Practice question #2

A child is in the nursery one day after birth. A nurse notices a urine-like discharge being expressed through the umbilical stump. What two structures in the embryo are connected by the structure that failed to obliterate during the embryologic development of this child?

A) Pulmonary artery - aorta
B) Bladder - yolk sac
C) Bladder - small bowel
D) Liver - umbilical vein
E) Kidney - large bowel

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Pharyngeal apparatus📝

🔹Pharyngeal apparatus consists of the following:
▫️Pharyngeal arches (1,2,3,4 and 6) composed of mesoderm and neural crest
▫️Pharyngeal pouches (1,2,3,4) lined with endoderm
▫️Pharyngeal grooves or clefts (1,2,3, and 4) lined with ectoderm

🔹Components of the Pharyngeal arch (mesoderm -> muscles):
▫️1st: four muscles of mastication (masseter, temporalis, lateral and medial pterygoid), digastric (anterior belly), mylohyoid, tensor tympani, tensor veli palatini
▫️2nd: muscles of facial expression, figastric (posterior belly), stylohyoid, stapedius
▫️3rd: stylopharyngeus muscle
▫️4th: cricothyroid muscle, soft palate, pharynx (5 muscles)
▫️5th: intrinsic muscles of larynx (except cricothyroid muscle)

🔹Components of the Pharyngeal arch (neural crest -> skeletal/cartilage) - will be covered later.

🔹Adult derivatives of Pharyngeal pouches
▫️1st: epithelial lining of auditory tube and middle ear cavity
▫️2nd: epithelial lining of crypts of palatine tonsil
▫️3rd: Inferior parathyroid gland, thymus
▫️4th: superior parathyroid gland, C-cells of thyroid

🔹Pharyngeal groove/cleft 1 gives to the epithelial lining of external auditory meatus. All other grooves are obliterated.

Source: Anatomy. Kaplan 2017
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Explaination # 1 👆D) Remember that in viewing axial or transverse CT scans through the body, the right side of the patient is to your left and the left side to your right. In other words, the feet of the patient are toward you and the head away from you. The back of the patient is at the bottom of the image and the front of the patient toward the top. Directional terms are always in reference to the patient. The insert at the bottom right indicates the level of the section. Arrow 1 indicates the right brachiocephalic vein. The left brachiocephalic vein (choice B) is seen as the elongated structure immediately posterior to the manubrium of the sternum and to the left of the right brachiocephalic vein. Immediately posterior to the left brachiocephalic vein is the brachiocephalic artery (choice A, arrow 2). To the left of the latter are the left common carotid artery (choice C) and the left subclavian artery (arrow 3). The superior vena cava (choice E) is not seen at this level because the right and left brachiocephalic veins are still separate.

Explaination 👆. (B) Arrow 2 points to the gallbladder, which will be removed during the cholecystectomy
surgical removal of the gallbladder). Biliary colic may be due to impaction of a gallstone in the cystic duct, resulting in cholecystitis (inflammation of the gallbladder). Arrow 1 (choice A) points to the liver. Arrow 3 (choice C) points to the transverse colon. Arrow 4 (choice D) points to the spleen and arrow 5 (choice E) indicates the stomach, recognizable by its internal rugae.

Explaination B) 👆The metanephric diverticulum or ureteric bud gives rise to the ureter, renal pelvis, calices, and collecting tubules. The metanephric mass of intermediate mesoderm (choice C) gives rise to the nephrons in the kidney. The mesonephric and paramesonephric ducts (choices Aand D) play essential roles in the development of the male and female reproductive system, respectively. The pronephric duct (choice E) is derived from the transitory, nonfunctional first set of kidneys or pronephroi and does not contribute to the development of the ureter.

Explaination
#1 in above question represent azygous venous arch🙈
It is unpaired, peirches diaphragm via aortic opening

Explanation (C) Benedikt’s syndrome results from a lesion situated in the tegmentum of the midbrain, at the level of the third cranial nerve (oculomotor) nucleus and its associated tracts, as exemplified by ptosis and third nerve palsy in this patient. The red nucleus is also affected at this level giving rise to motor impairment displayed by the intention tremor. Since the rubrospinal tract crosses at the level of the midbrain to project to the opposite side of the body, the tremor will manifest itself contralateral to the side to the lesion. The seventh cranial nerve (facial) nucleus is located in the pons, and the facial musculature (choice A) in this patient would not be affected. Likewise, the twelfth cranial nerve (hypoglossal) nucleus is located in the medulla, and the innervation of the tongue (choice B) would be spared in this patient. A lesion causing a pure Benedikt’s syndrome would be confined to the midbrain tegmentum and not affect the corticospinal tract. Ipsilateral hemiplegia (choice D) would not be present in this patient. Finally, vertical gaze palsy (choice E) results from a lesion or compression of the midbrain tectum and not of the tegmentum.

C) A vascular lesion affecting the left caudal medulla involves the left medial lemniscus, left hypoglossal nerve fibers, and the left medulary
pyramid. Involvement of the left medial lemniscus produces somatosensory deficits involving the right side of the body. Damage to the left hypoglossal nerve would result in deviation of the protruded tongue to the left (and other lower motoneuron signs), and damage to the left pyramid results in right hemiplegia (choices A and B involve incorrect combinations) along with other upper motoneuron signs. Choices D and E are incorrect because they fail to combine involvement of the tongue and contralateral hemiplegia.

Q#6 During development, the notochord grows in a cranial direction until it reaches the prechordal plate. This plate is the primordium of the oropharyngeal (or buccopharyngeal) membrane, which, in the embryo, will separate the stomodeum from the foregut. At 26 days of gestation, the oropharyngeal membrane will break down, allowing communication of the foregut with the oral cavity.

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B) The palatoglossus muscle, which can be observed in the oral cavity to form the palatoglossal arch anterior to the palatine tonsil, lies in the same location as the embryonic oropharyngeal membrane. It lies at the junction line between the stomodeum and the foregut. The buccinator (choice A) is a muscle of the cheek and thus is located in the original stomodeum. The palatopharyngeus (choice C) is located posterior to the palatoglossus and palatine tonsil, forming the palatopharyngeal arch. The palatopharyngeus, stylopharyngeus (choice D), and superior constrictor (choice E) muscles are all pharyngeal muscles and thus are located in the original foregut.