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Dr Campbell EXAM 3 > Pituitary & Thyroid > Flashcards

Pituitary & Thyroid Flashcards

1
Q

Primary Function of the endocrine system

A

Coordinate growth & development

Maintain homeostasis

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2
Q

Endocrine system established by release of hormones which are chemical substances

A

Steroids (Cholesterol derived compounds)
Small peptides and proteins
Amines (derived from tyrosine)

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3
Q

hypothalamus

A

part of the diencephalon, extends from optic chiasm to caudal border of mamillary bodies
Strategically well placed close to the limbic system, thalamus, and the pituitary

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4
Q

The median eminance

A

The lower portion of the hypothalamus that connects with pituitary stalk
This network of blood vessels is where hypothalamic releasing & inhibitory hormones are secreted
This area has a leaky BBB

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5
Q

Release of hormones from the anterior pituitary

A 
Thyroid stimulating hormone (TSH)-thyrotropin
Adrenocorticotropin hormone (ACTH)
Follicular stimulating hormone (FSH)
Luteinizing hormone (LH)
Prolactin
Growth hormone (GH)
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6
Q

Pituitary Cells

A 
Thyrotropes
Adrenocorticolipotropes
Gonadotropes
Somatotropes
Lactotropes
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7
Q

Thyrotropes

A

produce thyroid stimulating hormone (TSH)

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8
Q

Adrenocorticolipotropes

A

Produce adrenocorticotropic hormone (ACTH)

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9
Q

Gonadotropes

A

Produce luteinizing hormone (LH) and follicle stimulating hormone (FSH)

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10
Q

Somatotropes

A

Produce somatotropin (growth hormone-GH)

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11
Q

Lactotropes

A

Produce prolactin (PR)

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12
Q

Hormones released by the hypothalamus which affect the anterior pituitary

A

Corticotropin-releasing hormone (CRH)
Thyrotropin-releasing hormone (TRH)
Growth hormone releasing hormone (GHRH) & Growth hormone inhibitory hormone (GHIH)- also known as somatostatin: Control growth hormone release
Gonadotropin-releasing hormone (GnRH)

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13
Q

Corticotropin-releasing hormone (CRH)

A

Stimulates secretion of adrenocorticotropin hormone (ACTH)

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14
Q

Thyrotropin-releasing hormone (TRH)

A

Stimulates secretion of thyroid stimulating hormone (TSH)

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15
Q

Growth hormone releasing hormone (GHRH) & Growth hormone inhibitory hormone (GHIH)- also known as somatostatin

A

Control growth hormone release

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16
Q

Gonadotropin-releasing hormone (GnRH)

A

stimulates production of LH and FSH

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17
Q

Posterior pituitary (neurohypophysis)

A

Mainly composed of pituicytes (glial-like cells): provide support
Hormones are secreted from terminal nerve ending traveling from neurons originating in the supraoptic and paraventricular nuclei of the hypothalamus. These nerve endings reach the posterior pituitary through the hypophysial stalk

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18
Q

The nerve endings (posterior pituitary) lie on surface of capillaries and secrete

A

Antidiuretic hormone (Vasopressin) & Oxytocin

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19
Q

Function of hypothalamus

A

Essential for maintaining homeostasis, regulates body temperature, body fluids, appetite, sexual behavior, and emotions
Produces and secretes many hormones which control the pituitary gland

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20
Q

This hormone stimulates production of LH and FSH

A

Gonadotropin-releasing hormone (GnRH)

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21
Q

Where is oxytocin produced and stored?

What is it important for?

A

Produced in the hypothalamus and stored in posterior pituitary.
It is important for the injection of milk, it is a love hormone, and causes contraction of uterine

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22
Q

Posterior pituitary (neurohypophysis) is mainly composed of what

A

Pituicytes (glial-like cells) which provide support

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23
Q

Growth hormone

A

This anterior pituitary hormone affects almost all tissues of the body
Also called somatotropic hormone or somatotropin

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24
Q

Growth hormone principle form is a small protein molecule of how many amino acids

A

191 amino acids;

Approximately 45% of GH is bound to a protein. Bound GH has a longer half-life but cannot bind to the GH receptor

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25
Q

GH Receptor:

STAT

A

Signal transducer and activator of transcription

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26
Q

GH receptor:

SHC

A

an adaptor protein

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27
Q

IRS-1

A

Insulin receptor substrate protein

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28
Q

What does GHRH activate and what are the short term and long term effects

A

GHRH activates cAMP second messenger system
Short term effect: increase in intracellular calcium levels which causes immediate release of GH
Long term effect: gene transcription which causes synthesis of GH

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29
Q

GH has what type of feedback control on levels of GHRH

A

negative feedback control

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30
Q

Effect of SST on GH

A

Somatostatin (SST) is synthesized as a 92 amino acid precursor which is cleaved to SST-14 or SST-28.
SST inhibits GH secretion by somatotropes in the anterior pituitary by inhibiting cAMP accumulation.
SST also indirectly inhibits GH release by negative feedback control of GHRH

