ENDOCRINE SYSTEM​ Nearly All Hormones are Classified as: ​

- The 2nd control system of the body, the ●​ Amino acid-based molecules
endocrine system releases chemicals called (proteins, peptides, amines)
hormones that regulate complex body ●​ Steroids (made from cholesterol)
processes.
- Hormones released by endocrine glands Steroid Hormones Include: ​
travel through the blood and alter the
activity of target cells. ●​ Sex Hormones from the Gonads
- Regulates complex processes such as (ovaries and testes)
growth, development, metabolism, ●​ Hormones from the adrenal cortex
reproduction.
- The scientific study of hormones and - Other hormones are nonsteroidal amino
endocrine organs is called endocrinology. acid derivatives.
- A third hormone class is prostaglandins,
ENDOCRINE SYSTEM AND HORMONE which act locally.
FUNCTION (4) - Prostaglandins are made from lipids
1. The organs of the endocrine system are released by nearly all cell membranes.
small and unimpressive compared to other
body organs. HORMONE ACTION
2. The endocrine system lacks structural or - Hormones travel through the blood but
anatomical continuity like most organ affect only specific target cells or target
systems. organs.
3. Endocrine tissues are scattered in - Target cells must have specific protein
separate regions of the body. receptors for the hormone to bind and take
4. They play a major role in maintaining effect.
body homeostasis. - The term hormone comes from the greek
word hormao which means “to arouse”, as
hormones alter cellular activity rather than
creating new functions

HORMONES CAN (5)

1. Change plasma membrane
permeability or membrane potential
(electrical state) by opening or closing ion
channels.
2. Activate or inactivate enzymes.
3. Stimulate or inhibit cell division.
4. Promote or inhibit secretion of a
product.
5. Turn on or off transcription of certain
genes (such as encoding proteins or
regulatory molecules)

MECHANISMS OF HORMONE ACTION

1. Direct Gene Activation

- steroid and thyroid hormones use the
THE CHEMISTRY OF HORMONES mechanism of direct gene activation
- Hormones are chemical substances because they are lipid-soluble molecules,
secreted by endocrine cells into the steroid hormones can diffuse through
extracellular fluids. the plasma membranes of their target cells.
- They regulate metabolic activity of other
cells in the body.
Process of Direct Gene Activation typical response of the target cell to the
hormone.
1. Once inside, the steroid hormone enters 4. The same hormone may have a variety of
the nucleus. possible second messengers (including
2. Binds to a specific hormone receptor. cyclic guanosine monophosphate, or cGMP,
3. The hormone-receptor complex then and calcium ions) and many possible target
binds to a specific site on the cell’s DNA. cell responses, depending on the tissue
4. Activating certain genes to transcribe type stimulated.
messenger RNA (mRNA).
5. The mRNA is translated in the
cytoplasm.
6. Resulting in the synthesis of new
proteins.

STIMULI FOR CONTROL OF HORMONE

RELEASE
- Negative feedback mechanisms are the
chief means of regulating blood levels of
nearly all hormones.
- In such systems, some internal or external
2. Second-Messenger System
stimulus triggers hormone secretion; then, a
- Steroid hormones can influence cell
rising level of the hormone inhibits further
activity by direct gene activation and indirect
hormone release (even while promoting a
activation of a second messenger
response in the target organ). As a result,
- Protein and peptide hormones are not
blood levels of many hormones vary within
water-soluble, unable to enter target cells
a very narrow range.
directly, Bind to hormone receptors on the
- The stimuli that activate endocrine
target cell’s plasma membrane and use a
glands fall into 3 major categories:
second-messenger system.
Hormonal, Humoral, Neural stimulus.
- These 3 mechanisms represent the most
Process of Second-Messenger System
common systems that control hormone
- The hormone (first messenger) binds to
release.
the receptor protein on the membrane and
- Some endocrine organs respond to many
different stimuli.
1. The activated receptor sets off a series of
reactions (a cascade) that activates an
HORMONAL STIMULI
enzyme.
- The most common stimulus is a hormonal
2. The enzyme, in turn, catalyzes the
stimulus, where endocrine organs are
reactions that produce second-messenger
prodded into action by other hormones.
molecules.
- Hormones of the hypothalamus stimulate
3. Cyclic Adenosine Monophosphate,
the anterior pituitary gland to secrete its
also known as cAMP, oversees additional
hormones.
intracellular changes that promote the
- Anterior pituitary hormones stimulate NEURAL STIMULI
other endocrine organs to release their - Nerve fibers stimulate hormone release in
hormones into the blood. isolated cases.
- As hormones from the final target glands - Endocrine cells respond to neural stimuli.
increase, they “feed back” to inhibit anterior - Sympathetic nervous system stimulation of
pituitary hormone release. the adrenal medulla causes the release of
- Hormone release is rhythmic, with blood catecholamines (norepinephrine and
levels rising and falling again and again. epinephrine) during periods of stress.

