Medical terminology
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Anatomical terminology [edit on Wikidata]

Medical terminology islanguage used to describe thecomponents,processes,conditions,medical procedures andtreatments of the human body.

In the English language, medical terminology generally has a regularmorphology; the sameprefixes andsuffixes are used to add meanings to differentroots. The root of a term often refers to anorgan,tissue, orcondition, andmedical roots and affixes are often derived fromAncient Greek orLatin (particularlyNeo-Latin). Many medical terms are examples ofneoclassical compounds. Historically, all Europeanuniversities used Latin as the dominant language of instruction and research, asNeo-Latin was thelingua franca of science, medicine, and education in Europe during theearly modern period.

Medical terminology includes a large part ofanatomical terminology, which includes theanatomical terms of location,motion,muscle,bone, andhistology. It also includes language frombiology,chemistry,physics, andphysiology, as well as vocabulary unique to the field of medicine, such asmedical abbreviations. Eachbranch of medicine has its own clinical and scientific terminology.Medical dictionaries are specialised dictionaries for medical terminology and may be organised alphabetically or according tomedical classification systems such as theSystematized Nomenclature of Medicine,International Classification of Diseases, orUnified Medical Language System.

Examples of modern medical dictionaries includeMosby's Dictionary of Medicine, Nursing & Health Professions,Stedman's,Taber's, andDorland's.

In the English language, medical terms generally have a regular morphology, often beingcompound words that comprise three kinds ofmorphemes:^{[citation needed]}roots,prefixes, andsuffixes.^[1][2] Theetymology of medical terms often originates fromLatin (particularlyNeo-Latin)^[3][4] andAncient Greek,^[5] with such medical terms being examples ofneoclassical compounds. Each language may supply relevant morphemes for medical terms. For example, there are two primary roots for medical terminology relating to kidneys – one from Greek (νεφρόςnephr(os)) and one from Latin (ren(es)).^{[citation needed]}

Lexical items of medical terminology, which forms part ofinternational scientific vocabulary (ISV), aretranslingual (that is, being used across multiple languages).^[6] The use of ISV was a driving force in the development of theconstructed language known asInterlingua.^[7] From the 1950s to late 1970s, a number of medical journals were published, or used, Interlingua.^{[8][9][10][11]}

Medical roots and affixes are often derived fromGreek orLatin.^[12]

The word root is developed to include a vowel sound following the term to add a smoothing action to the sound of the word when applying a suffix. The result is the formation of a new term with a vowel attached (word root + vowel) called acombining form. In English, the most common vowel used in the formation of the combining form is the letter-o-, added to the word root. For example, if there is an inflammation of the stomach and intestines, this would be written asgastro- andenter- plus-itis,gastroenteritis.^{[citation needed]}

The formation of plurals should usually be done using the rules of the source language. Greek and Latin each have differing rules to be applied when forming the plural form of the word root.^{[citation needed]}

Prefixes and suffixes, primarily in Greek—but also in Latin, have a droppable-o-. As a general rule, this vowel almost always acts as a joint-stem to connect two consonantal roots (e.g.arthr- +-o- +-logy =arthrology), but generally, the-o- is dropped when connecting to a vowel-stem (e.g.arthr- +-itis =arthritis, instead ofarthr-o-itis). Generally, Greek prefixes go with Greek suffixes and Latin prefixes with Latin suffixes. Although it is technically considered acceptable to createhybrid words, it is strongly preferred in coining new terms not to mix different lingual roots. Examples of accepted medical words that do mix lingual roots areneonatology andquadriplegia.^{[citation needed]}

Prefixes do not normally require further modification to be added to a word root because the prefix normally ends in a vowel or vowel sound, although in some cases they may assimilate slightly and anin- may change toim- orsyn- tosym-.^{[citation needed]} Suffixes are attached to the end of a word root to add meaning such as condition, disease process, or procedure.^{[citation needed]} Suffixes are categorized as either (1) needing the combining form, or (2) not needing the combining form since they start with a vowel.^{[citation needed]}

Descriptivehuman anatomy often uses terminology that is fairly correct descriptive Latin. For example,musculus gluteus maximus simply means the "largest rump muscle", wheremusculus was Latin for "little mouse" and applied to muscles;^[13] afrenum, a structure for keeping something in place, is Latin forbridle; and aforamen is Latin for a passage or perforation.^[14]

A standardised set of terminology is used in anatomy to describe relative and absolute location and movement of anatomical parts.^[15] Thestandard anatomical position is the orientation thatanatomical terms of location andmotion are typically used in reference to.^[15] In humans, this refers to the body in a standing position with arms at the side and palms facing forward.^[15] Other positions referenced in medicine includeprone (lying facing down) andsupine (lying facing up).^[16]

Relative to the standard anatomical position, threeanatomical planes are widely used in medicine:

• The parasagittal (Greekπᾰρᾰ́ (pará), beside) or paramedian orsagittal planes (Latinsagitta, arrow), which include themedian or midsagittal plane and divide the body into left and right (in reference to the subject and not the observer).^{[16][17][18][19]}
• The frontal orcoronal plane (Latincorona, crown), which divide the body into front and back.^[20][21]
• The axial or horizontal ortransverse plane (Latintrans, across;vetere, to turn), which is perpendicular to the other two planes.^[22]

Thetranspyloric plane, thesubcostal plane, and thetransumbilical plane planes are also considered in the division of thetorso into thequadrants and regions of the abdomen.^[23]

The three main axes of a human are the left-right (or horizontal or frontal), the craniocaudal (or rostrocaudal, longitudinal, or cephalocaudal),^[a] and the anteroposterior (or dorsoventral or sagittal) axes.^{[24][25][26][b]} Otheranatomical lines include theaxillary lines,parasternal line, andscapular line.

