Cornea - organogenesis of eye and limb, Biology

Assignment Help:

Cornea - Organogenesis of Eye and Limb

The fully formed cornea contains 2-cell layered epithelium and the stroma made of extra cellular secreted materials. The bulk of the cornea is build up of the stroma Cornea development. The ectoderm overlying the lens vesicle, containing 2 layers of cells, is the presumptive cornea. The cells of the basal layer divide by mitosis during life to replace those of the upper layer that are shed by desquamation. Under the effect of the lens vesicle the cells of basal layer turns columnar and secrete about 20 layers of type I and type II collagen.

The alternate layers of collagen secreted are parallel to the corneal epithelium but at right angles to each other making an orthogonal ply and constitute the primary stroma among the corneal epithelium and the lens. In the meantime, mesenchymal cells (of neural crest origin) from blood capillaries migrate into this region and make a one-cell thick endothelium that secretes hyaluronic acid into the primary stroma. The stroma swells up and after that into this migrate two waves of mesenchymal cells as well of neural crest origin. These cells then secrete layers of their own collagen forming the secondary or adult stroma. Starting on 10th day of incubation in chick embryo the enzyme hyaluronidase is secreted that destroys the hyaluronic acid and causes the stroma to shrink. The stroma is dehydrated later under the influence of thyroxine secreted through the thyroid gland making it transparent. In the amphibians the outer cornea is made by the epidermal ectoderm and the stroma by this and by inner corneal cells of mesoderm (probably of neural crest origin). The adult cornea is completed during metamorphosis under thyroid influence.


Related Discussions:- Cornea - organogenesis of eye and limb

Alfieri repair-technique of operation, Alfieri Repair: This is advised ...

Alfieri Repair: This is advised for ischaenlic mitral regurgitation. In the area of prolapse, the anterior and posterior leaflet edges are approximated with one or two mattress

Explain signal hypothesis, A classical secretory protein vary from a cytoso...

A classical secretory protein vary from a cytosolic protein by having a sequence about 13-35 amino acids long at its N-terminal end called as a signal peptide or signal sequence.

Determine the pre-conditions for gtt, Pre-conditions for GTT You are ad...

Pre-conditions for GTT You are advised to carry out the GTT (OGTT) test to confirm a diagnosis of diabetes mellitus for a person with: a) The history of glycosuria (glucose

Explain electron volt, Explain Electron Volt Electron Volt: Amount of k...

Explain Electron Volt Electron Volt: Amount of kinetic energy obtained by an electron, initially at rest, after undergoing an acceleration by a one volt potential difference.

Explain ribosomes in eukaryotic and in prokaryotic cells, How different are...

How different are the location of ribosomes in eukaryotic and in prokaryotic cells? In prokaryotes ribosomes are create free in cytoplasm. In eukaryotic cells they can also be

What are the proteins, Q. What are the proteins? How can the protein divers...

Q. What are the proteins? How can the protein diversity of living beings be described? Proteins are molecules made of sequences of amino acids bound by a peptide bond. The g

Explain the bases, The bases in DNA have carbon-nitrogen ring structures; d...

The bases in DNA have carbon-nitrogen ring structures; due to the nitrogen atoms they are known as nitrogenous bases. There are two parts of ring structure. Adenine and guanine are

Bluetongue, B l u e t on g u e Bluetongue (BT) is a non-contagi...

B l u e t on g u e Bluetongue (BT) is a non-contagious and arboviral disease of both domestic and wild ruminants. The disease is enzootic in areas where reservoirs (cat

What do you understand by pericardium, Q. What do you understand by Pericar...

Q. What do you understand by Pericardium? Pericardium is the covering sac of the heart. The pericardium prevents acute cardiac chamber dilatation. Acute pericarditis, pericardi

Explain lipase, Lipase Pancreatic lipase specifically  hydrolyses the p...

Lipase Pancreatic lipase specifically  hydrolyses the primary ester linkages i.e.  at the position 1 and 3 of triacylglycerols. The presence of bile salt helps  in  emulsificat

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd