thyroid gland Flashcards
is the thyroid gland the largest endocrine gland
yes
where is the thyroid gland located
in the anterior neck ( 2 lateral lobes connected by the isthmus)
what does the parathyroid gland do
Increases plasma Ca2+/PO4-
Stimulates bone osteoclasts
Increases kidney reabsorption
Enhances GI absorption
what is hypoparathyroidism cause
Autoimmune Accidental removal (thyroid surgery)
symptoms of hypoparathyroidism
due to hypocalcaemia Rickets – children Osteomalacia - adults Tingling/burning in fingertips/toes/lips Twitchy muscles
treatments of hypoparathyroidism
Vitamin D3 (cholecalciferol)
Sunlight
Natpara (synthetic PTH)
symptoms of hyperparathyroidism
neurological (tiredness, depression)
osteoporosis
what is in the thyroid gland
follicles, colloid, parafollicular
what do follicular cells do
Composed of follicles with follicular cells that produce the glycoprotein thyroglobulin
what does colloid do
containing (thyroglobulin) fills the lumen of the follicles and stores the hormones
what do parafollicular cells
(C cells), produce the hormone calcitonin
how is calcitonin released
The release is regulated by calcium concentration in the blood (a negative feedback mechanism operates).
actions of calcitonin
Calcitonin targets the skeleton, where it:
- Inhibits osteoclast activity (and thus bone resorption) and release calcium from the bone matrix
Stimulates calcium uptake and incorporation into the bone matrix - Reduces calcium absorption from the intestine
- Increase calcium excretion by the kidneys.
what do follicular cells do
Produce the colloid of each follicle.
Produce the thyroglobulin.
Synthesise the hormones (T3 & T4) on the thyroglobulin.
effects of thyroid hormone
increased metabolic rate, critical for growth/maturation and increased reactivity of the nervous system
increased metabolic rate from thyroid hormone
Increased heat production
Increased delivery of oxygen and substrates
critical for growth/maturation
Fetus needs hypothal/pituitary/thyroid from 12 weeks
Needed for fetal development of CNS and skeleton
increased reactivity of the nervous system from thyroid hormone
Increased blood pressure, blood flow, GI motility
what are the secondary effects of thyroid hormone
increased: heat production respiration blood pressure (Heart rate & force, CO) gastrointestinal motility neuromuscular activity
reduced
bodyweight
sleep
what do thyroid hormones contain
consist of 2 closely related iodine-containing compounds
T3 and T4
T3 thyroid hormone
T3 (3,5,3’-triiodothyronine)
10% of synthesised hormones
Most active form (3-5 x T4 activity)
T4 thyroid hormone
T4 (3,5,3’,5’-tetraiodothyronine) 90% of synthesised hormone Less active than T3 Acts as prohormone Converted to T3 in some tissues Used clinically as thyroxine
what are the body actions of T3
- increased basal metabolic rate
Increased oxygen consumption & heat production
Range -40% to +180% of normal
[increased ventilation, cardiac output, heat loss, substrates]
(fats & proteins to glucose)
2. growth and development Bone/teeth Nervous system Lack of T3/4 in child cretinism (dwarfism/mental retardation)
what are T4 and T3 synthesised from
tyrosine and iodine
