Endocrine System Guide: Hormones, Glands & Their Functions

The Endocrine System
 The endocrine
system is a
network of glands
in body that
produce and
secrete
hormones that
help cells talk to
each other.

Endocrine System Functions
 Endocrine glands release hormones into the
bloodstream. This lets the hormones travel to cells in
other parts of the body & control mood, growth and
development, the way our organs work, metabolism ,
and reproduction.
 The endocrine system regulates how much of each
hormone is released.
 This can depend on levels of hormones already in the
blood, or on levels of other substances in the blood, like
calcium.
 Many things affect hormone levels, such as stress,
infection, and changes in the balance of fluid and
minerals in blood.

What Is a Gland?
 A gland is an organ that makes and puts out
hormones that do a specific job in body. Endocrine
glands release the substances they make into
bloodstream.

Endocrine Gland
 The endocrine system consists of the following
glands:
 the pituitary gland
 the pineal gland
 the thyroid gland
 the parathyroid glands
 the adrenal glands
 the pancreas
 the thymus
 the testes (male)
 the ovaries (female)

Endocrine Gland
 Pituitary: Considered the "master control
gland," the pituitary gland controls other
glands and makes the hormones that
trigger growth.
 Parathyroid: This gland controls the amount
of calcium in the body.
 Pancreas: This gland produces the insulin
that helps control blood sugar levels.
 Thyroid: The thyroid produces hormones
associated with calorie burning and heart
rate.

Endocrine Gland
 The thymus gland: located behind sternum &
between lungs, is only active until puberty.
After puberty, it starts to slowly shrink &
become replaced by fat.
 Adrenal: Adrenal glands produce the hormones
that control sex drive and cortisol, the stress
hormone.
 Pineal: it produces melatonin which affect
sleep.
 Ovaries: Only in women, ovaries secrete
estrogen, testosterone and progesterone,
female sex hormones.

Hormone Regulation
Endocrine system hormones are regulated in
several ways.
 They can be regulated by other hormones,
by glands and organs, by peripheral nervous
system neurons, and by negative feedback
mechanisms.
 During hormone regulation, hormones are
released, either directly by an endocrine
gland or indirectly through the action of the
hypothalamus of the brain,
 which stimulates other endocrine glands to
release hormones in order to maintain
homeostasis.
 In negative feedback systems, a stimulus

Hormone Regulation
 it sends a signal that stops further release of
substance. In this way, concentration of
hormones in blood is maintained within a narrow
range.
 For example, amount of glucose in blood controls
secretion of insulin & glucagons via negative
feedback.
 The hormones activate target cells, which initiate
physiological changes that adjust body
conditions.
 When normal conditions have been recovered,
corrective action- production of hormones – is
discontinued.
 Thus, in negative feedback, when original
(abnormal) condition has been repaired, or

PITUITARY GLAND
Pituitary gland or hypophysis is a small endocrine gland
with a diameter of 1 cm and weight of 0.5 to 1 g. It is
situated in a depression called ‘sella turcica’, present in
the sphenoid bone at the base of skull. Pituitary gland is
divided into two divisions:
1. Anterior pituitary or adenohypophysis
2. Posterior pituitary or neurohypophysis.

HORMONES SECRETED BY
ANTERIOR PITUITARY
Six hormones are secreted by the anterior
pituitary:
 1. Growth hormone (GH) or somatotropic hormone
(STH)
 2. Thyroid-stimulating hormone (TSH) or thyrotropic
hormone
 3. Adrenocorticotropic hormone (ACTH)
 4. Follicle-stimulating hormone (FSH)
 5. Luteinizing hormone (LH) in females or interstitial-
cell-stimulating hormone (ICSH) in males
 6. Prolactin.

