Histology Flashcards
Latin terminology for the eye?
Bulbus oculi
Components of the bulbus oculi?
Three layers - outer supporting - middle - inner Accessory structures
Components of the outer supporting layer of the eye?
Cornea
Corneoscleral junction (limbus)
Sclera
What does the cornea consist of, histologically?
Transparent and avascular anterior supporting layer with nutrition from endothelium
- Outer layer (squamous stratified epithelium)
- Bowman’s membrane (acellular, collagen)
- Substantia propria (thickest layer, 25 pallel lamellae of collagen fibres)
- Descemet’s membrane (basement membrane)
- Inner layer (Descemet’s endothelium)
Another term for the substance propria of the cornea?
Stroma
Histology of the limbus
+/- 1mm transition zone from corneal epithelium to scleral epithelium
Functions of the sclera
Protect the eye
Maintain intraocular pressure
Insertion point of extrinsic ocular muscles
What does the sclera consist of, histologically?
Dense connective tissue (mostly collagen (fibroblasts) + some elastic fibres)
Few blood vessels
No lymphatics
Components of the middle layer of the eye?
Choroid
Ciliary body
Iris
What does the choroid consist of, histologically?
- Suprachoroid (collagen, elastic fibres + melanocytes)
- Vessel layer (thickest, many blood vessels with loose CT + melanocytes)
- Choriocapillary (single capillaries, wide lumens, fenestrated endothelium)
- Bruch’s membrane
What does Bruch’s membrane of the choroid consist of, histologically?
- Outer basal membrane of choriocapillary
- Collagen fibres
- Network of elastic fibres
- Collagen fibres
- Inner basal lamina of the pigment epithelium
What is the structure of the ciliary body, histologically?
Loose connective tissue rich in elastic fibres, vessels + melanocytes
Surrounded by ciliary muscle
Simple columnar cells rich in melanin
Derived from sensory layer of the retina (simple, non-pigmented columnar epithelium)
What is the structure of ciliary muscle, histologically?
2 bundles of smooth muscle
What is the structure of the ciliary processes, histologically?
Ridge-like extensions of he ciliary body
Loose CT core
Numerous fenestrated capillaries covered by the same epithelium
Zonule fibres from the ciliary processes insert in the lens capsule
What are fenestrated capillaries?
Capillaries with pores that allow larger molecules through for extensive molecular exchange with the blood
What is the structure of the iris, histologically?
Circular diaphragm with a distensible aperture (pupil)
An extension of the choroid that partially covers the lens
Has a rough, irregular anterior surface with grooves and ridges
What does the iris consist of, histologically?
- Endothelium
- Stromal layer
- Vessel layer
- Smooth muscle layer
- Pigmented epithelium layer
What is the structure of the zonula, histologically?
Suspensory ligaments of the lens that consist of filaments and bundles of fibres
Attached to ciliary body and lens equator
Components of the inner layer of the eye?
Lens
Retinal layer
What are the components of the lens?
- Lens capsule
- resembles a basement membrane
- serves for zonula implantation on equator of lens - Anterior cuboidal epithelium
- Lens substance
- elongated prismatic lens fibres
Components of the retina?
Anterior = pigmented epithelium (non-light sensitive) Posterior = neural retina (light sensitive + photoreceptive organ)
What are the two modification sites of the retina?
Posterior pole of the eye (macula lutea)
Optic papilla
Another name for optic papilla?
Optic disc
Layers of the retina
- Pigmented epithelium
- Rod + cone layers
- Outer limiting membrane
- tights junctions between Muller’s cells + photoreceptors - Cells bodies of rods and cones
- photoreceptor nuclei - Outer plexiform layer
- axons of photoreceptors synapse w/ bipolar + horizontal cells - Integrating bipolar cell layer
- nuclei of bipolar cells, horizontal cells, amacrine cells + Muller’s cells - Inner plexiform layer
- axons of bipolar cells, processes of amacrine cells + dendrites of ganglion cells - Ganglion cell layer
- nuclei and cell bodies of multipolar ganglion cells - Optic nerve fibres
- axons of ganglion cells - Inner limiting membrane
- terminal endings of Muller’s cell processes + their basal laminae
nuclei -> axon
Histology of the pigmented epithelium of the retina
Single layer of columnar cells w/ tight junctions, melanin granules and microvilli on their inner surface Function - absorption of light - prevention of light reflection - nutrition of photoreceptors
1st order neurons of the retina
Photoreceptors
How many rods are there?
120 million
How many cones are there?
7 million
Fovea centralis contains?
Only cones
Rods function in which light?
Poor light
Cones function in?
Bright light
Are responsible for colour observation
What are photoreceptors?
Modified dendrites
What is the structure of rods, histologically?
Contains rhodopsin/visual purple
- Outer segment
- elongated + rests against pigment epithelium
- light sensitive
- encapsulated with cell membrane
- flattened membranous sacs piled in stacks - Connecting segment
- narrowed + connects the outer and inner segments
- modified cilium - Inner segment
- mitochondria, free ribosomes + Golgi apparatus
What is the structure of cones, histologically?
Similar to rods BUT
- outer segment is cone shaped
- membranous vesicles are attached to cell membrane at some places
- contains iodopsin
2nd order neurons of the retina
- Bipolar neurons
- dendrites synapse w/ axons of the rods and cones
- axons synapse with the neurons of the third order - Horizontal cells
- synapse in horizontal plane
- dendrite synapse w/ axons of rods
- axons synapse w/ axons of cones
What is the structure of amacrine cells?
No axons
Only dendrites
Connected to bipolar and ganglion cells in horizontal plane
3rd order neurons of the retina
Ganglion cells The axons are - unmyelinated - along the inner retinal surface - come together to form optic nerve - exit at the optic disc
What are Muller’s cells?
A type of neuroglia that is present throughout the thickness of the retina
What is the blood supply of the pigmented epithelium?
No blood vessels
Diffusion of nutrients from choriocapillary layer
What is the blood supply of the axon layer?
Blood vessels from central artery that enters the eye through the optic nerve
These vessels supply other layers of the retina
What is the structure of the optic nerve, histologically?
Axons from the retina congregate at the optic disc, turn outwards and run through the lamina cribrosa as the optic nerve
The nerve fibres are unmyelinated, arranged into bundles + surrounded by neuroglial processes before they enter the lamina cribrosa
After the lamina cribrosa, the nerve fibres acquire myelin sheaths
What is the structure of the conjunctiva, histologically?
Transparent mucosal membrane covering the eyeball that continues on the inner surface of the eyelid
- Epidermis
- stratified columnar epithelium -> stratified squamous epithelium -> skin epidermis - Lamina propria
- delicate loss CT w/ infiltrated lymphocytes
What is the structure of the eyelid, histologically?
Anterior surface - thin skin - fine hair - sebaceous/sweat glands Border - several gland types + hair follicle rows - loose dermis structure Tarsal plate - dense CT Posterior surface - skeletal mm - unkeratinized stratified squamous epithelium -> stratified columnar epithelium that rests on thin CT layer
What is the structure of the lacrimal gland, histologically?
Serous compound tubulo-alveolar glands that open via +/- 12 secretory ducts Functions - maintains eye moisture - bactericidal - flushes foreign bodies from eye
What is the name of the accessory lacrimal glands?
Glands of Krause
