Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

HMO202 > Physiology of Cornea and Tear Film > Flashcards

Physiology of Cornea and Tear Film Flashcards

1
Q

What are the layers of the cornea starting most anterior?

A

Epithelium (55um), Bowmans layer (5um), Stroma (485um), Descemets membrane (10um), Endothelium (5um)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Focusing system of eye?

A

cornea, aqueous, iris, crystalline lens, vitreous

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Imaging system of eye

A

retina, optic nerve/tract, visual cortex

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How does cornea anatomically stay transparent

A

avascular, non pigmented cells, un-myelinated nerves, optical surface (tear film)

*collagen fibril orientation: equal diameter and separation. Specific arrangement generating constructive interface

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Epithelium for transparency

A

semi permeable membrane

tears/epithelium:

  • Na+ movement by passive diffusion
  • Cl- actively pumped to tears, creates water gradient towards tears

epithelium/stroma:
- Requires energy Na+K+ATPase transporter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Endothelium for transparency

A

permeable membrane

aqueous humour to stroma:
transports glucose, amino acids and nutrients driven by IOP and stroma pressure

Stroma to Aqueous Humour:

  • pumps fluid into aqueous humour
  • Bicarbonate pump
  • Carbonic anhydrase within cell
  • Na+K+ATPase pump
  • lateral cell walla
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Corneal Function - Metabolism

A

energy needed to maintain corneal hydration

epithelium –> tears passive (osmosis)

Stroma –> epithelium active

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what is glucose stored as?

A

glycogen in epithelial cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what is glycolysis?

A

enzymatic breakdown of glucose to pyruvate and energy

oxygen needed for aerobic metabolism

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Epithelial function - nutrient source

A

nutrient supply via tear film + aqueous

glucose –> epithelial glucose from AqHumour (diffusion through stroma and endothelium)

Oxygen –> no blood vessels so mostly atmospheric diffusion from tears. When eyelids closed palpebral conjunctiva is source

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Aerobic Epithelial Function

A

glycolysis via two mechanisms:

Krebs cycle –> conversion of pyruvate by mitochondria lead to generating ATP (energy)

Pentose phosphate pathway –> oxidises glucose to generate NADPH, fatty acid synthesis, glycolysis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Anaerobic epithelial function

A

glycolysis via two anaerobic mechanisms:
- pentose phosphate pathway. Oxidises glucose to generate NADPH, fatty acid synthesis and glycolysis

Anaerobic pathway produces pyruvate and lactate that breaks down CO2 and H20. Increased acidity, cellular damage, dysfunction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Endothelial function -metabolism

A

oxygen delivery via AqHumour. Independent of eyelid closure

Glucose vis AqHumour

Glycolysis and ATP generated mostly from Krebs cycle. High density of mitochondria

Uses alot of energy due to high metabolic demand for ion transport

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Corneal function - Defence

A

epithelium major defence mechanism:

  • absence of vascular system
  • tight junctions and tear film
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Epithelium turnover

A

rapid wound healing. 24-48 hours

epithelial cell migration, monolayer slides over wound within 5 hours

cell proliferation at the limbus to support migration

cell adhesion, rapid from plaque adhesion to hemidesmosomal complexes

keratocytes (fibroblats) dormant until compromise (injury, inflammation)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

endothelial repair

A 
Cell density: 
Birth 5000 (cells/mm2)
Age 5 - 3500
Teenager - 3000
Adult - 2500

Coverage compensation:
Lost cells are replaced by expansion and thinning of neighbouring cells
Leads to variation in cell shapes (polymorphism) and sizes (polymegathism) with age

17
Q

how do tears stick to corneal surface?

