Human development is the process of growing to maturity. In biological terms, this entails growth from a one-celled zygote A zygote , or zygocyte, is the initial cell formed when a new organism is produced by means of sexual reproduction. A zygote is synthesized from the union of two gametes, and constitutes the first stage in a unique organism's development. Zygotes are usually produced by a fertilization event between two haploid cells — an ovum from a female and to an adult human being Humans commonly refers to the species Homo sapiens , the only extant member of the Homo genus of bipedal primates in Hominidae, the great ape family. However, in some cases the term is used to refer to any member of the genus Homo.
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Biological development
Sperm fertilizing an eggDevelopment begins with fertilization Fertilisation , is the fusion of gametes to produce a new organism. In animals, the process involves the fusion of an ovum with a sperm, which eventually leads to the development of an embryo. Depending on the animal species, the process can occur within the body of the female in internal fertilisation, or outside in the case of external, the process by which the male gamete A gamete is a cell that fuses with another gamete during fertilization (conception) in organisms that reproduce sexually. In species that produce two morphologically distinct types of gametes, and in which each individual produces only one type, a female is any individual that produces the larger type of gamete—called an ovum (or egg)—and a, the sperm cell, and the female gamete, the egg In most birds, reptiles, insects, fish, and two types of mammals an egg (Latin, ovum) is the zygote, resulting from fertilization of the ovum. To enable incubation the egg is usually kept within a favourable temperature range as it nourishes and protects the growing embryo. When the embryo is adequately developed it breaks out of the egg in the, fuse to produce a zygote. In pregnancy the 3 stages are commonly referred as Z.E.F.[by whom?] - meaning Zygote, Embryo, Fetus.
In medicine, the beginning of pregnancy is the instant a sperm cell enters an ovum and forms a viable zygote A zygote , or zygocyte, is the initial cell formed when a new organism is produced by means of sexual reproduction. A zygote is synthesized from the union of two gametes, and constitutes the first stage in a unique organism's development. Zygotes are usually produced by a fertilization event between two haploid cells — an ovum from a female and.[citation needed] Recently,[citation needed] in western medicine, pregnancy is defined as beginning when a zygote becomes implanted Implantation is an event that occurs early in pregnancy in which the embryo adheres to the wall of uterus. At this stage of prenatal development, the embryo is a blastocyst. It is by this adhesion that the fetus receives the oxygen and the nutrients from the mother to be able to grow in a woman's uterus The uterus (from Latin "uterus" , plural uteruses or uteri) or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species. It is within the uterus that the fetus. This occurs when the zygote then becomes embedded into the endometrium The endometrium functions as a lining for the uterus, preventing adhesions between the opposed walls of the myometrium, thereby maintaining the patency of the uterine cavity. During the menstrual cycle or estrous cycle, the endometrium grows to a thick, blood vessel-rich, glandular tissue layer. This represents an optimal environment for the (lining of the uterus) where it forms a placenta The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. Placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and lizards with varying levels of development up to, for the purpose of receiving essential nutrients A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. Nutrients are the substances that enrich the body. They build and repair tissues, give heat and energy, and regulate body processes. Methods for nutrient intake vary, with animals and through the uterus The uterus (from Latin "uterus" , plural uteruses or uteri) or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species. It is within the uterus that the fetus wall. The umbilical cord In placental mammals, the umbilical cord is the connecting cord from the developing embryo or fetus to the placenta. During prenatal development, the umbilical cord comes from the same zygote as the fetus and (in humans) normally contains two arteries (the umbilical arteries) and one vein (the umbilical vein), buried within Wharton's jelly. The in a newborn child helps get the nutrients to the child and helps get rid of the waste from the child. Before the placenta is developed the blastocyst receives its nutrients from the yoke sak which is contained within the blastocyst.
The zygote undergoes rapid cell divisions with no significant growth (a process known as cleavage In embryology, cleavage is the division of cells in the early embryo. The zygotes of many species undergo rapid cell cycles with no significant growth, producing a cluster of cells the same size as the original zygote. The different cells derived from cleavage are called blastomeres and form a compact mass called the morula. Cleavage ends with the) and cellular differentiation In developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type. Differentiation occurs numerous times during the development of a multicellular organism as the organism changes from a single zygote to a complex system of tissues and cell types. Differentiation is a common, leading to development of an embryo An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination. In humans, it is called an embryo until about eight weeks after fertilization (i.e. ten weeks LMP), and from then it is instead called a fetus.
Childbirth Childbirth is the culmination of a human pregnancy or gestation period with the birth of one or more newborn infants from a woman's uterus. The process of normal human childbirth is categorized in three stages of labour: the shortening and dilation of the cervix, descent and birth of the infant, and birth of the placenta. In many cases, with is the process in which the baby is born. Age is defined relative to this event in most cultures.
