Editing Anatomy (section)

== Animal tissues ==
[[File:Anima cell notext.svg|right|thumb|Stylized cutaway diagram of an animal cell (with flagella)]]
The [[Kingdom (biology)|kingdom]] [[Animalia]] contains [[multicellular organism]]s that are [[heterotroph]]ic and [[motile]] (although some have secondarily adopted a [[Sessility (zoology)|sessile]] lifestyle). Most animals have bodies differentiated into separate [[Tissue (biology)|tissues]] and these animals are also known as [[eumetazoa]]ns. They have an internal [[digestion|digestive]] chamber, with one or two openings; the [[gamete]]s are produced in multicellular sex organs, and the [[zygote]]s include a [[blastula]] stage in their [[Embryogenesis|embryonic development]]. Metazoans do not include the [[sponge]]s, which have undifferentiated cells.<ref name=Dorit549>{{cite book |title=Zoology |url=https://archive.org/details/zoology0000dori |url-access=registration |last1=Dorit |first1=R. L. |last2=Walker |first2=W. F. |last3=Barnes |first3=R. D. |year=1991 |publisher=Saunders College Publishing |isbn=978-0-03-030504-7 |pages=[https://archive.org/details/zoology0000dori/page/547 547–549] }}</ref>

Unlike [[plant cell]]s, [[animal cells]] have neither a cell wall nor [[chloroplast]]s. Vacuoles, when present, are more in number and much smaller than those in the plant cell. The body tissues are composed of numerous types of cells, including those found in muscles, nerves and skin. Each typically has a cell membrane formed of [[phospholipid]]s, [[cytoplasm]] and a [[Cell nucleus|nucleus]]. All of the different cells of an animal are derived from the embryonic [[germ layer]]s. Those simpler invertebrates which are formed from two germ layers of ectoderm and endoderm are called [[diploblastic]] and the more developed animals whose structures and organs are formed from three germ layers are called [[triploblastic]].<ref name=Ruppert60>{{cite book |title=Invertebrate Zoology, 7th edition |last1=Ruppert |first1=Edward E. |last2=Fox |first2=Richard, S. |last3=Barnes |first3=Robert D. |year=2004 |publisher=[[Cengage Learning]] |isbn=978-81-315-0104-7 |pages=59–60 }}</ref> All of a triploblastic animal's tissues and organs are derived from the three germ layers of the embryo, the [[ectoderm]], [[mesoderm]] and [[endoderm]].

Animal tissues can be grouped into four basic types: [[connective tissue|connective]], [[epithelial]], [[muscle]] and [[nervous tissue]].
[[File:Cartilage polarised.jpg|thumb|Hyaline cartilage at high magnification ([[H&E stain]])]]

===Connective tissue===
[[Connective tissue]]s are fibrous and made up of cells scattered among inorganic material called the [[extracellular matrix]]. Often called [[fascia]] (from the Latin "fascia," meaning "band" or "bandage"), connective tissues give shape to organs and holds them in place. The main types are loose connective tissue, [[adipose tissue]], fibrous connective tissue, [[cartilage]] and bone. The extracellular matrix contains [[protein]]s, the chief and most abundant of which is [[collagen]]. Collagen plays a major part in organizing and maintaining tissues. The matrix can be modified to form a skeleton to support or protect the body. An [[exoskeleton]] is a thickened, rigid [[cuticle]] which is stiffened by [[mineralisation (biology)|mineralization]], as in [[crustacean]]s or by the cross-linking of its proteins as in [[insect]]s. An [[endoskeleton]] is internal and present in all developed animals, as well as in many of those less developed.<ref name="Ruppert60" />

===Epithelium===
[[File:Normal gastric mucosa low mag.jpg|thumb|right|Gastric mucosa at low magnification ([[H&E stain]])]]
[[Epithelial tissue]] is composed of closely packed cells, bound to each other by [[cell adhesion molecule]]s, with little intercellular space. Epithelial cells can be [[Squamous epithelial cell|squamous]] (flat), [[Simple cuboidal epithelium|cuboidal]] or [[Columnar epithelial cell|columnar]] and rest on a [[basal lamina]], the upper layer of the [[basement membrane]],<ref>{{cite book|last=Dorland's|title=Illustrated Medical Dictionary|date=2012|publisher=Elsevier Saunders|isbn=978-1-4160-6257-8|page=203}}</ref> the lower layer is the reticular lamina lying next to the connective tissue in the extracellular matrix secreted by the epithelial cells.<ref>{{cite book|last=Dorland's|title=Illustrated Medical Dictionary|date=2012|publisher=Elsevier Saunders|isbn=978-1-4160-6257-8|page=1002}}</ref> There are many different types of epithelium, modified to suit a particular function. In the [[respiratory tract]] there is a type of [[pseudostratified ciliated columnar epithelium|ciliated]] epithelial lining; in the small intestine there are [[microvilli]] on the epithelial lining and in the large intestine there are [[intestinal villi]]. Skin consists of an outer layer of [[keratin]]ized stratified squamous epithelium that covers the exterior of the vertebrate body. [[Keratinocyte]]s make up to 95% of the cells in the [[epidermis (skin)|skin]].<ref>McGrath, J.A.; Eady, R.A.; Pope, F.M. (2004). Rook's Textbook of Dermatology (7th ed.). Blackwell Publishing. pp. 3.1–3.6. {{ISBN|978-0-632-06429-8}}.</ref> The epithelial cells on the external surface of the body typically secrete an extracellular matrix in the form of a [[cuticle]]. In simple animals this may just be a coat of [[glycoproteins]].<ref name="Ruppert60" /> In more advanced animals, many [[gland]]s are formed of epithelial cells.<ref>{{cite web |url=https://www.bio.davidson.edu/people/kabernd/BerndCV/Lab/EpithelialInfoWeb/Glandular%20Epithelium.html |title=Glandular epithelium |last=Bernd |first=Karen |year=2010 |work=Epithelial Cells |publisher=Davidson College |access-date=25 June 2013 |archive-url=https://web.archive.org/web/20200128053412/https://www.bio.davidson.edu/people/kabernd/BerndCV/Lab/EpithelialInfoWeb/Glandular%20Epithelium.html |archive-date=28 January 2020 |url-status=live }}</ref>

