Atrophy is the partial or complete

wasting In medicine, wasting, also known as wasting syndrome, refers to the process by which a debilitating disease causes muscle and fat tissue to "waste" away. Wasting is sometimes referred to as "acute malnutrition" because it is believed that episo ...

away of a part of the body. Causes of atrophy include

mutation In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, mi ...

s (which can destroy the gene to build up the organ), poor nourishment, poor circulation, loss of

hormonal A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required fo ...

support, loss of

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the e ...

supply to the target organ, excessive amount of

apoptosis Apoptosis (from grc, ἀπόπτωσις, apóptōsis, 'falling off') is a form of programmed cell death that occurs in multicellular organisms. Biochemical events lead to characteristic cell changes (morphology) and death. These changes incl ...

of cells, and disuse or lack of

exercise Exercise is a body activity that enhances or maintains physical fitness and overall health and wellness. It is performed for various reasons, to aid growth and improve strength, develop muscles and the cardiovascular system, hone athletic ...

or disease intrinsic to the tissue itself. In medical practice, hormonal and nerve inputs that maintain an organ or body part are said to have ''trophic'' effects. A diminished muscular trophic condition is designated as ''atrophy''. Atrophy is reduction in size of cell, organ or tissue, after attaining its normal mature growth. In contrast,

hypoplasia Hypoplasia (from Ancient Greek ὑπo- ''hypo-'' 'under' + πλάσις ''plasis'' 'formation'; adjective form ''hypoplastic'') is underdevelopment or incomplete development of a tissue or organ.physiological Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...

process of reabsorption and breakdown of tissues, involving apoptosis. When it occurs as a result of disease or loss of trophic support because of other diseases, it is termed ''pathological atrophy'', although it can be a part of normal body development and

homeostasis In biology, homeostasis (British English, British also homoeostasis) Help:IPA/English, (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physics, physical, and chemistry, chemical conditions maintained by organism, living systems. Thi ...

as well.

Normal development

Examples of atrophy as part of normal development include shrinking and the involution of the

thymus The thymus is a specialized primary lymphoid organ of the immune system. Within the thymus, thymus cell lymphocytes or ''T cells'' mature. T cells are critical to the adaptive immune system, where the body adapts to specific foreign invaders. ...

in early childhood, and the

tonsil The tonsils are a set of lymphoid organs facing into the aerodigestive tract, which is known as Waldeyer's tonsillar ring and consists of the adenoid tonsil, two tubal tonsils, two palatine tonsils, and the lingual tonsils. These organs play ...

s in adolescence. In old age, effects include, but are not limited to, loss of teeth, hair, thinning of skin that creates wrinkles, weakening of muscles, loss of weight in organs and sluggish mental activity.

Muscle atrophies

''Disuse atrophy'' of muscles and bones, with loss of mass and strength, can occur after prolonged immobility, such as extended bedrest, or having a body part in a cast (living in darkness for the eye, bedridden for the legs etc.). This type of atrophy can usually be reversed with exercise unless severe. There are many diseases and conditions which cause atrophy of muscle mass. For example, diseases such as cancer and AIDS induce a body wasting syndrome called ''

cachexia Cachexia () is a complex syndrome associated with an underlying illness, causing ongoing muscle loss that is not entirely reversed with nutritional supplementation. A range of diseases can cause cachexia, most commonly cancer, congestive heart f ...

'', which is notable for the severe muscle atrophy seen. Other syndromes or conditions which can induce

skeletal muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

atrophy are

congestive heart failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, a ...

and liver disease. During aging, there is a gradual decrease in the ability to maintain skeletal muscle function and mass. This condition is called ''

sarcopenia Sarcopenia is a type of muscle loss ( muscle atrophy) that occurs with aging and/or immobility. It is characterized by the degenerative loss of skeletal muscle mass, quality, and strength. The rate of muscle loss is dependent on exercise level, ...

'', and may be distinct from atrophy in its pathophysiology. While the exact cause of sarcopenia is unknown, it may be induced by a combination of a gradual failure in the

satellite cells Myosatellite cells, also known as satellite cells, muscle stem cells or MuSCs, are small multipotent cells with very little cytoplasm found in mature muscle. Satellite cells are precursors to skeletal muscle cells, able to give rise to satellite ...

which help to regenerate skeletal muscle fibers, and a decrease in sensitivity to or the availability of critical secreted growth factors which are necessary to maintain muscle mass and satellite cell survival.

Dystrophies, myositis, and motor neuron conditions

Pathologic atrophy of muscles can occur with diseases of the motor nerves or diseases of the muscle tissue itself. Examples of atrophying nerve diseases include Charcot-Marie-Tooth disease,

poliomyelitis Poliomyelitis, commonly shortened to polio, is an infectious disease caused by the poliovirus. Approximately 70% of cases are asymptomatic; mild symptoms which can occur include sore throat and fever; in a proportion of cases more severe sym ...

amyotrophic lateral sclerosis Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND) or Lou Gehrig's disease, is a neurodegenerative disease that results in the progressive loss of motor neurons that control voluntary muscles. ALS is the most comm ...

