Types of Hormones — Revision Notes

⚡ 30-Second Revision

Peptide/Protein Hormones: — Water-soluble, membrane receptors, second messengers (cAMP, $IP_3$), rapid/short-lived. Ex: Insulin, GH.
Steroid Hormones: — Lipid-soluble, intracellular receptors, gene expression, slow/prolonged. Ex: Cortisol, Estrogen.
Amino Acid Derivatives:

- Catecholamines: Water-soluble, membrane receptors. Ex: Adrenaline. - **Thyroid Hormones ($T_3$, $T_4$):** Lipid-soluble, intracellular receptors. Ex: Thyroxine.

Fatty Acid Derivatives (Eicosanoids): — Local action (autocrine/paracrine), membrane receptors. Ex: Prostaglandins.
Transport: — Water-soluble (free), Lipid-soluble (carrier proteins).

2-Minute Revision

Hormones are chemical messengers classified by their chemical nature, which dictates their function. Peptide/protein hormones (e.g., insulin, growth hormone) are water-soluble, transported freely in blood, bind to membrane receptors, and activate second messenger systems for rapid, short-lived effects.

Steroid hormones (e.g., cortisol, estrogen) are lipid-soluble, derived from cholesterol, transported bound to carrier proteins, diffuse across membranes to bind to intracellular receptors, and regulate gene expression for slower, prolonged effects.

Amino acid derivatives are a mixed group: catecholamines (e.g., adrenaline) are water-soluble, acting via membrane receptors, while thyroid hormones ($T_3$, $T_4$) are lipid-soluble, acting via intracellular receptors.

Fatty acid derivatives (eicosanoids) like prostaglandins act locally (autocrine/paracrine) and are rapidly degraded. Key distinctions lie in solubility, receptor location, and mechanism of action.

5-Minute Revision

To master hormone types for NEET, focus on the four main chemical classes and their defining characteristics.

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Peptide and Protein Hormones: — These are chains of amino acids (e.g., insulin, glucagon, growth hormone). They are water-soluble, meaning they travel freely in the blood. Because they cannot cross the lipid cell membrane, their receptors are located on the cell surface (membrane receptors). Binding activates second messenger systems (like cAMP or $IP_3$/DAG), leading to rapid, but often short-lived, cellular responses. Think of a quick 'on/off' switch.

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Steroid Hormones: — Derived from cholesterol (e.g., cortisol, estrogen, testosterone). They are lipid-soluble and thus require carrier proteins for transport in the aqueous blood. Their lipid nature allows them to easily diffuse across the cell membrane to bind with intracellular receptors (in the cytoplasm or nucleus). The hormone-receptor complex then directly influences gene transcription, leading to the synthesis of new proteins. This mechanism results in slower, but more prolonged and sustained effects, like a 'long-term programming' change.

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Amino Acid Derivatives: — This group is tricky due to its varied solubility.

* Catecholamines (e.g., adrenaline, noradrenaline), derived from tyrosine, are water-soluble. They act rapidly by binding to membrane receptors and using second messengers, similar to peptide hormones. * Thyroid hormones ($T_3$, $T_4$), also from tyrosine but with iodine, are uniquely lipid-soluble. They are transported by carrier proteins and bind to intracellular (nuclear) receptors, regulating gene expression like steroid hormones.

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Fatty Acid Derivatives (Eicosanoids): — Derived from arachidonic acid (e.g., prostaglandins). These are primarily local hormones, acting on the producing cell (autocrine) or nearby cells (paracrine). They are rapidly synthesized and degraded, typically binding to membrane receptors to exert diverse local effects.

Key takeaway: Solubility dictates transport and receptor location, which in turn determines the mechanism, speed, and duration of hormone action. Memorize key examples for each category and understand the 'why' behind their different actions.

