Systems Embryology

Question 1

Name the three primary germ layers and the systems they develop into, including specific examples of organs or structures for each.

Answer 1

The three primary germ layers are the…

• Ectoderm: develops into the nervous system, skin, and sensory organs like the eyes and ears.
• Mesoderm: forms muscles, bones, the cardiovascular system, and connective tissues
• Endoderm: develops into the digestive and respiratory systems, including organs such as the lungs and liver.

Question 2

At what age does ossification begin and end in human development, and what is ossification?

Answer 2

• Ossification is the process of bone formation.
• It begins around the 6th or 7th week of embryonic development and continues until about age 25.

Question 3

How do the bones of the skull form, and what types of ossification are involved?

Answer 3

• The bones of the skull form through intramembranous ossification, where mesenchymal cells differentiate directly into bone-producing cells.
• Additionally, some skull bones form via endochondral ossification, where a cartilage model is gradually converted into bone.

Question 4

Describe the development process of the vertebrae, ribcage, and sternum.

Answer 4

• The cells of the vertebrae differentiate into a hyaline cartilage model, which grows and ossifies into bone through endochondral ossification.
• Ribs originally develop as part of the cartilage from the vertebrae but separate in the thorax region by week 8.
• The sternum forms as paired hyaline cartilage models on either side of the anterior midline, beginning in the 5th week.

Question 5

What is achondroplasia, and what are its characteristics and inheritance pattern?

Answer 5

• Achondroplasia is the most common form of skeletal dysplasia, primarily affecting long bones.
• It is characterized by short stature, a large skull, and spinal curvature.
• Achondroplasia is inherited as an autosomal dominant trait.

Question 6

What are pectus excavatum and pectus carinatum, and what are their clinical presentations?

Answer 6

• Pectus excavatum is a chest wall deformity where the sternum is sunken, leading to symptoms like easy fatigue, dyspnea on mild exertion, decreased exercise tolerance, chest pain, and tachycardia.
• Pectus carinatum is characterized by a protruding sternum; while mental health and body image may be affected, it generally does not impact the cardiopulmonary system or other parts of the skeletal system.

Question 7

What is Duchenne Muscular Dystrophy (DMD), including its genetic cause, typical onset age, and progression?

Answer 7

Duchenne Muscular Dystrophy (DMD) is a severe X-linked recessive disorder caused by mutations affecting the protein dystrophin.

• It typically presents in males around age 2–3 with muscle weakness starting in the lower limbs and is usually diagnosed around ages 5–6.
• Patients are often wheelchair-bound by age 12, and the general lifespan is around age 35 due to cardiovascular and pulmonary complications.

Question 8

List and describe the hallmark signs and gait abnormalities associated with DMD.

Answer 8

Hallmark signs of DMD include…

• hypotonia of musculature overall
• lack of head control
• muscle weakness more pronounced in the lower extremities and proximal muscles
• Gower’s sign
• pseudohypertrophy of the calves
• gait abnormalities (Trendelenburg gait, waddling, gluteal lurch)

Question 9

What are the physical therapy implications and interventions for patients with DMD?

Answer 9

Physical therapy for DMD focuses on increasing range of motion and preventing contractures.

• Early goals include family education, use of ankle-foot orthoses (AFOs) in the ambulatory stage to maintain gastrocnemius and soleus length, progressing to knee-ankle-foot orthoses (KAFOs) to prolong walking and prevent contractures, and using a standing frame after ambulation ceases to improve bone mineral density.
• Aquatic therapy is also highly recommended to improve strength and flexibility.

Question 10

What is Spinal Muscular Atrophy (SMA), and how does it affect the body?

Answer 10

• Spinal Muscular Atrophy (SMA) is a genetic disorder characterized by degeneration of alpha motor neurons, leading to muscle weakness and atropy.
• Severity ranges based on the type of SMA, and while the lower extremities are more affected, all muscles can experience changes.

Question 11

Describe the characteristics and prognosis of SMA Type 0 and Type 1.

Answer 11

- Type 0 SMA is the congenital form presenting with severe hypotonia and respiratory complications; fetal movement is reduced, and arthrogryposis may be present.

• Prognosis is extremely poor.

- Type 1 SMA (Werdnig-Hoffman) has onset within six months and presents with hypotonia, areflexia, lack of head control, limited movement into flexion and extension, respiratory issues, and dysphagia.

• These patients are ‘non-sitters’ with a poor prognosis and a lifespan around 2 years.

Question 12

What are the key features and life expectancy of SMA Type 2 and Type 3?

Answer 12

- Type 2 SMA (Dubowitz) onset is between 6–18 months, with lower extremity weakness, scoliosis, restrictive lung diseases, hand tremors, and contractures.

• Patients are ‘sitters’ with a lifespan into their twenties and beyond, with respiratory failure as a likely cause of death.

- Type 3 SMA (Kugelberg-Welander) onset is after 18 months; patients experience lower extremity weakness but become ambulatory.

• They may have delayed motor milestones, exaggerated lumbar lordosis, Trendelenburg gait, toe walking, Gower’s sign, and muscle fasciculations. They are ‘walkers’ with a normal lifespan.

Question 13

What are the physical therapy implications and goals for patients with SMA?

Answer 13

• Physical therapy aims to preserve function by working on stability in sitting and standing, head and neck control, and functional reach.
• Assistive devices like wheelchairs and standing frames may be used, along with cough assist machines.
• Aquatic therapy has shown benefits in improving gross motor function and gait.

Question 14

When does the human heart start beating during embryonic development?

Answer 14

The heart starts beating between day 22 and 29 of embryonic development.

Question 15

What is Patent Ductus Arteriosus (PDA), its causes, and potential side effects?

Answer 15

Patent Ductus Arteriosus (PDA) is a condition where the ductus arteriosus fails to close after birth, causing abnormal circulation.

• In utero, the ductus arteriosus shunts blood away from the lungs to the placenta.
• PDA can lead to increased respiratory support needs, chronic lung disease (bronchopulmonary dysplasia), pulmonary hemorrhage, and intestinal injury due to flow reversal in the abdominal aorta and systemic arteries.

Question 16

Which infants are most at risk for persistent PDA, and what are the treatment options?

Answer 16

• Preterm infants are at higher risk due to physiological immaturity.
• More than half of infants born before 26 weeks of gestation have a PDA after 2 months.
• Treatments include medications like indomethacin, ibuprofen, acetaminophen, and surgical closure.

Question 17

What is Bronchopulmonary Dysplasia (BPD), its risk factors, and treatments?

Answer 17

• Bronchopulmonary Dysplasia (BPD) is a chronic lung disease primarily affecting preterm infants, associated with long-term ventilator use and oxygen therapy.
• Risk factors include premature delivery, long-term breathing treatments, infections, and lung inflammation.
• Treatments involve nasal continuous positive airway pressure (nCPAP), surfactant replacement therapy, and medications.

Question 18

Describe Respiratory Distress Syndrome (RDS), its cause, and symptoms.

Answer 18

• Respiratory Distress Syndrome (RDS) is caused by insufficient surfactant production in the lungs, common in preterm infants.
• Symptoms include fast and shallow breathing, grunting, flaring nostrils with each breath, cyanosis of the skin and legs, and retractions during breathing.

Question 19

What is surfactant, and why is it crucial for lung function in infants?

Answer 19

• Surfactant is a substance that reduces surface tension in the lungs, preventing the collapse of alveoli and enabling proper lung function.
• Most quantities are produced during weeks 36 and 37 of gestation, making preterm infants susceptible to RDS due to lack of sufficient surfactant.

Question 20

What is arthrogryposis, its causes, and typical treatment options?

Answer 20

• Arthrogryposis is a condition characterized by joint contractures in more than one area of the body, present at birth.
• It is caused by decreased fetal movement leading to multiple joint abnormalities.
• Treatment includes splinting, casting, stretching, strengthening, and in severe cases, surgery on affected areas such as feet, knees, and elbows.

Question 21

Describe congenital hip dysplasia, including its risk factors, diagnosis, and treatment.

Answer 21

• Congenital hip dysplasia is a condition where the acetabulum and head of the femur are underdeveloped, causing joint laxity and instability.
• Risk factors include female gender and breech delivery. It is diagnosed via imaging or special tests like the Barlow or Ortolani maneuvers.
• Treatment involves using a hip abduction splint or hip spica cast, and affected individuals are more likely to have hip issues later in life.

Question 22

What is clubfoot, its characteristics, and how is it typically treated?

Answer 22

• Clubfoot is a congenital deformity where the foot is twisted out of shape, stuck in plantar flexion and inversion (supination).
• It can be unilateral or bilateral and is usually idiopathic, though genetics may play a role.
• Treatment involves casting and stretching, or surgery in severe cases.

Question 23

What is hydrocephalus, its causes, effects, and typical treatment?