ANTERIOR PITUITARY
Growth Hormone
Actions of Growth Hormone
 GH is responsible for the general growth of the
body. Hypersecretion of GH causes enormous
growth of the body, leading to gigantism.
Deficiency of GH in children causes stunted
growth, leading to dwarfism.
 GH is responsible for the growth of almost all
tissues of body, which are capable of growing. It
increases size and number of cells by mitotic
division. GH also causes specific differentiation of
certain types of cells like bone cells and muscle
cells.

ANTERIOR PITUITARY
Regulation of GH Secretion
Hypothalamus regulates GH secretion via three
hormones:
1. Growth hormone-releasing hormone (GHRH): It
increases the GH secretion by stimulating the
somatotropes of anterior pituitary
2. Growth hormone-releasing polypeptide (GHRP): It
increases the release of GHRH from hypothalamus
and GH from pituitary
3. Growth hormone-inhibitory hormone (GHIH) or
somatostatin: It decreases the GH secretion.
Somatostatin is also secreted by delta cells of islets

ANTERIOR PITUITARY
Feedback control
 Hypothalamus releases GHRH and GHRP, which in
turn promote release of GH from anterior pituitary.
 It also activates liver cell to secrete somatomedin C .
 Now, somatomedin C increases release of GHIH from
hypothalamus.
 GHIH nhibits release of GH from pituitary.
 Somatomedin also inhibits release of GHRP from
hypothalamus.
 It acts on pituitary directly and inhibits secretion of GH.
 GH inhibits its own secretion by stimulating the release of
GHIH from hypothalamus.

ANTERIOR PITUITARY

ANTERIOR PITUITARY
Prolactin
 It is also known as lactogenic hormone is
secreated during pregnancy to prepare breast
for lactation after child birth.
 The blood level of prolactin is stimulated by
prolactin releasing hormone (PRH) released
from hypothalamus and it is lowered by prolactin
inhibiting hormone (PIH, dopamine) & by an
increased blood level of prolactin.
 Immediately after birth, suckling stimulates
prolactin secretion and lactation.

ANTERIOR PITUITARY
Gonadotropins
 Just before puberty two gonadotrophins (sex
hormones) are secreted in gradually increasing
amounts by the anterior pituitary in response to
luteinising hormone releasing hormone (LHRH),
also known as gonadotrophin releasing hormone
(GnRH). Rising levels of these hormones at puberty
promotes mature functioning of the reproductive
organs. In both males and females the hormones
responsible are:
• follicle stimulating hormone (FSH)
• luteinising hormone (LH).

ANTERIOR PITUITARY
Follicle-stimulating Hormone (FSH)
Actions of FSH
 In males, FSH acts along with testosterone and
accelerates the process of
spermeogenesis(maturation of the spermatids
into sperm cells.)
 In females FSH:
1. Causes the development of graafian follicle
2. causes secretion of estrogen
3. Promotes conversion of androgens into
estrogen

ANTERIOR PITUITARY
Luteinizing Hormone (LH) ori nterstitial cell-
stimulating hormone (ICSH)
In Males, LH:
it stimulates the interstitial cells of Leydig in testes. This
hormone is essential for the secretion of testosterone
from Leydig cells
In females, LH:
 1. Causes maturation of vesicular follicle into graafian
follicle along with follicle-stimulating hormone
 2. Induces synthesis of androgens
 3. Is responsible for ovulation
 4. Is necessary for the formation of corpus luteum
 5. Activates the secretory functions of corpus luteum.

ANTERIOR PITUITARY
Adrenocorticotropic Hormone (ACTH)
 ACTH is necessary for the structural integrity and the
secretory activity of adrenal cortex. It has other
functions also.
 Corticotrophin releasing hormone (CRH) from
hypothalamus promotes synthesis and release of ACTH
by anterior pituitary.
 This increases concentration of cholesterol & steroids
within adrenal cortex & output of steroid hormones,
especially cortisol.
 ACTH levels are highest at 8 a.m. & fall to their lowest
about midnight,This circadian rhythm is maintained
throughout life.

