Exam 1 Remington- Corneal Physiology Flashcards Preview

Anatomy and Biochemisty > Exam 1 Remington- Corneal Physiology > Flashcards

Flashcards in Exam 1 Remington- Corneal Physiology Deck (106):
1

What are the 4 functions of the cornea?

Transmits light, absorbs short wavelength UV, refracts light, and proper corneal function requires minimal scattering and distortion

2

Cornea scatters less than __% incident light.

1

3

Cytoplasm of epi and endo cells in the cornea contain what?

Corneal crystallins, water soluble proteins

4

What do corneal crystallins do?

They make cytoplasm homogenous and decrease light scattering

5

What range does the cornea transmit?

UV 310 nm to IR 2500 nm

6

What is the reason for photokeratitis?

The cornea absorbs short wavelength UV

7

Photokeratitis

Inflammation caused by absorption of UV

8

What are causes of photokeratitis?

Welder's arc, tanning beds, and snowblindness

9

What is the refraction of light of the cornea determined by?

Curvatures of the various surfaces, interfaces between different indices of light, and length of pathway through the structures

10

Proper corneal function requires what?

Minimal scattering and distortion, no blood vessels, proper hydration

11

Relative corneal deturgescenes means the corneal is ___% water

78

12

Corneal hydration is dependent on what?

Temperature, swells when cooled and returns to normal at body temperature

13

What is the role of tears in maintaing proper hydration?

As tears evaporate the tear fluid becomes more concentrated, tear film osmolarity increases relative to the cornea, the hypertonicity of tear film draws water from cornea and the blink response is elicited because hypertonicity causes a slight sting and thus tear film is restored

14

What is the role of the epithelium in maintaining proper hydration?

ZO barrier prevents intercellular water influx from tears, ions move across both surfaces, aquaporins are water transport channels

15

What do channels of the epithelium allow?

Channels allows Na+ to pass into epi from tears and Cl- to pass into tears

16

What are major driving forces for water transport?

Cl- extrusion and Na+ influx

17

The co-transporter mechanism moves what ions in the cornea?

Na, K, and Cl ions

18

Na+/K+ ATPase pumps located in ______ ______ of the cornea actively move ions

Basolateral membrane

19

Aquarporins are present where?

Epithelial cell membranes

20

There is a ________ flow of water across the plasma membrane in the cornea.

Bidirectional

21

What is the role of the stroma in maintaining proper hydration?

GAGs are present in ground substance surrounding collagen fibers, increasing hydration leads to decreasing transparency

22

What is the role of GAGs in the stroma of the cornea?

Due to anionic characteristics they bind with water- there is an inherent tendency to imbibe water and to swell

23

Water content of the stroma should be approximately ___%

78

24

The normal water content of the sclera is ___%, if it falls below ___% or above ___% the sclera becomes lucent

68, 40, 80

25

What is the role of endothelium in the cornea in maintaining proper hydration?

These cells have high metabolic activity, apparent by large number of mitochondria and Golgi apparatus, slow leak of fluids and solutes from the aqueous, the Na+/K+ ATPase pump is located in the basolateral membrane of the endothelium

26

How does the Na+/K+ ATPase pump located in the basolateral membrane of the endothelium act?

Pumps act at a steady rate and the rate of leakage is dependent upon the pressure gradient across the endo

27

What are the ions that cotransporters move across membranes?

Na, K, Cl, HCO3

28

Where are aquaporins located in the endothelium?

In the endo cell membrane

29

What are 4 measures of endothelial function?

Coefficient of variation CV, cell density, polymegathism, and pleomorphism

30

What is the coefficient of Variation CV?

Indicates the degree of uniformity among endo cells

31

What is the CV equation?

Sd of mean cell area/ mean cell area

32

What is normal CV?

0.25

33

As CV increases there is an _____ in amount of variation in size

Increase

34

What is cell density?

Number of cells per unit area

35

How many cells in young?

4000-3000 cells/ mm^2 in young

36

How many cells by age 80?

2000 cell/ mm^2

37

How many cells necessary for normal function?

400-700

38

Polymegathism

Variation in cell size

39

Pleomorphism

Variation in cell shape

40

What is the most efficacious shape?

Hexagonal

41

Endothelial stress resulting from CL wear, disease, age, surgery etc. can lead to what?

Endothelial remodeling, including change in size, shape, or both

42

Corneal ATP is generated by what?

Glucose metabolism

43

Glucose enters cornea primarily from what?

Aqueous

44

Oxygen enters cornea primarily from what?

Tear film

45

In closed lid, oxygen is mostly from what?

Palpebral conj

46

Utilizing anaerobic metabolism ~__ ATPs are produced per molecule of glucose

2

47

Under aerobic conditions ~___ ATPs per molecule of glucose

36

48

Cell proliferation includes what?

Nutrients, including glucose and amino acids

49

Some glucose goes through the ____ ____ shunt providing building blocks for nucleic acid synthesis

Hexose monophosphate

50

What are 2 manifestationss of corneal edema?

Change in dimension and change in appearance

51

What happens when there is a change in dimension in corneal edema?

Diameter remains same, thickness increases

52

How does the thickness increase in corneal edema?

Stromal matrix accumulates fluid, fiber diameter remains the same, swelling directed posteriorly, increase in corneal hydration positively linearly correlated with corneal thickness

53

What is the change in appearance in corneal edema?

Normally ~1% light scattering, with fluid retention light scattering increases, cornea becomes cloudy, buckling of Descemet's occurs and striae (folds) are seen

54

What causes epithelial damage?

