The human life cycleThe human life cycle

Chapter 16-3Chapter 16-3

What are the stages of What are the stages of human development human development that occur before and that occur before and

after birth?after birth?

The zygoteThe zygote

Once the zygote is formed it Once the zygote is formed it takes about takes about 44 days for it to days for it to reach the reach the uterusuterus..

The zygote then divides into 2 The zygote then divides into 2 cells, then 4, then 8 and so on cells, then 4, then 8 and so on until it becomes an until it becomes an embryoembryo; a ; a hollow ball made up of hundreds hollow ball made up of hundreds of cells.of cells.

ZygoteZygote

Cell Differentiation

• DNA directs changes in DNA directs changes in cells from a general cell cells from a general cell type (embryonic stem type (embryonic stem cells) to cells) to specializedspecialized cell cell types in the adulttypes in the adult

• Until recently, scientists Until recently, scientists thought that once cells thought that once cells became specialized in the became specialized in the adult, the DNA could not adult, the DNA could not be reprogrammed back to be reprogrammed back to its undifferentiated stateits undifferentiated state

Based on: Scientific American, June 2004

The embryoThe embryo

Once the embryo attaches itself Once the embryo attaches itself to the uterus it will take to the uterus it will take 88 weeks weeks to become a fetus.to become a fetus.

First the hollow ball will grow First the hollow ball will grow inward forming new inward forming new membranesmembranes. .

EmbryoEmbryo

MembranesMembranes

What is the amniotic sac?What is the amniotic sac?

A membrane which surrounds the A membrane which surrounds the embryo that is filled with amniotic embryo that is filled with amniotic fluid to fluid to cushioncushion and and protectprotect the the developing baby.developing baby.

MembranesMembranes

What is the placenta?What is the placenta? The The linklink between the embryo and the between the embryo and the

mother. mother. The blood vessels align with the The blood vessels align with the

mother’s so the embryo can receive mother’s so the embryo can receive nutrientsnutrients, , OO22, and other important , and other important substances. substances.

It It removesremoves CO CO22 and other wastes. and other wastes. Next, an Next, an umbilical cordumbilical cord forms between forms between

the placenta and the embryo. It also the placenta and the embryo. It also contains blood vessels that link the contains blood vessels that link the embryo to the mother.embryo to the mother.

4 weeks

Yolk sac: produces baby’s RBCs & delivers nutrients until the placenta takes over

5 weeks5 weeks

Embryo is about the size of a sesame seed

6 weeks6 weeks

The baby’s heart is beating! It will soon divide into the left & right chambers.

7 weeks7 weeks

Eyelid folds cover the baby’s eyes

Tailbone: what looks like a tail is the formation of the tailbone

The baby’s intestines begin to grow into the umbilical cord

8 weeks8 weeks

9 weeks9 weeks

The baby is the size of a kidney bean!

The embryo becomes a FETUS!

The fetusThe fetus

On week On week 99 the embryo becomes the embryo becomes a fetus until birth.a fetus until birth. The The brainbrain is developing rapidly. is developing rapidly. The eyes are developing.The eyes are developing. It has It has fingersfingers and and toestoes..

On week 12 the fetus is about 9 On week 12 the fetus is about 9 cm long and has a mass of cm long and has a mass of about 26g.about 26g.

The fetusThe fetus

Between week 13 and week 24 the Between week 13 and week 24 the tissues develop into recognizable tissues develop into recognizable shapes.shapes. BonesBones become distinct. become distinct. A A heart beatheart beat can be heard. can be heard. A layer of soft hair grows over the skin.A layer of soft hair grows over the skin. MusclesMuscles are growing. are growing. It is now about 20 cm long and has a mass It is now about 20 cm long and has a mass

of 700g.of 700g.

13 weeks13 weeks

Baby has its own set of unique fingerprints;

The head is more proportional to the body

Week 16Week 16

The circulatory system is fully developed; the heart pumps about 25 quarts of blood a day

The fetusThe fetus

Between week 25 and 36 the fetus Between week 25 and 36 the fetus prepares to live prepares to live outsideoutside the mother’s the mother’s body.body. The The brainbrain surface develops grooves surface develops grooves

and ridges.and ridges. The lungs can carry out the exchange of The lungs can carry out the exchange of

OO22 and CO and CO2.2.

The The eyelidseyelids can open. can open. It is now about 40cm long and has a It is now about 40cm long and has a

mass of about 3kg.mass of about 3kg. After about After about 3636 weeks the baby is weeks the baby is

ready to be born.ready to be born.

Week 24Week 24The mother’s uterus is about the size of a soccer ball; the baby’s lungs are developing the bronchial tubes; baby can hear well & other senses like taste are being developed.

Six MonthsSix Months(weeks 25 – 29)(weeks 25 – 29)

The baby weighs about a The baby weighs about a pound and a halfpound and a half. His wrinkled . His wrinkled skin is starting to skin is starting to smooth outsmooth out as he puts on baby fat. as he puts on baby fat.

