Lecture 13.2 Cornea Anatomy (stroma, Descemet, endothelium)

how much does the stroma account for in terms of corneal thickness

90%

what is stroma consisted of

regularly arranged lamellae of collagen bundles, lie in proteoglycan ground substance with bundles

what type of cells are present in stroma (3)

keratocytes, immune cells and granulocytes

another way to address stroma

Substantia propia

how many bundles are there in centrally in proteoglycan ground substance

200-300

how many bundles are there in peripherally in proteoglycan ground substance

500

composition of human cornea

water, collagen, other protein, keratan sulphate, condroitin/dermatan sulphate, hyaluronic acid, salts

how much does water take up in human cornea composition

78%

how much does collagen take up in human cornea composition

15%

how much does keratan sulphate take up in human cornea composition

0.7%

how much does other protein take up in human cornea composition

5%

how much does Condroitin/dermatan sulphate take up in human cornea composition

0.3%

how much does salts take up in human cornea composition

1%

How does cornea maintain the transparency?

with arrangement of stromal lamellae

basic building block of all collagen fibers in cornea

each collagen molecule (aka tropocollagen)

what is tropocollagen

a basic building block of all collagen fibers

Individual collagen molecules self assemble to what

fibrils

length of individual collagen molecules

300 nm long and 1.5 nm diameter

Collagen fibril diameter

25–35 nm (around 30 nm average)

length of Center-to-center spacing (intrafibrillar lattice)

49-60 nm (around 45 nm as mid value)

center-to-center spacing is a defining measurement of what in the corneal stroma

intrafibrillar lattice

what is intrafibrillar lattice

organization of collagen fibril packed together

lamella thickness in stromal cornea

1.5-2.5 um (1500-2500 nm)

for a lamella thickness of 1.5 um, how many layers are there

33

for a lamella thickness of 2.5 um, how many layers are there

56 layers

collagen type I function in cornea

strength and framework

collagen type V function in cornea

Controls fibril size

collagen type VI function in cornea

Connects lamellae and keratocytes

collagen type XII/XIV function in cornea

Link fibrils to extracellular matrix

collagen type III function in cornea

Repair collage

how much of type I collagen do we find in cornea

75%

how much of type V collagen do we find in cornea

10%

how much of type VI collagen do we find in cornea

5%

how much of type XII/XIV collagen do we find in cornea

1-2%

how much of type III collagen do we find in cornea

trace amount

How does cornea maintain the shape?

with Keratocytes, Granulocytes, Immune cells

what are the ground substances in stroma

Proteoglycans and Glycosaminoglycans

many collagen fibrils come together to form what

lamellae

how are the corneal proteoglycans classified

by their side chains

what proteoglycans do we find in the cornea that helps maintain shape

Keratan sulphate (KS) and chondroitin/dermatan sulphate (CS/DS)

what kind of proteoglycan is Decorin

a chondroitin/dermatan sulphate proteoglycan

what is the specific chondroitin/dermatan sulphate proteoglycan in cornea

Decorin

where is Decorin presented

anterior stroma

what are the specific Keratan sulphates proteoglycan in the cornea

Lumican, keratocan, and mimican

Lumican, keratocan, and mimican are what types of proteoglycans?

Keratan sulphate proteoglycans

what are  Lumican, keratocan, and mimican the most abundant

posterior stroma

what is the charge of Glycosaminoglycans (GAGs) molecules?

negatively charged carbohydrate molecules

what is the water property for Glycosaminoglycans (GAGs) molecules?

hydrophilic and high affinity to water because it is important for maintaining transparency of cornea

where are Glycosaminoglycans (GAGs) molecules located

at specific sites around each collagen fibril

primary function of proteoglycans

provide tissue volume, maintain spatial order of collagen fibrils

secondary function of proteoglycans

regulating collagen fibril assembly

function of Glycosaminoglycans (GAGs) in terms of structure

Linking different next nearest-neighbor collagen fibrils together by forming dumbbell-like structures

function of Glycosaminoglycans (GAGs) in terms of spatial relationship

Attract and bind with water, maintaining the precise spatial relationship between individual fibrils

