UNIT 5 BIOLOGY: FEEBACK MECHANISMS

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  • Created by: dom
  • Created on: 13-04-15 13:53

OESTROUS CYCLE

LASTS 28 DAYS ,IT INVOLVES:

  • A FOLLICLE DEVELOPING IN OVARY
  • OVULATION - EGG RELEASED 
  • UTERUS LINGINNG BECOMING THCIKER SO THAT A FERTILISED EGG CAN IMPLANT 
  • A STRUCYRE CALLED A CORPUS LUTEUM DEVELOPING IN REMAINS OF FOLLICLE 

IF NO FERTILISATION, THE UTERUS LINING BREAKS DOWN AND LEAVE THE BODY THROUGH VAGINA - MEUSTRATION 

CONTRLLED BY ACTION OF 4 HORMONES:

  • FOLLICLE STIMULATING HORMONE - stimulates folicle to develop - secreted by pitutary gland
  • LUTENISING HORMONE - stimulates ovulation and corpus luteum to develop - secreted by pitutary gland
  • OESTROGEN - stimulates uteruslining to thicken - secreted by ovaries 
  • PROGESTERONE - maintains the thick uterus linng - ovaries 
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PROCESS

  • begins when uterus lining is shed days 1-5
  • from day 1 pitutary gland releases FSH into blood which stimulates follicles in ovary to grow 
  • growing follicles secrete oestrogen - helping uterus lining to build up - inhibits the release of FSH AND LH = negative feedback 
  • as follicles grow more oestrogen is produced - until around day 10 where it stimulates pituatary gland to release more FSH AND LH = postive feedback 
  • surge in FSH AD LH, surge in LH causes one of follicles in ovary to release egg - ovulation occurs on day 14 
  • after ovulation - LH stimulates empty follicle to form into corpus luteum - which secretses progesterone 
  • progesterone maintains thick lining and inhibits release of FSH AND LH = negative feeback
  • if egg is not fertilised - corpus luteum degenerates - no more progesterone
  • no more progesterone means uterus lining breaks down 
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