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Physiology > Aqueous > Flashcards

Aqueous Flashcards

1
Q

What is the ciliary epithelium derived from?

A

Neuroectoderm

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2
Q

What is the ciliary epithelium a continuation of?

A

Neural layer of retina

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3
Q

What is the outer pigmented layer a continuation of?

A

RPE

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4
Q

What is the AC volume?
What is the rate of aqueous formation?

A

200-250uL

2-3uL/min

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5
Q

What form the blood aqueous barrier?

A

Tight junction between inner non-pigmented epithelial cells precent exudate from the fenestrated ciliary capillaries reaching the aqueous

Non-fenestrated iris vessels

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6
Q

How is aqueous humour formed?

A

70% active secretion
20% ultrafiltration
10% osmosis

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7
Q

What cells secrete aqueous

A

Mitochondiria rich non-pigmented epithelium

Pigmented epithelium also plays a part

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8
Q

What is the rate of aqueous flow?

A

2.75uL/min

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9
Q

What are the functions of the aqueous

A

Supply nutrition to the lens, corneal endothelium and stroma
Maintain IOP
Remain transparent

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10
Q

What is the composition of aqueous?

A

LOW PROTEIN
HIGHT ASCORBATE -reduce oxidtive damage from UV

Similar to plasma
Na 140mmol/l
K 4mmol/l
Glucose 80% of plasma
Lactate 2x plasma level
Ascorbic acid 50x that of plasma
Protein 1/500 of plasma as blood aqueous barrier
IgG and IgM
Plasminogen
Growth factors

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11
Q

What are the outflow pathways of aqueous

A

Mostly through trabecular meshwork and canal of Schlemm

Into the episcleral veins

Uveoscleral outflow 0.3uL.min

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12
Q

What cells line Schlemms canal? How does aqueous transport occur?

A

Non fenestrated single layer of endothelium with tight junctions

Micropinocytic vesicles and giant vacuoles within endothelial cells allow aqueous transport

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13
Q

How does IOP change through the day

A

diurnal rhythm
Peaks in late morning and trough in early afternoon

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14
Q

What is mean IOP

A

15-16mmHg

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15
Q

What effect does sleep/GA have on IOP

A

Decrease due to reduction in extraocular muscle tone

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16
Q

What effect does suxamethonium have on IOP

A

Transient marked rise

17
Q

What does an increase in central venous pressure do to IOP

A

Raise in episcleral venous pressure and hence IOP

18
Q

What is the path of the aqueous humour?

A

WSecreted by the non-pigmented ciliary epithelium in ciliary processes of anteiror pars plicata

Ciruclates into posteiror chamber

Through pupil
Towards anteiror chamber angle (area where cornea and iris join)

Drains through outflow apparatus (trabecular meshwork via canal of schlemm into episcleral veins)

10% drains through uveoscleral route

19
Q

What factors affect aqueous production and drainage hence IOP

A

Episcleral venous pressure
Rate of flow of aqueous
Circadian rhythm
Neural and hormonal influences

20
Q

What is the process of aqueous production?

A

Diffusion and ultrafiltration of plasma - reservoir int he stroma - active secretion across ciliary epithelium to form posterior chamber aqueous humour

21
Q

What enzymes are involved in active secretion

A

Na/K/ATPase
Carbonic anhydrase - CO2+H2O - HCO3- +H+ - inhibtion of HCO3 leads to inhibition of active transport of Na into the NPE, reducing aqueous formation

22
Q

What is the function of the ciliary body?

A

Provides neovascular supply to the anteiror segment,
constitutes part of blood aqueous barrier
Reponsible for accommodation

23
Q

What is blood supply to cilairy body?

A

Long posteiror cilairy arteries
Major iris circle

24
Q

What are the arrangement of muscle fibres in the ciliary muscle?

A

External longitudinal attached to scleral spur

Middle radial

Internal circular

25
Q

What forms the blodo aquoeus barrier between the ciliary body and anteiror sement?

A

Tight junctions between non-pigmented ciliary epithelial cells

  • occludins and cingulin proteins form tight junctions
26
Q

What maintains blood aqueous barrier between iris and AC?

A

TIght junction between endothelial cells and lack of fenestrations

27
Q

What are functions of tight junctions?

A

Limit passage of molecules and ion so materieals must enter cells by diffusion or active transport in order to pass through
Block movement of integral membrane proteins between apical and basolateral surfaces of cell - specialised function of each cell surface

Restrict passage of water, electrolytes, other small molecules

28
Q

Compared to plasma aqueous has

A

Slight acidity
Marked excess of ascorbate
Slight excess of chloride and lactic acid

Slight deficit of sodium, bicarb, CO2 and glucose
Marked deficit of protein

Physiology (15 decks)

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