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History of construction
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The History of construction overlaps many other fields like structural engineering and relies on other branches of science like archaeology, history and architecture to investigate how the builders lived and recorded their accomplishments. Those fields allow us to analyse constructed buildings and other structures built since prehistory, the tools used and the different uses of building materials.
History of building is evolving by different trends in time, marked by few key principles : durability of the materials used, the increasing of height and span, the degree of control exercised over the interior environment and finally the energy available to the construction process.[1]
Contents
[hide]
1 Chronological development
1.1 Neolithic construction
1.2 Gallery of Neolithic tools
2 Copper Age and Bronze Age construction
3 Iron Age construction
3.1 Ancient Mesopotamia
3.1.1 Materials
3.2 Ancient Egypt
3.2.1 Materials
3.2.2 Technology
3.2.3 Achievements
3.3 Ancient Greece
3.4 Roman Empire
3.4.1 Materials
3.4.2 Organisation of labour
3.4.3 Technology
3.5 China
3.5.1 Stone Great Wall Sections
3.5.2 Soil Great Wall Sections
3.5.3 Sand (and Reed/Willow) Great Wall Sections
3.5.4 Brick Great Wall Sections
4 Middle ages
4.1 Materials
4.2 Design
4.3 Labour
4.4 Techniques
4.5 Achievements
5 Renaissance
5.1 Materials
5.2 Design
5.3 Labour
5.4 Technical advances
6 The seventeenth century
6.1 Materials and tools
6.2 Methods
7 The eighteenth century
7.1 Materials
8 The nineteenth century: Industrial Revolution
9 The twentieth century
10 Academic discipline
10.1 Early writers
10.2 Nineteenth-century studies
10.3 The early twentieth century studies
10.4 The late twentieth century
11 See also
12 References
13 External links
Chronological development[edit]
Neolithic construction[edit]
Wikimedia Commons has media related to Neolithic reconstructions.
A reconstruction of a pit-house type dwelling made with mammoth bones
Neolithic, also known as the New Stone Age, was a time period roughly from 9000 BC to 5000 BC named because it was the last period of the age before wood working began. The tools available were made from natural materials including bone, antler, hide, stone, wood, grasses, animal fibers, and the use of water. These tools were used by people to cut such as with the hand axe, chopper, adze, and celt. Also to scrape, chop such as with a flake tool, pound, pierce, roll, pull, leaver, and carry.
Building materials included bones such as mammoth ribs, hide, stone, metal, bark, bamboo, clay, lime plaster, and more. For example, the first bridges made by humans were probably just wooden logs placed across a stream and later timber trackways. In addition to living in caves and rock shelters, the first buildings were simple shelters, tents like the Inuit's tupiq, and huts sometimes built as pit-houses meant to suit the basic needs of protection from the elements and sometimes as fortifications for safety such as the crannog. Built self-sufficiently by their inhabitants rather than by specialist builders, using locally available materials and traditional designs and methods which together are called vernacular architecture.
The very simplest shelters, tents, leave no traces. Because of this, what little we can say about very early construction is mostly conjecture and based on what we know about the way nomadic hunter-gatherers and herdsmen in remote areas build shelters today. The absence of metal tools placed limitations on the materials that could be worked, but it was still possible to build quite elaborate stone structures with ingenuity using dry stone walling techniques such as at Skara Brae in Scotland, Europe's most complete Neolithic village. The first mud bricks, formed with the hands rather than wooden moulds, belong to the late Neolithic period and were found in Jericho. One of the largest structures of this period was the Neolithic long house. In all cases of timber framed and log structures in these very early cultures, only the very lowest parts of the walls and post holes are unearthed in archaeological excavations, making reconstruction of the upper parts of these buildings largely conjectural.
A reconstruction of a neolithic fortified village showing a palisade wall and stilt houses at the Pfahlbau Museum Unteruhldingen, Germany.
Neolithic architecture ranges from the tent to the megalith (an arrangement of large stones) and rock-cut architecture which are frequently temples, tombs, and dwellings. The most remarkable Neolithic structure in Western Europe is the iconic megalith known as Stonehenge, regarded by some archaeologists as displaying methods of timber construction such as at woodhenge translated into stone,[2] a process known as petrification. The now ruinous remains are of post and lintel construction and include massive sandstone lintels which were located on supporting uprights by means of mortise and tenon joints; the lintels themselves being end-jointed by the use of tongue and groove joints.[3] There is also evidence of prefabrication of the stonework; the symmetrical geometric arrays of stone clearly indicate that the builders of Stonehenge had mastered sophisticated surveying methods.[4] Neolithic villages large enough to have rural and urban features are called proto-cities to distinguish them from cities beginning with Eridu.
Gallery of Neolithic tools[edit]
Man using a hand axe
A Neolithic stone axe with a wooden handle.
A sickle for harvesting crops and thatching materials.
Various bone tools from China
Bone hammer from the Linear Pottery Culture
A chisel made of bone, Sechseläutenplatz, Zürich
A sledge for moving heavy materials.
A stone drill
Copper Age and Bronze Age construction[edit]
A bronze saw from the archaeological site of Akrotiri - Museum of prehistoric Thera - Santorini, Greece. Image: Norbert Nagel / Wikimedia Commons
The Copper Age is the early part of the Bronze Age. Bronze is made when tin is added to copper and brass is copper with zinc. Copper came into use before 5,000 BC and bronze around 3,100 BC, although the times vary by region. Copper and bronze were used for the same types of tools as stone such as axes and chisels, but the new, less brittle, more durable material cut better. Bronze was cast into desired shapes and if damaged could be recast. A new tool developed in the copper age is the saw. Other uses of copper and bronze were to "harden" the cutting edge of tools such as the Egyptians using copper and bronze points for working soft stone including quarrying blocks and making rock-cut architecture.
During the Bronze Age the corbelled arch came into use such as for beehive tombs. The wheel came into use but was not common until much later. Heavy loads were moved on boats, sledges (a primitive sled) or on rollers. The Egyptians began building stone temples with the post and lintel construction method and the Greeks and Romans followed this style.
Iron Age construction[edit]
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The Iron Age is a cultural period from roughly 1200 BC to 50 BC with the widespread use of iron for tools and weapons. Iron is not much harder than bronze but by adding carbon iron becomes steel which was being produced after about 300 BC. Steel can be hardened and tempered producing a sharp, durable cutting edge. A new woodworking tool allowed by the use of steel is the hand-plane.