A
  • corneal microvilli
  • membrane spanning mucus
  • secreted mucus

sticky surface with water soluble glue

18
Q

Tear film - function

A
  • maintains health of ocular surface; proteins, nutrients
  • acts as a lubricant for lid and corneal interaction
  • disposal system to wash debris away and dilute toxins
  • optically smooth surface
19
Q

Tear film - composition:

A

Three components:

  • inner mucin layer
  • aqueous phase (bulk)
  • outer lipid layer (most anterior surface)

A mucin gradient exists between inner mucin layer and aqueous layer

20
Q

What is mucin layer

A

product of corneal and conjunctival cells

sticks tear film down, anchors aqueous phase to corneal surface

lubricant

bounding of debris/ bacteria

21
Q

what is aqueous layer

A

liquid layer

volume of tears from lacrimal gland

source of electrolytes, proteins, peptides and oxygen

removal of debris, bacteria

22
Q

what is lipid layer

A

stops tearms from evaporating

acts as lubricant

produced by meibomium glands (eyelid margins)

23
Q

source of tear film

A

mucin –> conjunctiva, squamous and goblet cells

aqueous –> lacrimal glands, acinus sacs

Lipids –>
Meibomium glands, acinus sacs

24
Q

tear film mucins

A

Combination of secreted:

  • Goblet cells (MUC5Ac)
  • Lacrimal gland (MUC7)
  • Mixes in aqueous phase
  • Cleaning up debris

Membrane spanning:
- Epithelium, cornea, conjunctiva
- Forms glycocalyx (glue)
MUC1, MUC4 and MUC16

25
Q

4 major proteins found in tear film aqueous

A

Lysozyme:
(2.07 mg/ml), a potent antibacterial enzyme, by hydrolysing the bonds in the outer wall of the bacteria (G+ve, streptococcus and staphylococcus)

Lipocalin:
(1.55mg/ml), plays a lipid binding role, maintains the surface tension of the tears. Binds with fatty acids which enhances function of Lysozyme

Lactoferrin:
(1.65mg/ml), antimicrobial (G+ve and G-ve Pseudomonas, Eschericha coli, Haemophillis influenza) binds to free iron preventing use by bacteria.

Part of innate defence mechanism

Secretory IgA:
(1.93mg/ml), part of the adaptive response system, adheres to bacteria thus a target for phagocytosis

Other –> (0.1mg/ml)

Aqueous largest component of tears. little glucose, also of K+ and Cl-

26
Q

tear film lipid layer

A

Produced by meibomian glands:

  • Modified sebaceous glands that secrete meibum
  • Mixture of lipids and proteins
  • Differs to seibum (more viscous)
  • Very thin complex oily layer (15-160nm)
  • Mixture of polar, non polar and neutral lipids, >236 lipids isolated
  • Melting point 19.5-32.9 degrees - always fluid on ocular surface
Optical finishing touch
Retard evaporation 
Evaporation - aqueous layers thin
Surface destabilises 
Non-wetting patches appear 
Poor optical performance

Observation easier:
Instillation of water soluble dye
Sodium fluorescein
Clinically known as Tear Break Up time TBUT

Temperature gradient:
Ocular surface 37 degrees (body temp)
Air –> ambient 24 degrees
Tear film must evaporate. Limited by lipid layer

Tear film needs:
- Replacing
- Refreshing
Reforming

27
Q

four phases of blink action

A

downstroke - upper lid to lower lid

turning point - lid stops before reversing motion

upstroke - upper lid moves away from lower lid

interblink - pause before downstroke

28
Q

function of blink

A

downstroke –> regenerates aqueous phase, sweeps mucin wrapped debris nasally

turning point –> forms new lipid layer

upstroke –> spreads lipid layer over tear film

interblink –> pause before downstroke. Vision processing

29
Q

types of tears

A

basal - mediated by Na+K+ATPase

reflex - parasympathetic control. sensory stimulation, retinal stimulation, pain, emotions

primarily through increased aqueous volume orbital/palpebral lobes of lacrimal glands

30
Q

corneal dysfunciton

A

opacification:
corneal dystrophy, opacification due to infection, cornea filled with blood vessels, stroma increasing thickness odema (milky cornea), plaques

31
Q

tear dysfunction:

A

Stability:

  • Aqueous dysfunction
  • Lipid dysfunction
  • Mucin dysfunction

Ectropion
TBUT
Dry Eye

32
Q

what is osmolarity

A

The concentration of an osmotic solution, measured in litres, the total number of particles dissolve in a solvent

For tears: 
- As aqueous reduces 
- Salt concentration increases 
- Osmolarity increases (hyperosmolarity) 
Symptoms of dry eye increase

HMO202 (5 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions