L1-2..INTRODUCTION to ENDOCRINOLOGY.pptx

INTRODUCTION TO
ENDOCRINOLOGY
ASSISTANT PROFESSOR DR BILAL NATIQ NUAMAN
CONSULTANT ENDOCRINOLOGIST
Al-Iraqia Medical College
2025

Endocrinology concerns the synthesis, secretion
and action of hormones. These are chemical
messengers released from endocrine glands
that coordinate the activities of many different
cells. Endocrine diseases can therefore affect
multiple organs and systems.
 The term endocrine was coined by Starling to
contrast the actions of hormones secreted
internally (endocrine) with those secreted
externally (exocrine) or into a lumen, such as
the gastrointestinal tract.

Unlike many other specialties in medicine, it is
not possible to define endocrinology strictly
along anatomic lines. The classic endocrine
glands—pituitary, thyroid, parathyroid,
pancreatic islets, adrenals, and gonads—
communicate broadly with other organs
through the nervous system, hormones,
cytokines, and growth factors.
 A hormone is a molecule— small or large,
protein or lipid— secreted in a regulated
fashion from one organ and acting on another.

 Hormones can be divided into ve major types:
(1) amino acid derivatives such as dopamine,
catecholamine, and thyroid hormone;
(2) small neuropeptides such as gonadotropin-
releasing hormone (GnRH), thyrotropin-releasing
hormone (TRH), somatostatin, and vasopressin;
(3) large proteins such as insulin, luteinizing hormone
(LH), and parathyroid hormone (PTH);
(4) steroid hormones such as cortisol and estrogen that
are synthesized from cholesterol-based precursors;
and
(5) vitamin derivatives such as retinoids (vitamin A)
and vitamin D.

 The physiologic functions of hormones can be
divided into :
(1) growth, differentiation, development
(2) maintenance of homeostasis, Metabolism
(3) Reproduction.

 MAINTENANCE OF HOMEOSTASIS
Although virtually all hormones affect homeostasis,
the most important among them are the following:
1. Thyroid hormone—controls about 25% o basal
metabolism in most tissues
2. Cortisol—exerts a permissive action or many
hormones in addition to its own direct effects
3. PTH—regulates calcium and phosphorus levels
4. Vasopressin—regulates serum osmolality by
controlling renal free-water clearance
5. Mineralocorticoids—control vascular volume and
serum electrolyte (Na+, K+) concentrations
6. Insulin—maintains euglycemia in the fed and fasted
states

 There are several organs whose primary
functions are non-endocrine but
that also possess endocrine functions. These
include the heart, kidneys, intestines, thymus,
gonads, and adipose tissue.
 The heart possesses endocrine cells in the
walls of the atria that are specialized cardiac
muscle cells. These cells release the
hormone atrial natriuretic peptide (ANP) in
response to increased blood volume.

 High blood volume causes the cells to be
stretched, resulting in hormone release. ANP
acts on the kidneys to reduce the
reabsorption of Na+
, causing Na+
and water to
be excreted in the urine. ANP also reduces the
amounts of renin released by the kidneys and
aldosterone released by the adrenal cortex,
further preventing the retention of water. In
this way, ANP causes a reduction in blood
volume and blood pressure, and reduces the
concentration of Na+
in the blood.

 The gastrointestinal tract produces several
hormones that aid in digestion. The endocrine
cells are located in the mucosa of the GI tract
throughout the stomach and small intestine.
Some of the hormones produced include
gastrin, secretin, and cholecystokinin, which
are secreted in the presence of food, and some
of which act on other organs such as the
pancreas, gallbladder, and liver. They trigger
the release of gastric juices, which help to
break down and digest food in the GI tract.

The kidneys themselves also possess
endocrine function. Renin is released
in response to decreased blood
volume or pressure and is part of the
renin-angiotensin-aldosterone
system that leads to the release of
aldosterone. Aldosterone then causes
the retention of Na+
and water,
raising blood volume. The kidneys
also release calcitriol, which aids in
the absorption of Ca2+
and phosphate
ions. Erythropoietin (EPO) is a

 EPO is released in response to low oxygen
levels. Because red blood cells are oxygen
carriers, increased production results in
greater oxygen delivery throughout the body.
EPO has been used by athletes to improve
performance, as greater oxygen delivery to
muscle cells allows for greater endurance.
Because red blood cells increase the viscosity
of blood, artificially high levels of EPO can
cause severe health risks.

 The thymus is found behind the sternum; it is most
prominent in infants, becoming smaller in size
through adulthood. The thymus produces
hormones referred to as thymosins, which
contribute to the development of the immune
response.
 Adipose tissue is a connective tissue found
throughout the body. It produces the hormone
Leptin in response to food intake. Leptin increases
the activity of anorexigenic neurons and decreases
that of orexigenic neurons, producing a feeling of
satiety after eating, thus affecting appetite and
reducing the urge for further eating. Leptin is also
associated with reproduction. It must be present
for GnRH and gonadotropin synthesis to occur.
Extremely thin females may enter puberty late.

 Feedback control, both negative and positive,
is a fundamental feature of endocrine systems.
Each o the major hypothalamic-pituitary
hormone axes is governed by negative
feedback, a process that maintains hormone
levels within a relatively narrow range

L1-2..INTRODUCTION to ENDOCRINOLOGY.pptx

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