Prenatal Development

Pediatric Dysphagia module #1

Label the maternal-fetal structures that facilitate prenatal life.

Uterus, placenta 

Describe the path of blood flow from the mother to the fetus and back.

1. Maternal artery: oxygen and nutrient rich blood from the mother is brought to the placenta via the maternal artery. 

   1. Then deposited into intervillous space 

2. Umbilical vein: vili that project into this space connect to the fetal side of the placenta facilitate diffusion of these molecules into the fetal cardiovascular system for utilization through the fetal vein 

3. Umbilical artery: oxygen and nutrient poor blood are carried form fetal systemic circulation to the intervillous space of the placenta by means of the fetal artery 

Maternal vein: oxygen and nutrient poor blood diffuses from intervillous space into the maternal cardiovascular system for processing through maternal vein

Identify the medical condition for the abbreviations HIE and IUGR (spelling included). And Describe intrauterine growth restriction and hypoxic ischemic encephalopathy

• Hypoxic Ischemic Encephalopathy (HIE): Fetal brain injury resulting from lack of oxygen during delivery. 

  • Typically caused by rupturing of the uterus during contractions

Intrauterine growth restriction (IUGR): restricted fetal growth that can be caused by placental structural deficits that restrict perfusion or diffusion of nutrients and gasses.

Identify the length of term gestation.

• 9 months

Identify periods of prenatal development, the gestational ages they span, and the primary processes that occur.

• Pre- Embryological Period (1-3 weeks): Cellular changes occurring from fertilization to the formation of the embryonic disk.

• Embryologic Period (3-8 weeks): Period of prenatal development when the structures necessary to sustain postnatal life are created.

Fetal Period (8-40 weeks): Period of prenatal development when the organs developed during the embryologic period mature for postnatal function.

Annotate birth age using weeks and days nomenclature.

• Because so much happens during each day of prenatal development, clinicians will record an infant’s age at birth using the week and day of development out of a seven-day week on which they were born 

  • (ex. 37 4/7 weeks = 37 weeks and 4 days).

Identify the number of chromosomes in the egg, sperm, and zygote.

• Egg: 23 chromosomes 

• Sperm: 23 chromosomes 

Zygote: 46 chromosomes

Describe the primary cellular changes that occur from fertilization to cell implantation.

• The egg (oocyte) is housed within the ovaries, where it undergoes meiosis to be reduced from 46 to 23 chromosomes.

• Once meiosis is complete , it departs through  ovaries and travels down into the

• fallopian tubes.

•  Here it is met by the sperm, which is also composed of 23 chromosomes. 

• The union of the oocyte with the sperm forms the 46 chromosome zygote. 

• Formation of the zygote marks the start of embryologic development and simply put, is the future child in its earliest form.

Cell Division: Over the subsequent 5 days, the cells of the zygote will repeatedly divide as it travels down the fallopian tubes towards the uterus for implantation. Initially this division creates strict replicas of the parent cell, however on day 5, the division starts to take on a different form with the cells taking on specific roles, and those with similar roles starting to cluster together.

Describe the source of most deficits that occur during this stage of development.

• Deficits in this stage of development are due to errors in genetic code 

  • Deficits in parent germ line 

  • Errors in meiosis or mitosis 

    • Typically responsible for miscarriages

Describe the difference between differentiated and undifferentiated cells and the process through which cells become differentiated.

• Undifferentiated cells = stem cells, cells that can become any type of cell in the future 

• Differentiated cells = Cells with a specific function 

  • Cells come together to form distinct layers, within these layers, the embryonic disk forms 2 semicircles each with their own cell type. 

  • 15 days into development the embryonic disk develops an

ingression in the top cell layer called the primitive streak. When cells move through the primitive streak, they become differentiated cells that are "branded for future roles”

Describe how gastrulation occurs and what its function is.

Gastrulation: characterized by ingression of un-differentiated cells through the primitive streak and emerging on the other end to become differentiated cells each branded with a specific function

Identify what structure appears and initiates the start of gastrulation.

Primitive streak

Label the layers of the trilaminar cellular disk and identify the future feeding-swallowing related structures they will give rise to

• During gastrulation the ingression of cells through the top cell layer forms the 3 layer embryonic disk 

  • Layer 1 = ectoderm: future nervous system, lining of nasal and oral cavities 

  • Layer 2 = mesoderm: skeleton, muscles 

Layer 3 = endoderm: digestive tract, respiratory tract

Describe what occurs during neurulation and identify the structure that emerges to initiate this process.

• Occurs after formation of the mesoderm during gastrulation 

Neurulation: Cells within the mesoderm begin to facilitate development of the notochord which is the development of the central nervous system

Identify what fetal structure the neural tube will become.

• Central nervous system

• Cranial portion = future cortex 

• Medial and caudal portion = future spinal cord

Identify when the primitive cranial nerve nuclei that control feeding and swallowing first emerge.

