reproduction and life stages

the blastocyst

The zygote spends the next few days traveling down the fallopian tube toward the uterus, where it will take up residence. As it travels, it divides many times by mitosis. It soon forms a tiny, fluid-filled ball of cells called a blastocyst. The blastocyst has an inner and outer layer of cells, as you can see in Figure 22.5. The inner layer, called the embryoblast, will develop into the new human being. The outer layer, called the trophoblast, will develop into other structures needed to support the new organism.

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from fertilization to birth

When a sperm penetrates the cell membrane of an egg, it triggers the egg to complete meiosis. The sperm also undergoes changes. Its tail falls off, and its nucleus fuses with the nucleus of the egg. The resulting cell, called a zygote, contains the diploid number of chromosomes. Half of the chromosomes come from the egg, and half come from the sperm. You can watch the process of fertilization and the development of a baby until birth in this amazing video: MEDIA Click image to the left or use the URL below. URL:

the fetus

From the eighth week following fertilization until birth, the developing human being is called a fetus. Birth typically occurs at about 38 weeks after fertilization, so the fetal period generally lasts about 30 weeks. During this time, the organs complete their development. The fetus also grows rapidly in length and weight. Some of the specific changes that occur during the fetal stage are listed in Figure 22.7. By the 38th week, the fetus is fully developed and ready to be born. A 38-week fetus normally ranges from about 36 to 51 centimeters (1420 inches) in length and weighs between 2.7 and 4.6 kilograms (about 610 pounds).

placenta and amniotic sac

The fetus could not grow and develop without oxygen and nutrients from the mother. Wastes from the fetus also must be removed in order for it to survive. The exchange of these substances between the mother and fetus occurs through the placenta. The placenta is a temporary organ that starts to form shortly after implantation. It forms from the trophoblast layer of cells in the blastocyst and from maternal cells in the uterus. The placenta continues to develop and grow to meet the needs of the growing fetus. A fully developed placenta, like the one in Figure 22.8, is made up of a large mass of blood vessels from both mother and fetus. The maternal and fetal vessels are close together but separated by tiny spaces. This allows the mothers and fetuss blood to exchange substances across their capillary walls without the blood actually mixing. The fetus is connected to the placenta through the umbilical cord. This is a long tube that contains two arteries and a vein. Blood from the fetus enters the placenta through the umbilical arteries. It exchanges gases and other substances with the mothers blood. Then it travels back to the fetus through the umbilical vein. Another structure that supports the fetus is the amniotic sac. This is a membrane that surrounds and protects the fetus. It contains amniotic fluid, which consists of water and dissolved substances. The fluid allows the fetus to move freely until it grows to fill most of the available space. The fluid also cushions the fetus and helps protect it from injury.

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pregnancy and birth

Pregnancy is the carrying of one or more offspring from the time of implantation until birth. It is the development of an embryo and fetus from the expectant mothers point of view.

role of the mother

The pregnant mother plays a critical role in the development of the embryo and fetus. She must avoid toxic substances such as alcohol, which can damage the developing offspring. She also must provide all the nutrients and other substances needed for normal growth and development. Most nutrients are needed in greater amounts by a pregnant woman because she is literally eating for two people. Thats why its important for a woman to eat plenty of nutritious foods during pregnancy. The pregnant woman in Figure 22.9 is eating a variety of fresh fruits, which provide energy, vitamins, and other nutrients.

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birth

Near the time of birth, the amniotic sac breaks in a gush of liquid. Labor usually begins within a day of this event. Labor involves contractions of the muscular walls of the uterus. With the mothers help, the contractions eventually push the fetus out of the uterus and through the vagina. Within seconds of birth, the umbilical cord is cut. Without this connection to the placenta, the baby cant exchange gases, so carbon dioxide quickly builds up in the babys blood. This stimulates the babys brain to trigger breathing, and the newborn takes her first breath.

the embryo

After implantation occurs, the blastocyst is called an embryo. The embryonic stage lasts from the end of the first week following fertilization through the end of the eighth week. During this time, the embryo grows in size and becomes more complex. It develops specialized cells and tissues. Most organs also start to form. You can see some of the specific changes that take place during weeks four to eight of the embryonic period in Figure 22.6. By the end of week eight, the embryo is about 30 millimeters (just over 1 inch) in length. It may also have begun to move.

