2. Endocrine Glands and Hormones
• Endocrine glands
• Ductless
• Secrete hormones into the blood
• Hormones are regulatory molecules secreted into the body by
endocrine glands
• Hormones affect the metabolism of their target organs and, by
this means, help to regulate total body metabolism, growth and
reproduction
3. Endocrine Gland Major Hormones Primary Target Organs Primary Effects
Adipose tissue Leptin Hypothalamus Suppresses Appetite
Adrenal cortex Glucocorticoids Liver and Muscle Glucocorticoids Influence
glucose metabolism;
Aldosterone Kidneys aldosterone promotes Na+
retention, K+ excretion
Adrenal Medulla Epinephrine Heart, Brochioles, and Causes adrenergic
blood vessels stimulation
Heart Atrial natriuretic Kidneys Promotes excretion of
hormone Na+ in the urine
Hypothalamus Releasing and inhibiting Anterior pituitary Regulates secretion of
hormones anterior pituitary
hormones
Small intestine Secretin and Stomach, liver and Inhibits gastric motility
cholecystokinin pancreas and stimulates bile and
pancreatic juice secretion
4. Islets of Langerhans Insulin Many organs Insulin promotes cellular
(pancreas) uptake of glucose and
Glucagon Liver and adipose tissue formation of glycogen and
fat; glucagon stimulates
hydrolysis of glycogen
and fat
Kidneys Erythropoietin Bone marrow Stimulates red blood cell
production
Liver Somatomedins Cartilage Stimulates cell division
and growth
Ovaries Estradiol-17β and Female reproductive tract Maintains structure of
progesterone and mammary gland reproductive tract and
promotes secondary sex
characteristics
Parathyroid glands Parathyroid hormones Bone, small intestine and Increases Ca2+
kidneys concentration in blood
Pineal gland Melatonin Hypothalamus and Affects secretion of
anterior pituitary gonadotrophic hormones
5. Pituitary, anterior Trophic hormones Endocrine glands and Stimulates growth and
other organs development of target
organs; stimulates
secretion of other
hormones
Pituitary, posterior Antidiuretic hormone Kidneys and blood vessels Antidiuretic hormone
Uterus and mammary promotes water retention
Oxytocin glands and vasoconstriction;
oxytocin stimulates
contraction of uterus and
mammary secretory units
Skin 1,25-Dihydroxyvitamin D3 Small intestine Stimulates absorption of
Ca2+
Stomach Gastrin Stomach Stimulates acid secretion
Testes Testosterone Prostate, seminal vesicles Stimulates secondary
and other organs sexual development
Thymus Thymopoietin Lymph nodes Stimulates WBC
6. Throid Gland Throxine (T4) and Most organs Throxine and
triiodothyronine (T3); triiodothyronine
calcitonin promotes growth and
development and
stimulates basal rate of
cell respiration (basal
metabolic rate or BMR);
calcitonin may participate
in the regulation in the
blood Ca2+ levels
8. CHARACTERISTIC NERVOUS SYSTEM ENDOCRINE SYSTEM
Mediator molecules Neurotransmitter released Hormones delivered to
locally in response to nerve tissues throughout the body
response by the blood
Site of mediator action Close to site of release, at a Far from site of release
synapse; binds to receptor in (usually) binds to receptors
postsynaptic membrane on or in target cells
Types of target cells Muscle (smooth, cardiac and Cells throughout the body
skeletal) cells, gland cells,
other neurons
Time to onset of action Typically within millisecond Seconds to hours or days
(thousandths of a second)
Duration of action Generally briefer Generally longer (seconds to
(milliseconds) days)
10. The Role of Hormone Receptors
Hormones like Neurotransmitter, influence their target cells by
chemically binding to specific protein receptors. Only the target
cells for a given hormone have receptors that bind and
recognize that hormone.
Receptors, like other cellular proteins, are constantly being
synthesized and broken down. Generally, a target cell has 2000
to 100,000 receptors for a particular hormone.
11. If a hormone is present in excess, the number of target-cell
receptors may
decrease—an effect called down-regulation. Down-
regulation makes a target cell less sensitive to a
hormone.
In contrast, when a hormone is deficient, the number of
receptors may increase. This phenomenon, known as
upregulation, makes a target cell more sensitive to a
hormone.
13. Circulating and Local Hormones
Circulating hormones—they pass from the secretory cells that make them into
interstitial fluid and then into the blood.
Local hormones, act locally on neighboring cells or on the same
cell that secreted them without first entering the bloodstream.
• Paracrines (para- beside or near) - Local hormones that act on neighboring cells
• Autocrines - act on the same cell that secreted them (auto- self ).
One example of a local hormone is interleukin 2 (IL-2), which is released by helper T cells
(a type of white blood cell) during immune responses. IL-2 helps activate other nearby
immune cells, a paracrine effect. But it also acts as an autocrine by stimulating the
same cell that released it to proliferate.
14.
15. • Local hormones usually are inactivated quickly;
circulating hormones may linger in the blood and exert
their effects for a few minutes or occasionally for a few
hours. In time, circulating hormones are inactivated by
the liver and excreted by the kidneys.
17. 1. Amines
• Hormones derived from amino acids tyrosine and tryptophan
• Include the hormones secreted by the adrenal medulla, thyroid and pineal
glands
2. Polypeptides and proteins
• Polypeptide hormones contain less than 100 amino acids (ex. Antidiuretic
hormone)
• Protein hormones are polypeptides with more than 100 amino acids (ex.
Growth hormones
18. 3. Glycoproteins
• Consist of a long polypeptide (more than 100 amino acids) bound
to one or more carbohydrate groups (ex. FSH and LH)
4. Steroids
• Lipids derived from cholesterol (ex.