ANTERIOR PITUITARY
Thyroid-stimulating Hormone (TSH)
 TSH is necessary for the growth and secretory
activity of the thyroid gland. It has many actions on
the thyroid gland.
 The release of this hormone is stimulated by
thyrotrophin releasing hormone (TRH) from the
hypothalamus.
 It stimulates growth and activity of thyroid gland,
which secretes hormones thyroxine (T4) and tri-
iodothyronine (T3)
 Release is lowest in early evening and highest
during night.

HORMONES OF POSTERIOR
PITUITARY
Antidiuretic hormone (ADH, vasopressin)
• ADH is also called arginine vasopressin. It’s a hormone
made by the hypothalamus in the brain and stored in the
posterior pituitary gland.
• It tells your kidneys how much water to conserve.
• ADH constantly regulates and balances the amount of
water in your blood.
• Higher water concentration increases the volume and
pressure of your blood.
• Osmotic sensors and baroreceptors work with ADH to
maintain water metabolism.

PITUITARY

PITUITARY
Oxytocin
Source of Secretion
 Oxytocin is secreted mainly by paraventricular
nucleus of hypothalamus.
 It is also secreted by supraoptic nucleus in small
quantity and it is transported from hypothalamus
to posterior pituitary through the nerve fibers of
hypothalamo-hypophyseal tract.
 In the posterior pituitary, the oxytocin is stored in
the nerve endings of hypothalamo-hypophyseal
tract.
 When suitable stimuli reach the posterior pituitary
from hypothalamus, oxytocin is released into the
blood.
 Oxytocin is secreted in both males and female

PITUITARY
Actions in Females
 In females, oxytocin acts on mammary glands and
uterus.
 Action of oxytocin on mammary glands Oxytocin
causes ejection of milk from the mammary glands.
 Ducts of the mammary glands are lined by myo-
epithelial cells. Oxytocin causes contraction of the
myo-epithelial cells and flow of milk from alveoli of
mammary glands to the exterior through duct system
and nipple.
 The process by which the milk is ejected from alveoli
of mammary glands is called milk ejection reflex or
milk let down reflex.

PITUITARY
Milk ejection reflex
 Plenty of touch receptors are present on the
mammary glands, particularly around the nipple.
 When the infant suckles mother nipple, the
touch receptors are stimulated.
 The impulses discharged from touch receptors
are carried by the somatic afferent nerve fibers
to paraventricular and supraoptic nuclei of
hypothalamus.
 Now hypothalamus, in turn sends impulses to
the posterior pituitary through hypothalamo-
hypophyseal tract.
 Afferent impulses cause release of oxytocin into
the blood.

PITUITARY
 When the hormone reaches the mammary gland,
it causes contraction of myoepithelial cells,
resulting in ejection of milk from mammary glands
 As this reflex is initiated by the nervous factors
 and completed by the hormonal action, it is called
a neuroendocrine reflex.
 During this reflex, large amount of oxytocin is
released by positive feedback mechanism.
 Action on uterus
 Oxytocin acts on pregnant uterus and also non-
pregnant uterus.

PITUITARY
Action in Males
 In males, the release of oxytocin increases during
ejaculation.
 It facilitates release of sperm into urethra by
causing contraction of smooth muscle fibers in
reproductive tract, particularly vas deferens.
Mode of Action of Oxytocin
 Oxytocin acts on mammary glands and uterus by
activating G-protein coupled oxytocin receptor.

