Endocrine Biochemistry

Question 1

What is a hormone?

Answer 1

Any substance elaborated by one cell to regulate another cell

Question 2

What determines the hormonal duration of action?

Answer 2

The type of receptor that it activates

Question 3

What provides the highest level of endocrine control?

Answer 3

Hypothalamus

Question 4

What are the actions of the hypothalamus?

Answer 4

Secretes regulatory hormones
Synthesises hormones and transports them to the posterior pituitary
Direct neural control - hypothalamic autonomic centres control secretion of adrenaline and noradrenaline from adrenal medulla

Question 5

What is the meaning of diurnal variation of hormone levels?

Answer 5

External cues such as light and dark can evoke fluctuations in hormone secretions

Question 6

What are the three classes of hormones?

Answer 6

Steroids
Amine-derived
Proteins

Question 7

What are examples of steroid hormones?

Answer 7

Oestrogen
Cortisol
Testosterone

Question 8

What are examples of amine-derived hormones?

Answer 8

Adrenaline
Epinephrine
Thyroxine
Triiodothyroxine

Question 9

What are examples of protein hormones?

Answer 9

Oxytocin
ADH
Growth Hormone
Insulin

Question 10

Describe steroid hormones…

Answer 10

Lipids derived from cholesterol
Hydrophobic
Transported in the blood by binding to carrier proteins - unbound steroid hormones are ‘biologically active’

Question 11

What is the action of steroid hormones?

Answer 11

They cross the plasma membrane by 2 steps:

1. Activated hormone-receptor complex forms within the cell
2. The complex binds to DNA and activates specific genes leading to gene activation and production of key proteins

Question 12

Describe Amine-derived hormones…

Answer 12

Catecholamines (epinephrine, adrenaline etc.) are transported free in the blood and are hydrophilic
Thyroid amine hormones (T3 and T4) are bound to carrier proteins
Secreted from the thyroid and adrenal medulla
Stored in vesicles or colloid (T3/T4)

Question 13

Describe peptide hormones…

Answer 13

Hydrophilic
Transported unbound in the blood
Secreted by the pituitary, parathyroid, heart, stomach, liver and kidneys
Synthesised as precursor molecules and stored in secretory vesicles

Question 14

What is the structure of peptide hormones?

Answer 14

They may be composed of a ring structure due to the presence of disulphide bonds e.g. somatostatin
They may also be composed of 2 chain structures due to the disulphide bonds e.g. insulin

Question 15

What type of hormones are bound to carrier proteins?

Answer 15

Steroid hormones
Thyroid hormones (amine-derived)

Question 16

What is the effect of binding to a carrier protein?

Answer 16

Facilitates hormone transport
Increases the half-life of the hormone
Acts as a reservoir for the hormone

Question 17

Name some specific carrier proteins…

Answer 17

Cortisol-binding protein - binds cortisol and some aldosterone
Thyroxine-binding globulin - binds T4 and some T3
Sex steroid-bindng globulin - binds mainly testosterone and some oestradiol