Endocrine basic science

Question 1

What is:
-autocrine
-paracrine
-endocrine
signalling?

Answer 1

Autocrine: cells release chemicals which act upon the cell itself to modify it

Paracrine: cells release chemicals which act locally on cells nearby

Endocrine: cells release hormone that travel in the blood stream to act on specific receptors in the body

Question 2

There are three different 'classes' of hormones:
-glycoproteins and peptides
-steroids
-tyrosine and tryptophanderivatives
give an example of each

Answer 2

Glycoproteins and peptides:

• most diverse class, amino acids of variable chains
• T1/2 minutes
• e.g. oxytocin/insulin

Steroid:

• derived from cholesterol
• T1/2 hours to days
• e.g. cortisol/testosterone

tyrosine and tryptophanderivatives

• e.g. adrenaline/thyroid hormones/melatonin
• Adrenaline T1/2 is seconds
• Thyroxine T1/2 hours to days

Question 3

How are:
-amines
-peptides and proteins
-steroids
synthesised and transported in blood stream`

Answer 3

Amines:

• presynthesised and stored, released when needed
• hydrophilic and transported free in plasma

Peptides and proteins

• presynthesised and stored, released when needed
• transported free in plasma

Steroids:

• synthesised in demand
• transported via carrier proteins (hydrophobic)

Question 4

Both specific and carrier proteins exist. Give examples of both.

Answer 4

Specific:

• thyroxine binding globulin
• sex-steroid binding globulin
• cortisol binding globulin

General carriers:

• albumin (carries many steroids and thyroxin)
• transthyretin (carries some steroids and throxin)

Question 5

Describe the 3 ways that hormonal levels are controlled

Answer 5

Negative feedback
Neuroendocrine (elicits a sudden burst in secretion to meet a specific stimulus) - e.g. hypothalamus releases corticotropin releasing hormone in response to stress
Diurnal rhythm - e.g. cortisol released in the morning

Question 6

Describe the H-P axis of thyroid hormones

Answer 6

Thyrotropin releasing hormone from hypothalamus stimulates thyroid stimulating hormone from anterior pituatary which acts on thyroid to release T3 and T4

Question 7

Which is more potent T3 or T4? what is used to make thyroid hormones?

Answer 7

T3 is 4 times more potent than T4 and T4 is converted to T3 in the liver
-iodine is used

Question 8

What are the two areas of the thyroid and what is released from each area?

Answer 8

Follicular cells release thyroid hormone

parafollicular (C cells) secrete calcitonin

Question 9

What regulates the release of thyroid hormones?

Answer 9

Low temperatures in babies/young children

stress: inhibits TRH and TSH release

Circadian rhythm: highest late at night and lowest in the morning