Question

Which of the following is not an adipokine? a. Leptin b. adiponectin c. ghrelin d. tumor necrosis factor alpha

Short answer

The correct answer is \(c. \)ghrelin.

Step-by-step solution

Determine if leptin is an adipokine

Leptin is an adipokine secreted by adipose tissue that has several critical roles, including in regulating appetite and energy homeostasis. Since leptin fits the definition of an adipokine, we can move on to the next option. #Step 2: Determine if adiponectin is an adipokine#

Determine if adiponectin is an adipokine

Adiponectin is another adipokine produced by adipose tissue that is involved in regulating glucose levels and fatty acid oxidation. Hence, adiponectin is also an adipokine, so we can move on to the next option. #Step 3: Determine if ghrelin is an adipokine#

Determine if ghrelin is an adipokine

Ghrelin is a hormone produced primarily by the stomach, with smaller amounts produced in the small intestine, pancreas, and brain. It is involved in regulating appetite and stimulating the release of growth hormone. Although it is a hormone, ghrelin is not produced by adipose tissue, making it not an adipokine. #Step 4: Determine if tumor necrosis factor alpha is an adipokine#

Determine if tumor necrosis factor alpha is an adipokine

Tumor necrosis factor alpha (TNF-alpha) is a cytokine, a signaling molecule produced by a variety of cells, including macrophages and adipocytes (fat cells). It is involved in inflammation, immune regulation, and other biological processes. TNF-alpha produced by adipose tissue can be considered an adipokine, as it meets the definition. #Conclusion: Identify which option is not an adipokine#

Conclusion: Identify which option is not an adipokine

Based on our analysis, ghrelin (option c) is the only hormone listed that is not predominantly secreted by adipose tissue and is, therefore, not an adipokine. Thus, the correct answer is \(c. \)ghrelin.

Key concepts

Leptin

Leptin is a well-known adipokine, which means it's a type of hormone that is secreted by fat cells, known as adipocytes. Leptin has a crucial role in regulating energy balance by inhibiting hunger. This function helps to maintain body weight. Simply put, when fat storage increases, leptin signals the brain to reduce hunger and food intake, helping the body maintain energy homeostasis.

• Reduces appetite and regulates energy balance.
• Secreted by adipose tissue.
• Directly influences brain centers that control hunger and energy use.

Without sufficient leptin, or when the brain doesn't respond to it properly (a condition known as leptin resistance), it can lead to overeating and obesity. Understanding leptin is vital for grasping concepts in metabolic disorders and weight management strategies.

Adiponectin

Unlike other adipokines, adiponectin is notably beneficial for metabolism. It is produced in high levels by adipose tissue and has anti-inflammatory effects. One of its primary roles is to enhance the body's sensitivity to insulin, which is key in maintaining healthy glucose levels. This function makes adiponectin an essential player in managing metabolic diseases like diabetes.

• Enhances insulin sensitivity and helps regulate glucose levels.
• Lowers the risk of type 2 diabetes and cardiovascular diseases.
• Supports fatty acid breakdown.

The unique characteristic of adiponectin is that higher levels are associated with being leaner and having better metabolic health, while lower levels are often found in obesity. This understanding is critical for therapeutic approaches aiming to boost adiponectin levels to combat metabolic disturbances.

Ghrelin

Ghrelin is a hormone often known as the "hunger hormone" because it stimulates appetite. Unlike leptin and adiponectin, ghrelin is not an adipokine since it is primarily produced in the stomach. It plays a significant role in signaling hunger to the brain, making you feel the need to eat.

• Produced mainly in the stomach.
• Promotes growth hormone secretion.
• Increases appetite and food intake.

Ghrelin levels rise when the stomach is empty and fall shortly after eating. Understanding ghrelin is important for addressing issues related to appetite regulation, such as obesity and eating disorders. It works in concert with leptin and other metabolic hormones to maintain body weight.

Tumor Necrosis Factor Alpha

Tumor Necrosis Factor Alpha (TNF-alpha) is a cytokine involved in systemic inflammation and is a part of the body’s immune response. Produced by various cell types, including adipocytes, it can be considered an adipokine when secreted by fat cells. TNF-alpha plays a role in several diseases, including cancer, where it was initially discovered.

• Involved in inflammation and immune system regulation.
• Produced by adipocytes and other immune cells.
• Linked to metabolic and inflammatory diseases.

In the context of obesity, TNF-alpha expression is often increased, contributing to insulin resistance that characterizes type 2 diabetes. Understanding TNF-alpha’s involvement in these processes is vital for developing new treatments for metabolic and inflammatory disorders.