THE MAJOR ENDOCRINE ORGANS

- Changing blood levels of certain ions - The major endocrine organs of the body
and nutrients may stimulate hormone include the pituitary, pineal, thyroid,
release. parathyroid, thymus and adrenal glands,
- Such stimuli are referred to as humoral pancreas, and gonads (ovaries and testes)
stimuli to distinguish them from hormonal (10).
stimuli, which are also bloodborne - The Hypothalamus, which is part of the
chemicals. nervous system, is also recognized as a
- The term humoral refers to the ancient use major endocrine organ because it
of the word humor to indicate various body produces several hormones.
fluids (blood, bile, and others). - some hormone-producing glands (the
- Other hormones released in response to anterior pituitary, thyroid, parathyroids,
humoral stimuli include calcitonin, and adrenals) have purely endocrine
released by the thyroid gland, and insulin, functions.
produced by the pancreas. - but others (pancreas and gonads) have
both endocrine and exocrine functions and
are mixed glands.
- both types of endocrine glands are
ductless glands that produce hormones
that they release into the blood or lymph.
- Exocrine glands release their products at
the body’s surface or into the body cavities
through ducts.

PITUITARY GLAND & HYPOTHALAMUS

- The pituitary gland is approximately the
size of a pea.
- It hangs by a stalk from the inferior surface - It acts as a storage area for hormones
of the hypothalamus of the brain, where it is made by hypothalamic neurons.
snugly surrounded by the Sella turcica
(Turk’s saddle) of the sphenoid bone. OXYTOCIN​
- Released in significant amounts only
Pituitary-Hypothalamus Relationships during childbirth and nursing.
- It has two functional lobes: the Anterior - Stimulates powerful contractions of the
pituitary (glandular tissue) and Posterior uterine muscle during sexual relations,
pituitary (nervous tissue). labor, and breastfeeding. ​
- The Anterior pituitary gland is called the - Causes milk ejection (let-down reflex) in
“master endocrine gland” because it nursing women.
controls many other endocrine glands. - Natural and synthetic oxytocic drugs
- Its removal or destruction causes severe (Pitocin and others) are used to induce or
effects, leading to atrophy of the adrenal, hasten labor and stop postpartum bleeding.
thyroid, and gonads.
- However, the anterior pituitary is ANTIDIURETIC HORMONE (ADH)​
regulated by the hypothalamus, which - Diuresis is urine production, and an
controls it using: releasing hormones (1) antidiuretic prevents urine production.
and inhibiting hormones (2). - ADH causes the kidneys to reabsorb more
- These hormones travel through the portal water, reducing urine output and increasing
circulation, which connects the blood blood volume.
supply of the hypothalamus and anterior - In larger amounts, ADH increases blood
pituitary. pressure by constricting arterioles (small
- The hypothalamus also produces arteries), also called vasopressin.
oxytocin and antidiuretic hormone (ADH) - Alcohol inhibits ADH, leading to excessive
- These hormones are transported by urine output, dry mouth, and intense thirst.
neurosecretory cells to the posterior - Diuretics counteract ADH, causing water
pituitary for storage. loss and are used to treat edema (water
- They are released into the blood in retention in tissues).
response to nerve impulses from the
hypothalamus. Homeostatic Imbalance: Diabetes
Insipidus
HORMONES RELEASED BY THE - Hyposecretion of ADH leads to excessive
POSTERIOR PITUITARY AND THEIR urine output.
TARGET ORGANS - Affected individuals are continually thirsty
and drink huge amounts of water.

