Smooth muscle plays a role in a large number of diseases affecting blood vessels, the respiratory tract (asthma), the digestive system (irritable bowel syndrome), and the urinary tract (urinary incontinence). However, these diseases are not usually confined just to the muscular tissue, and affect other tissues too.
Lesson Summary
The human body has three types of muscle tissue: skeletal, smooth, and cardiac.
One of the main characteristics of skeletal muscle tissue is its ability to contract. Nearly all movement in the body is the result of muscle contraction.
Cardiac and skeletal muscles contain highly-regular arrangements of bundles of protein fibers that give them a striped appearance. Smooth muscle does not have such bundles of fibers, and so is not striated.
In addition to movement, muscle contraction also fulfills some other important functions in the body, such as posture, joint stability, and heat production.
Skeletal muscle fibers respond to the neurotransmitter acetylcholine.
The thick myosin filament has small extensions or “heads,” that “walk” along the thin actin filaments during a muscle contraction. In this way the thick filament slides over thin filament, and the muscle fiber shortens.
Muscle fibers need ATP to contract and to relax.
Muscle tissue is built up in the process of hypertrophy, and is lost in the process of atrophy.
Review Questions
Distinguish between striated and non-striated muscle.
Distinguish between voluntary and involuntary muscle.
Identify the three types of muscle in the body, and give an example of where each type is found.
Which type of muscle cell is multinucleated?
Is the quadriceps muscles in the leg an example of a smooth muscle? Explain your answer.
Which type of muscle cell metabolism results in the greater production of ATP, aerobic or anaerobic? Give a reason for your answer.
Describe the components of a sacromere.
Distinguish between fast twitch and slow twitch muscle fibers.
After an athlete has completed a 100 meter sprint, his or her breathing rate will be greatly increased, and they need time to “catch their breath.” Can you identify the process that leads to a person needing to catch their breath?
Further Reading / Supplemental Links
Anatomy and Physiology © 2002 Elaine Marieb. Published by Pearson Education Inc. as Benjamin Cummings.
Biology 6th Edn. © 2002 Campbell and Reece. Published by Pearson Education Inc. as Benjamin Cummings.
Zierath JR, Hawley JA (2004) Skeletal Muscle Fiber Type: Influence on Contractile and Metabolic Properties. PLoS Biol 2(10): e348 doi:10.1371/journal.pbio.0020348; Available online at:
http://biology.plosjournals.org/perlserv/?request=getdocument&doi=10.1371/journal.pbio.0020348
Published: October 12, 2004.
http://training.seer.cancer.gov/module_anatomy/unit4_1_muscle_functions
http://www.nismat.org/physcor/muscle
http://www.berkeley.edu/news/media/releases/2006/04/19_lactate
http://www.cdc.gov/nccdphp/dnpa/physical/components/index
http://www.cdc.gov/nccdphp/dnpa/physical/terms/index
http://muscle.ucsd.edu/musintro/hypertrophy
http://www.physsportsmed.com/issues/2002/07_02/puffer
http://www.nlm.nih.gov/medlineplus/ency/article/000688
http://www.imcpl.org/kids/guides/health/muscularsystem
http://training.seer.cancer.gov/module_anatomy/unit4_1_muscle_functions
http://en.wikipedia.org
Vocabulary
actin
A thread-like protein filament that is involved in muscle contraction.
aerobic respiration
The breakdown of food energy to generate ATP, occurs in the presence of oxygen.
anaerobic glycolysis (anaerobic respiration)
The breakdown of stored energy in the absence of oxygen to produce ATP.
atrophy
The loss of muscle mass.
cardiac muscle
Involuntary muscle that makes up the heart.
delayed onset muscle soreness (DOMS)
The pain or discomfort often felt 24 to 72 hours after exercising and generally goes away within 2 to 3 days, caused by tiny tears in muscle fibers.
extensor
A muscle that causes the angle of a joint to become larger.
flexor
A muscle that causes the angle of a joint to become smaller.
hypertrophy
The growth in size of muscle fibers and muscles.
isometric contraction
Occurs when the muscle remains the same length despite building tension.
isotonic contraction
Occurs when tension in the muscle remains constant despite a change in muscle length.
muscle contraction
The generation of tension in a muscle fiber by the movement of actin and myosin.
motor unit
A group of individual muscle fibers along with their motor neuron.
muscle fiber
Long thin cell, composed of actin and myosin, that is able to contract.
myofibril
Long cylindrical organelle that is made up of two types of protein filaments: actin and myosin.
myosin
A protein filament that uses ATP to move along an actin filament, causing muscle contraction.
sarcomeres
Repeating units of actin and myosin filaments.
skeletal muscle
Used to move the body, usually attached to the skeleton, controlled voluntarily by the somatic nervous system and involuntarily through reflexes.
smooth muscle
Found within the walls of organs and structures such as the esophagus, under involuntary control.
tendinitis
A painful disorder of a tendon.