Many anatomical terms can be combined to indicate a position in two axes simultaneously or the direction of a movement relative to the body: Anterolateral indicates a position that is both anterior and lateral to the standard anatomical position (such as the bulk of thepectoralis major muscle) or a named organ such as theanterolateral tibial tubercle;^[36][37] anteromedial is used, for example, in theanteromedial central arteries;^[38] proximodistal describes the axis of anappendage such as an arm or a leg, taken from its tip at the distal part to where it joins the body at the proximal part.^[39] Combined terms were once generally hyphenated, but typically the hyphen is omitted.^[40]

Inradiology, various X-ray views useterminology based on where the X-ray beam enters and leaves the body, including the front to back view (anteroposterior), the back to front view (posteroanterior), and the side view (lateral).^[41]

Circumduction is a conical movement of a body part, such as aball and socket joint or theeye. Circumduction is a combination of flexion, extension, adduction and abduction. Circumduction may be performed at ball and socket joints, such as thehip andshoulder, as well as other parts of the body such as fingers, hands, feet, and head.^[53] For example, circumduction occurs when spinning the arm when performing a serve intennis or bowling acricket ball.^[54]

Theintegumentary system is the set of organs forming the outermost layer of the human body, comprising theskin,hair, andnails. It acts as a protective physical barrier between the external environment and the internal environment, while maintaining water balance, protecting deeper tissue, excreting waste, and regulatingbody temperature.^[66]

The skin (or, integument) is a composite organ, made up of the outermostepidermis and the innerdermis.^[67] The epidermis comprises five layers: thestratum corneum,stratum granulosum,stratum spinosum andstratum basale. Where the skin is thicker, such as in the palms and soles, there is an extra layer of skin between the stratum corneum and the stratum granulosum known as thestratum lucidum. The dermis comprises two sections, the papillary and reticular layers, and containsconnective tissues, blood vessels, glands, follicles,hair roots, sensory nerve endings, and muscular tissue.^[68] Between the integument and the deep body musculature there is a transitional subcutaneous zone, thehypodermis.^[69]

Front and back views of the major skeletal muscles of the human body

Front view of major skeletal muscles

Back view of major skeletal muscles

Themusculoskeletal system theorgan system that giveshumans the ability to move using theirmuscular andskeletal systems, and is described by theanatomical terms of bone andmuscle. It is made up of thebones of theskeleton,muscles,cartilage,tendons,ligaments,joints, and otherconnective tissue that supports and binds tissues and organs together:^[70]

• Bones are surrounded by a membrane known as theperiosteum (Greekπερῐ́ (perí), around; Greekὀστέον (ostéon), bone), and comprise multiple layers, depending on the type of bone, includingyellow and redbone marrow, spongy bone, and theendosteum. There are five general classifications ofbones:
  • Long bones are characterized by a shaft known as thediaphysis, which is much longer than its width, and anepiphysis (Greekἐπι- (epi-) upon, outside, over), a rounded head at each end of the shaft, connected to the diaphysis by theepiphyseal plate. They are made up mostly ofcompact bone, with lesser amounts ofmarrow, located within themedullary cavity, and areas of spongy, cancellous bone at the ends of the bones.^[71]
  • Short bones are roughlycube-shaped, and have only a thin layer of compact bone surrounding a spongy interior. Short bones provide stability and support as well as some limited motion.^[72]
  • Flat bones are thin and generally curved, with two parallel layers of compact bone sandwiching a layer of spongy bone.^[73]
  • Sesamoid bones are bones embedded in tendons. Since they act to hold the tendon further away from the joint, the angle of the tendon is increased and thus the leverage of the muscle is increased.^[74]
  • Irregular bones do not fit into the above categories. They consist of thin layers of compact bone surrounding a spongy interior. As implied by the name, their shapes are irregular and complicated. Often this irregular shape is due to their many centers of ossification or because they contain bony sinuses.^[75]
• Atendon is a tough, flexible band offibrous connective tissue that connects muscles to bones. The extra-cellular connective tissue between muscle fibers binds to tendons at the distal and proximal ends, and the tendon binds to theperiosteum of individual bones at the muscle's origin and insertion. Asmuscles contract, tendons transmit the forces to the relatively rigid bones, pulling on them and causing movement. Tendons can stretch substantially, allowing them to function as springs during movement.
• Cartilage is a resilient and smooth type ofconnective tissue that covers and protects theends oflong bones,^[76] and forms a structural component of many body parts including therib cage, the neck and the bronchial tubes, and theintervertebral discs. It is classified into three types —elastic cartilage,hyaline cartilage, andfibrocartilage.
• Joints, also known as articulations, are structures that connect individual bones and may allow bones to move against each other to cause movement. Joints can be classified by structure and by function. Structurally,synovial joints are joints that are not directly joined, which are lubricated by a solution calledsynovial fluid;^[77]fibrous, bony, andcartilaginous joints are characterised by the presence of their respective connective tissues. There are three functional divisions of joints:
  • Diarthroses, which allow extensive mobility between two or more articular heads.
  • Amphiarthroses, which allowsome movement.
  • False joints orsynarthroses, which allow little or no movement and are predominantlyfibrous.
• Aligament is a small band of dense, white,fibrouselastic tissue.^[78] Ligaments connect the ends of bones together in order to form a joint. Most ligaments limitdislocation, and prevent certain movements, such as hyperextension and hyperflexion, which may lead to breaks.^[79]
• Anenthesis is the connective tissue that attaches tendons and ligaments to bones.^[80]
• Fascia (from Latin fascia 'band') is a generic term formacroscopicmembranous bodily structures.^[81]: 42

The human skeleton may be divided into two distinct divisions: theaxial skeleton, which includes thevertebral column, and theappendicular skeleton.^[82]

The action of muscles often involve antagonistic pairs of agonist muscles and antagonist muscles, which, respectively, cause and inhibit a movement.^[83]

• Through the activation of agonist muscle, which produces most of the force and control of an action, movement occurs.^[84]
• Antagonist muscles are the muscles that produce an opposing joint torque to the agonist muscles.^[85]
• Synergist muscles, also calledfixators orneutralisers, act around a joint to help, counter, or neutralise the action of an agonist muscle.^[86]

