Brief Endocrinology
2015
The Endocrine System
• Exocrine glands - transport their hormones to target tissues via ducts.
• Endocrine• Are ductless &
secrete hormones into bloodstream
Endocrine glands: are those glands that has no ducts so called (ductless) and secret its products (Hormones) directly to the blood as the thyroid and pituitary glands
The functions of the body are regulated by the nervous and the endocrine
system.
A hormone :-
A hormone is a chemical messenger, secreted from endocrine glands, released directly into the blood transported by the circulation to the tissues upon which they exert their effects and exerts a regulatory effect on the body cells
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Hormones•Hormones are made by the gland’s cells, possibly stored, then released
•Circulate throughout the body vasculature, fluids
•Influences only specific tissues:
•target cells that have a receptor for that particular hormone
•A hormone can have different effects on different target cells: depends on the receptor
Target Cell
• A target cell is only a target cell
if it is has a functional receptor
(a protein) for the hormone.
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What is a “receptor”?• It is a protein made by the target cell (protein
synthesis after gene expression)
• The protein is made, then inserted into plasma
membrane, or found in cytoplasm or
nucleoplasm
• The active site on the protein “fits” the hormone
• Acts to convert the signal into a response
Chemical characteristics of hormones
• 1-Proteins and Polypeptides, including hormones secreted by the anterior and posterior pituitary gland, the pancreas (insulin and glucagon), the parathyroid gland (parathyroid hormone), and many others.
• 2- . Steroids hormones:-are derived mainly from cholesterol secreted by the adrenal cortex (cortisol and aldosterone), the ovaries (estrogen and progesterone), the testes (testosterone), and the placenta (estrogen and progesterone
• 3-. Derivatives of the amino acid
• Tyrosine, secreted by the thyroid (thyroxine and triiodothyronine) and the adrenal medullae (epinephrine and norepinephrine)
Regulation of hormone secretion
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Regulation & Communication
Nervous system •System of neurons transmits “electrical” signal to target tissue• release neurotransmitters into a
synapse, affecting postsynaptic cells
Endocrine system• The collection of endocrine glands
makes up the endocrine system.• Glands release hormones into the
blood stream to target cells
Comparison between endocrine and nervous systems
1. Nervous system
2. “wired”3. Chemical
signal at target cell
4. Rapid5. Brief
duration
1.Endocrine system
2.“Wireless”3.Chemical
signal at target cell
4.Slow5.Long
duration
Functional Classification of hormones•Trophic hormone: Acts on another endocrine gland to
stimulate secretion of its hormone. Called trophic hormones; ‘trophic’ means “feed”.
•For example, thyrotropin, or thyroid-stimulating hormone (TSH), stimulates the secretion of thyroid hormones. Adrenocorticotropin, or
adrenocorticotropic hormone (ACTH), stimulates the adrenal cortex to secrete the hormone cortisol. Both trophic hormones are produced by
the pituitary gland; in fact, many trophic hormones are secreted by the pituitary. The pituitary gland is sometimes referred to as the “Master gland” because its hormones regulate the activity of other endocrine
glands.•Nontrophic hormone: Acts on nonendocrine target tissues. For
example, parathormone released from the parathyroid glands acts on bone tissue to stimulate the release of calcium into the blood.
Aldosterone released from the cortical region of the adrenal glands acts on the kidney to stimulate the reabsorption of sodium into the blood.
