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Ophthalmology > Physiology I > Flashcards

Physiology I Flashcards

1
Q

What is cerebrospinal fluid (CSF)?

A

Clear and colourless liquid composed mostly of water = produced by secretory epithelium of the choroid plexus

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2
Q

How quickly is CSF produced?

A

At a rate of 0.4ml/min/gtissue = 500-600ml produced per day

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3
Q

How much CSF is in the central nervous system?

A

150ml = replaced 3-4 times a day

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4
Q

Where is CSF produced?

A

Formed in the ventricles of the brain = circulates in subarachnoid space before being absorbed into venous circulation

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5
Q

What does CSF supply tissues with?

A

Supplies water, amino acids and ions

Removes metabolites

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6
Q

What are the functions of CSF?

A

Mechanical protection, homeostatic function and circulation

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7
Q

How does CSF protect the brain?

A

Acts as shock absorbing medium

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8
Q

What does the pH of the CSF have an effect on?

A

Pulmonary ventilation and cerebral blood flow = due to transport of hormones

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9
Q

Where does the CSF allow exchange of materials between?

A

Blood and brain tissue

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10
Q

How are samples of CSF for clinical analysis obtained?

A

Via lumbar puncture = aids diagnosis of brain, meninges and spinal cord

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11
Q

What are the features of normal CSF?

A

Clear and colourless, contains little protein (15-45mg/dl), has little immunoglobulins (1-5 cells/ml)

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12
Q

What does the developing nervous system consist of at 3 weeks gestation?

A

Consists of tube = neural canal

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13
Q

What does the cavity of the neural tube give rise to?

A

The adult brain’s ventricles and the central canal of the spinal cord

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14
Q

Where does the choroid plexus develop from?

A

Cells in the walls of the ventricles

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15
Q

What is the specialisation of choroid cells?

A

Secrete cells that produce CSF

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16
Q

What forms the choroid fissure?

A

Developing arteries invaginate the roof of the ventricle

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17
Q

What forms the choroid plexus?

A

The involuted ependymal cells along with the vessels enlarge into villi

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18
Q

Where is the choroid plexus located?

A

In the third, fourth and lateral ventricles of the adult brain

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19
Q

What does CSF secretion involve?

A

Transport of ions (Na, Cl, HCO3) across the epithelium from blood to CSF

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20
Q

What allows CSF secretion to occur?

A

The polarised distribution of specific ion transporters in the apical or basolateral membrane in the epithelial cells

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21
Q

What does the secretion of fluid by the choroid plexus depend on?

A

Active transport of Na across cells into the CSF = electrical gradient pulls Cl and both ions drag water by osmosis

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22
Q

How does CSF compare to blood?

A

CSF has higher concentrations of Na and Cl, and lower concentrations of K, glucose and protein than blood

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23
Q

Does CSF production depend on arterial blood pressure?

A

No = is independent process

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24
Q

What connects the lateral and third ventricles?

A

The interventricular foramina

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25
Q

Where is the foramen of Magendie found?

A

In the medial aperture = connects fourth ventricle to subarachnoid space through single opening

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26
Q

Where is the foramen of Luschka found?

A

In the lateral aperture = connects fourth ventricle to subarachnoid space through paired opening

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27
Q

What connects the third and fourth ventricles?

A

The cerebral aqueduct of Sylvius

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28
Q

Where does the CSF flow in the brain?

A

Flows into third ventricle through interventricular foramina, flows through aqueduct of Sylvius into fourth ventricle

29
Q

What happens to the CSF when it is in the third ventricle?

A

More CSF is added to it by the choroid plexus in the roof of the ventricle

30
Q

What happens to the CSF when it enters the fourth ventricle?

A

Another choroid plexus adds more CSF to it

31
Q

Where does CSF go once it has left the fourth ventricle?

A

Enters subarachnoid space and circulates in the central canal of the spinal cord

32
Q

What is the main producer of CSF?

A

The choroid plexus

33
Q

Where does the CSF flow through in the subarachnoid space?

A

Between the pia and the dura mater

34
Q

How does the CSF return to venous blood?

A

Through arachnoid granulations into the superior sagittal sinus

35
Q

What restricts the blood supply to the brain?

A

The blood brain barrier

36
Q

What makes up the final portion of the CSF?

A

Brain interstitial fluid = drains to CSF through the perivascular spaces

37
Q

What forms the blood brain barrier?

A

Endothelial cells in brain capillaries = consists of capillary epithelium, its basement membrane and perivascular astrocytes

38
Q

What prevents paracellular movement of molecules into the brain?

