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Smooth muscle is present in the walls of hollow organs such as the urinary bladder, uterus, stomach, intestines, and in the walls of passageways, including arteries, veins, and tracts of the respiratory, urinary, and reproductive systems. Smooth muscle is also found in the eyes, where it adjusts the iris size and lens shape, and in the skin, where it causes goosebumps. This muscle type is involuntary, with contractions triggered by hormones, neural stimulation, and local factors. Its unique properties allow it to maintain muscle tone with minimal energy expenditure, making it essential for the functioning of visceral organs.
| Characteristics | Values |
|---|---|
| Type of Muscle | Smooth Muscle |
| Muscle Control | Involuntary |
| Muscle Triggers | Hormones, Neural Stimulation by the ANS, Local Factors |
| Muscle Response to Stretch | Contraction |
| Muscle Response to Stretch Relaxation | Prevents Premature Emptying of Contents |
| Muscle Tone | Maintained with Little Energy Expenditure |
| Muscle Structure | Spindle-Shaped Fibers, Single Nucleus |
| Muscle Fiber Size | 30-200 μm |
| Muscle Fiber Organization | Sheets of Tissue, Gap Junctions |
| Muscle Cell Type | Single-Unit, Multi-Unit |
| Muscle Cell Location | Walls of Hollow Organs, Airways to Lungs, Large Arteries |
| Muscle Cell Function | Synchronous Contraction, Spontaneous Action Potential |
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What You'll Learn
Smooth muscle lines visceral organs
Smooth muscle, also known as visceral muscle, is found in the walls of hollow visceral organs such as the urinary bladder, uterus, stomach, and intestines. It is also present in the walls of passageways, including arteries, veins, and tracts of the respiratory, urinary, and reproductive systems. Smooth muscle is involuntary, meaning it contracts and relaxes without conscious control. This muscle type has unique properties that allow it to maintain muscle tone with minimal energy expenditure, making it well-suited for its functions in various organ systems.
Smooth muscle is composed of thick and thin filaments arranged in a non-striated pattern, giving it a homogeneous appearance under a microscope. Its cytoplasm contains high levels of actin and myosin, the main proteins involved in muscle contraction. The actin filaments attach to dense bodies spread throughout the cell, which can be observed as dark structures under an electron microscope. Additionally, the calcium-containing sarcoplasmic reticulum plays a crucial role in sustaining contractions.
One of the key characteristics of smooth muscle is its ability to maintain muscle tone with very little energy expenditure. This energy efficiency is due to the presence of latch-bridges, which are cross-bridges between myosin heads and actin that can remain linked for extended periods without requiring ATP. This feature is particularly important in visceral organs, where maintaining muscle tone is essential for their proper functioning.
Smooth muscle exhibits a stress-relaxation response, which is crucial for the functioning of hollow organs. As the muscle of a hollow organ stretches, the mechanical stress triggers a contraction. This is immediately followed by relaxation, preventing premature emptying of the organ's contents. This response allows organs like the stomach and urinary bladder to expand and contract smoothly without becoming flaccid when empty.
Smooth muscle plays a vital role in regulating blood flow and pressure in the cardiovascular system by controlling the diameter of blood vessels. It is also found in the gastrointestinal tract, where it aids in the propulsion of food. Additionally, smooth muscle is involved in the urinary system, helping to rid the body of toxins and maintaining electrolyte balance. Overall, smooth muscle is essential for maintaining the body's basic functions and homeostasis.
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Smooth muscle is involuntary
Smooth muscle, or involuntary muscle, is found within the walls of hollow organs and structures such as the esophagus, stomach, intestines, bronchi, uterus, urethra, bladder, blood vessels, and the arrector pili in the skin, in which it controls the erection of body hair. Smooth muscle is not under conscious control, and its contraction is triggered by hormones, neural stimulation by the ANS, and local factors. For example, in the walls of visceral organs, stretching the muscle can trigger its contraction (the stretch-relaxation response).
Smooth muscle is present throughout the body and serves a variety of functions. In the stomach and intestines, it helps with digestion and nutrient collection. It exists throughout the urinary system, where it helps rid the body of toxins and works to maintain electrolyte balance. Smooth muscle is also present in the eyes, where it functions to change the size of the iris and alter the shape of the lens.
Smooth muscle is one of the three major types of vertebrate muscle tissue, the others being skeletal and cardiac muscle. It can be further divided into two subgroups: single-unit and multi-unit. Single-unit smooth muscle consists of multiple cells connected through connexins that can become stimulated in a synchronous pattern from a single synaptic input. This type of smooth muscle is commonly referred to as visceral muscle and is found in the walls of most internal organs, lining blood vessels, the urinary tract, and the digestive tract.
Multi-unit smooth muscle, on the other hand, is found in the trachea, in the iris of the eye, and lining the large elastic arteries. This type of smooth muscle is neurogenic, meaning its contraction must be initiated by an autonomic nervous system neuron. Smooth muscle differs from skeletal and cardiac muscle in terms of structure, function, and regulation of contraction. It demonstrates greater elasticity and function within a larger length-tension curve than striated muscle.
