arteries
What happens to the 3rd & 4th Pharyngeal grooves and what disappers?
3rd & 4th Pharyngeal groove fuse, & the cervical sinus disappears
What does the 3rd pouch endoderm contribute to?
3rd pouch endoderm contributes to neck endocrine glands
List the structures formed from the 3rd Pharyngeal Arch:
- Bones
- Muscles
- Nerve
- Blood supply
- Bones: Greater horn and the inferior part of the body of the hyoid bone
- Muscles: Stylopharyngeus muscle
- Nerve: Glosspharyngeal nerve (CN IX)
- Blood supply: Common carotid artery and the first part of the internal carotid artery
What happens with the 4th and 6th Pharyngeal Arches and what structure do they become?
4th/6th arches fuse→common neck structure
The 4th/6th arches connective tissues fuse and form what?
4/6th arch connective tissue fuse→Laryngeal Cartilages (Thyroid, Cricoid, Arytenoid, Corniculate & Cuneiform cartilage); but NOT the epiglottis
What does the 4th/6th arch connective tissue NOT form?
Epiglottis
What creates phonation? (3)
the Constrictors of the pharynx, palate (levator veli palatine) & Cricothyroid (phonation)
Originate from the 4/6th arch mesoderm
6th arch forms the intristic muscle of what?
6th arch→intrinsic muscles of the larynx
What innervates the 4/6th arches?
Vagus nerve (CN X) innervate 4/6th arches in TWO BRANCHES:
- 4th arch→superior laryngeal branch of the Vagus (CN X)
- 6th arch→recurrent laryngeal nerve CN X that innervate the larynx
The superior laryngeal branch of the Vagus (CN X) innervates what branch?
4th Arch
The recurrent laryngeal nerve CN X innverates what?
6th arch; Larynx
List the structures formed from the 4th/6th Pharyngeal Arch:
- Cartilage
- Muscles
- Nerve
- Blood supply
- Cartilage: Thyroid, cricoid, arytenoid, corniculate, cuneiform
Muscles:
- Arch IV: cricothyroid, levator veli palatini and the pharyngeal constrictors
- Arch VI: intrisic muscle of the larynx (except cricothroid)
Nerve
- Arch IV: Superior laryngeal, branch of vagus nerve
- Arch VI: Reccurent laryngeal, branch of the vagus nerve
Blood supply (At this level in the embryo we see differences in the cardiovascular system develop bte left and right sides)
- Arch IV: Left-aortic arch; right-subclavian artery
- Arch VI: left-pulmonary artery and ductus arterious; right-pulmonary artery
What causes Superfical face distribution?
Two Caudal Trigeminal branches of 1st pouch (CN V) →Superficial facial distribution.
List the distribution of nerves from all arches
- 1st Pharyngeal Arch: Trigemenal (CN V)→V2 (Maxillary division), V3 (Mandibular)
- 2nd Pharyngeal Arch: Facial (CN VII)
- 3rd Pharyngeal Arch: Glosspharyngeal (CN IX)
- 4th Pharyngeal Arch: Vagus (CN X)
Which pouch does the primary lymphoid organ develop and what is it made of?
- Primary lymphoid organ develops from 3rd pouch
- Made of (endoderm + mesoderm + neural crest cells)
Explain the steps for the formation of the Thymus
- What descends into the mesenchyme? Cords form what?
- What fills the septa and develop into what?
- The cervical sinus ectodermal cells converts to?
- Epithelial tubes/solid cords descend into the mesenchyme. Cords form reticulated thymus lobules, trap the mesenchyme & form septa
- Lymphocytes fill the septa & develop into thymocytes (precursor T cells)
- The cervical sinus ectodermal cells converts to Thymus “Hassall’s corpuscles” (cytokines for T-cell maturation)
What is the structure of the Parathyroid gland?
2 Superior (top of thyroid) + 2 Inferior glands (Thymus)
NOTE: Thyroid forms forms from both pouch 3 and 4 but 4 is critical for the superior parathyroid
Explain the steps for the formation of the Parathyroid gland
- What happens at week 5?
- What secretes PTH? What does it regulate?
- 4th pouch ventrally forms what? And produces what?
- What is differentiate from neural crest cell?