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31
Q

Functions of GH

A

Increases size of cells, cell division, and cell differentiation (osteocytes)
Metabolic functions are: increase in protein synthesis, increase in fatty acid mobilization, decrease in glucose utilization
Stimulates cartilage and bone growth
Has been implicated in immune function
GH exerts its effect by comatomedins (insulin-like growth factors): most important is somatomedin C (aka: IGF-1)

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32
Q

Factors which increase GH secretion

A 
Starvation (severe protein deficiency)
Hypoglycemia or low concentrations of fatty acids
Strenuous exercise
Excitement
Trauma
First two hours of deep sleep
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33
Q

Growth hormone secretion is high in___ and during ___ , maximal levels are formed

A

children; puberty

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34
Q

Hypopituitarism

A

GH deficiency

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35
Q

GH deficiency is usually a result of pituitary disease

A

Adenoma or radiotherapy; may also be due to hypothalamic defect

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36
Q

Diagnostic testing- insulin-induced hypoglycemia

A

If values are less than 10 ng/ml, there is GH deficiency

If values are less than 5 ng/ml, there is severe deficiency

37
Q

Dwarfism

A

Due to lack of GH in children

In pygmies of Africa, a congenital inability to synthesize IGF-1 leads to abnormally short stature

38
Q

Replacement therapy: formerly used GH purified from___

A

human cadaver pituitaries

39
Q

If GH excess occurs in children before the fusion of the epiphysis, there will be increased longitudinal growth. This is known as

A

Gigantism

40
Q

Acromegaly

A

If GH excess occurs in adulthood

41
Q

Diagnosis of excess GH

A

Need to show excess GH or IGF-1 in the blood
For acromegaly, oral glucose tolerance test is used.
Normal subjects: suppress GH to <1 ng/ml
Acromegaly: no suppression or increase in GH

42
Q

Treatment

A

Surgery or radiation
Pharmacological therapy:
Somatostatin analogs- octapeptides: octreotide, lanreotide, vapreotide; Hexapeptides: seglitide, pasireotide
Growth hormone antagonists: Pegvisomant (SOMAVERT) binds to GH receptor but does not cause signaling or IGF-1 secretion

43
Q

PIH

A

decreases the release of prolactin

44
Q

If defect is due to GH receptor deficits, what is used?

A

recombinant human IGF-1 (INCRELEX) or a combination of IGF-1 and its binding domain (IPLEX) is used.

45
Q

What is used to treat excess GH

A

Somatostatin analogs

GH antagonist: Pegvisomant (SOMAVERT)

46
Q

What is the structural unit of the thyroid

A

The follicle

47
Q

Follicle

A

A spheroid compartment which is lined with follicular epithelial cells.
Lumin of the follicle is filled with the gel-like substance known as the colloid

48
Q

Cellular composition of the thyroid gland

A

There are two functional cell types in the thyroid:
Principal (follicular cells)
Secrete T3 & T4
Parafollicular (C cells)
Secrete calcitonin
Follicles are surrounded by fenestrated capillaries derived from superior and inferior thyroid arteries.

49
Q

What do Principal (follicular cells) secrete

A

T3 and T4

50
Q

What do Parafollicular (C cells) secrete

A

Calcitonin

51
Q

Parafollicular cells are not in contact with the colloid (T/F)

A

True

52
Q

What is the function of calcitonin?

A

Antagonizes function of parathyroid hormone: lowers blood calcium by suppressing bone resorption and increasing bone calcification.

53
Q

What causes the secretion of calcitonin to increase?

A

High plasma calcium increases secretion of this hormone.

54
Q

What is the first step in synthesis and storage of thyroid hormones T3 and T4?

A

Protein portion of thyroglobulin is synthesized in the rER of follicular cells

55
Q

In the second step of synthesis and storage of thyroid hormones T3 and T4, what happens after iodide is actively transported into the follicular cells?

A

It is then oxidized to iodine by thyroperoxidase in cytoplasm

56
Q

What is Step 3 of synthesis, storage, and secretion of T3 & T4

A

Organification of thyroglobulin:

The iodinated thyroglobin is not active. It is the storage form of thyroid hormones.

57
Q

Release of T3 & T4

What is Step 4

A

Thyroglobulin is taken up by the cells from the colloid by receptor mediated endocytosis to form colloidal resorption droplets.

58
Q

Release of T3 & T4

Steps 5 & 6

A
  1. Lysosomes fuse with the droplets and hydrolyze thyroglobulin. MIT & DIT are deiodinated by deiodinase enzyme which allows iodine recycling.
  2. Thyroid hormones are formed and released into the blood.
59
Q

In Tissues T4 is converted into

A

T3

60
Q

T4 and T3 have high affinity for plasma binding which causes

A

Slow release to tissue cells and long half life (T4= 6-8 days, T3= 1 day)

61
Q

What does extensive binding of these T3 and T4 cause

A

Because of extensive binding, there is latency before action and these hormones are long-acting

62
Q

Thyroid hormones increase transcription of genes leading to enhancement of general activity of cells, which lead to:

A

Increase metabolic activity 60-100% above normal

Increase carbohydrate & fat metabolism

63
Q

Thyroid hormones increase size and number of mitochondria which then increase?

