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Chapter 9
Chemistry of Hormones
Hormone-Most hormones can be classified as either amino acid based or steroid bases.
-Others, prostaglandins, are derived from lipids.
Mechanisms of Hormone Action
-Target cells/organs-Specific receptors must be found on the target cells to react to the specific
hormones.
-Precise changes in a cell following hormone binding are specific to the hormone
and cell, but typically one or more of the following occur:
-There are usually two mechanisms by which hormones trigger changes in cells.
Direct Gene Activation:
Second-Messenger System:
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Control of Hormone Release
-Negative feedback mechanisms are the main way of regulating blood levels of
most hormones
-Stimuli that activate the endocrine organs fall into three major categories:
HormonalHumoralNeural-
Major Endocrine Organs- include pituitary, thyroid, parathyroid, adrenal, pineal, and
thymus glands, pancreas and gonads.
-Hypothalamus is also considered an endocrine organ, produces several
hormones
-Pituitary Gland- hangs from a stalk from the inferior surface of the
hypothalamus, has two functional lobes, anterior and posterior.
Anterior Lobe- six hormones released
growth hormone (GH)prolactin (PRL)follicle-stimulating hormone (FSH)luteinizing hormone (LH)thyroid-stimulating hormone (TSH)-
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adrenocorticotropic hormone (ACTH)-
-All protein based chemicals
-All but GH and PRL stimulate their target organs to release other
hormones (tropic)
-All act through second-messengers systems
-All are regulated by hormonal stimuli and, in most cases, negative
feedback.
-Hypothalamus regulates the release of hormones from the anterior
lobe by secreting releasing and inhibiting hormones, delivered by
the portal circulation
Posterior Lobe- releases two hormones
OxytocinAntidiuretic hormone (ADH)Thyroid Gland- located at the base of the throat, bi-lobed, connected by an
isthmus.
-Release three hormones:
thyroxine (T4)triiodothyronine (T3)calcitonin3
Parathyroid Gland- tiny masses of glandular tissue found on the posterior surface
of the thyroid gland.
-Releases one hormone:
Parathyroid hormone (PTH)-
Adrenal Glands- found at the top of the kidneys, two main parts:
Adrenal cortex- outer part of the gland, produces three major groups of
steroid hormones: mineralocorticoids, glucocorticoids, and sex hormones.
Aldosterone-
Cortisone and cortisol-
Adrenal medulla- inner part of the gland, produces two similar hormones:
epinephrine and norepinephrine. Stimulated by the sympathetic NS.
Epinephrine (E) and norepinephrine (NE)-
*See Fig. 9.13 for the Roles of the hypothalamus, adrenal medulla, and adrenal cortex
in the stress response*
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Pancreatic Islets- found within the mixed gland of the pancreas.
-Produces two major hormones; insulin and glucagon.
Insulin-
Glucagon-
Pineal gland- found in the roof of the 3rd ventricle of the brain.
-Still much of a mystery, produces one hormone:
Melatonin-
Thymus- located in the upper thorax
-Large in infants and children, decreases in size as we mature. Produces
one hormone:
ThymosinGonads- ovaries in females, testes in males.
-Ovaries produce two groups of steroid hormones, estrogens and
progesterone.
EstrogensProgesterone-
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-Testes produce androgens, testosterone is the most important.
Androgens-
Other Hormone-Producing Tissues and Organs
-Small intestine, stomach, kidneys, and heart
-Placenta and some tumors also make hormones
-Placenta produces many hormones during pregnancy
-hCG-In the 3rd month, the placenta starts producing and releasing estrogen
and progesterone, ovaries remain inactive for the rest of the pregnancy.
-hPL-relaxin-
Developmental Aspects of the Endocrine System
-Most endocrine organs continue to work smoothly until “old age”
-Menopause in women is the result of reproductive organs beginning to atrophy
-During “old age” efficiency of endocrine tissues declines
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