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Ophthalmology > Physiology > Flashcards

Physiology Flashcards

1
Q

what is CSF

A

clear, colourless liquid that supplies water, amino acids and ions while removing metabolites

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2
Q

three major functions of CSF

A
  1. mechanical protection= shock absorbing
  2. Homeostatic= pH of CSF affects pulmonary ventilation and cerebral blood flow. Hormone transport.
  3. circulation
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3
Q

how is clinical analysis of CSF obtained?

A

lumbar puncture

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4
Q

define the choroid plexus

A

network of capillaries in the walls of ventricles that produces CSF

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5
Q

what does the secretion of CSF by the choroid plexus depend on?

A

active transport of Na+ across the cells into CSF as the electrical gradient pulls along Cl- and both ions drag water by osmosis

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6
Q

is the concentration of K+, glucose and protein lower in CSF than blood?

A

yes

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7
Q

is the concentration of Na+ and Cl- higher in CSF than the blood?

A

yes

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8
Q

structure of the BBB

A
  • consists of capillary endothelium, basal membrane and perivascular astrocytes
  • tight junctions prevent paracellular movement of molecules
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9
Q

what parts of the brain lack the BBB?

A

circumventricular organs

pineal gland

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10
Q

tumour pathologies of the ventricles, choroid plexus and CSF

A

colloid cyst
ependymomas
choroid plexus tumours

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11
Q

examples of ventricular haemorrhage

A
  • epidural haematoma
  • subdural haematoma
  • subarachnoid haemorrhage
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12
Q

describe an epidural haematoma

A

arterial bleed between skull and dura

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13
Q

describe a subdural haematoma

A

venous bleed between dura and arachnoid

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14
Q

describe hydrocephalus

A

accumulation of CSF in the ventricle system or around the brain
subsequent enlargement of one or more ventricles and increase in CSF pressure

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15
Q

what causes hydrocephalus

A

obstruction

overproduction

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16
Q

symptoms of idiopathic intracranial hypertension/pseudotumour cerebri

A 
headache
visual disturbance (fields > blindness, due to papilloedema)
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17
Q

what ion does aqueous humour contain?

A

bicarbonate HCO3-

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18
Q

what is the role of bicarbonate HCO3- in the aqueous humour?

A

it buffers H+ produced by the cornea and lens in anaerobic glycolysis

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19
Q

what are the two layers that cover the ciliary body and posterior surface of the iris

A

pigmented retinal layer (RPE)

non-pigmented epithelial layer (NPE)

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20
Q

how are HCO3- and H+ produced?

A

hydration of CO2 catalysed by carbonic anhydrase

21
Q

where are HCO3- and H+ transported?

A

across the basolateral membranes of the pigmented epithelial cells into interstitial fluid in exchange for Cl- and Na+

22
Q

how do Cl- and Na+ reach the aqueous humour?

A

they diffuse through gap junctions between PE and NPE and are transported into the aqueous humour via Na+/K+/Cl- co-transporter

23
Q

what is the net movement of Cl- and Na+ to the aqueous humour accompanied by?

A

water moving through ciliary epithelial aquaporins and paracellular pathway

24
Q

define glaucoma

A

raised intra-ocular pressure due to imbalance in secretion and removal of aqueous humour

25
Q

management of glaucoma

A

CA inhibitors reduce production of aqueous humour e.g. dorzolamide and acetazolamide

26
Q

side effects of acetazolamide

A

acidosis in kidneys

27
Q

retinal structure

A

epithelial layer contains pigment
first neural layer is photoreceptors which release glutamate which attaches to bipolar cells which release neurotransmitters to ganglion cells
lateral connections- horizontal cells and amacrine cells

28
Q

what is the photoreceptors resting membrane potential?

A

more positive -20mV than other neurones

29
Q

what happens to the photoreceptors resting membrane potential with light exposure?

A

hyperpolarises

30
Q

describe the dark currant

A

the positive resting membrane potential is due to a cGMP-gated Na+ channel being open in the dark causing a constant release of glutamate

31
Q

what happens to the cGMP-gated Na+ channel when exposed to light

A

it closes

32
Q

Na+/K+ in the dark

A

pump is equally permeable to both ions

Vm is therefore between ENa and EK

33
Q

Na+/K+ in response to light

A

PNa is reduced (outer segments close), therefore Vm becomes closer to ion potential of K+ (-90mV)

34
Q

what is the visual pigment in rods called?

A

rhodopsin= retinal (vitamin A) and opsin (GPCR)

35
Q

describe how hyperpolarisation happens?

A

all-trans-retinal activates transducing (GPCR) activates PDE which hydrolyses cGMP closing Na+ channels

36
Q

what is high visual acuity facilitated by?

A

photoreceptor spacing

37
Q

what lighting do rods see best in?

A

dim light

38
Q

how are rods distributed on the retina?

A

all across the retina with large spaces (low density= high convergence)

39
Q

what lighting do cones see best in?

A

daylight

40
Q

where are cones distributed on the retina?

A

concentrated at the fovea

41
Q

three types of cone cells

A
  1. short-wave cones= blue
  2. medium-wave cones= green
  3. long-wave cones= red
42
Q

properties of rod cells

A 
achromatic
peripheral retina
high convergence
high light sensitivity
low visual acuity
43
Q

properties of cones

A 
chromatic
central retina (fovea)
low convergence
low light sensitivity 
high visual acuity
44
Q

visual fields on the retina

A
  • each eye sees monocular visual field +/- 45 degrees
  • they overlap to create a binocular visual field +/- 45 degrees
  • retina is divided in half relative to the fovea into nasal and temporal hemiretina
  • nasal cross at the optic chiasm, temporal do not
45
Q

what do people with congenital cataracts struggle with?

A

perceiving shape and form as they cannot be removed until 10-20 years

46
Q

define amblyopia (cortical blindness)

A

variety of visual disorders where there is no problem with the eye but one eye has better vision than the other

47
Q

causes of amblyopia

A

strabismus (wandering eye) if not corrected in infancy

48
Q

management of strabismus in childhood

A

cover good eye for some hours each day so weak eye still grows connections until it can be surgically corrected

49
Q

define Hebb’s postulate

A

cells that fire together wire together (if not working, invades space)

Ophthalmology (28 decks)

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