Oestradiol and Progesterone Regulate Gene Expression in Specific Target Cells
- Hormones like oestradiol and progesterone play key roles in regulating processes in specific target cells by binding to intracellular receptors.
- Their effects are highly localized to particular cell types, such as cells in the hypothalamus or the endometrium, and involve the regulation of gene expression.
Remember that steroid hormones like oestradiol can pass through cell membranes because they are lipid-soluble.
Oestradiol: Regulating Hormone Release in the Hypothalamus
Definition
Oestradiol
A form of estrogen that promotes the growth of the uterine lining (endometrium) and regulates FSH and LH via feedback loops.
- Oestradiol is a steroid hormone produced mainly in the ovaries.
- It plays a central role in the menstrual cycle, influencing reproductive organs and the brain.
- The hypothalamus is a small but critical region in the brain that regulates hormone release.
- Gonadotropin-Releasing Hormone (GnRH): The hypothalamus produces GnRH, which triggers the pituitary gland to release luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
During the follicular phase of the menstrual cycle, rising oestradiol levels eventually trigger a surge in LH, leading to ovulation.
Mechanism of Action
- Entry into the Cell: Oestradiol diffuses through the plasma membrane of hypothalamic cells.
- Binding to Receptor: It binds to an intracellular receptor in the cytoplasm.
- Activation of Gene Expression: The hormone-receptor complex enters the nucleus and acts as a transcription factor, enhancing the production of GnRH mRNA.
- Don’t confuse positive and negative feedback.
- Oestradiol’s effect depends on its concentration and the timing within the menstrual cycle.
