Module 3: Development of the Thorax, Head, and Placenta Flashcards
Cavities in the body
-pleural
-pericardial
-peritoneal
Pleural cavity
-houses the lungs
-found within thoracic cavity
Pericardial cavity
-houses the heart
-also found within thoracic cavity
Peritoneal cavity
-surrounds several organs found in abdomen and pelvic cavity
Formation of the diaphragm
-formed by fusion of the septum transversum, pleuroperitoneal folds and mesenchymal ingrowths
Septum tranversum
-grows from ventral body wall
-separates the heart from the developing liver
Which way is the septum transversum pulled when folding
-pulled down
-partially separates the thoracic and peritoneal cavities
Pleuropericardial folds
-form on lateral body wall
-each contain a phrenic nerve
Pleural and pericardial cavities medial growth
-pleuropericardial folds grow medially towards eachother while lungs and heart continue to develop
Pleural and pericardial cavities
-pleurocardial folds fuse with eachother dividing the thorax into pleural and pericardial cavities
When does lung development begin
-day 22
Respiratory diverticulum
-forms as an outpocketing in ventral wall
-expands into splanchnic mesoderm which will cover the lung buds as well as the entire gut tube
Tracheal buds
-when respiratory diverticulum grows, it pinches off and elongates to form 2 parallel tubes (trachea and esophagus)
When do paired tracheal buds begin forming
-week 4
Bronchioles formation
-tracheal buds form left and right bronchi
Alveoli formation
-development progresses after 16 weeks as alveoli form and extensive vascularization occurs
When do fetal breathing movements occur
-week 20 or 21
What does the fetal inhale and exhale
-amniotic fluid
When do breathing movements happen until
-until birth
-help to tone the muscles in preparation for breathing after birth and a sign of good health
Tracheoesophageal fistula
-abnormal connection (fistula) between the esophagus and trachea
-due to abnormal separation of the tracheal bud from esophagus during development
How many pharyngeal arches are there
-6
Arch 1
-cranial nerve 5
-muscles of mastication
-bones of neck and inner ear
Arch 2
-cranial nerve 7
-muscles of facial expression
-bones of neck and inner ear
Arch 3
-cranial nerve 9
-stylopharyngeus muscle
-part of hyoid bone
Arch 5
-regresses and doesn’t form anything
Arch 4 & 6
-cranial nerve 10
-constrictor muscles of the pharynx
-intrinsic muscles of the larynx
-cartilages of the larynx
Pharyngeal clefts
-ectodermal lined recesses that appear on the outside of the pharynx between arches
What clefts form temporary cervical sinus
-2-4
What does the first cleft invaginate to form
-the external auditory meatus membrane
Pharyngeal pouches
-endodermal lined pouches that form on the inside of the pharynx between the arches
Pouch 1
-auditory tube
-middle ear cavity
Pouch 2
-palatine tonsil
Pouch 3
-inferior parathyroid gland
-thymus
Pouch 4
-superior parathyroid gland
-ultimobranchial body
Anterior 2/3 of tongue
-mobile portion
Posterior 1/3 of tongue
-closest to throat
-rough appearance
Terminal sulcus
-junction between anterior and posterior tongue
Foramen cecum
-apex of terminal sulcus
-indicates place of origin of thyroid gland
Epiglottis
-helps prevent food and liquids from entering larynx and trachea
Arch 1 tongue development
-median tongue bud marks beginning of development
-pair of lingual lateral swellings develop
Arch 2 tongue development
-rapidly overgrown by swellings of 3rd and 4th arches
-no contribution
Arch 3 tongue development
-give rise to portion of the posterior 1/3 of tongue
Arch 4 tongue development
-give rise to remainder of posterior 1/3 of tongue
-also forms epiglottis
What is the thyroid gland formed from
-thyroid diverticulum
Where is thyroid diverticulum located
-caudal to the 1st pharyngeal arch
As thyroid descends, what does it remain connected to
-thyroglossal duct
What causes formation of thyroglossal duct cysts
-failure of thyroglossal duct to close before birth
Parathyroid glands migration
-once formed, attach to thyroid gland and descend from top of ventral pharynx to final location at level of 4th arch
Thymus migration
-migrates posteriorly and medially, independent of thyroid gland
-after migration it is located inferior to thyroid and parathyroid glands
Mandibular prominences
-derived from first arch mesenchyme
-make up lower stomodeal boundary
Maxillary prominences
-derived from the mesenchyme in first pharyngeal arch