Points to Consider
Identify ways in which damage to the integumentary system (for example, in a person with a severe burn) may affect the muscular and skeletal systems.
Consider how the daily exercise routine and diet of an Olympic weightlifter would differ from that of a professional marathon runner.
Lesson 21.3: Integumentary System
Lesson Objectives
Identify the structures that make up the integumentary system.
Outline the role of the skin in providing a physical barrier to the external environment.
Distinguish between the two layers that make up the skin.
Identify two types of glands that are found in the skin.
Outline the function of melanin.
Outline the structure of hair.
Examine the structure of nails, and compare them to the structure of nails.
Introduction
Your integumentary system is the external covering of your body. It is made up of your skin, hair, and nails. The integumentary system of other animals such as birds and reptiles includes their feathers and scales. The name comes from the Latin term integumentum, which means “a covering.”
Figure 21.40
Your skin acts like a waterproof barrier so that you can swim without water leaking into your body.
The integumentary system has multiple roles in homeostasis, including protection, temperature regulation, sensory reception, biochemical synthesis, and absorption. Keeping water out of the body is an important role for your integumentary system, as is shown by Figure above. Your body systems all work together to maintain relatively stable internal conditions. Each of the parts that make up your integumentary system has a special role in maintaining homeostasis which we will explore a little later. An introduction to the Integumentary System can be viewed at http://www.youtube.com/watch?v=no_XRnoNGfE.
Structure and Function of Your Skin
The skin is a vital organ that covers the entire outside of the body, forming a protective barrier against pathogens and injuries from the environment. T
he skin is the body's largest organ, covering the entire outside of the body, and it is only about 2 mm thick. It shields the body against heat, light, injury, and infection. The skin also helps regulate body temperature, gathers sensory information from the environment, stores water, fat, and vitamin D, and acts as a physical barrier in protecting us from disease.
Your skin is constantly in contact with your external environment so it gets cut, scratched, and exposed to radiation, such as ultraviolet (UV) light. You also naturally shed many skin cells every day. Your body replaces damaged or missing skin cells by growing more of them, through the process of mitosis. Two distinct layers make up the skin: the epidermis and the dermis. A fatty layer, called subcutaneous tissue, or hypodermis (below skin), lies under the dermis, but it is not considered to be part of your skin. The layers that make up your skin are shown in Figure below.
Figure 21.41
Structure of the skin. The structures of the epidermis, dermis, and the subcutaneous tissue (called the subcutis in this diagram). Note how there are no blood vessels in the epidermis.
The color, thickness and texture of skin vary over the body. There are two general types of skin; thin and hairy, which is the most common type on the body, and thick and hairless, which is found on parts of the body that are used heavily and experience a lot of friction, such as the palms of the hands or the soles of the feet.
Epidermis
Epidermis is the outermost layer of the skin. It forms the waterproof, protective wrap over the body's surface and is made up of many layers of epithelial cells, shown in Figure below.
Figure 21.42
The epidermis is made up of many layers of epithelial cells. The uppermost layer is made up of many flat, dead, keratin-filled cells called keratinocytes. Every day, thousands of keratinocytes get scraped off the surface of your skin, and are replaced by cells that move up from lower layers.
The epidermis is divided into several layers where epithelial cells are formed through mitosis in the lowest layer. The epithelial cells move up through the layers of the epidermis, changing shape and composition as they differentiate and become filled with a tough, fibrous protein called keratin. At this point the cells are called keratinocytes. Keratinocytes at the surface of the epidermis form a thin layer of flattened, dead cells, (the stratum corneum in Figure above). Although the top layer of epidermis is only about as thick as a sheet of paper, it is made up of 25 to 30 layers of keratinocytes. Keratinocytes get scraped off through everyday activities, and are usually shed about a month after they reach the surface of the epidermis.
The epidermis also contains cells called melanocytes that produce the pigment melanin. Melanin is the brownish pigment that gives skin and hair their color. Melanocytes are located in the bottom layer of the epidermis, the stratum basale, shown in Figure above. The difference in skin color between light-skinned people and dark-skinned people is not due to the number of melanocytes in their skin, but to the melanocytes' level of activity. The amount of melanin produced in a person’s skin is dependent on his or her genetics and the amount of ultraviolet (UV) light exposure. Melanin absorbs UV rays from the sun or other sources of UV light, such as a tanning bed. When UV light penetrates the skin and damages DNA; the damaged DNA triggers the synthesis of more melanin. The skin also makes vitamin D by absorbing energy from UV light. Melanin acts like a UV filter, so the more melanin in a person’s skin, the more time the person has to spend in sunlight to produce the same amount of vitamin D as a person with less melanin in their skin.