4 weeks into the pregnancy

Describe what spina bifida and encephalocele are caused by and how they present.

• spina bifida: condition caused by incomplete closure of the neural tube, often times, resulting in a pouch protruding out the back beyond the spinal cord 

  • Most severe cases lead to nerve damage in the spinal cord that can impact ambulation 

• Encephalocele: caused by incomplete neural tube closure, site of incomplete closure is on the cranial portion. 

  • Results in pouch protruding from the skulls that is filled by the brain and meninges and results in brain damage

Describe how the craniofacial structures are formed

Through the development of the first 4 pharyngeal arches that give rise to the bones, cartilages and muscles of the face, pharynx and larynx

Identify which pharyngeal arches form the lip, alveolar ridge, palate, larynx, and oropharyngeal musculature.

Pharyngeal arch 1:  Forms the lips, alveolar ridge, palate and chin 

Pharyngeal arch 2-4: Make up the bones and muscles of the larynx as well as oropharyngeal musculature for speech and swallowing

Name the two branches of pharyngeal arch 1.

Maxillary = Forms lip, alveolar ridge and palate

Mandibular = forms the chin

Identify the structure that gives rise to the peripheral cranial nerves that control feeding and swallowing.

• Neural crest (cells): create peripheral nerves for oropharyngeal sensation and movement 

Describe cause and manifestation of orofacial clefts and Pierre Robin Sequence

• Orofacial crests: incomplete midline fusion of the maxillary branch of pharyngeal arch 1, results in gap of hard or soft tissue where fusion should've occurred 

  • Can lead to cleft lip or palate and can influence an infant's ability to generate suction during feeding 

• Pierre Robin sequence: result of impairments in genes regulating developmental sequences of the tongue, lip and mandible 

  • Problems with breathing due to unstable airway and feeding deficits due to poor respiratory - swallow coordination 

Identify the three deficits commonly seen in Pierre Robin Sequence

Cleft, micrognathia and glossoptosis 

Describe what cellular layer forms the gastrointestinal tract, and how this is formed.

Endoderm cells become the respiratory and digestive tract

Identify how the larynx, trachea, and lungs are formed from the tracheal diverticulum.

• one long tube running from the stomodeum, the future mouth, to the anus. and eventually an offshoot pouch appears near the pharyngeal arches.

  • This pouch is called the tracheal diverticulum, and though it starts out small, it will elongate and increase in complexity to become the larynx, trachea, and lungs

Describe the source and manifestation of esophageal fistula, esophageal atresia, and laryngeal cleft.

• Esophageal fistula is a condition where there is a hole between the esophagus and the trachea as a result of impaired tracheoesophageal septum development. 

  • The hole results from the lower part of the esophagus connecting to the trachea, while the upper part, coming down from the pharynx, ends in a dead-end pouch.

    •  Both of these can cause profound airway compromise as they cause whatever enters the esophagus (i.e. food, reflux) to go directly into the lungs and require immediate surgical repair.

• Laryngeal cleft: caused by incomplete formation of the tracheoesophageal septum leading to open communication between esophagus and airway 

  • the extent of issue can be minimal, just a slight notch in the cricoid cartilage that may not cause any functional impairment, or it can be large, extending from the cricoid down through the trachea.

    • severe forms of this condition cause esophageal content to go directly into the lungs and require surgical repair.

Identify the gestational age when the first primitive feeding movements can be observed and describe how these presentations change with development.

• 12 weeks gestation 

  • Critical for successful postnatal feeding 

  • Early feeding patterns are shaky and immature, therefore feeding with occasionally lack refined control

Describe the purpose of fetal sucking and swallowing patterns.

• Neuromaturation over the subsequent 12 weeks will improve/finesse and result in more frequent utilization and precision in execution. In addition to providing the infant with safe opportunities for feeding practice

  • Patterns also serve to regulate amniotic fluid levels to provide infant with key nutrients for development

Define polyhydramnios and what it can implicate for swallowing integrity.

• polyhydramnios: Condition characterized by excessive accumulation of amniotic fluid which results from deficits in oropharyngeal swallowing 

  • Deficits may be similar to those caused by esophageal arteria or profound neurologic deficits that inhibit swallowing 

    • Presence does not necessarily indicate swallowing impairment 

Describe how neuromaturation takes place including its proliferation and pruning process.

• Makes primitive movements as well as bodily systems more refined  

• Neurons on created then refined

  • Pruning = refining neural networks so that only the most efficient neural networks are present

Identify the stages of lung development when primitive alveoli and surfactant development first initiates.

• Canalicular stage: Terminal sacs (primitive alveoli) and surfactant synthesis first initiates 

  • Around 17-26 weeks post gestation 

  • Surfactant synthesis: Creates film over interior wall of alveolar sacs to optimize gas exchange 

Identify the stage of lung development when maturation of the above structures and the thinning of epithelial lining make oxygenation more efficient.

Saccular stage

Identify what age lung development completes.

alveolar