Physical stages of human life
There are no universally unanimous definitions for terms of age-related physical development stages, but following are some approximate age ranges:
Stages in prenatal development Prenatal or antenatal development is the process in which an embryo or fetus gestates during pregnancy, from fertilization until birth. Often, the terms fetal development, foetal development, or embryology are used in a similar sense.- Prenatal Prenatal or antenatal development is the process in which an embryo or fetus gestates during pregnancy, from fertilization until birth. Often, the terms fetal development, foetal development, or embryology are used in a similar sense (fertilization - birth)
- Embryo Human embryology is the study of human development during the first eight weeks from gametogenesis pre-conception through fertilization (conception of sperm and oocyte in the ampulla arm where the fallopian tube and ovary adjoin) up to and including the 8th week after implantation of the zygote (fertilized egg) in the uterus. After the 8th week of - (fertilization - 8 weeks of gestational phase)
- Zygote A zygote , or zygocyte, is the initial cell formed when a new organism is produced by means of sexual reproduction. A zygote is synthesized from the union of two gametes, and constitutes the first stage in a unique organism's development. Zygotes are usually produced by a fertilization event between two haploid cells — an ovum from a female and, the point of conception Fertilisation , is the fusion of gametes to produce a new organism. In animals, the process involves the fusion of an ovum with a sperm, which eventually leads to the development of an embryo. Depending on the animal species, the process can occur within the body of the female in internal fertilisation, or outside in the case of external, fertilization
- Blastocyst The blastocyst is a structure formed in the early embryogenesis of mammals, after the formation of the morula. It is a specifically mammalian example of a blastula. It possesses an inner cell mass , or embryoblast, which subsequently forms the embryo, and an outer layer of cells, or trophoblast, which later forms the placenta. The trophoblast the period between conception and embryonic stages
- Embryo An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination. In humans, it is called an embryo until about eight weeks after fertilization (i.e. ten weeks LMP), and from then it is instead called a fetus; the embryonic period starts at three weeks and continues until the end of the 8th week of pregnancy
- Fetus A fetus Pronounced Fee-tus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth (8 weeks of gestational phase - birth)
- Embryo Human embryology is the study of human development during the first eight weeks from gametogenesis pre-conception through fertilization (conception of sperm and oocyte in the ampulla arm where the fallopian tube and ovary adjoin) up to and including the 8th week after implantation of the zygote (fertilized egg) in the uterus. After the 8th week of - (fertilization - 8 weeks of gestational phase)
- Child Biologically, a child is generally a human between the stages of birth and puberty. The legal definition of "child" generally refers to a minor, otherwise known as a person younger than the age of majority. "Child" may also describe a relationship with a parent or authority figure, or signify group membership in a clan, tribe, (birth Childbirth is the culmination of a human pregnancy or gestation period with the birth of one or more newborn infants from a woman's uterus. The process of normal human childbirth is categorized in three stages of labour: the shortening and dilation of the cervix, descent and birth of the infant, and birth of the placenta. In many cases, with - puberty)
- Neonate (newborn) (0 - 30 days)
- Infant An infant or baby is the very young offspring of humans. A newborn is an infant who is within hours, days, or up to a few weeks from birth. In medical contexts, newborn or neonate refers to an infant in the first 28 days of life (from birth up to 4 weeks after birth, less than a month old). The term "newborn" includes premature infants, (baby) (1 month - 11 months)
- Toddler A toddler is a young child who is of the age of learning to walk, between infancy and childhood. Toddling usually begins between the ages of 12 and 18 months. During the toddler stage, the child also learns a great deal about social roles, develops motor skills, and first starts to use language (1 - 2 years)
- Play age (3 - 5 years)
- Primary school A primary school is an institution in which children receive the first stage of compulsory education known as primary or elementary education. Primary school is the preferred term in the United Kingdom and many Commonwealth Nations, and in most publications of the United Nations Educational, Scientific, and Cultural Organization (UNESCO). In some age (also called prepubescence) (4-12)
- Elementary school An elementary school is an institution where children receive the first stage of compulsory education known as elementary or primary education. Elementary school is the preferred term in some countries, particularly those in North America. Primary school is the preferred term in the United Kingdom, India, Pakistan, Australia, Latin America, South age (also called middle childhood) (4-8)
- Preadolescence Preadolescence is a stage of human development through childhood that occurs in a child's years before adolescence (preteen, or late childhood. The child in this and the previous phase are called schoolchild (schoolboy or schoolgirl), when still of primary school age.) (10 - 12 years)
