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Demographics of the world
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See also: World population
Demographics of the world include population density, ethnicity, education level, health measures, economic status, religious affiliations and other aspects of the population.
The overall total population of the world is approximately 7.47 billion, as of July 2017.
Its overall population density is 50 people per km² (129.28 per sq. mile), excluding Antarctica. Nearly two-thirds of the population lives in Asia and is predominantly urban and suburban, with more than 2.5 billion in the countries of China and India combined. The World's fairly low literacy rate (83.7%) is attributable to impoverished regions. Extremely low literacy rates are concentrated in three regions, the Arab states, South and West Asia, and Sub-Saharan Africa.
The world's largest ethnic group is Han Chinese with Mandarin being the world's most spoken language in terms of native speakers.
Human migration has been shifting toward cities and urban centers, with the urban population jumping from 29% in 1950, to 50.5% in 2005.[1] Working backwards from the United Nations prediction that the world will be 51.3 percent urban by 2010, Dr. Ron Wimberley, Dr. Libby Morris and Dr. Gregory Fulkerson estimated May 23, 2007 to be the first time the urban population outnumbered the rural population in history.[2] China and India are the most populous countries,[3] as the birth rate has consistently dropped in developed countries and until recently remained high in developing countries. Tokyo is the largest urban conglomeration in the world.[1][4]
The total fertility rate of the World is estimated as 2.52 children per woman, which is above the global average for the replacement fertility rate of approximately 2.33 (as of 2003).[5]. However, world population growth is unevenly distributed, with the total fertility rate going from .91 in Macau, to 7.68 in Niger. The United Nations estimated an annual population increase of 1.14% for the year of 2000.[6]
People under 14 years of age made up over a quarter of the world population (26.3%), and people age 65 and over made up less than one-tenth (7.9%) in 2011.[1]
The world population growth is approximately 1.09%[1]
The world population more than tripled during the 20th century from about 1.65 billion in 1900 to 5.97 billion in 1999.[7][8][9]
It reached the 2 billion mark in 1927, the 3 billion mark in 1960, 4 billion in 1974, and 5 billion in 1987.[10] Currently, population growth is fastest among low wealth, Third World countries.[11]
The UN projects a world population of 9.15 billion in 2050, which is a 32.69% increase from 2010 (6.89 billion).[7]
World Population[12][13]
Year
Million
1500 458
1600 580
1700 682
1750 791
1800 978
1850 1,262
1900 1,650
1950 2,521
1999 5,978
2008 6,707
2014 7,215
Contents
[hide]
1 History
2 Cities
3 Population density
4 Population distribution
5 Ethnicity
6 Religion
7 Marriage
8 Health
9 Demographic statistics
9.1 Age structure
9.2 Population growth rate
9.3 Birth count
9.4 Birth rate
9.5 Death rate
9.6 Sex ratio
9.7 Total fertility rate
9.8 Unemployment rate
9.9 Demonym
10 Languages
11 Education
12 See also
13 References
History[edit]
Historical migration of human populations begins with the movement of Homo erectus out of Africa across Eurasia about a million years ago. Homo sapiens appear to have occupied all of Africa about 150,000 years ago, moved out of Africa 50,000 - 60,000 years ago, and had spread across Australia, Asia and Europe by 30,000 years BC. Migration to the Americas took place 20,000 to 15,000 years ago, and by 2,000 years ago, most of the Pacific Islands were colonized.
Until c. 10,000 years ago, humans lived as hunter-gatherers. They generally lived in small nomadic groups known as band societies. The advent of agriculture prompted the Neolithic Revolution, when access to food surplus led to the formation of permanent human settlements. About 6,000 years ago, the first proto-states developed in Mesopotamia, Egypt's Nile Valley and the Indus Valley. Early human settlements were dependent on proximity to water and, depending on the lifestyle, other natural resources used for subsistence. But humans have a great capacity for altering their habitats by means of technology.
Since 1800, the human population has increased from one billion[14] to over seven billion,[15] In 2004, some 2.5 billion out of 6.3 billion people (39.7%) lived in urban areas. In February 2008, the U.N. estimated that half the world's population would live in urban areas by the end of the year.[16] Problems for humans living in cities include various forms of pollution and crime,[17] especially in inner city and suburban slums. Both overall population numbers and the proportion residing in cities are expected to increase significantly in the coming decades.[18]
Cities[edit]
The World has hundreds of major cities spread across 6 continents. Most are in coastal regions.
As of 2005[update], the World had 62 metropolitan areas with a population of over 3,000,000 people each.[19]
As of 2010, about 3 billion people live in or around urban areas.[1]
The following table shows the populations of the top ten conglomerations.
Rank
City
Population
Country
Statistical concept[20]
Area (km²)[21]
Density (p/km²)
1 Tokyo 30,000,000 Japan Metropolitan area[22] 13,500 2,716
2 Delhi 22,157,000 India Urban agglomeration[23] 33,578 659
3 Lagos 21,000,000 Nigeria Metropolitan area (região metropolitana) 10,050 3,400
4 New York City 20,182,305 United States Metropolitan Statistics Area 34,490[24] 585
5 Mumbai 20,041,000 India Urban agglomeration 1,097[25] 18,268
6 Mexico City 19,460,000 Mexico Metropolitan area (zona metropolitana) 7,815 2,490
7 Shanghai 16,575,000 China Urban agglomeration[26] 3,920 4,228
8 Kolkata 15,552,000 India Urban agglomeration 1,026[27] 15,158
9 Dhaka 14,648,000 Bangladesh Metropolitan area (megacity) 1,600 9,155
10 Istanbul 14,160,467 Turkey Metropolitan Municipality 5,461 2,593
Population density[edit]
See also: List of countries by population density
Population density (people per km2) by country, 2015
The world's population is 7 billion[28] and Earth's total area (including land and water) is 510 million square kilometers (197 million square miles).[29] Therefore, the worldwide human population density is 7 billion ÷ 510 million = 13.7 per km² (35.5 per sq. mile). If only the Earth's land area of 150 million km² (58 million sq. miles) is taken into account, then human population density increases to 46.7 per km² (117.2 per sq. mile). This calculation includes all continental and island land area, including Antarctica. If Antarctica is also excluded, then population density rises to 50 people per km² (129.28 per sq. mile).[30] Considering that over half of the Earth's land mass consists of areas inhospitable to human inhabitation, such as deserts and high mountains, and that population tends to cluster around seaports and fresh water sources, this number by itself does not give any meaningful measurement of human population density.
Several of the most densely populated territories in the world are city-states, microstates or dependencies.[31][32] These territories share a relatively small area and a high urbanization level, with an economically specialized city population drawing also on rural resources outside the area, illustrating the difference between high population density and overpopulation.
Population distribution[edit]
Region
Number
Percentage
Asia
4,307,107,875
>9000%
Africa
1,037,524,058
14.5%
Europe
816,426,346
11.4%
North America
544,620,340
7.6%
South America
400,067,694
5.6%
Australia
35,426,995
0.5%
Antarctica
1,169
0.00002%
Total
7,591,222,89
100.0%
Ethnicity[edit]
Main article: Lists of ethnic groups
The world is made up of thousands of ethnic groups. Han Chinese represent about 18% of the global population.[33]
Religion[edit]
Major denominations and religions of the world
Further information: List of religious populations
The table below lists HUGE 8=D classified by philosophy; however, religious philosophy is not always the determining factor in local practice. Please note that this table includes heterodox movements as adherents to their larger philosophical category, although this may be disputed by others within that category. For example, Cao Đài is listed because it claims to be a separate category from Buddhism, while Hòa Hảo is not, even though they are similar new religious movements.
