UNIT 5 BIOLOGY: FEEBACK MECHANISMS

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 

• 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