Part A: Transport and Metabolism of Hormones
1. Hormone Transport
Hormones are secreted by endocrine glands and then transported to target organs through the bloodstream. Based on their solubility, hormones are transported in two main ways:
- Water-Soluble Hormones (e.g., insulin, adrenaline): Travel freely in the blood and act on receptors on the cell surface.
- Lipid-Soluble Hormones (e.g., steroid hormones, thyroid hormones): Require carrier proteins like albumin or specific globulins to travel in the blood. They can enter cells directly and bind to intracellular receptors.
2. Hormone Metabolism
Hormones are metabolized to inactivate them and remove them from the body. The liver and kidneys play a major role in hormone metabolism and excretion:
- Liver: Modifies hormones through oxidation, reduction, and conjugation, making them easier to eliminate.
- Kidneys: Excrete hormones and their metabolites in urine.
The half-life of a hormone (how long it remains active in the body) depends on its chemical structure. Peptide hormones usually have short half-lives, while steroid and thyroid hormones have longer half-lives.
Part B: Hormones Secreted by the Hypothalamus
The hypothalamus is a region in the brain that controls the pituitary gland and connects the nervous system to the endocrine system. It secretes several important hormones, also called releasing or inhibiting hormones.
Three Hormones Secreted by the Hypothalamus:
- Thyrotropin-releasing hormone (TRH)
- Corticotropin-releasing hormone (CRH)
- Gonadotropin-releasing hormone (GnRH)
Structure and Functions of Gonadotropin-Releasing Hormone (GnRH)
Structure:
- GnRH is a peptide hormone composed of 10 amino acids.
- It is synthesized in the hypothalamus and released in a pulsatile manner into the hypothalamic-pituitary portal system.
Functions:
- GnRH acts on the anterior pituitary gland and stimulates the release of two important gonadotropins:
- Luteinizing Hormone (LH)
- Follicle-Stimulating Hormone (FSH)
- These gonadotropins regulate sexual development, reproductive functions, and gamete production.
- In females, GnRH indirectly controls the menstrual cycle and ovulation.
- In males, it supports sperm production and testosterone secretion.
Conclusion
The transport and metabolism of hormones ensure that these vital chemical messengers reach their target organs effectively and are deactivated at the right time. The hypothalamus plays a central role in hormonal regulation through hormones like GnRH, which orchestrate the function of reproductive organs and maintain hormonal balance.