THE ENDOCRINE SYSTEM
HOMEOSTASIS THROUGH INTERCELLULAR
COMMUNICATION
FUNCTIONS OF THE ENDOCRINE
SYSTEM
• The endocrine system regulates long-term ongoing
physiological process using hormones to preserve
homeostasis in the body.
• The endocrine system is made up of eight major
glands each of which produces chemicals that are
used to regulate; metabolic processes, growth and
development, tissue function, sexual function,
reproduction, sleep and mood, among other things.
• Just about every organ in the body is affected by
the functions of the endocrine system.
MAJOR STRUCTURES OF THE
ENDOCRINE SYSTEM
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Hypothalamus
Pituitary Gland
Thyroid Gland
Adrenal Glands
Thymus
Suprarenal Glands
Pineal Gland
Parathyroid Gland
Adipose Tissue
Pancreas
Gonads
(Other related structures; Heart, Digestive Tract, Kidney)
AN OVERVIEW OF THE ENDOCRINE
SYSTEM
HORMONES
• Hormones: Chemical messengers used produces
and released by the endocrine system to regulates
physiologically processes of the human body.
• Release and distributed to work on specific cells
(target cells) that respond to there presence.
• The hormones of the endocrine system are divided
into three groups based on their chemical structure
(Amino Acid Derivatives, Peptide Hormones, Lipid
Derivatives).
• There are 50+ different hormones in the human
body.
HORMONES OF THE BODY BY GROUP
• Peptide Hormones
• The largest category of hormones
• Consist of amino acid chains
• Includes all of the hormones secreted by the hypothalamus,
pituitary gland, heart, kidney, thymus, digestive tract, and
pancreas.
• Examples; Antidiuretic Hormone, Oxytocin, Growth
Hormone, Prolactin, Insulin, etc.
HORMONES OF THE BODY BY GROUP
Lipid Derivative Hormones
Lipid Derivative Hormones
• Steroids Versions
• Eicosanoids Versions
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Androgens
Estrogens
Progestins
Mineralocorticoids
Glucocorticods
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Prostaglandins
Leukotrienes
Prostacyclin
Thromboxane
HORMONES OF THE BODY BY GROUP
• Amino Acid Derivative Hormones
• Small chemicals that are structurally similar to amino acids.
• Examples of amino acid derived hormones would be;
epinephrine, norepinephrine, melatonin, and thyroid
hormones.
HORMONE ACTION & TRANSPORT
• Hormone Transport:
• Hormones can be
• Freely circulating
• Rapidly removed from bloodstream
• Bound to transport proteins e.g. albumin or globulin
HORMONE ACTION & TRANSPORT
• Each hormones’ shape is specific and can be recognized
by the corresponding target cells (Lock & Key)
• The binding sites on the target cells are called hormone
receptors.
• Receptors for peptide hormones, are located on the surface of cell
membranes because they can not cross the membrane to enter
the cell
• Thyroid and steroid hormones can cross the membrane and bind
to receptors in the cytoplasm or nucleus
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Hormones
that can not
cross the
membrane
(e.g. Peptide
hormones)
bind to the
receptor on
the surface
of the cell
Binding of
hormones to
the receptor
activate
secondary
messenger
(in this figure
binding of
hormone
activates G
protein, and
activated G
protein
activates
adenylcyclas
e
or activate
PDE or
activates
PLC
• Hormones
that can
cross the
membrane
(e.g. steroid
hormones)
bind to the
receptor
inside the
cell, at the
cytoplasm,
or they will
enter the
nucleus and
bind to the
receptor at
the nucleus
and initiate
transcription)
CONTROLLING ENDOCRINE ACTIVITY
• Hypothalamus regulates the activity of the nervous and
endocrine systems
• Hypothalamus secrets regulatory hormones (releasing hormones
and inhibiting hormones) that control the activity of the pituitary
gland
• Releasing/inhibiting hormones secreted by the hypothalamus
either stimulate or inhibit activity of pituitary gland
THREE METHODS OF HYPOTHALAMIC
CONTROL OVER THE ENDOCRINE
SYSTEM
THE PITUITARY GLAND
• The pituitary gland is called the “master gland” but it
is under the control of the hypothalamus.
• Hypothalamus and pituitary gland control many other
endocrine functions.
• Pituitary Gland releases nine important peptide
hormones.
• All nine bind to membrane receptors and use cyclic AMP
as a second messenger.
• Pituitary gland is divided into posterior and anterior
lobe.
ANTERIOR PITUITARY GLAND
• Anterior lobe of pituitary gland produces 7 hormones (the first four
regulate the production of other hormones)
• 1) Thyroid stimulating hormone (TSH)
• TSH triggers the release of thyroid hormones by the thyroid glands.
• Thyrotropin releasing hormone promotes the release of TSH.
• 2) Adrenocorticotropic hormone (ACTH)
• ACTH stimulates the release of glucocorticoids by the adrenal gland.
• Corticotrophin releasing hormone causes the secretion of ACTH.
• 3) Follicle stimulating hormone (FSH)
• FSH stimulates follicle development and estrogen secretion in females and
sperm production in males.
