Endomysium

Structure of a skeletal muscle. (Endomysium labeled at bottom center.)

Wispy layer of areolar connective tissue that ensheaths each individual muscle fiber, or muscle cell.

- Endomysium
Structure of a skeletal muscle. (Endomysium labeled at bottom center.)

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Tropocollagen molecule: three left-handed procollagens (red, green, blue) join to form a right-handed triple helical tropocollagen.

Collagen

Main structural protein in the extracellular matrix found in the body's various connective tissues.

Main structural protein in the extracellular matrix found in the body's various connective tissues.

Tropocollagen molecule: three left-handed procollagens (red, green, blue) join to form a right-handed triple helical tropocollagen.
Action of lysyl oxidase
Three polypeptides coil to form tropocollagen. Many tropocollagens then bind together to form a fibril, and many of these then form a fibre.
The D-period of collagen fibrils results in visible 67nm bands when observed by electron microscopy.
A salami and the collagen casing (below) it came in

In muscle tissue, it serves as a major component of the endomysium.

Tropocollagen molecule: three left-handed procollagens (red, green, blue) join to form a right-handed triple helical tropocollagen.

Type I collagen

Most abundant collagen of the human body.

Most abundant collagen of the human body.

Tropocollagen molecule: three left-handed procollagens (red, green, blue) join to form a right-handed triple helical tropocollagen.

It is present in scar tissue, the end product when tissue heals by repair, as well as tendons, ligaments, the endomysium of myofibrils, the organic part of bone, the dermis, the dentin, and organ capsules.

A top-down view of skeletal muscle

Skeletal muscle

Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system that are mostly attached by tendons to bones of the skeleton.

Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system that are mostly attached by tendons to bones of the skeleton.

A top-down view of skeletal muscle
3D rendering of a skeletal muscle fiber
Muscle types by fiber arrangement
Types of pennate muscle. A – unipennate; B – bipennate; 
C – multipennate
ATPase staining of a muscle cross section. Type II fibers are dark, due to the alkaline pH of the preparation. In this example, the size of the type II fibers is considerably less than the type I fibers due to denervation atrophy.
Structure of muscle fibre showing a sarcomere under electron microscope with schematic explanation.
Diagram of sarcoplasmic reticulum with terminal cisternae and T-tubules.
Human embryo showing somites labelled as primitive segments.
When a sarcomere contracts, the Z lines move closer together, and the I band becomes smaller. The A band stays the same width. At full contraction, the thin and thick filaments overlap.
Contraction in more detail
(a) Some ATP is stored in a resting muscle. As contraction starts, it is used up in seconds. More ATP is generated from creatine phosphate for about 15 seconds. (b) Each glucose molecule produces two ATP and two molecules of pyruvic acid, which can be used in aerobic respiration or converted to lactic acid. If oxygen is not available, pyruvic acid is converted to lactic acid, which may contribute to muscle fatigue. This occurs during strenuous exercise when high amounts of energy are needed but oxygen cannot be sufficiently delivered to muscle. (c) Aerobic respiration is the breakdown of glucose in the presence of oxygen (O2) to produce carbon dioxide, water, and ATP. Approximately 95 percent of the ATP required for resting or moderately active muscles is provided by aerobic respiration, which takes place in mitochondria.
Exercise-induced signaling pathways in skeletal muscle that determine specialized characteristics of slow- and fast-twitch muscle fibers
Jogging is one form of aerobic exercise.
In muscular dystrophy, the affected tissues become disorganized and the concentration of dystrophin (green) is greatly reduced.
Prisoner of war exhibiting muscle loss as a result of malnutrition.

Deep fascia specialises within muscles to enclose each muscle fiber as endomysium; each muscle fascicle as perimysium, and each individual muscle as epimysium.

General structure of a skeletal muscle cell and neuromuscular junction: 1. Axon

2. Neuromuscular junction

3. Skeletal muscle fiber

4. Myofibril

Muscle cell

Also known as a myocyte when referring to either a cardiac muscle cell , or a smooth muscle cell as these are both small cells.

Also known as a myocyte when referring to either a cardiac muscle cell , or a smooth muscle cell as these are both small cells.

General structure of a skeletal muscle cell and neuromuscular junction: 1. Axon

2. Neuromuscular junction

3. Skeletal muscle fiber

4. Myofibril
Diagram of skeletal muscle fiber structure

These satellite cells remain adjacent to a skeletal muscle fiber, situated between the sarcolemma and the basement membrane of the endomysium (the connective tissue investment that divides the muscle fascicles into individual fibers).

