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last week anatomy > Eye histology > Flashcards

Eye histology Flashcards

1
Q

What is the white part of the eye?

A

The sclera which is covered by a transperant tissue called the conjunctiva.

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2
Q

What is the colored part of the eye?

A

The iris which has a center opening that appears black called the pupil. The iris and pupil are covered by the transparent cornea and the junction between the cornea and the sclera is referred to as the limbus of the eye or the corneal sclera junction.

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3
Q

Describe the outer layer of the eye (fibrous tunic)

A

Sclera: dense irregular connective tissue. Supports and maintains the shape of the eye. Protects the internal structures, attachment site for extraocular muscles.
Cornea: Two layers of epithelium and connective tissue in between .Protects anterior surface of the eye. Refracts (bends) the incoming light onto the lens.

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4
Q

Describe the middle layer (Vascular tunic) of the eye

A

Choroid: connective tissue; highly vascularized. Supplies nourishment ot the retina, pigment absorbs extraneous light
Cilliary body: smooth muscle covered with a secretory epithelium. Holds suspensory ligaments that attach to the lens and change lens shape for far and near vision. Epithelim secretes aqueous humor
Iris: Two layers of smooth muscle (sphincter pupillae and dilator pupillae) and connective tissue, with a central pupil. Controls the pupil diameter and thus the amount of light entering the eye.

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5
Q

Describe the internal layer (Retina)

A

Pigmented layer: pigmented epithelial cells. Absorbs extraneous light, provides vitamin A for photoreceptors, recycles photoreceptors products.
Neural layer: neurons and glial cells. Detects incoming light, converts light rays to nerve signals and transmits signals to the brain.

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6
Q

What are the 3 innerconnected chambers of the eyeball?

A

Anterior, posterior, vitreous

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7
Q

What is the anterior chamber of the eye.

A

The anterior chamber-between the cornea and the iris. The anterior chamber is filled with aqueous humor, a liquid that resembles blood plasma with less protein and glucose and more lactate and ascorbate.

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8
Q

What is the posterior chamber of the eye

A

Between the iris and the lens. It is filled with aqueous humor. The aqueous humor is produced by the secretory epithelium linging the cilliary body, fills the posterior chamber and flows into the anterior chamber through the pupil.

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9
Q

What is the vitreous cavity?

A

It is surrounded by the retina and is posterior to the lens. It contains large transparent gelatinous mass called the vitreous body composed of hyaluronic acid.

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10
Q

What is the cornea?

A

A colorless, transparent, highly innervated and completely avascular structure composed of cells and connective tissue.

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11
Q

What are the 5 layers of the cornea?

A
  1. The corneal epithelium
  2. The bowmans layer
  3. corneal stroma
  4. descemets membrane
  5. The conreal endothelium
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12
Q

What is the corneal epithelium?

A

non-keratinized stratified squamous and consists of five to seven layers of cells. These cells provide a barrier to the outside world and contain numerous sensory nerve endings involved in the blink reflex. Corneal epithelial cells undergo continuous renewal fro mstem cells at the corneal sclera junction (limbus)

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13
Q

What is bowmans layer?

A

A 6 to 9 micro meter thick layer of connective tissue that supports the overlying corneal epithelium and represents an additional protective barrier to trauma and bacterial invasion.

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14
Q

What is corneal stroma?

A

A highly transparent layer representing 90% of thickness of the cornea. It consists of collagen fibers forming a lattice that is highly resistant to deformations and trauma. Cells of the stroma are called Karatocytes which proudce and maintain the collagen matrix.

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15
Q

What is descemets membrane?

A

one of the thickest basement membranes in the body

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16
Q

What is the corneal endothelium?

A

It lines the posterior surface of Descemets membrane and consists of a single layer of squamous epithelial cells, with impermeable intercellular junctions that regulate the influx of aqueous humor into the corneal stroma. The structural and fuctional integrity of the corneal endothelium is vital of a proper hydration state of the stroma and corneal transparency.

