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hubs191 > Thyroid and parathyroid gland > Flashcards

Thyroid and parathyroid gland Flashcards

1
Q

thyroid gland location

A

on the anterior and lateral surfaces of the trachea.

just below the larynx

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2
Q

hormone made and secreted by the thyroid gland

A

thyroid hormone - essential for optimal metabolic activity

calcitonin - hormone involved in calcium homeostasis

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3
Q

thyroid gland structure

A

composed of small spherical sacs called follicles
each follicle is surrounded by follicular cells (simple cuboidal cells) and is the site of thyroid hormone synthesis
parafollicular cells or C cells lie in clusters between the follicles and make the hormone calcitonin

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4
Q

Thyroid hormone synthesis

A

follicle cells release protein thyroglobulin (TGB) into the follicle
iodine reacts with tyrosine in the TGB molecules
iodised TGB moves into the follicular cells
thyroid hormone detaches from TGB as needed.
T3 and T4 are produced and travel bound to a carrier protein (thyroid-binding globulin) TBG to target cells

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5
Q

T3 and T4

A

T3 is the active from of the thyroid hormone and is formed quickly
T4 is the more plentiful form and it released in higher quantity.

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6
Q

target cell activation by thyroid hormone

A

the thyroid hormone is made in advance and stored until required.
travels bound to carrier proteins.
it detaches from the carrier protein and enters the target cell.
T3 binds to the T3 receptor in the nucleus (receptor is already bound to the specific DNA site)
specific genes are activated to transcribe mRNA
mRNA translation occurs in the cytoplasm and specific proteins are synthesised.

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7
Q

thyroid hormone secretion

A

stimulus = external and internal CNS input
hypothalamus secretes the thyroid releasing hormone
the anterior pituitary secretes the thyroid stimulating hormone.
the thyroid gland secretes thyroid hormones (T3 and T4)

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8
Q

metabolic effect of the thyroid hormone

A

increase in basal metabolic rate

by increase in synthesis and activity of the Na+ and K+ pump

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9
Q

other effects of the thyroid hormone

A 
stimulated growth (fetus and early childhood) 
nervous system = normal alertness and reflexes
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10
Q

what is basal metabolic rate (BMR)

A

BMR is the body’s rate of energy expenditure under basal conditions = person is awake and physical and mental rest, lying down, no muscle movement, at comfortable temp and fasted
old peoples is smaller and mens is bigger

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11
Q

actions of the thyroid hormone

A

growth
alertness
metabolism
- increased body heat production (increased oxygen consumption and ato hydrolysis)
- stimulate fat mobilisation and oxidation of fatty acids in many tissues. decreased triglyceride and cholesterol levels breakdown.
- stimulate carbohydrate metabolism, enhance insulin - dependant entry of glucose into cells, increase glycogenesis and glycogenolysis.
- increased proteolysis, predominantly from muscle

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12
Q

Hypersecretion of TH

A 
graves disease 
high metabolic rate 
weight loss 
heat intolerant 
increased heart rate 
nervousness 
hair loss 
thyroid swelling 
exopthalamos - swelling behind the eyes
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13
Q

diagnosis of graves disease

A

thyroid stimulating immunoglobulin (TSI) antibody assay

radioactive iodine scan- iodine is concentrated in the thyroid so huge accumulation when scanned

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14
Q

hyposecretion of TH (in adults)

A 
myxedema 
low metabolic rate 
weight gain 
cold intolerant 
lethargic
slow heart rate
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15
Q

hyposecretion of TH (in children)

A

cretinism
same as in adults but growth is retarded
brain development is inhibited
caused by lack of iodine in mothers diet
maternal iodine supplement is recommended

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16
Q

what is Goitre

A

iodine deficiency disorder
thyroid gland is unable to make enough thyroid hormone
when stored TH is depleted, TRH and TSH secretion increase to stimulate the thyroid to make more TH.
without iodine TH cannot be made

17
Q

net result of goitre

A

loss of negative feedback control and over stimulation of the thyroid glans
excess TSH stimulates growth of the thyroid glans causes swelling.

18
Q

Calcium homeostasis

A

calcium is essential for many physiological functions.
the concentration of extracellular (blood) calcium is tightly controlled.
bone is the body’s major store of calcium
immediate adjustments can be made by rapid exchanges of calcium between bone and blood
normally a balance exists between content build-up and breakdown of bone

19
Q

hormones involved in calcium homeostasis

A

Parathyroid hormone (PTH) and calcitonin

20
Q

Parathyroid gland

A

secrets parathyroid hormone (PTH)
PTH is essential for life
one the posterior part of the thyroid gland

21
Q

low blood calcium system

A

stimulus = low blood calcium concentration
parathyroid gland secretes PTH
the kidneys then increase calcium reabsorption and decrease urinary excretion of calcium
the bone increases bone breakdown an increases the release of calcium into the blood.
this results in an increase of calcium in the blood

22
Q

calcitonin

A

parafollicular cells or C cells that lie in clusters between the follicles and make the hormone calcitonin.

23
Q

Calcitonin secretion pathway

A

stimulus = increase in blood calcium concentration
the thyroid gland (parafollicular cells) secrete calcitonin
the bone decreases bone breakdown and this decreases the release of calcium into the blood
this also decreases the blood calcium concentration
and it is restored back to normal

24
Q

calcium regulation: PTH and calcitonin

A

pth and calcitonin have opposite effects n blood calcium concentration
both act on cone (have receptors on bone cells) to increase (PTH) or decrease (calcitonin) bone breakdown
together they maintain homeostasis but it is not controlled by the hypothalamus

25
Q

what happens when calcium concentration is too low?

A

hypocalcemia
increased excitability of the nervous system
leads to muscle tremors and spasms or cramps
begins as plasma ca2+ concentration falls below 2.2mmol/L
under 1.9 paraesthesia develops (tingling sensation in the hands and face, muscle cramps and some can cause the larynx to contract tightly and swell which can cause suffocation.

26
Q

what causes hypocalcemia?

A

vitamin D deficiency
diarrhoea
thyroid hormones
under active parathyroid glands, parathyroid gland removal
pregnancy and lactation (calcium goes to the baby and not the mother)

27
Q

what happens when blood calcium is too high?

A

hypercalcaemia
nerve and muscle cells are less responsive and excitable
at more than 3mmol/L can lead to depression of the nervous system, emotional disturbances, muscle weakness, sluggish reflexes
once plasma levels are above 3.5 can lead to cardiac arrest - the thresholds aren’t met so action potentials don’t happen and the heart stops beating

hubs191 (31 decks)

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