Biopsy of small bowel showing coeliac disease manifested by blunting of villi, crypt hypertrophy, and lymphocyte infiltration of crypts

Coeliac disease

Long-term autoimmune disorder, primarily affecting the small intestine, where individuals develop intolerance to gluten, present in foods such as wheat, rye and barley.

Long-term autoimmune disorder, primarily affecting the small intestine, where individuals develop intolerance to gluten, present in foods such as wheat, rye and barley.

Biopsy of small bowel showing coeliac disease manifested by blunting of villi, crypt hypertrophy, and lymphocyte infiltration of crypts
DQ α5-β2 -binding cleft with a deamidated gliadin peptide (yellow), modified from
HLA region of chromosome 6
Illustration of deamidated α-2 gliadin's 33mer, amino acids 56–88, showing the overlapping of three varieties of T-cell epitope
The active form of tissue transglutaminase (green) bound to a gluten peptide mimic (blue).
Immunofluorescence staining pattern of endomysial antibodies on a monkey oesophagus tissue sample.
Endoscopic still of duodenum of a person with coeliac disease showing scalloping of folds and "cracked-mud" appearance to mucosa
Schematic of the Marsh classification of upper jejunal pathology in coeliac disease.

In patients with villous atrophy, anti-endomysial (EMA) antibodies of the immunoglobulin A (IgA) type can detect coeliac disease with a sensitivity and specificity of 90% and 99%, respectively.

Structure of a skeletal muscle (epimysium labeled at bottom center)

Epimysium

Fibrous tissue envelope that surrounds skeletal muscle.

Fibrous tissue envelope that surrounds skeletal muscle.

Structure of a skeletal muscle (epimysium labeled at bottom center)

It is continuous with fascia and other connective tissue wrappings of muscle including the endomysium and perimysium.

Transverse section of human tibial nerve (perineurium labeled at upper right)

Perineurium

Protective sheath that surrounds a nerve fascicle.

Protective sheath that surrounds a nerve fascicle.

Transverse section of human tibial nerve (perineurium labeled at upper right)

This grouping structure is analogous to the muscular organization system of epimysium, perimysium and endomysium.

Gluten-related disorders

Gluten-related disorders

Term for the diseases triggered by gluten, including celiac disease , non-celiac gluten sensitivity (NCGS), gluten ataxia, dermatitis herpetiformis (DH) and wheat allergy.

Term for the diseases triggered by gluten, including celiac disease , non-celiac gluten sensitivity (NCGS), gluten ataxia, dermatitis herpetiformis (DH) and wheat allergy.

Gluten-related disorders
Villous atrophy of the small intestine
Crossed-grain symbol, similar to that of the Association Of European Coeliac Societies (AOECS)

Persons suspected of having celiac disease may undergo serological testing for IgA anti-tissue transglutaminase antibodies (abbreviated anti-tTG antibodies or anti-TG2 antibodies) and anti-endomysial antibodies (abbreviated EMA) provided the IgA-level is high, and if IgA is low, testing for certain IgG antibodies; in case of positive serological indication, a duodenal biopsy may confirm active celiac disease.

Muscles of the iliac and anterior femoral regions. (Rectus femoris highlighted in red.)

Pennate muscle

Type of skeletal muscle with fascicles that attach obliquely (in a slanting position) to its tendon.

Type of skeletal muscle with fascicles that attach obliquely (in a slanting position) to its tendon.

Muscles of the iliac and anterior femoral regions. (Rectus femoris highlighted in red.)
Figure 1 Pennate muscle fiber arrangements: A, unipennate; B, bipennate; C, multipennate. Blue: anatomical cross-section. Green: physiological cross-section.
Pennation angle
Figure 2 Architectural gear ratio

In skeletal muscle tissue, 10-100 endomysium-sheathed muscle fibers are organized into perimysium-wrapped bundles known as fascicles.

Areas of body affected in myotonic dystrophy, types 1 and 2, colored in red

Myotonic dystrophy

Type of muscular dystrophy, a group of genetic disorders that cause progressive muscle loss and weakness.

Type of muscular dystrophy, a group of genetic disorders that cause progressive muscle loss and weakness.

Areas of body affected in myotonic dystrophy, types 1 and 2, colored in red
40-year-old with myotonic dystrophy who presented with muscle wasting, bilateral cataracts, and complete heart block
Myotonic dystrophy is inherited in an autosomal dominant pattern.
Histopathology of DM2. Muscle biopsy showing mild myopathic changes and grouping of atrophic fast fibres (type 2, highlighted). Immunohistochemical staining for type-1 ("slow") myosin.

There is modest fibrosis of the endomysium.