T3 - L2 Endocrine investigations Flashcards
1
Q
What are hormones?
A
‘messenger molecules’ secreted by endocrine glands.
2
Q
what are the three types of intercellular signally performed by hormones?
A
endocrine
paracrine
autocrine
3
Q
what is endocrine signalling?
A
hormones ecreted into the blood stream and trigger a response in the target cell
4
Q
what is paracrine signalling?
A
hormones affecting neighbouring cells
5
Q
what is autocrine signalling?
A
hormones secreted by a cell to bind to same cell
6
Q
do hormones produce short or long term changes?
A
capable of both
7
Q
what enables hormones to have specificity?
A
A hormone can only influence cells that have specific target receptors
for that particular hormone.
8
Q
what are the 3 types of hormone?
A
peptide
steroid
tyrosine-based
9
Q
give examples of peptide hormones
A
PTH
ACTH
TSH
10
Q
give examples of steroid hormones
A
testosterone
oestradiol
cortisol
11
Q
give examples of tyrosine-based hormones
A
Thyroxine (T4) and Triiodothyronine (T3)
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
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
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
15
Q
where is GnRH (Gonadotropin-releasing hormone) released from?
A
hypothalamus
16
Q
where does GnRH (Gonadotropin-releasing hormone) act on?
A
anterior pituitary
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)
18
Q
what hormones are released from the anterior pituitary?
A
LH FSH GH TSH Prolactin ACTH
19
Q
what hormones are released from the hypothalamus?
A
GnRH GHRH somatostatin TRH Dopamine PRH CRH
20
Q
which hormones released from the anterior pituitary act on the gonads?
A
LH
FSH
21
Q
which hormones released from the anterior pituitary act on the thyroid?
A
TSH (thyroid stimulating hormone)
22
Q
which hormones released from the anterior pituitary act on the breasts?
A
prolactin
23
Q
which hormones released from the anterior pituitary act on the adrenal cortex?
A
ACTH
Adrenocorticotropic hormone
24
Q
what does FSH do?
A
regulates the development, growth, pubertal maturation, and reproductive processes of the body.
25
what does LH do?
females: an acute rise of LH triggers ovulation
males: stimulates production of testosterone
26
what cells are FSH and LH released from?
gonadotropic cells of the anterior pituitary gland
27
what hormone stimulates the production of LH and FSH?
GnRH
28
what hormone stimulates the production of GH?
GHRH
29
what hormone stimulates the production of TSH?
TRH
30
what hormones stimulates the production of Prolactin?
TRH
| PRH
31
what hormone stimulates the production of ACTH?
CRH
32
what is hyperprolactinemia?
Hyperprolactinemia is a condition of elevated serum prolactin.
33
explain how hyperprolactinemia can develop in patients taking antipsychotics?
- Antipsychotics are dopamine antagonists
- they inhibit the negative inhibition of dopamine on prolactin
- Resulting in high prolactin
34
what affect does dopamine have on prolactin?
inhibits prolactin release
35
what hormone inhibits GH release?
somatostatin
36
what affect does somatostatin have on GH?
inhibits GH release
37
explain how hyperprolactinemia can develop in patients with hypothyroidism?
- Hypothyroidism is low levels of thyroxine
- results in loss of the negative feedback on TRH
- Resulting in high prolactin
38
what does prolactin do?
Prolactin is mainly used to help women produce milk after childbirth
39
how does Thyroxine-binding Globulin affect thyroid function test interpretation?
- 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
what factors cause an abnormal increase of Thyroxine-binding Globulin concentrations?
- genetic causes
- pregnancy
- oestrogens (oral contraceptive pill)
41
what factors cause an abnormal decrease of Thyroxine-binding Globulin concentrations?
- genetic causes
- protein-ionising states
- malnutrition
- malabsorption
- acromegaly
- Cushing's disease
- high dose corticosteroids
- severe illness
- androgens
42
low TSH and low thyroxine indicates what?
pituitary failure
secondary hypothyroidism
43
low TSH high thyroxine indicates what?
primary hyperthyroidism
thyroid gland overproduction
(most commonly caused by autoimmune disease)
44
Low thyroxine and high TSH indicates what?
Unresponsive thyroid (primary hypothyroidism)
45
High thyroxine and high TSH indicates what?
Pituitary gland overproduction or feedback fails (secondary
| hyperthyroidism)]
46
why is TSH as a frontline test?
cheap
47
what is the problem with using TSH as a frontline test?