25 weeks25 weeks

Seven Months Seven Months (30 – 33 weeks)(30 – 33 weeks)

By now, the baby weighs about By now, the baby weighs about 3 pounds3 pounds and is more than 15 and is more than 15 inches long. She can open and inches long. She can open and close her eyes and close her eyes and follow a follow a lightlight..

Eight Months Eight Months (34 – 37 weeks)(34 – 37 weeks)

The baby now weighs about 4 The baby now weighs about 4 3/4 pounds. His 3/4 pounds. His layers of fatlayers of fat are filling him out, making him are filling him out, making him rounder, and his rounder, and his lungslungs are well are well developed.developed.

36 weeks36 weeks

Nine MonthsNine Months(38 – 41 weeks)(38 – 41 weeks)

The The average babyaverage baby is more than is more than 19 inches long and weighs 19 inches long and weighs nearly 7 pounds now, but nearly 7 pounds now, but babies vary widelybabies vary widely in size at in size at this stagethis stage

40 weeks40 weeks

BirthBirth What are the What are the 33 stages of birth? stages of birth?

LaborLabor - strong muscular - strong muscular contractionscontractions of the uterus, that cause the cervix to of the uterus, that cause the cervix to enlarge, so the baby can fit through the enlarge, so the baby can fit through the opening.opening.

DeliveryDelivery - during this stage the baby is - during this stage the baby is pushed out of the pushed out of the uterusuterus, through the , through the vagina, and out of the mother’s body. vagina, and out of the mother’s body. Then the umbilical cord is clamped and Then the umbilical cord is clamped and cut, separating the baby from the cut, separating the baby from the mother. mother.

AfterbirthAfterbirth- about - about 1515 minutes later minutes later contractions push the contractions push the placentaplacenta and and other membranes out of the uterus other membranes out of the uterus though the vagina.though the vagina.

Multiple BirthsMultiple Births

What are the two types of twins?What are the two types of twins? IdenticalIdentical twins- come from on twins- come from on

zygote that splits into two identical zygote that splits into two identical embryos. They have the same embryos. They have the same inherited traits and are the same inherited traits and are the same sex.sex.

FraternalFraternal twins- develop from two twins- develop from two different zygotes and may or may different zygotes and may or may not be the same sex.not be the same sex.

InfancyInfancy From birth to From birth to twotwo years of age the years of age the

human nervous and muscular human nervous and muscular systems become better coordinated.systems become better coordinated. Birth - 3 months: the human can cry, Birth - 3 months: the human can cry,

suck, yawn, and blink.suck, yawn, and blink. 3 - 7 months: it can hold its head up and 3 - 7 months: it can hold its head up and

reach for objects.reach for objects. 7 - 10 months: it can 7 - 10 months: it can crawlcrawl.. 10 -16 months: it begins to walk by itself 10 -16 months: it begins to walk by itself

and and speakspeak it’s first word. it’s first word. 16- 24 months: it can understand simple 16- 24 months: it can understand simple

directions, play with toys, and feed itself.directions, play with toys, and feed itself.

ChildhoodChildhood From 2 to about From 2 to about 1212 years of age years of age

the human becomes more the human becomes more active and active and independentindependent.. 3 - 6 years: the human learns to 3 - 6 years: the human learns to

share and play with others, carry share and play with others, carry conversations, and express conversations, and express themselves clearly.themselves clearly.

7 - 10 years: it thinks and cares 7 - 10 years: it thinks and cares more for others, more for others, friendsfriends become become important.important.

10 -12 years: the human develops 10 -12 years: the human develops the need to the need to fit infit in with others of with others of their age group.their age group.

AdolescenceAdolescence The stage of development when The stage of development when

children become children become adultsadults physically physically and mentally.and mentally. 9 -14 years: the human enters 9 -14 years: the human enters pubertypuberty, ,

the period of sexual development in the period of sexual development in which the body becomes able to which the body becomes able to reproduce.reproduce.

13 - 15 years: the teenager gradually 13 - 15 years: the teenager gradually becomes able to becomes able to thinkthink and and reasonreason like like an adult.an adult.

Consider consequences.Consider consequences. Problem solving-skills improve.Problem solving-skills improve. Develop specific interests. Develop specific interests.

AdulthoodAdulthood

Being grown up or Being grown up or maturemature. It is difficult to . It is difficult to define adulthood.define adulthood. 16 years old: can start driving.16 years old: can start driving. 18 years old: can vote and join the armed 18 years old: can vote and join the armed

forces.forces. 21 years old: can consume alcohol.21 years old: can consume alcohol. About 30 years old: About 30 years old: agingaging begins. begins. 45 - 60 years old: skin becomes wrinkled, eyes 45 - 60 years old: skin becomes wrinkled, eyes

loose ability to focus on close objects, hair loose ability to focus on close objects, hair looses color, muscle strength decreases.looses color, muscle strength decreases.

65 - Death: less efficient organ action.65 - Death: less efficient organ action. Adults can slow the aging process by Adults can slow the aging process by

maintaining a healthy diet and maintaining a healthy diet and exercisingexercising consistently.consistently.

CreditsCredits

http://www.babycenter.com/pregnancy-fetal-development-index