Negative Feedback Loop

Definition

A negative feedback loop is a regulatory mechanism in biological systems where the output of a process acts to reduce or inhibit further changes in that output. This process helps maintain homeostasis and balance within the body's physiological systems.

5 Must Know Facts For Your Next Test

1. Negative feedback loops are essential in the regulation of the renin-angiotensin-aldosterone system, growth hormone secretion, and thyroid hormone production.
2. In the renin-angiotensin-aldosterone system, increased blood pressure triggers a decrease in renin secretion, leading to reduced angiotensin II and aldosterone levels, which in turn lowers blood pressure.
3. Growth hormone secretion is regulated by a negative feedback loop, where high levels of growth hormone and insulin-like growth factor-1 (IGF-1) inhibit the release of growth hormone-releasing hormone from the hypothalamus.
4. Thyroid hormone production is controlled by a negative feedback loop involving the hypothalamus, pituitary gland, and thyroid gland. High levels of thyroid hormones suppress the release of thyroid-stimulating hormone (TSH), which in turn reduces thyroid hormone synthesis.
5. Negative feedback loops help maintain homeostasis by counteracting changes and keeping physiological variables within a narrow, optimal range.

Review Questions

• Explain how a negative feedback loop regulates the renin-angiotensin-aldosterone system.
  • In the renin-angiotensin-aldosterone system, a decrease in blood pressure triggers the release of renin from the kidneys, which leads to the production of angiotensin II and the subsequent release of aldosterone from the adrenal glands. Aldosterone then acts on the kidneys to increase sodium and water reabsorption, raising blood pressure. Once blood pressure returns to a normal level, the negative feedback loop is activated, suppressing renin secretion and reducing angiotensin II and aldosterone production, thereby preventing further increases in blood pressure.
• Describe the role of negative feedback loops in the regulation of growth hormone secretion.
  • Growth hormone secretion is controlled by a negative feedback loop involving the hypothalamus, pituitary gland, and target tissues. When growth hormone and its downstream mediator, insulin-like growth factor-1 (IGF-1), reach sufficient levels in the body, they inhibit the release of growth hormone-releasing hormone from the hypothalamus. This, in turn, reduces the secretion of growth hormone from the pituitary gland, preventing further increases in growth hormone and IGF-1 levels. This negative feedback mechanism helps maintain growth hormone within a physiologically appropriate range, ensuring proper growth and development.
• Analyze how negative feedback loops contribute to the regulation of thyroid hormone production.
  • Thyroid hormone production is regulated by a negative feedback loop involving the hypothalamus, pituitary gland, and thyroid gland. The hypothalamus secretes thyrotropin-releasing hormone (TRH), which stimulates the pituitary gland to release thyroid-stimulating hormone (TSH). TSH then acts on the thyroid gland to promote the synthesis and release of thyroid hormones, thyroxine (T4) and triiodothyronine (T3). When T4 and T3 levels are high, they inhibit the release of both TRH and TSH, thereby reducing further thyroid hormone production. This negative feedback mechanism ensures that thyroid hormone levels are maintained within a narrow, optimal range to support various metabolic processes in the body.

Related terms

Homeostasis: The process of maintaining a stable, relatively constant internal environment in a living organism despite changes in external conditions.

Hormone: A chemical substance produced in the body that regulates the activity of cells or organs.

Receptor: A molecule in a cell that binds to a specific substance, such as a hormone or neurotransmitter, and triggers a specific physiological response.