ANTERIOR PITUITARY HORMONES

- The anterior pituitary produces several
hormones that affect many body organs
- Growth hormone (GH) and prolactin
exert their major effects on nonendocrine
targets.
- The remaining four—follicle-stimulating
hormone, luteinizing hormone,
thyrotropic hormone, and
adrenocorticotropic hormone—are tropic
hormones.
Posterior Pituitary and Hypothalamic - Tropic hormones stimulate their target
Hormones organs (other endocrine glands) to secrete
- The posterior pituitary is not an endocrine hormones.
gland in the strict sense because it does
not make the peptide hormones it releases.
ALL ANTERIOR PITUITARY HORMONES:​ - The facial bones, particularly the lower jaw
1. Are proteins (or peptides). and the bony ridges under the eyebrows,
2. Act through second-messenger systems. enlarge tremendously.
3. Are regulated by hormonal stimuli and, in - The feet and hands also enlarge.
most cases, negative feedback. - Thickening of soft tissues leads to coarse
or malformed facial features.
HORMONES OF THE ANTERIOR
PITUITARY AND THEIR MAJOR TARGET Most cases of hypersecretion by
ORGANS​ Endocrine organs (the pituitary and the
other endocrine organs) result from
tumors of the affected gland:​
- The tumor cells act in much the same way
as the normal glandular cells do; that is,
they produce the hormones normally made
by that gland.
- Pharmacological doses of GH have been
used to reverse some of the effects of
aging.

Growth Hormone (GH)​

- A general metabolic hormone.
- Major Effects: Directed to the growth of
skeletal muscles and long bones.

Functions:
1. Protein-sparing and anabolic - causes
the building of amino acids into proteins.
2. Stimulates most target cells to grow in PROLACTIN (PRL)​
size and divide. - A protein hormone structurally similar to
3. Causes fats to be broken down and growth hormone.
used for energy while sparing glucose, - Only known target in humans is the breast
helping to maintain blood sugar (pro = for ; lact = milk).
homeostasis. - After childbirth, stimulates and maintains
milk production by the mother’s breasts.
HOMEOSTATIC IMBALANCE - Function in men is not known.
- If untreated, both deficits and excesses of
GH may result in structural abnormalities. Gonadotropic Hormones
- Regulate the hormonal activity of the
Hyposecretion of GH during childhood gonads (ovaries and testes).
leads to Pituitary Dwarfism
- Body proportions are fairly normal. Follicle-stimulating hormone (FSH):
- The person as a whole is a living miniature - In women: Stimulates follicle development
(with a maximum adult height of 4 feet). in the ovaries.
- As follicles mature, they produce estrogen,
Hypersecretion during childhood results and eggs are readied for ovulation.
in Gigantism - In men: Stimulates sperm development by
- The individual becomes extremely tall; the testes.
height of 8 to 9 feet is common.
- Body proportions are fairly normal.