- Week 5: Dorsal epithelium of 3 & 4th pouches proliferate & form small dorsal nodules & become vascularized
- Parathyroid CHIEF CELLS (PRINCIPAL CELLS) differentiate & secrete parathyroid hormone (PTH), regulating fetal Ca++ metabolism & bone formation
- 4th pouch ventrally forms the ultimopharyngeal body, which fuses with the thyroid gland & produce the PARAFOLLICULAR CELLS (C cells that produce Calcitonin)
- C CELLS differentiate from neural crest cells .
By Week 5, what does the nasal placodes form?
The Nasal placodes form nasal pits→nasal sacs
What deepens the nasal pits and what does it eventually form?
Week 5
Nasal mesenchymal prominences deepen the pits→Primordial nasal sacs→ Nostrils
The primordial nasal sacs are ectodermal in origin but are formed by mesoderm surrounding the nasal pit and pushing to form sac like structure
What seperates the nasal and oral cavity?
The Oronasal membrane separates the nasal & oral cavity
Oronasal membrane formed by ectodermal cell
By week 6, what happens to the oronasal membrane and what does it connect?
Oronasal membrane ruptures (lacunae)→connects the nasal and oral cavities
By Week 7, what connects the oral cavity to nasal pharynx and what is formed?
Primordial choana connects oral cavity to nasal pharynx, and an epithelial plug forms; (lost by wk-16).
Plug fromed to keep fluid from entering nasal cavity
What type of fibers from the brain enter the nasal cavity?
Week 7
Olfactory nerve fibers from the brain come into nasal cavity
What palates forms during Week 12?
Palates (hard primary + secondary + soft) forms
Plug still present
Week 12:
- What matures from choana?
- What does the Ectodermal epithelium (nasal roof) differentiate into?
- Where do the Olfactory nerve fibers connect?
-
Nasal conchae matures from choana.
Ectodermal epithelium (nasal roof)→differentiate into olfactory epithelium→olfactory receptor cells
Olfactory nerve fibers (axons) connect dorsally into the olfactory bulbs of the brain
Nasal conchae: flap like structure
Which paranasal sinus develops in late fetal stage? When do the others form?
Week 12
Only Maxillary sinuses develop in late fetal life; others form after birth
When is the Palatogenesis phase? And when is the most critcial period?
- Week 6-12: Palatogenesis phase
- Critical (6th-9th week) (If there are environmental factors like alcohol, tabacoo fetus will develop.a cleft palate)
When is the formation of the complete palate primorida? What is formed?
9-12th week: Complete palate primordia of (Primary + Secondary palate)
Where does the Primary palate (Median palatine process) originate from?
Primary palate (Median palatine process): Originates from the inter-maxillary segment (mesoderm migrating and condensing)
How is the Inter-maxillary segment formed?
Origin of the Primary palate (median palatine process)
Formed by merging of the medial nasal prominences (a wedge-shaped mass of mesenchyme) between the maxillary prominences
What develops later to give rise to the primary palate or small hard palate?
Later, primordium of premaxillary part of the maxilla develops giving rise to primary palate or small hard palate
Explain the formation of the Secondary Palate (Definitive Plate):
- Week 6-12: What emerges from the maxillary prominences?
Week 6-12: Two mesenchymal projections emerge laterally from the maxillary prominences, called the lateral palatine processes (palatal shelves)
Explain the formation of the Secondary Palate (Definitive Plate):
- Week 6: Where are the palatal shelves located?
- Week 7: What elongates?
- Week 8: What helps fuse the two palatal shelves?
- Week 12: How is the hard palate formed?
- Week-6: the palatal shelves lie inferomedially to the tongue
- Week-7: Jaws elongate & pull the tongue lower
Week-8: Hyaluronic acid in the palatine mesenchyme helps fuse the two palatal shelves.
Week-12: Bone from the maxillae moves into the palatine shelves, forming palatine bones, which forms the hard palate.
After the fromation of the hard palate what remains dorsally? And what does it fuse with?
Dorsally: Soft palate remains & fuses with the Uvula
What are the (3) functions of the Uvlva?
- Guards the nasal passage
- Makes saliva, lubricates throat
- Critical for phonation; highly evolved
Respiratory Primordium
By 4th week, what forms the Laryngotracheal groove?
4th week: a median endodermal outgrowth in the floor of the 4th pouch of the anterior foregut forms the Laryngotracheal groove
Respiratory Primordium
By the 5th week, what does the Laryngotracheal groove (4/6 pouch endoderm) undergo? What does it form and later gives rise to?
