BS - Connective Tissue, Sclera and Vitreous - Week 1

Question 1

Where does connective tissue originate embryonically? What are the origins of the corneal stroma?

Answer 1

Most connective tissue is mesoderm-derived.

Corneal stroma is ectoderm-derived.

Question 2

What is connective tissue made of?

Answer 2

Cells and extracellular matrix.

Question 3

What kind of connective tissue is the conjunctiva?

Answer 3

Loose

Question 4

What kind of connective tissue is the sclera?

Answer 4

Dense regular

Question 5

What kind of connective tissue is the tarsal plate?

Answer 5

Dense irregular

Question 6

What kind of connective tissue is the episclera?

Answer 6

Loose

Question 7

What kind of connective tissue is the cornea?

Answer 7

Dense regular

Question 8

Can adipose tissue be considered connective tissue? Give an example of adipose relating to the eye.

Answer 8

Yes, it is a specialised form of connective tissue.

Orbital fat.

Question 9

Name the 4 main functions of connective tissue.

Answer 9

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)

Question 10

Name one function of connective tissue that is specific to the eye.

Answer 10

Light refraction (cornea).

Question 11

Which form of connective tissue is responsible for acting as the medium of exchange for waste and resources?

Answer 11

Loose connective tissue

Question 12

What is the extracellular matrix composed of primarily?

Answer 12

Ground substance and fibres.

Question 13

What is the ground substance of the ECM made of? Is it organised or disorganised?

Answer 13

Made of specialised glycosaminoglycans, glycoproteins, and proteoglycans.
Highly organised interfibrillar matrix.

Question 14

What are the three main components of fibres within the ground substance of the ECM?

Answer 14

Primarily collagen
Also elastic fibres - elastin and fibrillin
Reticular fibres

Question 15

What are reticular fibres?

Answer 15

Small collagen fibres

Question 16

What are glycosaminoglycans?

Answer 16

Repeating dissacharide units of amino sugar and uronic acid.

Question 17

What are glycoproteins?

Answer 17

Proteins conjugated to saccharides lacking a serial repeat unit.

Question 18

What 3 functions of glycosaminoglycans make it an important component of connective tissue?

Answer 18

Attracts water

Confers viscosity for resistance to pressure

Question 19

Are all glycosaminoglycans charged? What charge do they carry?

Answer 19

All but one class carry a negative charge due to the presence of sulphur groups.
Hyaluronic acid lacks sulphur, and is neutral - unique.

Question 20

What cell is present in all connective tissue, and why?

Answer 20

Fibroblasts, as they make collagen.

Question 21

How does connective tissue appear histologically?

Answer 21

Amorphous, due to the fixation process - doesn’t mean the space is empty however.

Question 22

Can hyaluronic acid attract water, being a glycosaminoglycan?

Answer 22

Alone, it cannot as it is not sulphonated like other GAGs. It instead associates with other GAGs.

Question 23

What are proteoglycans? What structure do they have, and what charge?

Answer 23

Heavily glycosylated glycoproteins.
They are a core protein, with one or more covalently attached GAG chains.
They are therefore negatively charged.

Question 24

What is the function of charge on proteoglycans? What does this allow for?

Answer 24

The negative charge allows it to bind to cations like Na, K, and Ca. Allows control over matrix hydration.

Question 25

How does hydration affect fibres in connective tissue?

Answer 25

Hydration controls fibre separation.

Question 26

How does hyaluronic acid complex with other proteins?

Answer 26

One hyaluronic acid associates with many core proteins via a link protein. The core proteins may have many sulphonated GAGs.

Question 27

Is collagen elastic?

Answer 27

Often referred to as inelastic. | Is actually highly elastic.

Question 28

In what form is collagen typically found?

Answer 28

As fibre bundles comprising fibrils.

Question 29

Do collagen fibres have uniform diameters?

Answer 29

Typically is relatively uniform, howver in different locations, and at different stages of development, may vary in size.

Question 30

What is the most abundant protein in the animal kingdom?

Answer 30

Collagen.

Question 31

How many kinds of collagen are there?

Answer 31

28 types.

Question 32

What structure does collagen have?

Answer 32

Is a triple-helix of 3 fibrils.

Question 33

In the eye, where is type I collagen found? What structure does it have?

Answer 33

Cornea and sclera | Is fibrillar

Question 34

In the eye, where is type II collagen found? | What structure does it have?

Answer 34

Vitreous | Is fibrillar

Question 35

In the eye, in what two structures is type IV collagen found? What structure does it have?

Answer 35

ILM of the retina Is a sheet Also the major collagen component of zonule fibres

Question 36

In the eye, where is type V collagen found? | What structure does it have?

Answer 36

Cornea | Is fibrillar

Question 37

In the eye, where is type VI collagen found? | What structure does it have?