Ancient Mesopotamia[edit]
The earliest large-scale buildings for which evidence survives have been found in ancient Mesopotamia. The smaller dwellings only survive in traces of foundations, but the later civilizations built very sizeable structures in the forms of palaces, temples and ziggurats and took particular care to build them out of materials that last, which has ensured that very considerable parts have remained intact. Major technical achievement is evidenced by the construction of great cities such as Uruk and Ur. The Ziggurat of Ur is an outstanding building of the period, despite major reconstruction work. Another fine example is the ziggurat at Chogha Zanbil in modern Iran. Cities created demands for new technologies such as drains for animal and human sewage and paved streets.
Archaeological evidence has shown the existence of pitched-brick vault[5] s such as at Tell al-Rimah in what is now Iraq.
Materials[edit]
The chief building material was the mud-brick, formed in wooden moulds similar to those used to make adobe bricks. Bricks varied widely in size and format from small bricks that could be lifted in one hand to ones as big as large paving slabs. Rectangular and square bricks were both common. They were laid in virtually every bonding pattern imaginable and used with considerable sophistication. Drawings survive on clay tablets from later periods showing that buildings were set out on brick modules. By 3500 BC, fired bricks came into use and surviving records show a very complex division of labour into separate tasks and trades.[citation needed] Fired bricks and stone were used for pavement.
Life in general was governed by complex ritual and this extended to rituals for setting-out buildings and moulding the first bricks. Contrary to popular belief the arch was not invented by the Romans, but was used in these civilizations.[citation needed] The later Mesopotamian civilizations, particularly Babylon and thence Susa, developed glazed brickwork to a very high degree, decorating the interiors and exteriors of their buildings with glazed brick reliefs, examples of which survive in the Tehran archaeological museum, the Louvre Museum in Paris and the Pergamon Museum in Berlin.
Detail of the Ishtar Gate (575 BC) showing the exceptionally fine glazed brickwork of the later period. Glazed bricks have been found from the 13th century B.C.
The pitched-brick vault is a type found in Mesopotamia circa 2000 BC.
Babylon,the archaeological site in 1932, before major reconstruction work undertaken by Sadam Hussein
Dried bricks stacked ready for firing without the use of a kiln.
Egyptian stonework showing tool marks and butterfly interlocks in the Temple of Kom Ombo begun 180-145 BC
Ancient Egypt[edit]
Wikimedia Commons has media related to Ancient architecture.
Further information: Ancient Egypt, Ancient Egyptian architecture, List of ancient Egyptian sites, List of Egyptian pyramids, and Egyptian pyramids
Aerial view of the Ramasseum in Thebes with its associated adobe structures
A copy of a wall painting in the tomb of Rekhmire between 1550 and 1292 BC.
As opposed to the cultures of ancient Mesopotamia which built in brick, the pharaohs of Egypt built huge structures in stone. The arid climate has preserved much of the ancient buildings.
Materials[edit]
Adobe (sun-baked mud brick) construction was used for ancillary buildings and normal houses in ancient times and is still commonly used in rural Egypt. The hot, dry climate was ideal for mud-brick, which tends to wash away in the rain. The Ramesseum in Thebes, Egypt (Luxor) provides one of the finest examples of mud brick construction. Extensive storehouses with mud-brick vaults also survive, all constructed with sloping courses to avoid the need for formwork.
The grandest buildings were constructed in stone, often from massive masonry blocks. The techniques used to move massive blocks used in pyramids and temples have been subject to extensive debate. Some authors have suggested that the larger may not be cut stone but fabricated with concrete.[citation needed]
Technology[edit]
Main article: Ancient Egyptian technology
Although the Egyptians achieved extraordinary feats of engineering, they appear to have done so with relatively primitive technology. As far as is known they did not use wheels or pulleys. They transported massive stones over great distances using rollers, ropes and sledges hauled by large numbers of workers. The ancient Egyptians are credited with inventing the ramp, lever, lathe, oven, ship, paper, irrigation system, window awning, door, glass, a form of plaster of Paris, the bath, lock, shadoof, weaving, a standardized measurement system, geometry, silo, a method of drilling stone, saw, steam power, proportional scale drawings, enameling, veneer, plywood, rope truss, and more. There are no surviving Egyptian manuals so there has been considerable speculation on how stones were lifted to great heights and obelisks erected. Most theories centre on the use of ramps.
Imhotep, who lived circa 2650–2600 BC, is credited with being the first recorded architect and engineer.
Achievements[edit]
The pyramids are chiefly impressive for their enormous size and the staggering manpower that must have been employed in their construction. The largest is the Great Pyramid of Giza which remained the tallest structure in the world for 3800 years (see List of tallest freestanding structures in the world). The engineering problems involved were chiefly to do with the transport of blocks, sometimes over long distances, their movement into location and exact alignment. It is now generally agreed that the skilled building workers were respected and well treated, but undoubtedly very large numbers of labourers were necessary to provide the brute force.
The methods used in the construction of the pyramids have been the subject of considerable research and discussion (see: Egyptian pyramid construction techniques).
Great Pyramid of Giza, the tallest building in the world for over 3800 years
Menkaures Pyramid, Giza
Ancient Greece[edit]
An illustration showing masonry techniques of ancient Greece and Rome.
Further information: Architecture of ancient Greece, List of ancient architectural records, and List of ancient Greek and Roman roofs
The ancient Greeks, like the Egyptians and the Mesopotamians, tended to build most of their common buildings out of mud brick, leaving no record behind them. However very many structures do survive, some of which are in a very good state of repair, although some have been partly reconstructed or re-erected in the modern era. The most dramatic are the Greek Temples. The Greeks made many advances in technology including plumbing, the spiral staircase, central heating, urban planning, the water wheel, the crane, and more.
The oldest "construction drawing" is in the Temple of Apollo at Didyma. An unfinished stone wall was etched with the profiles of columns and moldings, and the wall was never finished so the drawing was not erased: a rare glimpse into the history of working construction drawings.[6]
No timber structures survive (roofs, floors etc.), so our knowledge of how these were put together is limited. The spans are, in the main, limited and suggest very simple beam and post structures spanning stone walls. For the longer spans it is uncertain if the Greeks or Romans invented the truss but the Romans certainly used timber roof trusses. Before 650 B.C.E. the now famous ancient Greek temples were built of wood, but after this date began to be built of stone.[7] The process of a timber structure being repeated in stone is called petrification[8] or "petrified carpentry".
Fired clay was mainly restricted to roofing tiles and associated decorations, but these were quite elaborate. The roof tiles allow a low roof pitch characteristic of ancient Greek architecture. Fired bricks began to be employed with lime mortar. Very prominent buildings were roofed in stone tiles, which mimicked the form of their terracotta counterparts. While later cultures tended to construct their stone buildings with thin skins of finished stones over rubble cores, the Greeks tended to build out of large cut blocks, joined with metal cramps. This was a slow, expensive and laborious process which limited the number of buildings that could be constructed. The metal cramps often failed through corrosion.