Generally, as one muscle contracts, the other muscle relaxes in a process known asreciprocal inhibition.^[87]Muscle contraction may be concentric (i.e. shortening), eccentric (i.e. lengthening), or isometric (i.e. involving no change in length).^{[88][89][90][91][92]} Muscle groups (e.g. elbow flexors) are sometimes named based on the joint action they produce during concentric contraction.^[93] During muscle contraction, the insertion of a muscle is the structure that is moved and is typically a bone that is distal and lighter than the origin; the origin is the bone, typically proximal, that remains more stable during contraction; the head of a muscle is the end part of the muscle that attaches to its origin.^[94]

Thecirculatory system is asystem of organs that includes theheart,blood vessels, andblood which is circulated throughout the body.^[95][96] It includes thecardiovascular system, which consists of the heart and blood vessels. Some sources use the termscardiovascular system,vascular system andcirculatory system interchangeably.^[97] Thelymphatic system (comprisinglymphatic vessels,lymph nodes, lymphoid organs, lymphatic tissue andlymph) is complementary to the circulatory system and forms part of theimmune system.^[98]

The network of blood vessels include thegreat vessels (comprising largeelastic arteries and largeveins),^[99] otherarteries (which carry blood away from the heart) and veins (which carry blood to the heart), smallerarterioles, andcapillaries, which join withvenules. Blood is afluid consisting ofplasma (comprisingserum andclotting factors),red blood cells,white blood cells, andplatelets. Components of the blood include nutrients (such asproteins andminerals),hemoglobin,hormones, andgases such as oxygen andcarbon dioxide.^[100] These substances provide nourishment, help theimmune system to fightdiseases, and help maintainhomeostasis through mechanisms such asthermoregulation,osmoregulation, andacid-base regulation.^[100]

The circulatory system has two divisions, a systemic circuit (i.e. the left heart pumping oxygenated blood to the rest of the body (via theaorta) and into the right heart (via thevenae cava)) and apulmonary circuit (i.e. the right heart pumping deoxygenated blood to the lungs (via thepulmonary artery) and into the left heart (via thepulmonary vein)).^{[101][102][100]} In thehuman heart:

• There is oneatrium (which receives blood) and oneventricle (which expels blood) for each circulation, with a total of four chambers:left atrium,left ventricle,right atrium andright ventricle.^[100]
• Chambers of the heart are separated by theatrioventricular valves, which include the tricuspid valve on the right and the mitral valve on the left.^[100]
• The ventricles are separated from the large arteries via thesemilunar valves.^[103]

The heart is lined by a doubkle-layered sac known as thepericardium. Further circulatory routes include thecoronary circulation to the heart itself, thecerebral circulation to thebrain,renal circulation to thekidneys, andbronchial circulation to thebronchi in the lungs.

The circulatory system processes an average of 20 litres of blood per day throughcapillary filtration, which removes plasma from the blood. Roughly 17 litres of the filtered blood are reabsorbed directly into theblood vessels. The lymphatic system provides an accessory return route to the blood for the remaining three litres ofinterstitial fluid.^[104]

• Lymph is circulated in the body via muscle contraction and drains into thelymphatic ducts,^[105] which empty into thesubclavian veins, returning fluid into blood circulation.^[106]
• Alymph node is an organised collection of lymphoid tissue through which the lymph passes on its way back to the blood.^[107] Lymph nodes are particularly numerous in themediastinum, neck, pelvis,axilla, andinguinal region.^[108]
• Gut-associated lymphoid tissue, includingPeyer's patch, plays a major role in the immune system.
• Thespleen producesimmune cells to fightantigens in itswhite pulp, removesparticulate matter and aged blood cells, mainlyred blood cells in itsred pulp, and produces blood cells during fetal life.

Thenervous system coordinates theactions andsensory information of a person by transmittingsignals to and from different parts of the body, working in tandem with theendocrine system to respond to environmental events.^[109] The endocrine system comprisesfeedback loops ofhormones that are released byglands directly into thecirculatory system, which target and regulate distantorgans.^[110] Invertebrates, thehypothalamus is the neural control center for all endocrine systems, being adjacent to the pituatary gland, and linking the two systems together as theneuroendocrine system.

The connections betweenneurons, the primary cell of the nervous system, formsneural pathways,neural circuits, andlarge-scale brain networks.

Subsystems of the human nervous system include:

• Thecentral nervous system (CNS), comprising thebrain andspinal cord. Nerves that transmit signals from the CNS are calledmotor nerves. Nerves that exit from the brain are calledcranial nerves while those exiting from the spinal cord are calledspinal nerves.
• Theperipheral nervous system (PNS), comprising mainlynerves, enclosed bundles of axons. The PNS is divided into:
  • Thesomatic nervous system, which links the brain and spinal cord to sensory receptors and skeletal muscle.
  • Theautonomic nervous system, which is subdivided into:
    • Thesympathetic nervous system.
    • Theparasympathetic nervous system.
    • Theenteric nervous system, which controls thegastrointestinal system.
• Theneurovascular unit comprises the cells and vasculature channels within the nervous system that regulate cerebral blood flow.^[111]

The majorendocrine glands are thethyroid,parathyroid,pituitary,pineal, andadrenal glands (Latinrēn, rēnes, kidney), and thetestis andovaries. Thethyroid secretesthyroxine, thepituitary secretesgrowth hormone, thepineal secretesmelatonin, the testis secretestestosterone, and theovaries secreteestrogen andprogesterone.^[112]

Thehypothalamus,pancreas, andthymus also function as endocrine glands. The bones,kidneys, liver, heart, andgonads have secondary endocrine functions.^[113]Glands that signal each other in sequence are often referred to as an axis, such as thehypothalamic–pituitary–adrenal axis.Endocrinology also comprises the study of theexocrine glands (such assalivary glands,mammary glands, andsubmucosal glands within thegastrointestinal tract), which secrete hormones to the outside of the body, and ofparacrine signalling between cells over a relatively short distance.^[113]

Theventral body cavity is acavity in the anterior aspect of thehuman body, comprising thethoracic cavity andabdominopelvic cavity.^[114]

• Thethoracic cavity is protected by thethoracic wall (comprising therib cage and associated skin, muscle, andfascia), comprising themediastinum, heart and great vessels, and the bulk of therespiratory tract.^[115]
• Theabdominal cavity, lined by theperitoneum, contains the bulk of thegastrointestinal tract, the spleen and thekidneys. Abdominal organs may be classified as solid organs or hollow organs.
  • The solid organs are theliver,pancreas, spleen, kidneys, andadrenal glands.
  • The hollow organs of the abdomen are thestomach,intestines,gallbladder,bladder, andrectum.^[116]
• Thepelvic cavity contains theurinary bladder,internal reproductive organs, andrectum.