- Adolescence Adolescence is a transitional stage of physical and mental human development generally occurring between puberty and legal adulthood (age of majority), but largely characterized as beginning and ending with the teenage stage. According to Erik Erikson's stages of human development, for example, a young adult is generally a person between the ages and puberty Puberty is the process of physical changes by which a child's body becomes an adult body capable of reproduction. Puberty is initiated by hormone signals from the brain to the gonads . In response, the gonads produce a variety of hormones that stimulate the growth, function, or transformation of brain, bones, muscle, skin, breasts, and (13 - 19 years)
- Adult An adult is a human being or living organism that is of relatively mature age, typically associated with sexual maturity and the attainment of reproductive age. In human context, the term has other subordinate meanings associated to social and legal concepts, for example a legal adult is a legal concept for a person who has attained the age of (20+ years)
- Early adulthood The term adult has at least three distinct meanings. It can indicate a biologically grown or mature person. It may also mean a plant, animal, or person who has reached full growth or alternatively is capable of reproduction, or the classification legal adult, generally determined as a person who has attained the legally fixed age of majority; as (20 - 39 years)
- Middle adulthood Middle age is the period of age beyond young adulthood but before the onset of old age. Various attempts have been made to define this age, which is around the third quarter of the average life span of human beings (40 - 59 years)
- Advanced adult Old age consists of ages nearing or surpassing the average life span of human beings, and thus the end of the human life cycle. Euphemisms and terms for old people include seniors , senior citizens (British and American usage) and the elderly. As occurs with almost any definable group of humanity, some people will hold a prejudice against others â€/Senior citizen Senior citizen is a common polite designation for an elderly person in both UK and US English, and it implies or means that the person is retired. This in turn implies or in fact means that the person is over the retirement age, which of course varies according to country. Synonyms include pensioner in UK English and retiree and senior in US (60+ years)
- Death Death is the termination of the biological functions that sustain a living organism. The word refers both to the particular processes of life's cessation as well as to the condition or state of a formerly-living body (occurs at various ages, depending on person)
Also sometimes used are terms that specify one's age in numbers, such as:
- Child (0-12)
- Teenager (13-19)
- Twentysomething Ageing or aging (American and Canadian English) is the accumulation of changes in an organism or object over time. Ageing in humans refers to a multidimensional process of physical, psychological, and social change. Some dimensions of ageing grow and expand over time, while others decline. Reaction time, for example, may slow with age, while (20-29)
- Thirtysomething Ageing or aging (American and Canadian English) is the accumulation of changes in an organism or object over time. Ageing in humans refers to a multidimensional process of physical, psychological, and social change. Some dimensions of ageing grow and expand over time, while others decline. Reaction time, for example, may slow with age, while (30-39)
- Fortysomething Ageing or aging (American and Canadian English) is the accumulation of changes in an organism or object over time. Ageing in humans refers to a multidimensional process of physical, psychological, and social change. Some dimensions of ageing grow and expand over time, while others decline. Reaction time, for example, may slow with age, while (40-49) (formerly also Quadragenarian, rarely used since 1980)
- Quinquagenarian Ageing or aging (American and Canadian English) is the accumulation of changes in an organism or object over time. Ageing in humans refers to a multidimensional process of physical, psychological, and social change. Some dimensions of ageing grow and expand over time, while others decline. Reaction time, for example, may slow with age, while (50-59)
- Sexagenarian Ageing or aging (American and Canadian English) is the accumulation of changes in an organism or object over time. Ageing in humans refers to a multidimensional process of physical, psychological, and social change. Some dimensions of ageing grow and expand over time, while others decline. Reaction time, for example, may slow with age, while (60-69)
- Septuagenarian (70-79)
- Octogenarian (80-89)
- Nonagenarian (90-99)
- Centenarian A centenarian is a person who has attained the age of 100 years or more. Because current average life expectancies across the world are less than 100, the term is invariably associated with longevity. Much rarer, a supercentenarian is a person who has lived to the age of 110 or more, something only achieved by about one in a thousand centenarians (100-109)
- Supercentenarian A supercentenarian is someone who has reached the age of 110 years. This age is achieved by only one in a thousand centenarians.[citation needed] Furthermore, only 2% of supercentenarians live to be 115.[citation needed] (110+)
Physical development milestones
- Ability to lift and control the orientation of the head
- Crawling Human gait is the way locomotion is achieved using human limbs. Different gaits are characterized by differences in limb movement patterns, overall velocity, forces, kinetic and potential energy cycles, and changes in the contact with the surface begins
- Walking begins
- Speech begins
- Voice lowers in pitch (especially noticeable in boys)
- Pubic hair appears
- Genitals and reproductive organs mature
- Menstrual cycle begins (females)
- Body hair and facial hair appears
Note: the Tanner stages can be used to approximately judge a child's age based on physical development.
See also
- Child development
- Developmental biology
- Auxology
- Embryogenesis
- Mammalian embryogenesis
- Life-history theory
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