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Flashcards in Feedback Mechanism Deck (14)
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Why do hormones only affect target cells

  • Other cells do not have the specific (oestrogen) receptors;


How can a corpus luteum in the left ovary prevent the development of a mature follicle in the right ovary?

  • Secretes progesterone
  • This inhibits FSH secretion by negative feedback
  • FSH normally stimulates follicle development
  • Hormones link by blood


Evidence for Ovulation from LH and Oestrogen conc

  1. Rise in oestrogen as this is associated with LH surge. It indicates increased follicle maturity/
  2. Decrease in oestrogen as Follice breaks down;
  3. Surge in LH before ovulation as it stimulates the release of egg;
  4.  Fall in LH after ovulation as its Inhibited by progesterone;


How is LH involved in the control of oestrous cycle?

  • LH is an hormone secreted by the pituitary gland
  • It causes ovulation at high concentration
  • stimulate growth of corpus luteum
  • Corpus luteum breaks down if fertilisation does not occur



  • Made by the developing follicle
  • Secreted by ovaries
  • causes uterus lining to thicken


Describe positive feedback with LH and Oestrogen

  • When Oestrogen conc is high, it stimulates the P gland to secrete FSH and LH
  • LH causes ovaries to secrete more oestrogen, which facilitates LH secretion. 
  • This leads to even more LH (surge)


When is fertilisation most likely to occur?

When FSH and LH both peak


How can you tell if there was unsuccessful pregnancy

  • If Progesterone decreases. The corpus luteum must have been broken down
  • Or if LH and FSH both start to increase again in another cycle



Describe the menstrual cycle

  1. FSH secreted by pituitary gland;
  2. Stimulates growth of follicle;
  3. Ovary and follicle cells produce oestrogen;
  4. This initially Inhibits secretion of FSH (Negative feedback)
  5. Oestrogen stimulates secretion of LH from pituitary gland;
  6. Oest causes lining thickening 
  7. LH spike stimulates ovulation;
  8. High LH causes corpus luteum to form, which secretes progesterone
  9. Prog inhibits FSH and LH secretion
  10. it also maintains lining


How does oestrogen act as a contraceptive

  • Inhibits FSH secretion (at low levels) 
  • So follicles don't develop;
  • Ovulation can't occur 
  • No fertilisation occurs


Describe negative feedback with LH and progesterone

  • LH increases
  • Leads to ovulation and formation of CL
  • CL secretes progesterone;
  • Progesterone inhibits LH;
  • Leading to a fall in LH ;


Describe negative feedback of FSH and Oestrogen

  • High FSH causes follicles to develop
  • Also causes ovaries to secrete oestrogen
  • Growing follicle releases oestrogen, leading to inc in con
  • Oestrogen inhibits FSH secretion
  • Leads to a fall in FSH conc


 Role of corpus luteum in early pregnancy 

  • Secrete progesterone which maintains uterine lining 
  •  Progest Stimulates growth of blood vessels in uterus lining 


When should eggs be extracted from a human?

At ovulation (spike in LH)