Trace Elements (Iodine, Copper, Selenium and Aluminium)) Flashcards
How much iodine is required daily?
about 150 micrograms
What is the function of iodine in the body
substrate used for thyroid hormone synthesis
Where is iodine primarily found and what foods are a good source of iodine?
primarily found in ocean (seafood and kelps)
food sources:
- fairy products
- seafood
- seaweed
- eggs
- bread
- some vegetables
Due to iodines low environmental levels it is the number one cause of
preventable intellectual disability in children
What are the 2 thyroid hormones?
- thyroxine (T4) prohormone
- transport from cell to cell form
- longer half life and more stable - triiodothyronine (T3)
- active form
Where is the thyroid gland located
on trachea
- 2 lobes joined by narrow isthmus
filled with major thyroid secretory cells around in hollow spheres (follicles)
What is the structure of the follicles in the thyroid gland
secretory cells (follicular cells) form rings around inner lumen (colloid) with a C cell in the connective tissue associated with the follicle
- colloid serves as the extracellular storage and production site of thyroid hormones
- C cells secrete calcitonin which regulates blood calcium levels and stops the breakdown of bone by releasing osteoclasts by releasing Ca2+
Where are thyroid hormones mostly found other than the thyroid gland
circulating in plasma:
- most complexed to T4 binding globulin
- small amount free active T3
How are thyroid hormone regulated
- thyrotropin-releasing hormone (TRH) secreted by the hypothalamus
- TRH stimulates thyroid stimulating hormone (TSH) produced by the anterior pituitary gland
- TSH regulates T3 and T4 synthesis in the thyroid gland
What is the first step in thyroid hormone synthesis
thyroglobulin (Tg) is synthesised in the rough ER and enters the colloid by exocytosis
meanwhile a sodium/iodide symporter (Na/I) pumps iodide actively into the cell
What is the second step in thyroid hormone synthesis
Iodide enters the colloid from cytoplasm by pendrin transporter and TPO (thyroperoxidase) converts iodide into active iodine
iodine iodinates Tg at tyrosyl residues causing the adjacent iodinated tyrosyl residues to be paired together forming MIT (monoiodotyrosine) and DIT (diiodotyrosine)
What is the third step in thyroid hormone synthesis
Tg then re-enters the follicular cell by endocytosis where lysosomes fuse and proteolysis occurs which liberates T3 and T4 molecules
T3 and T4 in cytoplasm then enter the colloid
What is the function of TSH other than stimulating the production of thyroid hormones
- stimulates expression of transporters and enzymes involved in T3 and T4 production (and endocytosis of Tg)
- also stimulates growth of thyroid gland
What happens when is no or excess TSH
no TSH = thyroid atrophies (shrinks)
- hypothyroidism
- hormones released at very low rate
too much TSH = thyroid hypertrophies
- hyperthyroidism
What is the consequence of iodine deficiency during pregnancy
stillbirth
spontaneous abortion
congenital abnormalities
if child is born can result in:
- stunted growth
- diminished intelligence
- retardation
Where is iodine deficiency most prominent
developing countries
- himalayas
- andes
- africa
How was iodine deficiency improved in australia?
iodised salt
iodised water
bread made with iodised salt
- provides enough iodine to avoid low thyroid activity for most people
What are the effects of long term iodine deficiency
thyroid gland adapt to insufficient supply of iodine by increasing trapping
- Goitre occurs (increase size of thyroid gland)
- hypothyroidism occurs (not enough thyroid hormones produced)
What are the symptoms of long term iodine deficiency
dry skin
hair loss
decreased metabolic rate
- fatigue/ lethargy
slowed reflexes
constipation
How is the negative feedback loop for thyroid hormone stimulation affected in hypothyroidism
due to lack of T3 and T4 being released from thyroid the hypothalamus keeps secreting TRH and in turn TSH.
As TSH keeps being secreted a goiter occurs
Are goiters found in iodine deficient children
no just adults
What is the symptoms of iodine toxicity
burning of mouth, throat and stomach
fever
nausea
vomiting
diarrhea
weak pulse
cyanosis
coma
What can cause iodine toxicity
- iodine supplementation programmes in iodine deficient populations
- can result in iodine induced hyperthyroidism (especially if goiter present) - excess iodine intake in healthy individuals
- elevated blood concentrations of TSH but inhibits thyroid hormone production
- leads to hypothyroidism and goiter (but not known how)
Iodine toxicity leads to Wolff Chaikoff effect. What is this effect?
reduction of thyroid hormone levels caused by ingestion of large amounts of iodine by rejecting the large amounts of iodine
How much copper is required per day? does this differ from the amount a regular diet provide?
required: about 900 micrograms
regular diet: 1-1.5 micrograms per day
What are good food sources for copper?
oysters and shellfish
seeds and nuts
meats (high in kidney and liver)
whole grains
What key enzymes in the body is copper essential in?
- superoxide dismutase
- removes superoxides by converting them into hydrogen peroxide - lysyl oxidase (extracellular copper enzyme)
- needed for collagen and elastin synthesis - cytochrome c oxidase
- last enzyme in the electron transport chain
Where in the process of collagen synthesis and secretion is lysyl oxidase needed?
After tropocollagen is formed Cu dependant lysyl oxidase deaminates lysine and hydroxylysine residues to form aldehyde groups which forms cross links
- turns tropocollagen into final collagen product