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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
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

Dr Campbell EXAM 3 (2 decks)

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