If hypersecretion occurs after long-bone

growth has ended, Acromegaly results:
Luteinizing hormone (LH): Thyroid Gland
- In women: Triggers ovulation and causes - is located at the base of the throat, just
the ruptured follicle to produce progesterone inferior to the Adam’s apple, where it is
and some estrogen. easily palpated during a physical
- In men: Stimulates testosterone examination.
production by the interstitial cells of the - It is a fairly large gland consisting of two
testes lobes joined by a central mass, or isthmus.
- Hyposecretion of FSH or LH leads to - The thyroid gland makes two hormones,
sterility, the lack of ability to successfully one called thyroid hormone, the other
reproduce, in both males and females. called calcitonin (produced by the
- In general, hypersecretion does not parafollicular cells).
appear to cause any problems. - Internally, the thyroid gland is composed of
- Some drugs used to promote fertility hollow structures called follicles, which
stimulate the release of the gonadotropic store a sticky colloidal material.
hormones, and multiple births (indicating - Thyroid hormone is derived from this
multiple ovulations at the same time rather colloid.
than the usual single ovulation each month)
are relatively common after their use. Thyroid Hormone
- Often referred to as the body’s major
Thyrotropic Hormone (TH) / metabolic hormone.
Thyroid-Stimulating Hormone (TSH) - Actually two active iodine-containing
- Influences the growth and activity of the hormones: Thyroxine (T₄) and
thyroid gland. Triiodothyronine (T₃).
- Thyroxine is the major hormone secreted
Adrenocorticotropic Hormone (ACTH) by the thyroid follicles.
- Regulates the Endocrine Activity of the - Most triiodothyronine is formed at the
cortex portion of the adrenal gland. target tissues by conversion of thyroxine to
triiodothyronine.
PINEAL GLAND​
- is a small, cone-shaped gland that hangs Thyroid Gland
from the roof of the third ventricle of the - These two hormones are very much alike:
brain. - Each is constructed from two tyrosine
- The endocrine function of this tiny gland is amino acids linked together.
still somewhat of a mystery. - Thyroxine has 4 bound iodine atoms,
- Although many chemical substances have whereas triiodothyronine has 3 (thus, T₄
been identified in the pineal gland, only the and T₃, respectively).
hormone melatonin appears to be secreted - Thyroid hormone controls the rate at which
in substantial amounts. glucose is "burned," or oxidized, and
converted to body heat and chemical
The level of Melatonin rises and falls energy (ATP).
during the course of the Day and Night - Because all body cells depend on a
- The peak level occurs at night and makes continuous supply of ATP for their activities,
us drowsy. every cell in the body is a target.
- The lowest level occurs during daylight
around noon. Thyroid Hormone is also important for
- Melatonin is believed to be a "sleep normal tissue growth and development,
trigger" that plays an important role in especially in the reproductive and nervous
establishing the body's sleep-wake cycle. systems.
- It is believed to coordinate the hormones
of fertility and to inhibit the reproductive
system (especially the ovaries of females)
until the body matures.
PARATHYROID GLANDS white blood cells (T lymphocytes) and the
- are tiny masses of glandular tissue most immune response.
often found on the posterior surface of the
thyroid gland. ADRENAL GLANDS
- Typically, there are two parathyroid glands - 2 adrenal glands curve over the top of the
on each thyroid lobe, that is, a total of four kidneys like triangular hats.
(4) parathyroid. - Although each adrenal gland looks like a
- But as many as eight (8) have been single organ, it is structurally and
reported; some may be in other regions of functionally 2 endocrine organs in one.
the neck or the thorax. - Like the pituitary gland, it has parts made
- The parathyroids secrete parathyroid of glandular (cortex) and neural tissue
hormones (PTH), which is an important (medulla). The central medulla region is
regulator of calcium ion ( Ca2+) enclosed by the adrenal cortex, which
homeostasis of the blood. contains three separate layers of cells.
- When the blood calcium ion concentration
drops below a certain level, the parathyroids
release PTH which stimulates bone
destruction cells (osteoclasts) to break
down bone matrix and release calcium ions
into the blood.
- PTH is a hypercalcemic hormone,
whereas calcitonin is a hypocalcemic
hormone.
- Although the skeleton is the major PTH
target, PTH also stimulates the kidneys and
intestine to absorb more calcium ions.