Viscera are the internal organs of the ventral cavity.^[117] The term "visceral" is contrasted with the term "parietal", meaning "of or relating to the wall of a body part,organ or cavity".^[118] The two terms are often used in describing a membrane or piece of connective tissue, referring to the opposing sides.^[119]

Therespiratory system allows forgas exchange, particularly ofcarbon dioxide andoxygen, in human beings. In the process ofbreathing or ventilation, themuscles of respiration pump air into the lungs, bringing it into close contact with the blood via millions of microscopic air sacs known asalveoli.^[120] The upper respiratory tract includes thenose,nasal cavities,sinuses,pharynx and the part of thelarynx above thevocal folds; the lower tract includes the lower part of thelarynx and the following aiways: thetrachea,bronchi,bronchioles andalveoli. The lungs are surrounded by flattened closed sacs known aspleura.

1. Contraction of thediaphragm (an upwardly domed sheet of muscle that separates the thoracic cavity from the abdominal cavity) and of theintercostal muscles (which lift up the ribs) increases the volume of the thoracic cavity.^[121] Because of this increased volume, the lungs (which comprise elastic connective tissue) begin to inflate.^{[122][123][124]}
2. Air, usually, enters from the nose.^[125] From the nose, air travels into the trachea (the largest of airways) into the two main bronchi,^[126] which branch into progressively narrower secondary and tertiary bronchi, which in turn branch into numerous smaller tubes known as the bronchioles,^[126] which in turn open into the alveoli.^[127]

The process of "respiration" is used to describe three distinct but related processes in the human body:cellular respiration,physiological respiration, and ventilation (or, breathing).^[128]

Thehuman digestive system, also known as the gastrointestinal system, comprises thegastrointestinal tract and the accessory organs of digestion: thetongue,salivary glands,pancreas,liver, andgallbladder.Digestion involves the breakdown of food into smaller and smaller components, until they can be absorbed and assimilated into the body. The process of digestion has three stages: thecephalic phase, thegastric phase, and theintestinal phase.

• Gallbladder: a hollow part of thebiliary tract that sits just beneath the liver, with the gallbladder body resting in a small depression.^[129] Commonly associated withgallstones, or cholelithiasis.^[130]

Thereproductive system in humans is typically classified into themale andfemale reproductive systems.

Theurinary system is the part of theexcretory system that removes waste in the form ofurine, comprising thekidneys,ureters,bladder, and theurethra. Other purposes of the urinary system include the regulation of blood volume and blood pressure; the control ofelectrolyte andmetabolite levels; and the regulation ofblood pH.^[131] Each kidney consists of functional units callednephrons. Followingfiltration of blood and further processing, theureters carryurine from the kidneys into theurinary bladder. Duringurination, theurethra carries urine out of the bladder through thepenis orvulva. The female and male urinary system are very similar, differing only in the length of the urethra.^[132]

Histology (also known as microanatomy or histoanatomy)^{[133][134][135]} is the branch of medicine that studies the microscopicanatomy of biologicaltissues.^{[136][137][138][139]} Histology is the microscopic counterpart togross anatomy, which looks at larger structures visible without amicroscope.^[139][140]Histopathology is the branch of histology that includes the microscopic identification and study of diseased tissue.^[141][142]

There are four basic types of tissue,^[143][144] of which all other tissues are considered to be subtypes.^[144]

• Muscle tissue comprisescardiac,skeletal, andsmooth muscle.^[145]
  • Smooth muscles control the flow of substances within thelumens of holloworgans, and are not consciously controlled. In the small intestine, smooth muscle contraction is characterised byperistalsis.
  • Skeletal muscles are attached to bones and arranged in opposing groups aroundjoints. Skeletal muscles and cardiac muscles havestriations, unlike smooth muscle. Only skeletal and smooth muscles are part of the musculoskeletal system and can move the body.^[145]
  • Cardiac muscles are found in theheart and are used only to circulateblood; like the smooth muscles, these muscles are not under conscious control.
• Nervous tissue comprisesneuroglia, which provide structural and metabolic support, andneurons, which send signals in the form of electrochemical impulses traveling alongaxons. Bundles of axons are known asnerve tracts andneural pathways. Impulses can be directly transmitted to neighbouring cells throughelectrical synapses or cause chemicals calledneurotransmitters to be released atchemical synapses.
  • The CNS includesastrocytes (-cyte, 'cell'; Greekκύτος (kútos), a hollow, vessel),^[146]oligodendrocytes,^[147]ependyma,^[148] andradial glia;^[149] the PNS includesSchwann cells,^[150]satellite glia,^[151] andenteric glia.^[152]
    • Astrocytes are star-shapedglial cells that have been observed to turn into neurons by virtue of theirpluripotency.^[153]
  • Microglia are specializedmacrophages capable ofphagocytosis that protect neurons of thecentral nervous system.^[154]
  • Pituicytes from theposterior pituitary are glial cells with characteristics in common to astrocytes.^[155]
  • Tanycytes in themedian eminence of thehypothalamus are a type ofependymal cell that descend from radial glia and line the base of thethird ventricle.^[156]
• Connective tissue is found in between other tissues and comprises connective tissue proper and special connective tissue.^[157] Most types of connective tissue consists of three main components:elastic andcollagen fibers,ground substance, andcells.^[158] Connectivetissue membranes include thesynovial membrane, which lines the inner surface ofcapsules ofsynovial joints,tendon sheaths, andsynovial bursas.^[159][160]
  • Connective tissue proper includesloose (or areolar) anddense (regular andirregular) connective tissue.Adipose (Latinadeps,adip-, fat) andreticular connective tissue are regarded by older sources as forms of loose connective tissue alongside areolar tissue, while some newer sources have termed them as forms of special connective tissue.^[161]
  • Special connective tissue includes supportive connective tissue (bone and cartilage) and fluid connective tissue (blood and lymph).^[162][163]
• Epithelial tissue are protective tissue that form theglands and outermost layer of many organs, including the skin (epidermis), internal organs (mesothelium), blood and lymphatic vessels (endothelium), as well as specialised organs (e.g.olfactory,respiratory,intestinal,transitional,vaginal,germinal (female), andgerminal (male) epithelia).^[164] Epithelia control the secretion of hormones into thecirculatory system, as well as the secretion of sweat, mucus, enzymes, and other products that are delivered byducts^[165]: 91 Epithelial membranes include theserous membrane (which lines body cavities), cutaneous membrane (i.e. theskin), andmucous membrane (which lines the interior of hollow organs). Other functions of epithelial cells includediffusion, filtration,secretion, selectiveabsorption, andtranscellular transport.