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17
Q

What happens when corneal fails to focus the light rays precisely on the retina?

A

myopia and hyperopia might result

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18
Q

What is myopia (near-sightedness)

A

The eyeball is too long or a cornea is too curved. Light rays fall short of the retina and objects in the distance appear blurred.

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19
Q

What is hyperopia (far-sightedness)

A

eyeball is too short or a cornea that is too flat. Light rays are focused behind the retina and object close up are blurred.

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20
Q

What is presbyopia?

A

similar to hyperopia but is due to an age-related change in the elasticity of the lens.

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21
Q

How can cornea fails to focus light be corrected?

A

with eyeglasses or a surgical procedure to alter the shape of the cornea called radial keratotomy.

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22
Q

Describe the conjunctiva

A

A thin, transparent mucosa that covers the exposed, anterior portion of the sclera and continues as the lining of the inner surface of the eyelid.

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23
Q

What is the primary function of the conjunctiva?

A

To keep the anterior surface of the eye moist and lubricated so they open and close without friction or causing eye irritation and to protect they eye from dust, debris and infection-causing microorganisms.

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24
Q

Describe the histology of the conjunctiva.

A

It is a stratified columnar epithelium, with numerous small cells resembling goblet cells. The mucous secretions of the goblet cells are added to the tear film that coats the corena and prevents the occurence of dry eye syndrome.

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25
Q

What is conjunctivitis?

A

A condition in which the conjunctiva is inflamed usually due to bacterial or viral infection or to allergies. The inflammation increases the discharge of the mucus and enlarges the microvasculature of the sclera, causing the white sclera to have a reddish appearance. Bacterial and viral conjunctivitis are contagious but have little effect on vision.

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26
Q

What are the two choroid layers. Describe them

A
  1. The choriocapillaris is a vascularized connective tissue containing numerous pigment cells important for nutrition of the outer retinal layers and absorbing scattered light rays
  2. Bruch’s membrane is a thin sheet of connective tissue between the choriocapilllaris and the pigmented layer of the retina.
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27
Q

What is the choroid a site of?

A

An age-related macular degeneration (AMD). AMD resutls from damage to the macula that is required for central vision.

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28
Q

What are the two forms of AMD? Describe them

A
  1. Dry (nonexudative >80%) characterized by diffuse or discrete deposits of lipid and protein in Bruch’s membrane of the choroid and atrophy and degeneration of the pigmented epithelium and associated photoreceptors of the retina leading to vision loss. No effective treatment at this time. Diet, multivitamin supplements and antioxidants may slow the progression
  2. Wet (exudative, 10-15%) characterized by the presence of angiogenic new vesels originating form the choriocapillaries and penetrating through Bruch’s membrane and the RPE. Vessels leak and cause scaring. Current treatment is injection of VEGF antagonists into the vireous cavity to inhibit the formation of new vessles and stop the leaking or laser treatment.
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29
Q

What is the ciliary body?

A

An anterior expanison of the choroid in the posterior chamber that encircles the lens at the level of the limbus. The ciliary muscle (smooth muscle) makes up most of the stroma of the ciliary body. Ciliary processes are ridges extedning from the ciliary body and lined by a double lyaer of epithelium. The inner layer is highly pigmented. The outer layer of cells are highly specialized for secretion of aqueous humor into the posterior chamber.

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30
Q

Describe the flow of aqueous humor

A

It is produced continuously and flows toward the lens, passing between it and the iris to reach the anterior chamber and the pupil. The aqueous then flows into the angle formed by the cornea with the basal part of the iris and penetrates the channels of the trabecular meshwork at the corneoscleral junction (limbus) from which it is pumped into the scleral venous sinus and eventually into the venous blood returning from the eye.

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31
Q

Why is normal intraocular pressure necessary?