Building structures mostly used a simple beam and column system without vaults or arches, which based strict limits on the spans that could achieved. However, the Greeks did construct some groin vaults, arch bridges and, with the Egyptians, the first "high rise", the Lighthouse of Alexandria, one of the Seven Wonders of the Ancient World.
Greek mathematics was technically advanced and we know for certain that they employed and understood the principles of pulleys, which would have enabled them to build jibs and cranes to lift heavy stonework to the upper parts of buildings. Their surveying skills were exceptional, enabling them to set out the incredibly exact optical corrections of buildings like the Parthenon, although the methods used remain a mystery. Simpler decoration, such as fluting on columns, was simply left until the drums of the columns were cut in place.
The ancient Greeks never developed the strong mortars which became an important feature of Roman construction.
Roman Empire[edit]
Further information: Roman engineering, Concrete Revolution, and Roman technology
Reconstructed Roman treadwheel crane at Bonn, Germany
The hand plane developed in the Iron Age and was known to be used by the Romans. These Roman planes were found in Germany and date to the 1st to 3rd century AD
In striking contrast to previous cultures, an enormous amount is known about Roman building construction. A very large amount survives, including complete intact buildings like the Pantheon, Rome and very well preserved ruins at Pompeii and Herculaneum. We also have the first surviving treatise on architecture by Vitruvius which includes extensive passages on construction techniques.
Materials[edit]
The great Roman development in building materials was the use of hydraulic lime mortar called Roman cement. Previous cultures had used lime mortars but by adding volcanic ash called a pozzolana the mortar would harden under water. This provided them with a strong material for bulk walling. They used brick or stone to build the outer skins of the wall and then filled the cavity with massive amounts of concrete, effectively using the brickwork as permanent shuttering (formwork). Later they used wooden shuttering that was removed for the concrete to cure.
An example of a temple made of Roman concrete in the 1st century BC is the Temple of Vesta in Tivoli, Italy. The concrete was made of nothing more than rubble and mortar. It was cheap and very easy to produce and required relatively unskilled labour to use, enabling the Romans to build on an unprecedented scale. They not only used it for walls but also to form arches, barrel vaults and domes, which they built over huge spans. The Romans developed systems of hollow pots for making their domes and sophisticated heating and ventilation systems for their thermal baths.[citation needed].
The Romans substituted bronze for wood in the roof truss(s) of the Pantheon's portico which was commissioned between 27 BC and 14 AD. The bronze trusses were unique but in 1625 Pope Urban VIII had the trusses replaced with wood and melted the bronze down for other uses. The Romans also made bronze roof tiles
Lead was used for roof covering material and water supply and waste pipes. The Latin name for lead is plumbum thus plumbing. Romans also made use of glass in construction with colored glass in mosaics and clear glass for windows. Glass came to be fairly commonly used in windows of public buildings.[9] Central heating in the form of a hypocaust, a raised floor heated by the exhaust of a wood or coal fire.
Organisation of labour[edit]
The Romans had trade guilds. Most construction was done by slaves or freed men. The use of slave labour undoubtedly cut costs and was one of the reasons for the scale of some of the structures. The Romans placed a considerable emphasis in building their buildings extremely fast, usually within two years. For very large structures the only way this could be achieved was by the application of vast numbers of workers to the task.
Technology[edit]
The invention of the waterwheel, sawmill, arch, and were by the Romans. The Romans also began using glass for architectural purposes after about 100 CE and used double glazing as insulated glazing. Roman roads included corduroy roads and paved roads, sometimes supported on raft or pile foundations and bridges. Vitruvius gives details of many Roman machines. The Romans developed sophisticated timber cranes allowing them to lift considerable weights to great heights. The upper limit of lifting appears to have been about 100 tonnes. Trajan's column in Rome contains some of the largest stones ever lifted in a Roman building, and engineers are still uncertain exactly how it was achieved.
A list of the longest, highest and deepest Roman structures can be found in the List of ancient architectural records. Roman building ingenuity extended over bridges, aqueducts, and covered amphitheatres. Their sewerage and water-supply works were remarkable and some systems are still in operation today. The only aspect of Roman construction for which very little evidence survives is the form of timber roof structures, none of which seem to have survived intact. Possibly, triangulated roof trusses were built, this being the only conceivable way of constructing the immense spans achieved, the longest exceeding 30 metres (see List of Ancient Greek and Roman roofs).
China[edit]
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The Far East used a different method of sawing logs than the West's method of pit-sawing with a saw pit: The concept is the same but as shown here the log is angled and no pit is used.
China is a cultural hearth area of eastern Asia, many Far East building methods and styles evolved from China. A famous example of Chinese construction is the Great Wall of China built between the 7th and 2nd centuries BC. The Great Wall was built with rammed earth, stones, and wood and later bricks and tiles with lime mortar. Wooden gates blocked passageways. The oldest archaeological examples of mortise and tenon type woodworking joints were found in China dating to about 5000 BC.
The Yingzao Fashi is the oldest complete technical manual on Chinese architecture. The Chinese followed the state rules for thousands of years so many of the ancient, surviving buildings were built with the methods and materials still used in the 11th century. Chinese temples are typically wooden timber frames on an earth and stone base. The oldest wooden building is the Nanchan Temple (Wutai) dating from 782 CE. However, Chinese temple builders regularly rebuild the wooden temples so some parts of these ancient buildings are of different ages. Traditional Chinese timber frames do not use trusses but rely only on post and lintel construction. An important architectural element are the dougong bracket sets. The Songyue Pagoda is the oldest brick pagoda dating to 523 AD. It was built with yellow fired bricks laid in clay mortar, with twelve sides and fifteen levels of roofs. The Anji Bridge is the worlds oldest "open-spandrel stone segmental arch bridge" built in 595-605 AD. The bridge is built with sandstone joined with dovetail, iron joints.
Most of the (restored) Great Wall sections we see today were built with bricks, and cut stone blocks/slabs. Where bricks and blocks weren't available, tamped earth, uncut stones, wood, and even reeds were used as local materials. Wood was used for forts and as an auxiliary material. Where local timber wasn't enough, they had it delivered in.
Stone Great Wall Sections[edit]
In mountain areas, workers quarried stone to build the Great Wall. Using the mountains themselves as footings, the outer layer of the Great Wall was built with stone blocks (and bricks), and filled with uncut stone and anything else available (like earth and dead workers).
