steroid hormone signalling

oestradiol and progesterone:

• oestradiol and progesterone are made in the overies

• there are oestradiol receptors in the hypothalamus

• the hypothalamus controls activity of the pituitary gland

• oestradiol causes the pituitary gland to release FSH and LH

• progesterone has direct effects on the lining of the uterus

• progesterone causes thickening and increased blood vessel formation in endometrium

• at the end of the menstrual cycle progesterone levels drop leading to shedding of the endometrium

• if embryo implants in endometrium, progesterone levels stay high

  negative feedback = a stimulus causes a response that decreases the stimulus

• if blood sugar rises beta cells secrete insulin causing cells to uptake glucose converted to glycogen or fat which decreases blood sugar levels

• if blood sugar levels drop alpha cells secrete glucagon causing a breakdown of glycogen in to glucose which raises blood sugar levels.

positive feedback = a stimulus causes a response that increases the stimulus

Fruit ripening:

• ethylene is produced by ripe fruit.

• ethylene gas is detected by nearby fruit

• nearby fruit begins to ripen causing it to release ethylene gas

Fever:

• body temperature increases in response to infection

• increased body temp increases metabolism

• increased metabolism increases body temperature

• this continues until fever breaks