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HUBS 191 > Thyroid, parathyroids and homeostasis of plasma calcium > Flashcards

Thyroid, parathyroids and homeostasis of plasma calcium Flashcards

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1
Q

where is the thyroid gland located

A

immediately below larynx, anterior and on each side of trachea

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2
Q

what are the 3 main parts of the thyroid gland

A
  1. right lateral lobe
  2. left lateral lobe
  3. isthmus
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3
Q

what 2 hormones does the thyroid hormone secrete

A
  1. thyroxine - T4
  2. Triiodothyronine - T3
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4
Q

how does the thyroid hormone synthesis T4 and T3

A

by attaching iodine to 2 tyrosine molecules which then get linked, The two tyrosine molecules, each with a benzene ring, are coupled to form the two-ring structure characteristic of T3 and T4.

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5
Q

what purpose does the benzene structures in the T4 and T3 hormones serve

A

confers lipid solubility

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6
Q

which hormone between T4 and T3 is most abundant in the bloodstream

A

T4 - about 90% of thyroid hormone in the bloodstream is T4

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7
Q

what happens to most of T4 once it diffuses into the tissue

A

most of T4 is converted to T3

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8
Q

how does T3 and T4 circulate the bloodstream

A

primarily bound to transport proteins, with thyroxine-binding globulin (TBG) being the main carrier

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9
Q

what are follicles in the thyroid gland filled with

A

large glycoproteins called thyroglobulin also referred to as colloid

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10
Q

where is thyroglobulin secreted

A

by the cuboidal cells that comprise the follicular walls in the thyroid gland

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11
Q

what are parafollicular cells (C cells)

A

specialized cells within the thyroid gland (lies between follicles) that are responsible for producing calcitonin

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12
Q

what type of hormone is calcitonin

A

a peptide hormone

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13
Q

what triggers the secretion of calcitonin

A

secretion is triggered by increased ECF calcium ion concentration

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14
Q

what are the 2 functions of calcitonin

A
  1. reduces osteoclast activity and shifts balance towards deposition in bone
  2. inhibits reabsorption of calcium by kidney
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15
Q

what is calcitonin

A

a hormone that helps regulate calcium and phosphate levels in the blood

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16
Q

In the synthesis and release of Thyroid hormones:
1. ______ in blood is actively transported into the cells of ______

A
  1. iodide ions
  2. follicles
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17
Q

In the synthesis and release of Thyroid hormones:
2. Iodide is ____ to iodine which then binds to ______ residues of large _______
________ are synthesised and secreted by _______ epithelial cells of follicular walls

A
  1. oxidized
  2. tyrosine
  3. thyroglobulin
  4. glycoproteins
  5. cuboidal
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18
Q

In the synthesis and release of Thyroid hormones:
3. _______ residues become coupled to each other to produce T3 and T4
thyroid hormones are stored within ______ in association with ______

A
  1. iodotyrosine
  2. follicles
  3. thyroglobulin
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19
Q

In the synthesis and release of Thyroid hormones:
4. follicle cells remove ________ from the follicle cavity by _________.

A
  1. thyroglobulin
  2. endocytosis
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20
Q

In the synthesis and release of Thyroid hormones:
5. Lysosome in cytoplasm fuse with ______ and digest thyroglobulin molecules to release ___ and ___, as well as _______.

A
  1. vesicles
  2. T3 and T4
  3. amino acids
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21
Q

In the synthesis and release of Thyroid hormones:
6. T3 and T4 _____ into surrounding capillaries into the bloodstream

A

diffuse

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22
Q

In the synthesis and release of Thyroid hormones:
7. T3 and T4 is transported in the blood stream via _____

A

plasma proteins - thyroid binding globulins (TBGs)

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23
Q

what factors stimulates the release of thyrotropin releasing hormone (TRH)

A
  • low levels of thyroid hormones
  • low metabolic rate
  • prolonged cold exposure
  • other signals relating to metabolism and growth
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24
Q

what is the thyrotropin releasing hormone (TRH) secreted by

A

the hypothalamic neurons

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25
where does thyrotropin releasing hormone (TRH) enter to trigger other hormones release
the hypothalamic hypophyseal-portal capillaries
26
where does TRH travel to in the hypothalamic hypophyseal-portal to release what hormone
1. the anterior pituitary 2. to cause the release of thyroid stimulating hormone (TSH)
27
once TSH has been released from the anterior pituitary, what does the hormone stimulate for
stimulates synthesis and secretion of thyroid hormones, and increases the number of thyroid cells and size
28
what type of feedback does thyroid hormones exert on the control of TSH (anterior pituitary) and TRH (hypothalamus)
a negative feedback system
29
once free thyroid hormones diffuse into the cell, what do they bind to
bind to thyroid hormone receptors in mitochondria and nucleus
30
what are the functions of free thyroid hormones
- increases mitochondrial numbers and activity - initiates the transcription of specific genes and the production of new proteins and enzymes - increases basal metabolic rate (BMR) - increases heart rate, cardiac output and systolic BP - stimulatory effects on the CNS - neural development in fetal and infant life - normal growth (with other hormones)
31
what is the basal metabolic rate (BMR)
the amount of energy per unit time required to keep the body functioning at rest
32
how does free thyroid hormones increase the basal metabolic rate
- increases oxygen consumption and ATP production - increases the activity of Na-K-ATPase (increases heat production)
33
what can be the cause of infantile hypothyroidism
- absent or poorly functioning thyroid gland - poorly functioning pituitary - lack of iodine in mothers diet
34
what can be the effects of infantile hypothyroidism
- low metabolic rate - delayed growth and neural development - swelling around eyes and tongue
35
what is the treatment for infantile hypothyroidism
treatment involves early diagnosis and administration of thyroxine
36
what could be the cause of a simple goiter
may be due to iodine deficiency
37
what causes the size of a goiter
the high levels of TSH which causes the excessive growth of thyroid tissue
38
what is Hashimoto's thyroiditis
an autoimmune disease where the immune cells attack their own thyroid gland
39
what effects are caused by Hashimoto's thyroiditis
thyroid is swollen and produces less thyroid hormone than usual
40
what could be possible signs and symptoms of adult hypothyroidism
- reduced metabolic rate - slowed heart and cardiac output - fatigue and sluggishness (mental and physical) - depression - weight gain - increased sensitivity to the cold - muscle weakness - constipation - goiter (depending on cause) - myxedema
41
what is myxedema
edematous (swollen) appearance throughout the body
42
what is Graves' disease
an autoimmune disease whereby antibodies attach to TSH receptors and act to stimulate (rather than destroy) the thyroid cells an autoimmune disorder where the immune system mistakenly attacks the thyroid gland
43
what does Grave's disease cause
the overproduction of thyroid hormones, a condition known as hyperthyroidism as well as an associated goiter
44
what can the antibodies cause in the case of Grave's disease
the swelling of tissues around/behind the eyes (exophthalmos)
45
what are some signs and symptoms of hyperthyroidism
- increased heart rate and BP - palpitations - heat intolerance - weight loss - nervousness - tremor - insomnia - breathlessness - increased bowel movements
46
what is the normal range of calcium concentration in adults
approx 2.2 to 2.6 mmol/L
47
where is calcium stored
in the bones
48
how is calcium stored in bone tissue
calcium is absorbed from intestines, enters the blood stream an can be deposited in the bone tissue by the action of osteoblasts
49
how is calcium taken out of the bone tissue
through the action of osteoclasts to transfer it back into the bloodstream
50
how does the kidneys regulate calcium concentration
the kidneys can adjust the amount of calcium lost in urine, or reabsorb more calcium from urine if required
51
in what form is most of the calcium stored (99%)
in the form hydroxyapatite - Ca10(PO4)6(OH)2
52
in what form is the other 1% of calcium stored as
in the form of readily mobilizable salts such as CaHPO4
53
what is the function of the changeable pool of mobilized salts
this is readily exchangeable with the ECF and acts as a quick acting buffer to short term fluctuations in calcium ion concentrations
54
what does longer lasting alterations of calcium require as the exchangeable pool is limited
an endocrine response
55
where are the parathyroid glands
partially embed in the posterior surface of the lateral lobes of the thyroid gland
56
how many parathyroid glands are there and where are they
usually 4 - 2 superior and 2 inferior some people can have up to 8
57
what is the shape of the parathyroid gland
pea shaped and sized
58
what is the function of the parathyroid glands
secrete parathyroid hormone (protein hormone) in response to low ECF calcium concentration
59
what are the 2 types of cells found in the parathyroid glands
1. chief cells or principal cells 2. oxyphil cells
60
what is the function of chief cells/principle cells
produce parathyroid hormone (PTH)
61
when does oxyphil cells become present
not normally present before puberty, may be modified or depleted chief cells as numbers increase with age
62
what is the function of oxyphil cells
help with identification of parathyroid tissue
63
what does the lack of parathyroid hormone (PTH) result in
in low blood calcium
64
what does the lack of parathyroid hormone (PTH) cause (disease)
1. Trousseau's sign 2. Chvostek's sign
65
what is Chvostek's sign
when tapping the face over the facial nerve in front of the tragus of the ear causes spasm of facial muscles, typically twitch of the nose or lips
65
what is Trousseau's sign
it is a compression of the forearm that produces spasm in the hand and wrist - the thumb id adducted - the fingers are bunched - the wrist is flexed
66
what are the signs and symptoms of Hypocalcemia mostly related to
related to the excitability of the nerve and muscle - can lead to muscle spasms, tetany and seizures if not treated
67
osteoclasts don't have membrane receptors for PTH, so where do they bind
PTH binds to receptors on osteoblasts
68
what do osteoblasts release once PTH binds to the receptors
release growth factor RANKL
69
what does the release growth factor RANKL stimulate
stimulates proliferation, development and activity of the osteoclasts
70
what do the osteoclasts do once the activity has been stimulated by RANKL
osteoclasts breakdown the bone and release the calcium into the blood
71
how does PTH act on the kidneys
acts on the kidneys to increase the reabsorption of calcium and stimulate the formation of calcitriol
72
what is calcitriol
active vitamin d
73
what is Ricketts
in kids - the lack of Vit D and/or dietary calcium in children leads to the inadequate calcification of new bone. the weakened, bowed lower limb bones and abnormal epiphyseal plates are evidence
74
what is osteomalacia
in adults - the lack of Vit D and/or calcium can result in abnormal mineralization of mature bones. bones are weaker and prone to atypical fractures

HUBS 191 (28 decks)

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