Problem 1. Your body’s chemical
messengers…
Learning goals:
1. What is a hormone? Steroids, peptides, amino acid derivatives fast, slow, secretion, membrane
transport etc.
2. What type of hormone is cortisol? (HPA axis)
- Explain the feedback loop
- Positive vs. negative
3. Cortisol and the CAR
4. The relation between chocolate and cortisol / mood / stress
Sources:
,1. What is a hormone? Steroids, peptides, amino acid derivatives
fast, slow, secretion, membrane transport, etc.
What is endocrinology?
Endocrinology is the study of hormones and their actions.
Hormones are chemical messengers, released into the blood, that act on receptors to cause a
change in the target cell.
The term ‘endocrine’ comes from the fact that the glands that release hormones are ductless.
Some organs are classical endocrine glands, meaning that their only function is to synthesize and
release hormones into the bloodstream. The thyroid gland is an example.
Other organs, such as the pancreas, have both endocrine functions and other functions. The
pancreas releases hormones directly into the blood and releases other secretions, called
exocrine secretions, into a duct.
The major or classical endocrine glands of the body and the hormones they release:
In addition, the gut, heart and skin have also been shown to produce hormones. Such tissues
form the diffuse endocrine system, which is located throughout the body. They secrete
hormones but do not form discrete endocrine glands.
Endocrine disorders are very common. An example is type 2 diabetes, which is a disease of
insulin resistance.
,The actions of hormones
The two major regulatory systems in the body are the neural system and the endocrine system.
Neural regulation is very rapid, while endocrine control is slower and acts over a longer period of
time. This is because the neural system delivers its chemical messenger directly to the surface of
its target cell, whereas the endocrine system puts its hormones into the blood in which they
travel to their target cells. The endocrine system can thereby reach a wider range of targets than
the neural system.
Hormones control regulatory systems in the body, including homeostasis (regulation of any of
the large physiological systems in the body, such as body temperature), metabolism, and
reproduction. Hormones also keep blood levels of glucose and different ions within set limits.
There is also a combination between endocrine and neural regulation, called neuroendocrine
regulation. An overview is shown below.
Type of regulation Mechanism
Endocrine regulation An endocrine gland releases a hormone into the
bloodstream where it travels to its target cells
Neural regulation In response to an action potential, a
neurotransmitter is released from a nerve
ending into the synaptic cleft, directly onto the
surface of the target cell
Neuroendocrine regulation In response to an action potential, a hormone is
secreted by a nerve cell into the bloodstream,
where it travels to its target cells
Synthesis and secretion of different types of hormones
There are three major basic types of hormones:
1. Peptide hormones
o Most numerous
o Made of chains of amino acids
o Can be small, e.g. thyrotropin releasing
hormone (TRH) or long, e.g. thyroid
stimulating hormone (TSH)
o Usually preformed and stored in granules
within the endocrine cell
o Released in response to the appropriate
signal
o Produced at the rough endoplasmic
reticulum
o After production, they often undergo
post-translational processing in the Golgi
apparatus and the secretory granules
before secretion, such as linking of
peptide chains by disulfide bridges, and glycosylation (addition of carbohydrate
residues).
o The secretory granules contain the finished hormone ready for secretion.
o The entire contents of the secretory granules are released via exocytosis. This is
triggered by an increase in Ca2+ levels in the cell, or depolarization of the cell.
, 2. Steroids
o All made from cholesterol
o Have a common core structure, and
small differences in this core
structure cause the relatively large
differences in their biological
effects
o Formed by metabolism of
cholesterol by enzymes in the
steroid-secreting cell, which are
located within the mitochondria or
the smooth endoplasmic
reticulum.
o Steroid-secreting cells also contain
significant lipid droplets, which
contain cholesterol esters. These cells namely store the precursor to hormone system
instead of the finished product. This is because esterified cholesterol is more easily
stored than the lipid-soluble steroid hormones.
o Once made, steroid hormones diffuse out of the cell without a specific secretory
mechanism. This is because they are small and lipophilic and can therefore simply diffuse
across the plasma membrane and out of the cell down a concentration gradient.
3. Modified amino acids
o Residues of the amino acid tyrosine can be iodinated to produce thyroid hormones
(thyroxine), or hydroxylated, ultimately producing the catecholamines: dopamine,
adrenaline, and noradrenaline.
o As with steroid hormones, the thyroid gland maintains a store of precursor, from which
thyroid hormones may be readily released.
The differences in chemical structure of hormones have implications for the way in which they
are stored, released, transported in blood, their mechanism of action, and their route of
administration with therapeutic use.
Those hormones that are water-soluble dissolve readily in plasma but cannot enter the target
cell (they are hydrophilic while the cell membranes of cells are lipophilic) and thus interact with
cell surface receptors. This is the case for peptide hormones and catecholamines. They are
synthesized and then stored in granules until they are released when needed.
Steroid and thyroid hormones are lipophilic and thus dissolve poorly in plasma. They are mostly
transported in blood bound to carrier proteins but readily enter cells to interact with
cytoplasmic or nuclear receptors.
With therapeutic use, steroid hormones and thyroid hormones are orally active, whereas most
peptide hormones (e.g. insulin) must be injected to avoid inactivation by digestive enzymes.
Lipophilic / Location of Carrier Active with oral Storage as
hydrophilic receptors protein administration?
Peptides Hydrophilic Cell membrane No Not usually Hormone
Steroids Lipophilic Cytoplasm/nucleus Yes Mostly Precursor
Thyroid Lipophilic Nucleus Yes Yes Precursor
hormone
Catecholamines Hydrophilic Cell membrane No No Hormone
messengers…
Learning goals:
1. What is a hormone? Steroids, peptides, amino acid derivatives fast, slow, secretion, membrane
transport etc.
