31. Cholesterol derivatives. Synthesis of bile acids, regulation, cholelithiasis. Steroid hormones – general idea about the structure, synthesis and biological role. Synthesis, transport in the blood, activation and biological function of Vitamin D3.

Derivatives of Cholesterol

Cholesterol serves as a precursor for several important molecules in the body, including steroid hormones, vitamin D, and bile acids, each with distinct structures and biological roles.

Steroid Hormones:

• Structure: Steroid hormones are derived from cholesterol and share a common four-ring structure. They are classified into glucocorticoids (e.g., cortisol), mineralocorticoids (e.g., aldosterone), and sex hormones (e.g., estrogen, testosterone).
• Biological Role: Steroid hormones play essential roles in regulating metabolism, stress response, electrolyte balance, and reproductive functions. For example, cortisol regulates glucose metabolism and immune responses, aldosterone regulates electrolyte balance and blood pressure, while sex hormones regulate secondary sexual characteristics and reproductive functions.
• Structure: Vitamin D is derived from cholesterol through a series of biochemical reactions in the skin upon exposure to sunlight. The active form of vitamin D, known as calcitriol, has a steroidal structure with a modified side chain.
• Biological Role: Vitamin D plays a crucial role in calcium and phosphate homeostasis, promoting the absorption of these minerals from the intestine and their deposition in bones. It also regulates immune function, cell growth, and differentiation.