Physiology

Question 1

Describe how aqueous humour is produced (ions and key enyzme)

Answer 1

Na+ / Cl- pumped through the retina (PE then NPE) in exchange for HCO3- and H+
H+ and HCO3- produced by carbonic anhydrase (from H2O + CO2).

Question 2

How is aqueous humour normally drained?

Answer 2

Produced into the posterior segment, then pumped through to anterior segment and out through the trabecular meshwork and canal of Schlemm

Question 3

Describe how light changes the membrane potential of rods.

Answer 3

light changes 11-cis-retinal to all-trans by optin (a GPCR)
all-trans activates a PDE which converts cGMP to GMP
this closes a Na+ channel preventing Na+ entering
More + ions means membrane potential decreases (below -40mv)

Question 4

What is the main difference between rods and cones?

Answer 4

Rods are useful for dim light; cones are useful for normal daylight (colour vision)

Question 5

Give the rough wavelength values for the different colour cones.

Answer 5

420 - blue
530 - green
570 - red
(500 - rods)

Question 6

Describe the key immune aspects of the eye.

Answer 6

No physical barrier and very few commensals
Blink reflex (wash away pathogens, like a window wiper), chemicals (e.g. lysozymes), cells (marophages etc.)

Question 7

Describe the key regional immune aspects of the eye.

Answer 7

conjunctiva - only lymph system, MALT
lacrimal system - MALT, plasma cells (CD8+)
cornea/sclera - avascular, lack of cells

Question 8

What is immune privilege and which sites in the body have it?

Answer 8

Toleration of foreign antigens without eliciting an inflammatory immune response

Question 9

Name the five key immune disorders associated with the eye (4 hypersensitivities).

Answer 9

Sympathetic ophthalmia (bilateral granulomatous disease, with ‘exciting’ to ‘sympathetic’ eye)
I - acute allergic conjunctivitis
II - ocular cicatrial pemphigoid (blistering, scarring)
III - autoimmune corneal melting
IV - corneal graft rejection

Question 10

Name the normal mucosa of the outer and middle ear, the nasopharynx, and salivary glands.

Answer 10

Outer ear - stratified squamous (contains hair follicles, sebaceous, and ceruminous glands)
Middle ear - columnar lined mucosa
Nasal vestibule lined by squamous epithelium. The rest is lined by pseudostratified squamous epithelium
Salivary glands - acinar (serous cells, amylase) and mucinous (glycoprotein) components. Myoepithelial cells help direct saliva to mouth

Question 11

Name the four taste bud types and the main tastes.

Answer 11

Vallate (back, sweet taste/glucose)
Foliate (side, bitter/H+, salty, NaCl)
Fungiform (central)
Filiform (tip)
Other taste - umami (all over the tongue, caused by amino acids)

Question 12

How does taste sensation travel from the tongue to the brain?

Answer 12

Taste receptor cells are much like an orange.
taste hairs and pores direct sensation to transitional and gustatory cells (‘wedges’ of the orange), which travel to the basal cells and afferent fibres.

Question 13

Describe how a smell sensation is created. What are the main causes of conductive and sensorineural smell loss?

Answer 13

Odourants diffuse (passive) or are sniffed (active) into the nose. Must be volatile and water soluble to be smelled. Odourants hit bipolar sensory neural cells and are conducted up the olfactory nerve (CN I).
Conductive - polyps, rhinitis, masses, septal deviation
Sensorineural - viruses (inc COVID), trauma, neurological (e.g. Parkinson’s), medication

Question 14

Describe how a sound impulse is created.

Answer 14

Pressure created from oscillating molecules is funneled into the external acoustic meatus by the outer ear.
The ossicular chain amplifies the sound 18:1 (e.g. 34dB).
This causes perilymph to vibrate and activate the organ of Corti, which sends signals via the cochlear nerve to CN VIII.
CN VIII travels via the cochlear nucleus, superior olivery complex, late lemniscus, inferior coliculus, to the primary auditory complex.