2. What type of hormone is cortisol? (HPA axis)
- Explain the feedback loop
- Positive vs. negative
3. Cortisol and the CAR
4. The relation between chocolate and cortisol / mood / stress
Sources:
,1. What is a hormone? Steroids, peptides, amino acid derivatives
fast, slow, secretion, membrane transport, etc.
What is endocrinology?
Endocrinology is the study of hormones and their actions.
Hormones are chemical messengers, released into the blood, that act on receptors to cause a
change in the target cell.
The term ‘endocrine’ comes from the fact that the glands that release hormones are ductless.
Some organs are classical endocrine glands, meaning that their only function is to synthesize and
release hormones into the bloodstream. The thyroid gland is an example.
Other organs, such as the pancreas, have both endocrine functions and other functions. The
pancreas releases hormones directly into the blood and releases other secretions, called
exocrine secretions, into a duct.
The major or classical endocrine glands of the body and the hormones they release:
In addition, the gut, heart and skin have also been shown to produce hormones. Such tissues
form the diffuse endocrine system, which is located throughout the body. They secrete
hormones but do not form discrete endocrine glands.
Endocrine disorders are very common. An example is type 2 diabetes, which is a disease of
insulin resistance.
,The actions of hormones
The two major regulatory systems in the body are the neural system and the endocrine system.
Neural regulation is very rapid, while endocrine control is slower and acts over a longer period of
time. This is because the neural system delivers its chemical messenger directly to the surface of
its target cell, whereas the endocrine system puts its hormones into the blood in which they
travel to their target cells. The endocrine system can thereby reach a wider range of targets than
the neural system.
Hormones control regulatory systems in the body, including homeostasis (regulation of any of
the large physiological systems in the body, such as body temperature), metabolism, and
reproduction. Hormones also keep blood levels of glucose and different ions within set limits.
There is also a combination between endocrine and neural regulation, called neuroendocrine
regulation. An overview is shown below.
Type of regulation Mechanism
Endocrine regulation An endocrine gland releases a hormone into the
bloodstream where it travels to its target cells
Neural regulation In response to an action potential, a
neurotransmitter is released from a nerve
ending into the synaptic cleft, directly onto the
surface of the target cell
Neuroendocrine regulation In response to an action potential, a hormone is
secreted by a nerve cell into the bloodstream,
where it travels to its target cells
Synthesis and secretion of different types of hormones
There are three major basic types of hormones:
1. Peptide hormones
o Most numerous
o Made of chains of amino acids
o Can be small, e.g. thyrotropin releasing
hormone (TRH) or long, e.g. thyroid
stimulating hormone (TSH)
o Usually preformed and stored in granules
within the endocrine cell
o Released in response to the appropriate
signal
o Produced at the rough endoplasmic
reticulum
o After production, they often undergo
post-translational processing in the Golgi
apparatus and the secretory granules
before secretion, such as linking of
peptide chains by disulfide bridges, and glycosylation (addition of carbohydrate
residues).
o The secretory granules contain the finished hormone ready for secretion.
o The entire contents of the secretory granules are released via exocytosis. This is
triggered by an increase in Ca2+ levels in the cell, or depolarization of the cell.
, 2. Steroids
o All made from cholesterol
o Have a common core structure, and
small differences in this core
structure cause the relatively large
differences in their biological
effects
o Formed by metabolism of
cholesterol by enzymes in the
steroid-secreting cell, which are
located within the mitochondria or
the smooth endoplasmic
reticulum.
o Steroid-secreting cells also contain
significant lipid droplets, which
contain cholesterol esters. These cells namely store the precursor to hormone system
instead of the finished product. This is because esterified cholesterol is more easily
stored than the lipid-soluble steroid hormones.
o Once made, steroid hormones diffuse out of the cell without a specific secretory
mechanism. This is because they are small and lipophilic and can therefore simply diffuse
across the plasma membrane and out of the cell down a concentration gradient.
3. Modified amino acids
o Residues of the amino acid tyrosine can be iodinated to produce thyroid hormones
(thyroxine), or hydroxylated, ultimately producing the catecholamines: dopamine,
adrenaline, and noradrenaline.
o As with steroid hormones, the thyroid gland maintains a store of precursor, from which
thyroid hormones may be readily released.
The differences in chemical structure of hormones have implications for the way in which they
are stored, released, transported in blood, their mechanism of action, and their route of
administration with therapeutic use.
Those hormones that are water-soluble dissolve readily in plasma but cannot enter the target
cell (they are hydrophilic while the cell membranes of cells are lipophilic) and thus interact with
cell surface receptors. This is the case for peptide hormones and catecholamines. They are
synthesized and then stored in granules until they are released when needed.
Steroid and thyroid hormones are lipophilic and thus dissolve poorly in plasma. They are mostly
transported in blood bound to carrier proteins but readily enter cells to interact with
cytoplasmic or nuclear receptors.
With therapeutic use, steroid hormones and thyroid hormones are orally active, whereas most
peptide hormones (e.g. insulin) must be injected to avoid inactivation by digestive enzymes.
Lipophilic / Location of Carrier Active with oral Storage as
hydrophilic receptors protein administration?
Peptides Hydrophilic Cell membrane No Not usually Hormone
Steroids Lipophilic Cytoplasm/nucleus Yes Mostly Precursor
Thyroid Lipophilic Nucleus Yes Yes Precursor
hormone
Catecholamines Hydrophilic Cell membrane No No Hormone
