Protists In
protists, syncytia can be found in some
rhizarians (e.g.,
chlorarachniophytes,
plasmodiophorids,
haplosporidians) and
acellular slime moulds,
dictyostelids (
amoebozoans),
acrasids (
Excavata) and
Haplozoon.
Plants Some examples of
plant syncytia, which result during
plant development, include: • Developing
endosperm • The
non-articulated laticifers • The
plasmodial tapetum, and • The "
nucellar plasmodium" of the family
Podostemaceae Fungi A syncytium is the normal cell structure for many
fungi. Most fungi of
Basidiomycota exist as a
dikaryon in which thread-like cells of the
mycelium are partially partitioned into segments each containing two differing nuclei, called a
heterokaryon.
Animals Nerve net The neurons which makes up the subepithelial
nerve net in comb jellies (
Ctenophora) are fused into a neural syncytium, consisting of a continuous plasma membrane instead of being connected through
synapses.
Skeletal muscle A classic example of a syncytium is the formation of
skeletal muscle. Large
skeletal muscle fibers form by the fusion of thousands of individual muscle cells. The
multinucleated arrangement is important in pathologic states such as
myopathy, where focal necrosis (death) of a portion of a skeletal muscle fiber does not result in necrosis of the adjacent sections of that same skeletal muscle fiber, because those adjacent sections have their own nuclear material. Thus, myopathy is usually associated with such "segmental necrosis", with some of the surviving segments being functionally cut off from their nerve supply via loss of continuity with the
neuromuscular junction.
Cardiac muscle The syncytium of
cardiac muscle is important because it allows rapid coordinated contraction of muscles along their entire length.
Cardiac action potentials propagate along the surface of the muscle fiber from the point of
synaptic contact through
intercalated discs. Although a syncytium, cardiac muscle differs because the cells are not long and multinucleated. Cardiac tissue is therefore described as a functional syncytium, as opposed to the true syncytium of skeletal muscle.
Smooth muscle Smooth muscle in the
gastrointestinal tract is activated by a composite of three types of cells –
smooth muscle cells (SMCs),
interstitial cells of Cajal (ICCs), and
platelet-derived growth factor receptor alpha (PDGFRα) that are electrically coupled and work together as an SIP functional syncytium.
Osteoclasts Certain animal immune-derived cells may form aggregate cells, such as the
osteoclast cells responsible for
bone resorption.
Placenta Another important vertebrate syncytium is in the
placenta of placental mammals. Embryo-derived cells that form the interface with the maternal blood stream fuse together to form a multinucleated barrier – the
syncytiotrophoblast. This is probably important to limit the exchange of migratory cells between the developing embryo and the body of the mother, as some
blood cells are specialized to be able to insert themselves between adjacent
epithelial cells. The syncytial epithelium of the placenta does not provide such an access path from the maternal circulation into the embryo.
Glass sponges Much of the body of
Hexactinellid sponges is composed of syncitial tissue. This allows them to form their large
siliceous spicules exclusively inside their cells.
Tegument The fine structure of the
tegument in
helminths is essentially the same in both the
cestodes and
trematodes. A typical tegument is 7–16
μm thick, with distinct layers. It is a syncytium consisting of multinucleated tissues with no distinct
cell boundaries. The outer zone of the syncytium, called the "distal cytoplasm," is lined with a
plasma membrane. This plasma membrane is in turn associated with a layer of carbohydrate-containing
macromolecules known as the
glycocalyx, that varies in thickness from one
species to another. The distal
cytoplasm is connected to the inner layer called the "proximal cytoplasm", which is the "cellular region or cyton or perikarya" through cytoplasmic tubes that are composed of
microtubules. The proximal cytoplasm contains
nuclei,
endoplasmic reticulum,
Golgi complex,
mitochondria,
ribosomes,
glycogen deposits, and numerous
vesicles. The innermost layer is bounded by a layer of
connective tissue known as the "
basal lamina". The basal lamina is followed by a thick layer of
muscle. ==Pathological examples==