THYROID GLAND
• The thyroid gland is situated in the neck in front
of the larynx and trachea at the level of the 5th,
6th and 7th cervical and 1st thoracic vertebrae.
• It is a highly vascular gland that weighs about
25 g and is surrounded by a fibrous capsule.
• It resembles a butterfly in shape, consisting of
two lobes, one on either side of the thyroid
cartilage and upper cartilaginous rings of the
trachea.
• The lobes are joined by a narrow isthmus, lying
in front of the trachea.The lobes are roughly
cone shaped, about 5 cm long and 3 cm wide
• The gland is composed of largely spherical

• These secrete and store colloid, a thick sticky
protein material. Between the follicles are other
cells found singly or in small groups:
• parafollicular cells, also called C-cells, which
secrete the hormone calcitonin.
THYROID GLAND

• Thyroxine and tri-iodothyronine
• Iodine is essential for the formation of the thyroid
hormones, thyroxine (T4) and tri-iodothyronine (T3),
so numbered as these molecules contain four and
three atoms of the element iodine respectively.
• The thyroid gland selectively takes up iodine from
the blood, a process called iodine trapping.
• Thyroid hormones are synthesised as thyroglobulin,
the major constituent of colloid.
• The release of T3 and T4 into the blood is stimulated
by thyroid stimulating hormone (TSH) from the
anterior pituitary.
THYROID GLAND

Secretion of TSH
• It is stimulated by thyrotrophin releasing hormone
(TRH) from the hypothalamus and secretion of TRH
is stimulated by exercise, stress, malnutrition, low
plasma glucose levels and sleep.
• TSH secretion depends on the plasma levels of T3
and T4 because it is these hormones that control the
sensitivity of the anterior pituitary to TRH.
• Through the negative feedback mechanism
increased levels of T3 and T4 decrease TSH
secretion and vice versa.
THYROID GLAND

• Thyroid hormones enter cell nucleus and
regulate gene expression, i.e. they increase or
decrease protein synthesis.
• They enhance effects of adrenaline and
noradrenaline (norepinephrine).
• T3 and T4 affect most cells of body by
increasing basal metabolic rate & heat
production regulating metabolism of
carbohydrates, proteins and fats.
• T3 and T4 are essential for normal growth &
development, especially of skeleton & nervous
THYROID GLAND

• Calcitonin
• This hormone is secreted
by the parafollicular or C-
cells in the thyroid
gland.Calcitonin lowers
raised blood calcium
(Ca2+) levels. It does this
by acting on:
• bone cells promoting their
storage of calcium
• kidney tubules inhibiting
the reabsorption of
THYROID GLAND

• Human beings have four
parathyroid glands,
which are situated on
posterior surface of
upper & lower poles of
thyroid gland.
• These are very small in
size, measuring about 6
mm long, 3 mm wide & 2
mm thick, with dark
brown color.
• Each parathyroid gland is
made up of chief cells .
Chief cells secrete
parathormone.
PARATHYROID GLAND

• Parathormone secreted by parathyroid gland is
essential for the maintenance of blood calcium level
within a very narrow critical level.
• The main function of PTH is to increase blood
calcium levels.This is needed for:
• muscle contraction
• transmission of nerve impulses
• blood clotting
PARATHYROID GLAND

• REGULATION OF PARATHORMONE SECRETION
• Blood level of calcium is the main factor regulating
the secretion of PTH. Blood phosphate level also
regulates PTH secretion.
• 1.Blood Level of Calcium
• 2.Blood Level of Phosphate
• This is achieved by increasing the calcium absorp-
tion from the small intestine and reabsorption from
the renal tubules. If these sources provide
inadequate sup-plies then PTH stimulates
osteoclasts (bone-destroying cells) and calcium is
released from bones into the blood.
PARATHYROID GLAND

Blood Level of Calcium
• Parathormone secretion is inversely proportional to
blood calcium level. Increase in blood calcium level
decreases PTH secretion.
• Conditions when PTH secretion decreases are:
• 1. Excess quantities of calcium in the diet
• 2. Increased vitamin D in the diet
• 3. Increased resorption of calcium from the bones,
• caused by some other factors such as bone
diseases.On the other hand, decrease in calcium ion
concentration of blood increases PTH secretion, as
in the case of rickets, pregnancy and in lactation.
PARATHYROID GLAND