Hormones of the Adrenal Cortex

- The adrenal cortex produces three (3)
major groups of steroid hormones, which
are collectively called corticosteroids---
mineralocorticoids, glucocorticoids, and
sex hormones.
- The mineralocorticoids, mainly
aldosterone, are produced by the outermost
adrenal cortex cell layer.
- are important in regulating the mineral (or
salt) content of the blood, particularly the
concentrations of sodium and potassium
ions.
- These hormones target the kidney tubules
that selectively reabsorb the minerals or
allow them to be flushed out of the body in
THYMUS urine.
- It is located in the upper thorax, posterior - When the blood level of aldosterone rises,
to the sternum. the kidney tubule cells reabsorb increasing
- Large in infants and children, and amounts of sodium ions and secrete more
decreases in size throughout adulthood. potassium ions into the urine. When sodium
- By old age, it is composed mostly of is reabsorbed, water follows.
fibrous connective tissue and fat. - The mineralocorticoids help regulate
- It produces a hormone called thymosin both water and electrolyte balance in body
and others that appear to be essential for fluid.
normal development of a special group of
- The release of aldosterone is stimulated - In both men and women, the adrenal
by humoral factors, such as fewer sodium cortex produces both male and female sex
ions or more potassium ions in the blood. hormones in relatively small amounts
- Renin, an enzyme produced by the throughout life.
kidneys when blood pressure drops, also - The bulk of the sex hormones produced by
causes aldosterone by triggering a series of the innermost cortex layers are
reactions that form angiotensin II, a potent androgens (male sex hormones), but some
stimulator of aldosterone release. are estrogens (female sex hormones) are
- A hormone released by the heart, atrial also formed.
natriuretic peptide (ANP), prevents
aldosterone release, its goal being to Hormones of the Adrenal Medulla
reduce blood volume and blood pressure. - The adrenal medulla, like the posterior
- The middle cortical layer mainly pituitary, is a knot of nervous tissue.
produces glucocorticoids, which includes - When the sympathetic nervous system
cortisone and cortisol. neurons stimulate the medulla, its cells
- It promotes normal cell metabolism and release 2 similar hormones, epinephrine
helps the body to resist long-term stressors, (adrenaline), and norepinephrine
primarily by increasing the blood glucose (noradrenaline), into the bloodstream.
level. - Collectively, these hormones are called
- Glucocorticoids are said to be catecholamines. Because some
hyperglycemic hormones. sympathetic neurons also release
norepinephrine as a neurotransmitter, the
- Glucocorticoids also seem to control the adrenal medulla is often thought of as a
more unpleasant effects of inflammation by “misplaced sympathetic nervous system
decreasing edema, and they reduce pain by ganglion”
inhibiting the pain causing prostaglandins. - So when you feel threatened physically or
- Because of their anti-inflammatory emotionally, your sympathetic nervous
properties, glucocorticoids are often system brings about the “fight-or-flight”
prescribed as drugs to suppress response to help you cope with the stressful
inflammation for patients with rheumatoid situation. It pumps its hormones into the
arthritis. bloodstream to enhance and prolong the
- Glucocorticoids are released from the effects of the neurotransmitters of the
adrenal cortex in response to a rising blood sympathetic nervous system.
level of ACTH.
- The catecholamines increase heart rate,
blood pressure, and the blood glucose level
and dilate the small passageway of the
lungs.
- It results in more oxygen and glucose in
the blood and a faster circulation of blood to
the body organs. It also prepares the body
to cope with short-term stressful situations
and causes the so-called alarm stage of
stress response.
- Glucocorticoids, by contrast, are
produced by the adrenal cortex and are
important when coping with prolonged or
continuing stressors. It operates primarily
during the resistance stage of the stress
response.
PANCREATIC ISLETS​ GONADS​
- The pancreas, located close to the - The female and male gonads produce sex
stomach in the abdominal cavity, is a mixed cells (an exocrine function).
gland. - They also produce sex hormones that are
- The pancreatic islets, also called the identical to those produced by adrenal
islets of Langerhans, are little masses of cortex cells.
endocrine (hormone-producing) tissue - The major differences from the adrenal
scattered among the exocrine (enzyme sex hormone production are the source
producing) tissue of the pancreas. and relative amount of hormones
- The exocrine, or acinar, part of the produced.
pancreas acts as part of the digestive
system. Although there are more than a Hormones of the Ovaries
million islets separated by exocrine cells, - The female gonads, or ovaries, are
each of these tiny clumps of cells works like paired, slightly larger than an almond-sized
an organ within an organ as it busily organ located in the pelvic cavity.
manufactures its hormones. - Besides producing female sex cells (ova,
or eggs), ovaries produce two groups of
steroid hormones, estrogens and
progesterone.
- Alone, the estrogens are responsible for
the development of sex characteristics in
women (primarily growth and maturation of
the reproductive organs) and the
appearance of secondary sex
characteristics (for example, hair in the
pubic and axillary regions) at puberty.
- Acting with progesterone, estrogens
promote breast development and cyclic
changes in the uterine lining (the menstrual
cycle, or menstruation)