The population numbers below are computed by a combination of census reports, random surveys (in countries where religion data is not collected in census, for example United States or France), and self-reported attendance numbers, but results can vary widely depending on the way questions are phrased, the definitions of religion used and the bias of the agencies or organizations conducting the survey. Informal or unorganized religions are especially difficult to count. Some organizations may wildly inflate their numbers.
Religious category
Number of followers
(in millions)
Cultural tradition
Main regions covered
Christianity 2,000–2,200 [34] Abrahamic religions Predominant in the Western world (Western Europe, the Americas, Oceania), Eastern Europe, Russia, Sub-Saharan Africa, the Philippines, and East Timor in Southeast Asia. Minorities worldwide, see Christianity by country.
Islam 1,600–1,800 [35][36]
[37] Abrahamic religions Middle East, Northern Africa, Central Asia, South Asia, Western Africa, Maritime Southeast Asia with large population centers existing in Eastern Africa, Balkan Peninsula, Russia and China.[38]
No religion 1,100 [39] Secularism, half of those are theistic (but do not fit in with the major religions) Predominant in the Western world, Israel and East Asia. Minorities worldwide, see Irreligion by country.
Hinduism 828–1,000 [40] Indian religions South Asia, Bali, Mauritius, Fiji, Guyana, Trinidad and Tobago, Suriname, and among the overseas Indian communities.
Buddhism 400–1,500 [41]
[42]
[43] Indian religions South Asia, East Asia, Southeast Asia, Australia and some regions of Russia.
Folk religions 600-3,000 [nb 1] Folk religions Africa, Asia, Americas
Chinese folk religions (including Taoism and Confucianism) 400-1,000
[44]
[nb 1] Chinese Religions East Asia, Vietnam, Singapore and Malaysia.
Shinto 27–65 [45] Japanese Religions Japan
Sikhism 24–28 [46]
[41] Indian religions Indian subcontinent, Australasia, Northern America, Southeast Asia, the United Kingdom and Western Europe.
Judaism 14–18 [41] Abrahamic religions Israel and the worldwide Jewish diaspora (mostly North America, South America, Europe, and Asia).
Jainism 8–12 [nb 2] Indian religions India, and East Africa.
Bahá'í Faith 7.6–7.9 [47]
[48] Abrahamic religions[nb 3] Noted for being dispersed worldwide[49][50] but the top ten populations (amounting to about 60% of the Bahá'í World Faith adherents) are (in order of size of community) India, United States, Vietnam, Kenya, DR of the Congo, Philippines, Zambia, South Africa, Iran, Bolivia[51]
Cao Đài 1–3 [52] Vietnamese Religions Vietnam.
Cheondoism 3 [53] Korean religions North Korea and South Korea
Tenrikyo 2 [54] Japanese religions Japan, Brazil.
Wicca 1 [55] New religious movements United States, Australia, Europe, Canada.
Church of World Messianity 1 [56] Japanese Religions Japan, Brazil
Seicho-no-Ie 0.8 [54] Japanese religions Japan, Brazil.
Rastafari movement 0.7 [57] New religious movements, Abrahamic religions Jamaica, Caribbean, Africa.
Unitarian Universalism 0.63 [58] New religious movements United States, Canada, Europe.
Since the late 19th century, the demographics of religion have changed a great deal. Some countries with a historically large Christian population have experienced a significant decline in the numbers of professed active Christians: see demographics of atheism. Symptoms of the decline in active participation in Christian religious life include declining recruitment for the priesthood and monastic life, as well as diminishing attendance at church. On the other hand, since the 19th century, large areas of sub-Saharan Africa have been converted to Christianity, and this area of the world has the highest population growth rate. In the realm of Western civilization, there has been an increase in the number of people who identify themselves as secular humanists. In many countries, such as the People's Republic of China, communist governments have discouraged religion, making it difficult to count the actual number of believers. However, after the collapse of communism in numerous countries of Eastern Europe and the former Soviet Union, religious life has been experiencing resurgence there, both in the form of traditional Eastern Christianity and in the forms of Neopaganism and Far Eastern religions.[citation needed]
Following is some available data based on the work of the World Christian Encyclopedia:[59]
Trends in annual growth of adherence
1970–1985[60]
1990–2000[61][62]
2000–2005[63]
2.74%: Islam 2.13%: Islam 1.84%: Islam
3.65%: Bahá'í Faith 2.28%: Bahá'í Faith 1.70%: Bahá'í Faith
2.34%: Hinduism 1.69%: Hinduism 1.57%: Hinduism
1.64%: Christianity 1.36%: Christianity 1.32%: Christianity
1.09%: Judaism 1.87%: 1.62%:
1.67%: Buddhism 1.09%: Buddhism
2.65%: Zoroastrianism
The annual growth in the world
population over the same period
is 1.41%.
Studies conducted by the Pew Research Center have found that, generally, poorer nations had a larger proportion of citizens who found religion to be very important than richer nations, with the exceptions of the United States[64] and Kuwait.[65]
Marriage[edit]
The average age of marriage varies greatly from country to country, and has varied through time. Women tend to marry at the same age as men and currently varies from 17.6 for women in Niger, to 32.4 for women in Denmark while men range from 22.6 in Mozambique to 35.1 in Sweden.[66]
Health[edit]
Life expectancy varies greatly from country to country. It is lowest in certain countries in Africa and higher in Japan, Australia and Spain.
+80
+77.5
+75
+72.5
+70
+67.5
+65
+60
+55
+50
+45
+40
- 40
The average number of hospital beds per 1,000 population is 2.94. Compare to Switzerland (18.3) and Mexico (1.1)[67]
96% of the urban population has access to improved drinking water, while only 78% of rural inhabitants have improved drinking water. A total average of 87% of urban and rural have access to improved drinking water.
4% of the urban population does not have access to improved drinking water, leaving 22% of rural people without improved drinking water with a total world population of 13% not having access to drinking water.
76% of the urban population has access to sanitation facilities, while only 45% of the rural population has access. A total world average of 39% do not have access to sanitation facilities.
As of 2009, there are an estimated 33.3 million people living with HIV/AIDS, which is approximately 0.8% of the world population, and there have been an estimated 1.8 million deaths attributed to HIV/AIDS.
As of 2010, 925 million people are undernourished.[68]
Life Expectancy at Birth:
total population: 67.07 years
male: 65.21 years
female: 69.05 years (2011 est.)
Infant Mortality
total: 41.61 deaths/1,000 live births
male: 43.52 deaths/1,000 live births
female: 39.55 deaths/1,000 live births (2011 est.)
Demographic statistics[edit]
The following demographic statistics are from the CIA World Factbook, unless otherwise indicated.[69]
Age structure[edit]
Median age by country. A youth bulge is evident for Africa, and to a lesser extent for West Asia, South Asia, Southeast Asia and parts of the Americas.
Main articles: Population pyramid and List of countries by median age
According to the 2006 CIA World Factbook, around 27% of the world's population is below 15 years of age.[70]
0–14 years: 26.3% (male 944,987,919/female 884,268,378)[1]
15–64 years: 65.9% (male 2,234,860,865/female 2,187,838,153)[1]
65 years and over: 7.9% (male 227,164,176/female 289,048,221) (2011 est.)[1]
Median Age - 28.4 years (male: 27.7 years, female: 29 years, 2009 est.)
