Nutrional disorders & the eye Flashcards
what are the major nutrients that our food is composed of
- carbohydrates
- protein
- fats
how do carbohydrates supply energy/ATP
broken down into glucose (monosaccharides)
what types of proteins are in the body
- amino acid chains - for structural support
- enzymes
- collagen
- hormones
what are fats useful for in the body
- help absorb vitamins
- energy source
- integral part of cell membranes
- insulation
what do vitamins act as
co-enzymes
what two things can co-enzymes be
- fat soluble
or - water soluble
what will vitamins be useless without
carbohydrates, proteins & fats
what are the fat soluble vitamins
A, D, E & K
what are the water soluble vitamins
B & C
what are the 7 minerals that the body requires moderate amounts of
- calcium
- phosphorus
- potassium
- sulphur
- sodium
- chloride
- magnesium
what are minerals not used for
not used for energy
what are minerals used for
functions such as:
- Ca - bone
- Fe - haemoglobin
- Ca/Na/K - nerve minerals
which mineral functions for nerves
Ca, Na, K
which mineral functions for bone
Ca
which mineral functions for haemoglobin
Fe
what are most minerals that we need synthesised from within the body
the liver from the food we ingest
give an example of a retinal nutrient which cannot be made by the body and only comes from the diet
carotenoid
what are the two sorts of nutritional deficiencies
primary & secondary
what is primary nutritional deficiency
insufficient intake
what is secondary nutritional deficiency
intake normally sufficient, yet cells receive less nutrients as they don’t arrive where they should e.g.
- failure of intestine to absorb (e.g. crohn’s disease)
- increased demand (pregnancy, lactation, growth)
- presence of antagonists (some substances can neutralise nutrients taken in)
what is crohn’s disease
failure of the intestine to absorb nutrients
what two diseases are the result of protein-energy malnutrition PEM
- marasmus
- kwashiorkor
what is protein-energy malnutrition PEM
deficiency of proteins and calories
what happens as a result of the disease marasmus
body compensates for the reduced calorific deficiencies by catabolising body tissues (fat and muscle).
the calories derived from the breakdown of these tissues are used to maintain normal cellular metabolism.
the result of this is extreme body wasting (but alert and recover quickly as normal cell function is retained)
what happens as a result of the disease kwashiorkor
body cannot compensate for catabolising tissues.
normal metabolism fails
patients lethargic and difficult to feed
characteristic symptom is the extended belly, caused by failure to maintain serum albumin levels resulting in oedema
what is a characteristic symptom of kwashiorkor disease
the extended belly, caused by failure to maintain serum albumin levels resulting in oedema
what are vitamin deficiencies hypovitaminosis
Not enough vitamins
Hyper = too many vitamins
what is an ocular vitamin of vitamin A
retinol
where does retinol come from
either directly from the diet or is produced in the body from a provitamin (carotene) which the body can convert to vitamin A
where does dietary retinol come from
dairy products and liver
where does carotene come from
leafy green/yellow vegetables
what are the ocular symptoms of vitamin A deficiencies
- night blindness (nyctalopia)
- epithelial changes
how does night blindness occur as a result of vitamin A deficiency
vitamin A is integral part of visual pigments (which are composed of a protein, opsin, bound to 11-cis retinal, which is derived from retinol)
the first photoreceptor to be effected are the rods, which underlie scotopic vision, in severe deficiency, cone mediated photopic vision is also effected
how does epithelial changes occur as a result of vitamin A deficiency
squamous epithelium becomes abnormally thickened and excessively keratinised (keratin plaques)
where does ocular covering epithelia occur
in the cornea and conjunctiva
what is the name of changes in ocular epithelia due to vitamin A deficiency
xeropthalmia
what happens to the conjunctiva as a result of ocular epithelial changes due to vitamin A deficiency
conjunctiva becomes wrinkled and dry and white bitot’s spots (raised keratin plaques) develop
what is the name of raised keratin plaques
Bitot’s spots
what happens to the cornea at a late stage of vitamin A deficiency
corneal epithelium is lost over the lower nasal part of the eye. also dry wrinkled conjunctiva
what happens to the cornea in advanced keratomalacia
the whole cornea becomes softened and opaque
what is the name for corneal ulceration
keratomalacia
what two ways is vitamin D (cholecalciferol) obtained
- absorbed by intestine from the diet along with fats
- UV light from the sun transforms a steroid in the skin (7-dehydroxycholesterol)
what are vitamin D deficiency usually resulted from
- insufficient dietary intake
- lack of sunlight
how can vitamin D deficiencies be eradicated in developed countries
adding vit D to milk
how can vitamin D deficiencies still occur in developed countries
- older people who rarely go outside
- vegetarians who don’t eat dairy products
what is vitamin D known as in Germany and why
known as english disease based on assumption the sun never shines in england
what is the main function of vitamin D
aiding absorption of calcium
what is a result of vitamin D deficiency
not enough calcium gets absorbed in the blood and there is inadequate calcification of bones
what is the name of children whose bones are still developing but have vitamin D deficiency
rickets
what is the result of a child with rickets
overall growth is retarded and because the bones becomes soft you can get a number of deformities.