Fibres found in theextracellular matrix arecollagen fibers,elastic fibers, andreticular fibers.^[166] Collagen fibres are fixated in intercellular spaces viaground substance, a clear, colorless, and viscous fluid containingglycosaminoglycans andproteoglycans.^[167][168]

Types of secretion include:

• Apocrine
• Merocrine
• Holocrine
• Endocrine
• Exocrine
• Paracrine

Theneuron is the primary cell of the nervous system, supported structurally and metabolically by theglia.^[170] Neurons comprise the following specialisedorganelles:

• Soma, the body of the neuron. Containing thenucleus, mostprotein synthesis occurs here.
• Dendrites, cellular extensions with many branches. The branches formfractal patterns that repeat at multiple size scales.^[171] The majority of input to the neuron occurs via thedendritic spine.
• Axon, a finer and longer cable-like projection. The axon primarily carriesnerve signals away from the soma and carries some types of information back to it. Many neurons have only one axon, but this axon will usually undergo extensive branching, enabling communication with many target cells.
  • Axon hillock, the part of the axon that emerges from the soma. The axon hillock also has the greatest density ofvoltage-dependent sodium channels and the most negativethreshold potential, making it the most easily-excited part of the neuron and thespike initiation zone for the axon.
  • Axon terminal, found at the end of the axon farthest from the soma. Containssynapses.

Neurons communicate with other cells viasynapses, specialised structures that connect neurons and facilitate the transmission of electrical and chemical signals.^[172][173]

• Inelectrical synapses, the presynaptic and postsynaptic cell membranes are connected by special channels calledgap junctions that are capable of facilitating the direct flow of electrical current without the need forneurotransmitters, causing voltage changes in the presynaptic cell to induce voltage changes in the postsynaptic cell.^{[174][175][176]}
• Inchemical synapses, the activation ofvoltage-gated calcium channels in the presynaptic neuron results in the release of neurotransmitters into the synaptic cleft, which thereafter bind toreceptors located in the plasma membrane of the postsynaptic cell.
  • The neurotransmitter may initiate an electrical response or a secondary messenger pathway that may either excite or inhibit the postsynaptic neuron. Chemical synapses can be classified according to the neurotransmitter released:glutamatergic (often excitatory),GABAergic (often inhibitory),cholinergic (e.g. vertebrateneuromuscular junction), andadrenergic (releasingnorepinephrine). Depending on their release location, the receptors they bind to, and the ionic circumstances they encounter, various transmitters can be either excitatory or inhibitory. For instance,acetylcholine can either excite or inhibit depending on the type of receptors it binds to.^[177]
    • Inexcitatory synapses, an influx of Na+ driven by excitatory neurotransmitters opens cation channels, enhancing the probability ofdepolarization in postsynaptic neurons and the initiation of an action potential.
    • Ininhibitory synapses, the opening of either Cl- or K+ channels diminish the probability of depolarization in postsynaptic neurons and the initiation of an action potential.

Astrocytes also exchange information with the synaptic neurons, responding to synaptic activity and, in turn, regulatingneurotransmission.^[172]

Types of connective tissue cells include:

• Fibrocyte
• Mesenchyme
• Adipocyte
• Fibroblast (Greekβλαστός (blastós), germinate or bud)

The basal surface of epithelial tissue rests on abasement membrane and the free, apical, or apex surface faces body fluid or the outside. The basement membrane acts as a scaffolding on which epithelium can grow and regenerate after injuries, and comprises thebasal lamina andreticular lamina; although, some older sources use basement membrane and basal lamina synonymously.^[178] The basement membrane acts as a selectively permeable membrane that determines which substances will be able to enter the epithelium, as epithelial tissue has a nerve supply though no blood supply.^[179]: 3

There are three principal shapes of epithelial cell: squamous (scaly), columnar, and cuboidal.^[180]Transitional epithelium has cells that can change from squamous to cuboidal, depending on the amount of tension on the epithelium.^[181] Epithelial tissue can be further categorised as having a singular layer of cells as simple epithelium; or as layers of two or more cells deep as stratified epithelium—stratified squamous epithelium,stratified cuboidal epithelium, andstratified columnar epithelium.^{[182]: 94, 97 [183]} When taller simple columnar epithelial cells are viewed in cross section showing several nuclei appearing at different heights, they can be confused with stratified epithelia, and are thus termed aspseudostratified columnar epithelium.^[184] Epithelial cells are oftenciliated.^[185]

Stratified epithelia be further divided into keratinised,parakeratinised, andtransitional epithelia or urothelia.^[186][187]

Cell junctions, protein complexes that provide contact between cells and neighbouring cells or theextracellular matrix, are especially abundant in epithelial tissues. They build up the paracellular barrier of epithelia and control theparacellular transport.^[188] There are five main types of cell junctions:tight junctions,adherens junctions,desmosomes,hemidesmosomes, andgap junctions.