- Progesterone as already noted, acts with

- 2 important hormones produced by the estrogen to bring about the menstrual cycle.
islet cells are insulin and glucagon. - During pregnancy, it quiets the muscles of
- Islet cells act as fuel sensors, secreting the uterus so that an implanted embryo will
insulin and glucagon appropriately during not be aborted and helps prepare breast
fed and fasting states. tissue for lactation.
- A high level of glucose in the blood - Ovaries are stimulated to release their
stimulates the release of insulin from the estrogens and progesterone in a cyclic way
beta cells of the islets. Insulin acts on just by the anterior pituitary gonadotropic
about all body cells, increasing their ability hormones.
to import glucose across their plasma - But keep in mind that hyposecretion of the
membranes. ovarian hormones severely hampers a
- Once inside the cells, glucose is oxidized woman's ability to conceive and bear
for energy or converted to glycogen of fat children.
for storage. Insulin also speeds up these
“use it” or “store it” activities. Because Hormones of the Testes
insulin sweeps the glucose out of the blood, - The paired oval testes of the male are
its effect is said to be hypoglycemic. suspended on a sac, the scrotum, outside
the pelvic cavity.
- In addition to male sex hormones, or
androgens, of which testosterone is the
most important.
- At puberty, testosterone promotes the the pregnancy) and prepare the breasts for
growth and maturation of the reproductive producing milk.
system organs to prepare the young man - Human placental lactogen (hPL) works
for reproduction. cooperatively with estrogen and
- It also causes the male's secondary sex progesterone in preparing the breasts for
characteristics (growth of facial hair, lactation.
development of heavy bones and muscles, - Relaxin, another placental hormone,
and lowering of the voice) to appear and causes the mother’s pelvic ligaments and
stimulates the male sex drive. the pubic symphysis to relax and become
more flexible, which eases birth passage.
- In adults, testosterone is necessary for
continuous production of sperm. MAJOR ENDOCRINE GLANDS AND
- In cases of hyposecretion, the man SOME OF THEIR HORMONES​
becomes sterile; such cases are usually
treated by testosterone injections. Hypothalamus
- Testosterone production is specifically Hormones released by the posterior
stimulated by LH (luteinizing hormone). pituitary; releasing and inhibiting hormones
that regulate the anterior pituitary.
OTHER HORMONE-PRODUCING
TISSUES AND ORGANS​ Pituitary Gland
- Besides the major endocrine organs, Posterior Lobe (releases hormones made
pockets of hormone-producing cells are by the hypothalamus.)
found in fatty tissue and in the walls of the
small intestine, stomach, kidneys, and Hormones in the Posterior Lobe of the
heart—organs whose chief functions have Pituitary Gland (2)
little to do with hormone production.
- The Placenta is a remarkable organ Hormone: Oxytocin
formed temporarily in the uterus of pregnant Chemical Class: Peptide
women. In addition to its roles as the Major Actions: Stimulates contraction of
respiratory, excretory, and nutrition-delivery uterus and the milk “let down” reflex.
systems for the fetus, it also produces Regulated by: Nervous system
several protein and steroid hormones (hypothalamus), in response to uterine
that help to maintain the pregnancy and stretching and/or suckling of a baby.
pave the way for delivery of the baby.
- During very early pregnancy, a hormone Hormone: Antidiuretic Hormone (ADH)
called human chorionic gonadotropin Chemical Class: Peptide
(hCG) is produced by the developing Major Actions: Promoted retention of water
embryo and then by the fetal part of the by kidneys.
placenta. Regulated by: Hypothalamus, in response
- Similar to LH (luteinizing hormone), hCG to water/salt imbalance.
stimulates the ovaries to continue producing
estrogen and progesterone so that the lining Hormones in the Anterior Lobe of the
of the uterus is not sloughed off in menses. Pituitary Gland (6)
(The home pregnancy tests sold over the
counter test for the presence of hCG in the Hormones: Growth hormone (GH)
woman’s urine.) Chemical Class: Protein
- In the third month, the placenta assumes Major Actions: Stimulates growth