5th week: Laryngotracheal groove (4/6 pouch endoderm) undergoes ventral evagination, forming a pouch-like laryngotracheal diverticulum (lung bud), which later gives rise to the Tracheobronchial tree
Ventral evagination into the mesoderm
Respiratory Primordium
What does the Tracheobronchial tree endoderm give rise to? (4)
Tracheobronchial tree endoderm
- Pulmonary epithelium
- Larynx
- Trachea
- Bronchi
Respiratory Primordium
What does the Tracheobronchial (splanchnic) mesoderm surround? And give rise to?
The tracheobronchial tree splanchnic mesoderm surrounding the foregut diverticulum gives rise to the connective tissue, cartilage, and smooth muscle of the lung
At the end of the 5th week:
- _____________develops, partitioning the foregut into _____________ and _______________
- The __________ (endodermal tube + surrounding mesenchyme), undergo _________ to give rise to ___________ & -_____________ bronchial buds.
- Tracheoesophageal septum develops, partitioning the foregut into esophagus (dorsal) and laryngotracheal tube (ventral)
- The Respiratory bud (endodermal tube + surrounding mesenchyme), undergo branching to give rise to primary & secondary bronchial buds.
Progressive stages in the development of the trachea
By week 4, the endoderm tube gives rise to?
The endoderm tube gives rise to the pulmonary epithelium
By week 12:
- What appears in the trachea?
- What does the surrounding mesenchyme form in the trachea? (3)
- 12 weeks: Epithelial glands (goblet/mucus cells & ciliary cells) of the trachea appear
- 12 wks: The surrounding mesenchyme forms the connective tissue, muscle, & Cartilaginous rings of the trachea
Development of bronchi, Pleura and Lung Lobes
- What invades the mesenchyme and where does it emerge?
- The buds soon divide into what?
- Two buds grow into what?
- Which bronchial buds develop and what forms?
- A respiratory bud invades the mesenchyme & emerges at the caudal end of the laryngotracheal diverticulum
- The bud soon divides into two outpouchings: Two primary bronchial buds
- Two buds grow laterally into the pericardioperitoneal canals (primordial pleural cavities)
- Secondary/Tertiary bronchial buds develop & Visceral pleura & Pleural cavity is formed
Sucessive Development of bronchial buds, bronchi, & lung lobes
- The main bronchi branches into?
- The Superior Lobar bronchus are what lobes and branches?
- The Inferior lobar bronchus are what lobes and branches?
- The main bronchi→Secondary bronchi→Lobar, segmental, and intra-segmental branches
- The Superior Lobar bronchus→Right & Left Upper lobes→Segmental/intra-segmental branches
- The Inferior Lobar bronchus→Right Middle and Right Lower lobe+Left Lower lobe→Segmental/intra-segmental branches
Sucessive Development of bronchial buds, bronchi, & lung lobes
- At Week 7, how many segmental branches are in the Right and Left Lung? What do they give rise to?
- At Week 24, what is formed and how many order of branches form it?
- At Postnatal, what is formed and how many order of branches form it?
- Week 7: Segmental branches (10 in R.Lung) & (8 in L.Lung)→Bronchopulmonary segments
- Week 24: 17 orders of branches form Respiratory bronchioles
- Postnatal: 7 orders of branches form Terminal airways (up to 8 to 10 yrs of age)
Lung mesenchyme surround all the tubes and forms what? (3)
- Bronchial smooth muscle
- Connective tissue & pulmonary fibroblasts
- Vasculature & capillaries
What are 4 stages of Lung Maturation?
- Pseudoglandular Stage (6-16 Wks)
- Canalicular Stage (16-26 Wks)
- Terminal Sac Stage (24 wks-Late fetal period)
- Alveolar Stage (Late fetal period-8 yrs)
- What does the Pseudoglandular Stage resemble?
- In the Canalicular Stage, what does the terminal bronchioles differenitate into? What becomes possible at week 26?
- Pseudoglandular Stage: 6 -16 Wks: (resemble exocrine glands) (Epithelial lining mesoderm→NO gas exchange)
- Canalicular Stage: 16-26 wks
-
Terminal bronchioles →Respiratory bronchioles→ Primordial alveolar ducts→ Primordial alveoli with
vascularization
At 26 weeks: Respiration possible due to surfactant & vasculature!! (Premature babies survive!!)
- Terminal Sac Stage:
- What is there many of?