===Muscle tissue===
[[File:Skeletal muscle - cross section, nerve bundle.jpg|right|thumb|Cross section through [[skeletal muscle]] and a small [[nerve]] at high magnification ([[H&E stain]])]]
[[Muscle cells]] (myocytes) form the active contractile tissue of the body. [[Muscle tissue]] functions to produce force and cause motion, either locomotion or movement within internal organs. Muscle is formed of contractile [[Myofibril|filaments]] and is separated into three main types; [[smooth muscle]], [[skeletal muscle]] and [[cardiac muscle]]. Smooth muscle has no [[Striated muscle tissue|striations]] when examined microscopically. It contracts slowly but maintains contractibility over a wide range of stretch lengths. It is found in such organs as [[sea anemone]] tentacles and the body wall of [[sea cucumber]]s. Skeletal muscle contracts rapidly but has a limited range of extension. It is found in the movement of appendages and jaws. Obliquely striated muscle is intermediate between the other two. The filaments are staggered and this is the type of muscle found in [[earthworm]]s that can extend slowly or make rapid contractions.<ref name=Ruppert103>{{cite book |title=Invertebrate Zoology, 7th edition |last1=Ruppert |first1=Edward E. |last2=Fox |first2=Richard, S. |last3=Barnes |first3=Robert D. |year=2004 |publisher=Cengage Learning |isbn=978-81-315-0104-7 |page=103 }}</ref> In higher animals striated muscles occur in bundles attached to bone to provide movement and are often arranged in antagonistic sets. Smooth muscle is found in the walls of the [[uterus]], [[bladder]], [[intestines]], [[stomach]], [[oesophagus]], [[respiratory airways]], and [[blood vessel]]s. [[Cardiac muscle]] is found only in the [[heart]], allowing it to contract and pump blood round the body.

===Nervous tissue===
{{See also|Neuroanatomy}}
[[Nervous tissue]] is composed of many nerve cells known as [[neuron]]s which transmit information. In some slow-moving [[radially symmetrical]] marine animals such as [[ctenophore]]s and [[cnidarian]]s (including [[sea anemone]]s and [[jellyfish]]), the nerves form a [[nerve net]], but in most animals they are organized longitudinally into bundles. In simple animals, receptor neurons in the body wall cause a local reaction to a stimulus. In more complex animals, specialized receptor cells such as [[chemoreceptor]]s and [[photoreceptor cell|photoreceptors]] are found in groups and send messages along [[biological neural network|neural networks]] to other parts of the organism. Neurons can be connected together in [[ganglia]].<ref name=Ruppert104>{{cite book |title=Invertebrate Zoology, 7th edition |last1=Ruppert |first1=Edward E. |last2=Fox |first2=Richard, S. |last3=Barnes |first3=Robert D. |year=2004 |publisher=Cengage Learning |isbn=978-81-315-0104-7 |page=104 }}</ref> In higher animals, specialized receptors are the basis of sense organs and there is a [[central nervous system]] (brain and spinal cord) and a [[peripheral nervous system]]. The latter consists of [[Sensory neuron|sensory nerves]] that transmit information from sense organs and [[motor nerves]] that influence target organs.<ref>{{cite book|title=Grey's Anatomy: Descriptive and Applied |year=1944 |edition=28 |page=1038 |publisher=Langmans |editor1-last=Johnston | editor1-first= T.B |editor2-last=Whillis | editor2-first=J }}</ref><ref name=Ruppert107>{{cite book |title=Invertebrate Zoology, 7th edition |last1=Ruppert |first1=Edward E. |last2=Fox |first2=Richard, S. |last3=Barnes |first3=Robert D. |year=2004 |publisher=Cengage Learning |isbn=978-81-315-0104-7 |pages=105–107 }}</ref> The peripheral nervous system is divided into the [[somatic nervous system]] which conveys sensation and controls [[voluntary muscle]], and the [[autonomic nervous system]] which involuntarily controls [[smooth muscle]], certain glands and internal organs, including the [[stomach]].<ref>{{cite web | url=https://www.inkling.com/read/essential-clinical-anatomy-keith-moore-4th/introduction-to-clinical-anatomy/nervous-system | title=Essesntial Clinical Anatomy | publisher=Inkling | work=Nervous System | date=2010 | edition=4th | access-date=30 April 2014 | author1=Moore, K. | author2=Agur, A. | author3=Dalley, A. F. | archive-date=8 March 2021 | archive-url=https://web.archive.org/web/20210308131326/https://www.inkling.com/read/essential-clinical-anatomy-keith-moore-4th/introduction-to-clinical-anatomy/nervous-system | url-status=live }}</ref>