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implantation

The blastocyst continues down the fallopian tube until it reaches the uterus, about 4 or 5 days after fertilization. When the outer cells of the blastocyst contact cells lining the uterus (the endometrium in Figure 22.5), the blastocyst embeds itself in the uterine lining. This process is called implantation. It generally occurs about a week after fertilization.

childhood

Childhood begins after the babys first birthday and continues until puberty. Between 1 and 3 years of age, a child is called a toddler. During the toddler stage, growth is still very rapid, but not as rapid as it was during infancy. Toddlers learn many new words and starts putting them together in simple sentences. Motor skills also develop quickly during the toddler stage. By the age of 3 years, most children can run and climb steps. They can hold crayons and scribble with them. They can also feed themselves, and most can use the toilet. From age 3 until puberty, growth slows down. The body also changes shape. The arms and legs grow longer relative to the trunk. Children continue to develop new motor skills. For example, many young children learn how to ride a tricycle and then a bicycle. Most learn how to play games and sports. By the age of 6 years, children start losing their baby teeth. Permanent teeth come in to replace them. Most children have started school by this age. They typically start learning to read and write around age 6 or 7 (see Figure 22.11). During the later years of childhood, children also start to develop friendships and become less dependent on their parents.

middle adulthood

Middle adulthood is the period from the mid-30s to the mid-60s. During this stage of life, people start showing signs of aging. Their hair may thin and slowly turn gray. Their skin develops wrinkles. The risk of serious health problems increases. For example, cardiovascular diseases, cancer, and type 2 diabetes become more common in people of middle age. This is also the stage when many people raise a family and strive to attain career goals.

from birth to adulthood

For the first year after birth, a baby is referred to as an infant. Childhood begins at the age of two years and continues until puberty. Adolescence begins with puberty and lasts until adulthood.

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early adulthood

Early adulthood refers to the 20s and early 30s. During early adulthood, most people are at their physical peak, and they are usually in good health. Often, they are completing their education and getting established in the workforce. Many people become engaged or marry during this time.

adulthood

Adulthood doesnt have a definite starting point. Teens may become physically mature by the age 16 years, but they are not adults in a legal sense until they are older. For example, in the U.S., you must be 18 years old to vote or serve in the armed forces. You must be 21 years old before you can take on many legal and financial responsibilities. Once adulthood begins, it can be divided into three stages: early, middle, and late adulthood.

adolescence

Adolescence is the stage of life between the start of puberty and the beginning of adulthood. Adolescence begins with the physical changes of puberty. It also includes many other changes, including mental, emotional, and social changes. During adolescence: Teens develop new thinking abilities. For example, they develop the ability to understand abstract ideas, such as honesty and freedom. Their ability to think logically also improves. They usually get better at problem solving as well. Teens try to establish a sense of identity. They typically become increasingly independent from their parents. Many teens have emotional ups and downs. This is at least partly due to their changing hormone levels. Teens usually start spending more time with their peers, like the girls in Figure 22.13. Adolescents usually spend much more time with their friends and classmates than they do with family members.

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puberty

Puberty is the stage of life when a child becomes sexually mature. Puberty lasts from about 10 to 16 years of age in girls and from about 12 to 18 years of age in boys. In both girls and boys, puberty begins when the pituitary gland signals the gonads (ovaries or testes) to start secreting sex hormones (estrogen in girls, testosterone in boys). Sex hormones, in turn, cause many other changes to take place. In girls, estrogen causes the following changes to occur: The uterus and ovaries grow. The ovaries start releasing eggs. The menstrual cycle begins. Pubic hair grows. The hips widen and the breasts develop. In boys, testosterone causes these changes to take place: The penis and testes grow. The testes start producing sperm. Pubic and facial hair grow. The shoulders broaden. The voice becomes deeper as the larynx in the throat grows larger (see Figure 22.12). Girls and boys of the same age are similar in height during childhood. In both girls and boys, growth in height and weight is very fast during puberty. But boys grow more quickly that girls do, and their period of rapid growth also lasts longer. In addition, boys generally start puberty later than girls, so they have a longer period of childhood growth. For all these reasons, by the end of puberty, the average height of boys is 10 centimeters (about 4 inches) greater than the average height of girls.

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infancy

The first year of life after birth is called infancy. During infancy, a baby grows very quickly. The babys length typically doubles and her weight triples by her first birthday. Many other important changes also occur during infancy: The baby starts smiling, usually by about 6 weeks of age (see Figure 22.10). The baby starts noticing people and grabbing toys and other objects The baby teeth start to come in, usually by 6 months of age. The baby begins making babbling sounds. By the end of the first year, the baby may be saying a few words, such as Mama and Dada. The baby learns to sit, crawl, and stand. By the end of the first year, the baby may be starting to walk.