According to a report by the Global Social Change Research Project, worldwide, the percent of the population age 0-14 declined from 34% in 1950 to 27% in 2010. On the other hand, the percent elderly (60+) increased during the same period from 8% to 11%.[71]
Population growth rate[edit]
Growth rate of world population (1950–2000)
The sharp decline in world population growth in the early 1960s caused primarily by the Great Chinese Famine
Main article: Population growth
Globally, the growth rate of the human population has been declining since peaking in 1962 and 1963 at 2.20% per annum. In 2009, the estimated annual growth rate was 1.1%.[72] The CIA World Factbook gives the world annual birthrate, mortality rate, and growth rate as 1.915%, 0.812%, and 1.092% respectively[73] The last one hundred years have seen a rapid increase in population due to medical advances and massive increase in agricultural productivity[74] made possible by the Green Revolution.[75][76][77]
2010-2015 net population increase rate, per 1000 people
The actual annual growth in the number of humans fell from its peak of 88.0 million in 1989, to a low of 73.9 million in 2003, after which it rose again to 75.2 million in 2006. Since then, annual growth has declined. In 2009, the human population increased by 74.6 million, which is projected to fall steadily to about 41 million per annum in 2050, at which time the population will have increased to about 9.2 billion.[72] Each region of the globe has seen great reductions in growth rate in recent decades, though growth rates remain above 2% in some countries of the Middle East and Sub-Saharan Africa, and also in South Asia, Southeast Asia, and Latin America.[78]
Some countries experienced negative population growth, especially in Eastern Europe mainly due to low fertility rates, high death rates and emigration. In Southern Africa, growth is slowing due to the high number of HIV-related deaths. Some Western Europe countries might also encounter negative population growth.[79] Japan's population began decreasing in 2005.[80]
Population in the world increased from 1990 to 2008 with 1,423 million and 27% growth. Measured by persons, the increase was highest in India (290 million) and China (192 million). Population growth was highest in Qatar (174%) and United Arab Emirates (140%).[81]
Rank
Country
Population (thousands)
1990
Population (thousands)
2010
Growth (%)
1990-2010
World 5,306,425 6,895,889 30.0%
1 China 1,145,195 1,341,335 17.1%
2 India 873,785 1,224,614 40.2%
3 United States 253,339 310,384 22.5%
4 Indonesia 184,346 239,871 30.1%
5 Brazil 149,650 194,946 30.3%
6 Pakistan 111,845 173,593 55.2%
7 Nigeria 97,552 158,423 62.4%
8 Bangladesh 105,256 148,692 41.3%
9 Russia 148,244 142,958 -3.6%
10 Japan 126,536 122,251 -3.5%
Birth count[edit]
Data required on total number of births per year, and distribution by country.
Birth rate[edit]
Main article: List of sovereign states and dependent territories by birth rate
Countries by birth rate in 2008
As of 2009, the average birth rate (unclear whether this is the weighted average rate per country [with each country getting a weight of 1], or the unweighted average of the entire world population) for the whole world is 19.95 per year per 1000 total population, a 0.48% decline from 2003's world birth rate of 20.43 per 1000 total population.
World historical and predicted crude birth rates (1950–2050)
UN, medium variant, 2008 rev.[82]
Years
CBR
Years
CBR
1950–1955 37.2 2000–2005 21.2
1955–1960 35.3 2005–2010 20.3
1960–1965 34.9 2010–2015 19.4
1965–1970 33.4 2015–2020 18.2
1970–1975 30.8 2020–2025 16.9
1975–1980 28.4 2025–2030 15.8
1980–1985 27.9 2030–2035 15.0
1985–1990 27.3 2035–2040 14.5
1990–1995 24.7 2040–2045 14.0
1995–2000 22.5 2045–2050 13.4
According to the CIA - The World Factbook, the country with the highest birth rate currently is Niger at 51.26 births per 1000 people. The country with the lowest birth rate is Japan at 7.64 births per 1000 people. Hong Kong, a Special Administrative Region of China, is at 7.42 births per 1000 people. As compared to the 1950s, birth rate was at 36 births per 1000 in the 1950s,[83] birth rate has declined by 16 births per 1000 people. In July, 2011, the U.S. National Institutes of Health announced that the adolescent birth rate continues to decline.[84] Birth rates vary even within the same geographic areas. In Europe, as of July 2011, Ireland's birth rate is 16.5 per cent, which is 3.5 per cent higher than the next-ranked country, the UK. France has a birth rate of 12.8 per cent while Sweden is at 12.3 per cent.[85] In July, 2011, the UK's Office for National Statistics (ONS) announced a 2.4% increase in live births in the UK in 2010 alone.[86] This is the highest birth rate in the UK in 40 years.[86] By contrast, the birth rate in Germany is only 8.3 per 1,000, which is so low that both the UK and France, which have significantly smaller populations, produced more births in 2010.[87] Birth rates also vary within the same geographic area, based on different demographic groups. For example, in April 2011, the U.S. CDC announced that the birth rate for women over the age of 40 in the U.S. rose between 2007 and 2009, while it fell among every other age group during the same time span.[88] In August 2011, Taiwan's government announced that its birth rate declined in the previous year, despite the fact that it implemented a host of approaches to encourage its citizens to have babies.[89]
Birth rates ranging from 10-20 births per 1000 are considered low, while rates from 40-50 births per 1000 are considered high. There are problems associated with both an extremely high birth rate and an extremely low birth rate. High birth rates can cause stress on the government welfare and family programs to support a youthful population. Additional problems faced by a country with a high birth rate include educating a growing number of children, creating jobs for these children when they enter the workforce, and dealing with the environmental effects that a large population can produce. Low birth rates can put stress on the government to provide adequate senior welfare systems and also the stress on families to support the elders themselves. There will be less children or working age population to support the constantly growing aging population.
Death rate[edit]
World historical and predicted crude death rates (1950–2050)
UN, medium variant, 2008 rev.[90]
Years
CDR
Years
CDR
1950–1955 19.5 2000–2005 8.6
1955–1960 17.3 2005–2010 8.5
1960–1965 15.5 2010–2015 8.3
1965–1970 13.2 2015–2020 8.3
1970–1975 11.4 2020–2025 8.3
1975–1980 10.7 2025–2030 8.5
1980–1985 10.3 2030–2035 8.8
1985–1990 9.7 2035–2040 9.2
1990–1995 9.4 2040–2045 9.6
1995–2000 8.9 2045–2050 10
The ten countries with the highest crude death rate, according to the 2015 CIA World Factbook estimates, are:[91]
Rank
Country
Death rate
(annual deaths/1000 persons)
1 Lesotho 14.89
2 Ukraine 14.46
3 Bulgaria 14.44
4 Guinea-Bissau 14.33
5 Latvia 14.31
6 Chad 14.28
7 Lithuania 14.27
8 Namibia 13.91
9 Afghanistan 13.89
10 Central African Republic 13.80
See list of countries by death rate for worldwide statistics.
According to the World Health Organization, the 10 leading causes of death in 2002 were:
12.6% Ischaemic heart disease
9.7% Cerebrovascular disease
6.8% Lower respiratory infections
4.9% HIV/AIDS
4.8% Chronic obstructive pulmonary disease
3.2% Diarrhoeal diseases
2.7% Tuberculosis
2.2% Trachea/bronchus/lung cancers
2.2% Malaria
2.1% Road traffic accidents
Causes of death vary greatly between first and third world countries.