Major processes ingenetics include:

• Translation (biology)
• Transcription (biology)

Molecules involved incell signalling include:

• Glycoprotein
• Steroid
• Prostaglandin

Immunology is the branch of medicine that deals with theimmune system, a network ofbiological systems that protects humans fromdiseases. The immune system detects and responds topathogens, such asviruses,bacteria, andparasites, as well ascancer cells andforeign bodies. Humans have two major immune subsystems: Theinnate immune system, which provides a preconfigured response (e.g.defensins,complement system) to broad groups of situations and stimuli; and theadaptive immune system, which provides a tailored response to each stimulus by developing animmunological memory of molecules previously encountered.^[189][190] Mechanisms common to both subsystems, includephagocytosis,humoural immunity,cell-mediated immunity.

Cells in the innate immune system usepattern recognition receptors to recognize molecular structures produced by pathogens,^{[191][192][193]} identifying two classes of molecules:pathogen-associated molecular patterns (PAMPs), which are associated with microbialpathogens, anddamage-associated molecular patterns (DAMPs), which are associated with components of hosts' cells that are released duringcell damage orcell death.^[194]

Leukocytes (commonly known as white blood cells) act like independent, single-celled organisms and are the second arm of the innate immune system. The innate leukocytes include:

• Theprofessional phagocytes, which generally patrol the body searching for pathogens, but can be called to specific locations bycytokines.^[195] Once a pathogen has been engulfed by a phagocyte, it becomes trapped in an intracellularvesicle called aphagosome, which subsequently fuses with alysosome vesicle to form aphagolysosome. The pathogen is then killed by the activity of digestive enzymes or following arespiratory burst that releasesfree radicals into the phagolysosome.^[196][197]
  • Macrophages andneutrophils, which travel around the body in pursuit of invading pathogens.^[198]
    • Macrophages are cells that reside within tissues and produce an array of chemicals including enzymes,complement proteins, and cytokines. They also rid the body of worn-out cells and other debris and act asantigen-presenting cells that activate the adaptive immune system.^[199]
    • Neutrophils are normally found in thebloodstream and are the most abundant type of phagocyte, representing 50% to 60% of total circulating leukocytes.^[200] During the acute phase ofinflammation, neutrophils migrate toward the site of inflammation in a process calledchemotaxis and are usually the first cells to arrive at the scene of infection.
  • Dendritic cells are phagocytes in tissues that are in contact with the external environment, located mainly in the skin, nose, lungs, stomach, and intestines.^[201] Dendritic cells are a link between bodily tissues and the innate and adaptive immune systems, as theypresent antigens toT cells.^[201]

• Granulocytes (i.e. leukocytes withspecific granules), which include the neutrophils,innate lymphoid cells,mast cells,eosinophils, andbasophils.^[202]
  • Innate lymphoid cells (ILCs) derived fromcommon lymphoid progenitor and belong to thelymphoid lineage.^[203]
  • Mast cells reside inconnective tissues andmucous membranes and regulate the inflammatory response.^[204] They are most often associated withallergy andanaphylaxis.^[200]
  • Basophils and eosinophils are related to neutrophils. They secrete chemical mediators that are involved in defending againstparasites and play a role in allergic reactions, such asasthma.^[205]
• Natural killer cells (NK cells) do not directly attack invading microbes but destroy compromised host cells, such as tumor cells or virus-infected cells.^[206][202] NK cells recognise such cells by a condition known as "missing self", which involves low levels of a cell-surface marker called MHC I (major histocompatibility complex)—a situation that can arise in viral infection.^[207] Normal body cells are not recognized and attacked by NK cells because they express intact self MHC antigens, which inhibit NK cell activity.^[208]
• Monocytes, upon moving to injured tissue, turn intodendritic cells andmacrophages while promoting tissue healing.^{[209][210][211]}

The major humoral component of the innate immune response is the complement system, abiochemical cascade that attacks the surfaces of foreign cells.^[212][213] This response is activated by the binding of complement proteins tocarbohydrates on the surfaces ofmicrobes, or to antibodies that have attached to these microbes, which creates acell signal that triggers a rapid killing response,^[214] whose speed is significantly amplified after sequentialproteolytic activation of complementprotease molecules, controlled bypositive feedback.^[215] The cascade results in the production of peptides that attract immune cells; increasevascular permeability; andopsonize the surface of a pathogen, marking it for destruction. Complement binding can also kill cells directly by disrupting theirplasma membrane via amembrane attack complex.^[212]

Inflammation is one of the first responses of the immune system to infection.^[216] It is produced byeicosanoids andcytokines, which are released by injured or infected cells. In response to cytosolic PAMPs and DAMPs, pattern-recognition receptors calledinflammasomes form in order to generate active forms of the inflammatory cytokines IL-1β and IL-18.^[217]

• Eicosanoids includeprostaglandins that producefever and thedilation ofblood vessels associated with inflammation andleukotrienes that attract certainwhite blood cells (leukocytes).^[218][219]
• Common cytokines includeinterleukins that are responsible for communication between white blood cells;chemokines that promotechemotaxis; andinterferons that haveantiviral effects, such as shutting downprotein synthesis in the host cell.^[220]

Growth factors and cytotoxic factors may also be released. These chemicals recruit immune cells to the site of infection and promote the healing of any damaged tissue following the removal of pathogens.^[221]

The adaptive immune system allows for a stronger immune response as well asimmunological memory, where each pathogen is "remembered" by a signatureantigen.^[222] The adaptive immune response is antigen-specific, allowing for the generation of tailored immune responses, and requiring the recognition of specific "non-self" antigens during a process calledantigen presentation. The ability to mount these tailored responses is maintained in the body bymemory T-cells andmemory B-cells, which may be employed rapidly should a pathogen infect the body more than once.^[223]

B cells andT cells are the major types of lymphocytes, which form the cells of the adaptive immune system.^[224][225] B cells are involved in thehumoral immune response, while T cells are involved incell-mediated immune response. When B or T cells encounter their related antigens they multiply, and many "clones" of the cells are produced that target the same antigen. This is calledclonal selection.^[226] Some of the offspring of these B and T cells become long-lived memory cells, which remember each specific pathogen encountered and can mount a strong response if the pathogen is detected again. T-cells recognize pathogens by antigens that bind directly to T-cell surface receptors.^[227] B-cells use the protein, immunoglobulin, to recognise pathogens by their antigens.^[228]

