09-0ct-24

ENDOCRINE SYSTEM - OVERVIEW

Biochemical Endocrinology
The endocrine system is a network
OUTLINE of glands and organs located throughout the
body.
Overview of the Endocrine system " It's similar to the nervous system in that it
Chemistry/Chemical nature of hormones plays a vital role in controlling and regulating
many of the body's functions.
" Regulation of hormone secretion " However, while the nervous system uses nerve
" Endocrine disorders irpulses and neurotransmitters for
communication, the endocrine system uses
Prof. S.A Funtua chemical messengers called hormones.

ENDOCRINE SYSTEM Endocrine system function

BRAIN
The endocrine system is responsible for requlating a range of bodily
functions through the release of hormones
Some examples of bodily functions that are controlled by the
endocrine system include:
metabolism
Adyel dads
growth and development
sexual function and reproduction
heart rate
blood pressure
appetite
ates
" sleeping and waking cycles
" body temperature

Gene expression through Nuclear Retinol

Receptors - RAR, RXR

Insplin Bloodstream

Glucose

Ortoplam
Complex carbohydrotes are broken down into smaller
molecules of GLUCOsE.

Insulin receptor
Nudeus
Glut4

Insulin causes GLUT4 glucose transporter proteins to

allow glucose into cells, where it is used as an energy
rgteneGht 4 Source.
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CHEMICAL NATURE OF HORMONES CHEMICAL NATURE OF HORMONES

" Like all molecules, hormones are synthesized, exist
Nature uses a diverse spectrum of molecules as in a biologically active state for atime, and then
hormones, and knowing the basic structure of a degrade or are destroyed.
hormone imparts considerable knowledge about its Most commonly, hormones are categorized into four
receptor and mechanism of action. structural groups, with members of each group
having many properties in common:
Additionally, the simpler structures can often be " Peptides and proteins
exploited to generate similar molecules - agonists " Steroids
and antagonists - that are therapeutically valuable. " Amino acid derivatives
"Fatty acid derivatives - Eicosanoids

PEPTIDES AND PROTEINS STEROIDS

Peptide hormones are synthesized in endoplasmic reticulum, Steroids are lipids and, more specifically, derivatives of
transferred to the Golgiand packaged into secretory vesicles cholesterol. Examples include the sex steroids such as
for export. testosterone and adrenal steroids such as cortisol.
They can be secreted by one of two pathways: The first and rate-limiting step in the synthesis of all
Regulated secretion: The cellstores hormone in secretory steroid hormones is conversion of cholesterol to
granules and releases them in "bursts" when stimulated. This pregnenolone.
is the most commonly used pathway and allows cells to Newly synthesized steroid hormones are rapidly secreted
secrete a large amount of hormone over a short period of from the cell, with little if any storage. Increases in
time. secretion reflect accelerated rates of synthesis.
Constitutive secretion: The celldoes not store hormone, but Following secretion, all steroids bind to some extent to
secretes it from secretory vesicles as it is synthesized. plasma proteins. This binding is often low affinity and non
" Most peptide hormones circulate unbound to other proteins, specific (e.g. to albumin), but some steroids are transported
but exceptions exist: for example, insulin-like growth factor by specific binding proteins, which clearly affects their half
1binds to one of several binding proteins. In general, the life and rate of elimination.
halflife of circulating peptide hormones is only a few Steroid hormones are typically eliminated by inactivating
minutes. metabolic transformations and excretion in urine or bile.
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AMINO ACID DERIVATIVES FATTY ACID DERIVATIVES - EICOSANOIDS