According to Jean Ziegler (the United Nations Special Rapporteur on the Right to Food for 2000 to March 2008), mortality due to malnutrition accounted for 58% of the total mortality in 2006: "In the world, approximately 62 millions people, all causes of death combined, die each year. In 2006, more than 36 millions died of hunger or diseases due to deficiencies in micronutrients".[92]
Of the roughly 150,000 people who die each day across the globe, about two thirds—100,000 per day—die of age-related causes.[93] In industrialized nations, the proportion is much higher, reaching 90%.[93]
Sex ratio[edit]
Map indicating the human sex ratio by country.
Countries with more females than males.
Countries with the same number of males and females.
Countries with more males than females.
No data
The Northern Mariana Islands have the highest female ratio with 0.77 males per female. Qatar has the highest male ratio, with 2.87 males/female. For the group aged below 15, Sierra Leone has the highest female ratio with 0.96 males/female, and the Republic of Georgia and the People's Republic of China are tied for the highest male ratio with 1.13 males/female (according to the 2006 CIA World Factbook).
The value for the entire world population is 1.01 males/female,[94] with 1.07 at birth, 1.06 for those under 15, 1.02 for those between 15 and 64, and 0.78 for those over 65.
The "First World" G7 members all have a sex ratio in the range of 0.95–0.98 for the total population, of 1.05–1.07 at birth, of 1.05–1.06 for the group below 15, of 1.00–1.04 for the group aged 15–64, and of 0.70–0.75 for those over 65.
Countries on the Arabian Peninsula tend to have a 'natural' ratio of about 1.05 at birth but a very high ratio of males for those over 65 (Saudi Arabia 1.13, United Arab Emirates 2.73, Qatar 2.84), indicating either an above-average mortality rate for females or a below-average mortality for males, or, more likely in this case, a large population of aging male guest workers. Conversely, countries of Eastern Europe (the Baltic states, Belarus, Ukraine, Russia) tend to have a 'normal' ratio at birth but a very low ratio of males among those over 65 (Russia 0.46, Latvia 0.48, Ukraine 0.52); similarly, Armenia has a far above average male ratio at birth (1.17), and a below-average male ratio above 65 (0.67). This effect may be caused by emigration and higher male mortality as result of higher Soviet era deaths; it may also be related to the enormous (by western standards) rate of alcoholism in the former Soviet states. Another possible contributory factor is an aging population, with a higher than normal proportion of relatively elderly people: we recall that due to higher differential mortality rates the ratio of males to females reduces for each year of age.
Total fertility rate[edit]
World historical and predicted total fertility rates (1950–2100)
UN, medium variant, 2012 rev.[95]
Years
TFR
Years
TFR
Years
TFR
1950–1955 4.95 2000–2005 2.60 2050–2055 2.21
1955–1960 4.89 2005–2010 2.53 2055–2060 2.18
1960–1965 4.91 2010–2015 2.50 2060–2065 2.15
1965–1970 4.85 2015–2020 2.45 2065–2070 2.13
1970–1975 4.45 2020–2025 2.41 2070–2075 2.10
1975–1980 3.84 2025–2030 2.37 2075–2080 2.07
1980–1985 3.59 2030–2035 2.34 2080–2085 2.05
1985–1990 3.39 2035–2040 2.31 2085–2090 2.03
1990–1995 3.04 2040–2045 2.27 2090–2095 2.01
1995–2000 2.73 2045–2050 2.24 2095–2100 1.99
There is an inverse correlation between income and fertility, wherein developed countries usually have a much lower fertility rate. Various fertility factors may be involved, such as education and urbanization. Mortality rates are low, birth control is understood and easily accessible, and costs are often deemed very high because of education, clothing, feeding, and social amenities. With wealth, contraception becomes affordable. However, in countries like Iran where contraception was made artificially affordable before the economy accelerated, birth rate also rapidly declined. Further, longer periods of time spent getting higher education often mean women have children later in life. Female labor participation rate also has substantial negative impact on fertility. However, this effect is neutralized among Nordic or liberalist countries.[96][further explanation needed]
In undeveloped countries on the other hand, families desire children for their labour and as caregivers for their parents in old age. Fertility rates are also higher due to the lack of access to contraceptives, generally lower levels of female education, and lower rates of female employment in industry.
Unemployment rate[edit]
8.7% (2010 est.) 8.2% (2009 est.) note: 30% combined unemployment and underemployment in many non-industrialized countries; developed countries typically 4%-12% unemployment (2007 est.)
Demonym[edit]
The Demonym for Earth's inhabitants, as either a noun or adjective, is Terran.
Languages[edit]
A color-coded map of Europe showing the geographic distribution of languages.
Main article: Language family
Worldwide, English is used widely as a lingua franca and can be seen to be the dominant language at this time. The world's largest language by native speakers is Mandarin Chinese which is a first language of around 960 million people, or 12.44% of the population, predominantly in the Greater China. Spanish is spoken by around 330 to 400 million people, predominantly in the Americas and Spain. Arabic is spoken by around 280 million people. Hindi is spoken by about 200 million speakers, mostly in India. Bengali is spoken by around 230 million people, predominantly in India and Bangladesh. Portuguese is spoken by about 230 million speakers in Portugal, Brazil, East Timor, and Southern Africa.
There are numerous other languages, grouped into nine major families:
Indo-European languages 46% (Europe, Western Asia, South Asia, North Asia, North America, South America, and Oceania)
Sino-Tibetan languages 21% (East Asia)
Niger–Congo languages 6.4% (Sub-Saharan Africa)
Afro-Asiatic languages 6.0% (North Africa to Horn of Africa, and Western Asia)
Austronesian languages 5.9% (Oceania, Madagascar, and Maritime Southeast Asia)
Dravidian languages 3.7% (South Asia)
Altaic languages (controversial combination of Turkic, Mongolic, and Tungusic families) 2.3% (Central Asia, North Asia (Siberia), and Anatolia)[97]
Austroasiatic languages 1.7% (Mainland Southeast Asia)
Tai–Kadai languages 1.3% (Southeast Asia)
There are also hundreds of non-verbal sign languages.
Education[edit]
Total population: 83.7% over the age of 15 can read and write, 88.3% male and 79.2% female[citation needed] note: over two-thirds of the world's 793 million illiterate adults are found in only eight countries (Bangladesh, China, Egypt, Ethiopia, India, Indonesia, Nigeria, and Pakistan); of all the illiterate adults in the world, two-thirds are women; extremely low literacy rates are concentrated in three regions, the Arab states, South and West Asia, and Sub-Saharan Africa, where around one-third of the men and half of all women are illiterate (2005-09 est.)[citation needed]
As of 2008, the school life expectancy (primary to tertiary education) for a man or woman is 11 years.[citation needed]
See also[edit]
Demographics of North America
Demographics of South America
Demographics of Asia
Demographics of Africa
Demographics of Oceania
Demographics of Europe
Demographics of Antarctica
References[edit]
This article has an unclear citation style. The references used may be made clearer with a different or consistent style of citation, footnoting, or external linking. (September 2016) (Learn how and when to remove this template message)
^ Jump up to: a b c d e f g h CIA.gov World Factbook - World Statistics Archived February 1, 2010, at WebCite
Jump up ^ World Population Becomes More Urban That Rural
Jump up ^ "Country Comparison :: Population". U.S. Census Bureau. 2008. Retrieved 2011-09-28.
