The principles of feedback mechanisms Flashcards
What stages are involved in homeostatic control of any system?
- Set point - Desired level system operates at
- Receptor - detects changes from set point
- Controller - coordinates information from various sources
- Effector - brings about response to return system to set point
- Feedback loop - Informs receptor of changes to system brought about by the effector
Why is the feedback loop important?
If the information is not fed back to the receptor, the receptor will continue to stimulate the effector leading to an over-correction and causing a deviation in the opposite direction
What are the two types of feedback?
Positive and negative feedback
What is negative feedback?
A series of changes that result in a substance/system being restored to it’s normal level, important in homeostasis
What is positive feedback?
Process which results in a substance that departs from its normal level becoming further from its norm. Occurs when the feedback causes the corrective measures to remain turned on.
What is the advantage of having separate negative feedback mechanisms to control deviations away from normal?
Gives a greater degree of homeostatic control
What does the menstrual cycle involve?
- A follicle developing in the ovary
- Ovulation
- Thickening of the uterus lining for a fertilised egg to be implanted
- Formation of a corpus luteum developing from the remains of a follicle
What is a follicle?
An egg and the protective cells surrounding it
What is ovulation?
An egg being released from the ovaries
What happens if no fertilisation occurs?
The uterus lining breaks down and leaves the body via the vagina (menstruation) marks the end of one cycle ( 5 -7 day bleed i.e. period) and start of another one
Which 4 hormones control the menstrual cycle?
FSH , LH , Oestrogen and Progesterone
Which hormones are produced by the pituitary gland (brain) ?
FSH (follicle stimulating hormone) and LH (Luteinising hormone)
Which hormones are produced by the ovaries?
Oestrogen and progesterone
What is the role of FSH in the oestrous cycle?
Stimulates follicle development in the ovaries and stimulates the follicles in the ovaries to produce oestrogen
What is the role of LH in the oestrous cycle?
Stimulates ovulation and stimulates ovary to produce progesterone from the corpus luteum
What is the role of oestrogen in the oestrous cycle?
Re-develops uterus lining after menstruation and stimulates production of LH from pituitary gland
What is the role of progesterone in the oestrous cycle?
Maintains uterus lining in readiness to receive fertilised egg and inhibits the production of FSH from the pituitary gland
What happens in the first part of the menstrual cycle?
Loss of lining (period) marks day 1, lining passes through cervix and vagina over 4-5 days. From day 1 the pituitary gland releases FSH which stimulate follicles in the ovary to grow and mature. As the follicle grows, it slowly begins to release oestrogen. The low level of oestrogen causing lining to build up again and inhibits release of FSH and LH (negative feedback)
What happens in the second part of the cycle?
As the follicle grows, more oestrogen is produced and by day 10 oestrogen reaches a critical point and there is now high levels, which promote release of FHS and LH (positive feedback). A surge in FSH and LH causes a follicle in the ovary to release it’s egg ( ovulation day 14)
What happens in the third part of the cycle?
After ovulation LH stimulates follicle to develop into a corpus luteum, which secretes progesterone. Progesterone maintains the thick lining of uterus and inhibits release of FSH and LH (negative feedback). If the egg is not fertilised corpus luteum breaks down and no more progesterone is produced, causing the lining to break down, also FSH release is no longer inhibited and therefore resumes and the cycle repeats itself