There are two groups of hormones derived from the amino acid
tyrosine: Thyroid hornonesand Catecholamines Eicosanoids are a large group of molecules derived from
Thyroid hormones are basically a "double" tyrosine with the critical polyunsaturated fatty acids. The principal groups of
incorporation of 3 or 4 iodine atoms.
Catecholamines include epinephrine and norepinephrine, which are hormones of this class are prostaglandins, prostacyclins,
used as both hormones and neurotransmitters. Catecholamines, are leukctrienes and thromboxanes.
rapidly degraded, with circulating half-lives of only a few minutes. Arachadonic acid is the most abundant precursor for
HO, HÌ H these hormones. Stores of arachadonic acid are present in
membrane lipids and released through the action of
various lipases, The specific eicosanoids synthesized bya
Throsine Epineplrine
cell are dictated by the battery of processing enzymes
Tyrosine expressed in that cell.
Twoother aminoacids are used for synthesis of hormones: These hormones are rapidly inactivated by being
Tryptophan is the precursor to serotonin and the pineal hormone metabolized, and are typically active for only a few
melatonin seco.ds.
Histidine is converted to histamine

REGULATION OF HORMONAL SECRETION.

Regulation of Hormonal Secretion Humoral Stimuli

The term "humoral" is derived from the term humor,"
which refers to bodily fluids such as blood.
There are three mechanisms by which endocrine glands are A humoral stimuli refers to the control of hormone release
stimulated to synthesize and release hormones:
1. Humoral stimuli, in response to changes in extracellular fluids such as blood
or the ion concentration in the blood.
2. Hormonal stimuli
Fer,example, a rise in blood glucose levels triggers the
3. Neural stimuli.
pancreatic release of insulin.
" Insulin causes blood glucose levels to drop, which signals
the pancreas to stop producing insulin in a negative
feedback loop.

REGULATION OF HORMONAL SECRETION.

REGULATION OF HORMONAL SECRETION.
Hormonal stimuli
. This refers to the release of a hormone in response to another Neural Stimui
hormone. :

. Anumber of endocrine glands release hormones when " In some cases, the nervous system directly stimulates
stimulated by hormones released by other endocrine glands. endocrine glands to release hormones, which is referred to
" For example, the hypothalamus produces hormones that as neural stimuli.
stimulate the anterior portion of the pituitary gland. " Recall that in a short-term stress response, the hormones
The anterior pituitary in turn releases hormones that regulate epinephrine and norepinephrine are important for providing the
hormone production by other endocrine glands. bursts of energy required for the body to respond. Here,
. The anterior pituitary releases the thyroid-stimulating hormone, neuronal signaling from the sympathetic nervous system
which then stimulates the thyroid gland to produce the Circtiy stimulates the adrenal medulla to release the hormones
hormones T; and T epinephrine and norepinephrine in response to stress.
. As blood concentrations of T, and T, rise, they inhibit both the
pituitary and the hypothalamus in a negative feedback loop.

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Feedback Regulation,
Regulationof Endoerine Activity Negative and Positive Feedbaek Regulation

The regulation of endoine activity is contolled by specitie The net result of any version of negative feedback is that
nehanisms of varying levels of complexity These echanisms wl,n hormone levels are judged to be adequate or
atimulale o nbbhonone synthesis and secretion and inuude high, further secretion of the hormone ís inhibited.
LFeedback, When hornone levels are judyed to be inadequate or
2 Nervous system control low, secretionof the hormone is stimulated.
J Physiolopic thythms
Positive feedback is uncommon, With positive fecdback,
Some feature of hornone action causes more secretion
f the hofmone

HEAaVE PEEORACH POSTVE EEOSACR

Nervous System Control
" Inaddition to chemical regulation, some endocrine glands are
Hyaorhalen Iypothlau

directly affected by the activity of the nervous system.

