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Clinical Pathology (RIP) > T3 - L2 Endocrine investigations > Flashcards

T3 - L2 Endocrine investigations Flashcards

1
Q

What are hormones?

A

‘messenger molecules’ secreted by endocrine glands.

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2
Q

what are the three types of intercellular signally performed by hormones?

A

endocrine
paracrine
autocrine

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3
Q

what is endocrine signalling?

A

hormones ecreted into the blood stream and trigger a response in the target cell

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4
Q

what is paracrine signalling?

A

hormones affecting neighbouring cells

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5
Q

what is autocrine signalling?

A

hormones secreted by a cell to bind to same cell

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6
Q

do hormones produce short or long term changes?

A

capable of both

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7
Q

what enables hormones to have specificity?

A

A hormone can only influence cells that have specific target receptors
for that particular hormone.

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8
Q

what are the 3 types of hormone?

A

peptide
steroid
tyrosine-based

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9
Q

give examples of peptide hormones

A

PTH
ACTH
TSH

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10
Q

give examples of steroid hormones

A

testosterone
oestradiol
cortisol

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11
Q

give examples of tyrosine-based hormones

A

Thyroxine (T4) and Triiodothyronine (T3)

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12
Q

what are 3 ways in which a steroid hormone can elicit a response?

A
  • classical model
  • receptor mediated endocytosis
  • signalling through cell-surface receptors
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13
Q

what is meant by the classical model of hormone signalling?

A

diffuse into the cell and bind to DNA binding domain,
changing transcription and translation of the cell

NB: leads to gene transcription/protein translation

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14
Q

describe the feedback regulation pathway in endocrine systems?

A
  • Hypothalamus produces hormone - acts on
    anterior pituitary, which produces a second hormone
    that acts on the endocrine organ
  • The products of the endocrine organ i.e. the final
    hormone will always inhibit the pathway, inhibiting
    the pituitary and hypothalamus
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15
Q

where is GnRH (Gonadotropin-releasing hormone) released from?

A

hypothalamus

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16
Q

where does GnRH (Gonadotropin-releasing hormone) act on?

A

anterior pituitary

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17
Q

what does GnRH (Gonadotropin-releasing hormone) acting on the anterior pituitary cause?

A

release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH)

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18
Q

what hormones are released from the anterior pituitary?

A 
LH
FSH 
GH
TSH 
Prolactin 
ACTH
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19
Q

what hormones are released from the hypothalamus?

A 
GnRH
GHRH
somatostatin 
TRH 
Dopamine 
PRH 
CRH
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20
Q

which hormones released from the anterior pituitary act on the gonads?

A

LH

FSH

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21
Q

which hormones released from the anterior pituitary act on the thyroid?

A

TSH (thyroid stimulating hormone)

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22
Q

which hormones released from the anterior pituitary act on the breasts?

A

prolactin

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23
Q

which hormones released from the anterior pituitary act on the adrenal cortex?

A

ACTH

Adrenocorticotropic hormone

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24
Q

what does FSH do?

A

regulates the development, growth, pubertal maturation, and reproductive processes of the body.

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25
Q

what does LH do?

A

females: an acute rise of LH triggers ovulation
males: stimulates production of testosterone

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26
Q

what cells are FSH and LH released from?

A

gonadotropic cells of the anterior pituitary gland

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27
Q

what hormone stimulates the production of LH and FSH?

A

GnRH

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28
Q

what hormone stimulates the production of GH?

A

GHRH

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29
Q

what hormone stimulates the production of TSH?

A

TRH

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30
Q

what hormones stimulates the production of Prolactin?

A

TRH

PRH

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31
Q

what hormone stimulates the production of ACTH?

A

CRH

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32
Q

what is hyperprolactinemia?

A

Hyperprolactinemia is a condition of elevated serum prolactin.

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33
Q

explain how hyperprolactinemia can develop in patients taking antipsychotics?

A
  • Antipsychotics are dopamine antagonists
  • they inhibit the negative inhibition of dopamine on prolactin
  • Resulting in high prolactin
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34
Q

what affect does dopamine have on prolactin?