Soil Great Wall Sections[edit]
On the plains Great Wall workers made use of local soil (sand, loess, etc.) and rammed it into compact layers. Jiayuguan's Great Wall section in west China was mainly built with dusty loess soil — "the most erodible soil on the planet". It's amazing that sections 2,000 years old still remain mostly intact!
Sand (and Reed/Willow) Great Wall Sections[edit]
Sand doesn't stick together, so how could a wall be built with sand? Sand was used as a fill material between reed and willow layers.
West China around Dunhuang is desert. Innovative builders there made use of reeds and willow brought in from rivers and oases to build a strong wall. Jade Gate Pass (Yumenguan) Great Wall Fort was built with 20-cm layers of sand and reed, an impressive 9 meters high.
Brick Great Wall Sections[edit]
The Ming Dynasty Great Wall was mostly built with bricks. To build a strong wall with bricks, they used lime mortar. Workers built brick and cement factories with local materials near the wall.
Middle ages[edit]
Further information: Medieval technology and Vault (architecture)
The Middle Ages of Europe span from the 5th to 15th centuries AD from the fall of the Western Roman Empire to the Renaissance and is divided into Pre-Romanesque and Romanesque periods.
Fortifications, castles and cathedrals were the greatest construction projects. The Middle Ages began with the end of the Roman era and many Roman building techniques were lost. But some Roman techniques, including the use of iron ring-beams, appear to have been used in the Palatine Chapel at Aachen, c. 800 AD, where it is believed builders from the Langobard Kingdom in northern Italy contributed to the work.[10] A revival of stone buildings in the 9th century and the Romanesque style of architecture began in the late 11th century. Also notable are the stave churches in Scandinavia.
Villard de Honnecourt's drawing of a flying buttress at Reims, ca. AD 1320–1335 (Bibliothèque nationale)
Materials[edit]
Most buildings in Northern Europe were constructed of timber until c. 1000 AD. In Southern Europe adobe remained predominant. Brick continued to be manufactured in Italy throughout the period 600–1000 AD but elsewhere the craft of brick-making had largely disappeared and with it the methods for burning tiles. Roofs were largely thatched. Houses were small and gathered around a large communal hall. Monasticism spread more sophisticated building techniques. The Cistercians may have been responsible for reintroducing brick-making to the area[clarification needed] from the Netherlands, through Denmark and Northern Germany to Poland leading to Backsteingotik. Brick remained the most popular prestige material in these areas throughout the period.[citation needed] Elsewhere buildings were typically in timber or where it could be afforded, stone. Medieval stone walls were constructed using cut blocks on the outside of the walls and rubble infill, with weak lime mortars. The poor hardening properties of these mortars were a continual problem, and the settlement of the rubble filling of Romanesque and Gothic walls and piers is still a major cause for concern.
Design[edit]
There were no standard textbooks on building in the Middle Ages. Master craftsmen transferred their knowledge through apprenticeships and from father to son. Trade secrets were closely guarded, as they were the source of a craftsman's livelihood. Drawings only survive from the later period. Parchment was too expensive to be commonly used and paper did not appear until the end of the period. Models were used for designing structures and could be built to large scales. Details were mostly designed at full size on tracing floors, some of which survive.
Labour[edit]
In general, medieval buildings were built by paid workers. Unskilled work was done by labourers paid by the day. Skilled craftsmen served apprenticeships or learned their trade from their parents. It is not clear how many women were members of a guild holding a monopoly on a particular trade in a defined area (usually within the town walls). Towns were in general very small by modern standards and dominated by the dwellings of a small number of rich nobles or merchants, and by cathedrals and churches.
Techniques[edit]
Church in Kizhi, Russia is listed as a UNESCO world heritage site as a building constructed entirely out of wood, in the log building technique
Romanesque buildings of the period 600–1100 AD[clarification needed] were entirely roofed in timber or had stone barrel vaults covered by timber roofs. The Gothic style of architecture with its vaults, flying buttresses and pointed gothic arches developed in the twelfth century, and in the centuries that followed ever more incredible feats of constructional daring were achieved in stone. Thin stone vaults and towering buildings were constructed using rules derived by trial and error. Failures were frequent, particularly in difficult areas such as crossing towers.
The pile driver was invented around 1500.
Achievements[edit]
The scale of fortifications and castle building in the Middle Ages was remarkable, but the outstanding buildings of the period were the Gothic cathedrals with thin masonry vaults and walls of glass. Outstanding examples are: Beauvais Cathedral, Chartres Cathedral, King's College Chapel and Notre Dame, Paris.
Renaissance[edit]
Further information: Renaissance Architecture
The Renaissance in Italy, the invention of moveable type and the Reformation changed the character of building. The rediscovery of Vitruvius had a strong influence. During the Middle Ages buildings were designed by the people that built them. The master mason and master carpenters learnt their trades by word of mouth and relied on experience, models and rules of thumb to determine the sizes of building elements. Vitruvius however describes in detail the education of the perfect architect who, he said, must be skilled in all the arts and sciences. Filippo Brunelleschi was one of the first of the new style of architects. He started life as a goldsmith and educated himself in Roman architecture by studying ruins. He went on to engineer the dome of Santa Maria del Fiore in Florence.
Materials[edit]
The major breakthroughs in this period were to do with the technology of conversion. Water mills in most of western Europe were used to saw timber and convert trees into planks. Bricks were used in ever increasing quantities. In Italy the brickmakers were organised into guilds although the kilns were mostly in rural areas because of the risk of fire and easy availability of firewood and brickearth. Brickmakers were typically paid by the brick, which gave them an incentive to make them too small. As a result, legislation was laid down regulating the minimum sizes and each town kept measures against which bricks had to be compared. An increasing amount of ironwork was used in roof carpentry for straps and tension members. The iron was fixed using forelock bolts. The screw-threaded bolt (and nut) could be made and are found in clockmaking in this period, but they were labour-intensive and thus not used on large structures. Roofing was typically of terracotta roof tiles. In Italy they followed Roman precedents. In northern Europe plain tiles were used. Stone, where available, remained the material of choice for prestige buildings.