Blood Level of Phosphate
• PTH secretion is directly proportional to blood
phosphate level. Whenever the blood level of
phosphate increases,it combines with ionized
calcium to form calcium hydrogen phosphate.
• This decreases ionized calcium level in blood which
stimulates PTH secretion.
PARATHYROID GLAND

 Pineal gland, also called conarium, epiphysis
cerebri, pineal organ, or pineal body.
 The pineal gland is a small, pea-shaped gland in
the brain.Once called the ‘third eye,’ the pineal
gland is a small gland located deep in the center of
the brain.
PINEAL GLAND

Melatonin: The Pineal Gland Hormone
 The pineal gland secretes a single hormone melatonin
(not to be confused with the pigment melanin).
 This simple hormone is special because its secretion is
dictated by light.
 melatonin has two primary functions in humans—to
help control your circadian (or biological) rhythm and
regulate certain reproductive hormones.
 Reproduction
 Melatonin blocks secretion of gonadotropins
(luteinizing hormone & follicle stimulating hormone)
from anterior pituitary gland.
 These hormones aid in the proper development and
functioning of the ovaries and testes.
PINEAL GLAND

Circadian Rhythm
 Your circadian rhythm is a 24-hour biological
cycle characterized by sleep-wake patterns.
Daylight and darkness help dictate your
circadian rhythm. Light exposure stops the
release of melatonin, and in turn, this helps
control your circadian rhythms.
 Melatonin secretion is low during the daylight
hours and high during dark periods, which has
some influence over your reaction to photoperiod
(the length of day versus night).
PINEAL GLAND

 The thymus is located in the upper anterior
(front) part of your chest directly behind sternum
and between lungs. The pinkish-gray organ has
two thymic lobes.
 The thymus gland is made up of a patchwork of
epithelial tissue and lymphatic tissue.
 The thymus reaches its maximum weight (about
1 ounce) during puberty. This gland is only active
until puberty.
 After puberty, thymus starts to slowly shrink &
become replaced by fat.
THYMUS GLAND

Thymosin: The Hormone of the Thymus
 It stimulates development of disease-fighting T cells.
It help.s body protect itself against autoimmunity,
which occurs when immune system turns against
itself.
 Before birth & throughout childhood, thymus is
instrumental in production & maturation of T-
lymphocytes or T cells,
THYMUS GLAND

Pancreatic hormones are secreted directly into the
bloodstream and circulate throughout the body.The
endocrine pancreas consists of clusters of cells, known
as the pancreatic islets (islets of Langerhans),
scattered throughout the gland.There are three main
types of cells in the pancreatic islets:
 • α (alpha) cells, which secrete glucagon
 • β (beta) cells, which are the most numerous,
secrete insulin
 • δ (delta) cells, which secrete somatostatin (GHRIH)
PANCREATIC ISLETS

The normal blood glucose level is between
3.5 and 8 mmol/litre (63 to 144 mg/100 mL).
Blood glucose levels are controlled mainly
by the opposing actions of insulin and
glucagon:
• glucagon increases blood glucose levels
• insulin reduces blood glucose levels.
HORMONE OF PANCREATIC
ISLETS

Insulin
It is a peptide hormone produced by beta
cells of the pancreatic islets.
Function of Insuline
it is considered to be the main anabolic
hormone of the body.
It regulates the metabolism of
carbohydrates, fats and protein by
promoting absorption of glucose from the
blood into liver, fat and skeletal muscle
cells.I
ts main function is to lower raised blood
ISLETS

Function of Insuline
 Accelerating uptake of amino acids by cells, and
the synthesis of protein
 Promoting synthesis of fatty acids and storage of
fat in adipose tissue (lipogenesis)
 Decreasing glycogenolysis (breakdown of
glycogen into glucose)
 Preventing the breakdown of protein and fat, and
gluconeogenesis
ISLETS

