Medical School Histology Basics Eye VIBS 289 lab Larry Johnson Texas A&M University

OUTLINE OVERVIEW CELLULAR STRUCTURES THROUGH WHICH LIGHT PASSES Aqueous humor OUTLINE OVERVIEW CELLULAR STRUCTURES THROUGH WHICH LIGHT PASSES CORNEA LENS RETINA STRUCTURES WHICH INFLUENCE THE IMAGE IRIS CILIARY BODIES TRABECULAR MESHWORK Vitreous humor

Aqueous humor VITREOUS BODY (VITREOUS HUMOR)

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Eye – conjuctiva on white of eye 192 Eye – conjuctiva on white of eye sclera Conjunctiva Stratified squamous epithelium with some goblet cells

Eye 192 human and 34412 monkey Aqueous humor 192 34412 Connective tissue Aqueous humor Nerve Posterior chamber 192 Retina Cornea Sclera Pupil Optic nerve Anterior chamber What is the function of the canal of Schlemm The canal of Schlemm functions to drain the aqueous humor from the anterior chamber. Where is aqueous humor produced? Aqueous humor is produced by ciliary processes. It then flows into the posterior chamber of the anterior cavity, through the pupil into the anterior chamber, and finally drains through the canal of Schlemm. What is the ora serrata? The ora serrata is the serrated junction between the retina and the ciliary body. What are the functions of the pigment epithelial layer of the retina? Absorbs scattered light that passes through the neural layer Part of the protective blood-retina barrier isolating retina photoreceptors from the highly vascular choroid and regulating ion transport between these compartments. Role in retinal regeneration Phagocytosis of shed components from the adjacent photoreceptors and degradation of this material Removal of free radicals by various protective antioxidant activities and support of the neural retina by secretion of ATP, various polypeptide growth factors, and immunomodulatory factors The sphincter pupillae muscle is innervated by what portion of the nervous system? Parasympathetic innervation What are fovea centralis and the macula lutea? Fovea centralis: a shallow depression with only cone cells at its center; ganglion cells and other conducting neurons are located only at its periphery. It lies directly opposite of the pupil and is where visual acuity or sharpness is maximal. Macula lutea: This surrounds the fovea centralis. Here all layers of the retina are present and the two plexiform layers are rich in various carotenoids, which give the area a yellowish color. The carotenoids have antioxidant properties and filter potentially damaging short wavelength light, thus helping to protect the cone cells of the fovea. What is the effect of light on the cGMP-gated sodium channel in the photoreceptor cell? Light > absorbed by retinal of rhodopsin > isomerize from 11-cis-retinal to all-trans-retinal > activates opsin > activate transducin > stimulates phosphodiesterase to hydrolyze cGMP > cGMP-gated sodium channels close > hyperpolarization of cell > decrease release of neurotransmitters at synapse > depolarizes sets of bipolar neurons > action potentials sent to optic nerve > brain produces image. Lens Iris 34412 Ciliary body 34412 Vitreous body Chorioid layer

192 Eye – corneal layers Stratified squamous Epithelium Bowman's membrane Corneal endothelium Corneal stroma Corneal fibroblasts Descemet's Membrane

corneal layers Iris of Eye (toluidine blue) 292 Ciliary muscle: smooth muscle Sclera Lens Sclera-cornea junction (limbus) Bowman's membrane Aqueous humor Corneal stroma Aqueous humor Corneal endothelium Iris Descemet's Membrane Iris Anterior chamber Posterior chamber

292 Ciliary muscle: smooth muscle Ciliary processes Blood vessel lens Nerves Ciliary muscle 192

192 Eye – ciliary muscle Iris Pupil Artifactual space Conjunctival sac Sclera-cornea junction (limbus) Ciliary muscle Posterior chamber Ciliary processes Anterior chamber Ciliary muscle (smooth muscle)

192 192 Eye – secretory cells Pigmented cells of the ciliary processes become the dilator muscle of the iris Pigmented cells Secretory cells Secretory cells become the pigmented cells of the iris Iris Ciliary processes

292 Eye (toluidine blue) Conjunctiva Iris Ciliary muscle Trabecular meshwork Air Canal of Schlemm Anterior chamber Limbus Endothelium of trabecular meshwork is continuous with the transport endothelium of the cornea Ciliary processes Iris Posterior chamber

Eye – trabecular meshwork and canal of Schlemm 192 Eye – trabecular meshwork and canal of Schlemm Canal of Schlemm Ciliary muscle Limbus Trabecular meshwork Anterior chamber with aqueous humor

Iris 34412 Canal of Schlemm Trabecular meshwork Blood vessels Posterior chamber with aqueous humor Monkey eye 34412

Eye (toluidine blue) 292 Iris Anterior chamber Dilator muscle Lens Anterior chamber Dilator muscle Lens capsule Lens Iris Posterior chamber Iris pupil Cuboidal epithelium on anterior surface of lens Constrictor muscle Iris Pupil

292 Eye (toluidine blue) Lens cuboidal epithelium Lens Lens capsule Iris constrictor smooth muscle

The capsule is a shared basement membrane of the lens epithelium

The capsule is a shared basement membrane of the lens epithelium

Lens and iris 192 and 34412 Iris Iris Lens anterior surface 192 Pigmented epithelium of iris Iris Lens capsule Posterior chamber Iris Lens cuboidal epithelium 34412 Iris constrictor muscle is smooth muscle

