Pituitary & Thyroid Flashcards Preview

Dr Campbell EXAM 3 > Pituitary & Thyroid > Flashcards

Flashcards in Pituitary & Thyroid Deck (89):
1

Primary Function of the endocrine system

Coordinate growth & development
Maintain homeostasis

2

Endocrine system established by release of hormones which are chemical substances

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

3

hypothalamus

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

4

The median eminance

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

5

Release of hormones from the anterior pituitary

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

6

Pituitary Cells

Thyrotropes
Adrenocorticolipotropes
Gonadotropes
Somatotropes
Lactotropes

7

Thyrotropes

produce thyroid stimulating hormone (TSH)

8

Adrenocorticolipotropes

Produce adrenocorticotropic hormone (ACTH)

9

Gonadotropes

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

10

Somatotropes

Produce somatotropin (growth hormone-GH)

11

Lactotropes

Produce prolactin (PR)

12

Hormones released by the hypothalamus which affect the anterior pituitary

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)

13

Corticotropin-releasing hormone (CRH)

Stimulates secretion of adrenocorticotropin hormone (ACTH)

14

Thyrotropin-releasing hormone (TRH)

Stimulates secretion of thyroid stimulating hormone (TSH)

15

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

Control growth hormone release

16

Gonadotropin-releasing hormone (GnRH)

stimulates production of LH and FSH

17

Posterior pituitary (neurohypophysis)

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

18

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

Antidiuretic hormone (Vasopressin) & Oxytocin

19

Function of hypothalamus

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

20

This hormone stimulates production of LH and FSH

Gonadotropin-releasing hormone (GnRH)

21

Where is oxytocin produced and stored?
What is it important for?

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

22

Posterior pituitary (neurohypophysis) is mainly composed of what

Pituicytes (glial-like cells) which provide support

23

Growth hormone

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

24

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

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

25

GH Receptor:
STAT

Signal transducer and activator of transcription

26

GH receptor:
SHC

an adaptor protein

27

IRS-1

Insulin receptor substrate protein

28

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

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

29

GH has what type of feedback control on levels of GHRH

negative feedback control

30

Effect of SST on GH

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

31

Functions of GH

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)

32

Factors which increase GH secretion

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

33

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

children; puberty

34

Hypopituitarism

GH deficiency

35

GH deficiency is usually a result of pituitary disease

Adenoma or radiotherapy; may also be due to hypothalamic defect

36

Diagnostic testing- insulin-induced hypoglycemia

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

Dwarfism

Due to lack of GH in children
In pygmies of Africa, a congenital inability to synthesize IGF-1 leads to abnormally short stature

38

Replacement therapy: formerly used GH purified from___

human cadaver pituitaries

39

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

Gigantism

40

Acromegaly

If GH excess occurs in adulthood

41

Diagnosis of excess GH

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

Treatment

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

PIH

decreases the release of prolactin

44

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

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

45

What is used to treat excess GH

Somatostatin analogs
GH antagonist: Pegvisomant (SOMAVERT)

46

What is the structural unit of the thyroid

The follicle

47

Follicle

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

Cellular composition of the thyroid gland

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

What do Principal (follicular cells) secrete

T3 and T4

50

What do Parafollicular (C cells) secrete

Calcitonin

51

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

True

52

What is the function of calcitonin?

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

53

What causes the secretion of calcitonin to increase?

High plasma calcium increases secretion of this hormone.

54

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

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

55

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?

It is then oxidized to iodine by thyroperoxidase in cytoplasm

56

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

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

57

Release of T3 & T4
What is Step 4

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

58

Release of T3 & T4
Steps 5 & 6

5. Lysosomes fuse with the droplets and hydrolyze thyroglobulin. MIT & DIT are deiodinated by deiodinase enzyme which allows iodine recycling.

6. Thyroid hormones are formed and released into the blood.

59

In Tissues T4 is converted into

T3

60

T4 and T3 have high affinity for plasma binding which causes

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

61

What does extensive binding of these T3 and T4 cause

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

62

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

Increase metabolic activity 60-100% above normal
Increase carbohydrate & fat metabolism

63

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

Increase production of ATP

64

Thyroid hormones increase transport of ions through cells

Enhance activity of Na, K-ATPase=heat production

65

What do thyroid hormones promote during fetal life and early childhood

promotes growth and development of brain

66

Function of thyroid hormones:
(increase/decrease) heart rate, (increase/decrease) body weight, (increase/decrease) respiration

increase, decrease, increase

67

What does TSH stimulate

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

Examples of hyperthyroidism

Toxic goiter, thyrotoxicosis, Graves' disease

69

What happens in hyperthyroidism

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

What are causes of hyperthyroidism

Thyroid adenoma
Autoimmune disease: (Grave's disease); thyroid stimulating immunoglobulin (TSI)

71

Symptoms of hyperthyroidism

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

72

Classes of antithyroid agents
Interfere directly with synthesis of thyroid hormone:

Propylthiouracil, methimazole

73

Classes of antithyroid agents
Block iodine transport mechanisms:

Ionic inhibitors such as thiocyanate, perchlorate, or lithium

74

Classes of antithyroid agents
Decrease release of thyroid hormone:

High concentrations of iodine

75

Classes of antithyroid agents
Damage Gland:

Radioactive iodine

76

Thioureylenes

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

by using antithyroid drugs, thyrotoxic state improves within __

3 to 6 weeks after initiation of drug therapy.

78

what can develop if overtreatment of antithyroid drugs occur?

HYPOthyroidism

79

High plasma concentration of iodine

Inhibits release of thyroid hormone

80

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

The Beta particles

81

What is the therapeutic procedure of choice for hyperthyroidism

Radioactive Iodine

82

In using radioactive iodine, this can be a common disadvantage

delayed hypothyroidism

83

Hypothyroidism

Insufficient production of T3 and T4

84

Causes of Hypothyroidism

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

Symptoms of Hypothyroidism

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

Treatments for hypothyroidism

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

Cretinism

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

88

Causes of Cretinism

Lack of thyroid gland (congenital cretinism)
Lack of iodide in diet (endemic cretinism)

89

Treatment for lack of thyroid gland (congenital cretinism)

Levothyroxine