Hormones can be derived from the following tissue types
- Endocrine glands (derived from epithelial tissue) give rise to traditional hormones
- Isolated endocrine cells give rise to hormones of the diffuse endocrine system
- Neurons give rise to neurohormones
- Cells of the immune system give rise to cytokines
- Made on demand as opposed to being premade and stored for release.
Traditional hormones are secreted into the blood.
- Secretion: movement of a substance inside a cell to ECF
- Ectohormones: signalling molecules secreted into the ECF or external environment (e.g.
pheromones)
- E.g. Hormones: signalling molecules secreted into the blood
Molecules suspected of being hormones are known as candidate hormones.
- Growth factors and eicosanoids: Not widely distributed in circulation and can act via paracrine or
autocrine signalling
- Cholecystokinin (CCK): molecule acts as a hormone when secreted from the gallbladder, but a
neuromodulator when secreted from the brain
Hormones act by binding target cell receptors and initiating biochemical responses. Responses must also be
terminated.
- Variations in responses occur due to variation in presence of receptors and type of receptors
- Hormones action is terminated by degradation of hormones to inactive metabolites in the bloodstream
- Degradation occurs via enzymes in the kidneys or liver, excreted as urine or bile.
- Rate of degradation is indicate by hormone half-life (time required to reduce hormone
concentration by half)
, HORMONE CLASSIFICATION (CHP 7)
Hormones can be classified in various ways:
1. According to control of release by the brain
2. According to binding to GCPRs, tyrosine kinases, intracellular receptors, etc.
3. According to structure (peptide, steroid, amino acid-derived)
a. Peptide hormone: Linked amino acids (majority of hormones)
b. Steroid hormone: Derived from cholesterol
c. Amino acid-derived hormone (amine): Modifications of single amino acids
i. Catecholamines or thyroid hormones
Peptide Hormones:
Examples: Insulin, parathyroid hormone, glucagon,
calcitonin, CCK, ghrelin, vasopressin, neuropeptide Y
- Peptide hormones are synthesized all over the body.
Peptide hormones are synthesized in advance and stored in
secretory vesicles.
- The initial product of the ribosome is the preprohormone
- Contains one or more copies of the peptide hormone
- Contains a signal sequence, directing the product
to the ER for processing
- The ER processes the preprohormone to an inactive
prohormone
- Prohormones are packaged in the golgi apparatus with
proteolytic enzymes for activation
- Peptide hormones are stored in vesicles until exocytosed
into ECF
Peptide hormones are water soluble
- Dissolve generally well in the blood and are lipophobic
- Peptide hormones have a generally short half-life
- Lipophobic nature results in primarily binding to surface membrane receptors
- Act via a signal transduction system (e.g. cAMP or tyrosine kinase)
- Signal transduction gene may activate changes to gene activity
Response of cells is generally fast due to the second messenger system modifying existing proteins.
“If a hormone is not a steroid or amine hormone, it must be a peptide hormone.”
, Steroid Hormones:
Examples: Sex hormones (progesterone, estradiol, testosterone), androgens, glucocorticoids,
vitamin D, aldosterone
- Steroid hormones are synthesized only in the adrenal cortex (adrenal glands), gonads, and skin
Steroid hormones are highly lipophilic and cannot be stored in vesicles.
- Cells secreting steroid hormones have high amounts of endoplasmic reticulum
- When a stimulus activates a secreting cell, precursors in the cytoplasm are converted into the
hormone needed
- The lipophilicity of steroid hormones implies that they are synthesized on demand and travel freely
out of their parent cell and into their target cell
The lipophilicity of steroid hormones implies they are not soluble in plasma and must be bound to protein
carrier molecules in the blood.
- Binding to carrier proteins protects the
hormones and promotes a long ½ life.
- Steroids must unbind from their lipophilic
carriers to enter the cell
The ultimate destination of steroid-hormone
complexes is the nucleus.
- Primarily acts with genomic effect, affecting
gene transcription and regulation
- Lack of second messenger system results in
slow responses from the cell
Amine Hormones:
Examples: Melatonin, thyroid hormones (), catecholamines (epinephrine, norepinephrine,
dopamine)
- Hormones derived from tryptophan, tyrosine, or both
- Can be created in the thyroid gland (thyroid hormones),
Tyrosine derived hormones can be divided into catecholamines or thyroid hormones.
