Mechanisms of Hormone Action

Summary

The endocrine system plays a crucial role in regulating homeostasis in the body by using hormones to communicate over long distances. Hormones are classified into three types: amino acid derivatives, peptide hormones, and lipid derivatives (steroids). These hormones exert their effects on target cells through two main mechanisms: non-steroid action, involving a signaling cascade with cAMP as a second messenger, and steroid action, where lipophilic hormones enter cells and alter gene activity. Examples include melatonin, oxytocin, epinephrine, and sex hormones like estrogen and testosterone.

Takeaways

• 😀 The endocrine system is essential for communication within the body and helps maintain homeostasis by regulating various physiological functions.
• 😀 Hormones are chemical messengers secreted by glands and travel through the bloodstream to affect target cells.
• 😀 There are three main types of hormones: amino acid derivatives, peptide hormones, and lipid derivatives (steroid hormones).
• 😀 Amino acid-derived hormones, such as melatonin, come from amino acids like tyrosine and tryptophan, which are found in foods like turkey, chocolate, and milk.
• 😀 Peptide hormones are composed of chains of amino acids, with examples including thyroid-stimulating hormone, oxytocin, and prolactin.
• 😀 Lipid derivative hormones (steroids) are lipophilic, meaning they have an affinity for fat and circulate in the blood bound to carrier proteins, allowing them to remain in circulation longer.
• 😀 There are two primary mechanisms through which hormones affect target cells: non-steroid action and steroid action.
• 😀 Non-steroid action is employed by amino acid and peptide hormones. These hormones cannot cross the cell membrane, so they bind to cell surface receptors, triggering a signaling cascade inside the cell.
• 😀 The non-steroid action involves a G-protein linked to an enzyme that converts ATP to cyclic AMP (cAMP), a second messenger that initiates a chain of events leading to a cellular response.
• 😀 Examples of hormones using the cyclic AMP mechanism include ACTH, calcitonin, epinephrine, glucagon, parathyroid hormone, and ADH.
• 😀 Steroid hormones, being lipophilic, can pass through the cell membrane, bind to intracellular receptors, and affect gene activity, leading to increased transcription and protein production within the cell.
• 😀 Examples of hormones using the steroid mechanism include testosterone, estrogen, progesterone, aldosterone, and calcitriol.

Q & A

What is the role of the endocrine system in the body?

The endocrine system is responsible for regulating a stable internal environment (homeostasis) and allowing the body to communicate over long distances through the secretion of hormones.

What are hormones and how do they work?

Hormones are chemicals secreted by glands into the bloodstream. They travel through the circulatory system to exert effects on target cells, helping to regulate various physiological processes.

What are the three basic groups of hormones?

The three basic groups of hormones are amino acid derivatives, peptide hormones, and lipid derivatives (steroid hormones).

What are amino acid derivatives, and can you give an example?

Amino acid derivatives are small molecules derived from amino acids like tyrosine and tryptophan. An example is melatonin, a hormone that regulates the sleep-wake cycle.

What are peptide hormones, and can you name some examples?

Peptide hormones are made up of chains of amino acids. Examples include thyroid-stimulating hormone, oxytocin, and prolactin.

How do lipid derivatives or steroid hormones differ from other hormones?

Lipid derivatives, or steroid hormones, are lipophilic, meaning they can easily pass through cell membranes. They are typically bound to carrier proteins in the bloodstream, which allows them to stay in circulation longer than other hormone types.

What are the two main mechanisms by which hormones exert their effects on target cells?

The two main mechanisms are non-steroid action (used by amino acid and peptide hormones) and steroid action (used by lipid derivatives or steroid hormones).

How do non-steroid hormones affect target cells?

Non-steroid hormones bind to receptors on the cell surface, triggering an intracellular signaling cascade that involves proteins like G-proteins and second messengers like cyclic AMP (cAMP), which eventually alter the enzymatic activity in the target cell.

What is the role of cyclic AMP (cAMP) in non-steroid hormone action?

Cyclic AMP (cAMP) acts as a second messenger in non-steroid hormone action. It is produced when an enzyme, activated by a G-protein, converts ATP into cAMP. This molecule triggers a cascade of events that alters the cell's enzymatic activity, leading to a target cell response.

How do steroid hormones exert their effects on target cells?

Steroid hormones, being lipophilic, can freely cross the cell membrane and either bind to intracellular receptors or directly enter the nucleus. This interaction leads to changes in gene activity, increasing mRNA production and protein synthesis within the cell.