• Killer T cells kill cells that are infected with pathogens or otherwise damaged or dysfunctional,^[229] which contain a complex of a specific antigen coupled to aClass I MHC receptor. When the receptor of a cytotoxic or "killer" T-cell contacts such cells, it releasescytotoxins, such asperforin, which form pores in the target cell'splasma membrane, allowingions, water and toxins to enter. The entry of another toxin calledgranulysin induces the target cell to undergoapoptosis.^[230]
• Helper T cells andregulatory T cells only recognize antigens coupled toClass II MHC molecules.
  • Helper T cells regulate both the innate and adaptive immune responses and help determine which immune responses the body makes to a particular pathogen.^[231][232] These cells have no cytotoxic activity and do not kill infected cells or clear pathogens directly. They instead control the immune response by directing other cells to perform these tasks.^[233]
• A third, minor subtype are theγδ T cells, which recognise intact antigens that are not bound to MHC receptors.^[234][235]
• AB cell identifies pathogens when antibodies on its surface bind to a specific foreign antigen.^[236] This antigen/antibody complex is taken up by the B cell and processed byproteolysis intopeptides. The B cell then displays these antigenic peptides on its surface MHC class II molecules, which attracts a matching helper T cell that releaseslymphokines and activates the B cell.^[237] As the activated B cell then begins todivide, its offspring (plasma cells)secrete millions of copies of the antibody that recognizes this antigen. These antibodies circulate inblood plasma andlymph, bind to pathogens expressing the antigen and mark them for destruction bycomplement activation or for uptake and destruction byphagocytes. Antibodies can also neutralize challenges directly, by binding to bacterial toxins or by interfering with the receptors that viruses and bacteria use to infect cells.^[238]

Lymph contains cellular debris, bacteria, proteins, andlymphocytes, the latter of which are generated largely in thebone marrow and matured or activated in thelymph nodes,spleen,thymus, andtonsils. Lymph also transportsantigen-presenting cells, such asdendritic cells, to the lymph nodes where an immune response is stimulated.^{[239][240][241][242][243][244]}

B cells andT cells are the major types of lymphocytes and are derived fromhematopoietic stem cells in the bone marrow.^[224] From the bone marrow, B cells immediately join the circulatory system and travel to secondary lymphoid organs in search of pathogens. T cells, on the other hand, travel from the bone marrow to the thymus, where they develop further, mature, and becomeimmunocompetent. In the thymus, T cells are exposed to a wide variety ofself-antigens;^[245] T cells can only recognize a "non-self" target only after antigens have been processed and presented in combination with the major histocompatibility complex (MHC) self-receptor.^[246] In contrast, the B cell antigen-specific receptor is an antibody molecule on the B cell surface, recognising unprocessed antigens (e.g. large molecules found on the surfaces of pathogens; smallhaptens, such aspenicillin, attached tocarrier molecules) without any need forantigen processing.^[247] Each lineage of B cell expresses a different antibody, so the complete set ofB cell antigen receptors represents all the antibodies that the human body can manufacture.^[224]

The secondary (or peripheral) lymphoid organs (e.g. lymph nodes and thespleen) maintain maturenaive T cells andnaive B cells; initiate theadaptive immune response;^[248] and are the sites of lymphocyte activation byantigens,^[249] which leads toclonal selection andaffinity maturation.^[209][250]

Dysfunction of the immune system can causeautoimmune diseases,inflammatory diseases andcancer.Immunodeficiency occurs when the immune system is less active than normal, resulting in recurring and life-threatening infections, and can be the result of agenetic disease such assevere combined immunodeficiency, acquired conditions such asHIV/AIDS, or the use ofimmunosuppressive medication.Autoimmunity describes a hyperactive immune system attacking normal tissues as if they were foreign organisms; diseases includeHashimoto's thyroiditis,rheumatoid arthritis,diabetes mellitus type 1, andsystemic lupus erythematosus.

• Immunomodulation

Hormones include:

• Calcitonin

List of cancer types:

• Carcinoma: Cancers derived fromepithelial cells. This group includes many of the most common cancers that occur in older adults. Nearly all cancers developing in thebreast,prostate,lung,pancreas, andcolon are carcinomas.
• Sarcoma: Cancers arising fromconnective tissue (i.e.bone,cartilage,fat,nerve), each of which develop from cells originating inmesenchymal cells outside of the bone marrow.
• Lymphoma andleukemia: These two classes of cancer arise from immature cells that originate in the bone marrow, and are intended to fully differentiate and mature into normal components of theimmune system and theblood, respectively. Acute lymphoblastic leukemia is the most common type ofcancer in children, accounting for ~30% of cases.^[251] However, far more adults than children develop lymphoma and leukemia.
• Germ cell tumor: Cancers derived frompluripotent cells, most often presenting in thetesticle or theovary(seminoma anddysgerminoma, respectively).
• Blastoma: Cancers derived from immature "precursor" cells or embryonic tissue. Blastomas aregenerally more common in children (e.g.neuroblastoma,retinoblastoma,nephroblastoma,hepatoblastoma,medulloblastoma, etc.) than in older adults.

Ophthalmology is the branch of medicine specialising in the eyes.

Neurology is the branch of medicine dedicated to thenervous system

Neuroanatomy is the study of the anatomy of thebrain and rest of thenervous system and uses a number of specialisedanatomical terms of neuroanatomy:^[35]

• Agyrus is an outward folding of the brain, for example theprecentral gyrus.
• Asulcus is an inward fold, or valley in the brain's surface, for example thecentral sulcus andlateral sulcus.

Structural and functional areas of the human brain

Human brain bisected in thesagittal plane, showing the white matter of the corpus callosum

Functional areas of the human brain. Dashed areas shown are commonly left hemisphere dominant.

The human brain containsmultiple regions, as does thespinal cord. There are multiple ways to divide the brain, including by theembryological development of the brain; into three parts: the cerebellum, brainstem, and cerebrum; theevolution of the brain; andcytoarchitecture, as in the case ofBrodmann areas. A popular model of the 'triune brain' — comprising the reptilian complex (basal ganglia), the paleomammalian complex (limbic system), and the neomammalian complex (neocortex) — was formerly popular during the 1960s, though is now regarded as a myth.^{[253][254][255][256]} 'Limbic system' and associated terms, however, remain in neuroanatomical use, although some neuroscientists have argued against such use.^[257]

Various other neuroanatomical systems have been developed according to functions, connections, and systems of the brain.