Major Endocrine Glands1. Hypothalamus2. Pituitary Gland3. Thyroid Gland4. Parathyroid Glands5. Thymus Gland6. Adrenal Glands 7. Pancreas8. Ovaries9. Testes10. Pineal Gland 12
Major endocrine glands in the body
•Hypothalamus is located at the base of the brain. It controls the autonomic nervous system and the endocrine systems. The hypothalamus controls the endocrine system by controlling the pituitary gland. Secretes releasing hormones to cause the pituitary to release its hormones andSecretes inhibiting hormones to turn off secretion of pituitary hormones
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Hypothalamus Hormones• Growth Hormone Releasing Hormone (GH-RH) stimulate GH secretion
• Prolactin Releasing Hormone (PRL-RH) stimulate PRL secretion
• Thyroid Stimulating Hormone Releasing Hormone (TSH-RH) stimulate TSH
secretion
• Adrenocorticotropic Hormone Releasing Hormone (ACTH-RH) stimulate ACTH
secretion
• Melanocyte Stimulating Hormone Releasing Hormone (MSH-RH) stimulate MSH
secretion
• Follicle Stimulating Hormone Releasing Hormone (FSH-RH) stimulate FSH
secretion
• Luteinizing Hormone Releasing Hormone (LH-RH) stimulate LH secretion
The Adenhypophysis•Growth hormone (GH) Causes the body to grow
•Prolactin (PRL): Stimulates lactation (milk production) in females
–Stimulated lacrimation (desire to cry) , Decreased in adolescent males so it decreases desire to cry
•Thyroid Stimulating Hormone (TSH): Causes the thyroid gland to release thyroid hormone
•Adrenocorticotropic hormone (ACTH) :Acts on adrenal cortex to stimulate the release of cortisol ,Helps people cope with stress
•Melanocyte-stimulating hormone (MSH):Darkens skin pigmentation
–Increases during pregnancy: Also has effects on appetite and sexual arousal
•Follicle-stimulating hormone (FSH) :Present in males and females, affects both, Stimulates maturation of sex cells
•Luteinizing hormone (LH) :Induces ovulation in females–Induces testosterone in males 17
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Two divisions:
• Anterior pituitary(adenohypophysis)
• Posterior pituitary(neurohypophysis)
Sits in hypophyseal fossa: depression in sella turcica of sphenoid bone
Pituitary secretes 9 hormonesThe Pituitary
1. TSH2. ACTH3. FSH4. LH5. GH6. PRL7. MSH
8. ADH (antidiuretic hormone), or vasopressin9. Oxytocin
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The first four are “tropic” hormones, they regulate the function of other hormones
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Hormones secreted by the pituitary gland
Anterior pituitary hormonesAnterior pituitary hormones
FSH & LH GH
Anterior Pituitary
GonadsThyroid gland
Mammary glands
Adrenal cortex
TSH Prolactin ACTH
+ + + +
Most tissues
+
protein synthesis;
Lipolysis; &
blood glucose
+ T4;
+ T3
+ thyroid
growth
+ milk;
+ breast dvlp.
regulate ♂
reproductive
system
glucocorticoids estrogen;
progeterone;
+ testosterone
+ gametes; + ovulation;
+ corpus Lut.
The Neurohypophysis
• This is a continuation of the brain; cell bodies of special
neurons in the hypothalamus have axons which go to
the neurohypophysis and synapse on capillaries there.
Instead of releasing neurotransmitter, they release
hormones.
• Oxytocin: Childbirth contractions, milk letdown
• Antidiuretic hormone (ADH)
– Signals kidneys to increase water reabsorption
Humoral Stimulation• Something in the blood is being monitored. When the level of
that substance is too high or low, it stimulates the release of the hormone.
• Examples are insulin, glucagon, parathyroid hormone, and aldosterone.
• When you eat, glucose gets high, releases insulin, which tells cells to take in the sugar. Excess sugar is then converted to glycogen, which is the storage form.
• When glucose is low, glucagon is released, glycogen is broken back down to glucose and released into the blood.
• When blood calcium is low, parathyroid gland hormone tells the intestinal cells to absorb more calcium, and kidneys to reabsorb more Ca++, and stimulates osteoclasts to degrade bone matrix so calcium goes into blood.
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Neuronal Stimulation• Examples are oxytocin, ADH (neurohypophysis
hormones) and Epinephrine (adrenal medulla hormone)
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Hormonal Stimulation • This is when one endocrine gland releases a
hormone that stimulates another endocrine gland to release its hormone.
• Examples are any of the hypothalamus or anterior pituitary hormones, and also the adrenal cortex (steroid) hormones (except aldosterone) and thyroid hormone.
Hormonal regulation of hormone secretion
• Short feedback loop:– Retrograde transport of blood from anterior pituitary to the hypothalamus.
• Hormone released by gonads (estrogen) inhibits anterior pituitary hormone FSH.
• Long feedback loop– Hormone released by gonads (Testosteronee) inhibits anterior
hypothalamic hormone as GnRH
Negative feed back: a hormone from a peripheral
gland, for example, testosterone binds to its receptor on
cells in the hypothalamus and pituitary gland, and inhibit the
secretion of the tropic hormones: FSH
Positive feed back: a hormone from a peripheral gland, for example, estrogen, binds to its receptor on cells in the hypothalamus and adenohypophysis, and has the effect of increasing secretion of tropic hormones LH