Design[edit]
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The rebirth of the idea of an architect in the Renaissance radically changed the nature of building design. The Renaissance reintroduced the classical style of architecture. Leon Battista Alberti's treatise on architecture raised the subject to a new level, defining architecture as something worthy of study by the aristocracy. Previously it was viewed merely as a technical art, suited only to the artisan. The resulting change in status of architecture and more importantly the architect is key to understanding the changes in the process of design. The Renaissance architect was often an artist (a painter or sculptor) who had little knowledge of building technology but a keen grasp of the rules of classical design. The architect thus had to provide detailed drawings for the craftsmen setting out the disposition of the various parts. This was what is called the process of design, from the Italian word for drawing. Occasionally the architect would get involved in particularly difficult technical problems but the technical side of architecture was mainly left up to the craftsmen. This change in the way buildings were designed had a fundamental difference on the way problems were approached. Where the Medieval craftsmen tended to approach a problem with a technical solution in mind, the Renaissance architects started with an idea of what the end product needed to look like and then searched around for a way of making it work. This led to extraordinary leaps forward in engineering.
Labour[edit]
The structure of the dome of Florence cathedral , showing the double skin structure
Pieter Bruegel the Elder's Tower of Babel, illustrating construction techniques of the 16th century
Labour in the Renaissance was much the same as in the Middle Ages: buildings were built by paid workers. Unskilled work was done by labourers paid by the day. Skilled craftsmen served apprenticeships or learned their trade from their parents. Craftsmen were organized in guilds which provided a limited form of building regulation in return for members of the guild holding a monopoly on a particular trade in a defined area (usually within the town walls). Towns were in general very small by modern standards and dominated by the dwellings of a small number of rich nobles or merchants and cathedrals and churches.
Technical advances[edit]
The wish to return to classical architecture created problems for the Renaissance buildings. The builders did not use concrete and thus comparable vaults and domes had to be replicated in brick or stone. The greatest technical feats were undoubtedly in these areas. The first major breakthrough was Brunelleschi's project for the dome of Santa Maria del Fiore. Brunelleschi managed to devise a way of building a huge dome without formwork, relying instead on the weight of the bricks and the way they were laid to keep them in position and the shape of the dome to keep it standing. The exact way the dome was built is still subject to debate today as it is not possible to take the dome apart to study its construction without destroying it. The dome is a double skin, linked by ribs, with a series of wooden and stone chains around it at intervals to attempt to deal with hoop stresses.
Brunelleschi's dome was completed (up to the base of the lantern) in 1446. Its size was soon surpassed by the dome of St Peter's, built using flying scaffolding supported on the cornices and constructed using two stone shells.
The seventeenth century[edit]
The seventeenth century saw the birth of modern science which would have profound effects on building construction in the centuries to come. The major breakthroughs were towards the end of the century when architect-engineers began to use experimental science to inform the form of their buildings. However it was not until the eighteenth century that engineering theory developed sufficiently to allow sizes of members to be calculated. Seventeenth-century structures relied strongly on experience, rules of thumb and the use of scale models.
Materials and tools[edit]
The major breakthrough in this period was in the manufacture of glass, with the first cast plate glass being developed in France. Iron was increasingly employed in structures. Christopher Wren used iron hangers to suspend floor beams at Hampton Court Palace, and iron rods to repair Salisbury Cathedral and strengthen the dome of St Paul's Cathedral. Most buildings had stone ashlar surfaces covering rubble cores, held together with lime mortar. Experiments were made mixing lime with other materials to provide a hydraulic mortar, but there was still no equivalent of the Roman concrete. In England, France and the Dutch Republic, cut and gauged brickwork was used to provide detailed and ornate facades. The triangulated roof truss was introduced to England and used by Inigo Jones and Christopher Wren.
Many tools have been made obsolete by modern technology, but the line gauge, plumb-line, the carpenter's square, the spirit level, and the drafting compass are still in regular use.
Methods[edit]
Despite the birth of experimental science, the methods of construction in this period remained largely medieval. The same types of crane that had been used in previous centuries were being still being employed. Flying scaffolds were employed at St Paul's Cathedral, England and in the dome of St Peters, Rome, but otherwise the same types of timber scaffolding that had been in use centuries before were retained. Cranes and scaffolding depended on timber. Complex systems of pulleys allowed comparatively large loads to be lifted, and long ramps were used to haul loads up to the upper parts of buildings.
The eighteenth century[edit]
The eighteenth century saw the development of many the ideas that had been born in the late seventeenth century. The architects and engineers became increasingly professionalised. Experimental science and mathematical methods became increasingly sophisticated and employed in buildings. At the same time the birth of the industrial revolution saw an increase in the size of cities and increase in the pace and quantity of construction.
Materials[edit]
The major breakthroughs in this period were in the use of iron (both cast and wrought). Iron columns had been used in Wren's designs for the House of Commons and were used in several early eighteenth-century churches in London, but these supported only galleries. In the second half of the eighteenth century the decreasing costs of iron production allowed the construction of major pieces of iron engineering. The Iron Bridge at Coalbrookdale (1779) is a particularly notable example. Large-scale mill construction required fire-proof buildings and cast iron became increasingly used for columns and beams to carry brick vaults for floors. The Louvre in Paris boasted an early example of a wrought-iron roof. Steel was used in the manufacture of tools but could not be made in sufficient quantities to be used for building.
Brick production increased markedly during this period. Many buildings throughout Europe were built of brick, but they were often coated in lime render, sometimes patterned to look like stone. Brick production itself changed little. Bricks were moulded by hand and fired in kilns no different to those used for centuries before. Terracotta in the form of Coade stone was used as an artificial stone in the UK.
The nineteenth century: Industrial Revolution[edit]
The industrial revolution was manifested in new kinds of transportation installations, such as railways, canals and macadam roads. These required large amounts of investment. New construction devices included steam engines, machine tools, explosives and optical surveying. The steam engine combined with two other technologies which blossomed in the nineteenth century, the circular saw and machine cut nails, lead to the use of balloon framing and the decline of traditional timber framing.[11]
As steel was mass-produced from the mid-19th century, it was used, in form of I-beams and reinforced concrete. Glass panes also went into mass production, and changed from luxury to every man's property.
Plumbing appeared, and gave common access to drinking water and sewage collection.
Building codes have been applied since the 19th century, with special respect to fire safety.
The twentieth century[edit]
Woolworth Building under construction in 1912
A structural worker on the Empire State Building. Workers such as this man were often referred to as "old timers" because in that time era, most men working on building structures were middle-aged.
Burj Khalifa, the world's tallest building, was finished in 2010.
With the Second Industrial Revolution in the early 20th century, elevators and cranes made high rise buildings and skyscrapers possible, while heavy equipment and power tools decreased the workforce needed. Other new technologies were prefabrication and computer-aided design.
Trade unions were formed to protect construction workers' interests. Personal protective equipment such as hard hats and earmuffs also came into use.
From the 20th century, governmental construction projects were used as a part of macroeconomic stimulation policies, especially during the Great depression (see New Deal). For economy of scale, whole suburbs, towns and cities, including infrastructure, are often planned and constructed within the same project (called megaproject if the cost exceeds US$1 billion), such as Brasília in Brazil, and the Million Programme in Sweden.