- What allows blood-air gaseous exchange?
- What type of pneumocytes are present and include function?
- What is the function of surfactants?
Terminal Sac Stage: 24 Wks-Late Fetal Period:
- Many primordial alveoli
- Blood–air gaseous exchange via epithelial sacs/endothelial capillaries
- Type I pneumocytes (gas exchange) & type II pneumocytes (make surfactant)
- Surfactants reduce surface tension & prevent alveolar collapse (atelectasis)
- Alveolar stage:
- Thin type I pneumocytes form what? That eventually becomes what?
Alveolar Stage: Late Fetal Period – 8yrs
- Thin type I pneumocytes form a alveolocapillary membrane in alveolar sacs → terminal alveolar ducts for respiration
95% of Mature alveoli develop when?
Develop postnatally from terminal alveolar ducts
What are the 3 regions defined by aortic blood supply of the early gut?
- Celiac trunk: foregut
- Superior mesenteric artery: midgut
- Interior mesenteric artery: hindgut
Development of the Esophagus
- Where does the esophagus develop from?
- What partitions the trachea from the espohagus and what does it form?
- Where is the striated muscle of the superior part of the esophagus derived from? And what does it form?
- Where is the smooth muscle of the inferior part of the esophagus coming from?
- What innervates both esophageal muscles?
- Esophagus develops from the foregut, caudal to the pharynx & dorsal to the lungs
- The partitioning of the trachea from the esophagus by the tracheoesophageal septum forms a distinct esophageal tube
- Striated muscles derived from 4 & 6th Arch forms the muscularis externa on superior part.
- Smooth muscles of the inferior part come from surrounding splanchnic mesenchyme
- Both Esophageal Muscles are innervated by branches of the vagus nerves (CN X)
- Striated muscle: paraxial mesoderm
- Smooth muscle: lateral mesoderm
Development of the Stomach, Duodenum, Liver & Pancreas
During the 4th Week:
- Foregut dilates caudal to esophagus and forms what?
- What is caudal to the stomach
- Hepatic diverticulum is near which two structures that forms what?
4th week:
- Foregut dilates caudal to esophagus→primordial fusiform Stomach
- Duodenum (foregut & part of midgut) caudal to the stomach
- Hepatic diverticulum near septum transversum & ventral mesogastrium, forms: Liver (cranially), Gallbladder & Bile duct (caudally)
Development of the Stomach, Duodenum, Liver & Pancreas
During the 5th Week:
- What emerges?
- What creates the Greater omentum?
- What creates the Lesser omentum? Where does it attach?
- Pancreatic buds (Dorsal & Ventral) & Hepatic Cords & Gall bladder emerge
- Dorsal mesentery (dorsal mesogastrium) will expand →Greater omentum (where the stomach grows)
- Ventral mesentery (ventral mesogastrium)→ Lesser omentum, attaching the liver
Septum transversum moves from cranial to ventral
Ventral mesogastrium becomes a pocket
What allows all the organs to be fixed for growth?
Ventral and Dorsal Mesogastrium
Early Development of Stomach, Duodenum, Liver and Pancreas
By Week 6:
- Dorsal stomach grows faster to form what?
- Duodenum grows and froms what?
- What structures fuse dorsally?
- On Day 42, foregut rotation (clockwise) moves what?
- Dorsal stomach grows faster to form dorsal greater curvature of the stomach (lesser ventrally)
- Duodenum grows & forms a C-shaped Ventral-loop
- Two Pancreatic buds fuse dorsally (ventral pancreatic duct rotates dorsally)
- Note: Day 42: Foregut rotation moves the bile duct to open posterior to the duodenum & pancreas
Duodenum is the axis of rotation (superior side-foregut, posterior side-midgut)
Liver flips but stays on the same side
Development of the Pancreas & Foregut rotation
5th-8th Week:
- Dorsal pancreatic bud grows how and where?
- Ventral pancreatic bud grows how and where?
- The two 90° rotations brings what structures together?
- Dorsal pancreatic bud: Grows early, cranially in the dorsal mesentery
- Ventral pancreatic bud: Grows later, caudally in the ventral mesentery
- Two 90° rotations: bring ventral pancreas + bile duct dorsally to fuse with dorsal pancreas & its duct
Development of the Pancreas & Foregut rotation
5th-8th Week:
- Ventral pancreatic duct forms what to fuse with what?