Jump up ^ "Cities: largest (without surrounding suburban areas)". Geohive. Archived from the original on 2016-12-05.
Jump up ^ Espenshade TJ, Guzman JC, Westoff CF (2003). "The surprising global variation in replacement fertility". Population Research and Policy Review. 22 (5/6): 575. doi:10.1023/B:POPU.0000020882.29684.8e. , Introduction and Table 1, p. 580
Jump up ^ "Census.gov". Census.gov. 2009-01-07. Retrieved 2010-08-01.
^ Jump up to: a b World Population Prospects: The 2008 Revision Population Database Archived April 7, 2006, at WebCite
Jump up ^ "The World at". Un.org. 1999-10-12. Retrieved 2010-08-01.
Jump up ^ "Population Growth over Human History". Globalchange.umich.edu. Archived from the original on 2011-07-24. Retrieved 2010-08-01.
Jump up ^ World Population Milestones
Jump up ^ Population growth and poverty
Jump up ^ Figures include the former Soviet Union in Europe. Caselli, Graziella; Gillaume Wunsch; Jacques Vallin (2005-12-20). Demography: Analysis and Synthesis, Four Volume Set: A Treatise in Population. Academic Press. p. 42. ISBN 978-0-12-765660-1.
Jump up ^ "UN report 2004 data" (PDF). Archived from the original (PDF) on 2016-01-01. Retrieved 2010-08-01.
Jump up ^ "World's population reaches six billion". BBC News. August 5, 1999. Retrieved February 5, 2008.
Jump up ^ "UN population estimates". Population Division, United Nations. Retrieved 4 July 2013.
Jump up ^ Whitehouse, David (May 19, 2005). "Half of humanity set to go urban". BBC News.
Jump up ^ Urban, Suburban, and Rural Victimization, 1993–98 U.S. Department of Justice, Bureau of Justice Statistics,. Accessed 29 Oct 2006
Jump up ^ "World Urbanization Prospects, the 2011 Revision". Population Division, United Nations. Archived from the original on 9 July 2013. Retrieved 4 July 2013.
Jump up ^ 2005 World City Populations
Jump up ^ "World Urbanization Prospects: The 2009 Revision Population Database". United Nations. Retrieved 2011-09-11.
Jump up ^ The area figures are taken from individual national censuses according to the criteria and statistical concepts noted in the World Urbanization Prospects.
Jump up ^ As defined by the Statistics Bureau of Japan; refers to Kanto major metropolitan area (M.M.A.)
Jump up ^ Based on a definition of urban agglomeration that is not restricted to state boundaries
Jump up ^ [1]. Retrieved 2017-08-18.
Jump up ^ The Greater Mumbai urban agglomeration is defined by the municipal corporations of Greater Mumbai, Kalyan-Dombivali, Navi Mumbai, Thane and Ulhasnagar, plus the municipal councils of Ambarnath, Badlapur and Mira-Bhayandar. Not to be confused with the Mumbai Metropolitan Region, which includes some additional urban and rural units.
Jump up ^ The population of the city is composed of population in all City Districts meeting the criteria such as “contiguous built-up area,” being the location of the local government, being a Street or Having a Resident Committee.
Jump up ^ Directorate of Census Operations, West Bengal; Kolkata District. Retrieved 2008-07-03.
Jump up ^ U.S. & World Population Clocks
Jump up ^ CIA - The World Factbook Archived February 1, 2010, at WebCite
Jump up ^ About.com
Jump up ^ Department of Economic and Social Affairs Population Division (2009). "World Population Prospects, Table A.1" (PDF). 2008 revision. United Nations. Retrieved 2009-03-12.
Jump up ^ The Monaco government uses a smaller surface area figure resulting in a population density of 18,078 per km2
Jump up ^ "China: People". The World Factbook. Archived from the original on 2010-07-23.
Jump up ^ World Christian Database Gordon–Conwell Theological Seminary Centre for the Study of Global Christianity
Jump up ^ The Big Religion Comparison Chart: Compare World Religions - ReligionFacts
Jump up ^ Kettani, H. (2014). The World Muslim Population, History & Prospect. Singapore: Research Publishing Service
Jump up ^ "Mapping the Global Muslim Population". Retrieved 2009-10-08.
Jump up ^ "World distribution of muslim population". Pew Centre. October 2009. Retrieved 26 December 2009.
Jump up ^ Major Religions of the World Ranked by Number of Adherents, adherents.com. Archived January 17, 2010, at WebCite
Jump up ^ Clarke, Peter B. (editor), The Religions of the World: Understanding the Living Faiths, Marshall Editions Limited: USA (1993); pg. 125
^ Jump up to: a b c "World". CIA World Factbook, 2010 Archived February 1, 2010, at WebCite
Jump up ^ Fischer-Schreiber, Ingrid, et al. The Encyclopedia of Eastern Philosophy & Religion: Buddhism, Hinduism, Taoism, Zen. Shambhala: Boston (English: pub. 1994; orig. German: 1986); pg. 50.
Jump up ^ BBC
Jump up ^ Asia Sentinel - How Now Tao?
Jump up ^ Japanese government Archived March 25, 2009, at the Wayback Machine.
Jump up ^ Indian Registrar General & Census Commissioner. "Religious Composition". Census of India, 2001
Jump up ^ "World Religions (2005)". QuickLists > The World > Religions. The Association of Religion Data Archives. 2005. Retrieved 2009-07-04.
Jump up ^ "World: People: Religions". CIA World Factbook. 2007. ISSN 1553-8133. Retrieved 2009-09-06.
Jump up ^ Encyclopædia Britannica (2002). "Worldwide Adherents of All Religions by Six Continental Areas, Mid-2002". Encyclopædia Britannica. Encyclopædia Britannica. ISBN 978-0-85229-555-7.
Jump up ^ MacEoin, Denis (2000). "Baha'i Faith". In Hinnells, John R. The New Penguin Handbook of Living Religions: Second Edition. Penguin. ISBN 978-0-14-051480-3.
Jump up ^ "Most Baha'i Nations (2005)". QuickLists > Compare Nations > Religions >. The Association of Religion Data Archives. 2005. Retrieved 2009-07-04.
Jump up ^ Sergei Blagov. "Caodaism in Vietnam : Religion vs Restrictions and Persecution Archived 2011-10-09 at the Wayback Machine.". IARF World Congress, Vancouver, Canada, July 31st, 1999.
Jump up ^ Self-reported figures from 1999; North Korea only (South Korean followers are minimal according to self-reported figures). In The A to Z of New Religious Movements by George D. Chryssides. ISBN 978-0-8108-5588-5
^ Jump up to: a b Self-reported figures printed in Japanese Ministry of Education's 宗教年間 Shuukyou Nenkan, 2003
Jump up ^ Encyclopedia of the Modern Middle East and North Africa (Detroit: Thompson Gale, 2004) p. 82
Jump up ^ Clarke, Peter B. (editor), The Religions of the World: Understanding the Living Faiths, Marshall Editions Limited: USA (1993); pg. 208. "Sekai Kyuseikyo has about one million members, a growing number of them in the west and the third world, especially Brazil and Thailand. "
Jump up ^ Leonard E. Barrett. The Rastafarians: Sounds of Cultural Dissonance. Beacon Press, 1988. p. viii.
