Classification of hormones biochemistry
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I now have excellent content from the Tietz Textbook and Kaplan & Sadock's. Here is the comprehensive answer:
Classification of Hormones - Biochemistry
Definition
Hormones are chemical messengers synthesized and secreted by endocrine glands, organs, or isolated cells that have specific regulatory effects on the activity of target cells. They are produced at one site in the body and, in general, exert their actions at distant sites. They circulate in body fluids at very low but variable concentrations.
- Tietz Textbook of Laboratory Medicine, 7th Ed.
Classification 1 - By Chemical Structure
Hormones are classified into three major groups based on their chemical structure:
1. Polypeptide / Protein Hormones
Examples: ACTH, Insulin, PTH, Growth Hormone, FSH, LH, TRH, glucagon, oxytocin, ADH
Biochemical properties:
- Water-soluble; circulate freely in plasma
- Stored in secretory vesicles (pre-formed storage)
- NOT lipid-soluble - cannot cross the cell membrane
- Relatively short plasma half-life (10-30 minutes)
- Act via cell surface receptors (GPCRs or enzyme-coupled receptors)
- Activate intracellular second messenger signal-transduction pathways (e.g., cAMP, IP3/DAG, Ca2+)
2. Amino Acid-Derived Hormones
These are further divided into two subgroups:
a) Catecholamines (derived from Tyrosine)
Examples: Epinephrine (Adrenaline), Norepinephrine, Dopamine
- Water-soluble; circulate freely in plasma
- Very short plasma half-life (~1 minute)
- Act via cell surface G-protein-coupled receptors (9 closely related adrenoceptors)
- Activate second messenger systems
b) Thyroid Hormones (derived from Tyrosine)
Examples: Thyroxine (T4), Triiodothyronine (T3)
- Water-soluble but circulate bound to specific transport proteins:
- Thyroid-Binding Globulin (TBG)
- Transthyretin (prealbumin)
- Albumin
- Long plasma half-life (~7-10 days for T4)
- Move freely across the cell membrane
- Act via intracellular nuclear receptors (NR): thyroid hormone receptors TRα and TRβ
- Directly regulate gene transcription
c) Indoleamines (derived from Tryptophan)
Examples: Serotonin, Melatonin
3. Steroid and Other Lipid-Derived Hormones
Examples: Cortisol, Estrogens, Testosterone, Progesterone, Aldosterone, DHEA, Vitamin D, Calcitriol
Biochemical properties:
- Synthesized from cholesterol (except Vitamin D which comes from cholesterol via skin photolysis)
- Hydrophobic (lipid-soluble); insoluble in water
- NOT stored in vesicles - diffuse out of the cell immediately after synthesis
- Circulate bound to specific transport proteins (cortisol-binding globulin, sex hormone-binding globulin, albumin); only a small free fraction is biologically active
- Plasma half-life: 30-90 minutes
- Enter target cells by passive diffusion due to hydrophobicity
- Act via intracellular nuclear receptors (NR superfamily) in cytoplasm or nucleus
- Regulate gene transcription directly
Classification 2 - By Location of Function (Mode of Action)
| Classification | Mode of Action | Example |
|---|---|---|
| Endocrine | Travel through bloodstream to act on a distant target organ | Insulin, cortisol, thyroxine |
| Paracrine | Act on adjacent/neighboring cells locally | Prostaglandins, somatostatin (in gut) |
| Autocrine | Act on the same cell that secreted them (self-regulatory) | Certain growth factors stimulating their own synthesis |
- Kaplan & Sadock's Comprehensive Textbook of Psychiatry
Comparison Table - Key Biochemical Differences
| Property | Polypeptide | Catecholamines | Thyroid Hormones | Steroids |
|---|---|---|---|---|
| Precursor | Amino acids | Tyrosine | Tyrosine + Iodine | Cholesterol |
| Solubility | Water-soluble | Water-soluble | Water-soluble | Lipid-soluble |
| Storage | Secretory vesicles | Chromaffin granules | Thyroglobulin (follicles) | Not stored (diffuse out) |
| Plasma transport | Free | Free | Bound (TBG, transthyretin) | Bound (CBG, SHBG) |
| Half-life | Short (mins) | Very short (~1 min) | Long (T4: 7-10 days) | Intermediate (30-90 min) |
| Receptor location | Cell surface | Cell surface | Intracellular (nucleus) | Intracellular (cytoplasm/nucleus) |
| Mechanism | 2nd messenger (cAMP, IP3) | 2nd messenger | Direct gene transcription | Direct gene transcription |
Receptor Families (Biochemistry)
| Receptor Type | Hormone Class | Signal Pathway |
|---|---|---|
| G-protein coupled receptors (GPCRs) | Polypeptides, catecholamines | cAMP, IP3/DAG, Ca2+ |
| Enzyme-coupled receptors (e.g., Receptor Tyrosine Kinases) | Insulin, growth factors | Phosphorylation cascades |
| Nuclear receptor (NR) superfamily | Steroids, thyroid hormones, Vitamin D | Gene transcription |
Biosynthesis Summary
- Polypeptide hormones: Synthesized as preprohormones on ribosomes → processed via RER and Golgi → stored in secretory vesicles → released by exocytosis
- Catecholamines: Tyrosine → DOPA → Dopamine → Norepinephrine → Epinephrine (via sequential enzymatic steps)
- Thyroid hormones: Tyrosine residues in thyroglobulin are iodinated by TSH-regulated thyroid peroxidase → T3 and T4 released on demand
- Steroid hormones: Cholesterol → Pregnenolone (rate-limiting step via StAR protein and P450scc) → various steroids via tissue-specific enzymatic pathways
Sources:
- Tietz Textbook of Laboratory Medicine, 7th Ed. - Classification of Hormones (Chapter 38)
- Kaplan & Sadock's Comprehensive Textbook of Psychiatry - Hormone Classification by Structure and Location (Table 1.12-1 & 1.12-2)
Can you satyanarain as a reference for this topic
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Finding Sources
Unfortunately, U. Satyanarayana's Biochemistry is not available in the medical textbook library. The biochemistry books currently available are:
- Basic Medical Biochemistry - A Clinical Approach, 6th Ed (Lieberman & Marks)
- Biochemistry, 8th Ed - Lippincott Illustrated Reviews
- Harper's Illustrated Biochemistry, 32nd Ed
Satyanarayana's Biochemistry is a widely used Indian medical textbook, but it is not in this library's collection. I can instead cover the classification of hormones using any of the three biochemistry books above - particularly Lippincott and Harper's, which are among the most comprehensive biochemistry references used globally and cover the same content with similar depth.
Would you like me to pull the hormone classification content from Lippincott or Harper's instead?
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