BS - Connective Tissue, Sclera and Vitreous - Week 1 Flashcards
Where does connective tissue originate embryonically? What are the origins of the corneal stroma?
Most connective tissue is mesoderm-derived.
Corneal stroma is ectoderm-derived.
What is connective tissue made of?
Cells and extracellular matrix.
What kind of connective tissue is the conjunctiva?
Loose
What kind of connective tissue is the sclera?
Dense regular
What kind of connective tissue is the tarsal plate?
Dense irregular
What kind of connective tissue is the episclera?
Loose
What kind of connective tissue is the cornea?
Dense regular
Can adipose tissue be considered connective tissue? Give an example of adipose relating to the eye.
Yes, it is a specialised form of connective tissue.
Orbital fat.
Name the 4 main functions of connective tissue.
Primary function is structural support Additonal functions are: Defence and protection of the body Fat storage Medium of exchange for waste and resources (oxygen and nutrients)
Name one function of connective tissue that is specific to the eye.
Light refraction (cornea).
Which form of connective tissue is responsible for acting as the medium of exchange for waste and resources?
Loose connective tissue
What is the extracellular matrix composed of primarily?
Ground substance and fibres.
What is the ground substance of the ECM made of? Is it organised or disorganised?
Made of specialised glycosaminoglycans, glycoproteins, and proteoglycans.
Highly organised interfibrillar matrix.
What are the three main components of fibres within the ground substance of the ECM?
Primarily collagen
Also elastic fibres - elastin and fibrillin
Reticular fibres
What are reticular fibres?
Small collagen fibres
What are glycosaminoglycans?
Repeating dissacharide units of amino sugar and uronic acid.
What are glycoproteins?
Proteins conjugated to saccharides lacking a serial repeat unit.
What 3 functions of glycosaminoglycans make it an important component of connective tissue?
Attracts water
Confers viscosity for resistance to pressure
Are all glycosaminoglycans charged? What charge do they carry?
All but one class carry a negative charge due to the presence of sulphur groups. Hyaluronic acid lacks sulphur, and is neutral - unique.
What cell is present in all connective tissue, and why?
Fibroblasts, as they make collagen.
How does connective tissue appear histologically?
Amorphous, due to the fixation process - doesn’t mean the space is empty however.
Can hyaluronic acid attract water, being a glycosaminoglycan?
Alone, it cannot as it is not sulphonated like other GAGs. It instead associates with other GAGs.
What are proteoglycans? What structure do they have, and what charge?
Heavily glycosylated glycoproteins.
They are a core protein, with one or more covalently attached GAG chains.
They are therefore negatively charged.
What is the function of charge on proteoglycans? What does this allow for?
The negative charge allows it to bind to cations like Na, K, and Ca. Allows control over matrix hydration.
How does hydration affect fibres in connective tissue?
Hydration controls fibre separation.
How does hyaluronic acid complex with other proteins?
One hyaluronic acid associates with many core proteins via a link protein. The core proteins may have many sulphonated GAGs.
Is collagen elastic?
Often referred to as inelastic.
Is actually highly elastic.
In what form is collagen typically found?
As fibre bundles comprising fibrils.
Do collagen fibres have uniform diameters?
Typically is relatively uniform, howver in different locations, and at different stages of development, may vary in size.
What is the most abundant protein in the animal kingdom?
Collagen.
How many kinds of collagen are there?
28 types.
What structure does collagen have?
Is a triple-helix of 3 fibrils.
In the eye, where is type I collagen found? What structure does it have?
Cornea and sclera
Is fibrillar
In the eye, where is type II collagen found?
What structure does it have?
Vitreous
Is fibrillar
In the eye, in what two structures is type IV collagen found?
What structure does it have?
ILM of the retina
Is a sheet
Also the major collagen component of zonule fibres
In the eye, where is type V collagen found?
What structure does it have?
Cornea
Is fibrillar
In the eye, where is type VI collagen found?
What structure does it have?