Answer 23

• Hydrocephalus is a condition characterized by excessive accumulation of cerebrospinal fluid (CSF) in the ventricles due to limited flow into the fourth ventricle, leading to increased intracranial pressure (ICP).
• It can cause widening of cranial sutures, thinning of skull bones, and enlargement of the head.
• Causes include aqueductal stenosis and Arnold-Chiari malformation.
• Treatment involves ventriculoperitoneal shunting to drain excess CSF and decrease pressure.

Question 24

What is anencephaly, its causes, and prognosis?

Answer 24

• Anencephaly is a severe neural tube defect where the brain and skull fail to fully form, leading to death shortly after birth.
• It is caused by failure of the neural tube’s cephalic part to close, resulting in exposed, malformed brain tissue that degenerates.
• There is no exact known cause, but genetic and environmental factors may play a role.
• It is a fatal condition, with infants rarely living longer than a few hours or days.

Question 25

List and explain the prenatal causes of cerebral palsy (CP).

Answer 25

• Prenatal causes of cerebral palsy include damage to the white matter of the brain, abnormal brain development, bleeding in the brain, and lack of oxygen to the brain.
• These factors can result in motor control deficits characteristic of CP.

Question 26

Outline the key stages of fetal eye development, including when the eyes respond to light.

Answer 26

• Eye development begins around week 5 with eyelid formation and optic nerve development.
• By week 10, eyeballs finish forming and eyelid fusion occurs. Eyelashes begin to form and spontaneous eye movements start around week 14.
• The eyelids reopen at week 26 after being fused.
• By week 28, the baby responds to light, and by week 31, the pupillary reflex develops with the pupil constricting and dilating in response to light.
• By week 36, eyelid development is almost complete with smooth eyelid margins formed.

Question 27

What is Retinopathy of Prematurity (ROP), its causes, symptoms, and potential outcomes?

Answer 27

• Retinopathy of Prematurity (ROP) is a condition caused by abnormal blood vessel growth in the retina, common in preterm infants.
• It may lead to blindness if untreated.
• Symptoms include unusual or jerky eye movements, white pupils instead of black, lack of appropriate response to light, and vision loss.
• Early detection and treatment are crucial to prevent long-term visual impairment.

Question 28

Describe congenital cataracts, their causes, and how they are diagnosed.

Answer 28

• Congenital cataracts are caused when the lens becomes opaque in utero.
• They are typically determined by a genetic component but can also result from maternal infections like rubella between weeks 4 and 7 of gestation.
• Diagnosis can be made via ultrasound, blood tests showing high levels of alpha-fetoprotein, or amniotic fluid samples.
• Early detection is important as congenital cataracts can lead to vision loss.

Question 29

What are the types of congenital hearing loss, and what causes them?

Answer 29

Types of congenital hearing loss include…

• microtia (underdevelopment of the pinna), sensorineural loss (impairment of the inner ear or vestibulocochlear nerve)
• conductive hearing loss (structural defects or buildup in the external or middle ear canal),
• mixed hearing loss (combination of sensorineural and conductive)
• auditory neuropathy (often caused by premature birth)

• Causes can be genetic, structural abnormalities, or exposure to certain medications or infections during pregnancy.

Question 30

Explain the difference between sensorineural and conductive hearing loss in infants.

Answer 30

• Sensorineural hearing loss is caused by abnormalities in the inner ear or vestibulocochlear nerve, leading to impaired reception and transmission of sound to the brain. It is often genetic and may develop at birth or later.
• Conductive hearing loss is due to structural defects or blockages in the external or middle ear canal that prevent sound from reaching the inner ear.

Question 31

How are hearing aids used in infants, and what types are commonly recommended?

Answer 31

• Hearing aids may be recommended for infants as early as 2–3 months once hearing loss is diagnosed.
• The most common type for babies is the behind-the-ear (BTE) hearing aid, which sits behind the ear and is connected to a custom earmold.
• Proper fitting is crucial to prevent sound leakage and feedback.
• Other types include in-ear hearing aids and auditory brainstem implants.

Question 32

What is the significance of the ossification center in the frontal bones, and when does it appear?

Answer 32

The two frontal bones develop from a primary ossification center at the front of the skull around the 8th week of embryonic development.

Question 33

What are the differences between intramembranous and endochondral ossification, and which bones develop through these processes?

Answer 33

• Intramembranous ossification involves mesenchymal cells differentiating directly into bone-producing cells, forming bones like the skull bones.
• Endochondral ossification involves a cartilage model that grows and is gradually converted into bone, forming bones like the vertebrae and long bones.

Question 34

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Answer 34

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Question 35

What are the common joints that require surgical intervention in arthrogryposis?

Answer 35

• In severe cases of arthrogryposis where surgery is needed, the most common areas are the feet (76%), knees (39%), and elbows (24%).
• Surgical interventions aim to improve joint function and alignment.

Question 36

What is the role of physical therapy in managing hydrocephalus?

Answer 36

Physical therapy goals for hydrocephalus include promoting physical milestones, improving balance and coordination, and enhancing functional skills to mitigate developmental delays caused by increased intracranial pressure.

Question 37

How does spina bifida relate to hydrocephalus, and what is the prevalence of hydrocephalus in patients with severe neural tube disorders?

Answer 37

• Hydrocephalus is often associated with spina bifida, a type of neural tube defect.
• Approximately 80–90% of patients with severe neural tube disorders like spina bifida require intervention due to hydrocephalus.

Question 38

Explain the role of surfactant replacement therapy in the treatment of BPD and RDS.

Answer 38

Surfactant replacement therapy provides artificial surfactant to the lungs of preterm infants with BPD or RDS, reducing surface tension in the alveoli, preventing collapse, and improving breathing and oxygenation.

Question 39

What is Gower’s sign, and in which conditions is it commonly observed?

Answer 39

• Gower’s sign is a clinical sign where a patient uses their hands and arms to ‘walk’ up their own body from a squatting position due to proximal muscle weakness.
• It is commonly observed in Duchenne Muscular Dystrophy and SMA Type 3.

Question 40

What are the potential effects of an untreated Patent Ductus Arteriosus on the gastrointestinal system?

Answer 40

An untreated PDA can lead to intestinal injury due to flow reversal in the abdominal aorta and systemic arteries, which can compromise blood flow to the gastrointestinal tract.

Question 41

Describe the role of aquatic therapy in managing patients with DMD and SMA.

Answer 41

Aquatic therapy is beneficial for patients with DMD and SMA as it allows for low-impact exercise that improves strength, flexibility, gross motor function, and gait, while reducing stress on weakened muscles and joints.

Question 42

What are the signs and symptoms that may indicate Retinopathy of Prematurity in infants?

Answer 42

Signs and symptoms of ROP include unusual or jerky eye movements, white pupils instead of black, lack of appropriate response to light, vision loss, and not following objects with their eyes.

Question 43

What are the risk factors for developing bronchopulmonary dysplasia in preterm infants?

Answer 43

Risk factors for BPD include…

• premature delivery
• long-term breathing treatments like mechanical ventilation
• infections
• inflammation of the lungs

Question 44

How does the closure of the ductus arteriosus differ between term and preterm infants?

Answer 44

• In term infants, the ductus arteriosus is closed by 96 hours post-birth in 100% of cases.
• In preterm infants, physiological immaturity can lead to delayed closure or persistent PDA due to lower oxygen levels and immature smooth muscle in the ductus arteriosus.

Question 45

What is the significance of fetal movement in the development of conditions like arthrogryposis and SMA Type 0?

Answer 45

• Decreased fetal movement can lead to conditions like arthrogryposis due to lack of joint mobility resulting in contractures.
• In SMA Type 0, reduced fetal movement raises concerns for severe hypotonia and respiratory complications at birth.

Question 46

What are common gait abnormalities observed in patients with Duchenne Muscular Dystrophy?

Answer 46

Common gait abnormalities in DMD include Trendelenburg gait, waddling gait, and gluteal lurch due to weakness in the proximal muscles of the lower limbs.

Question 47

Explain how standing frames are used in the management of neuromuscular disorders and their benefits.

Answer 47

• Standing frames are used for patients who are no longer ambulatory to allow them to stand upright for a few hours a day.
• Benefits include improving bone mineral density, aiding in digestion, enhancing respiratory function, and preventing contractures.

Question 48

Why are females more likely to develop congenital hip dysplasia, and how does breech delivery contribute to the risk?

Answer 48

• Females are more likely to develop congenital hip dysplasia possibly due to hormonal influences that increase joint laxity.
• Breech delivery contributes to the risk by placing abnormal stress on the hip joints during development and birth.

Question 49

What is the function of the pupillary reflex, and at what gestational age does it develop?

Answer 49

The pupillary reflex controls the constriction and dilation of the pupil in response to light, protecting the retina from excessive light exposure. It develops around week 31 of gestation.

Question 50

Summarize the key physical therapy interventions for infants and children with neuromuscular disorders covered in this material.

Answer 50

Key physical therapy interventions include promoting increased range of motion to prevent contractures, using orthotic devices like AFOs and KAFOs, employing assistive devices such as wheelchairs and standing frames, aquatic therapy to improve strength and flexibility, family education on stretching and positioning, and focusing on preserving function by enhancing stability, head and neck control, and functional reach.