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late adulthood

Late adulthood begins in the mid-60s and continues until death. This is the stage of life when most people retire from work. This frees up their time for hobbies, grandchildren, or other interests. For example, the man in Figure During late adulthood, the risk of developing diseases such as cardiovascular diseases and cancer continues to rise. Most people also have a decline in strength and stamina. Their senses may start failing, and their reflex time typically increases. Their immune system also doesnt work as well as it used to. As a result, common diseases like the flu may become more serious and even lead to death. The majority of late adults develop arthritis, and as many as one in four develop Alzheimers disease. Despite problems such as these, many people remain healthy and active into their 80s and even 90s. Do you want

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instructional diagrams

description_image

This diagram shows a blastocyst, which is a small, fluid-filled ball of cells that travels through the fallopian tube until it implants on the wall of the uterus and continues to develop as an embryo. The blastocyst is composed of an outer, circular layer and an internal mass. The outside is known as the trophoblast and looks like a single layer of cells. It will eventually develop into structures that support the developing fetus. The internal mass is called the inner cell mass, also known as the embryoblast. It will eventually develop into a fetus.

description_image

This diagram shows the six stages of development of a human embryo, in two rows that are arranged left to right. The first stage, at the top left, is a fertilized egg, which is a single cell. After fertilization, the egg undergoes mitosis, which replicates the cells so that the embryo can grow. The 2-, 4-, 8-, and 16-cell stages each show a progressively larger number of cells, seemingly arranged at random. The final stage is the blastocyst, where the cells appear to form a ball. After this, the embryo will implant on the wall of the uterus and be known as a fetus.

description_image

This diagram shows the blastocyst stage in the process of fertilization. The blastocyst has an inner and outer layer of cells. The inner layer is called the embryoblast, will develop into the new human being. The outer layer is called the trophoblast, will develop into other structures needed to support the new organism. This layer surrounds the inner cell mass or the embryoblast and a fluid-filled cavity known as the blastocoele. When the outer cells of the blastocyst embeds itself in the uterine lining or the endometrium. This process is called implantation. It generally occurs about a week after fertilization.

questions

The layer of a blastocyst that develops into the placenta is the

a. embryoblast.

b. blastoblast.

-->  c. trophoblast.

d. photoblast.

What happens when a sperm penetrates the cell membrane of an egg?

a. The egg completes meiosis.

b. The sperms tail falls off.

c. The nuclei of sperm and egg fuse.

-->  d. all of the above

After fertilization occurs, how long does it normally take for the blastocyst to reach the uterus and implant in the uterine lining?

a. about an hour

b. about a day

-->  c. about a week

d. about a month

By the end of the embryonic stage, the embryo is about

-->  a. 1 inch long.

b. 6 inches long.

c. 1 foot long.

d. 1.5 feet long.

During which stage of development do most organs start to form?

a. blastocyst

-->  b. embryo

c. fetus

d. infancy

Which of these events occurs during the embryonic stage?

a. The eyelids form.

-->  b. The heart begins to beat.

c. Tooth buds appear.

d. all of the above

Which of the following changes does not occur during the fetal stage?

-->  a. The blood starts to circulate.

b. The brain becomes active.

c. Alveoli form in the lungs.

d. Muscles develop.

About how much does a 38-week fetus weigh?

a. 12 pounds

b. 35 pounds

-->  c. 610 pounds

d. 1116 pounds

At about how many weeks after fertilization does birth typically occur?

a. 16

b. 24

c. 32

-->  d. 38

The placenta allows the maternal and fetal blood to

a. mix together.

b. come close together.

c. exchange substances.

-->  d. two of the above

During infancy, which of these developments generally occurs first ?

a. sitting

b. babbling

c. crawling

-->  d. smiling

During which of the following life stages is growth in height and weight usually most rapid?

-->  a. infancy

b. early childhood

c. middle childhood

d. late childhood

A babys first teeth start coming in at about 12 months of age.

a. true

-->  b. false

Toddlers grow more rapidly than infants.

a. true

-->  b. false

Puberty occurs at the same age in all children.

a. true

-->  b. false

A boys voice deepens at puberty as his larynx grows bigger.

-->  a. true

b. false

People generally start showing signs of aging in middle adulthood.

-->  a. true

b. false

A zygote has the haploid number of chromosomes.

a. true

-->  b. false

As soon as a zygote starts to divide, it is called an embryo.

a. true

-->  b. false

Most organs start to form during the embryonic stage.

-->  a. true

b. false

The fetal period typically lasts about 30 weeks.