Cornea
Fibril-associated
In the eye, where is type VII collagen found?
What structure does it have?
Hemidesmosomes in the cornea
Is anchoring
What are the four main types of elastic fibres, and what confers this elasticity?
Elastin (main) Fibrillin Fibronectin Laminin Elasticity due to unusual polypeptide backbone of random coiled molecules
Where are elastic fibres typically found in the connective tissue?
Interwoven amongst collagen microfibrils.
What are reticular fibres?
Delicate network of fibres composed of collagen fibrils, but of different composition.
Small diameter, and do not form bundles.
What collagen type is localised to reticular fibres?
Type III.
Name 5 exampes of fixed cells in connective tissue?
Fibroblasts Pericytes Adipose Macrophages Mast cells
What is the function of fibroblasts?
Synthesise collagen, elastic, and reticular fibres
Where are myofibroblasts found?
Stressed tissue like the cornea.
What are pericytes?
Cells that surround endotheial cells of small blood vessels.
Where are mast cells derived from?
What is characteristic of them?
Stem cells in the bone marrow.
Have granules with histamine, heparin, and factors for initiating an inflammatory response.
What are transient cells in connective tissue typically associated with? Where are they derived from?
Immune system activation and inflammation. Derived from stem cells in the bone marrow.
What are the 6 functions of the sclera?
Protection Refractive stability Conduit for neurovascular vessels Anchor for extraoccular muscles Anchor for cilliary muscles Facilitates ocular drainage
What are the two major foramina of the sclera?
Anterior - cornea
Posterior - scleral canal
Where is the minor foramen of the sclera?
The optic disc where the neurovascular bundle pierces the sclera
What is the orientation of the scleral fibre bundles at the scleral canal? What purpose does this have?
2/3rds of the fibres turn 90 degrees forming meninges.
Remaining 1/3rd continues forming a mesh-like structure providing support to the nerve bundles.
What is the lamina cribrosa?
Sieve of interwoven collagen fibres whose chief purpose is to support the optic nerve bundle at the scleral canal.
Where is the weakest part of the outer eye, and when is this apparent?
Lamina cribrosa/scleral canal, affected most when intraoccular pressure is high.
What is Tenon’s capsule, what is its name in latin, what does it enclose, and where does it terminate anteriorly/posteriorly?
Fascia bulbi, a thin membrane enclosing the extraoccular muscles and episclera posteriorly.
Terminates at the limbal conjunctiva anteriorly, and optic nerve posteriorly.
What does the fascia bulbi merge with, and where?
Merges with the conjunctival tissue anteriorly.
What is the episclera?
Loose vascularised connective tissue overlying the sclera, connecting posteriorly to fascia bulbi via fine strands.
What is the scleral stroma?
Dense fibrous tissue intermingles with fine elastic fibres.
What is the limbal region?
Junction where the sclera, overlying episclera, and overlying conjunctiva meet the cornea.
What is the maina fusca also known as? What colour is it, and what is it attached to, and how?
Suprachoroid, brown in colour.
Attached to the choroid by fine collagen fibres.
What two structures does the perichoroidal space seperate?
Choroid from the suprachoroid.
What is the fibre bundle organisation in the sclera?
They run in whorls, interwoven for strength.
What is the purpose of varying sizes of cllagen fibril diameters?
Large diameters provide strength, low diameters provide flexibility and allow for tight packaging.
Why is the sclera opaque, and what is the advantage of this?
Irregular fibril sizes and bundle orientation.
Opacity means less stray light entering the eye.
What are the three main functions of the vitreous?
Shock absorber, protecting the retina and lens
Internal tamponade preventing retinal tears
Mainenance of a globe shape for image stability
Which type of collagen is typically found in vitreous?
Type II
What is the vitreous primarily composed of?
99% water, rest includes collagen, and hyaluronan
What 3 features of the vitreous allow for decreased light scattering?
Small, regular collagen fibril diameters
Few cells
Regular interfibrillar seperation