- Dorsal pancreatic duct forms what to fuse with what?
- 10% have 2nd-Opening into what?
- Ventral pancreatic duct→main pancreatic duct, fusing with the bile duct
- Dorsal pancreatic duct→ accessory pancreatic duct
fuses with the main pancreatic duct - 10% have 2nd-Opening into the minor duodenal papilla (90% Dorsal duct closes and ventral becomes the main pancreatic duct)
Development of the Liver
- Hepatic diverticulum invades into what? What expands?
- What does the septum transversum fuses with?
- Ventrally, liver is attached to what?
- Dorsally, liver is attached to what?
- Liver attach to stomach via what?
- Liver attach to duodenum via what?
- Hepatic diverticulum invades into the septum transversum & the peritoneal cavity expands.
- The septum transversum fuses with the ventral mesentery (mesogastrium).
- Ventrally, liver is attached to the parietal peritoneum by the Falciform ligament.
- Dorsally, liver is attached to the Lesser omentum (ventral mesentery of stomach/duodenum)
- Attached to stomach→ Hepatogastric ligament
- Attached to duodenum →Hepatoduodenal ligament
Falciform ligament (ventral mesentry)
Liver Development together with the Biliary Apparatus
- The hepatocytes (endoderm derived cells) form what?
- Hepatic cords anastomose with endothelium-lined spaces form what?
- Kupffer cells (from septum transversum) form what and where?
- What happens at 6th week?
- Bile formation by what and when? Secreted and opened in what?
- Cystic duct of gall bladder opens in what? To form what?
- What is the biliary apparatus?
- The hepatocytes (endoderm derived cells) form hepatic cords
- Hepatic cords anastomose with endothelium-lined spaces→hepatic sinusoids
- Kupffer cells (from septum transversum) form macrophages in hepatic sinusoids.
- Hematopoiesis →6th week in the hepatic sinusoids
- Bile formation by hepatocytes→12th week & is secreted in bile canaliculi, opening in the bile duct
- Cystic duct of gall bladder →open in the hepatic duct to form the bile duct
- Biliary Apparatus: (Hepatic ducts + Gall bladder + Cystic duct + Bile duct)
Spleen in a rotating foregut
What is formed by the dorsal megastrium in the 5th week?
5-Week: Spleen as a vascular lymphatic organ, formed by dorsal mesogastrium cells
By week 5, the stomach rotates how? What is position of the liver a spleeen? And what is fromed d/t the rotation?
The stomach rotates clockwise: the liver→right & spleen→left, forming the Gatrosplenic ligament ventrally & Splenorenal ligament dorsally
- Before rotation all organs method were in a linear position (liver most ventral, spleen most dorsal)
- Gastrosplenic ligament: Spleen to stomach
- Splenorenal ligament: Spleen to mesonphros (rudimentary kidney)
- Ligaments all dorsal mesentry
Retroperitoneal position of the pancreas
By week 6, what allows the retroperitoneal positioning of the pancreas?
6-Week:
Left surface of the dorsal mesogastrium fuses with the peritoneum over the left kidney, allowing retroperitoneal positioning of the pancreas. (kidney behind pancreas)
Easily fuses with the body wall d/t mesodermal origin of both the wall and pancreas (kidney also fuses)
What does the Splenic mesenchyme differentiate into? (3)
Splenic mesenchyme differentiate→the capsule, connective tissue framework, & spleen parenchyma
What is the function of the Spleen?
For hematopoiesis in fetal life; & retains the potential to form blood cells in adults too!
What are the Midgut derivatives (7)? And where does the midgut end?
- Distal duodenum
- Opening of the bile duct
- Small intestine
- Cecum
- Appendix
- Ascending colon
- Right 2/3rd of the transverse colon
- It ends where the branches of the superior mesenteric artery ends
When and how does Umbilical Herniation occur?
Day 36:
1. Growing midgut forms a ventral U-shaped loop of intestine (midgut loop) in the extraembryonic coelom (proximal umbilical cord), connecting to Yolk sac via the Omphaloenteric duct
2. Three 90° rotations = 270° rotations on the superior mesenteric artery axis herniates the midgut intestine (into the omphalenteric duct)
3. 10th week: Retraction of Intestinal Loops
4. Cecum descends down to get correct colon orientation.
Fixation of Midgut Intestines:
- The enlarged transverse colon presses what?