• 4) Leutinizing hormone (LH)
• LH causes ovulation and progestin (progesterone) production in females
and androgen (testosterone) production in males
• Gonadotropin releasing hormone (GNRH) promotes the secretion of FSH
and LH
ANTERIOR PITUITARY GLAND
• 5) Prolactin (PH)
• PH stimulates the development of mammary glands and milk
production.
• 6) Growth hormone (GH or somatotropin)
• GH stimulates cell growth and replication through release of
somatomedins or IGF.
• Growth-hormone releasing hormone
(GH-RH)
• Growth-hormone inhibiting hormone
(GH-IH)
• 7) Melanocyte stimulating hormone (MSH)
• Stimulates melanocytes to produce melanin.
PITUITARY GLAND
POSTERIOR PITUITARY GLAND
• The posterior lobe of the pituitary gland secretes two
hormones: Antiduretic Hormone and Oxytocin.
• 1) Antidiuretic hormone (ADH)
• Decreases the amount of water lost at the kidneys
• Elevates blood pressure
• 2) Oxytocin
• Stimulates contractile cells in mammary glands
• Stimulates smooth muscle cells in uterus
THYROID GLAND
• Thyroid gland is located near the thyroid cartilage of the larynx.
• The two lobes of thyroid gland are connected by an isthmus.
• It has 2 distinct population of cells: Flicular Cell (produce thyroid
hormone) and C cell (produce calcitonin).
• Thyroid gland release several hormones such as thyroxine (T4) and
triiodothyronine (T3)
• Functions of Thyroid hormones include:
• Increasing ATP production, when bound to mitochondria.
• Activating genes that control energy utilization, when bound to
receptors
• Exert a calorigenic effect
• C cells of thyroid gland produce calcitonin
• Calcitonin helps to regulate calcium concentration in body fluids
THYROID
PARATHYROID
• Four parathyroid glands embedded in the posterior
surface of the thyroid gland.
• Chief cells produce parathyroid hormone (PTH) in
response to lower than normal calcium concentrations.
• Parathyroid hormones plus calcitonin are primary
regulators of calcium levels in healthy adults.
PARATHYROID GLAND
ADRENAL GLAND
• Adrenal Cortex
• Manufactures steroid hormones derived from cholesterol
(corticosteroids).
• Corticosterioid hormones are divided into 3 functional groups
• Mineralocorticoids (Aldosterone)
• Regulate mineral and salt balance by renin-angiotensis-aldosterone
system
• Glucocorticoids (cortisol and cortisone)
• Regulate glucose levels i.e. they increase gluconeogenesis and
decrease protein synthesis
• Decrease inflammation response
• Androgens also called sex hormones
• Adrenal Medulla
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Responsible for flight-or-fight response
Produces epinephrine and norepinephrine
ADRENAL GLAND
PINEAL GLAND
• Contains pinealocytes
• Synthesize melatonin
• Suggested functions include inhibiting reproductive
function, protecting against damage by free radicals,
setting circadian rhythms (biological clock)
PANCREAS
• Pancreatic Islets
• Clusters of endocrine cells within the pancreas called Islets of
Langerhans or pancreatic islets
• Alpha cells secrete glucagons
• Glucagon raises blood glucose by increasing the rates
of glycogen breakdown and glucose manufacture by
the liver
• Beta cells secrete insulin
• Insulin lowers blood glucose by increasing the rate of
glucose uptake and utilization
• Delta cells secrete GH-IH
• F cells secrete pancreatic polypeptide
PANCREAS
KIDNEY
• Produce calcitriol and erythropoietin (EPO) and the enzyme
rennin
• Calcitriol = stimulates calcium and phosphate ion
absorption along the digestive tract
• EPO stimulates red blood cell production by bone marrow
• Renin converts angiotensinogen to angiotensin I
• Angiotensin I is converted to angiotensin II at the lungs
• Agiotensin II:
1. Stimulates production of aldosterone by the adrenal
glands
2. Stimulates release of ADH by the pituitary gland
3. Promotes thirst
4. Elevates blood pressure
ENDOCRINE ACTIVITY
• The Heart
• Specialized muscle cells produce natriuretic peptides in
response to high blood pressure
• Natriuretic peptide generally has the opposite actions of
angiotensin II
• The Intestine
• Produce hormones important to the coordination of
digestive activities
• The Thymus
• Produces thymosins
• Help develop and maintain normal immune defenses
GONADS
• Interstitial cells of the testes produce testosterone
• Most important sex hormone in males
• In females, oocytes develop in follicles
• Follicle cells produce estrogens
• After ovulation, the follicle cells form corpus luteum.
Corpus luteum releases a mixture of estrogens and
progesterone
ADIPOSE TISSUE
• Leptin, a feedback control for appetite
• Resistin, which reduces insulin sensitivity
HORMONE GROWTH & BEHAVIOR
• Behavior
• Many hormones affect the CNS
• Changes in the normal mixture of hormones significantly alters
intellectual capabilities, memory, learning and emotional states
• Growth
• Normal growth requires the interaction of several endocrine organs
• Six hormones are important
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GH
Thyroid hormones
Insulin
PTH
Calcitriol
Reproductive hormones