the job of producing estrogen and (especially of bones and muscles) and
progesterone, and the ovaries become metabolism.
inactive for the rest of the pregnancy. Regulated by: Hypothalamic releasing and
inhibiting hormones.
- The high estrogen and progesterone blood
levels maintain the lining of the uterus (thus,
Hormones: Prolactin (PRL) PARATHYROID GLAND (1)
Chemical Class: Protein ​
Major Actions: Stimulates milk production Hormones: Parathyroid hormone (PTH)
Regulated by: Hypothalamic hormones Chemical Class: Peptide
Major Actions: Raises blood calcium ion
Hormones: Follicle-stimulating hormone level
(FSH) Regulated by: Calcium ion level in blood
Chemical Class: Protein
Major Actions: Stimulates production of THYMUS (1)
ova and sperm.
Regulated by: Hypothalamic hormones Hormones: Thymosin
Chemical Class: Peptide
Hormones: Luteinizing hormone (LH) Major Actions: “Programs” T lymphocytes
Chemical Class: Protein Regulated by: Not known
Major Actions: Stimulates ovaries and
testes. ADRENAL GLANDS
Regulated by: Hypothalamic hormones
Adrenal Medulla (1)
Hormones: Thyroid-stimulating hormone
Chemical Class: Protein Hormones: Epinephrine and
Major Actions: Stimulates thyroid gland. norepinephrine
Regulated by: Thyroxine in blood; Chemical Class: Amines
hypothalamic hormones. Major Actions: Raise blood glucose level;
increase rate of metabolism; constrict
Hormones: Adrenocorticotropic hormone certain blood vessels.
(ACTH) Regulated by: (sympathetic division)
Chemical Class: Protein Nervous system
Major Actions: Stimulates adrenal cortex to
secrete glucocorticoids Adrenal Cortex (2)
Regulated by: Glucocorticoids;
hypothalamic hormones Hormones: Glucocorticoids
Chemical Class: Steroids
PINEAL GLAND (1) Major Actions: Increase blood glucose
level
Hormones: Melatonin Regulated by: ACTH (adrenocorticotropic
Chemical Class: Amine hormone)
Major Actions: Involved in biological
rhythms (daily and seasonal) Hormones: Mineralocorticoids
Regulated by: Light/dark cycles Chemical Class: Steroids
Major Actions: Promote reabsorption of
THYROID GLAND (2) Na+ and excretion of K+ (potassium) in the
kidney.
Hormones: Thyroxine (T4) and Regulated by: Changes in blood volume or
triiodothyronine (T3) blood pressure; K+ or Na+ level in blood.
Chemical Class: Amine
Major Actions: Stimulates metabolism PANCREAS (2)
Regulated by: TSH (thyroid-stimulating
hormone) Hormones: Insulin
Chemical Class: Protein
Hormones: Calcitonin Major Actions: Reduces blood glucose
Chemical Class: Peptide level.
Major Actions: Reduces blood calcium ion Regulated by: Glucose level in blood
level.
Regulated by: Calcium ion level in blood
Hormones: Glucagon of the uterus, promoting menstrual pain and
Chemical Class: Protein labor; enhance blood clotting; promote
Major Actions: Raises blood glucose level inflammation and pain; increase output of
Regulated by: Glucose level in blood digestive secretions by stomach; cause
fever.
GONADS
2. Gastrin
Testes (1)
Chemical Composition: Peptide
Hormones: Androgens Source: Stomach
Chemical Class: Steroids Stimulus for secretion: Food
Major Actions: Support sperm formation; Target organ/Effects: Stomach: stimulates
development and maintenance of male glands to release hydrochloric acid (HCl).
secondary sex characteristics
Regulated by: FSH (follicle-stimulating 3. Intestinal Gastrin
hormone) and LH (luteinizing hormone)
Chemical Composition: Peptide
Ovaries (2) Source: Duodenum (first segment) of small
intestine
Hormones: Estrogens Stimulus for secretion: Food, especially
Chemical Class: Steroids fats.
Major Actions: Stimulate uterine lining Target organ/Effects: Stomach: stimulates
growth; development and maintenance of gastric glands and motility.
female secondary sex characteristics.
Regulated by: FSH (follicle-stimulating 4. Secretin
hormone) and LH (luteinizing hormone)
Chemical Composition: Peptide
Hormones: Progesterone Source: Duodenum
Chemical Class: Steroids Stimulus for secretion: Food
Major Actions: Promotes growth of uterine Target organ/Effects: Pancreas: stimulates
lining. release of bicarbonate-rich juice. ; Liver:
Regulated by: FSH (follicle-stimulating increases release of bile. ; Stomach:
hormone) and LH (luteinizing hormone) reduces secretions and motility.