load bearing bones, such as tibia bow out and children become pigeon-chested as the intercostal muscles pull on the ribs
what is the name of vitamin D deficiency in adults
osteomalacia
what is vitamin K required for
synthesis of blood coagulation factors e.g. prothrombin (being converted into thrombin)
what is the main source of vitamin K
synthesis by intestinal bacteria
some derived from leafy green vegetables and dairy products
when can vitamin K deficiency occur
after prolonged antibiotic treatment that kills the intestinal bacteria
what will lack in vitamin K result in
excessive bleeding (rat poison e.g. is a vitamin K antagonist)
why is excessive bleeding a result of vitamin K deficiency
as blood does not clot
what does vitamin E tocopherol act as
an antioxidant
what do oxidation reactions result in
the loss of electrons
oxidation reactions are crucial for life, but how can they be damaging
they can produce free radicals
what are free radicals
unstable molecules with unpaired electrons, they are highly reactive and can damage cells by penetrating the cell wall and damaging DNA & cell membranes
what is an antioxidant
a molecule capable of slowing or preventing the oxidation of other molecules
how do antioxidants have a therapeutic value
oxidative stress is an important part of many human diseases inc AMD and cataract
antioxidants mop up free radicals
what does deficiency of vitamin E result in
its rare but can cause haemolytic anaemia (red blood cells rupture)
also some neuromuscular degeneration
what is vitamin C ascorbic acid required for
the manufacture of connective tissue (collagen & ground substance)
what type of collagen is vitamin C important for manufacturing
tropocollagen (needed to make scars)
what is a consequence of vitamin C deficiency
increased fragility of blood vessels (which contain a lot of tropocollagen) leading to bleeding including haemorrhaging of the eye lids, anterior chamber, vitreous cavity and retina
what ocular bleeding occurs as a result of vitamin C deficiency
- haemorrhaging of the eye lids
- anterior chamber
- vitreous cavity
- retina
which other parts of the body results in bleeding due to deficiency of vitamin C
gums
what can vitamin C deficiency also lead to apart rom bleeding
old scars reopening and bone abnormalities
what is the name for a condition of vitamin C deficiency
scurvy
what is a type of vitamin B1
thiamine
what is vitamin B1 thiamine
a Co-enzyme in the decarboxylation (involved in energy production) of pyruvate (citric acid cycle)
what is the result in the lack of vitamin B1 thiamine
leads to impaired energy production
what secondary role does vitamin B1 thiamine have
in the production of acetylcholine
what does a deficiency in production of acetylcholine from lack of vitamin B1 thiamine result in
(wet and dry) beriberi
what do 70% of patients with beriberi have
ocular abnormalities associated with changes in the corneal and conjunctival epithelium, producing dry eyes
what is a type of vitamin B2
riboflavin
what is vitamin B2 riboflavin involved in
energy production (electron transfer)
what are symptoms of vitamin B2 riboflavin deficiency
vascularisation of the cornea, followed by corneal opacities, ulceration of the cornea and ultimately blindness
what is vitamin B niacin (nicotinic acid) involved in
most oxidation-reduction reactions
what are the ocular abnormalities of vitamin B niacin deficiency
rare but may result in optic neuritis and retinitis
what is a type of vitamin B6
pyridoxine
what is vitamin B6 pyridoxine involved in
as a co-enzyme in many of the bodies enzyme systems and has a role in GABA synthesis
what can lack of vitamin B6 pyridoxine result in in the eye
can cause blepharitis (inflammation of the eyelids)
what is a type of folic acid & vitamin B12
cyanocobalamin
what is folic acid & vitamin B12 cyanocobalamin important in
nucleic acid synthesis
what does a lack of folic acid & vitamin B12 cyanocobalamin result in
causes disrupted DNA synthesis resulting primarily in megaloblastic anaemia (maturation phase of erythropoiesis abnormal)
how long can stores of vitamin B12 last for
very extensive lasts for up to 10 years for deficiency may not become apparent for a long time
what are the minerals & trace elements, sodium, potassium & calcium needed for
sodium & potassium - action potential generation
calcium - synaptic transmission and muscle contraction
what is the mineral iron a part of
haemoglobin
what does a lack of iron result in
anaemia
what does the mineral, iodine deficiency result in
decreased thyroid hormone output
what is the mineral fluoride important for
maintenance of teeth
what are the minerals calcium and phosphate major components of
bone
what are the functions of the minerals, magnesium, zinc, copper and selenium
- being required for enzymatic activity
- zinc - is anti-inflammatory
what can high concentrations of zinc cause to the eye
toxic to the eye
involved in ARMD, drusen caused by high amount of zinc in the eye
what vitamins and minerals prevent vision loss and less likely to develop advanced AMD than control groups
antioxidants: vitamin C, vitamin E and beta-carotene
along with: zinc and copper
what is the AREDS formulation composed of
- 500mg of vitamin C
- 400 international units of vitamin E
- 15 mg of beta-carotene
- 80mg of zinc
- 2 mg of copper (to prevent copper deficiency anaemia, a condition associated with high levels of zinc intake)
however later studies suggested that zinc may be harmful to the retina
what does the AREDS formulation have no effect on
cataract formation
what carotenoids of the retinal macular pigment a mixture of
zeaxanthin & lutein
what type of pigment is the carotenoids, zeaxanthin & lutein
yellow pigmentation
what does the yellow pigment of the carotenoids, zeaxanthin & lutein remove
short wavelengths (absorbs blue light) which serves to reduce the amount of scatter (as short wavelengths are more prone to Rayleigh scatter) and lessen the amount of chromatic aberration. image quality is therefore increased
carotenoids also remove the wavelengths most damaging to the retina and act as antioxidants
what do zeaxanthin & lutein decrease with
age
what can low levels of zeaxanthin & lutein be associated with due to lack of it with age
diseases such as, cataract and macular degeneration
as carotenoids can only be obtained from the diet, what can increased intake result in
higher macular pigment density
what is smoking the biggest risk factor of developing AMD
smoking
what supplement, which protects against AMD increases the risk of lung cancer in smokers and ex-smokers by 24&
beta carotene, so can’t be given nutritional supplements if a smoker