A

inhibits prolactin release

35
Q

what hormone inhibits GH release?

A

somatostatin

36
Q

what affect does somatostatin have on GH?

A

inhibits GH release

37
Q

explain how hyperprolactinemia can develop in patients with hypothyroidism?

A
  • Hypothyroidism is low levels of thyroxine
  • results in loss of the negative feedback on TRH
  • Resulting in high prolactin
38
Q

what does prolactin do?

A

Prolactin is mainly used to help women produce milk after childbirth

39
Q

how does Thyroxine-binding Globulin affect thyroid function test interpretation?

A
  • Thyroxine-binding Globulin binds to thyroid hormones.
  • only “free” hormones are active.
  • If the level of TBG changes, this results in a change in the level of the free hormones.
40
Q

what factors cause an abnormal increase of Thyroxine-binding Globulin concentrations?

A
  • genetic causes
  • pregnancy
  • oestrogens (oral contraceptive pill)
41
Q

what factors cause an abnormal decrease of Thyroxine-binding Globulin concentrations?

A
  • genetic causes
  • protein-ionising states
  • malnutrition
  • malabsorption
  • acromegaly
  • Cushing’s disease
  • high dose corticosteroids
  • severe illness
  • androgens
42
Q

low TSH and low thyroxine indicates what?

A

pituitary failure

secondary hypothyroidism

43
Q

low TSH high thyroxine indicates what?

A

primary hyperthyroidism

thyroid gland overproduction

(most commonly caused by autoimmune disease)

44
Q

Low thyroxine and high TSH indicates what?

A

Unresponsive thyroid (primary hypothyroidism)

45
Q

High thyroxine and high TSH indicates what?

A

Pituitary gland overproduction or feedback fails (secondary

hyperthyroidism)]

46
Q

why is TSH as a frontline test?

A

cheap

47
Q

what is the problem with using TSH as a frontline test?

A

the problem with TSH frontline testing is that if TSH is normal, there will not be
followed up

(but secondary hyperthyroidism = Normal TSH with a low free T4)

48
Q

if TSH is low what do you add?

A

Add on free T3 and T4 to pick up the hyperthyroid patients

49
Q

if TSH is high what do you add?

A

Add on free T4 to pick up the hypothyroid patients

50
Q

what is non-thyroidal illness also referred to as?

A

sick euthyroid disease

51
Q

what does euthyroid mean?

A

having a normally functioning thyroid gland.

52
Q

what is Non-Thyroidal Illness [sick euthyroid disease]?

A

abnormalities within their thyroid function tests, despite being euthyroid.

53
Q

why are TFTs impossible to interpret in sick patients?

A

free T3 decreases depending on severity of illness

free T4 increases depending on severity of illness

54
Q

How often should we repeat TFTs in a healthy person?

A

3 years

55
Q

what do TFTs detect?

A

high sensitivity immunoassay for thyroid stimulating hormone (TSH)

immunoassay estimation of non-protein bound thyroxine (fT4)

56
Q

what TFTs result would support the diagnosis of hypothyroidism?

A

raised TSH and low FT4

57
Q

what TFTs result would support the diagnosis of hyperthyroidism?

A

undetectable TSH

elevated FT4

58
Q

what are the two types of immunoassay used in clinical chemistry?

A

immunometric assays

competitive immunoassays

59
Q

advantages of immunoassays?

A
  • specific due to antibody specificity
  • sensitive
  • amenable to automation
60
Q

what is an immunoassay?

A

An immunoassay is a biochemical test that measures the presence or concentration of a macromolecule or a small molecule in a solution through the use of an antibody or an antigen.

61
Q

what are the two types of adrenal medullary tumours?

A

Phaeochromocytoma (adults)

Neuroblastoma (children)

62
Q

what is a Phaeochromocytoma?

A

Tumour of neuroendocrine chromaffin cells – the majority in the adrenal medulla

63
Q

a tumour of neuroendocrine chromaffin cells is called what?