The epidermis also contains cells that take up and process certain marker proteins (called antigens) from microbes that enter through the skin. This helps the immune system recognize the microbe as an intruder, and to mount an attack on it. The epidermis contains no blood vessels, so the lower portion of the epidermis is nourished by diffusion from the blood vessels of the dermis.
Structure and Function of Dermis
The dermis is the layer of skin directly under the epidermis and is made of a tough elastic connective tissue. The dermis is tightly connected to the epidermis by a membrane made of collagen fibers. The dermis contains the hair follicles, sweat glands, sebaceous glands, and blood vessels. It also holds many nerve endings that provide the sense of touch, pressure, heat, and pain. Tiny muscles, called arrector pili, contract and pull on hair follicles which cause hair to stand up. This can happen when you are cold or afraid, and the resulting little “bumps” in the skin are commonly called goose bumps.
The dermis has two layers, each of which contains different structures:
Papillary region (upper layer): The papillary region is made up of loose connective tissue and contains touch receptors which communicate with the central nervous system. It is named for its finger-like projections called papillae, which extend toward the epidermis, and help secure the dermis to the epidermis. The papillae can be seen in Figure above. The papillae provide the dermis with a "bumpy" surface that causes distinctive friction ridges. They are called friction ridges, because they help the hand or foot to grasp things by increasing friction. Friction ridges, as shown in Figure below, occur in patterns that are unique to the individual, making it possible to use fingerprints or footprints as a means of identification.
Figure 21.43
Close-up image of a toe print. The friction ridges that originate in the dermis and make up the whorls and lines of finger and toe prints are clearly visible. Both fingers and toes have these distinctive ridges.
Reticular region (lower layer): The reticular region is made of dense elastic fibers (collagen), which contains the hair follicles and roots, nerves, and glands. It gets its name from the dense concentration of protein fibers that weave throughout it. These protein fibers give the dermis its properties of strength, extensibility, and elasticity. Heat, cold and pressure receptors, nails, and blood vessels are also located in this region. Tattoo ink is injected into the dermis. Stretch marks are also located in the dermis.
Glands and Follicles
Glands and follicles open out into the epidermis, but they originate within the dermis. A sebaceous gland, also known as an oil gland, secretes an oily substance, called sebum, into the hair follicle. Sebum is made of lipids and the debris of dead lipid-producing cells. The word sebum comes from the Latin word for fat, or tallow. It “waterproofs” hair and the skin surface to prevent them from drying out. It can also inhibit the growth of microorganisms on the skin. Sebum is the cause of the oily appearance of skin and hair. It is odorless, but the breakdown of sebum by bacteria can cause odors. A sebaceous gland is shown in Figure below. If a sebaceous gland becomes plugged and infected, it develops into a pimple, also called acne.
Figure 21.44
A sebaceous gland an associated hair follicle. Sebum acts to protect and waterproof hair and skin, and keep them from becoming dry, brittle and cracked.
Sweat glands open to the epidermal surface through the skin pores. They occur all over the body and are controlled by the sympathetic nervous system. Evaporation of sweat from the skin surface helps to lower the skin temperature, which in turn helps to control body temperature. The skin also functions as an excretory organ because it releases excess water, salts, and other wastes in sweat. A sweat gland is shown in Figure below. There are two types of sweat glands, eccrine glands and apocrine glands. Eccrine glands are the “regular” sweat glands that release sweat to cool the body. Apocrine glands are larger than eccrine glands and are located in the armpits and groin areas. They effectively act as scent glands because they produce a solution that bacteria break down which produces "body odor."
Mammary glands are the organs that, in the female mammal, produce milk to feed their young. Mammary glands are enlarged and modified sweat glands and are a major characteristic of mammals.
Figure 21.45
Location of sweat glands in the dermis. Note that the sweat glands are called sudoriferous glands in this image.
Subcutaneous Tissue
The subcutaneous tissu
e (also called the hypodermis), lies below the dermis and contains fat and loose connective tissue that holds larger blood vessels and nerves. Its purpose is to attach the skin to underlying bone and muscle as well as to supply the skin with blood vessels and nerves. This layer is important is the regulation of body temperature. It is mostly made up of adipose tissue (which is made up of fat cells or adipocytes); the subcutaneous tissue contains about 50 percent of the body’s fat. The functions of subcutaneous tissue include insulation and the storage of nutrients. The size of this layer varies throughout the body and from person to person.
Functions of Skin: Skin and Homeostasis
The skin has multiple roles in homeostasis, including protection, control of body temperature, sensory reception, water balance, synthesis of vitamins and hormones, and absorption of materials. The skin's main functions are to serve as a barrier to the entry of microbes and viruses, and to prevent water and extracellular fluid loss. Acidic secretions from skin glands also stop the growth of fungi on the skin. Melanocytes form a second barrier: protection from the damaging effects of UV radiation. When a microbe gets into the skin (or when the skin is cut) an immune system reaction occurs.
CK-12 Biology I - Honors Page 105