In the end of the 20th century, ecology, energy conservation and sustainable development have become more important issues of construction.
Academic discipline[edit]
There is no established academic discipline of construction history but a growing number of researchers and academics are working in this field, including structural engineers, archaeologists, architects, historians of technology and architectural historians. Although the subject has been studied since the Renaissance and there were a number of important studies in the nineteenth century, it largely went out of fashion in the mid-twentieth century.[12] In the last thirty years there has been an enormous increase in interest in this field, which is vital to the growing practice of building conservation.[13]
Early writers[edit]
The earliest surviving book detailing historical building techniques is the treatise of the Roman author, Vitruvius, but his approach was neither scholarly nor systematic. Much later, in the Renaissance, Vasari mentions Filippo Brunelleschi's interest in researching Roman building techniques, although if he wrote anything on the subject it does not survive. In the seventeenth century, Rusconi's illustrations for his version of Leon Battista Alberti's treatise explicitly show Roman wall construction but most of the interest in antiquity was in understanding its proportions and detail and the architects of the time were content to build using current techniques. While early archaeological studies and topographic works such as the engravings of Giovanni Battista Piranesi show Roman construction they were not explicitly analytical and much of what they do show is made up.
Nineteenth-century studies[edit]
In the nineteenth century, lecturers increasingly illustrated their lectures with images of building techniques used in the past and these type of images increasingly appeared in construction text books, such as Rondelet's. The greatest advances however were made by English and French (and later German) architects attempting to understand, record and analyse Gothic buildings. Typical of this type of writing are the works of Robert Willis in England, Viollet-le-Duc in France and Ungewitter in Germany. None of these however were seeking to suggest that the history of construction represented a new approach to the subject of architectural history. August Choisy was perhaps the first author to seriously attempt to undertake such a study.
The early twentieth century studies[edit]
Santiago Heurta has suggested that it was modernism, with its emphasis on the employment of new materials, that abruptly ended the interest in construction history that appeared to have been growing in the last few decades of the nineteenth century and the early years of the twentieth. With the advent of concrete and steel frame construction, architects, who had been the chief audience for such studies, were no longer as interested as they had been in understanding traditional construction, which suddenly appeared redundant. Very little was thus published between 1920 and 1950. The revival of interest started in archaeology with the studies of Roman construction in the 1950s, but it was not until the 1980s that construction history began to emerge as an independent field.
The late twentieth century[edit]
By the end of the twentieth century, steel and concrete construction were themselves becoming the subject of historical investigation.The Construction History Society was formed in the UK in 1982.[14] It produces the only academic international journal devoted to the subject annually. The First International Congress on Construction History was held in Madrid in 2003.[15] This was followed by the Second International Congress in 2006 [16] in Queens College, Cambridge, England and the Third International Congress held in Cottbus in 2009,[17] and the Fourth International Congress held in Paris in July 2012 [18]
See also[edit]
Architecture portal
History of architecture
History of structural engineering
History of water supply and sanitation
The Construction History Society
Timeline of architecture
References[edit]
Jump up ^ Alfred Swenson and Pao-Chi Chang, "History of Building"
Jump up ^ Atkinson, Richard, Stonehenge Penguin Books 1956
Jump up ^ A paper showing the joints used at Stonehenge
Jump up ^ Johnson, Anthony, Solving Stonehenge: The New Key to an Ancient Enigma. (Thames & Hudson, 2008) ISBN 978-0-500-05155-9
Jump up ^ Trudy S. Kawami, "Parthian Brick Vaults in Mesopotamia, Their Antecedents and Descendants" Columbia University
Jump up ^ Alfred Swenson and Pao-Chi Chang (Britannica), "The History of Building Construction
Jump up ^ Hunt, Norman. Living in ancient Greece. New York, N.Y.: Chelsea House Publishers, 2009. 24. ISBN 0816063397
Jump up ^ Strickland, Carol, and Amy Handy. The Annotated Arch: A Crash Course in the History of Architecture. Kansas City, MO: Andrews McMeel Pub., 2001. 12. ISBN 0740710249
Jump up ^ "The History of Building"
Jump up ^ Stephany, Erich Der Dom zu Aachen (Aachen Cathedral) Arend und Ortmann, Aachen, 1972
Jump up ^ Upton, Dell. Architecture in the United States. Oxford: Oxford University Press, 1998. 153. ISBN 019284217X
Jump up ^ Bill Addis. Building: 3000 years of Design Engineering and Construction. Phaidon. 2007. p. 632
Jump up ^ A.Becchi, M.Corradi, F.Foce & O. Pedemonte (eds.). Construction History: Research Perspectives in Europe. Associazione Eduardo Benvenuto. 2004
Jump up ^ http://www.constructionhistory.co.uk
Jump up ^ First International Congress on Construction History Madrid 2003
Jump up ^ Second International Congress on Construction History'at University of Cambridge, 2006
Jump up ^ Third International Congress on Construction History May 2009
Jump up ^ Fourth International Congress on Construction History Paris, July 2012.
External links[edit]
Wikimedia Commons has media related to Historical building construction.
History of construction at Curlie (based on DMOZ)
Construction History Society (International) [1]
Construction History Society (USA) [2]
Sociedad Espanola de Historia de la Construction (in Spanish) [3]
I. International Congress on Construction History: Congress Page (English) including free online proceedings [4]
II. International Congress on Construction History: Congress Page (English) including free online proceedings [5]
III. International Congress on Construction History: Congress page (English) including free online proceedings [6] and review [7] (German)
IV. International Congress on Construction History: to be held in Paris in 2012 [8]
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Sebaceous gland
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Sebaceous gland
Schematic view of hair follicle and sebaceous gland.
Cross-section of all skin layers. A hair follicle with associated structures. (Sebaceous glands labeled at center left.)
Details
Identifiers
Latin
glandula sebacea
MeSH
A10.336.827
Dorlands
/Elsevier
12392642
TA
A16.0.00.030
FMA
59160
Anatomical terminology
[edit on Wikidata]
Sebaceous glands are microscopic exocrine glands in the skin that secrete an oily or waxy matter, called sebum, to lubricate and waterproof the skin and hair of mammals. In humans, they occur in the greatest number on the face and scalp, but also on all parts of the skin except the palms of the hands and soles of the feet. The type of secretion of the sebaceous glands is referred to as holocrine.