A

it is necesary for functioning optical system, partly because it maintains a smooth curvature of the corneal surface and helps keep the photoreceptor cells in contact with the pigmented epithelium.

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32
Q

What happens during glaucoma?

A

the intraocular pressure is elevated and the optic nerve becomes constricted where it emerges from the eyeball through the sclera.

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33
Q

What does constriction of the optic nerve lead to?

A

it may lead to vision loss and blindness

34
Q

Elevated pressure is caused by an obstruction that hampers with the normal drainage of aqueous humor, which can no longer overcome the pupillary or trabecular resistance. What two conditions may develop?

A
  1. Acute or closed angle glaucoma: the flow of aqueous fluid frojm the posterior chmaber to the anterior chamber is obstructed by iris tissue. Pressure builds up in the posterior chamber and pushes portions of the iris upwards, blocking the chamber angle.
  2. Chronic or open-angle galucoma: in which the chamber angle is open but drainage through the trabeccular meshwork is impaired. Most common type of glaucoma that becomes more prevelant after the age of 40.
35
Q

It is glaucoma if there is optic nerve damage and associated vision loss, otherwise it is called what?

A

ocular hypertension.

36
Q

What are the ciliary body and its associated zonular fibers important for?

A

lens accomodations.

37
Q

What are the zonular fibers?

A

a system of radially oriented fibers that extend from the ciliary processes. They are important for holding the lens in place and together with the ciliary body these fibers also regulate the shape of the lens during the accomodation reflex.

38
Q

What is the accomodation reflex?

A

the process by which the shape of the lens changes to maintain a clear image or focus on an object as its distance varies from the eye.

39
Q

How are light rays focused on a distant object as opposed to a nearby object.

A

light rays from a distant object are focused on the retina by a flattened lens while a nearby object are focused on the retina by a more rounded lens.

40
Q

What happens to the zonular fibers when the ciliary muscle relaxes or contracts.

A

When the ciliary is relaxed the zonular fibers are put under increased tension and the lens flattens. Conversely, when the ciliary muscle contracts the zonular fibers becojme lax and the lens becomes more round.

41
Q

What is the ciliary body innervated by?

A

Parasympathetic fibers of the occulomotor nerve.

42
Q

Describe the iris.

A

it is the anterior extension of the middle vascular tunic that covers part of the lens, leaving a round central pupil that regulates the input of light into the eye.

43
Q

What does the posterior surface of the iris have histologically?

A

It has a two-layered epithelium continuous with that covering the ciliary processes, but very heavily filled with melanin. The highly pigmented posterior epithelium of the iris blocks all light from entering the eye except that passing through the pupil.

44
Q

What two layers of smooth muscles are present in the iris

A
  1. an outer radially oriented layer called the dilator pupillae muscle
  2. an inner circular bundle near the pupil known as the sphincter pupillae muscle.
    The dilator and sphincter muscles of the iris have sympathetic and parasympathetic innervation respectively, for enlarging and constricting the pupil.
45
Q

What is the sphincter pupillae innervated by?

A

parasympathetic fibers of the oculomotor nerve; contraction causes decreased pupillary aperture

46
Q

What is the dilator pupillae muscle innervated by?

A

sympathetic fibers; contraction causes increased pupillary apeture.

47
Q

What is the retina, what does it contain?

A

It is the layer of tissue lining the inner surface of the ey consisting of the light-sensitive neurosensory layer and the pigmented epithelium. The retina consists of several innerconnected layers of neurons supported by specialized glial cells.

48
Q

What is the retinal pigmented epithelium?

A

It is a layer of cuboidal epithelial cells in close association with the photoreceptors of the retina. The RPE carry out many functions including the conversion and storage of retinoid, the phagocytosis of shed photoreceptor outer segments the absorption of scattered light and ion and fluid transport. Dysfunction of RPE can result in photoreceptor death and blindness.

49
Q

What is the outer nuclear layer of the retina?

A

It contains the cell bodies and nuclei of the potoreceptors (rods and cones). Rods contain the visual pigment rhodopsin and are responsible for vision in low light levels. Cones are responsible for color vision and are the sight of color blindness. These cells generate a signal in response to a photon of light and transmit a signal to the neurons of the inner nuclear layer.

50
Q

What does the inner nuclear layer consist of?

A

bipolar cells, amacrine cells and horizontal cells. All responsible for integrating the signals produced by the photoreceptors and transmitting signals to the ganglion cell layer.

51
Q

What is the ganglion cell layer?

A

It has neurons with very long axons that make up the nerve fiber layer which come together to form the optic nerve.

52
Q

What are the retinal neurons supported by?

A

muller glial cells which extend the full thickness of the neurosensory retina and microglial cells which have phagocytic and other immune type functions.

53
Q

Light rays pass through the full-thickness of the retina in order to initiate what?

A

The production of a visual image that is transmitted to the brain via the optic nerve.

54
Q

What is the optic disc?

A

The location where axons from ganglion cells of the retina exit the eye to form the optic nerve and the retinal blood vessels enter and leave the eye.

55
Q

What is the macula?

A

A 6mm oval-shaped highly pigmented spot near the center of the retina. In the center of the macula is a small pit called the fovea that is responsible for central, high resolution/high acuity vision.

56
Q

What does the external ear contain

A
  1. The auricle which consist of elastic caritlage covered by keratinized stratified squamous epithelium which hairs, sebaceous glands, and sweat gladns.
  2. The external audtiory meatus extends from the auricle to the tympanic membrane of the middle ear. The outer one third of the wall is composed of elastic cartilage that is continuous with the auricle. The inner two-thirds of the wall is formed by the temporal bone. The external auditory meatus is lined by stratified squamous epithelium with hairs, sebaceous glands, and ceruminous glands. Secretions of sebaceous and ceruminous glands combine to form cerumen.
57
Q

What does the middle ear contain?

A

The air-filled tympanic cavity, an irregular space that lies within the temporal bone between the tympanic membrane and the bony surface of the internal ear. Anteriorly this cavity communicates with the pharynx via the auditory tube and posteriorly with the smaller, air filled mastoid cavities of the temporal bone.

58
Q

What is the primary function of the middle ear?

A

To equalize air pressure between the tympanic cavity and the external enviornment. The walls are normally opposed to one another; however, during swallowing and yawning, the walls separate, allowing air to enter the tympanic cavity.

59
Q

What is the tympanic cavity lined with?

A

mainly simple cuboidal epithelium resting on a thin lamina propria that is strongly adherent to the periosteum. In the medial bony wall of the middle ear are two membrane-covered regions devoid of bone: the oval and round windows.

60
Q

How is the tympanic membrane indirectly connected to the oval window?

A

By three small bones, the auditory ossicles, which transmit the mechanical vibrations of the tympanic membrane to the internal ear.

61
Q

What are the names of the ossicles?

A

malleus, incus, and stapes.

62
Q

What do the two small skeletal muscles that insert into the malleus and stapes do?

A

they restrict movement of the ossicles and help to protect the internal ear from extremely loud noises (tensor tympani attached to the malleus, and the stapedius attached to the stapes).

63
Q

What is the internal ear?

A

it is located completely within the temporal bone, where an intricate set of inerconnected spaces, the bony labyrinth, houses a set of continuous fluid-filled, epithelium-lined tubes and chambers that make up the membranous labyrinth.

64
Q

What is the vestibule?

A

A central cavity of the bony labyrinth. Contains the utricle and the saccule that mediates the sense of equilibrium.

65
Q

What is the semicircular canals?

A

(superior, lateral, and posterior) extend posteriorly from the vestibule, oriented right angles to one another. At one end of each is a dilatation called the ampulla. The semicircular canals mediate the sense or equilibrium.