A

Tight junctions

39
Q

What parts of the brain have no blood brain barrier?

A

Circumventricular organs and pineal gland

40
Q

What is the function of the blood brain barrier?

A

Protects brain from many bacterial infections and toxins, is determining factor for clinical CSF analysis

41
Q

What are some common tumours related to CSF?

A

Colloid cysts = often at interventricular foramen
Ependymomas = arise from ependymal cells
Choroid plexus tumours

42
Q

What is a ventricular haemorrhage?

A

An accumulation of blood in the ventricles

43
Q

What are some common ventricular haemorrhages?

A

Epidural haematoma = arterial bleed between skull and dura
Subdural haematoma = venous bleed between dura and arachnoid
Subarachnoid haemorrhage

44
Q

What is hydrocephalus?

A

Accumulation of CSF in ventricular system or around the brain

45
Q

What does hydrocephalus cause?

A

Subsequent enlargement of one or more ventricles and increase in CSF pressure

46
Q

What is idiopathic intracranial hypertension?

A

Enigmatic condition = no imaging features of hydrocephalus despite increased CSF pressure

47
Q

What are the symptoms of idiopathic intracranial hypertension?

A

Headache and visual disturbances = due to papilloedema

48
Q

What is papilloedema?

A

Optic disc swelling due to increased intracranial pressure transmitted to the subarachnoid space surrounding the optic nerve

49
Q

What are the visual symptoms of papilloedema?

A

Enlarged blind spot, blurred vision, loss of vision, visual obscurations

50
Q

What is the aqueous humor?

A

Specialised fluid that bathes the structures within the eye = provides oxygen and metabolites, contains HCO3

51
Q

What is the function of the HCO3 in the aqueous humor?

A

Buffers H produced in the cornea and lens by anaerobic glycolysis

52
Q

How is the aqueous humor produced?

A

Via energy dependent process in epithelial layer of ciliary body into the posterior chamber of the eye

53
Q

Where does the aqueous humor flow to once it has left the posterior chamber of the eye?

A

Flows into anterior chamber and drains to scleral venous sinus through a trabecular meshwork and the canal of Schlemm

54
Q

Where is the canal of Schlemm located?

A

In the angle between the iris and the cornea (iridocorneal angle)

55
Q

Where does a small amount of the aqueous humour diffuse through?

A

The vitreous = is then absorbed across the retinal pigment epithelium

56
Q

What covers the ciliary body and the posterior surface of the iris?

A

Two juxtaposed layers of epithelial cells = forward continuation of pigment epithelium of retina overlain by an inner non-pigmented epithelial layer

57
Q

How are HCO3 and H transported into the aqueous humor?

A

Transported mostly across the basolateral membrane of pigment epithelium into interstitial fluid in exchange for Cl and Na respectively

58
Q

What produces the HCO3 and H found in the aqueous humor?

A

Formed in epithelial cells from hydration of CO2 catalysed by carbonic anhydrase

59
Q

How does Na and Cl enter the cells of the eye?

A

Diffuse through gap junctions between the pigment epithelium and the non-pigmented epithelium

60
Q

What transports Na and Cl out of the non-pigmented epithelium into the aqueous humour?

A

The Na/K/2Cl co-transporter = K leaving the cell is recycled by Na/K pump and some Cl leaves the cell through channels

61
Q

What accompanies the net movement of Cl and Na from the interstitial fluid to the aqueous humour?

A

Water = moves through ciliary epithelial cell water channels, aquaporins and through the paracellular pathway down the osmotic gradient created by solute movement

62
Q

How much aqueous humour is secreted?

A

1-3 ml/min = flows into the anterior chamber

63
Q

What is the volume of the anterior and posterior chambers of the eye?

A 
Anterior = 250ml
Posterior = 60ml
64
Q

How long does it take to completely replace the aqueous humour of the posterior and anterior chambers?

A 
Posterior = 30 mins
Anterior = 120 mins
65
Q

What maintains the intra-ocular pressure at 17mmHg?

A

Balance between secretion and drainage of fluid

66
Q

What causes raised intra-ocular pressure in glaucoma?

A

Imbalance between rates of secretion and removal of aqueous humour

67
Q

What drugs are used to treat glaucoma?

A

Carbonic anhydrase inhibitors = reduce aqueous humor production

68
Q

What are some examples of carbonic anhydrase inhibitors?

A 
Dorzolamide = given as eye drops, avoids systemic side effects 
Acetazolomide = taken orally, targets kidney, causes acidosis

Ophthalmology (20 decks)

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