University:
Winston-Salem Forsyth County Schools
Course:
AP Biology
Academic year:

2014
Views:

437

Pages:

1
Author:

owalenzacvjp

Section 1 - The Endocrine System The endocrine system produces chemicals that control many of the body's daily activities. The endocrine system also regulates long-term changes, such as growth and development. The endocrine system is made up of glands. Endocrine glands produce and release their chemical products directly into the bloodstream. The blood then carries those chemicals throughout the entire body. The chemical product of an endocrine gland is called a hormone. Hormones turn on, turn off, speed up, or slow down the activities of different organs and tissues. Because hormones are carried by blood, they can regulate activities in tissues and organs far from the glands that produced them. Hormones are released when nerve impulses travel to the brain and are interpreted. The brain then sends a nerve impulse to a speciﬁc endocrine gland. The gland then releases the hormone into the bloodstream. A hormone interacts only with certain target cells, cells that recognize the hormone's chemical structure. A hormone and its target cell ﬁt together the way a key ﬁts into a lock. The endocrine glands include the hypothalamus, pituitary, thyroid, parathyroid, adrenal, thymus, and pancreas. They also include the ovaries in females and testes in males. The nervous system and the endocrine system work together. The hypothalamus, a tiny part of the brain near the middle of your head, is the link between the two systems. Nerve messages controlling sleep, hunger, and other conditions come from the hypothalamus. The hypothalamus plays a major role in maintaining homeostasis. The pituitary gland is located just below the hypothalamus. The pituitary gland communicates with the hypothalamus to control many body activities. Nerve impulses or hormone signals from the hypothalamus cause the pituitary gland to release hormones. Some hormones from the pituitary gland turn on other endocrine glands. Other pituitary hormones control body activities directly. Pituitary hormones regulate growth from infancy to adulthood and the amount of water in the blood. The type of signal used in a heating system is called negative feedback because the system is turned off by the condition it produces. For example, suppose you set a thermostat at 20°C. If the temperature falls below 20°C, the thermostat signals the furnace to turn on. Once the furnace heats the room to the proper temperature, the thermostat sends a negative signal to the furnace that means "no more heat.” Many hormones are controlled by a negative feedback system. Through negative feedback, when the amount of a particular hormone in the blood reaches a certain level, the endocrine system sends signals that stop the release of that hormone. Negative feedback is an important way that the body maintains homeostasis.