In the eyelids, meibomian glands, also called tarsal glands, are a type of sebaceous gland that secrete a special type of sebum into tears. Fordyce spots are ectopic (misplaced) sebaceous glands found usually on the lips, gums and inner cheeks, and genitals. Areolar glands surround the female nipples. Preputial glands also known as Tyson's glands are found in the genitals of both sexes of mice and rats.
Several related medical conditions involve sebum—including acne, sebaceous cysts, hyperplasia, and sebaceous adenoma. These are usually attributable to overactive sebaceous glands, which produce excess sebum.
Contents
[hide]
1 Structure
1.1 Location
1.2 Development
2 Function
2.1 Sebum
2.2 Immune function and nutrition
2.3 Unique sebaceous glands
3 Clinical significance
3.1 Acne
3.2 Other
4 History
5 Other animals
6 See also
7 References
8 External links
Structure[edit]
Location[edit]
The sebaceous glands are found throughout all areas of the skin except the palms of the hands and soles of the feet.[1] There are two types of sebaceous gland, those connected to hair follicles, in pilosebaceous units, and those that exist independently.[2]
Sebaceous glands are found in hair-covered areas, where they are connected to hair follicles. One or more glands may surround each hair follicle, and the glands themselves are surrounded by arrector pili muscles. The glands have an acinar structure (like a many-lobed berry), in which multiple glands branch off a central duct. Relative to keratinocytes that make up the hair follicle, sebaceous glands are composed of huge cells with many large vesicles that contain the sebum.[3] These cells express Na+ and Cl− ion channels, ENaC and CFTR (see Fig. 6 and Fig. 7 in reference[3]).
The glands deposit sebum on the hairs, and bring it to the skin surface along the hair shaft. The structure consisting of hair, hair follicle, arrector pili muscles, and sebaceous gland is an epidermal invagination known as a pilosebaceous unit.[2]
Sebaceous glands are also found in hairless areas (glabrous skin) of the eyelids, nose, penis, labia minora, the inner mucosal membrane of the cheek, and nipples.[2] Some sebaceous glands have unique names. Sebaceous glands on the lip and mucosa of the cheek, and on the genitalia, are known as Fordyce spots, and glands on the eyelids are known as meibomian glands. Sebaceous glands of the breast are also known as Montgomery's glands.[4]
Development[edit]
Sebaceous glands are first visible from the 13th to the 16th week of fetal development, as bulgings off hair follicles.[5] Sebaceous glands develop from the same tissue that gives rise to the epidermis of the skin. Overexpression of the signalling factors Wnt, Myc and SHH all increase the likelihood of sebaceous gland presence.[4]
The sebaceous glands of a human fetus secrete a substance called vernix caseosa, a waxy, translucent white substance coating the skin of newborns.[6] After birth, activity of the glands decreases until there is almost no activity during ages 2–6 years, and then increases to a peak of activity during puberty, due to heightened levels of androgens.[5]
Base of pilosebaceous unit
Insertion of sebaceous glands into hair shaft
Sagittal section through the upper eyelid.
A hair follicle with associated structures.
Function[edit]
Sebaceous glands secrete the oily, waxy substance called sebum (Latin: fat, tallow) that is made of triglycerides, wax esters, squalene, and metabolites of fat-producing cells.[7][8] Sebum waterproofs and lubricates the skin and hair of mammals.[9] Sebaceous secretions in conjunction with apocrine glands also play an important thermoregulatory role. In hot conditions, the secretions emulsify the sweat produced by the eccrine glands and this produces a sheet of sweat that is not readily lost in drops of sweat. This is of importance in delaying dehydration. In colder conditions, the nature of sebum becomes more lipid and in coating the hair and skin, rain is effectively repelled.[10][11]
Sebum is produced in a holocrine process, in which cells within the sebaceous gland rupture and disintegrate as they release the sebum and the cell remnants are secreted together with the sebum.[12][13] The cells are constantly replaced by mitosis at the base of the duct.[2]
Sebum[edit]
Sebum, secreted by the sebaceous gland in humans, is primarily composed of triglycerides (~41%), wax esters (~26%), squalene (~12%), and free fatty acids (~16%).[6][14] The composition of sebum varies across species.[14] Wax esters and squalene are unique to sebum and not produced as final products anywhere else in the body.[4] Sapienic acid is a sebum fatty acid that is unique to humans, and is implicated in the development of acne.[15] Sebum is odorless, but its breakdown by bacteria can produce strong odors.[16]
Sex steroids are known to affect the rate of sebum secretion; androgens such as testosterone have been shown to stimulate secretion, and estrogens have been shown to inhibit secretion.[17] Dihydrotestosterone acts as the primary androgen in the prostate and in hair follicles.[18][19]
Immune function and nutrition[edit]
Sebaceous glands are part of the body's integumentary system and serve to protect the body against germs. Sebaceous glands secrete acids that form the acid mantle. This is a very fine, slightly acidic film on the surface of the skin that acts as a barrier to bacteria, viruses, and other potential contaminants that might penetrate the skin.[20] The pH of the skin is between 4.5 and 6.2,[21] and this acidity helps to neutralise the primarily alkaline nature of contaminants.[22]
Sebaceous lipids make an important contribution in maintaining the integrity of the skin barrier, and express both pro-inflammatory and anti-inflammatory properties.[10][23] Sebum may act as a delivery system for antioxidants, antimicrobial lipids, pheromones, and hydration of the stratum corneum.[24] The insoluble fatty acids contained within sebum have broad antimicrobial activity.[24][25] Additionally, sebaceous gland secretion provides vitamin E to the upper layers of facial skin.[26]
Unique sebaceous glands[edit]
During the last three months of fetal development, the sebaceous glands of the fetus produce vernix caseosa, a waxy white substance that coats the skin to protect it from amniotic fluid.[27]
The areolar glands are in the areola that surrounds the nipple in the female breast. These glands secrete an oily fluid that lubricates the nipple, and also secrete volatile compounds that are thought to serve as an olfactory stimulus for the newborn. During pregnancy and lactation these glands, also called Montgomery's glands, become enlarged.[28]
Meibomian glands, in the eyelids, secrete a form of sebum called meibum onto the eye, that slows the evaporation of tears.[29] It also serves to create an airtight seal when the eyes are closed and its lipid quality also prevents the eyelids from sticking together. The meibomian glands are also known as tarsal glands, Zeis glands and palpebral glands.[30] They attach directly to the follicles of the eyelashes, which are arranged vertically within the tarsal plates of the eyelids.
Fordyce spots, or Fordyce granules, are ectopic sebaceous glands found on the genitals and oral mucosa. They show themselves as yellowish-white milia (milk spots).[31]
Earwax is partly composed of sebum produced by glands in the ear canal. These secretions are viscous and have a high lipid content, which provides good lubrication.[32]
Clinical significance[edit]
Conditions of sebaceous glands.
