Athena Vale
The human body contains over 600 muscles, which help us perform a wide range of movements and functions, from pumping blood and supporting movement to lifting heavy weights or giving birth. Skeletal muscles, which make up 30-40% of our total body mass, are the most common type of muscle in the body. They are attached to bones and allow us to move. Recent studies have also indicated that skeletal muscles may act as an endocrine organ by secreting interleukin-6 (IL-6) into the systemic circulation. Furthermore, skeletal muscles have been found to secrete an unidentified hormone, which has been named musculin.
| Characteristics | Values |
|---|---|
| Types of muscles | Skeletal, cardiac and smooth muscle |
| Skeletal muscle mass | 30% to 40% of total body mass |
| Skeletal muscle composition | Flexible muscle fibers that range from less than half an inch to just over 3 inches in diameter |
| Skeletal muscle functions | Allow humans to perform a wide range of movements and functions |
| Skeletal muscle as a secretory organ | Secretes interleukin-6 (IL-6) into the systemic circulation |
| Skeletal muscle secretions | 654 proteins, 30 of which are regulated by physical exercise |
| Hormones secreted by skeletal muscle | Musculin |
| Hormones secreted by skeletal muscle cells | Interleukin-7 (IL-7) |
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What You'll Learn
Skeletal muscle as a secretory organ
Skeletal muscles are the most common type of muscle in the body, comprising 30% to 40% of total body mass. They are located between the bones and consist of flexible muscle fibres that contract, allowing movement.
During the past decade, skeletal muscle has been identified as a secretory organ. It has been found to produce, express, and release several hundred secreted peptides, known as myokines. This discovery has provided a new understanding of the role of skeletal muscle in organ crosstalk, including communication with the liver, adipose tissue, pancreas, bones, and brain.
Myokines are cytokines and other peptides that are produced, expressed, and released by muscle fibres. They exert autocrine, paracrine, or endocrine effects, which can regulate the functions of several organs. Secretion of these proteins is often accelerated in response to exercise and muscle contraction. Some of these secreted proteins can improve nutrient metabolism and muscle/bone mass, while others have anti-inflammatory and anti-tumourigenesis effects.
Recent studies have also indicated that skeletal muscle may secrete a hormone called musculin, which acts on the endocrine pancreas to restrain beta-cell mass and inhibit insulin secretion. It also appears to act on the hypothalamus to coordinate neuroendocrine and appetite responses to exercise.
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Muscles secrete interleukin-6 (IL-6)
The human body has more than 600 muscles that help us perform a wide range of movements and functions, from moving our body to breathing and keeping us alive. There are three types of muscles in the human body: skeletal, cardiac, and smooth muscle. Skeletal muscles are voluntary muscles, meaning we control how and when they move and work. Cardiac and smooth muscles are involuntary muscles that our autonomic nervous system controls.
Skeletal muscle, the body's largest endocrine organ, may act as an endocrine organ by secreting interleukin-6 (IL-6) into the systemic circulation. Contracting muscles secrete a variety of immunomodulatory and metabolic factors called myokines, with IL-6 being the foremost among these. IL-6 is an interleukin that acts as both a pro-inflammatory cytokine and an anti-inflammatory myokine. It is encoded by the IL6 gene in humans.
The secretion of IL-6 during exercise has been observed in multiple studies. For instance, a study found that IL-6 levels modestly increased during 2-hour and 3-hour walking trials, suggesting that small frequent increases in IL-6 signalling may be important for the health benefits of regular walking. Another study on the effects of training on exercise-induced muscle damage and IL-6 production found that endurance running increased circulating IL-6 levels. Furthermore, IL-6 is secreted by macrophages in response to specific microbial molecules, referred to as pathogen-associated molecular patterns (PAMPs).
IL-6 has been found to have extensive anti-inflammatory functions and plays a role in preventing obesity, stimulating lipolysis, and reducing abdominal obesity. It is also considered a myokine, a cytokine produced from muscle, which is elevated in response to muscle contraction.
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Muscles secrete an unidentified hormone
The human body has over 600 muscles that help us move, breathe, and stay alive. There are three types of muscles: skeletal, cardiac, and smooth muscles. Skeletal muscles, which are attached to bones, enable us to perform a wide range of movements and functions. They are voluntary muscles, meaning we control their movement. Cardiac muscles, found only in the heart, contract and relax to pump blood through our cardiovascular system. Smooth muscles are involuntary and line the inside of some organs, aiding essential functions like digestion and respiration.