A

Phaeochromocytoma

64
Q

what are clinical features of a Phaeochromocytoma?

A
  • hypertension
  • sweating, pallor
  • panic attacks
  • headaches
  • abdominal pain
  • can be asymptomatic
65
Q

Excessive and often episodic release of catecholamines due to a Phaeochromocytoma may result in what?

A

paroxysmal features (are a sudden recurrence or intensification of symptoms)

66
Q

what do you measure to diagnose a Phaeochromocytoma?

A

Catecholamines excess = Phaechromocytoma

Metanephrines are often measured these days (Metabolites of catecholamines i.e. breakdown products)

  • both measured in urine or blood
67
Q

what is the problem with measuring Catecholamines to detect a Phaechromocytoma ?

A

Catecholamines are secreted in a pulsatile manner so the peak can be missed

NB Metanephrines are often measured these days as they are Elevated more consistently across the day

68
Q

is it better to test for Plasma metanephrines (blood) or urine fractionated metanephrines
when diagnosing Phaechromocytoma?

A

24 hour urine fractionated metanephrines - more stable

NB – Plasma metanephrines:

  • Unstable – collect on ice
  • Need to arrive in the local lab within 30 minutes of collection
69
Q

what follow up tests should be done in patients with suspected phaeochromocytoma and borderline changes in
catecholamines or Metanephrines?

A

Clonidine suppression test

Plasma Chromogranin A

MRI or CT of adrenals

Genetic counselling and screening for MEN mutations

70
Q

what is hypoglycaemia?

A
  • low plasma glucose level

- Less than 3 or 3.5 mmol/L

71
Q

what are the 3 components of Whipple’s triad that suggest a patient’s symptoms result from hypoglycemia ?

A
  • Low Plasma Glucose Level
  • Signs & Symptoms of Hypoglycaemia
  • Resolution of Symptoms once Glucose Level Rises [i.e. treated]
72
Q

what is a symptom? What is a sign?

A

A symptom is any subjective evidence of disease, while a sign is any objective evidence of disease. Therefore, a symptom is a phenomenon that is experienced by the individual affected by the disease, while a sign is a phenomenon that can be detected by someone other than the individual affected by the disease.

73
Q

what hormones are stimulated in hypoglycaemia?

A

growth hormones, cortisol and catecholamine secretion

74
Q

what is the most common cause of hypoglycaemia in the adult UK population?

A

diabetes

75
Q

what is an insulinoma?

A
  • [Insulin secreting tumour]

- Most common tumours arising from islets of Langerhans

76
Q

what is the most common tumour arising from islets of Langerhans?

A

insulinoma

77
Q

how would you diagnose a insulinoma?

A
  • Diagnosed through a simple fasting blood test.
  • a low blood sugar with high level of insulin will confirm diagnosis of insulinoma.
  • Low blood sugar (less than 2.2 mmol/l)
  • High insulin (6 microunits/ml or higher)
78
Q

a blood test showing a low blood sugar but high insulin conc will indicate what?

A

insulinoma

79
Q

what is the most common cause of Cushing’s syndrome?

A

Administration of steroids

Exogenous cause

80
Q

what is the most common endogenous cause of Cushing’s syndrome?

A

Cushing’s disease = Pituitary ACTH secreting tumour

Produces ACTH acting on the adrenal glands causing excess cortisol production

81
Q

what are the four causes of Cushing’s syndrome?

A
  • Administration of steroids
  • Cushing’s disease
  • Adenoma in the adrenal gland
  • Ectopic ACTH secreting tumour
82
Q

low ACTH would indicate a primary tumour in the adrenal gland or a secondary tumour in a higher centre?

A

Primary (tumour in the adrenal gland) shows low ACTH

83
Q

high ACTH would indicate a primary tumour in the adrenal gland or a secondary tumour in a higher centre?

A

Secondary (higher centre i.e. pituitary problems) shows high ACTH

84
Q

what is an ectopic ACTH secreting tumour?

A

Tumour outside the pituitary gland producing a lot of ACTH

Clinical Pathology (RIP) (49 decks)

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