Feedback Loops Normal endocrine function depends on the normal plasma levels of

Feedback loops normal endocrine function depends on

This preview shows page 2 - 4 out of 14 pages.

Feedback Loops - Normal endocrine function depends on the normal plasma levels of hormones. Life-threatening complications develop when the glands hypersecrete or hyposecrete hormones. It “knows” through a negative feedback control loop . The pattern of adrenocorticotropic hormone (ACTH) and cortisol secretion is one example of a negative feedback loop. ACTH, secreted by the anterior pituitary gland, stimulates its target organ (adrenal cortex) to secrete cortisol. As blood levels of cortisol increase, the cortisol in the blood chemically “tells” the anterior pituitary gland to slow further secretion of ACTH. The diminished ACTH, in turn, decreases the secretion of cortisol by the adrenal cortex. 1. What information was fed back to the anterior pituitary gland? It was the increasing level of cortisol in the blood. 2. What was the response of the anterior pituitary gland? The gland decreased its secretion of ACTH. Because the cortisol diminished the secretion of the anterior pituitary gland, the response is referred to as negative feedback control. 3. Why doesn’t the adrenal cortex completely stop its secretion of cortisol? Over time, the plasma level of cortisol declines as the hormone is degraded and eliminated from the body; the negative inhibition by cortisol is relieved, and ACTH is again secreted. A positive feedback loop causes an enhanced response, a self- amplification cycle in which a change is the stimulus for an even greater change in the same direction. For example, during early labor, the head of the baby stretches the cervix, the neck of the uterus. The stretch causes nerve impulses to travel from the cervix to the brain, which in turn causes the secretion of a hormone called oxytocin. The oxytocin is carried by the blood to the uterus, where it stimulates the contraction of the uterus. In response to uterine contraction, the cervix is stretched further by the baby’s head, causing the release of additional oxytocin. This positive feedback cycle continues until the
Image of page 2

Subscribe to view the full document.

baby is born. Positive feedback loops are often designed to produce a rapid response. Biorhythms Blood levels of most hormones are also controlled by biorhythms. A biorhythm is a rhythmic alteration in a hormone’s rate of secretion. Some hormones, such as cortisol, are secreted in a circadian rhythm. A circadian rhythm is a 24-hour rhythm; its pattern repeats every 24 hours. Because of its circadian rhythm, cortisol secretion is highest in the morning hours (peak at 8 AM) and lowest in the evening hours (lowest at midnight). Control by the Central Nervous System The CNS helps control the secretion of hormones in two ways: activation of the hypothalamus and stimulation of the sympathetic nervous system In fact, the functions of the nervous system and the endocrine system are so closely related that the word psychoneuroendocrinology is used.
Image of page 3
Image of page 4

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Ask Expert Tutors You can ask 0 bonus questions You can ask 0 questions (0 expire soon) You can ask 0 questions (will expire )
Answers in as fast as 15 minutes