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Smooth muscle is found in the urinary bladder, uterus, stomach and intestines
Smooth muscle is a type of muscle tissue that is present in the walls of hollow organs like the urinary bladder, uterus, stomach, and intestines. It is also found in the walls of passageways such as arteries and veins of the circulatory system, as well as in the tracts of the respiratory, urinary, and reproductive systems. Smooth muscle differs from skeletal muscle in that it is not under voluntary control, and its contraction is triggered by hormones, neural stimulation, and local factors. This quality of involuntary contraction is essential for the body to regulate many of its subsystems without conscious thought, such as adapting blood pressure to meet increasing oxygen demands during exercise.
In the urinary bladder, smooth muscle plays a critical role in preserving contractile tone, which is necessary to prevent conditions like neurogenic bladder disease. Similarly, in the uterus, smooth muscle is responsible for creating the contractile force during childbirth. Pharmaceuticals can be used to enhance smooth muscle contraction in the uterus during labour.
Smooth muscle is also integral to the functioning of the stomach and intestines, where it aids in digestion and nutrient collection. Any damage to the smooth muscle in these organs can have severe consequences, such as gastroparesis, a condition characterised by a loss of motility in the gastrointestinal tract.
Furthermore, smooth muscle is involved in maintaining electrolyte balance and ridding the body of toxins through the urinary system. It also helps regulate blood flow and pressure by controlling the diameter of blood vessels. This regulatory function is vital for the body's basic functions, and its dysfunction can lead to conditions like atherosclerosis and pulmonary hypertension.
The unique properties of smooth muscle, including its ability to tense and relax, make it essential for the proper functioning of various organ systems in the body. Its presence in hollow organs like the urinary bladder, uterus, stomach, and intestines highlights its diverse and critical roles in maintaining human health.
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Smooth muscle lines the eyes and skin
Smooth muscle is one of the three major types of vertebrate muscle tissue, the others being skeletal and cardiac muscle. Smooth muscle is present in the walls of hollow organs like the urinary bladder, uterus, stomach, and intestines. It is also found in the walls of passageways, such as the arteries and veins of the circulatory system, and the tracts of the respiratory, urinary, and reproductive systems.
Smooth muscle is also present in the eyes and the skin. In the eyes, it functions to change the size of the iris and pupil and alter the shape of the lens. This type of muscle is called the ciliary muscle, iris dilator muscle, and iris sphincter muscle. Multi-unit smooth muscle is found in the iris of the eye and the hair erector muscles.
In the skin, smooth muscle causes hair to stand erect in response to cold temperatures or fear. This is also known as piloerection or goosebumps. The skin also contains blood vessels that respond to norepinephrine and epinephrine, producing vasoconstriction.
Smooth muscle is not under voluntary control and is, therefore, called involuntary muscle. The triggers for smooth muscle contraction include hormones, neural stimulation by the autonomic nervous system, and local factors. For example, in the walls of visceral organs, stretching the muscle can trigger its contraction (the stretch-relaxation response). Smooth muscle cells contract slower than skeletal muscle cells, but they are stronger and require less energy.
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Smooth muscle lines arterioles
Smooth muscle, so-called because the cells do not have striations, is found in the walls of hollow organs like the urinary bladder, uterus, stomach, and intestines. It is also present in the walls of passageways, such as the arteries and veins of the circulatory system, and the tracts of the respiratory, urinary, and reproductive systems.
The diameter of an arteriole is determined by neural and chemical controls, and vasoconstriction and vasodilation in the arterioles are the primary mechanisms for distributing blood flow. Each smooth muscle cell in an arteriole has its own neuron that receives signals to expand or contract, allowing the arteriole to adjust its diameter and control blood pressure and flow.
Arterioles have three layers: the tunica intima, which is a critical endothelial lining; the tunica media, which is a middle layer with smooth muscle cells and elastic tissue; and the tunica externa, which is an outer layer of connective tissue, collagen fibers, and nerve endings. The tunica media is restricted to one or two smooth muscle cell layers in thickness. The muscle fibers in arterioles are normally slightly contracted, allowing them to maintain a consistent muscle tone, similar to the muscular tone of skeletal muscle.
Vascular smooth muscle, which makes up most of the walls of blood vessels, contracts or relaxes to change the volume of blood vessels and local blood pressure. This mechanism is responsible for redistributing blood within the body to areas where it is needed, such as areas with temporarily enhanced oxygen consumption.
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Frequently asked questions
Smooth muscle lines hollow organs.
Smooth muscle is so-called because the cells do not have striations.
Smooth muscle is found in the walls of hollow organs like the urinary bladder, uterus, stomach, intestines, and in the walls of passageways, such as arteries and veins.
No, smooth muscle is not under voluntary control. It is, therefore, called an involuntary muscle.
Smooth muscle contraction can be triggered via hormones, neural stimulation by the ANS, and local factors.
