An Introduction to the Endocrine System *

Question 1

what is endocrinology?

Answer 1

study of hormones

Question 2

what is a hormone?

Answer 2

a substance secreted directly into the blood by specialised cells

Question 3

what do hormones do in the body?

Answer 3

• Are present in only minute concentrations in the blood
• Bind to specific receptors in target cells to influence cellular reactions

Question 4

what are the 6 terms used to refer to different ways that hormones are secreted? (JAPINE)

Answer 4

J - juxtacrine
A - autocrine
P - paracrine
I - intracrine
N - neuroendocrine
E - endocrine

Question 5

what is endocrine?

Answer 5

secretes hormone directly into bloodstream which then acts on a distant target tissue.

Question 6

what is intracrine?

Answer 6

cell synthesise its own hormone which then acts within the cell (hormone does not leave the cell)

Question 7

what is autocrine?

Answer 7

The hormone leaves the cell and then docks back onto the same cell via its receptors

Question 8

what is paracrine?

Answer 8

acts on nearby cells within the same tissue or organ

Question 9

what is juxtacrine?

Answer 9

secreted hormone acts on neighbouring cells

Question 10

what is neuroendocrine?

Answer 10

An electrical stimulus passes down a neurone (usually in the brain e.g. Hypothalamus) to a specialised cell causing it to secrete a hormone which will affect a distant target cell

Question 11

what are the 2 different types of hormones?

Answer 11

steroid hormones
peptide hormones

Question 12

what are steroid hormones?

Answer 12

fat soluble (and hydrophobic) meaning they can cross the phospholipid bilayer to bind to receptors in the cytoplasm which are usually transcription factors.
Once activated they travel to the cell nucleus and activate or inhibit transcription of a protein.

Question 13

what are peptide hormones?

Answer 13

hydrophilic- need to bind to receptors on protein channels
Receptors undergo a conformational change moving the hormone across the plasma membrane into the cell to initiate a response.

Question 14

what are the 6 ways in which hormones are regulated? (bob sold chris really hot peppers)

Answer 14

(BOB) Biosynthesis
(SOLD) Secretion
(CHRIS) Circulation/distribution
(REALLY) Receptor interaction
(HOT) Hormone metabolism/excretion
(PEPPERS) Peripheral modification

Question 15

give an example of faulty biosynthesis?

Answer 15

Congenital adrenal hyperplasia- mutations in genes that code for enzymes involved in making steroid hormones in the adrenal glands
–> ambiguous genitalia

Question 16

give an example of faulty secretion?

Answer 16

Congenital hypothyroidism - Thyroid gland is undeveloped so unable to secret the correct hormones or enough hormones.

Question 17

give an example of faulty modification?

Answer 17

5-alpha reductase deficiency - Testosterone is a pre-hormone, it needs 5-alpha reductase to form to 5-alpha Dihydrotestosterone (final hormone). Leads to ambiguous genitalia, or female appearance

Question 18

give an example of faulty receptors?

Answer 18

Androgen Insensitivity Syndrome- X-linked condition, Caused by faulty androgen receptor
Because there is so much testosterone (produced by Gonads) the body is able to convert it to oestrogen further exemplifying female characteristics e.g. breast development.

Question 19

How to measure hormones?

Answer 19

Bioassays
Immunoassays
Mass spectrometry

Bioassays or immunoassays is where the hormone is bound to an antibody that is linked to a signal e.g. fluorescence. Measuring the fluorescence or frequency of signals shows the measurement of the hormones present
MS is more accurate method of measuring hormones

Question 20

where is the pituitary located?
what are the main anterior and posterior pituitary hormones?

Answer 20

located in Sella turcica

Anterior pituitary hormones
ACTH - Regulation of adrenal cortex hormones
TSH - Thyroid hormone regulation
Growth hormone- Regulates Growth (+), metabolism
LH/FSH - Reproductive control and puberty
(PRL) Prolactin - Breast milk production

Posterior pituitary hormones
ADH - Water regulation
Oxytocin - Breast milk expression (lactation)

Question 21

how does a hormone negative feedback loop work?
give example

Answer 21

e.g thyroid gland

Question 22

name and explain the symptoms of 3 diseases that occur due to excess hormone production

Answer 22

WHEN GLANDS GO WRONG – EXCESS PRODUCTION

Grave’s disease (Hyperthyroidism)
Symptoms:
Bulging eyes
Thickening and reddening of the skin, especially on the shins and upper feet, Tiredness or muscle weakness, Trouble sleeping
Shaky hands
Rapid and irregular heartbeat
Weight loss without dieting

Cushing’s disease: Glucocorticoid excess
Symptoms:
increased fat on your chest and tummy, but slim arms and legs
buffalo hump: a build-up of fat on the back of your neck and shoulders
skin that bruises easily 🡪 large purple stretch marks
depression and mood swings

Acromegaly - Growth hormone excess, Due to pituitary tumour
Symptoms:
Increased frontal bossing
Enlargement of base of the nose
Thickening of the lips
Broad based fingers

Question 23

name and explain the symptoms of 3 diseases that occur due to insufficient hormone production

Answer 23

WHEN GLANDS GO WRONG – TOO LITTLE PRODUCTION

Severe hypothyroidism
symptoms:
Fatigue
Dry skin
Hair loss
Weight gain
Puffy face
Enlarged thyroid gland (goiter)

Iodine deficiency goitre – due to lack of negative feedback which results in TSH excess
If iodine is deficient in the diet thyroid hormone can’t be produced.
As a result you get a low negative feedback
As a result you get excess TSH – which is a growth factor - tumour like growths on the neck near thyroid gland (goitre)
This is an example of TSH excess

Adrenal insufficiency (Addison’s disease) – ACTH excess
The adrenal gland is destroyed by auto antibodies
Disrupted feedback loop - due to cortisol deficiency, ACTH production is enhanced
Hyperpigmentation: of the skin
Large amounts of POMC is produced because it is required to produce ACTH.
Another product of POMC in this process is MSH => more MSH is produced.
MSH stimulates melanocyte cells activity in the skin which causes the skin to darken especially in Palmer crease (crease on palm).
Symptoms:
weight loss
lethargic
reduced stress response
more prone to infection

Question 24

what general principles are used to manage hormone excess or deficiency?

Answer 24

If hormones are in excess
Remove the hormone gland
or
Block secretion/synthesis of hormone

If there is hormone deficiency
REPLACE the hormone e.g. injection of replacement hormone

Question 25

what do you need to do if someone has an underactive gland?

Answer 25

Underactive glands need hormone replacement therapy

Underactive thyroid - thyroxine (as a tablet)
Underactive adrenals – hydrocortisone(cortisol) + fludrocortisone (aldosterone)
(Premature) menopause – oestrogen replacement therapy
Underactive testes – testosterone

Question 26

what is the treatment for thyrotoxicosis (hyperthyroidism)?

Answer 26

Destruction of thyroid tissue using radioiodine (131I) which specifically accumulated in the thyroid tissue which then selectively destroys thyroid tissue
Antithyroid drugs to block hormone synthesis
Surgery to take gland out
If you have pituitary tumour – remove that as well (go through the nose)

Question 27

what drug can be used to treat functioning pituitary tumours?

Answer 27

A pituitary tumour may result in excess secretion of GH.
This can be treated with Pegvisomant
Pegvisomant: GH receptor antagonists - competes with growth hormone (secreted by tumour) for the growth hormone receptor – also replaces all growth hormones currently in the receptors. When bound the antagonist blocks the usual effect of when GH is bound to the receptor.