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Class-11 Biology CHAPTER-22

CHEMICAL COORDINATION AND
INTEGRATION

In animals, control and coordination is performed by neural system and endocrine system

jointly. As the nerve fibres do not innervate all cells of the body, the endocrine system is
required to coordinate the functions.

Endocrine Glands

• Endocrine glands are ductless glands. They release their secretion directly into blood
which is then transported to specific target organs to initiate a particular metabolic

change.

• The endocrine glands secrete chemicals called hormones.

• Hormones are non-nutrient chemicals which act as intercellular messengers and are

produced in trace amount.

Human Endocrine System

The endocrine glands and hormone producing tissues/cells are located in different parts of

the body. Gastrointestinal tract, kidney, liver and heart also produce small quantity of
hormones to control and coordinate the function of respective organs.

Hypothalamus contains several groups of neurosecretory cells called nuclei which produce

hormones. Hormones released by Hypothalamus regulate the synthesis and secretion of
pituitary hormones.

Hypothalamus produces two types of Hormones:

• The hormones released from hypothalamus reaches the anterior pituitary through

portal circulatory system and regulate its function.
• The posterior pituitary is under direct control of hypothalamus.

Pituitary Gland is located in sella tursica, a bony cavity. It is attached to the hypothalamus

by a stalk.

• Excess secretion of Growth Hormone causes over growth of the body leading to

gigantism and low secretion causes stunted growth called dwarfism.

• Prolactin stimulates growth of mammary gland and production of milk.
• TSH stimulates production and release of thyroid hormone.