- Which organs become retroperitoneal?
- What is the Dorsal intestinal mesentery bound to? What does it attach to?
- What other organs become retroperitoneal?
- Greater Omentum mesentery fuse with what?
- Other derivatives of the midgut loop (jejunum & ileum) retain what?
- The enlarged transverse colon presses the duodenum & pancreas against the posterior (dorsal) abdominal (parietal) wall
- Thus, duodenum, pancreas→Retroperitonal
- Also, Dorsal intestinal mesentery bound to colon attaches to the posterior abdominal wall
- So, the Ascending colon+Descending colon→ Retroperitoneal
- The Greater Omentum mesentery fuse with the Transverse colon mesentery, fixing it
- Other derivatives of the midgut loop (jejunum & ileum) retain their mesenteries (fan-shaped) and do not attach to the abdominal / body wall
What organs retain in their mesenteries and do not attach to the abdominal/body wall?
jejunum & ileum
Midgut derivatives
Midgut: Cecum and Appendix
- What happens at week 6?
- What is the Appendix?
- How does the appendix positioned?
- Week 6: The Cecal swelling (Cecum+Appendix) at the caudal limb of the midgut loop.
- Appendix: A long tube arising at the distal end of cecum, grows in the fetus & after birth.
- Posterior to the cecum (64%); Reterocecal Appendix
- Anterior to the cecum (36%); Retrocolic or Reteropelvic Appendix (1%)
Hindgut: Partitioning of the Cloaca & Anal Canal
- What is the cloaca?
- Cloaca (_ lining) is in contact with what? forming what?
- Allantois attaches to what?
- What degenerates as the rectum forms?
- Cloaca is a chamber into which the hindgut and allantois empty waste.
- Cloaca (endodermal lining) is in contact with the surface ectoderm, forming a two layered cloacal membrane (endoderm + ectoderm of anal pit)
- Allantois (finger-like diverticulum) attaches to the cloaca ventrally.
- Post-anal portion degenerates as the rectum forms.
Hindgut: Partitioning of the Cloaca & Anal Canal
- What develops in the angle between the allantois and hindgut?
- Uro-rectal septum partitions the Cloaca into 3 Endodermal parts:
- Cloacal membrane ruptures by what? what is temporarily closed?
- Mesenchymal cells do what? And form what?
- A wedge of mesenchyme, the Uro-rectal septum(mesoderm origin), develops in the angle between the allantois and hindgut.
- Uro-rectal septum partitions the Cloaca into 3 Endodermal parts: (1) Rectum; (2) Superior Anal canal; (3) Urogenital sinus (Urinary bladder)
-
Cloacal membrane ruptures by apoptosis; anorectal lumen is temporarily closed by an epithelial (endodermal origin) plug
8.Mesenchymal cells proliferate & ** push surface ectoderm** around the epithelial anal plug & recanalization occurs by apoptosis of epithelial plug; this forms the Ectodermal Anal Pit
Anal Canal
- Superior 2/3rd of anal canal is what?
- Inferior 1/3rd develops from what?
- Hindgut & Anal pit are separated by what?
- About 2 cm superior to the anus is what?
- Hindgut: has what type of epithelium?
- Above Hilton’s white line:
- Below Hilton’s white line:
- The muscular wall of the anal canal are derived from what?
- Superior 2/3rd of anal canal→Hindgut
- Inferior 1/3rd develops from the Anal pit
- Hindgut & Anal pit are separated by a Pectinate line.
- About 2 cm superior to the anus is the “Anocutaneous line” (Hilton’s white line).
- Hindgut: Has Simple Columnar epithelium
- Above Hilton’s white line: Anal Pit has Stratified squamous epithelium
- Below Hilton’s white line: Anal pit near the anus is Keratinized Stratified squamous epithelium with sweat glands & sebaceous glands
- The Muscular Wall of the anal canal are derived from splanchnic mesenchyme
Urogenital System:
- Day 18: the urogenital system develops from what?
- Day 28: longitudinal elevation of Intermediate mesoderm, the urogenital ridge, flanks what?
- Urogenital ridge gives rise to (2)?
- Day 18: the urogenital system develops from intermediate mesenchyme
- Day 28: A longitudinal elevation of Intermediate mesoderm, the urogenital ridge, flanks the dorsal aorta
-
Urogenital ridge gives rise to:
1. Urinary system (nephrogenic cords)
2. Genital System (Gonadal ridge)
Function of:
1. Kidneys:
2. Ureters:
3. Urinary bladder:
4. Urethra:
- Kidneys: produce and excrete urine.
- Ureters: transport urine: kidneys→urinary bladder
- Urinary bladder: stores urine temporarily.
- Urethra: discharges urine: bladder→outside
Explain the 3 sets of Nephroi Formation
- The Pronephroi (4th week: rudimentary & degenerates)
- The Mesonephroi (Fetal (5-12th Wk): functions briefly & disappears)
- The Metanephroi (Forms the TWO Permanent Kidneys) flanking the dorsal Aorta.
All originate from the Intermediate Mesoderm
NOTE: Mesonephric duct remains →male reproductive system
What is the overlap of mesonephroi and metanephroi?
- Over: 9-12 week of mesonephroni+metanephroni
- After 12th week, metanephroi creates permanent kidneys and forms urinary bud
Mesonephric duct remain as what?
male reproductive system
- What is Mesonephroni (intermim kidney) role?
- What structures do they consist of?
- Where do the tubules open into? Where are they dervied?
- Where do the Mesonephroni ducts open into?
- When do they degrade?What remains?
- What do the Mesonephric tubules eventually form?
Mesonephroi: Day 28: Elongated excretory interim kidneys before permanent kidney start functioning (remains for 8 weeks)
- Glomeruli + Mesonephric tubules
- Tubules open into bilateral mesonephric ducts, derived from pronephric ducts
- Mesonephric ducts open into the cloaca
- Mesonephroi degenerate by week 12; Mes. Tubules remain
- Mesonephric Tubules→”Efferent ductules” of the testes, which connects the epididymis to the testis
Development & Function of the Mesonephroi
- By 5 weeks, what does the Nephrogenic cords form?
- By Week 8, what structures fuse?
Week 11
- The expanded medial end (cup) of the mesonephric tubule is invaginated by what? And forms what?
- Aorta-> Afferent vessels bring blood to where?
- Efferent vassals-> takes back filtered blood to where?
- Fluid waste goes where?
- What is formed at the gonadial ridge?
- 5-week: Nephrogenic cords form mesonephric tubules & mesonephric duct
- Week 8: Mesonephric tubules & mesonephric duct fuse.
Week 11:
- The expanded medial end (cup) of the mesonephric tubule is invaginated by blood vessels coming from the aorta to form a glomerular capsule.
- Aorta→Afferent vessels bring blood to the capsule
- Efferent vassals→takes back filtered blood→Posterior Cardinal Vein
- The fluid waste→Mesonephric duct→Cloaca.
- Gonad Primordia are formed at the gonadal ridge.
- What are the primordia of the permanent kidneys?
- What happens of week 5 of kidneys?
- Urine formation continues when?
- Where is urine excreted into what?
- Metanephroi are the primordia of the permanent kidneys
- 5th week: Begin to develop; functional by 9th week(Overlap!!).
- Urine formation continues throughout fetal life.
- Urine is excreted into the amniotic cavity – part of the amniotic fluid.
Kidneys develop from two sources. What are they?
- The ureteric bud (is metanephric diverticulum –originate from mesonephric duct) →intermediate mesoderm
- The metanephric blastema (metanephric mass of mesenchyme)-> cap meschyme outside
BLADDER IS ENDODERMAL
Ureteric Bud branches are? List the different structures?
Ureteric Bud branches→collecting parts of the adult kidney:
- Ureter, Renal pelvis, Calyses (Major & Minor Calyx) & Collecting tubules.
Ureteric Bud invades the what and induces what?
Ureteric Bud invades the intermediate mesoderm and induces the metanephric blastema (metanephric mass of mesenchyme) to form many NEPHRONS, linking collecting tubules (derived from ureteric bud)
Development of Nephrons (structural & functional units of the kidney):
- When does nephrogensis begin?
- Metanephric tubules of blastema (primordial nephrons), connect with what and to form what?
- Cap mesenchym goes through what and forms what?
- The proximal tubule gets invaginated by what?
- Nephrogenesis begins by week 8
- Metanephric tubules of blastema (primordial nephrons), connect with the collecting tubules to form uriniferous tubules
- Cap mesenchyme-> mesenchymal-to-epithelial transition (EMT) & form Nephron epithelium
- The proximal tubule gets invaginated by glomeruli & become cup shaped
What is the nephron consisted of? (3)
- Nephron loop (Henle Loop)
- Glomerulus
- Glomerular (Bowman Capsule)
What are the positonal changes of the kidney?