Recent studies have revealed that skeletal muscle may act as an endocrine organ, secreting interleukin-6 (IL-6) into the systemic circulation. Additionally, it is hypothesized that skeletal muscle releases an unidentified hormone. This hypothesis suggests a new understanding of how muscles communicate with other organs, such as the liver, adipose tissue, pancreas, bones, and brain.
Skeletal muscle has been found to produce, express, and release several hundred secreted peptides, known as myokines. These myokines are believed to mediate the health benefits of exercise and play a role in organ crosstalk. Proteomic studies of the secretome of skeletal muscle cells help elucidate the processes governing synthesis, interactions, and adaptations to exercise, aging, and degeneration.
While the specific unidentified hormone mentioned in the prompt was not found in the search results, the evidence suggests that skeletal muscle is indeed a secretory organ with various endocrine functions, including the potential secretion of unidentified hormones or peptides. Further research and studies are likely being conducted to comprehensively understand the complex secretory functions of skeletal muscle and their implications for human health and physiology.
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Muscles secrete myostatin
The human body has more than 600 muscles that help us move, breathe, and perform a wide range of functions. There are three types of muscles: skeletal, cardiac, and smooth muscles. Skeletal muscles are voluntary muscles, meaning we control their movement. They make up 30-40% of our total body mass and are connected to bones through tendons. Cardiac muscles make up the middle layers of the heart and help pump blood through the cardiovascular system. Smooth muscles are involuntary and line the inside of some organs, aiding essential functions like waste removal and lung expansion.
Studies have shown that obese and insulin-resistant human skeletal muscle exhibits increased secretion and expression of myostatin, contributing to metabolic deterioration and potentially type 2 diabetes. This discovery may have therapeutic applications in treating muscle-wasting diseases such as muscular dystrophy.
Myostatin is inactive until a protease cleaves its NH2-terminal portion, resulting in an active COOH-terminal dimer. This dimer binds to the activin type II receptor, initiating a cell signaling cascade in the muscle that includes the activation of SMAD transcription factors. When applied to myoblasts, myostatin inhibits their proliferation and stimulates differentiation or quiescence. In mature muscle, myostatin inhibits Akt, a kinase causing muscle hypertrophy, through protein synthesis stimulation and ubiquitin ligase production.
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Muscles secrete interleukin-7 (IL-7)
Skeletal muscle, which makes up between 30% and 40% of total body mass, has recently been identified as an endocrine organ. This means that skeletal muscles secrete cytokines and other peptides that exert paracrine, autocrine, or endocrine effects. These secretions are called "myokines". The first identified and most studied myokine is interleukin-6 (IL-6). IL-6 was discovered as a myokine due to its increased presence in the circulation during physical exercise.
However, there is no clear evidence that muscles secrete interleukin-7 (IL-7). IL-7 is produced by human follicular dendritic cells and vascular cells, as well as human keratinocytes. IL-7 has been shown to be indispensable for T-cell development in humans and has potent effects on mature T cells. Administration of IL-7 to mice has resulted in an increase in B and T cells, and increased recovery of T cells after bone marrow transplantation. IL-7 has also been examined as a potential immunotherapy agent in human clinical trials for various malignancies and during HIV infection.
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Frequently asked questions
Muscles are pieces of soft tissue that help your body perform a wide range of movements and functions, from pumping blood to supporting movement and lifting heavy weights. There are about 600 muscles in the human body, including skeletal, smooth, and cardiac muscles.
Muscles, particularly skeletal muscles, secrete various substances, including proteins, peptides (myokines), interleukin-6 (IL-6), and a hormone called musculin. These secretions play a role in muscle communication with other organs, such as adipose tissue, liver, pancreas, bones, and brain.
Understanding the secretions of skeletal muscle cells helps us comprehend the processes governing their synthesis, interactions, and adaptations to exercise, ageing, and degeneration. This knowledge can lead to identifying therapeutic targets and biochemical markers for muscle diseases.
Muscle secretions, such as myokines, have been linked to mediating the health benefits of exercise. Additionally, musculin, a hormone secreted by skeletal muscle, may influence the endocrine pancreas, hypothalamus, and neuroendocrine and appetite responses to exercise.
