Answers&Explanations for #Embryology.Mini_Test -- 2

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#Embryology.Mini_Test -- 2

Answers with Explanations:

1.   Q) What is true about development & maturation of sperms except
A:   D) Stored in the seminal vesicle before ejaculation

     o   Sperms are stored in the epididymis before ejaculation. Here they get matured and gain motility progressively.
o   Primordial germ cells remain dormant till puberty in a male and start the process of spermatogenesis only at puberty.
o    In females oogenesis starts before birth only and there are no primordial germ cells available at birth itself. The ovary contains only the primary oocytes at birth.
o     Spermatogenesis takes 74 days to produce a mature sperm.

  

2.   Q) Correct statement concerning sexual development is

A:   A) Gonadal ridge appear at week 5

     o    Gonadal ridge appears at the 5^th week of gestation and is populated by the primordial germ cells by the end of 5^th week.
o   Gonadal (Genital) ridge forms the testis/ovary depending upon the genotype of the individual conceptus.
o    Short arm of chromosome Y has the SRY gene, which results in the formation of the protein TDF (testis determining factor). TDF is important for the male development.
o    Absence of SRY gene from the Y chromosome may result in female phenotype in a male genotype (XY).
o     Testes Start developing by the 7^th week of intrauterine life whereas, ovaries start developing only after 10^th week.
o       External genitalia are not well developed before week 12.

3.   Q) Cells of the adrenal medulla are derived from the same embryonic cells as those  that form

A:  C). Mandible

      o   Cells of the adrenal medulla (chromaffin cells) are neural crest derivatives and so are the skull bones like mandible.
o   Kidney collecting tubules are derived from ureteric bud ( mesoderm); Neural tube forms Preganglionic neurons &  thymus comes from gut tube which is endodermal (third pharyngeal pouch)

4.   Q) Which nerve carries special visceral efferent fibers

A:   D)  7th

      o   Special visceral efferent supply the branchial (pharyngeal) arch musculature.
o  7^th nerve supplies the second branchial arch musculature like muscles of facial expression.
o  All other remaining skeletal muscles are under a bigger heading called as GSE (General somatic efferent).
o   (LR₆SO₄)₃  is the formula for the eyeball muscles and hence cranial nerves 3, 4 & 6 belong to GSE.

5. Q) The cardiac jelly formed around the heart tube during early development, contributes to the formation of

A:  D)  Endocardium

      o   Cardiac jelly is sandwiched between heart tube & myocardium and forms the sub-endothelial connective tissue of the endocardium (Dorland’s Medical Dictionary).
o    The external layer of the embryonic heart tube—the myocardium—is formed from splanchnic mesoderm sur­rounding the pericardial cavity .
o   At this stage, the heart is composed of a thin endothelial tube, separated from a thick myocardium by gelatinous connective tissue, known as cardiac jelly.
o The endothelial tube becomes the internal endothelial lining of the heart—endocardium—and the primordial myocardium becomes the muscular wall of the heart or myocardium. The visceral pericardium or epicardium is derived from mesothelial cells that arise from the external surface of the sinus venosus and spread over the myocardium
o   Remember: Cardiac jelly forms the connective tissue & not the muscles.