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
if TSH is low what do you add?
Add on free T3 and T4 to pick up the hyperthyroid patients
49
if TSH is high what do you add?
Add on free T4 to pick up the hypothyroid patients
50
what is non-thyroidal illness also referred to as?
sick euthyroid disease
51
what does euthyroid mean?
having a normally functioning thyroid gland.
52
what is Non-Thyroidal Illness [sick euthyroid disease]?
abnormalities within their thyroid function tests, despite being euthyroid.
53
why are TFTs impossible to interpret in sick patients?
free T3 decreases depending on severity of illness
free T4 increases depending on severity of illness
54
How often should we repeat TFTs in a healthy person?
3 years
55
what do TFTs detect?
high sensitivity immunoassay for thyroid stimulating hormone (TSH)
immunoassay estimation of non-protein bound thyroxine (fT4)
56
what TFTs result would support the diagnosis of hypothyroidism?
raised TSH and low FT4
57
what TFTs result would support the diagnosis of hyperthyroidism?
undetectable TSH
elevated FT4
58
what are the two types of immunoassay used in clinical chemistry?
immunometric assays
competitive immunoassays
59
advantages of immunoassays?
- specific due to antibody specificity
- sensitive
- amenable to automation
60
what is an immunoassay?
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
what are the two types of adrenal medullary tumours?
Phaeochromocytoma (adults)
Neuroblastoma (children)
62
what is a Phaeochromocytoma?
Tumour of neuroendocrine chromaffin cells – the majority in the adrenal medulla
63
a tumour of neuroendocrine chromaffin cells is called what?
Phaeochromocytoma
64
what are clinical features of a Phaeochromocytoma?
- hypertension
- sweating, pallor
- panic attacks
- headaches
- abdominal pain
- can be asymptomatic
65
Excessive and often episodic release of catecholamines due to a Phaeochromocytoma may result in what?
paroxysmal features (are a sudden recurrence or intensification of symptoms)
66
what do you measure to diagnose a Phaeochromocytoma?
Catecholamines excess = Phaechromocytoma
Metanephrines are often measured these days (Metabolites of catecholamines i.e. breakdown products)
- both measured in urine or blood
67
what is the problem with measuring Catecholamines to detect a Phaechromocytoma ?
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
is it better to test for Plasma metanephrines (blood) or urine fractionated metanephrines
when diagnosing Phaechromocytoma?
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
what follow up tests should be done in patients with suspected phaeochromocytoma and borderline changes in
catecholamines or Metanephrines?
Clonidine suppression test
Plasma Chromogranin A
MRI or CT of adrenals
Genetic counselling and screening for MEN mutations
70
what is hypoglycaemia?
- low plasma glucose level
| - Less than 3 or 3.5 mmol/L
71
what are the 3 components of Whipple's triad that suggest a patient's symptoms result from hypoglycemia ?
- Low Plasma Glucose Level
- Signs & Symptoms of Hypoglycaemia
- Resolution of Symptoms once Glucose Level Rises [i.e. treated]
72
what is a symptom? What is a sign?
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
what hormones are stimulated in hypoglycaemia?
growth hormones, cortisol and catecholamine secretion
74
what is the most common cause of hypoglycaemia in the adult UK population?
diabetes
75
what is an insulinoma?
- [Insulin secreting tumour]
| - Most common tumours arising from islets of Langerhans
76
what is the most common tumour arising from islets of Langerhans?
insulinoma
77
how would you diagnose a insulinoma?
- 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
a blood test showing a low blood sugar but high insulin conc will indicate what?
insulinoma
79
what is the most common cause of Cushing's syndrome?
Administration of steroids
Exogenous cause
80
what is the most common endogenous cause of Cushing's syndrome?
Cushing’s disease = Pituitary ACTH secreting tumour
Produces ACTH acting on the adrenal glands causing excess cortisol production
81
what are the four causes of Cushing’s syndrome?
- Administration of steroids
- Cushing’s disease
- Adenoma in the adrenal gland
- Ectopic ACTH secreting tumour
82
low ACTH would indicate a primary tumour in the adrenal gland or a secondary tumour in a higher centre?
Primary (tumour in the adrenal gland) shows low ACTH
83
high ACTH would indicate a primary tumour in the adrenal gland or a secondary tumour in a higher centre?
Secondary (higher centre i.e. pituitary problems) shows high ACTH
84
what is an ectopic ACTH secreting tumour?
Tumour outside the pituitary gland producing a lot of ACTH
