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PinkMonkey Online Study Guide-Biology
In adults hypofunction results in myxedema;
the symptoms are a low metabolic rate, reduction in mental and physical
activity, increase in weight, puffy skin, a decrease in heart beat
and body temperature, and loss of hair. When hypofunction results
due to lack of iodine in diet, enlargement of the thyroid results
in a condition called simple goiter (Fig. 22.7 B). In an
effort to capture more iodine from the blood, the gland increases
follicles and grows disproportionately. Hypofunction is treated
with a supply of iodized salt, sea food, and by surgery to remove
excess of thyroid tissue.
In amphibians, thyroxine plays a critical
role during metamorphosis. If thyroid function of an embryo
or young tadpole is inhibited (for example by excising the thyroid
gland), then the animal remains a tadpole permanently. Conversely,
if a young tadpole is given an excess of thyroxin, the larva metamorphoses
prematurely into a tiny froglet.
Hyperfunction results in an increased metabolic
rate (up to (40%), profuse sweating, increased food intake but loss
of weight, high blood pressure, nervous tension and muscular weakness.
Some patients with hyperthyroidism have protruding eyeballs, a condition
called exophthalmos (Figure 22.7 C). The swelling of thyroid
due to hypersecretion produces exophthalmic goiter.
Another hormone produced by the thyroid gland is
calcitonin. It maintains the blood calcium level. Calcitonin
is secreted by the thyroid when there is a high level of calcium
in the blood. The excess Calcium is then decreased and deposited
in bones.
Table
Summary of Pituitary and Thyroid gland Hormones
Glands
Pituitary
Thyroid |
Position
Bottom surface of the brain
Neck region |
Hormone
and main effects
Trophic hormones :
Stimulate the following endocrine glands to release their hormones.
a)Thyroid-Thyrotropin
b) Adrenal-ACTH (Corticotropin)
c) Ovaries & Testes Gonadotropins
Growth hormone:
Somatotropin promotes growth of whole body.
Neurosecretions:
a) ADH(Vasopressin)
Kidney water reabsorption
b) Oxytocin-Uterus contraction.
c) Prolactin-milk secretion
Thyroxine
a) Controls body metabolism energy release in mitochondria
b) Influences growth |
Deficiency
and excess effects
Disorders of normal gland function
Excess : gigantism
Deficiency : dwarfism.
Disorders of normal functions e.g. water regulation, diabetes
Deficiency : Cretinism in adults slowdown metabolism; sluggishness.
Excess: eyeballs protrude, metabolism increased, restlessness
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SUMMARY
(1) The chemicals controlling most systems
of vertebrates are composed of secretory cells, which are
organized into exocrine and endocrine glands.
Endocrine glands secrete hormone into the blood. A
hormone is a biological molecule (chemical transmitter) which
acts on target organs and influences a variety of cellular
activities. (2) Important endocrine organs are the hypothalamus,
pituitary, thyroid, parathyroids, adrenal glands, islets of
Langerhans, testis and ovary. (3) The pituitary, called the
master endocrine gland, is located below the brain, and has
three divisions, i.e. anterior lobe, middle lobe and posterior
lobe. (4) The anterior lobe secretes six hormones, namely
TSH, somatotrophic hormone, FSH, ACTH, LH and prolactin, while
the posterior lobe secretes oxytocin and antidiuretic hormone
(ADH). Middle lobe has no function in humans. (5) Malfunctions
of the pituitary cause various conditions like gigantism,
acromegaly, pituitary infantilism, diabetes insipidus, etc.
(6) The thyroid gland is located in the neck and consists
of thyroid follicles containing colloid. (7) Thyroid secretes
the hormone thyroxin; (8)hypofunctin Hyperthyroidism results
in exophthalmos and exophthalmic goiter. (9) The hormone calcitonin
maintains blood calcium level. (10) Most biological or chemical
control systems work on feed back system.
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Table of Contents
22.0 Introduction
22.1 Pituitary gland
22.2 Thyroid gland
Chapter 23
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