Testosterone, estradiol, progesterone and cortisol)
19.
20. Hormone Structure Gland Primary Effects
Antidiuretic hormone 8 amino acids Posterior pituitary Water retention and
vasoconstriction
Oxytocin 8 amino acids Posterior pituitary Uterine and mammary
contraction
Insulin 21 and 30 amino acids Beta cells in islets of Cellular glucose uptake,
(double chain) Langerhans lipogenesis and
glycogenesis
Glucagon 29 amino acids Alpha cells in islets of Hydrolysis of stored
Langerhans glycogen and fat
ACTH 39 amino acids Anterior pituitary Stimulation of adrenal
cortex
Parathyroid hormone 84 amino acids Parathyroid Increase in blood Ca2+
concentration
FSH, LH, TSH Glycoproteins Anterior pituitary Stimulation of growth,
development and
secretory activity of
target glands
21. Hormone molecules can be divided into those that are polar, and therefore
water soluble, and those that are nonpolar, and thus insoluble in water. (in
terms of their actions in target cells)
• Lipophilic hormones – nonpolar hormones soluble in lipids. They can
gain entry into their target cells. These include the steroid hormones
and thyroid hormones.
Steroid hormones are secreted only by 2 endocrine glands:
• Adrenal Cortex – secrete corticosteroids (cortisol and aldosterone)
and small amounts of sex steroid
• Gonads – secrete sex steroids
22. The major thyroid hormones are composed of two derivatives of
the amino acid tyrosine bonded together.
• Tetraiodothyronine (T4) or throxine – contains 4 iodine atoms
• Triiodothyronine (T3) – contains 3 iodine atoms
23. The pineal gland secretes melatonin, hormone derived from the
amino acid tryptophan
The adrenal medulla secretes the catecholamines epinephrine and
norepinephrine which are derived from the amino acid tyrosine.
24. Endocrine Gland Prehormone Active Products Comments
Skin Vitamin D3 1,25-Dihydroxyvitamin D3 Hydroxylation reactions
occur in the liver and
kidneys
Testes Testosterone Dihydrotestosterone DHT and other 5α-
(DHT) reduced androgens are
formed in most androgen-
dependent tissue
E2 is formed in the brain
Estradiol-17β (E2) from testosterone, where
it si beleived to affect
both endocrine function
and behavior; small
amounts of E2 are also
produced in the testes
Thyroid Thyroxine (T4) Triiodothronine (T3) Conversion of T4 to T3
occurs in almost all
tissues
26. Hormone molecules that affect the metabolism of target cells are often
derived from less active ―parent‖ or precursor, molecules.
Insulin for example is derived from proinsulin within the beta cells of islets
of Langerhans of the pancreas.
In some cases, the prohormone itself is derived from an even larger
precursor molecule; in the case of insulin, this molecule is calle
preproinsulin.
Prehormone is used to indicate such precursors of prohormone.
The term prehormone designate those molecules secreted by endocrine
glands that are inactive until changed by their target cells.
28. Regardless of whether a particular chemical is acting as a neurotransmitter
or as a hormone, in order for it to function in physiologic condition:
(1) target cells must have specific receptor proteins that combine with
the regulatory molecule;
(2) the regulation of the regulatory molecule with the receptor proteins
must cause a specific sequence of changes in the target cells; and
(3) there must be a mechanism to quickly turn off the action of the
regulator. This mechanism which involves rapid removal and/or chemical
inactivation of the regulatory molecules, is essential because without an
―off-switch‖ physiological control would be impossible.
30. Synergistic and Permissive Effects
When two or more hormones work together to produce a
particular result, their effects are said to be synergistic. These
effects may be additive or complementary.
• Additive – action of the epinephrine and norepinephrine on the
heart
• Complementary – action of FSH and testosterone
31. A hormone is said to have a permissive effect on the action of a
second hormone when it enhances the responsiveness of a
target organ to the second hormone or when it increases the
activity of the second hormone
-Estrogen has a permissive effect on the responsiveness of the
uterus to progesterone
-Glucocorticoids exert permissive effects on the actions of
catecholamins
-Parathyroid hormones has a permissive effect on the actions of
Vitamin D3
32. Antagonistic Effect
The action of one hormone antagonize the effects of
another.
-Lactation during pregnancy (estrogen and prolactin)
-Antagonism in the action of insulin and glucagon on
adipose tissue
34. The half-life of a hormone – the time required for the plasma concentration
of a given amount of the hormone to be reduced to half its reference level
– ranges from minutes to hours for most hormones (thyroid hormone
however is for several days)
Normal tissue responses are produced only when the hormones are present
within their normal, or physiological, range of concentrations.
When some hormones are taken in abnormally high, or pharmacological,
concentrations, their effects may be different from those produced by
lower, more physiologic, concentrations.
35. Priming Effects
Variations in hormone concentration within the
normal, physiological range can affect the
responsiveness of target cells. This is due in part to the
effects of the polypeptide and glycoprotein hormones on
the number of their receptor proteins in target cells.
More receptors may be formed in the target cells in
response to particular hormones.
Sometimes also called upregulation
Example: GnRH
36. Desensitization and Downregulation
Subsequent exposure to the same concentration of the
same hormone produces less of a target tissue
response. This desensitization may be due to the fact that
high concentrations of these hormones cause a decrease
in the number of receptor proteins in their target cells –
a phenomenon called DOWN REGULATION. (ex. Adipose
cells and testicular cells)
37. In order to prevent desensitization from occuring under
normal conditions, many polypeptide and glycoprotein
hormones are secreted in spurts rather than
continuously. This pulsatile secretion is an important
aspect in the hormonal control in the reproductive
system.
Pulsatile secretion of GnRH and LH is needed to prevent
desensitization (in gonadal function).