- Catecholamines behave more like peptides (extracellular action)
- Thyroid hormones behave more like steroid (intracellular action)
- Endocrine glands (derived from epithelial tissue) give rise to traditional hormones
- Isolated endocrine cells give rise to hormones of the diffuse endocrine system
- Neurons give rise to neurohormones
- Cells of the immune system give rise to cytokines
- Made on demand as opposed to being premade and stored for release.
Traditional hormones are secreted into the blood.
- Secretion: movement of a substance inside a cell to ECF
- Ectohormones: signalling molecules secreted into the ECF or external environment (e.g.
pheromones)
- E.g. Hormones: signalling molecules secreted into the blood
Molecules suspected of being hormones are known as candidate hormones.
- Growth factors and eicosanoids: Not widely distributed in circulation and can act via paracrine or
autocrine signalling
- Cholecystokinin (CCK): molecule acts as a hormone when secreted from the gallbladder, but a
neuromodulator when secreted from the brain
Hormones act by binding target cell receptors and initiating biochemical responses. Responses must also be
terminated.
- Variations in responses occur due to variation in presence of receptors and type of receptors
- Hormones action is terminated by degradation of hormones to inactive metabolites in the bloodstream
- Degradation occurs via enzymes in the kidneys or liver, excreted as urine or bile.
- Rate of degradation is indicate by hormone half-life (time required to reduce hormone
concentration by half)
, HORMONE CLASSIFICATION (CHP 7)
Hormones can be classified in various ways:
1. According to control of release by the brain
2. According to binding to GCPRs, tyrosine kinases, intracellular receptors, etc.
3. According to structure (peptide, steroid, amino acid-derived)
a. Peptide hormone: Linked amino acids (majority of hormones)
b. Steroid hormone: Derived from cholesterol
c. Amino acid-derived hormone (amine): Modifications of single amino acids
i. Catecholamines or thyroid hormones
Peptide Hormones:
Examples: Insulin, parathyroid hormone, glucagon,
calcitonin, CCK, ghrelin, vasopressin, neuropeptide Y
- Peptide hormones are synthesized all over the body.
Peptide hormones are synthesized in advance and stored in
secretory vesicles.
- The initial product of the ribosome is the preprohormone
- Contains one or more copies of the peptide hormone
- Contains a signal sequence, directing the product
to the ER for processing
- The ER processes the preprohormone to an inactive
prohormone
- Prohormones are packaged in the golgi apparatus with
proteolytic enzymes for activation
- Peptide hormones are stored in vesicles until exocytosed
into ECF
Peptide hormones are water soluble
- Dissolve generally well in the blood and are lipophobic
- Peptide hormones have a generally short half-life
- Lipophobic nature results in primarily binding to surface membrane receptors
- Act via a signal transduction system (e.g. cAMP or tyrosine kinase)
- Signal transduction gene may activate changes to gene activity
Response of cells is generally fast due to the second messenger system modifying existing proteins.
“If a hormone is not a steroid or amine hormone, it must be a peptide hormone.”
, Steroid Hormones:
Examples: Sex hormones (progesterone, estradiol, testosterone), androgens, glucocorticoids,
vitamin D, aldosterone
- Steroid hormones are synthesized only in the adrenal cortex (adrenal glands), gonads, and skin
Steroid hormones are highly lipophilic and cannot be stored in vesicles.
- Cells secreting steroid hormones have high amounts of endoplasmic reticulum
- When a stimulus activates a secreting cell, precursors in the cytoplasm are converted into the
hormone needed
- The lipophilicity of steroid hormones implies that they are synthesized on demand and travel freely
out of their parent cell and into their target cell
The lipophilicity of steroid hormones implies they are not soluble in plasma and must be bound to protein
carrier molecules in the blood.
- Binding to carrier proteins protects the
hormones and promotes a long ½ life.
- Steroids must unbind from their lipophilic
carriers to enter the cell
The ultimate destination of steroid-hormone
complexes is the nucleus.
- Primarily acts with genomic effect, affecting
gene transcription and regulation
- Lack of second messenger system results in
slow responses from the cell
Amine Hormones:
Examples: Melatonin, thyroid hormones (), catecholamines (epinephrine, norepinephrine,
dopamine)
- Hormones derived from tryptophan, tyrosine, or both
- Can be created in the thyroid gland (thyroid hormones),
Tyrosine derived hormones can be divided into catecholamines or thyroid hormones.
- Catecholamines behave more like peptides (extracellular action)
- Thyroid hormones behave more like steroid (intracellular action)
