V) Fertilization, Pregnancy and Birth IV) Embryonic and Fetal Development

  the development of organisms is called morphogenesis.   morphogenesis in humans and other

organisms involves two processes:   growth (increase in the number of cells)   differentiation (cell specialization)

V) Fertilization, Pregnancy and Birth IV) Embryonic and Fetal Development

  the nine months of human pregnancy are divided into three trimesters   the first trimester

  is from fertilization to the end of the third month.   by the second week of development the inner

cells of the blastula have reorganized into a flattened disk made up of two layers.   gastrulation is the process in which the two layered

structure develops into a three layered structure called a gastrula.

V) Fertilization, Pregnancy and Birth IV) Embryonic and Fetal Development

  gastrulation is a very important developmental phase.   each of the three layers has a particular

developmental fate.   each layer will give rise to specific organs and

structures in the fetus.   the three layers are the:

  Ectoderm (“ecto” means out)   Mesoderm (“meso” means middle)   Endoderm (“endo” means in)

Gastrula Layer Structures

Ectoderm

  Skin, hair finger nails, sweat glands   Nervous system   Lens, retina, cornea   Inner ear, cochlea, semicircular canals   Teeth, inside lining of mouth

Mesoderm

  Muscles (skeletal, cardiac and smooth)   Blood vessels and blood   Kidneys, reproductive structures   Connective tissue, cartilage, bones

Endoderm

  Liver, pancreas, thyroid, parathyroid   Urinary bladder   Lining of the digestive tract   Lining of the respiratory tract

V) Fertilization, Pregnancy and Birth IV)Embryonic and Fetal

Development

V) Fertilization, Pregnancy and Birth IV)Embryonic and Fetal Development

Human Sex Determination   sex is determined by the genetic make up of the fetus

xx = girl, xy = boy, the y chromosome is much smaller

  the principal gene for sex determination on the y chromosome is called SRY

Sex-determining Region of the Y chromosome  This gene is mainly responsible for the male

phenotype  The male fetus does not differ from the female

fetus until about the sixth or seventh week of pregnancy.

V) Fertilization, Pregnancy and Birth IV)Embryonic and Fetal Development

Sex-determining Region of the Y chromosome   this gene is mainly responsible for the male phenotype   the male fetus does not differ from the female fetus until about the sixth or

seventh week of pregnancy.

  in the presence of the SRY gene   the developing gonads becomes the testis.   the testis produce the hormone of male characteristics.   the testis develop inside the body cavity in the same

location as the ovaries and gradually descend.   current thinking is that the absence of the SRY gene lets

development proceed in the female direction.

V) Fertilization, Pregnancy and Birth IV)Embryonic and Fetal Development

  the developing gonad becomes the testis.   the testis produce the hormone of male characteristics.   the testis develop inside the body cavity in the same location as the ovaries and

gradually descend.   current thinking is that the absence of the SRY gene lets development proceed in the

female direction.

  women often produce some male sex hormones (androgens)   males often produce female sex hormones in very small amounts.   the balance between male and female hormones is most important

during fetal development.   too much estrogen at the wrong time can transform an

embryo with the male genes into outwardly appearing females.

  an overabundance of androgens during fetal development can produce sex organs of a male in a genetic body of a female.

V) Fertilization, Pregnancy and Birth IV)Embryonic and Fetal Development

Environmental Agents and Development   the fetus is no more dependent on the mother than during

development.   proper nutrition prevents many development problems.

~ spina bifida is a condition that results from a failure of the spinal cord to develop properly. ~ it is linked to low levels of folic acid (member of the vitamin B complex). ~ because nervous system development occurs in the first month, women of childbearing years are told to take folic acid supplements.

V) Fertilization, Pregnancy and Birth IV)Embryonic and Fetal Development

~ spina bifida is a condition that results from a failure of the spinal cord to develop properly. ~ it is linked low levels of folic acid (one of the vitamin Bs). ~ because nervous system development occurs in the first month, women of childbearing years are told to take folic acid supplements.

  women who smoke have smaller babies.   nicotine constricts blood vessels which reduces blood flow

to the placenta.   less oxygen and fewer nutrients are available for growth

of the fetus.   there is a link between smoking and low levels of

vitamin C, this would mean low levels of Vitamin C for the fetus also.

V) Fertilization, Pregnancy and Birth IV)Embryonic and Fetal Development

  nicotine constricts blood vessel which reduces blood flow to the placenta.   less oxygen and fewer nutrients are available for growth of the fetus.   there is a link between smoking and low levels of vitamin C, this would

mean low levels of Vitamin C for the fetus also.

  agents that are capable of causing developmental abnormalities in utero are called teratogens

in vivo ~in the living ex vivo ~out of the living in situ ~in the place in utero ~in the uterus in vitro ~within the glass (laboratory) in silico ~on the computer (simulation)

  many drugs can cross the placental membrane and have adverse affects on fetal development.

V) Fertilization, Pregnancy and Birth IV)Embryonic and Fetal Development

  many drugs can cross the placental membrane and have adverse affects on fetal devlopment.

Social Drugs   alcohol

~ crosses the placenta ~ can accumulate in the amniotic fluid surrounding the

baby causing miscarriages, stillbirth, bleeding and premature births.

  cigarettes ~ carbon monoxide and nicotine reduce the amount of oxygen available in the mother’s blood ~ affects development and size of the baby

V) Fertilization, Pregnancy and Birth IV)Embryonic and Fetal Development

  cigarettes ~ carbon monoxide and nicotine reduce the amount of oxygen available in the mother’s blood ~ affects development and size of the baby

  cocaine ~ increases the heart rate in the mother and baby. ~ reduces the oxygen available to the baby making it more likely to be small and slow growing. ~ can cause bleeding in the brain of the baby.

