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26.3 Overview
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Thyroid and Pituitary glands-only secrete hormones
Some glands have endocrine and non-endocrine functions
Some organs are primarily non-endocrine but have cells that
secrete hormones
Only sex organs and the cortex of the adrenal gland produce
steroid hormones
Most endocrine glands produce water soluble hormones
Hormones have many different targets
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The Pineal gland-secretes melatonin, a
hormone that links environmental light
conditions with biological rhythms.
The Thymus gland secretes hormones,
including a peptide that stimulates the
development of T cells.
26.5 The Thyroid gland
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Located under larynx and the hormones affect all the tissues of
the vertebrate body
Produces two hormones each with the element iodine
Thyroxine(T4) and Triiodothyronine(T3)
Role is in development and maturation
Cretinism-thyroid deficiency at birth
Also has many important homeostatic functions
Increase the rate of oxygen consumption and cellular
metabolism
Excess=hyperthyroidism
Insufficient=hypothyroidism
26.6 Calcium Homeostasis
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Function in the homeostasis of calcium ions
Calcitonin and parathyroid hormone (PTH)
are secreted by the thyroid and parathyroids
and regulate blood calcium levels
Antagonistic hormones
Calcitonin lowers the calcium level in the
blood where as PTH raises it
26.7 Pancreas
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Produces two hormones that manage the body’s
energy supplies
Clusters of endocrine cells, called islets of
Langerhans, are scattered throughout the Pancreas
Each islet has a population of beta cells, which
produce insulin, and alpha cells, which produce
glucagon
Antagonistic and regulate the concentration of
glucose in the blood
Diabetes Mellitus
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Condition in which a person has a high blood
glucose level because the body doesn’t produce
enough insulin, or because body cells don’t properly
respond to the insulin produced
Hyperglycemia-accumulation of glucose in the blood
Type 1 diabetes
Type 2 diabetes
Gestational diabetes
26.10 The Gonads
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Sex hormones are steroid hormones that affect growth and
development and regulate reproductive cycles and sexual
behavior
Three categories of sex hormones-estrogens, progestins, and
androgens
Estrogens maintain the female reproductive system
Progestins prepare and maintain the uterus to support an
embryo
Androgens stimulate the development and maintenance of the
male reproductive system
Androgens have different effects in other animals
The hypothalamus regulates the synthesis of sex hormones by
the gonads
26.11 Hormones can perform a variety
of functions
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Some hormones can be found in vertebrates that are
only distantly related
The same hormone can have different actions in
different animals
Hormone regulation=early evolutionary adaptation
The Peptide hormone Prolactin (PRL) is a good
example
In humans it performs several important functions
related to childbirth whereas it has a variety of roles
unrelated to childbirth in nonhuman mammals.