Endocrinology intro

Question 1

Endocrinology: what’s it all for?

Answer 1

Control systems needed to maintain homeostasis across:
• milliseconds–minutes=nervous system
• minutes–hours–days–years–entire lifetime = endocrine system

Question 2

The Endocrine system: functions

Answer 2

regulate metabolism,water and electrolyte balance
• allow body to cope with stress
• regulate growth
• control reproduction
• regulate circulation and red blood cell production
• control digestion & absorption of food

Question 3

Blood-borne chemical messengers:

Answer 3

Hormones - produced by endocrine cells & Neurohormones - produced by nerves

Question 4

Endocrine system:

Answer 4

all hormone-secreting
tissues; including, in the brain, the hypothalamus, pituitary & pineal gland, and in the periphery the thyroid, parathyroid & adrenal glands, gonads, pancreas, kidneys, liver, thymus, and
also parts of the intestines,
the heart and skin.

Question 5

Classes of hormones - Peptides:

Answer 5

chains of amino acids, eg ADH, growth hormone. Hydrophilic (ie water soluble). Stored prior to release.
* most common

Question 6

Classes of hormones -

Amines:

Answer 6

derived from the amino acid ‘tyrosine’. All are stored. Hydrophilic - catecholamines (adrenaline, noradrenaline & dopamine); or Lipophilic (ie fat soluble): thyroid hormones.
- Thyroxine - in white foods, eg chicken, fish, nuts

Question 7

Classes of hormones -

Steroids

Answer 7

Steroids: derived from cholesterol where appropriate enzymes for conversion are present eg cortisol, testosterone, oestrogens.
Lipophilic. Not stored, released by diffusion

Question 8

Hydrophilic

Answer 8

Most transported in blood dissolved in plasma (some also carried on binding proteins).
• Can’t pass through cell membrane, therefore binds to specific receptors on surface of target cell.
• Elicit response either by changing cell permeability (few) or by activating ‘second-messenger’ system to alter activity of intracellular proteins (most).
• Vulnerable to metabolic inactivation so short-term effects

Question 9

hydrophilic actions

Answer 9

extracellular messenger binds to receptor > binding of receptor leads to opening of ion channel > ions enter > ion entry brings desired result

changes cell permeability > activating second - messenger system

• Have to act outside of cell therefore cell must show certain receptors

Question 10

Lipophilic hormones (thyroid hormones & steroids):

Answer 10

• Transported in blood mostly bound to plasma proteins. Small, unbound amount dissolved – only dissolved portion physiologically active.
• Free hormone (unbound) easily passes through cell membrane, binds to specific receptor within target cell (mostly in cell nucleus).
• Elicit response by activating specific genes within target cell to cause formation of new intracellular proteins.
• Less vulnerable to metabolic inactivation so effects last longer

Question 11

Summary: Hydrophilic vs Lipophilic

Answer 11

• Hydrophilic – Likes water
– Can’t get through plasma membrane
– Fast onset, short-acting
• Lipophilic (hydrophobic) – Hates water
– Can diffuse across plasma membrane
– Slower onset, longer- acting