-forms lateral boundaries of stomodeum
Frontonasal prominence
-derived from cranial neural crest mesenchyme
-upper border of stomodeum
Invagination of the face
-frontonasal prominence develops 2 sets of swellings called nasal placodes
-nasal placodes form the nasal pits
-which then results in formation of lateral and median nasal prominences
Fusion of the face
-maxillary prominences increase in size and merge laterally with mandibular prominences to form the cheeks
What does the nasolacrimal groove form
-the nasolacrimal duct
Chorion of placenta
-membrane that produces chorionic fluid
-outermost membrane
Amnion of placenta
-membrane that holds amniotic fluid
-innermost membrane containing fetus
Umbilical cord
-cord like structure arising from naval that connects fetus with placenta and contains 2 umbilical arteries and veins
Chorionic villi
-fingerlike projections that contain genetic material of the fetus
Chorionic villi purpose
-serve to increase surface area
-maximize contact with maternal blood
Primary villi
-formed when cytotrphoblast penetrates syncytiotrophoblast and expands
Secondary villi
-in week 3
-develop as extraembryonic mesoderm grows
Tertiary villi
-end of week 3
-characterized as vascularization of secondary villi
Anchoring villi
-tertiary villi that grow towards decidua basalis
Branching villi
-grow from anchoring villi
-increase surface area for exchange
When does spinal remodelling happen
-2nd month
Spinal artery remodelling
-maternal spiral arteries undergo remodelling to produce low resistance, high blood flow conditions to meet demands of fetus
How does spinal artery remodelling happen
-they undergo a epithelial to endothelial differentiation to increase diameter and reduce resistance
When does placenta development mainly happen
-3-4 months
When are the chorion frondosum and laeve formed
-month 3
Chorion frondosum
-formed from villi at embryonic pole
Chorion laeve
-formed from villi at abembryonic pole
When is the fetal membrane formed
-month 4
Fetal membrane formation
-chorion laeve fuses with decidua parietalis and the amniotic and chorionic membranes fuse
When does cytotrophoblast membrane dissipate
-month 4
Why does cytotrophoblast layer need to dissipate
-to decrease distance for diffusion and gas exchange
When does the placenta divide into cotyledons
-month 4
How are cotyledons formed
-from materal decidua protruding into intervillous space to create decidual septa
How do cotyledons divide placenta
-into lobules
What is the fetal side called
-villous chorion
What does the fetal side form
-the chorionic sac including the amnion, chorion, yolk sac, and allantois
What is the maternal side called
-the decidua
3 parts of the decidua
-decidua basalis
-decidua capsularis
-decidua parietalis
Decidua basalis
-deep at implantation site
Decidua capsularis
-covers implantation site
Decidua parietalis
-everything else
Exchange from maternal to fetal
-mainly oxygen and nutrients
Exchange from fetal to maternal
-mainly for elimination of carbon dioxide and other waste materials
Fetal circulation
-umbilical cord is not directly connected to mothers circulatory system
-allows transfer of materials to and from mothers blood without direct mixing
What do umbilical arteries carry
-deoxygenated, nutrient depleted blood from fetus to placenta
What do umbilical veins carry
-oxygen, nutrient rich blood from placenta to fetus
Maternal circulation
-blood supply is derived from spiral arteries of endometrium
How does maternal blood flow
-flows around villi where exchange occurs
-instead of being bounded in blood vessels
Reduction in maternal blood flow
-reduced size of fetus
What is the stomodeum
-primitive oral opening
Primary palate
-forms via the fusion of 2 medial prominences
What teeth are within the primary palate
-4 incisors of the upper jaw
Secondary palate
-forms via outgrowths of maxillary prominences called palatine shelves
Migration of the palatine shelves
-palatine shelves are outgrowth from maxilla
-these shelves migrate obliquely downwards on either side of tongue
Fusion of the palatine shelves
-as the mouth grows and the tongue drops down, the palatine shelves fuse creating the secondary palate
Fusion of the palates
-anteriorly, the shelves fuse with the triangular primary palate incompletely
-this formed the incisive foramen at the midline
Abnormal palate development: Cleft lip
-results from the palates and facial structures not developing properly
