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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.


Summary of Pituitary and Thyroid gland Hormones




Bottom surface of the brain

Neck region
Hormone and main effects

Trophic hormones :
Stimulate the following endocrine glands to release their hormones.
b) Adrenal-ACTH (Corticotropin)
c) Ovaries & Testes Gonadotropins

Growth hormone:
Somatotropin promotes growth of whole body.

a) ADH(Vasopressin)
Kidney water reabsorption
b) Oxytocin-Uterus contraction.
c) Prolactin-milk secretion

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


(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.


Table of Contents

22.0 Introduction
22.1 Pituitary gland
22.2 Thyroid gland

Chapter 23


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