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. 2 A young couple brings their 8-month-old boy to the pediatrician because of an upper respiratory infection. This is the tenth such infection the boy has lA• A] had In the past 4 months. Medical history is also significant for a cleft palate repair. The pediatrician is concerned, and subsequent genetic testing reveals a 22qll chromosomal deletion. Intravenous immunoglobulin and antibiotic prophylaxis are begun to compensate for the abnormal development of a specific organ.

From which of the following embryonic structures is this organ derived?

: A. First branchial (pharyngeal) arch

B. Second branchial (pharyngeal) arch

c. Third branchial (pharyngeal) pouch

o. Third branchial (pharyngeal) cleft

E. Fourth branchial (pharyngeal) cleft

F. Fourth branchial (pharyngeal) pouch

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The correct answer is c. 600/o chose this.

This child has DiGeorge syndrome, which can be characterized by a variety of features including Cleft palate, Abnormal facies, Thymic aplasia, cardiac defects, and Hypocalcemia (remember the mnemonic "CATCH-22"). Because of hypoplasra of the thymus, children wit h DiGeorge syndrome may have a T-lymphocyte defidency. To prevent infection, t hese children are often given Intravenous immunoglobulins and antibiotic prophylaxis. The thymus normally derives from the third branchial (pharyngeal) pouch.

biotics DiGeorge syndrome T cell Antibody Intravenous therapy Immunoglobulon therapy Pharynx Palate Hypoplasia Preventive healthcare

A is not correct. 20/o chose this.

The first branchial arch plays no role in DiGeorge syndrome. For first-arch derivatives, think " M": Mandible, Malleus, sphenoMandibular ligament; Muscles of Mastication (teMporalis, Masseter, Medial and lateral pterygoids). Derivatives of the first branchial arch are innervated by cranial nerve v. Branchial arch Lateral pterygoid muscle Cranial nerves Pharyngeal arch DiGeorge synd orne Pterygoid bone Ugament

B is not correct. 40/o chose t his.

The second branchial arch is not involved in DiGeorge syndrome. For second-arch derivatives, think "S" : Stapes, Styloid process, Stylohyoid ligament; muscles of facial expression, Stapedius, Stylohyoid. Cranial nerve VII Innervates derivatives of the second arch. Branchial arch DiGeorge syndrome Cranial nerves Facial muscles Pharyngeal arch Facial nerve

0 is not correct . 100/o chose this.

The second, third, and fourth branchial clefts form temporary sinuses, but are obliterated before fetal maturation. Thus they have no derivatives In the adult . Sinus (anatomy) Paranasal sinuses

E i s no t correct . 70fo chose this.

The second, third, and fourth branchial clefts form temporary sinuses but are obliterated before fetal maturation. Thus they have no derivatives In the adult . Sinus (anatomy) Paranasal sinuses

F i s not correct. 170/o chose this.

The fourth pharyngeal pouch gives rise to superior parathyroid glands and ultlmobranchial body, which forms the parafollicular c cells (adjacent to the thyroid follicles).

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- + - · - - + -

The second, third, and fourth branchial clefts form temporary sinuses but are obliterated before fetal maturation. Thus they have no derivatives in the adult. Sinus (anatomy) Paranasal sinuses

F is not correct. 17% chose this . The fourth pharyngeal pouch gives rise to superior parathyroid glands and ultimobranchial body, which forms the parafollicular C cells (adjacent to the thyroid follicles). Parafollicular cell Ultimopharyngeal body Pharyngeal pouch (embryology) Thyroid Parathyroid gland Pharynx

Bottom Line:

In DiGeorge syndrome the third and fourth branchial pouches do not develop. Absence of the third branchial pouch leads to T-lymphocyte deficiency, whereas absence of the fourth branchial pouch causes hypocalcemia secondary to lack of parathyroid development. Pharyngeal pouch (embryology) Hypocalcaemia DiGeorge syndrome Parathyroid gland T cell

lijl;fiiJI•l toryear:[ 2017 • ] FI RST AI D FAC TS

Branchial pouch derivatives

POUCH

1st pouch

2nd pouch

DERIVATIVES

Iiddie ear cavity, eustachian tube, mastoid air cells.

Epithelial lining of palatine tonsil.

NOTES

1st pouch contributes to endoderm-lined structures of ear.

FA17 p 588.1

MNEMONIC

Ear, tonsils, bottom-to-top: I (ear), 2 (tonsils), 3 dorsal (bottom for inferior

parathyroids}, ... 1 / o . ' \

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--- -· - . . parathyroids.

Ventra l wings - ultimobranchial body - parafollicular (C) cells of thyroid.

DiGeorge syndrome Chromosome 22qll deletion. Aberrant development of 3rd and 4th pouches - T-cell deficiency (thymic aplasia) and hypocalcemia (failure of parathyroid development). Associated with cardiac defects (conotrunca 1 anomalies).