-->  a. true

b. false

The purpose of the placenta is to cushion the fetus and protect it from injury.

a. true

-->  b. false

The umbilical cord is cut only after the baby starts to breathe on its own.

a. true

-->  b. false

Puberty generally occurs at an earlier age in girls than in boys.

-->  a. true

b. false

__process in which a blastocyst embeds in the uterine lining

a. placenta

b. blastocyst

c. amniotic sac

d. zygote

e. trophoblast

-->  f. implantation

g. umbilical cord

__fluid-filled membrane that surrounds and protects a fetus

a. placenta

b. blastocyst

-->  c. amniotic sac

d. zygote

e. trophoblast

f. implantation

g. umbilical cord

__fluid-filled ball of cells that forms soon after fertilization occurs

a. placenta

-->  b. blastocyst

c. amniotic sac

d. zygote

e. trophoblast

f. implantation

g. umbilical cord

__cell layer in the blastocyst that will develop into the placenta

a. placenta

b. blastocyst

c. amniotic sac

d. zygote

-->  e. trophoblast

f. implantation

g. umbilical cord

__tube containing blood vessels that connects a fetus to the placenta

a. placenta

b. blastocyst

c. amniotic sac

d. zygote

e. trophoblast

f. implantation

-->  g. umbilical cord

__cell that results when a sperm fertilizes an egg

a. placenta

b. blastocyst

c. amniotic sac

-->  d. zygote

e. trophoblast

f. implantation

g. umbilical cord

__temporary organ consisting of blood vessels from both the mother and fetus

-->  a. placenta

b. blastocyst

c. amniotic sac

d. zygote

e. trophoblast

f. implantation

g. umbilical cord

diagram questions

question_image

What stage is considered the blastocyst?

a. H

-->  b. J

c. E

d. Y

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Which letter represents the 4-cell stage?

a. Y

b. R

c. H

-->  d. V

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What is the 4-cell stage?

-->  a. V

b. R

c. Y

d. X

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Where is the two cell stage?

-->  a. H

b. X

c. R

d. V

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What is represented by the label V?

a. INNER CELL MASS

b. BLASTOCYST CAVITY

c. TROPHOBLAST CAVITY

-->  d. TROPHOBLAST SPHERE

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What is the part identified by V in the diagram?

a. BLASOCELL

b. BLASOCYST CAVITY

-->  c. TROPHOBLAST SPHERE

d. INNER CELL MASS

question_image

Which letter represents the Inner Cell Mass?

-->  a. R

b. V

c. NONE

d. D

question_image

What is located between inner cell mass and trophoblast sphere of a blastocyst?

-->  a. BLASTOCYST CAVITY

b. EMBRYOBLAST

c. CAVITY

d. MITOSIS

question_image

Which label indicates the trophoblast of the blastocyst?

-->  a. N

b. T

c. P

d. L

question_image

Which label shows the trophoblast?

a. T

b. L

c. L&N

-->  d. N

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Which label indicates the 2-cell stage in the development of the embryo?

a. L

-->  b. J

c. E

d. W

question_image

Will label refers to the Morula?

a. E

-->  b. W

c. A

d. P

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Where is the endometrium?

a. E

-->  b. P

c. M

d. U

question_image

At which stage is a human embryo most developed?

a. 8-cell stage

-->  b. Blastocyst

c. 16-cell stage

d. Fertilized egg

question_image

What comes after the 2-cell stage?

a. 8-cell stage

b. Fertilized egg

c. 16-egg stage

-->  d. 4-cell stage

question_image

How many stages are there in human embryonic development?

a. 4

b. 5

c. 7

-->  d. 6

question_image

How does the number of cells in increase in each stage before Blastocyst?

-->  a. The cells double in each stage

b. the cells quadrupled in each stage

c. the cells tripled in each stage

d. the number of cells remains the same

question_image

Which stage of human embryonic development occurs just after 2-cell stage?

a. 8-cell stage

-->  b. 4-cell stage

c. Fertilized egg

d. 16-cell stage

question_image

In the diagram below, what do you call the final stage of a fertilized egg?

a. 8-cell stage forming

b. 2-cell stage forming

-->  c. Blastula

d. 4-cell stage forming

question_image

Identify the biological function that permits cell migration during gastrulation.

-->  a. Blastocoel

b. Animal pole

c. Gray Crescent

d. Zygote

question_image

What comes after 4-cell stage?

