Answers&Explanations for #Embryology.Mini_Test -- 1

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#Embryology.Mini_Test -- 1 

Answers with Explanations:

 1.   Q)The auricle develops from
A:   C) 1st  and 2nd branchial arch

The auricle develops from the mesenchyme of 1^st and 2^nd branchial arch.

Tragus develops from the tubercle of the first arch while the rest of the pinna develops from the remaining five tubercles of the second arch

 Ref :  Diseases of Ear, Nose and Throat & Head and Neck Surgery, 6/e  PL Dhingra,  Pg No

 

2.   Q)Incorrect statement about allantois is    
A:   C)  Urachus is the remnant lying in the medial umbilical ligament

o    Allantois is an endodermal diverticulum of yolk sac, which joins the urogenital sinus – a part of cloaca.

o    Cloaca forms the urogenital sinus, which later gives rise to urinary bladder. Since, allantois opens into the urogenital sinus part of cloaca, it remains continuous with the urinary bladder.

o    Later, lumen of allantois obliterates and forms a fibrous cord – the urachus. It runs in a midline peritoneal fold – called as the median umbilical ligament.

o    If allantoic lumen is persistent – it leads to a rare surgical condition- the  urachal fistula.

o    Allantoic mesoderm expands beneath the chorion and forms the blood vessels that serve the placenta.

 Ref :  langman’s embr yology 13/e  Pg No 256,117

3.   Q) False regarding autonomic nervous system
A:   C) Occulomotor nerve carries the post-ganglionic parasympathetic fibers

o    Occulomotor nerve carries the pre-ganglionic parasympathetic fibers from the Edinger Westphal nucleus to the two smooth muscles – Ciliaris & Sphincter pupillae.

o    Post-ganglionic fibers are carried by the short ciliary nerves – branches of ophthalmic division of trigeminal nerve.

o    Lateral horns are mainly observed in the thoraco-lumbar region of the spinal cord and contain the sympathetic neurons.

o    Parasympathetic pre-ganglionic fibers are comparatively longer, since the parasympathetic ganglia are located far in the periphery (near the effector organ). Sympathetic ganglia are usually very close to the spinal cord (for e.g., sympathetic chain) and hence sympathetic pre-ganglionic fibers are shorter than the corresponding para-sympathetic fibers.

o    Both sympathetic & para-sympathetic ganglia use acetylcholine as their neurotransmitter. But at the effector level the neurotransmitter for sympathetic system are adrenaline & nor-adrenaline. Though skin still uses acetylcholine for sympathetic control – blood vessels, arrector pilorum muscle and sweat gland – all are under the cholinergic sympathetic system.

4.   Q) All are neural crest cell derivatives except
A:   D) Olfactory epithelium

o    Olfactory epithelium is contributed by the surface ectoderm.

o    Most of the skull bones are derivative of the neural crest cells like mandible, maxilla, zygomatic, frontal, vomer, squamous temporal etc.

o    Tunica media of the great vessels like aorta, pulmonary trunk is derived from neural crest cells. A-P septum of Truncus arteriosus is also a derivative of neural crest cells.

o    Choroid & sclera are also derivatives of neural crest cells

5.   Q) Wrong statement regarding oogenesis is
A:   B) Primary oocyte is arrested in metaphase- 1 till puberty

o    Primary oocyte is arrested in prophase- 1 of meiosis -1 till puberty. This arrest is due to the OMI (Oocyte maturation inhibitor) factor produced by follicular cells.

o    LH surge occurs at puberty breaking the arrest and the cell proceeds further into the cell division.

o    LH surge occurs ~ 36 hrs prior to ovulation and results in secondary oocyte along with polar body one. Polar body-1 may be seen as early as 24 hours prior to ovulation.

Secondary oocyte then enters meiosis – 2 and gets arrested at metaphase – 2. The metaphase arrest occurs three hours prior to the ovulation of secondary oocyte

 

Ref : Langman’s embryology 13/e  pg  no : 28,29