HORMONES PRODUCED BY ORGANS 5. Cholecystokinin (CCK)​

OTHER THAN THE MAJOR ENDOCRINE
ORGANS (10)​ Chemical Composition: Peptide
​ Source: Duodenum
1. Prostaglandins (PGs); several groups Stimulus for secretion: Food
indicated by letter A-I (PGA-PGI) Target organ/Effects: Pancreas: stimulates
release of enzyme rich juice.; Gallbladder:
Chemical Composition: Derived from fatty stimulates expulsion of stored bile. ;
acid molecules. Duodenal papilla (entry point at the small
Source: Plasma membranes of virtually all intestine): causes sphincter to relax,
body cells. allowing bile and pancreatic juice to enter
Stimulus for secretion: Various (local duodenum.
irritation, hormones, etc.)
Target organ/Effects: Have many targets 6. Erythropoietin
but act locally at the site of release. Chemical Composition: Glycoprotein
Source: Kidney
Examples of effects include the following: Stimulus for secretion: Hypoxia (low
increase blood pressure by acting as oxygen level)
vasoconstrictors; cause constriction of Target organ/Effects: Bone marrow:
respiratory passageways; stimulate muscle stimulates production of red blood cells.
7. Active Vitamin D3 - Many men remain fertile throughout their
lifespan, indicating that testosterone is still
Chemical Composition: Steroid being produced in adequate amounts.
Source: Kidney (activates provitamin D
made by epidermal cells) Aging Effects on the Endocrine System
Stimulus for secretion: PTH (5)
Target organ/Effects: Intestine: stimulates
active transport of dietary calcium ions - Growth hormone output declines →
across intestinal cell membranes. Muscle atrophy in old age.
- Elderly persons are less able to resist
8. Atrial Natriuretic Peptide (ANP)​ stress and infection.
. - Exposure to pesticides, industrial
Chemical Composition: Peptide chemicals, and pollutants diminishes
Source: Heart endocrine function.
Stimulus for secretion: Stretching of atria - Older people are often mildly
(receiving chambers) of heart. hypothyroid.
Target organ/Effects: Kidney: inhibits - Decline in insulin production → Type 2
sodium ion reabsorption and renin release. ; diabetes is most common in this age group.
Adrenal cortex: inhibits secretion of
aldosterone, thereby decreasing blood
volume and blood pressure.

9. Leptin

Chemical Composition: Peptide

Source: Adipose tissue
Stimulus for secretion: Fatty foods
Target organ/Effects: Brain: suppresses
appetite and increases energy expenditure.

10. Resistin

Chemical Composition: Peptide

Source: Peptide
Stimulus for secretion: Unknown
Target organ/Effects: Fat, muscle, liver:
antagonizes insulin’s action on liver cells.

DEVELOPMENTAL ASPECTS OF THE

ENDOCRINE SYSTEM​

- Menopause (“the change of life”). A

woman’s reproductive organs begin to
atrophy, and the ability to bear children
ends.
- Problems associated with estrogen
deficiency such as Arteriosclerosis,
osteoporosis, decreased skin elasticity, and
changes in the operation of the sympathetic
nervous system that result in Hot flashes,
fatigue, nervousness, mood changes
(depression).