NEGATIVE FEEDBACK MECHANISM | FERTILIZATION

• Hormone regulation must be activated at a specific time
• Hormones alter conditions inside the cell, usually in response to a stimulus.
• Hormones control many cell activities, so they are very important for homeostasis
• Most hormones are regulated by feedback mechanisms. To return to its normal state/homeostasis
• homeostasis - state of balance to function correctly
• A feedback mechanism is a loop in which a product feeds back to control its own production. Most hormone feedback mechanisms involve negative feedback loops.
• Positive feedback occurs when a product feeds back to increase its own production. This causes conditions to become increasingly extreme
• As the baby suckles, nerve messages from the nipple cause the pituitary gland to secrete prolactin. Prolactin, in turn, stimulates the mammary glands to produce milk, so the baby suckles more
• Negative feedback occurs when a product feeds back to decrease its own production. This type of feedback bring things back to normal whenever they start to become too extreme.
• Thyroid gland is controlled by the negative feedback loop.
• Here’s how the thyroid regulation works:

  1. The hypothalamus secretes thyrotropin-releasing hormone, or TRH.
  2. TRH stimulates the pituitary gland to produce thyroid stimulating hormone, or TSH.
  3. TSH, in turn, stimulates the thyroid gland to secrete its hormones
• When the level of thyroid hormones is high enough, the hormones feedback to stop the hypothalamus from secreting TRH and the pituitary from secreting TSH.

  Without the stimulation of TSH, the thyroid gland stops secreting its hormones. Soon, the level of thyroid hormone starts to fall too low
• In males, the secretion of testosterone is controlled by the negative feedback system. If the concentration of testosterone increases, it prevents the production of GnRH by the hypothalamus. If this happens, the release of LH from the anterior pituitary gland also decreases. If LH decreases, the production and secretion of testosterone from the testes also decreases.
• The negative feedback system of females occurs through a complex interaction of the endocrine and reproductive systems.

  It begins when the hypothalamus secretes GnRH that stimulates the release of FSH and LH.

  These cycles are known as the ovarian and menstrual cycles.
• The monthly ovarian cycle regulates the development of the egg in the ovary. It includes the development of follicle, secretion of hormones by the follicle, ovulation and formation of corpus luteum.
• The menstrual cycle refers to the series of changes that prepare the body for the implantation of a fertilized egg. The ovarian cycle is tightly coordinated with the menstrual cycle.
• The menstrual cycle has four phases – menstruation, follicular phase, ovulation, and luteal phase
• The menstruation is the first stage of the menstrual cycle. This phase starts when an egg from the previous cycle isn’t fertilized. Because pregnancy hasn’t taken place, levels of the hormones estrogen and progesterone drop
• The thickened lining of the uterus is no longer needed, so it sheds through the vagina. During menstruation, a combination of blood, mucus, and tissue from the uterus is released
• the ovarian cycle occurs in the cortex of the ovary, whereas the menstrual cycle occurs in the uterus.
• the ovarian cycle prepares the egg for fertilization and reproduction; the menstrual cycle prepares the uterine wall to receive a fertilized egg/ possible implantation
• A corpus luteum is a mass of cells that forms in an ovary. The source of progesterone and it produces a dominant follicle.
• Ovulation is part of the ovarian cycle.

  During the ovarian cycle, follicles in the ovaries mature and rupture. They release an oocyte into the uterine tube in a process called ovulation
• 4 PHASES OF MENSTRUAL CYCLE: Menstruation, Follicular Phase, Ovulation, Luteal Phase
• The menstruation is the first stage of the menstrual cycle. This phase starts when an egg from the previous cycle isn’t fertilized. Because pregnancy hasn’t taken place, levels of the hormones estrogen and progesterone drop.
• The next phase of the cycle is called the follicular phase.

  The hypothalamus will send GnRH to the pituitary gland to release FSH and LH. These will cause a few follicles to develop to maturity.
• Dominant follicle - release estrogen, nourish egg, thicken the endometrium of uterus
• Atretic Follicles - ovarian follicles that began to mature but did not become a dominant follicle which will disintegrate.
• Rising estrogen levels during the follicular phase trigger the pituitary gland to release luteinizing hormone (LH).

  This is what starts the process of ovulation.
• Ovulation is when the ovary releases a mature egg. The egg travels down the fallopian tube.
• Ovulation lasts about 24 hours. After a day, the egg will die or dissolve if not fertilized.
• The luteal phase begins after the egg is released. As the egg moves from the ovary to the fallopian tube, the follicle transforms into corpus luteum.
• The corpus luteum will continue the secretion of estrogen and will also begin to secrete progesterone.
• At day 14 of the cycle, the rising estrogen develops the endometrium of the uterus. The progesterone stimulates the formation of blood vessels in the uterine lining.
• Regulation of Testosterone Secretion

  1. Stimulus
  2. Hypothalamus
  3. Pituitary Gland
  4. FSH and LH
  5. Testes
• Thermostat - regulates the temperature and controls aircon
• Steroids can cause infertility and has synthetic hormone
• Azoospermia - no sperm in ejaculate and may happen in vasectomy
• Human Chorionic Gonadotropin

  in pregnancy, possible if you are delayed after a month.
• 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