Types of Hormones

Question 1

Peptide/Protein hormones structure

Answer 1

Chains of amino acids.

Synthesised as preprohormone.

Question 2

Preprohormone

peptide hormones

Answer 2

Produced by ribosomes. Large and inactive.

Cleaved in endoplasmic reticulum to prohormones.

Question 3

Prohormone

peptide hormones

Answer 3

Inactive.
Packaged into vesicles in Golgi apparatus.
Broken down by proteolytic enzymes into active hormone and fragments.

Question 4

Hormone and fragments

peptide hormones

Answer 4

Stored in vesicles in endocrine cells until release triggered.
Inactive fragments can be measured e.g. C-peptide in diabetes.

Question 5

Solubility of peptide hormones

Answer 5

Water-soluble - dissolve easily in plasma.
Vulnerable to degredation.
Short half-life (prolonged secretion).
Cannot cross cell membrane.

Question 6

Mechanism of action of peptide hormones

Answer 6

G-protein couple receptor or tyrosine kinase-linked signalling pathway: phosphorylate proteins

• GPCR: activates 2nd messenger system and/or ion channels (rapid) leading to modification of existing proteins
• Tyrosine: alters gene expression

Question 7

Amine hormones

Answer 7

Derived from tyrosine or tryptophan.

Question 8

Tyrosine derived hormones and solubility

Answer 8

Catecholamines (hydrophilic)

• Dopamine
• Norepinephrine
• Epinephrine

Thyroid hormones (lipophilic)

• Thyroxine
• Triiodothyronine

Question 9

Tryptophan derived hormone

Answer 9

Melatonin - regulates circadian rhythm

Question 10

Steroid hormones

Answer 10

Synthesised directly as needed from cholesterol.

Question 11

Steroid hormone solubility and transportation

Answer 11

Highly lipophilic

• Bound to carrier proteins
• Only free hormone can diffuse (physiologically important fraction)

Question 12

Steroid hormone production

Answer 12

• Gonads (sex)
• Placenta (hCG, sex)
• Kidney (Vit D3)
• Adrenal cortex (corticosteroids: aldosterone, cortisol)

Question 13

Steroid hormone mechanism of action

Answer 13

Cross plasma membrane easily.
Bind to cytoplasmic/nuclear receptors (within cells).
Trigger activation/repression of gene function (genomic effect).
- Effect persists

Question 14

Law of Mass Action in regards to steroid hormone

Answer 14

As free hormone leaves the plasma more hormone is released from carriers.

• Minute quantities of hormone required
• Allows for reservoir of hormone
• Prolonged activity

Question 15

Hormone carrier proteins

Answer 15

Steroid/thyroid hormones are lipophilic and so poor plasma solubility.

• Specific/non-specific (albumin) carriers
• Protected from degradation (increased half life)