(ALS or Lou Gehrig's disease), and

Guillain–Barré syndrome Guillain–Barré syndrome (GBS) is a rapid-onset muscle weakness caused by the immune system damaging the peripheral nervous system. Typically, both sides of the body are involved, and the initial symptoms are changes in sensation or pain often ...

. Examples of atrophying muscle diseases include

muscular dystrophy Muscular dystrophies (MD) are a genetically and clinically heterogeneous group of rare neuromuscular diseases that cause progressive weakness and breakdown of skeletal muscles over time. The disorders differ as to which muscles are primarily affe ...

myotonia congenita Myotonia congenita is a congenital neuromuscular channelopathy that affects skeletal muscles (muscles used for movement). It is a genetic disorder. The hallmark of the disease is the failure of initiated contraction to terminate, often referred to ...

, and

myotonic dystrophy Myotonic dystrophy (DM) is a type of muscular dystrophy, a group of genetic disorders that cause progressive muscle loss and weakness. In DM, muscles are often unable to relax after contraction. Other manifestations may include cataracts, intel ...

. Changes in Na+ channel isoform expression and spontaneous activity in muscle called fibrillation can also result in muscle atrophy. A

flail limb A flail is an agricultural tool used for threshing, the process of separating grains from their husks. It is usually made from two or more large sticks attached by a short chain; one stick is held and swung, causing the other (the swipple) to st ...

is a medical term which refers to an extremity in which the primary nerve has been severed, resulting in complete lack of mobility and sensation. The muscles soon wither away from atrophy.

Gland atrophy

The

adrenal gland The adrenal glands (also known as suprarenal glands) are endocrine glands that produce a variety of hormones including adrenaline and the steroids aldosterone and cortisol. They are found above the kidneys. Each gland has an outer cortex which ...

s atrophy during prolonged use of exogenous

glucocorticoid Glucocorticoids (or, less commonly, glucocorticosteroids) are a class of corticosteroids, which are a class of steroid hormones. Glucocorticoids are corticosteroids that bind to the glucocorticoid receptor that is present in almost every vertebr ...

s like

prednisone Prednisone is a glucocorticoid medication mostly used to immunosuppressive drug, suppress the immune system and decrease inflammation in conditions such as asthma, COPD, and rheumatologic diseases. It is also used to treat high blood calcium ...

. Atrophy of the breasts can occur with prolonged

estrogen Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal acti ...

reduction, as with

anorexia nervosa Anorexia nervosa, often referred to simply as anorexia, is an eating disorder characterized by low weight, food restriction, body image disturbance, fear of gaining weight, and an overpowering desire to be thin. ''Anorexia'' is a term of Gr ...

menopause Menopause, also known as the climacteric, is the time in women's lives when menstrual periods stop permanently, and they are no longer able to bear children. Menopause usually occurs between the age of 47 and 54. Medical professionals often d ...

Testicular atrophy Testicular atrophy is a medical condition in which one or both testicles (or "testes") diminish in size and may be accompanied by reduced testicular function. Testicular atrophy is not related to the temporary shrinkage of the surrounding scrotum, ...

can occur with prolonged use of enough exogenous sex steroids (either

androgen An androgen (from Greek ''andr-'', the stem of the word meaning "man") is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This inc ...

) to reduce

gonadotropin Gonadotropins are glycoprotein hormones secreted by gonadotropic cells of the anterior pituitary of vertebrates. This family includes the mammalian hormones follicle-stimulating hormone (FSH) and luteinizing hormone (LH), the placental/ chorioni ...

secretion.

Vaginal atrophy

In post-menopausal women, the walls of the vagina become thinner (

atrophic vaginitis Atrophic vaginitis is inflammation of the vagina as a result of tissue thinning due to not enough estrogen. Symptoms may include pain with sex, vaginal itchiness or dryness, and an urge to urinate or burning with urination. It generally does ...

). The mechanism for the age-related condition is not yet clear, though there are theories that the effect is caused by decreases in estrogen levels. This atrophy, and that of the breasts concurrently, is consistent with the homeostatic (normal development) role of atrophy in general, as after menopause the body has no further functional biological need to maintain the reproductive system which it has permanently shut down.

Research

One drug in test seemed to prevent the type of muscle loss that occurs in immobile, bedridden patients. Testing on mice showed that it blocked the activity of a protein present in the muscle that is involved in muscle atrophy. However, the drug's long-term effect on the heart precludes its routine use in humans, and other drugs are being sought.

References

External links

{{Authority control Anatomical pathology Gross pathology