Prelims Revision Notes

Types of Hormones: NEET Revision Notes

I. Classification by Chemical Nature:

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Peptide/Protein Hormones:

* Composition: Chains of amino acids (small peptides to large proteins). * Solubility: Water-soluble (hydrophilic). * Synthesis: RER (preprohormone) $\rightarrow$ Golgi (prohormone $\rightarrow$ active hormone) $\rightarrow$ Secretory vesicles.

* Storage: Stored in vesicles until released by exocytosis. * Transport: Free in blood plasma. * Receptors: Membrane-bound (on cell surface). * Mechanism: Second messenger system (e.

g., cAMP, $IP_3$/DAG, $Ca^{2+}$). Activates enzyme cascades. * Response: Rapid, short-lived. * Examples: Insulin, Glucagon, Growth Hormone (GH), Prolactin, Oxytocin, Vasopressin (ADH), Parathyroid Hormone (PTH), Calcitonin, TSH, FSH, LH, ACTH.

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Steroid Hormones:

* Composition: Derived from cholesterol (lipid). * Solubility: Lipid-soluble (hydrophobic). * Synthesis: Smooth ER and mitochondria. Not stored; diffuse out upon synthesis. * Transport: Bound to carrier proteins (e.

g., albumin, globulins) in blood plasma. * Receptors: Intracellular (cytoplasmic or nuclear). * Mechanism: Hormone-receptor complex binds to DNA (HREs), regulating gene transcription and protein synthesis.

* Response: Slower, prolonged. * Examples: Cortisol, Aldosterone, Estrogen, Progesterone, Testosterone, Calcitriol (active Vitamin D).

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Amino Acid Derivative Hormones:

* Origin: Modified amino acids (primarily tyrosine or tryptophan). * Subtypes: * Catecholamines (e.g., Adrenaline, Noradrenaline, Dopamine): * Origin: Tyrosine. * Solubility: Water-soluble.

* Receptors: Membrane-bound. * Mechanism: Second messenger systems. * Response: Rapid, short-lived ('fight or flight'). * **Thyroid Hormones (Thyroxine $T_4$, Triiodothyronine $T_3$):** * Origin: Tyrosine + Iodine.

* Solubility: Lipid-soluble (unique for amino acid derivative). * Transport: Bound to carrier proteins (e.g., TBG). * Receptors: Intracellular (nuclear). * Mechanism: Regulate gene transcription.

* Response: Slower, prolonged (metabolism, growth). * Melatonin: * Origin: Tryptophan. * Solubility: Water-soluble. * Receptors: Membrane-bound. * Mechanism: Circadian rhythms.

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Fatty Acid Derivative Hormones (Eicosanoids):

* Origin: Derived from arachidonic acid (a fatty acid). * Examples: Prostaglandins, Thromboxanes, Leukotrienes. * Action: Primarily local (autocrine or paracrine). * Synthesis: Produced on demand, not stored. * Receptors: Membrane-bound. * Response: Rapidly metabolized, localized effects (inflammation, pain, smooth muscle contraction).

II. Key Distinctions for NEET:

Solubility: — Determines transport and receptor location.
Receptor Location: — Membrane (water-soluble) vs. Intracellular (lipid-soluble).
Mechanism: — Second messengers (water-soluble) vs. Gene regulation (lipid-soluble).
Speed/Duration: — Rapid/short (water-soluble) vs. Slow/prolonged (lipid-soluble).
Exceptions: — Thyroid hormones (amino acid derivative but lipid-soluble, intracellular receptors).

Vyyuha Quick Recall

To remember the main hormone types and their key characteristics:

Peptide Steroid Amino Fatty Acid

Peptide: Plasma (free transport), Protein receptor (membrane), Prompt action (second messengers) Steroid: Slow action (gene expression), Soluble in lipids, Secreted by gonads/adrenal cortex, Secret (not stored) Amino: Always remember Thyroid is Atypical (lipid-soluble, intracellular receptor) while Adrenaline is Aqueous (water-soluble, membrane receptor) Fatty Acid: Fast local action, From arachidonic acid (eicosanoids)