Sebaceous glands are involved in skin problems such as acne and keratosis pilaris. In the skin pores, sebum and keratin can create a hyperkeratotic plug called a comedo.
Acne[edit]
Main article: Acne
Acne is a very common problem, particularly during puberty in teenagers, and is thought to relate to an increased production of sebum due to hormonal factors. The increased production of sebum can lead to a blockage of the sebaceous gland duct. This can cause a comedo, (commonly called a blackhead or a whitehead), which can lead to infection, particularly by the bacteria Propionibacterium acnes. This can inflame the comedones, which then change into the characteristic acne lesions. Comedones generally occur on the areas with more sebaceous glands, particularly the face, shoulders, upper chest and back. Comedones may be 'black' or 'white' depending on whether the entire pilosebaceous unit, or just the sebaceous duct, is blocked.[33] Sebaceous filaments—innocuous build-ups of sebum—are often mistaken for whiteheads.
There are many treatments available for acne from reducing sugars in the diet, to medications that include antibiotics, benzoyl peroxide, retinoids and hormonal treatments.[33] Retinoids reduce the amount of sebum produced by the sebaceous glands.[34] Should the usual treatments fail, the presence of the Demodex mite could be looked for as the possible cause.[35]
Other[edit]
Other conditions that involve the sebaceous glands include:
Seborrhoea refers to overactive sebaceous glands, a cause of oily skin [4] or hair.[16]
Sebaceous hyperplasia, referring to excessive proliferation of the cells within the glands, and visible macroscopically as small papules on the skin, particularly on the forehead, nose and cheeks.[36]
Seborrhoeic dermatitis, a chronic, usually mild form of dermatitis effected by changes in the sebaceous glands.[37] In newborn infants seborrhoea dermatitis can occur as cradle cap.
Seborrheic-like psoriasis (also known as "Sebopsoriasis,"[38] and "Seborrhiasis") is a skin condition characterized by psoriasis with an overlapping seborrheic dermatitis.[1]:193
Sebaceous adenoma, a benign slow-growing tumour—which may, however, in rare cases be a precursor to a cancer syndrome known as Muir–Torre syndrome.[4]
Sebaceous carcinoma, an uncommon and aggressive cutaneous tumour.[39]
Sebaceous cyst is a term used to refer to both an epidermoid cyst and a pilar cyst, though neither of these contain sebum, only keratin and do not originate in the sebaceous gland and so are not true sebaceous cysts. A true sebaceous cyst is relatively rare and is known as a steatocystoma.[40]
Phymatous rosacea is a cutaneous condition characterized by an overgrowth of sebaceous glands.[38]
History[edit]
The word sebaceous, meaning "consisting of sebum", was first termed in 1728 and comes from the Latin for tallow.[41] Sebaceous glands have been documented since at least 1746 by Jean Astruc, who defined them as "...the glands which separate the fat."[42]:viii He describes them in the oral cavity, on the head, eyelids and ears, as "universally" acknowledged.,[42]:22–25 viii Astruc describes them being blocked by "small animals" that are "implanted" in the excretory ducts,[42]:64 and attributes their presence in the oral cavity to apthous ulcers, noting "these glands naturally [secrete] a viscous humour, which puts on various colours and consistencies... in its natural state is very mild, balsamic, and intended to wet and lubricate the mouth" [42]:85–86 In The Principles of Physiology 1834, A. Combe noted that the glands were not present in the palms of the hands or soles of the feet.[43]
Other animals[edit]
File:Cheiromeles torquatus.jpg
Example of a gular gland in a male black bonneted bat[44]
The preputial glands of mice and rats are large modified sebaceous glands that produce pheromones used for territorial marking.[4] These and the scent glands in the flanks of hamsters have a similar composition to human sebaceous glands, are androgen responsive, and have been used as a basis for study.[4] Some species of bat, including the Mexican free-tailed, have a specialized sebaceous gland occurring on the throat called a "gular gland."[45] This gland is present more frequently in males than females, and it is hypothesized that the secretions of the gland are used for scent-marking.[46]
Sebaceous adenitis is an autoimmune disease that affects sebaceous glands. It is mainly known to occur in dogs, particularly poodles and akitas, where it is thought to be generally autosomal recessively inherited. It has also been described in cats, and one report describes this condition in a rabbit. In these animals, it causes hair loss, though the nature and distribution of the hair loss differs greatly.[47]
See also[edit]
List of specialized glands within the human integumentary system
Sebaceous filament
References[edit]
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Jump up ^ Doucet, Sébastien; Soussignan, Robert; Sagot, Paul; Schaal, Benoist (2009). Hausberger, Martine, ed. "The Secretion of Areolar (Montgomery's) Glands from Lactating Women Elicits Selective, Unconditional Responses in Neonates". PLoS ONE. 4 (10): e7579. PMC 2761488  . PMID 19851461. doi:10.1371/journal.pone.0007579.
Jump up ^ McCulley, JP; Shine, WE (March 2004). "The lipid layer of tears: dependent on meibomian gland function.". Experimental eye research. 78 (3): 361–5. PMID 15106913. doi:10.1016/s0014-4835(03)00203-3.
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^ Jump up to: a b c d Astruc, Jean (1746). A General and Compleat Treatise on All the Diseases Incident to Children. J. Nourse.
Jump up ^ Rosenthal, Stanley A; Furnari, Domenica (1958). "Slide Agglutination as a Presumptive Test in the Laboratory Diagnosis of Candida Albicans1". The Journal of Investigative Dermatology. 31 (5): 251–253. PMID 13598929. doi:10.1038/jid.1958.50.
Jump up ^ Dobson, G. E. (1878). Catalogue of the Chiroptera in the collection of the British Museum. Order of the Trustees.
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External links[edit]
Histology image: 08801loa – Histology Learning System at Boston University - "Integument: scalp"
Sebaceous Glands at the US National Library of Medicine Medical Subject Headings (MeSH)
[show]
v
t
e
Epithelial tissue
Cells
Squamous
Cuboidal
Columnar
Types
Simple squamous epithelium
Endothelium
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Glands
Types
Mechanism
Merocrine
Eccrine
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Sebaceous
Meibomian
Shape
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Components
Myoepithelial cell
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Ducts:
Interlobar
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[show]
v
t
e
Skin and related structures
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Sebaceous
Hair
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Henle's layer
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Hair shaft
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Arrector pili muscle
Pilosebaceous unit
Hair sebaceous gland
Nail
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Eponychium
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