NEGATIVE FEEDBACK MECHANISM

• Positive Feedback Mechanism


  • Occurs when a product feeds back to increase its own production
  • Causes conditions to become increasingly extreme
• Hormones

  • Control many cell activities
  • Important for homeostasis
• Negative Feedback Mechanism

  • The thyroid gland is a good example of this type of regulation
• Positive Feedback Mechanism


  1. As the baby suckles, nerve messages from the nipple cause the pituitary gland to secrete prolactin

  2. Prolactin stimulates the mammary glands to produce milk, so the baby suckles more

  3. This causes more prolactin to be secreted and more milk to be produced
• Ovarian and Menstrual Cycles

  1. Complex interaction of the endocrine and reproductive systems

  2. Begins with the hypothalamus secreting GnRH that stimulates the release of FSH and LH

  3. Known as the ovarian and menstrual cycles
• Hormone Regulation

  1. Hormones alter conditions inside the cell, usually in response to a stimulus

  2. Activated at specific times
• Feedback Mechanisms

  • Loop in which a product feeds back to control its own production
  • Most hormone feedback mechanisms involve negative feedback loops
• Negative Feedback Mechanism


  • Occurs when a product feeds back to decrease its own production
  • Brings things back to normal whenever they start to become too extreme
• Regulation of Testosterone Secretion

  1. If the concentration of testosterone increases, it prevents the production of GnRH by the hypothalamus

  2. If this happens, the release of LH from the anterior pituitary gland also decreases

  3. If LH decreases, the production and secretion of testosterone from the testes also decreases
• Positive Feedback Mechanism

  • milk production by a mother for her baby
• Ovarian cycle


  Tightly coordinated with the menstrual cycle
• Ovarian and Menstrual Cycles

  1. Monthly ovarian cycle regulates the development of the egg in the ovary

  2. Includes development of follicle, secretion of hormones by the follicle, ovulation, and formation of corpus luteum
• Menstrual Cycle

  1. Has four phases - menstruation, follicular phase, ovulation, and luteal phase

  2. Menstruation is the first stage of the menstrual cycle

  3. Thickened lining of the uterus sheds through the vagina during menstruation

  4. Follicular phase involves the development of a dominant follicle and thickening of the endometrium

  5. Rising estrogen levels trigger the release of luteinizing hormone (LH) which starts ovulation

  6. Ovulation is when the ovary releases a mature egg

  7. Luteal phase begins after the egg is released, corpus luteum secretes estrogen and progesterone

  8. Estrogen develops the endometrium, progesterone stimulates the formation of blood vessels in the uterine lining
• The menstrual cycle refers to the series of changes that prepare the body for the implantation of a fertilized egg
• Negative feedback system of females

  • Occurs through a complex interaction of the endocrine and reproductive systems
  • Begins with the hypothalamus secreting GnRH that stimulates the release of FSH and LH