what is the purpose of stromal wound healing

repair tissue by regeneration rather than fibrosis (formation of scar tissue)

what cells are use in stromal wound healing

keratocytes, bone marrow-derived cells, myofibroblasts

function of keratocytes in stromal wound healing

they are specialized fibroblasts, and non contractile molecules that synthesize extracellular matrix components-dormant until exposed to trauma or surgery

the purpose of bone-marrow derived cells in stromal wound healing

acts as the immune response

function of Myofibroblasts in stromal wound healing

they are contractile cells that promote wound closure and are associated with haze

which stromal wound healing cell is associated with haze

myofibroblasts

where does bidirectional interactions take place during corneal wound healing

between corneal epithelium and stroma 

types of cells involved during bidirectional wound healing

keratocyte —> fibroblast —> myofibroblast —> apoptosis

Interleukin-1 (IL-1) and tumor necrosis factor α (TNFα) are releaed by what cells

epithelial cells

what does the release of Interleukin-1 (IL-1) and tumor necrosis factor α (TNFα) lead to

apoptosis of keratocytes

how is the apoptosis of keratocytes activated

release of Interleukin-1 (IL-1) and tumor necrosis factor α (TNFα) by epithelial cells

Activated keratocytes and myofibroblasts secrete what

provisional matrix

Activated keratocytes and myofibroblasts secrete provisional matrix that consist of what

fibronectin, proteoglycans, and hyaluronan

IL-1 contribute to what type of cell activation

keratocyte activation

activated keratocytes are able to produce what

autocrine IL-1 

how do we activate the IL-1 loop happen

when activated keratocytes acquire the ability for autocrine IL-1 production

what is the basement membrane of the endothelium and posterior limiting membrane

Descemet membrane

Descemet membrane is also known as

posterior limiting membrane

describe Descemet membrane in terms of location

basement membrane of the endothelium and posterior limiting membrane

when does Descemet membrane first appear

at 2nd month of gestation and synthesis continue throughout adult life

thickness of Descemet membrane at birth

3-4 um

thickness of Descemet membrane at childhood

about 5 um

thickness of Descemet membrane in adults

10-12 um

how many laminae does Descemet membrane have

two

the two laminae of Descemet membrane are

the anterior lamina and poster lamina

what is the anterior lamina composed of

banded latticework of collagen fibrils

thickness of anterior lamina in Descemet membrane

3 um

describe the structure of posterior lamina of Descemet membrane

banded and homogenous

what is posterior lamina secreted by

endothelium throughout life

what happens to Descemet membrane in corneal degenerative conditions

it thickens with age

what is the major type of protein in Descemet membrane

type IV collagen

what is type IV collagen the major type of protein in Descemet’s membrane

because it is highly elastic that can bend and help other layers stay tightly attached

describe the structure of corneal endothelium

single layer of hexagonal, cuboidal cells, attached posterior aspect of Descemet membrane

Endothelial cell density: At birth

about 6000 cells/mm²

Endothelial cell density: tennage

about 4500 cells/ mm²

Endothelial cell density: adult

about 2500 cells/mm²

Endothelial cell density: geriatric (65+) population

 cells density falls up to 500 cells/mm²

corneal oedma happens to which population

geriatric (65+) population

height of corneal endothelium at birth

10 um

dimensions of corneal endothelium with age after birth

it becomes flattened to 4-5 um in height and 10-20 um width

shape of corneal endothelium from youth to adult

hexagonal to polymorphic

what is Polymegathism in corneal epithelial cells

variability of cell size

what is Pleomorphism in corneal epithelial cells

variability of cell shape

what is Hassal-Henle warts

It is the peripheral excrescence produced by focal overproduction of basal lamina like material in aging cornea

what is Cornea Guttata

Descemet’s warts of central cornea (tiny collagen-like deposits or bumps (guttae) appear on the Descemet membrane due to aging, genetic factors, and oxidative stress

what is Cornea Guttata associated with

increased permeability of endothelium

why does our corneal endothelial cells change in shape and size, or become polymorphic as we age

because the loss of cells causes gaps, and the remaining cells need to flatten to stay attached and reach other neighbouring cells