Immunodeficiencies DISEASE DEFECT

B-cell disorders

X-linked (Bruton) Defect in BTK, a tyrosine agammaglobulinemia kinase gene - no B-cell

maturation. X-linked recessi,·e (t in Boys).

Selective lgA deficiency

Unknown. Most common 1° immunodeficiency.

PRESENTATION

Recurrent bacterial and enteroviral infect ions after 6 months U maternal lgG).

Majority Asymptomatic. Can see Airway and Gl

infections, Autoimmune disease, Atopy, Anaphylaxis to lgA-containing products.

FA17p112.1

FINDINGS

Absent B cells in peripheral blood, l lg of all classes.

Absent/scanty lymph nodes and tonsils. Live vacci nes contraindicated.

l lgA with normal lgG, lgM levels. t susceptibility to giardiasis.

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D

Chronic granulomatous disease

22q11 deletion syndromes

phagosome-lysosome fusion; autosomal recessive.

albin ism, peripheral Ivlild coagulation defects.

Defect of 'ADPII oxidase - ' reactive oxygen species (eg, superoxide) and ' respiratory burst in neutrophils; X-I inked recessi\·e most common.

neuropal hy, progressi\·e neurodegeneralion, infiltrative I ymphoh istiocytosis.

t susceptibility to catalase <±> organ1sms.

CATCII-22.

Abnormal dihydrorhodamine (Aow cytometry) test (' green fluorescence). ' itroblue tetrazolium dye reduction test (obsolete) fails to turn blue.

FA17p61 .1

licrodeletion at chromosome 22qll - v<Hiable presentations including C left palate, Abnormal facies, T hymic aplasia - T-cell deficiency, Cardiac defects, and Hypocalcemia zo to parathyroid aplasia.

Due to aberrant development of 3rd and 4th branchial pouches.

DiGeorge syndrome-thymic, parathyroid, and cardiac defects.

Velocardiofacial syndrome-palate, facial, and cardiac defects.

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. 2 Several organs are responsible for hematopoiesis during development.

Which of the following is the last to begin hematopoiesis?

A. Bone marrow

B. Liver

c. Lungs

o. Spleen

E. Yolk sac

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The correct a nswer is A. 71% chose this.

Bone marrow is the last to undergo hematopoiesis and maintains hematopoiesis in adult life. It begins to synthesize blood at 18 weeks' gestation. Haematopoiesis Bone marrow Gestation Bone

B is not correct. 10% chose this.

The liver is the second to begin hematopoiesis. It begins in gestational week 6 and ends at birth. Haematopoiesis liver

c is not correct. 6 % chose this.

The lungs do not participate in hematopoiesis. Haematopoiesis lung

D is not correct. 10% chose this.

The spleen undergoes hematopoiesis in gestational weeks 10 through 28 . Haematopoiesis Spleen

E is not correct. 3 % chose this.

The yolk sac is the first to begin hematopoiesis. It begins in gestational week 3 and continues through week 8 . Yolk sac Haematopoiesis Yolk

Botto m Line:

Fetal erythropoiesis occurs in the yolk sac (3 - 8 weeks), liver (6- birth), spleen (10 -28 weeks), and bone marrow (18 weeks onward) . Erythropoiesis Yolk sac Spleen liver Bone marrow Yolk Bone Fetus

I iii I •ti 1!1 It) fo r VP.il r :l /017 .. J

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The yolk sac is the first to begin hematopoiesis. It begins in gestational week 3 and continues through week 8. Yolk sac Haematopoiesis Yolk

Bottom Line:

Fetal erythropoiesis occurs in the yolk sac (3 - 8 weeks), liver (6- birth), spleen (10 -28 weeks), and bone marrow (18 weeks onward). Erythropoiesis Yolk sac Spleen liver Bone marrow Yolk Bone Fetus

I iii I ;fi 1!1 I•J fo r year:l 2 0 17 .. FI RST AI D FACTS

Fetal erythropoiesis

Hemoglobin development

Fetal erythropoiesis occurs in: • Yolk sac (3-8 weeks) • Liver (6 weeks- birth) • Spleen (10-28 weeks) • Bone marrow (18 weeks to adult)

Embryonic globins: sand E.

Fetal hemoglobin (HbF) = CJ.z'Yz· Adult hemoglobin (HbA 1) = nzP2•

HbF has higher affinity for 0 2 due to less avid binding of 2,3-BPG, allowing HbF' to extract 0 2 from maternal hemoglobin (HbA1 and HbA2) across the placenta. HbA2 (nzo2) is a

FA17 p 389.2

Young Liver Synthesizes Blood.

From feta l to adult hemoglobin: Alpha Always; Gamma Goes, Becomes Beta.

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