Derivatives Of Ectoderm

DERIVATIVES OF ECTODERM

Q. 1

Which of the following is a derivative of the ectoderm of the trilaminar embryo?

 A

Bone

 B

Germ cells

 C

Muscle

 D

Spinal cord

Q. 1

Which of the following is a derivative of the ectoderm of the trilaminar embryo?

 A

Bone

 B

Germ cells

 C

Muscle

 D

Spinal cord

Ans. D

Explanation:

The neural plate, a thickened area of ectoderm, gives rise to the nervous system.

The first step is the development of a groove in the neural plate. On either side of this groove are the raised neural folds.

These neural folds then begin to fuse in the midline at approximately the midpoint of the neural plate.

Fusion proceeds in a rostral and caudal direction; once completed, there still remains an open area of the “tube” at both the rostral and caudal ends. These openings are referred to as the rostral and the caudal neuropore.

The rostral neuropore closes around day 26 and the caudal neuropore closes on approximately day 28. With the closure of the caudal neuropore, closure of the neural tube is completed. It has been convincingly shown that folic acid plays an important role in the closure of the neural tube. By giving women of childbearing age folic acid supplements, the rate of neural tube defects can be reduced dramatically. Yet, based on the embryology of the neural tube (with closure of the tube roughly by day 28), it is obvious that in order for folic acid supplementation to work, it should be started pregestationally. Unfortunately, most women do not seek prenatal care until after the neural tube has undergone its period of closure.

Bone, muscle, and spleen are all derivatives of the mesoderm. This mesoderm is formed at the end of the second week post-fertilization, when some cells of the primitive streak migrate laterally between the endodermal and the ectodermal layer.
 
Germ cells are derived from the endodermal layer of the trilaminar embryo. They migrate as primordial sex cells from the endoderm of the yolk sac to the urogenital ridge.

Q. 2

Surface ectoderm gives rise to all of the following structures except.

 A

Lens

 B

Corneal epithelium

 C

Conjunctival epithelium

 D

Anterior layers of iris.

Q. 2

Surface ectoderm gives rise to all of the following structures except.

 A

Lens

 B

Corneal epithelium

 C

Conjunctival epithelium

 D

Anterior layers of iris.

Ans. D

Explanation:

D. i.e. Anterior layer of iris


Q. 3

All are developed from ectoderm except ‑

 A

Lens

 B

Brain

 C

Spinal cord

 D

Retinal vascular endothelium

Q. 3

All are developed from ectoderm except ‑

 A

Lens

 B

Brain

 C

Spinal cord

 D

Retinal vascular endothelium

Ans. D

Explanation:

D i.e. Retinal vascular endothelium


Q. 4

Neural ectoderm derivatives are:

 A

Corneal stroma

 B

Cilliary epithelium

 C

Iris stroma

 D

Corneal epithelium

Q. 4

Neural ectoderm derivatives are:

 A

Corneal stroma

 B

Cilliary epithelium

 C

Iris stroma

 D

Corneal epithelium

Ans. B

Explanation:

B i.e. Cilliary epithelium; E i.e. Sphincter and dilator pupillae muscles

Neural crest cells form the mesenchyme of head & neck and contribute to most of the eye including endothelium of cornea & trabecular meshworkQ stroma of cornea, iris, ciliary body and choroid; melanocytes of conjunctiva & uvea; ciliary muscle ganglion & nerves (Schwann cells); Orbital bones & connective tissue; connective sheath & muscle layer of orbital blood vessels; meningeal sheath of optic nerve, sclera & part of vitreous.

  • All Epithelia (except that of iris & ciliary body), the lens and the Lacrimal & Tarsal glands are derived from the surface ectodermQ. Iris and ciliary body epitheliumsQ are derived from neural ectoderm.
  • Structures derived from neural ectoderm include Iris & Ciliary body Epithelium, Smooth muscles of iris (constrictor & dilator pupilae), Retina (REE & 9 sensory layers), Vitreous parts, Optic Nerve, Cup and Vesicle. Mn: “ICE (I see) smooth (constricted & Dilated) Retinal vital parts of Optic NCV (nerve conduction velocity)”
  • Melanocytes present in iris stroma develop from neural crest.
  • Sclera is of neural crest and mesodermal originQ
  • Lacrimal & tarsal glands, epithelium of cornea & conjunctiva, and crystalline lens develops from surface epitheliumQ; whereas sclera is mesodermalQ in origin.
  • Usually the epithelium develop from ectoderm; & muscles from paraxial mesoderm. But the unique feature of iris is that it’s epithelium and musculature (constrictor & dilator pupillae) develop from Neuroectoderm.Q

Q. 5

Surface ectoderm gives rise to all of the following structures except.

 A

Lens

 B

Corneal epithelium

 C

Conjunctival epithelium

 D

Anterior layers of iris

Q. 5

Surface ectoderm gives rise to all of the following structures except.

 A

Lens

 B

Corneal epithelium

 C

Conjunctival epithelium

 D

Anterior layers of iris

Ans. D

Explanation:

D. i.e. Anterior layer of iris

Usually the epithelium develop from ectoderm; & muscles from paraxial mesoderm. But the unique feature of iris .0, that it’s epithelium and musculature (constrictor & dilator pupillae) develop from Neuroectoderm.Q


Q. 6

All of the following ocular structures are derived embryologically from the neuroectoderm except:

 A

Epithelial layers of ciliary body and iris

 B

Sphincter and dilator pupillae muscles

 C

Optic nerve

 D

Optic nerve sheaths

Q. 6

All of the following ocular structures are derived embryologically from the neuroectoderm except:

 A

Epithelial layers of ciliary body and iris

 B

Sphincter and dilator pupillae muscles

 C

Optic nerve

 D

Optic nerve sheaths

Ans. D

Explanation:

Ans. Optic nerve sheaths


Q. 7

All of the following are derived from ectoderm except:

 A

Hair follicles

 B

Arrector pili

 C

Sebaceous glands

 D

Mammary gland

Q. 7

All of the following are derived from ectoderm except:

 A

Hair follicles

 B

Arrector pili

 C

Sebaceous glands

 D

Mammary gland

Ans. B

Explanation:

Ans. b. Arrector pill

Arrector pill is a smooth muscle in the dermis, derived from lateral plate mesoderm.”— Langmans Medical embryology 12/e p341

“The arrector pili is a mesodermally derived smooth muscle that lifts the hair to a nearly vertical position in a cold environment.”- Human embryology and developmental biology by Carlson-5/chapter-9/integumentary-system



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