AMeter ptuy
" Pain, emotion, sexual excitement, and stress can stimulate the
nervous system to modulate hormone secretion.
" Neural involvement is initiated by the central nervous system
(CNS) and implemented by the sympathetic nervous system
(SNS).
For example, stress is sensed or perceived by the CNS with
subsequent stimulation of the SNS.
e.oalenee) (eg.uatak) " The SNS secretes catecholarnines that increase heart rate and
blood pressure to deal with stress more effectively.
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RHYTHMS. Mechanism of Hormone Action

" A
common physiologic rhythm is the circadian rhythm. This is an
endogenous 24-hour rhythm that can be driven and altered by sleep Generally, Hormones are target specific and bindto
wake or dark-light 24-hour (diurnal) cycles. tle specific receptor. On the basis of binding of
" Hormone levels fluctuate predictably during these cycles. For hormone on their specific receptor, the mechanism of
example, cortisol rises early in the day, declines toward evening, and hormonal action is categorized into two group.
rises again toward the end of sleep to peak by morning. GH,
thyroid-stimulating hormone (TSH), and prolactin secretions peak
Fixed membrane receptor mechanism
during sleep.
" Mobile receptor mechanism
The menstrual cycle is an example of a body rhythm that is longer
than 24 hours (ultradian). These rhythms nmust be considered when
interpreting laboratory results for hormone levels.
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Fixed membrane receptor mechanism

Fixed membrane receptor mechanism
protein or amines hormones such as Growth hormone, ADH,
oxytocin, Insulin, Adrenaline, FSH, TSH etc shows this
mechanism of action.
These hormones are water soluble and cannot passes through
the lipid membrane and they have their target receptor on the
cellmembrane.
Binding of hormone on specific receptor on target cell activates
the enzyme Adenylcyclase in the cell membrane and causes
production of cyclic AMP (CAMP).
CAMP act as secondary messenger. It diffuse through the cell
membrane and activates (Protein Kinase) various enzymatic
reaction to cause biochemical changes.
After the target cell responded to the changes, cAMP is
deactivated by a group of enzyme Phosphodiesterase

Mobile receptor mechanism

Lipid soluble hommones such as steroid homones and Fatty acids Mobile receptor mechanism
hormones can easily passes through the plasma menmbrane.
They have their receptor inside the cell, freely floating in the Uieine cell
cytoplasm. membrane
Binding of homone to the specific receptor activates the enzymatic Hormone
(Cg, ocstrogon)
activity of the cell for biochemical changes.
Some hormones (testosterone, progesterone, estrogen, cortisol,
thyroxine) have their receptor localized inside the nucleus, the Nucleus
hormone-receptor complex are carried inside the nucleus. Gonom
The hormone-receptor complex initiate transcription of the DNA to
Receptor-hormone mRNA
form specific mRNA. complex
mRNA initiate protein synthesis in the cytoplasm. The protein Proteins
(enzyme) causes biochemical changes in the cell.
K Physiological responses
(Tissue growth and
differentiation)

Endocrine Disorders Common Types of Endocrine Disorders

Some of the most common types of endocrine disorders
" There are a wide variety of endocrine disorders, all of which intude:
disrupt the production of hormones in the body. a. Disorders resulting from a problem in the gland itself,
An endocrine disorder results from the improper function of the b. Or because the hypothalamic-pituitary axis (interplay of
endocrine system, which includes hormonal signals between the hypothalamus, and the
-the glands that secrete hormones, pituitary gland) provides too much or too litle stimulation.
-the receptors that respond to hormones and c. Depending on the type of cell they originate in, tumors
-the organs that are directly impacted by hormones. can produce excess hormones or destroy normal glandular
tissue, decreasing hormone production.
" At any one of these points, dysfunction can occur and cause
d. Sometimes the body's immune system attacks an
wide-ranging effects on the body. endocrine gland (an autoimmune disorder), decreasing
homone production.
 Examples of Endocrine Disorders
Hyperthyroidism - thyroid gland produces too many hormones
Hypothyroidism - thyroid does not produce enough hormones
Cushing disease - Excess cortisol
Addison disease - Adrenal glands doesn't produce enough
cortisol and aldosterone
Acromegaly - Excess growth hormone
Diabetes - Insulin
Disorders of puberty andreproductive function