How do lipid-soluble (steroid) and water-soluble hormones differ in their mechanisms of action?
• Lipid-soluble hormones can move through the lipid bi-layer into a cell where the receptors reside. A hormone receptor complex moves to the DNA to activate genes. • Water-soluble hormones are composed of amino acids and cannot pass through the lipid bi-layer. They attach to receptors on the surface of the cell (first messenger). The second messenger molecule inside of the cell is activated to influence enzymes within the cell. • Compare negative and positive feedback mechanisms with regard to regulation of hormone secretion. Provide an example of each. • A negative feedback system – the pancreas secretes the hormone insulin when blood glucose is high to stimulate glucose storage. When the blood glucose becomes low, the pancreas stops secreting insulin. • A positive feedback system – during childbirth the pituitary secretes the hormone oxytocin to stimulate uterine contractions which in turn stimulate the production of more oxytocin which increases the frequency and intensity of uterin