A

Increase production of ATP

64
Q

Thyroid hormones increase transport of ions through cells

A

Enhance activity of Na, K-ATPase=heat production

65
Q

What do thyroid hormones promote during fetal life and early childhood

A

promotes growth and development of brain

66
Q

Function of thyroid hormones:

(increase/decrease) heart rate, (increase/decrease) body weight, (increase/decrease) respiration

A

increase, decrease, increase

67
Q

What does TSH stimulate

A 
proteolysis of thyroglobulin
activity of iodide pump
iodination of thyroglobulin
increase in size and secretory activity of thyroid
Increase in number of follicular cells
68
Q

Examples of hyperthyroidism

A

Toxic goiter, thyrotoxicosis, Graves’ disease

69
Q

What happens in hyperthyroidism

A

The thyroid increases 2-3x its normal size
Number of follicular cells and rate of secretion of T3 & T4 are increased
TSH levels are low

70
Q

What are causes of hyperthyroidism

A

Thyroid adenoma

Autoimmune disease: (Grave’s disease); thyroid stimulating immunoglobulin (TSI)

71
Q

Symptoms of hyperthyroidism

A 
Excitability &amp; nervousness
Intolerance to heat
Increased sweating
Weight loss
Fatigue but inability to sleep
Exophthalmos
Blood tests show: Increase T4 &amp; T3, Very low or absent TSH, presence of TSI
72
Q

Classes of antithyroid agents

Interfere directly with synthesis of thyroid hormone:

A

Propylthiouracil, methimazole

73
Q

Classes of antithyroid agents

Block iodine transport mechanisms:

A

Ionic inhibitors such as thiocyanate, perchlorate, or lithium

74
Q

Classes of antithyroid agents

Decrease release of thyroid hormone:

A

High concentrations of iodine

75
Q

Classes of antithyroid agents

Damage Gland:

A

Radioactive iodine

76
Q

Thioureylenes

A

Interfere with the incorporation of iodine into tyrosyl residues of thyroglobulin by inhibiting thyroperoxidase
Propylthiouracil is a prototypic example of thioureylenes
Most important SE is agranulocytosis
1/2 life of propylthiouracil= 75 min. Methimazole = 4-6 hours

77
Q

by using antithyroid drugs, thyrotoxic state improves within __

A

3 to 6 weeks after initiation of drug therapy.

78
Q

what can develop if overtreatment of antithyroid drugs occur?

A

HYPOthyroidism

79
Q

High plasma concentration of iodine

A

Inhibits release of thyroid hormone

80
Q

(In terms of Radioactive Iodine) What rays destroy the follicular cells of the thyroid

A

The Beta particles

81
Q

What is the therapeutic procedure of choice for hyperthyroidism

A

Radioactive Iodine

82
Q

In using radioactive iodine, this can be a common disadvantage

A

delayed hypothyroidism

83
Q

Hypothyroidism

A

Insufficient production of T3 and T4

84
Q

Causes of Hypothyroidism

A

Deterioration of gland due to chronic autoimmune thyroiditis (Hashimoto’s thyroiditis)
Endemic colloid goiters: Low iodine in soil allows synthesis of thyroglobulin but no hormone formed. TSH is increased which causes more thyroglobulin to be made. Thyroid can grow 10-20x its normal size
Idiopathic nontoxic colloid goiters- Due to deficient: iodide trapping, peroxidase system, iodination of tyrosine, deiodinase enzyme

85
Q

Symptoms of Hypothyroidism

A

Fatigue and somnolence
Sluggishness
Slow heart rate and decrease in cardiac output
Increase in weight
Scaly skin and husky voice
Myxedema
Blood tests show: Decrease T4 & T3 and high TSH

86
Q

Treatments for hypothyroidism

A

Thyroid hormone replacement therapy:
Levothyroxine sodium (L-T4, Synthroid)
Liothyronine sodium (L-T3): Tabs- Cytomel
Combination of T4 & T3: Liotrix (Thyrolar)
Desiccated thyroid preparations (armour thyroid)

87
Q

Cretinism

A

Caused by extreme hypothyroidism during fetal life, infancy, and childhood
Leads to failure to grow and mental retardation

88
Q

Causes of Cretinism

A

Lack of thyroid gland (congenital cretinism)

Lack of iodide in diet (endemic cretinism)

89
Q

Treatment for lack of thyroid gland (congenital cretinism)

A

Levothyroxine

Dr Campbell EXAM 3 (2 decks)

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