Eye (toluidine blue) elongation of lens cuboidal cells at bow region 292 Eye (toluidine blue) elongation of lens cuboidal cells at bow region Lens cuboidal epithelium on its anterior surface gives rise to elongated lens fibers in the bow region, and the shared basement membrane of these cells is the capsule Capsule Lens cuboidal epithelium Capsule flattened lens fibers No cuboidal epithelium on the posterior surface of the lens and the capsule is thinner there Artifactual space 34412

34412 Eye monkey Sites of attachment of zonules to the lens’ capsule Anterior surface Eye monkey Iris Anterior surface Posterior surface Ligaments (zonules) lens 192 One site of attachment of a zonule to the capsule on the lens on its posterior surface lens

34412 Sclara Ciliary muscle Zonules 192 Lens fibers Capsule and cuboidal epithelium on the anterior surface of lens Thinner capsule on the posterior surface of the lens

Eye monkey 34412 Capillary network in retina Pigmented layer of epithelial cells Elaborate network of vessels, the choroid plexus. Central artery of the retina

34412 Cones Rods Ganglion cell layer Bipolar cells Vitreous body Retinal pigmented epithelium Artifactual space Photosensitive portion of rod and cone cells Retinal pigmented epithelium Artifactual space Venule in the choroid plexus Sclera

Rods Cones Photosensitive portion of rod and cone cells Nuclei of rod and cone cells = outer nuclear layer Retinal pigmented epithelium

Eye - Retina and choroid: Blood vessels in the retina Artifact space 292 Choroid Choroid plexus Melanin granules Retina Nucleus Retinal pigment epithelium Optic nerve

Retina (toluidine blue) 292 Bipolar cells Artifactual space Photoreceptor cells Rods Optic nerve Cones Capillary

Macula with top two layers pulled back to aid vision Typical retina Macula with top two layers pulled back to aid vision Ganglion cell layer Bipolar cells Rods and cones Rods and cones Retinal pigmented epithelium Retinal pigmented epithelium

192 Conjunctiva Cornea Sclera lens Choroid plexus Cornea Iris Sclera Vitreous body Retina Lens 292 Anterior chamber Optic nerve Posterior chamber Aqueous humor

34412 Pigmented epithelium Blind spot where optic nerve enters Choroid the retina Choroid Bipolar cell layer Ganglion cell layer Photosensitive region of rods and cones

Eye (toluidine blue) 292 Blind spot where optic nerve enters the retina

34412 Choroid plexus Retina OPTIC CUP AND NERVE HEAD Retina

In summary

Questions on the eye 1. The integrity of the relationship among structures of the eye is produced/maintained by: supporting layer of the eye holding pressure precise regulation of pressure via aqueous humor production and outflow the bony structure of the sclera in mammals a and b a, b, and c 2. Which structure is not correctly paired with its function? a. the iris regulates the amount of light that reaches the retina b. ciliary bodies alter the shape of the lens by the attached zonules c. the trabecular meshwork enhances the outflow of vitreous humor d. the cornea focuses the image on the retina e. the retinal and choroid blood vessels provide nutrients to the retina 3. Which function(s) least match(s) that of the cornea? a. protection b. structural support c. filter out undesirable light rays d. focus image on photosensitive portion of the photoreceptor cells e. none of the above

Many illustrations in these VIBS Histology YouTube videos were modified from the following books and sources: Many thanks to original sources! Bruce Alberts, et al. 1983. Molecular Biology of the Cell. Garland Publishing, Inc., New York, NY. Bruce Alberts, et al. 1994. Molecular Biology of the Cell. Garland Publishing, Inc., New York, NY. William J. Banks, 1981. Applied Veterinary Histology. Williams and Wilkins, Los Angeles, CA. Hans Elias, et al. 1978. Histology and Human Microanatomy. John Wiley and Sons, New York, NY. Don W. Fawcett. 1986. Bloom and Fawcett. A textbook of histology. W. B. Saunders Company, Philadelphia, PA. Don W. Fawcett. 1994. Bloom and Fawcett. A textbook of histology. Chapman and Hall, New York, NY. Arthur W. Ham and David H. Cormack. 1979. Histology. J. S. Lippincott Company, Philadelphia, PA. Luis C. Junqueira, et al. 1983. Basic Histology. Lange Medical Publications, Los Altos, CA. L. Carlos Junqueira, et al. 1995. Basic Histology. Appleton and Lange, Norwalk, CT. L.L. Langley, et al. 1974. Dynamic Anatomy and Physiology. McGraw-Hill Book Company, New York, NY. W.W. Tuttle and Byron A. Schottelius. 1969. Textbook of Physiology. The C. V. Mosby Company, St. Louis, MO. Leon Weiss. 1977. Histology Cell and Tissue Biology. Elsevier Biomedical, New York, NY. Leon Weiss and Roy O. Greep. 1977. Histology. McGraw-Hill Book Company, New York, NY. Nature (http://www.nature.com), Vol. 414:88,2001. Arthur C. Guyton,1971.Textbook of Medical Physiology W.B. Saunders company, Philadelphia, PA WW Tuttle and BA Schottelius 1969 Textbook of Physiology C.V. Mosby Co. A.L. Mescher 2013 Junqueira’s Basis Histology text and atlas, 13th ed. McGraw

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