Loss of ZO, localized area of swelling and haziness, causes abrasion, injury

55

What causes endothelial damage?

More serious, implies loss of active pump mechanism, caused by disease, surgery, injury, poorly fit contact lens may allow stagnation of tears

56

What are 3 clinical manifestations of endothelial damage?

Formation of guttata, endothelial cells thin, and apical junctions deteriorate

57

What is Fuch's dystrophy?

Problem with cellular function, results in loss of endo function

58

What are manifestations of Fuch's dystrophy?

Guttata form, stromal edema, and epithelial microcysts

59

What is metabolic edema?

Hypoxic condition causes an increase in anaerobic metabolism, concentration of lactate increases, osmotic balance changes and induces stromal edema

60

What is the normal range of IOP?

10-20 mmHg

61

What is borderline IOP?

21-25 mmHg

62

What is high IOP?

> 25 mmHg

63

What is very high IOP?

> 50 mmHg

64

What happens with very high IOP?

Endo transport system overwhelmed, must be treated quickly

65

What are 3 effects of corneal edema?

Hypoxia affects cellular function and causes decrease in intracellular pH, scarring can occur with dysfunction in collagen formation, neovascularization and new vessel growth

66

What is acidification?

Cellular damage

67

What is neovascularization?

Body's defense mechanism to provide a source of O^2

68

What is treatment of corneal edema?

Eliminate cause, temporary clearing with hypertonic solution of glycerin instillation

69

Corneal injury induces activation of what molecules that initiate and direct corneal repair?

Integrins, cytokines, and growth factors

70

Integrins

Facilitate and maintain cellular function

71

Cytokines

Facilitate cellular communication

72

Growth factors

Mediate proliferation and differentiation

73

What happens in the epithelium in corneal wound healing?

Mitosis stops, cells at wound edges lose hemidesmosome attachments, basal cells migrate, when defect is covered protein synthesis increases, mitosis resumes and cell proliferation replaces lost cells, after the wound is healed hemidesmosomes reformed, cell membrane and BM are linked via a biochemical bond prior to reformation of hemidesmosomes, epithelium generally heals in 24-48 hours with hemidesmosomes reformed (usually no scarring evident)

74

What happens when basal cells migrate in the epithelium?

Epidermal growth factor is released after injury and enhances cell migration and proliferation

75

If BM injured, normal adhesion may take ___ months to be complete

12

76

What happens to Bowman's layer in corneal wound healing?

Cannot be regenerated, is replaced by epithelial or stromal tissue

77

What happens to stroma in corneal wound healing?

Increase in number of keratocytes, collagen deposition in stroma, stromal healing not as rapid as epithelial healing

78

What happens to collagen deposition in stroma during corneal wound healing?

Fiber arrangement not as regular, diameter of regenerated fibers is greater than normal, scar may result

79

How long does stromal healing take?

May take up to 48 months for tensile strength to approach normal

80

What happens in Descemet's membrane during corneal wound healing?

Is very resistant to injury, will be secreted by the stromal fibroblasts and the endothelium

81

What happens to endothelium during corneal wound healing?

Migration to cover area, cells thin and remodel into hexagonal shape, pump and barrier functions are reestablished

82

What is the cause of neovascularization?

Disease, inflammation, or lack of oxygen

83

New vessels sprout from what in corneal neoascularization?

Perilimbal capillaries

84

What happens to the new vessels in corneal neovascularization?

Enzymes degrade BM of capillary, endothelial cells migrate, endothelial cells proliferate to form new vessels

85

_____ _____ have been identified in the normal cornea

Antiangiogenic factors

86

____ _____ are released in some diseases

Angiogenic factors

87

What are ghost vessels?

Vessels do not resorb, but when the situation that produced them is reversed, they no longer carry blood

88

Will ghost vessels be visible with slit lamp?

Yes

89

Sensory nerves terminate in free nerve endings tightly surrounded by ____ ____

Epithelial cells

90

Nerve ending pattern changes as the retract, reinsert or shift position apparently with ___ ___ ___

Epithelial cell turnover

91

Sensory innervation is ____ times higher than any other epithelial tissue

400

92

Sensory nerves have a ______ effect

Neurotrophic (influence corneal metabolism)

93

In animal studies denervation be ablating ablating the ophthalmic division of the trigeminal leads to what?

Increased epithelial layer permeability, decreased cellular adhesion, impaired wound healing, reduced mitosis, and reduced cell migration

94

What is the primary sensation in corneal sensitivity?

Pain

95

Is corneal sensitivity high or low?

High

96

Contact lenses _____ corneal sensitivity

Decreases

97

How is corneal sensitivity clinically measured?

Blink response, atheiometer

98

What is temperature corneal sensitivity like?

Registers changes but does not accurately recognize hot/cold

99

In central corneal damage, normal nerve pattern is present by what week?

Week 4

100

What happens in peripheral corneal damage?

Reinnervation takes longer than 60 days and density of pattern is lower than normal

101

What type of fibers have been identified in the cornea?

Sympathetic

102

The fibers in the cornea may affect what?

Cl ion channels

103

Substances such as ______ and ______ have been identified in the cornea

Acetylcholine and acetylcholinesterase

104

Why are acteylcholine and acetylcholinesterase in the cornea?

Transmitters for pain, contribute to tissue reaction that occurs in response to pain, mediate inflammatory response, play a role in transport processes and affect cellular permeability, regulate cell mitosis (perhaps because ACh can stimulate cGMP production and cGMP stimulates mitosis

105

The sclera is a _____ tissue

Dynamic

106

What happens in progressive myopia?

Collagen degradation, loss of proteoglycans, and changes in fibroblasts