Feedback Mechanisms

Set point= Desired level/ norm at which the system operates

Receptor= Dectects any deviation from the set point

Controller= coordinates information from the set pint

Effector= Brings about corrective measures needed to return system to set point

Feedback loop= Informs receptor of the changes to the system brought about by the effector

Occurs when feedback results in the corrective measures being turned off

Having spereate negative feedback mechanisms that control departures from the nrm in either direction give a greater degree of homeostatic control

Occurs when feedback causes corrective measures to remain turned on

Eg. When a stimulus causes sodium ions to enter axon. When more sodium ions enter, the potential difference across the membrane increases and causes sodium gated channels to open, causing an even greater amount of sodium ins to move into the axon 

The pituitary gland is found in the base of the brain and releases two hormones:

• Follicle Stimulating Hormone (FSH)- stimulates the development of follicles in ovary and stimulates follicles to produce oestrogen
• Luteinising Hormone (LH)- cuases ovulation and stimulates the ovary to produce progesterone from corpus luteum

The ovaries prduce two other hormones:

• Oestrogen- produced from growing follicle and causes the rebuilding of the uterus lining. Stimulates the production of LH.
• Progesterone- Maintains the lining of the uterus and inhibits the production of FSH.

• Day 1-5: uterus lining is shed
• Day 1: Pituitary gland produces FSH, which travels in the blood and stimulates follicles to grow/mature. The follicles secrete oestogen which causes the rebuilding of the uterus lining and inhibits the production of FSH and LH from the pituitary gland.
• Day 10: As the follicle grows, it produces increasing amounts of oestrogen, reaching a critical point when it begns to stimulate the prodution of FSH and LH (postive feedback). There is a surge in FSH and LH production
• Day 14: More LH produced causing ovulation and so the matured follicle releases the egg
• Once ovulation has occured, LH stimulates the empty follicle to develop into a corpus luteum, which secretes progesterone and a small amount of oestrogen
• The progesterone maintains the lining of the uterus and inhibits the production of FSH and LH.
• If the egg isn't fertilised the corpus luteum will degenerate and will no longer produce progesterone, so the uterus lining breaks down.
• Since there is less progesterone produced, FSH is no longer inhibited and cycle resumes