V) Fertilization, Pregnancy and Birth IV)Embryonic and Fetal Development

  cocaine ~ increases the heart rate in the mother and baby. ~ reduces the oxygen available to the baby making it more likely to have a small, slow growing baby. ~ can cause bleeding in the brain of the baby.

Medications   Thalidomide

~ blocks blood vessels that lead to the limbs of the babies (birth defects)

  Seizure Medication ~ reduces blood flow to the central nervous system of the baby

V) Fertilization, Pregnancy and Birth IV)Embryonic and Fetal Development

Medications   Thalidomide

~ blocks blood vessels that lead to the limbs of the baby’s (birth defects)   Seizure Medication

~ reduces blood flow to the central nervous system of the baby

Infectious Diseases   Rubella (German Measles)

~ infection during pregnancy can cause congenital rubella syndrome (CRS) with serious malformations of the developing fetus

  Genital Herpes ~ the virus can be passed to the fetus increasing the risk for premature delivery.

~ half of those that become infected either die or suffer neurological damage.

V) Fertilization, Pregnancy and Birth IV)Embryonic and Fetal Development

V) Fertilization, Pregnancy and Birth  Birth

V) Fertilization, Pregnancy and Birth V) Birth

  approximately 226 days after implantation uterine contractions begin signaling the beginning of parturition (labour).

  the cervix thins and begins to dilate.   the amnion is forced into the birth canal

  it often bursts and the fluid lubricates the canal (breaking of the water).

  as the cervix dilates uterine contractions move the baby through the birth canal.

  after the birth the placenta is delivered.

V) Fertilization, Pregnancy and Birth V) Birth   as the cervix dilates uterine contractions move the baby through the birth

canal.   after the birth the placenta is delivered.

  hormones play a vital role in the birthing process   Relaxin,

  produced by the placenta prior to labour   causes the ligaments within the pelvis to loosen and the cervix to

soften.   provides a more flexible passageway for the baby during

delivery.   the decrease in progesterone is important to the onset of delivery.

V) Fertilization, Pregnancy and Birth V) Birth

  causes the ligaments within the pelvis to loosen and the cervix to soften.

  provides a more flexible passageway for the baby during delivery.

  the decrease in progesterone is important to the onset of delivery.

  Oxytocin   a hormone from the pituitary gland   causes strong uterine contractions   appears in the mother’s blood prior to labour.

  labour can be induced by administering prostaglandins or pitocin which is a synthetic form of oxytocin.

V) Fertilization, Pregnancy and Birth V) Birth

V) Fertilization, Pregnancy and Birth V) Birth

Estrogen Oxytocin

from ovaries

Induces oxytocin receptors on uterus

from fetus and mother’s posterior pituitary

Stimulates uterus to contract

Stimulates placenta to make

Prostaglandins

Stimulate more contractions

of uterus

Posi

tive

feed

back

+

+

Placenta Umbilical cord

Uterus Cervix

Dilation of the cervix 1

V) Fertilization, Pregnancy and Birth V) Birth

Expulsion: delivery of the infant 2

V) Fertilization, Pregnancy and Birth V) Birth

Delivery of the placenta

Uterus

Placenta (detaching)

Umbilical cord

3

V) Fertilization, Pregnancy and Birth V) Birth

V) Fertilization, Pregnancy and Birth

VI) Lactation

V) Fertilization, Pregnancy and Birth VI) Lactation

  elevated estrogen and progesterone levels during pregnancy prepare the breasts for milk.   each breast contains about 20 lobes of glandular tissue each

with a duct that carries fluid toward the nipple.   prolactin stimulates the glands to produce fluid.   prolactin is a hormone that is produced by the pituitary gland.

  estrogen stimulates the release of prolactin during pregnancy   the action of prolactin is inhibited by progesterone.

V) Fertilization, Pregnancy and Birth VI) Lactation

  estrogen stimulates the release of prolactin during pregnancy   the action of prolactin is inhibited by progesterone.

  a decrease in progesterone and estrogen after birth results in   a decrease in prolactin production   an increase in prolactin activity

  prolactin initially causes the production of colostrum   colostrum closely resembles breast milk.   contains milk sugar and milk proteins but lacks the milk fats.

  a few days after birth, prolactin stimulates the production of milk.

V) Fertilization, Pregnancy and Birth VI) Lactation

  colostrum closely resembles breast milk.   contains milk sugar and milk proteins but lacks the milk fats.

  a few days after birth, prolactin stimulates the production of milk.

  colostrum and mother’s milk supply the baby with nutrients and antibodies.

  prolactin may increase milk production but the milk still does not flow easily.   Milk produced in the lobes of the glandular tissue must be forced

into the ducts that lead to the nipple.   newborn suckling stimulates nerve endings in the areola of the

breast.   sensory nerves carry information to the pituitary gland.

V) Fertilization, Pregnancy and Birth VI) Lactation

  newborn suckling stimulates nerve endings in the areola of the breast.   sensory nerves carry information to the pituitary gland.

  oxytocin is released.   oxytocin is carried by the blood to the breasts and

uterus.   in the breast oxytocin causes weak contractions of

smooth muscle, forcing milk into the ducts.   in the uterus oxytocin causes weak contractions of

smooth muscle allowing the uterus to return to pre-pregnancy size and shape.