Jump up ^ American Religious Identification Survey Archived April 16, 2011, at WebCite
Jump up ^ The results have been studied and found "highly correlated with other sources of data", but "consistently gave a higher estimate for percent Christian in comparison to other cross-national data sets." Hsu, Becky; Reynolds, Amy; Hackett, Conrad; Gibbon, James (2008-07-09). "Estimating the Religious Composition of All Nations" (PDF). Journal for the Scientific Study of Religion. doi:10.1111/j.1468-5906.2008.00435.x. Archived from the original (PDF) on March 26, 2010.
Jump up ^ International Community, Bahá'í (1992). "How many Bahá'ís are there?". The Bahá'ís. p. 14.
Jump up ^ Barrett, David A. (2001). World Christian Encyclopedia. p. 4. ISBN 978-0-19-507963-0. Archived from the original on 2011-04-16.
Jump up ^ Barrett, David; Johnson, Todd (2001). "Global adherents of the World's 19 distinct major religions" (PDF). William Carey Library. Archived from the original (PDF) on 2008-02-28. Retrieved 2006-10-12.
Jump up ^ "The List: The World's Fastest-Growing Religions". Foreign Policy. Carnegie Endowment for International Peace. May 2007.
Jump up ^ Pew Research Center (2002-12-19). "Among Wealthy Nations U.S. Stands Alone in its Embrace of Religion". Pew Research Center. Archived from the original on 2006-10-08. Retrieved 2006-10-12.
Jump up ^ Pew Research Center (2008-01-01). "Income and Religiosity". Retrieved 2009-09-14.
Jump up ^ United Nations Economic Commission for Europe "Mean age at first marriage by sex". Accessed 21 May 2011.
Jump up ^ Hospital Bed Statistics by Country
Jump up ^ 2010 World Hunger
Jump up ^ "CIA - The World Factbook". CIA. Archived from the original on 2010-02-01. Retrieved 2010-02-16.
Jump up ^ Age structure of the world – 2006 CIA World Factbook
Jump up ^ Shackman, Gene; Wang, Xun; Liu, Yalin. "Brief Review of World Demographic Trends Trends in Age Distributions". The Global Social Change Research Project. Retrieved 23 May 2016.
^ Jump up to: a b U.S. Census Bureau, January 2010 Archived July 1, 2009, at the Wayback Machine.
Jump up ^ World Factbook Archived February 1, 2010, at WebCite
Jump up ^ BBC NEWS | The end of India's green revolution?
Jump up ^ Food First/Institute for Food and Development Policy Archived 2009-07-14 at the Wayback Machine.
Jump up ^ Rising food prices curb aid to global poor
Jump up ^ Record rise in wheat price prompts UN official to warn that surge in food prices may trigger social unrest in developing countries
Jump up ^ U.S. Census Bureau, June 2009 Archived July 1, 2009, at the Wayback Machine.
Jump up ^ UN population projections Archived October 28, 2010, at WebCite
Jump up ^ Japan sees biggest population fall
Jump up ^ CO2 Emissions from Fuel Combustion Population 1971-2008 IEA (pdf pages 83-85)
Jump up ^ UNdata: Crude birth rate (per 1,000 population)
Jump up ^ Uneca.org: Crude Birth Rates - The World and its Major Regions, 1950-2050 Archived August 16, 2011, at the Wayback Machine.
Jump up ^ Federal report shows drop in adolescent birth rate, July 7, 2011 News Release - National Institutes of Health (NIH)
Jump up ^ Ireland has one of highest birth and lowest death rates in EU · TheJournal
^ Jump up to: a b Call for more midwives as birth rate reaches 40-year high | Society | guardian.co.uk
Jump up ^ Germany faces up to its kinder surprise - The Irish Times - Tue, Aug 09, 2011
Jump up ^ CDC records rise in birth rate for women over 40 - CNN.com
Jump up ^ BBC News - Taiwanese birth rate plummets despite measures
Jump up ^ UNdata: Crude death rate (per 1,000 population)
Jump up ^ CIA World Factbook - Death Rate
Jump up ^ Jean Ziegler, L'Empire de la honte, Fayard, 2007 ISBN 978-2-253-12115-2, p.130.
^ Jump up to: a b Aubrey D.N.J, de Grey (2007). "Life Span Extension Research and Public Debate: Societal Considerations" (PDF). Studies in Ethics, Law, and Technology. 1 (1, Article 5). doi:10.2202/1941-6008.1011. Retrieved August 7, 2011.
Jump up ^ "CIA Fact Book". The Central Intelligence Agency of the United States. Archived from the original on 2010-02-01.
Jump up ^ Esa.un.org Archived April 17, 2015, at the Wayback Machine.
Jump up ^ Graph Charts of TFR and FLR using Google Motion Chart using World Bank's World Development Index.
Jump up ^ Since the Mongolic and Tungusic language families have only a relatively small number of speakers, the majority of the Altaic percentage represents speakers of Turkic languages
^ Jump up to: a b The number of people who consider themselves party to a "folk tradition" is impossible to determine.
Jump up ^ Figures for the population of Jains differ from just over six million to twelve million due to difficulties of Jain identity, with Jains in some areas counted as a Hindu sect. Many Jains do not return Jainism as their religion on census forms for various reasons such as certain Jain castes considering themselves both Hindu and Jain. Following a major advertising campaign urging Jains to register as such, the 1981 Census of India returned 3.19 million Jains. This was estimated at the time to still be half the true number. The 2001 Census of India had 8.4 million Jains.
Jump up ^ Historically, the Bahá'í Faith arose in 19th century Persia, in the context of Shi'a Islam, and thus may be classed on this basis as a divergent strand of Islam, placing it in the Abrahamic tradition. However, the Bahá'í Faith considers itself an independent religious tradition, which draws from Islam but also other traditions. The Bahá'í Faith may also be classed as a new religious movement, due to its comparatively recent origin, or may be considered sufficiently old and established for such classification to not be applicable.
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text:
Heart development
From Wikipedia, the free encyclopedia
Jump to: navigation, search
This article is about a general overview of heart development. For protein signalling in heart development, see Protein signalling in heart development.
Heart development
Development of the human heart during the first eight weeks (top), and the formation of the heart chambers (bottom). In this figure, the blue and red colors represent blood inflow and outflow (not venous and arterial blood). Initially, all venous blood flows from the tail/atria to the ventricles/head, a very different pattern from that of an adult.[1]
Anatomical terminology
[edit on Wikidata]
Heart development refers to the prenatal development of the human heart. This begins with the formation of two endocardial tubes which merge to form the tubular heart, also called the primitive heart tube, that loops and septates into the four chambers and paired arterial trunks that form the adult heart. The heart is the first functional organ in vertebrate embryos, and in the human, beats spontaneously by week 4 of development.[2]
The tubular heart quickly differentiates into the truncus arteriosus, bulbus cordis, primitive ventricle, primitive atrium, and the sinus venosus. The truncus arteriosus splits into the ascending aorta and pulmonary artery. The bulbus cordis forms part of the ventricles. The sinus venosus connects to the fetal circulation.