-->  a. 8-cell stage

b. Blastula

c. 2-cell stage

d. Vegetal pole

question_image

How many steps are there in the zygote becoming a blastula?

a. 2

b. 3

c. 5

-->  d. 4

question_image

Which stage of reproduction and life occurs directly after 4-cell stage forming?

a. 2-cell stage forming

-->  b. 8-cell stage

c. Blastula

d. Zygote

question_image

What is the inner part of the blastocyst called?

-->  a. inner cell mass

b. palets

c. sphere

d. zenoth

question_image

What is the outermost layer of the blastocyst called?

a. Blastocyst sphere

b. Inner Mass Cell

c. Blastocycst cavity

-->  d. Trophoblast sphere

question_image

How many layers of cells are there in a Blastocyst?

-->  a. 2

b. 3

c. 1

d. 4

question_image

What is the space inside of a blastocyst?

a. inner cell mass

-->  b. blastocyst cavity

c. ganglian nerves

d. trophoblast sphere

question_image

Which part of the Blastocyst will develop into an adult human?

a. Trophoblast

b. Blastocoele

-->  c. Inner Cell Mass (Embryoblast)

d. Nucleus

question_image

How many embryoblasts are shown in this image?

a. 5

-->  b. 7

c. 6

d. 4

question_image

What is the embryoblast covered by?

a. Blastocoele

b. Protoplast

c. Blastocyst

-->  d. Trophoblast

question_image

What is the second stage in an embryo's development?

a. morula

b. 2-cell stage

c. egg

-->  d. Zygote

question_image

What is the stage of embryo development after zygote?

a. Blastocyst

-->  b. 2-cell stage

c. Morula

d. Egg

question_image

Which stage of embryonic development contains an Inner Cell?

a. Egg

b. Zygote

c. Morula

-->  d. Blastocyst

question_image

How many steps are in the development of an embryo?

a. 2

b. 7

c. 4

-->  d. 6

question_image

What is inside the zygote

a. sac

b. embryo

c. placenta

-->  d. inner cell mass

question_image

How many centers are present in an inner cell?

-->  a. one

b. five

c. three

d. two

question_image

How many inner cells are depicted?

-->  a. 19

b. 11

c. 13

d. 14

question_image

What do you call the outer layer of cells?

-->  a. Trophectoderm

b. Embryo Cells

c. Inner Cell Mass

d. Blastocyst

question_image

The inner layer, called the embryoblast, will develop into the new human being. The layer that will develop into other structures needed to support the new organism is called what?

-->  a. trophoblast

b. blastocyst

c. blastocyst cavity

d. inner cell mass

question_image

What is the outer layer of the blastocyst?

-->  a. trophoblast

b. inner cell mass

c. epidermis

d. blastocyst cavity

question_image

How many layers does a developing embryo have?

a. 2

b. 4

-->  c. 3

d. 1

question_image

Considering a Blastocyst, what cell portion will develop into the new human being?

-->  a. Embryoblast

b. Trophoblast

c. Blastocyst Cavity

d. Zygote

question_image

What would occur if the trophoblast was removed from the blastocyst?

-->  a. The embryoblast will not have enough nutrients to fully develop.

b. The blastocyst will eat other cells.

c. The blastocyst will have more room for the embryoblast.

d. The embryoblast will become bigger.

question_image

What is the center of the cell called?

a. Disappearing zona pellucida

-->  b. Blastocyst cavity

c. Trophoblast

d. Inner cell mass

question_image

How many parts are shown in the picture?

-->  a. 4

b. 2

c. 3

d. 1

question_image

How many trophoblasts appear in this cell?

-->  a. 14

b. 16

c. 4

d. 10

question_image

As the embryo grows the amount of inner cells gets...

a. Stays the same

-->  b. Larger

c. Shrinks

d. Fewer

question_image

How long does it take to form a blastocyst?

a. 4 hours

b. 72 hours

-->  c. 4 days

d. 2 days

question_image

What is the cell called after 72 hours?

a. Cell Stage

b. Blastocyst

c. Zygote

-->  d. Morula

question_image

How many stages are there between the zygote stage and the blastocyst stage?

a. 5

b. 1

c. 6

-->  d. 4

question_image

How many stages of the cell are shown in this diagram?

-->  a. 6

b. 3

c. 2

d. 4

question_image

What would happen if the cells during the development divided at a rate twice as slow as normal?

-->  a. It would take 8 days for the blastocyst to develop.

b. The morula would develop in 48 hours.

c. The pregnancy would take half the time that it normally does.

d. The blastocyst would develop in 10 days.

question_image

Can you identify the blastocyst cavity?

a. U

b. M

c. P

-->  d. E