Regulation of Insuline
 Secretion is stimulated by
increased blood glucose
levels, for example after
eating a meal, and by
parasympathetic stimulation,
 Secretion is decreased by
sympathetic stimulation,
glucagon, adrenaline, cortisol
and somatostatin (GHRIH),
which is secreted by the
hypothalamus and pancreatic
ISLETS

Glucagon
 Glucagon has a major role in maintaining normal
concentrations of glucose in blood, and is often
described as having the opposite effect of insulin.
That is, glucagon has the effect of increasing blood
glucose levels.
ISLETS

Glucagon
Glucagon increases blood glucose levels by
stimulating:
 Glycogenolysis- Glucagon stimulates breakdown of
glycogen stored in liver. When blood glucose levels
are high, large amounts of glucose are taken up by
liver.
 Gluconeogenesis-Glucagon activates hepatic
gluconeogenesis
ISLETS

Somatostatin (GHRIH)
 This hormone, also produced by the hypothalamus,
inhibits .Somatostatin, also known as growth
hormone-inhibiting hormone (GHIH) or by several
other names.
 It is a peptide hormone that regulates the
endocrine system and affects neurotransmission
and cell proliferation via interaction with G protein-
coupled somatostatin receptors
 inhibition of the release of numerous secondary
hormones. Somatostatin inhibits insulin and
glucagon secretion.
ISLETS

Function of Somatostatin
In the anterior pituitary gland, the effects of somatostatin
are:
 Inhibiting the release of growth hormone (GH)
 Inhibiting the release of thyroid-stimulating hormone
(TSH)
 Inhibiting the release of prolactin (PRL)
In Gastrointestinal System, the effects of somatostatin are:
 Suppresses the release of pancreatic hormones
 Somatostatin release is triggered by the beta cell peptide
urocortin3 (Ucn3) to inhibit insulin release.
ISLETS

Adrenal glands are called the ‘life-saving glands’ or
‘essential endocrine glands’. It is because the
absence of adrenocortical hormones causes death
within 3 to 15 days and absence of adrenomedullary
hormones, drastically decreases the resistance to
mental and physical stress.
FUNCTIONAL ANATOMY OF ADRENAL GLANDS
There are two adrenal glands. Each gland is situated
on the upper pole of each kidney. Because of the
situation, adrenal glands are otherwise called
suprarenal glands. Each gland weighs about 4 g.
ADRENAL GLAND

PARTS OF ADRENAL GLAND
Adrenal gland is made of two distinct parts:
1. Adrenal cortex: Outer portion, constituting 80% of
gland
2. Adrenal medulla: Central portion, constituting 20%
of the gland.
These two parts are different from each other in
development, structure and functions. Adrenal
medulla develops from the neural crest, which gives
origin to sympathetic nervous system. So, its
secretions and functions resemble that of
sympathetic nervous system. Adrenal cortex
develops from the mesonephros, which give rise to
the renal tissues. It secretes entirely a different
ADRENAL GLAND

ADRENAL MEDULLA
 The medulla is completely surrounded by the adrenal
cortex. It develops from nervous tissue in the embryo
and is part of the sympathetic nervous system.When
stimulated by extensive sympathetic nerve supply,
the glands release hormones adrenaline
( e p i n e p h r i n e , 8 0 % ) a n d n o r a d r e n a l i n e
(norepinephrine, 20%).
ADRENAL GLAND

Adrenaline (epinephrine) and noradrenaline
(norepinephrine)
 Noradrenaline is the postganglionic neurotransmitter
of the sympathetic division of the autonomic nervous
system Adrenaline and some noradrenaline are
released into the blood from the adrenal medulla
during stimulation of the sympathetic nervous
system.The action of these hormones prolongs and
augments stimulation of the sympathetic nervous
system. Structurally they are very similar, which
explains their similar effects. Together they
potentiate the fight or flight response by:
ADRENAL GLAND

 increasing heart rate
 increasing blood pressure
 diverting blood to essential organs, including the
 heart, brain and skeletal muscles, by dilating their
 blood vessels and constricting those of less essential
 organs, such as the skin
 increasing metabolic rate
 dilating the pupils.
 Adrenaline has a greater effect on the heart and
metabolic processes whereas noradrenaline has
more influence on blood vessel diameter.
ADRENAL GLAND