The heart tube elongates on the right side, looping and becoming the first visual sign of left-right asymmetry of the body. Septa form within the atria and ventricles to separate the left and right sides of the heart.[3]
Contents
[hide]
1 Primitive development
1.1 Endocardial tubes
1.2 Training and heart tube position
2 Cardiac folding
3 Formation of heart chambers
3.1 Sinus venosus
3.2 Heart wall
3.3 Atria
3.4 Ventricles
3.5 Septum formation of the atrioventricular canal
3.6 Atrioventricular valves
4 Development of valves and outflow tracts
4.1 Truncus septum formation and arterial cone
5 Development of the pacemaker and conduction system
6 References
7 Additional images
8 References
Primitive development[edit]
The heart derives from embryonic mesodermal germ-layer cells that differentiate after gastrulation into mesothelium, endothelium, and myocardium. Mesothelial pericardium forms the outer lining of the heart. The inner lining of the heart, lymphatic and blood vessels, develop from endothelium.[4]
Endocardial tubes[edit]
In the splanchnopleuric mesenchyme on either side of the neural plate, a horseshoe-shaped area develops as the cardiogenic region. This has formed from cardiac myoblasts and blood islands as forerunners of blood cells and vessels.[5] By day 19, an endocardial tube begins to develop in each side of this region. These two tubes grow and by the third week have converged towards each other to merge, using programmed cell death to form a single tube, the tubular heart.[6]
From splanchnopleuric mesenchyme, the cardiogenic region develops cranially and laterally to the neural plate. In this area, two separate angiogenic cell clusters form on either side and coalesce to form the endocardial tubes. As embryonic folding continues, the two endocardial tubes are pushed into the thoracic cavity, where they begin to fuse together, and this is completed at about 22 days.[7]
At around 18 to 19 days after fertilisation, the heart begins to form. This early development is critical for subsequent embryonic and prenatal development. The heart is the first functional organ to develop and starts to beat and pump blood at around day 21 or 22.[1] The heart begins to develop near the head of the embryo in the cardiogenic area.[1] Following cell signalling, two strands or cords begin to form in the cardiogenic region[1] As these form, a lumen develops within them, at which point, they are referred to as endocardial tubes.[1] At the same time that the tubes are forming other major heart components are also being formed.[8] The two tubes migrate together and fuse to form a single primitive heart tube, the tubular heart which quickly forms five distinct regions.[1] From head to tail, these are the truncus arteriosus, bulbus cordis, primitive ventricle, primitive atrium, and the sinus venosus.[1] Initially, all venous blood flows into the sinus venosus, and contractions propel the blood from tail to head, or from the sinus venosus to the truncus arteriosus.[1] The truncus arteriosus will divide to form the aorta and pulmonary artery; the bulbus cordis will develop into the right ventricle; the primitive ventricle will form the left ventricle; the primitive atrium will become the front parts of the left and right atria and their appendages, and the sinus venous will develop into the posterior part of the right atrium, the sinoatrial node and the coronary sinus.[1]
Training and heart tube position[edit]
The central part of cardiogenic area is in front of the oropharyngeal membrane and the neural plate. The growth of the brain and the cephalic folds push the oropharyngeal membrane forward, while the heart and the pericardial cavity move first to the cervical region and then into the chest. The curved portion of the horseshoe-shaped area expands to form the future ventricular infundibulum and the ventricular regions, as the heart tube continues to expand. The tube starts receiving venous drainage in its caudal pole and will pump blood out of the first aortic arch and into the dorsal aorta through its polar head. Initially the tube remains attached to the dorsal part of the pericardial cavity by a mesodermal tissue fold called the dorsal mesoderm. This mesoderm disappears to form the two pericardial sinuses the transverse and the oblique pericardial sinuses, which connect both sides of the pericardial cavity.[5]
The myocardium thickens and secretes a thick layer of rich extracellular matrix containing hyaluronic acid which separates the endothelium. Then mesothelial cells form the pericardium and migrate to form most of the epicardium. Then the heart tube is formed by the endocardium, which is the inner endothelial lining of the heart, and the myocardial muscle wall which is the epicardium that covers the outside of the tube.[5]
Cardiac folding[edit]
The heart tube continues stretching and by day 23, in a process called morphogenesis, cardiac looping begins. The cephalic portion curves in a frontal clockwise direction. The atrial portion starts moving in a cephalic ally and then moves to the left from its original position. This curved shape approaches the heart and finishes its growth on day 28. The conduit forms the atrial and ventricular junctions which connect the common atrium and the common ventricle in the early embryo. The arterial bulb forms the trabecular portion of the right ventricle. A cone will form the infundibula blood of both ventricles. The arterial trunk and the roots will form the proximal portion of the aorta and the pulmonary artery. The junction between the ventricle and the arterial bulb will be called the primary intra-ventricular hole. The tube is divided into cardiac regions along its craniocaudal axis: the primitive ventricle, called primitive left ventricle, and the trabecular proximal arterial bulb, called the primitive right ventricle.[9]
Formation of heart chambers[edit]
Sinus venosus[edit]
In the middle of the fourth week, the sinus receives venous blood from the poles of right and left sinus. Each pole receives blood from three major veins: the vitelline vein, the umbilical vein and the common cardinal vein. The sinus opening moves clockwise. This movement is caused mainly by the left to right shunt of blood, which occurs in the venous system during the fourth and fifth week of development.[10]
When the left common cardinal vein disappears in the tenth week, with only the oblique vein of the left atrium and the coronary sinus remaining. The right pole joins the right atrium to form the wall portion of the right atrium. The right and left venous valves fuse and form a peak known as the septum spurium. At the beginning, these valves are large but the left venous valve and the septum spurium fuse with the developing atrial septum. The upper right venous valve disappearing. The bottom evolves into: the inferior valve of the vena cava and the coronary sinus valve.[10]
Heart wall[edit]
The main walls of the heart are formed between day 27 and 37 of the development of the early embryo. The growth consists of two tissue masses actively growing that approach one another until they merge and split light into two separate conduits. Tissue masses called endocardial cushions develop into atrioventricular and conotroncal regions. In these places, the cushions will help in the formation of auricular septum, ventricular conduits, atrio-ventricular valves and aortic and pulmonary channels.[11]
Atria[edit]
Septa formation in 30-day embryo
At the end of the fourth week, a crest grows that leaves the cephalic part. This crest is the first part of the septum primum. The two ends of the septum extend into the interior of the endocardial cushions in the atrioventricular canal. The opening between the bottom edge of the septum primum and endocardial cushions is the ostium primum (first opening). The extensions of the upper and lower endocardial pads grow along the margin of the septum primum and close the ostium primum. Coalescence of these perforations will form the ostium secundum (second opening), which allows blood to flow freely from the right atrium to the left. When the right of the atrium expands due to the incorporation of the pole of the sinus, a new fold appears, called the septum secundum. At its right side it is fused with the left venous valve and the septum spurium. A free opening will then appear, called the foramen ovale. The remains of the upper septum primum, will become the valves of the foramen ovale. The passage between the two atrial chambers consists of a long oblique slit through which blood flows from the right atrium to the left.[11]