66
Q

What is the cochlea?

A

Coils like a snail shell around a central pillar of bone containing the cochlear duct. Mediates the sense of hearing.

67
Q

What does the epithelial lining of the utricle, saccule and semicircular canals contain?

A

large areas of columnar sensory mechanoreceptors called hair cells. Each hair cell contains numerous sterocilia and a kincilium that respond to motion. Detection of motion of the kinocilium results in signals conveyed to the brain of the vestibular nerve.

68
Q

What is the choclear duct?

A

A part of the membranous labyrinth is highly specialized as a sound receptor. It is about 35 mm long, coiled two and one-half times, and is suspensed within the bony labyrinth surrounded by specialized spaces (scala vestibuli and scala tympani) containing perilymph fluid.

69
Q

What is perilymph?

A

It is similar in ionic composition to csf and extracellular fluid of other tisssues, but contains little protein. Perilymph emerges from the microvasculature of the periosteum and is drained by the perilymphatic duct into the ajoining subarachnoid space. The fluid suspends and supports the closed membranous labyrinth, protecting it from the hard wall of the bony labyrinth.

70
Q

What is the cochlear duct filled with?

A

Endolymph, which also contains few proteins and is further characterized by a high potassium and low sodium content, similar to that of intracellular fluid. Endolymph is generated largely by capillaries in the stria vascularis in the wall of the chochlear duct and is drained from the vestibule into the venous sinuses of the dura mater.

71
Q

What is the cochlear duct separated from the scala vestibuli by?

A

the vestibular membrane.

72
Q

What is the spiral organ?

A

It is in the wall the separates the choclear duct from the scala tympani. It contains special auditory receptors in the form of hair cells that respond to different sound frequencies.

73
Q

Describe the spiral organ histology

A

It rests on a thick basal lamina-the basilar membrane. Two major types of hair cells are present each with sterocilia on their surface. The tips of the tallest sterocilia of the hair cells are embedded in the tectorial membrane, an acellular layer extending over the organ of cotri.

74
Q

What are the base of each hair cell in the tectorial membrane innervated by?

A

a branch of the choclear division of the eigth cranial nerve. These nerve endings transmit impulses to the bipolar neurons of the spiral ganglion.

75
Q

How is sound heard?

A

Sound waves collected by the auricle of the external ear cause they tympanic membrane to vibrate, which causes movement of ossicles in the middle ear.
Fluid waves within the perilymph begin at the oval window and move along the scala vestibuli. Each fluid wave causes momentary movement of the vestibular and/or basilar membranes and the endolymph surrounding the spiral organ.

76
Q

What is associated with the sound waves’ frequency?

A

A region of maximal displacement of the vestibular and basilar membrane.

77
Q

High frequency sounds produce maximal movement near what?

A

The oval window.

78
Q

Sounds of progressively lower frequency sound produce fluid waves where?

A

that move farther along the scala vestibuli and displace the spiral organ at a point farther from the oval window. The sounds of the lowest frequency that can be detected produce movement of the basilar membrane at the apex or helicotrema of the cochlea. After crossing the cochlear duct and spiral organ at these various points, fluid waves are transferred to the scala tympani and exit the inner ear at the round window.

79
Q

Where are the sterocilia of the hair cells?

A

Embedded in the tectorial membrane.

80
Q

What does fluid displacement in the inner ear cause?

A

The sterocilia of the hair cells to bend resulting in the release of neurotransmitters from the basal portion of the hair cells that leads to neural impulses.

81
Q

How does the aqueous humor flow?

A

It is produced continuously and flows toward the lens, passing between it and the iris to reach the anterior chamber through the pupil. The aqueous then flows into the angle formed by the cornea with the basal part of the iris and penetrates the channels of the trabecular network at the corneoscleral junction (limbus), from which it is pumped into the scleral venous sinus and eventually into the venous blood returning from the eye.

last week anatomy (4 decks)

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