RESPONSE TO STRESS
 When the body is under stress homeostasis is
disturbed. To restore it and, in some cases, to
maintain life there are immediate and, if necessary,
longer-term responses. Stressors include exercise,
fasting, fright, temperature changes, infection,
disease and emotional situations.The immediate
response is sometimes described as preparing for
‘fight or flight’ . This is mediated by the
sympathetic nervous system
 In the longer term, ACTH from the anterior pituitary
stimulates the release of glucocorticoids and
mineralocorticoids from the adrenal cortex
providing a more prolonged response to stress
ADRENAL GLAND

ADRENAL CORTEX
 Adrenal cortex is formed by three layers of structure.
Each layer is distinct from one another.
 1. Outer zona glomerulosa
 2. Middle zona fasciculata
 3. Inner zona reticularis.
ADRENAL GLAND

„HORMONES OF ADRENAL CORTEX
 Adrenocortical hormones are steroids in nature,
hence the name ‘corticosteroids’. Based on their
functions, corticosteroids are classified into three
groups:
 1. Mineralocorticoids
 2. Glucocorticoids
 3. Sex hormones.
ADRENAL GLAND

GLUCOCORTICOIDS
G l u c o c o r t i c o i d s a c t m a i n l y o n g l u c o s e
metabolism.Glucocorticoids are:
 1. Cortisol
 2. Corticosterone
 3. Cortisone.
 Glucocorticoids are secreted mainly by zona
fasciculata of adrenal cortex. A small quantity of
glucocorticoids is also secreted by zona reticularis.
ADRENAL GLAND

MINERALOCORTICOIDS
 Mineralocorticoids are the corticosteroids that act on
the minerals (electrolytes), particularly sodium and
potassium.Mineralocorticoids are:
 1. Aldosterone
 2. 11-deoxycorticosterone.
 Aldosterone is the main mineralocorticoid. It is
involved in maintaining water and electrolyte
balance.
ADRENAL GLAND

Through a negative feedback system it
stimulates the reabsorption of sodium (Na+)
by the renal tubules and excretion of
potassium (K+) in the urine. Sodium
reabsorption is also accompanied by retention
of water and therefore aldosterone is involved
in the regulation of blood volume and blood
pressure too.
Blood potassium levels regulate aldosterone
secretion by the adrenal cortex. When blood
potassium levels rise, more aldosterone is
secreted . Low blood potassium has the
opposite effect. Angiotensin also stimulates
the release of aldosterone.
ADRENAL GLAND

 Renin–angiotensin–aldosterone system. When renal
blood flow is reduced or blood sodium levels fall, the
enzyme renin is secreted by kidney cells. Renin
converts the plasma protein angiotensinogen,
produced by the liver, to angiotensin 1. Angiotensin
converting enzyme (ACE), formed in small quantities
in the lungs, proximal kidney tubules and other
tissues, converts angiotensin 1 to angiotensin 2,
which stimulates secretion of aldosterone.
Angiotensin 2 causes vasoconstriction and increases
blood pressure closing the negative feedback loop.
ADRENAL GLAND

ADRENAL SEX HORMONES
 Adrenal sex hormones are secreted mainly by zona
reticularis. Zona fasciculata secretes small quantities
of sex hormones. Adrenal cortex secretes mainly the
male sex hormones, which are called androgens. But
small quantity of estrogen and progesterone are also
secreted by adrenal cortex.Androgens secreted by
adrenal cortex:
 1. Dehydroepiandrosterone (responsible for
masculine features of the body.)
 2. Androstenedione
 3. Testosterone.
ADRENAL GLAND

Endocrine System Guide: Hormones, Glands & Their Functions

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