• Neuroendocrine axes
  • Hypothalamic–pituitary–adrenal axis
  • Hypothalamic–neurohypophyseal system
  • Hypothalamic–pituitary–gonadal axis
  • Hypothalamic–pituitary–thyroid axis
• Limbic system, corresponding to

• • Cortical areas:
    • Limbic lobe
    • Orbitofrontal cortex
    • Piriform cortex part of theolfactory system
    • Entorhinal cortex
    • Hippocampus and associated structures
    • Fornix andseptal nuclei
  • Subcortical areas:
    • Septal nuclei
    • Amygdala
    • Nucleus accumbens
  • Diencephalic structures:
    • Hypothalamus
    • Mammillary bodies
    • Anterior nuclei of thalamus

In the peripheral nervous system, the most common problem is the failure ofnerve conduction, which can be due to different causes includingdiabetic neuropathy anddemyelinating disorders such asmultiple sclerosis andamyotrophic lateral sclerosis.

• List of mental disorders

• Lists of diseases
• Pathology
• List of abbreviations for diseases and disorders

The suffix -plasia refers to the formation and development of cells, tissue, and organs, coming from Greekπλᾰ́σῐς (plásis), moulding, conformation.

• Achondroplasia (dwarfism)
• Anaplasia (structural differentiation loss within a cell or group of cells)
• Aplasia (organ or part of organ missing)
• Desmoplasia (connective tissue growth)
• Dysplasia (change in cell or tissuephenotype)
• Hyperplasia (proliferation of cells)
• Hypoplasia (congenital below-average number of cells, especially when inadequate)
• Metaplasia (conversion in cell type)
• Neoplasia (abnormal proliferation)
• Prosoplasia (development of new cell function)

The suffix trophy refers to the nourishment and development of cells, tissue, and organs, coming from Greekτροφή (trophḗ), food, nourishment.

• Abiotrophy (loss in vitality of organ or tissue)
• Atrophy (reduced functionality of an organ, with decrease in the number or volume of cells)
• Hypertrophy (increase in the volume of cells or tissues)
• Hypotrophy (decrease in the volume of cells or tissues)
• Dystrophy (any degenerative disorder resulting from improper or faulty nutrition)
• Pseudohypertrophy (false enlargement of muscle)

• Anticholinergic
• Alpha blocker
• Beta blocker

The publication ofmedical abbreviations for use in thejournals published by the American Medical Association is dictated by theAMA Manual of Style is thestyle guide of theAmerican Medical Association.^[259][260]

Periods are generally not used.^[261] Plurals for medical acronyms are represented by affixes a lowercases with noapostrophe.^[262] Arrows may also be used to indicate elevation (↑), diminution (↓), and causation (→, ←).^[263]

Medical slang such as, "TTFO", meaning "told tofuck off", may be used on a patient's chart in an informal and derogatory manner.^[265]

• Medical diagnosis
• Differential diagnosis

• Signs and symptoms

Although some medical authorities recommend mirroring the terminology transgender people use to describe their own genitals, such usage may feel uncomfortable and intimate to some transgender people, who prefer to use different terms in medical contexts than they would in personal settings. At the same time, patients may also be uncomfortable with anatomical terms they perceive as gendered.^[266]

Specialists recommend being open to using sex-neutral terms for organs, such asexternal genitals orlateral folds for the labia,internal reproductive organs for the uterus and ovaries, andchest for the breasts.^[267]

Style guides such as thePublication Manual of the American Psychological Association andAMA Manual of Style recommend usinggender-neutral language anddistinguishing between gender and biological sex, but do not give guidance on specific anatomical terminology.^[268]

Surveys of medical students show that approximately 20% usemedical mnemonics.^[269]

The earliest known glossaries of medical terms were discovered on Egyptian papyrus authored around 1600 B.C.^[270] Other precursors to modernmedical dictionaries include lists of terms compiled from theHippocratic Corpus in the first century AD.^[271][272] TheSynonyma Simonis Genuensis (theSynonyms ofSimon of Genoa), attributed to the physician toPope Nicholas IV in the year 1288, was printed by Antonius Zarotus at Milan in 1473. Referring to a copy held in the library of theCollege of Physicians of Philadelphia, Henry wrote in 1905 that "It is the first edition of the first medical dictionary."^[273] However, this claim is disputed as the composition only included lists of herbs and drugs.^[272]

At the beginning of theRenaissance, Italian universities began teaching a broader range of courses, such as law and medicine, whilst universities in northern Europe were still dominated by theology and related topics. All Europeanuniversities required Latin proficiency for admission. Latin was the dominant language of university education, where rules were enforced against the use of vernacular languages.^[274] Lectures and debates took place in Latin, and writing was in Latin, across the curriculum.

Latin dominated topics of international academic and scientific interest, especially at the level of abstract thought addressed to other specialists. To begin with, knowledge was already transmitted through Latin and it maintained specialised vocabularies not found in vernacular languages.^[275] By theearly modern period,Neo-Latin had become thelingua franca of science, medicine, legal discourse, theology, and education in Europe.^[276] Over time, the use of Latin continued where international communication with specialist audiences was paramount. Later, where some of the discourse moved to French, English or German, translations into Latin would allow texts to cross language boundaries, while authors in countries with much smaller language populations or less known languages would tend to continue to compose in Latin.^[277]

Latin's dominance over medicine began to change in the late seventeenth century, as philosophers and others began to write in their native language first, afterwards translating into Latin for international audiences.^[278] In the early part of the 1700s, Latin was still making a significant contribution to academic publishing, but was no longer dominant.^[279]

Examples of modern medical dictionaries includeMosby's Dictionary of Medicine, Nursing & Health Professions,Stedman's,Taber's, andDorland's.

• Glossary of medicine
• Glossary of scientific naming
• List of deprecated terms for diseases
• List of Greek and Latin roots in English