- Primordial kidneys lie close to each other in the pelvis (ventral to the sacrum)
- As the abdomen and pelvis grow, the kidneys gradually ascend to the abdomen, protected by the rib-cage & move farther apart.
- As they move up the renal arteries change their blood supply: (1) Common iliac arteries to (2) Abdominal aorta to (3) new branches from the Aorta as it ascends.
- The Ureters elongate as the Urinary bladder remains fixed in the pelvic region
Development of Gonads are formed from what?
cells from the umbilical vesicle
- The gonads (testes or ovaries) produce what?
- The gonads are derived from three sources:
- The gonads (testes or ovaries) produce sex cells (sperms or oocytes).
- The gonads are derived from three sources:
- Mesothelium: mesodermal epithelium lining the posterior abdominal wall
- Underlying mesenchyme (embryonic connective tissue)
- Primordial germ cells (PGCs; endodermal undifferentiated sex cells)
Explain the Indifferent Gonads development until Week 7
- Day 24: Primordial germ cells (PGCs) from the Umbilical vesicle (Yolk Sac) migrate via the dorsal mesentery into both Urogenital ridges or Gonadal ridges
- A medial bulge in the mesonephros is the gonadal ridge or primordium of gonad
Gonadal Cortex and Medulla containing PGCs:
- Migration of PGCs via what? to where?
- Mesodermal epithelium (abdominal wall) covers what and forms what?
- Gonadal cords grow where?
- The indifferent gonads (male or female) now consist of what?
- Migration of PGCs via hind gut dorsal mesentery to the gonadal ridge
- Mesodermal epithelium (abdominal wall) covers the PGCs & form the gonadal cords.
- Gonadal cords grow in the underlying mesenchyme (Medulla)
- The indifferent gonads (male or female) now consist of an external cortex (epithelial layer) & an internal medulla.
XY embryo (Male):
- What gene is present
- Gonadal cords differentiate into what?
- The medulla differentiates into what?
- The Y-Chromosome with an SRY-gene (sex- determining region on the Y chromosome) make TDF (Testis Determining Factor), which determines testicular differentiation
- Gonadal cords differentiate into Seminiferous Cords ->Seminiferous tubules with PGCs
- The medulla differentiates into a testis, and the cortex regresses
XX embryo (Female):
- What type of pathway?
- The Cortex differentiates into what?
- Default Pathway (no Y-chromosome)
- The Cortex differentiates into an Ovary (Oocytes resides), and the medulla regresses.
XY embryo (Male): Development of Testes:
- Seminiferous cords condense, branch, anastomose to form what?
- Seminiferous cords detach from what?
- Seminiferous cords go into?
- What does sertoli cells do?
- Rete testis connects with?
- Mesonephric duct becomes what?
- Mature testis where?
- Seminiferous cords condense, branch, anastomose to form the rete testis
- Seminiferous cords detach from the cortex as the fibrous tunica albuginea develops.
- Seminiferous cords-> seminiferous tubules; surrounding mesenchyme forms Leydig cells (produced by medulla that has mesodermal cells); secrete testosterone, inducing masculine differentiation
- Sertoli cells (produced by cortex epithelium) nourishes the Spermatogonia (derived from PGCs)-> SPERMS
- Rete testis connects with mesonephric tubules, which then becomes efferent ductules.
- Mesonephric duct->duct of the epididymis
- Mature testis: Out of the body before birth; (cooler by 40C)
- No sperms till puberty.
XX embryo (Female): Development of Ovaries:
- No Y, thus X chromosome genes determine what?
- Gonadal cords form what?
- Cortical cords extend where?
- Cords break into what?
- Oogonium-> _ -> _
- The ovary separates from what? what is it suspended by?
- No Y, thus X chromosome genes determine ovarian development.
- Gonadal cords form a rudimentary rete ovarii-> degenerates.
- Cortical cords extend in the mesenchyme & incorporate PGCs.
- Cords break->primordial ovarian follicles, each with a PGC; (Oogonium). No Oogonia from postnatally.
- Oogonium->Primary Oocyte→OVUM
- The ovary separates form the regressing mesonephros & is suspended by Ovarian ligament & the surrounding mesentery, the Mesovarium.