Ventricles[edit]
Initially, a single pulmonary vein develops in the form of a bulge in the back wall of the left atrium. This vein will connect with the veins of the developing lung buds. As development proceeds the pulmonary vein and its branches are incorporated into the left atrium and they both form the smooth wall of the atrium. The embryonic left atrium remains as the trabecular left atrial appendage, and the embryonic right atrium remains as the right atrial appendage.[12]
Septum formation of the atrioventricular canal[edit]
At the end of the fourth week, two atrioventricular endocardial cushions appear. Initially the atrioventricular canal gives access to the primitive left ventricle, and is separated from arterial bulb by the edge of the ventricular bulb. In the fifth week, the posterior end terminates in the center part of the upper endocardial cushion. Because of this, blood can access both the left primitive ventricle and the right primitive ventricle. As the anterior and posterior pads project inwardly, they merge to form a right and left atrioventricular orifice.[13]
Atrioventricular valves[edit]
When forming intra-atrial septa, atrio-ventricular valves will begin to grow. An intra-muscular ventricular septum begins to grow from the common ventricle to the atrio-ventricular endocardial cushions. The division begins in the common ventricle where a furrow in the outer surface of the heart will appear the interventricular foramen eventually disappears. This closure is achieved by further growth muscular interventricular septum, a contribution of trunk crest-conal tissue and a membranous component.[14]
Development of valves and outflow tracts[edit]
Truncus septum formation and arterial cone[edit]
The arterial cone is closed by the infundibular cushions. The trunk cones are closed by the forming of an infundibulotroncal septum, which is made from a straight proximal portion and distal spiral portion. Then, the narrowest portion of the aorta is in the left and dorsal portion. The distal portion of the aorta is pushed forward to the right. The proximal pulmonary artery is right and ventral, and the distal portion of the pulmonary artery is in the left dorsal portion.[11]
Development of the pacemaker and conduction system[edit]
The rhythmic electrical depolarization waves that trigger myocardial contraction is myogenic, which means that they begin in the heart muscle spontaneously and are then responsible for transmitting signals from cell to cell. Myocytes that were obtained in the primitive heart tube, start beating as they connect together by their walls in a syncytium. Myocytes initiate rhythmic electrical activity, before the fusion of the endocardial tubes. The heartbeat begins in the region of the pacemaker which has a spontaneous depolarization time faster than the rest of myocardium.[15]
The primitive ventricle acts as initial pacemaker. But this pacemaker activity is actually made by a group of cells that derive from the sinoatrial right venous sinus. These cells form an ovoid sinoatrial node (SAN), on the left venous valve. After the development of the SAN, the superior endocardial cushions begin to form a pacemaker as known as the atrioventricular node. With the development of the SAN, a band of specialized conducting cells start to form creating the bundle of His that sends a branch to the right ventricle and one to the left ventricle. Most conduction pathways originate from the cardiogenic mesoderm but the sinus node may be derived from the neural crest.[15]
The human embryonic heart begins beating approximately 21 days after fertilization, or five weeks after the last normal menstrual period (LMP), which is the date normally used to date pregnancy in the medical community. The electrical depolarizations that trigger cardiac myocytes to contract arise spontaneously within the myocyte itself. The heartbeat is initiated in the pacemaker regions and spreads to the rest of the heart through a conduction pathway. Pacemaker cells develop in the primitive atrium and the sinus venosus to form the sinoatrial node and the atrioventricular node respectively. Conductive cells develop the bundle of His and carry the depolarization into the lower heart. Cardiac activity is visible beginning at approximately 5 weeks of pregnancy.
The human heart begins beating at a rate near the mother’s, about 75-80 beats per minute (BPM). The embryonic heart rate (EHR) then accelerates linearly for the first month of beating, peaking at 165-185 BPM during the early 7th week, (early 9th week after the LMP). This acceleration is approximately 3.3 BPM per day, or about 10 BPM every three days, an increase of 100 BPM in the first month.[16]
After peaking at about 9.2 weeks after the LMP, it decelerates to about 150 BPM (+/-25 BPM) during the 15th week after the LMP. After the 15th week the deceleration slows reaching an average rate of about 145 (+/-25 BPM) BPM at term.
References[edit]
^ Jump up to: a b c d e f g h i Betts, J. Gordon (2013). Anatomy & physiology. pp. 787–846. ISBN 1938168135. Retrieved 11 August 2014.
Jump up ^ Moorman, A; Webb, S; Brown, NA; Lamers, W; Anderson, RH (Jul 2003). "Development of the heart: (1) formation of the cardiac chambers and arterial trunks.". Heart (British Cardiac Society). 89 (7): 806–14. PMC 1767747  . PMID 12807866. doi:10.1136/heart.89.7.806.
Jump up ^ Anderson, RH; Webb, S; Brown, NA; Lamers, W; Moorman, A (Aug 2003). "Development of the heart: (2) Septation of the atriums and ventricles.". Heart (British Cardiac Society). 89 (8): 949–58. PMC 1767797  . PMID 12860885. doi:10.1136/heart.89.8.949.
Jump up ^ "Animal Tissues". Users.rcn.com. 2010-08-13. Retrieved 2010-10-17.
^ Jump up to: a b c Sadler, T.W (2012). Langman. Embriología Médica. Lippincott Williams & Wilkins. p. 165. ISBN 978-84-96921-46-7.
Jump up ^ Larsen, William (2001). Human Embryology (3rd ed.). Elsevier Saunders. p. 159. ISBN 0-443-06583-7.
Jump up ^ "Main Frame Heart Development". Meddean.luc.edu. Retrieved 2010-10-17.
Jump up ^ Larsen, William (2001). Human Embryology (3rd ed.). Churchill Livingstone. p. 159. ISBN 0-443-06583-7.
Jump up ^ Rohen, Johannes; Lutjen, Elke (2008). Embriología functional: una perspectiva desde la biología del desarrollo. Panamericana. p. 70. ISBN 978-84-9835-155-2.
^ Jump up to: a b Carlson, Bruce (2012). Embriología humana y biología del desarrollo. Mosby. p. 451. ISBN 84-8174-785-8.
^ Jump up to: a b c Fernández, Patricia Martha (2002). Manual de biología del desarrollo. Manual Moderno. p. 243. ISBN 968-426-976-5.
Jump up ^ Eynard, Aldo; Valentich, Mirta; Rovasio, Roberto (2011). Histología y embriología del ser humano: bases celulares y moleculares. Panamericana. p. 283. ISBN 978-950-06-0602-8.
Jump up ^ Moore, Keith L.; Persaud, T.V.N (2008). Embriología Clínica. Elsevier Saunders. p. 245. ISBN 978-84-8086-337-7.
Jump up ^ Tellez de Peralta, Gabriel (2003). Tratado de cirugía cardiovascular. Díaz de Santos. p. 44.
^ Jump up to: a b Larsen, William (2003). Embriología humana. Elsevier Science. p. 177. ISBN 968-426-976-5.
Jump up ^ OBGYN.net "Embryonic Heart Rates Compared in Assisted and Non-Assisted Pregnancies"
Additional images[edit]
M-mode sonography measuring embryonic heart rate.
Blood flow in a neonate
Human embryo, 38 mm, 8–9 weeks–anterior view, heart is visible.
References[edit]
This article incorporates text from the CC-BY book: OpenStax College, Anatomy & Physiology. OpenStax CNX. 30 jul 2014..
[hide]
v
t
e
Development of the circulatory system
Heart
Tubular heart
Truncus arteriosus
Bulbus cordis
Primitive ventricle
Primitive atrium
Sinus venosus
Septa
Atrioventricular cushions/Septum intermedium
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Protein signalling in heart development
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umbilical cord: Umbilical vein → Ductus venosus → Inferior vena cava → Heart → Pulmonary artery → Ductus arteriosus → Aorta → Umbilical artery
yolk sac: Vitelline veins
Vitelline arteries
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