W5 Hormones Refresher (SM)

Question 1

What are examples of intercellular messengers systems? (5)
Examples of hormones in each?

Answer 1

Neurotransmission- Noradrenaline, acetylcholine
Neuroendocrine- Oxytocin, ADH
Endocrine- Insulin, TSH, cortisol, thyroxine
Autocrine- Prostaglandins
Paracrine- Glucagon, somatostatins

Question 2

Define the Endocrine System:
examples of hormones?
functions? (5)

Answer 2

Factors (hormones) produced by the glandular cells (site of production) are secreted into the bloodstream and travel to
their target cells (site of action) to produce a physiological response.

Insulin, thyroxine, cortisol, growth hormone, TSH

• Homeostasis
• Growth
• Development
• Metabolism
• Reproduction

Question 3

Functions of hormones?
Where are hormones secreted from/ travel to?

Answer 3

• – “to arouse” or “to excite”
• Glands secrete hormones directly into bloodstream (ductless)
• Carried to target cells/tissue (away from the endocrine gland)

e.g. parathyroid gland, pineal gland, hypothalamus. thyroid gland, adrenal glands, pancreas

Question 4

What are the types of hormones? (4)

Answer 4

Peptide
Steroidal
Tyrosine containing
Eicosanoids

Structural (chemical) differences distinguish the synthesis, storage, transportation and biological functions of hormones.

Question 5

Peptide hormones:
What are they formed from?
Where are they secreted from?

Answer 5

Chemical structure: chains of amino acids
* Small chains (e.g., TRH: contains 3 AAs)
* Large chains (e.g., LH/ FSH 80aas)
Mostly secreted from hypothalamus, pituitary, pancreas and GIT

Question 6

How are peptide hormones synthesised?
How are they released?
Transported?

Answer 6

Synthesis: like any protein synthesis
Transcription/Translation-preprohormone-prohormone-hormone-secretory granules/vesicles
Stored in the cells

Release: Require stimuli
Exocytosis (ca2+ responsible)

Transport:
Hydrophilic,
freely circulate in the blood vessel
No plasma protein binding
Short Half-life: minutes

Question 7

Steroidal hormones
What is the base?

Answer 7

Chemical structure: cholesterol is the base
cortisol, aldosterone (adrenal cortex) & sex hormones (gonads)

Synthesis: like any steroidal synthesis
* Enzymatic conversion of precursor
(cholesterol base) molecules into hormone
* Not stored in the cells

Release
* Stimulus increase precursor level and enzyme activation
* Simple diffusion across the membrane

Transport
* Lipophilic
* Binds with Plasma protein
* Half-life: hours to days

can easily pass the phospholipid bilayer but hydrophobic so req carrier proteins

Question 8

Tyrosine containing hormones

Answer 8

Chemical structure: tyrosine as the base
thyroid hormones and catecholamines (adrenal medulla)
Synthesis:
Thyroxine, Tyrosine, Epinephrine

Release
* Stimulus required
* Simple diffusion across the membrane

Transport
* Lipophilic
* Binds with Plasma protein (Weak and reversible bonds)
* Half-life: hours to days

Question 9

Eicosanoids

Answer 9

Chemical structure: Polyunsaturated fatty acid derivatives
Eg; prostaglandins, leukotrienes, prostacyclins and thromboxanes

Synthesis
* Precursor- Arachidonic acid (membrane lipid)
* Enzymes- Lipase dictates the production of various eicosanoids

Synthesised by stereo- and regio-specific peroxidation of arachidonic acid by three enzyme families, namely
lipoxygenases, cyclooxygenases, and phospholipases

Release
* Stimulus required
* Poorly diffuse through the cell
membrane

Transport
* Eicosanoids require a transporter (anionic)
* Half-life: in seconds: rapidly inactivated:
Limited to autocrine and paracrine effects