Answer 37

Cornea | Fibril-associated

Question 38

In the eye, where is type VII collagen found? | What structure does it have?

Answer 38

Hemidesmosomes in the cornea | Is anchoring

Question 39

What are the four main types of elastic fibres, and what confers this elasticity?

Answer 39

``` Elastin (main) Fibrillin Fibronectin Laminin Elasticity due to unusual polypeptide backbone of random coiled molecules ```

Question 40

Where are elastic fibres typically found in the connective tissue?

Answer 40

Interwoven amongst collagen microfibrils.

Question 41

What are reticular fibres?

Answer 41

Delicate network of fibres composed of collagen fibrils, but of different composition. Small diameter, and do not form bundles.

Question 42

What collagen type is localised to reticular fibres?

Answer 42

Type III.

Question 43

Name 5 exampes of fixed cells in connective tissue?

Answer 43

``` Fibroblasts Pericytes Adipose Macrophages Mast cells ```

Question 44

What is the function of fibroblasts?

Answer 44

Synthesise collagen, elastic, and reticular fibres

Question 45

Where are myofibroblasts found?

Answer 45

Stressed tissue like the cornea.

Question 46

What are pericytes?

Answer 46

Cells that surround endotheial cells of small blood vessels.

Question 47

Where are mast cells derived from? | What is characteristic of them?

Answer 47

Stem cells in the bone marrow. | Have granules with histamine, heparin, and factors for initiating an inflammatory response.

Question 48

What are transient cells in connective tissue typically associated with? Where are they derived from?

Answer 48

Immune system activation and inflammation. Derived from stem cells in the bone marrow.

Question 49

What are the 6 functions of the sclera?

Answer 49

``` Protection Refractive stability Conduit for neurovascular vessels Anchor for extraoccular muscles Anchor for cilliary muscles Facilitates ocular drainage ```

Question 50

What are the two major foramina of the sclera?

Answer 50

Anterior - cornea | Posterior - scleral canal

Question 51

Where is the minor foramen of the sclera?

Answer 51

The optic disc where the neurovascular bundle pierces the sclera

Question 52

What is the orientation of the scleral fibre bundles at the scleral canal? What purpose does this have?

Answer 52

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.

Question 53

What is the lamina cribrosa?

Answer 53

Sieve of interwoven collagen fibres whose chief purpose is to support the optic nerve bundle at the scleral canal.

Question 54

Where is the weakest part of the outer eye, and when is this apparent?

Answer 54

Lamina cribrosa/scleral canal, affected most when intraoccular pressure is high.

Question 55

What is Tenon's capsule, what is its name in latin, what does it enclose, and where does it terminate anteriorly/posteriorly?

Answer 55

Fascia bulbi, a thin membrane enclosing the extraoccular muscles and episclera posteriorly. Terminates at the limbal conjunctiva anteriorly, and optic nerve posteriorly.

Question 56

What does the fascia bulbi merge with, and where?

Answer 56

Merges with the conjunctival tissue anteriorly.

Question 57

What is the episclera?

Answer 57

Loose vascularised connective tissue overlying the sclera, connecting posteriorly to fascia bulbi via fine strands.

Question 58

What is the scleral stroma?

Answer 58

Dense fibrous tissue intermingles with fine elastic fibres.

Question 59

What is the limbal region?

Answer 59

Junction where the sclera, overlying episclera, and overlying conjunctiva meet the cornea.

Question 60

What is the maina fusca also known as? What colour is it, and what is it attached to, and how?

Answer 60

Suprachoroid, brown in colour. | Attached to the choroid by fine collagen fibres.

Question 61

What two structures does the perichoroidal space seperate?

Answer 61

Choroid from the suprachoroid.

Question 62

What is the fibre bundle organisation in the sclera?

Answer 62

They run in whorls, interwoven for strength.

Question 63

What is the purpose of varying sizes of cllagen fibril diameters?

Answer 63

Large diameters provide strength, low diameters provide flexibility and allow for tight packaging.

Question 64

Why is the sclera opaque, and what is the advantage of this?

Answer 64

Irregular fibril sizes and bundle orientation. | Opacity means less stray light entering the eye.

Question 65

What are the three main functions of the vitreous?

Answer 65

Shock absorber, protecting the retina and lens Internal tamponade preventing retinal tears Mainenance of a globe shape for image stability

Question 66

Which type of collagen is typically found in vitreous?

Answer 66

Type II

Question 67

What is the vitreous primarily composed of?

Answer 67

99% water, rest includes collagen, and hyaluronan

Question 68

What 3 features of the vitreous allow for decreased light scattering?

Answer 68

Small, regular collagen fibril diameters Few cells Regular interfibrillar seperation