REB 6. Effects of Hypo- and Hyperthyroidism Flashcards
(36 cards)
Where is the thyroid gland located?
above the trachea and below the larynx
What shape is the thyroid gland? What can you say about the size of the organ?
- a butterfly or bowtie shape
- it is one of the largest endocrine glands (15 to 20g)
What connects both lobes of the thyroid gland?
the isthmus
What is the isthmus?
it connects both lobes of the thyroid gland
What are the percentages of T4 and T3 secreted by the thyroid gland?
93% of T4 secreted
7% of T3 secreted
*T3 is 10x more potent than T4
What are some characteristics of the response of thyroid hormone?
- response to an increase in TH is detectable only after a delay of several hours
- max. response not evident for days
- duration of response is quite long (this is because TH is not rapidly degraded + response to an increase in secretion of TH continues for days/weeks even after plasma TH concentration has returned to normal)
Is thyroid hormone essential for life?
no, it is not, but it is essential for normal development + physical and mental well being
What is the thyroid response element of DNA?
It is to which the thyroid hormone binds and gene transcription is initiated
- T3 has an increased affinity for DNA than T4
What are some of the general effects of thyroid hormone?
- activates nuclear transcription of large numbers of genes in virtually all cells of the body
- great numbers of proteins - enzymes, structural + transport proteins are synthesized
- net result: generalized increase in functional activity throughout the body
What are the effects of thyroid hormone on metabolic rate and heat production?
- TH increases body’s overall basal metabolic rate (TH regulates body’s rate of oxygen consumption and energy expenditure under resting conditions)
- there is a calorigenic/heat producing effect (the increased metabolic activity results in increased heat production)
What are the effects of thyroid hormone on intermediary metabolism?
- influence synthesis + degradation of fat, carbs and protein
- small and large amounts may induce opposite effects
e. g.- adequate amounts of TH essential for protein synthesis needed for normal bodily growht
- high doses of TH favours protein degradation
What are the effects of thyroid hormone on the nervous system in childhood?
- essential for normal myelination + development of CNS
- hormone deficiency causes mental retardation
What are the effects of thyroid hormone on the nervous system in adults?
- excess causes restlessness + hypersensitivity
- deficiency causes lethargy + blunting of intellect
What are the effects of thyroid hormone on the cardiovascular system?
- increases blood flow + cardiac output
- increase heart rate
- increased heat load generated by TH
(peripheral vasodilation occurs to carry extra heat to body’s surface for elimination)
What are the effects of thyroid hormone on growth?
They are essential for growth because of effects on GH + IGF1
- TH stimulates GH secretion + increases production of IGF-1 by liver
- promotes effects of GH and IGF-1 on synthesis of new structural proteins + skeletal growth
- thyroid deficient children have stunted growth that can be reversed by thyroid replacement therapy [excess TH does not cause excessive growth]
Does excess TH not cause excssive growth?
No, it does not. An excess of GH will lead to excessive growth
What is the most important regulator of TH secretion?
Thyroid Stimulating Hormone (TSH)/thyrotropin released from the anterior pituitary gland
Exposure to cold in newborn infants increase….secretion
TRH
Can emotional reactions affect TRH and TSH?
yes
What are some causes of hypothyroidism?
[1] failure of thyroid gland
[2] autoimmune disease (Hashimoto disease - the body produces antibodies that destroy the thyroid gland)
[3] deficiency of TRH or TSH
[4] inadequate dietary supply of iodine (around 50mg a year)
What are the symptoms of hypothyroidism?
[1] reduced basal metabolic rate
[2] displays poor tolerance to cold (lack of calorigenic effect)
[3] tendency to gain weight (not burning fuels at a normal rate)
[4] easily fatigued/lower energy production
[5] extreme somnolence
[6] slow weak pulse
[7] slow reflexes + slow mental responsiveness
[8] depressed growth of hair
[9] scaliness of skin
[10] development of a frog-like husky voice
[11] in severe cases, oedematous appearance throughout body (myxedema)
What is Cretinism? What are some characteristics of the illness?
Cretinism: when a person has hypothyroidism from birth
- adequate levels of TH is essential for normal growth
Characteristics:
- dwarfism
- mental retardation
- other general symptoms of thryoid deficiency
What are the 2 types of Cretinism? (in other words, the 2 main causes of it)
[1] Congenital Cretinism
- born without a thyroid gland
[2] Endemic Cretinism
- failure of thyroid gland to produce TH (genetic defect)
Why does cretinism only be seen in children only a few weeks after birth? What is the treatment?
neonate with no thyroid gland may have normal appearance and function as it is supplied with TH by mother in utero
- note: need to treat neonate with adequate iodine or thyroxine
- need to be treated within a few weeks to prevent mental growth retardation
