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FERTILIZATION DETAILS
1. Review
a. Sperm are deposited in the vagina
b. Eggs are released by the ovary, one ovary at a time
c. The sperm swims to meet the egg
i. Passes through cervix (many get trapped in vagina)
ii. Crosses uterus
iii. Swims up fallopian tubes (may be wrong tube)
d. Many sperm arrive at the egg at the same time
e. Enzymes in the head of the sperm loosen the protective layer of
cells around the egg
f. Head of sperm enters egg and fuses with genetic information inside
the egg
g. Protective shield goes around the egg so no more sperm can get
through
h. Sperm (haploid) fuse with egg (haploid) to form a diploid zygote (23
chromosomes each – zygote with 46 chromosomes)
2. Travel of Zygote (draw page 1055)
a. Newly fertilized egg is called a zygote
b. Begins mitotic division (cleavage) after 30 hours (embryo)
i. These cells don’t increase in size
ii. Cleavage produces a ball of cells called a morula (not much
larger than zygote)
iii. Cells of the morula divide and form a blastocyst (ball of cells
with a fluid filled cavity)
c. Travels through fallopian tubes down to uterus as divides
d. 4-5 days, the embryo reaches the uterus and is made up of 100 or
more cells;
e. By the time it reaches the uterus, the morula becomes a blastocyst
f. When it reaches the uterus, the morula embeds itself in the thick
uterine lining; implantation
g. If doesn’t implant in correct location  can be ectopic pregnancy
h. Implantation: HCG is produced so lining isn’t shed (no period) and
can be detected on home pregnancy kit
i. Pregnancy begins at implantation (6 days after fertilization)
Pregnancy
1. After implantation, the blastocyst slowly takes on human features; this
nine month period is called gestation or pregnancy
a. First Trimester
i. For first 2-3 weeks, the embryo looks like embryo of other
animals
ii. The embryo develops from the mass of cells on the inner
surface of the blastocyst
iii. At first, all of the cells look alike but then they organize into
three major layers: ectoderm, mesoderm and endoderm.
iv. Different parts of the body develop from these different
layers
1. Ectoderm; nervous tissue and skin
2. Mesoderm: muscle, connective tissue, organs
3. Endoderm: linings of digestive, respiratory and urinary
tract; also liver, glands, pancreas, thyroid and thymus
v. Membranes that help the embryo also form during this time
1. Amnion: amniotic fluid cushions the embryo
2. Yolk sac: where first blood cells and reproductive cells
originate
3. Allantois: forms near yolk sac
4. Chorion: surrounds other membranes; one side has
chorion villi that extend into the uterine lining
vi. Placenta
1. made of chorion villi and part of the uterine lining.
2. 6-8 “ in diameter and 1” thick
3. nutrients, gasses, pathogens, drugs pass from mother
to fetus through placenta
4. Developing fetus is attached to placenta by umbilical
cord which has arteries and veins that carry blood
between fetus and placenta
5. Blood between mother and fetus never mixes;
materials are exchanged through diffusion
6. Developing placenta secretes a hormone calle HCG
(human chorionic gonadotropin) early in second week
after fertilization.
7. HCG stimulates production of sex hormones which
keeps uterine lining and embryo
8. As placenta grows, its secretes large amounts of
estrogen and progesterone which maintain the uterus
and prevents ovulation
9. If the egg is not fertilized: no more sex hormones
would be made, and menstruation would follow
vii. Organogenesis: process that forms the organs
1. Cell determination: organize according to function
2. Cell differentiation: get special structures
3. Morphogenesis: produces shape and structure of
body regions
viii. Brain, nervous system and spinal cord form in third week
ix. Heart beats at 21 days and is smooth beating at 28 days
x. By fifth week: arms, legs, eyes, ears, and digestive system
develop
xi. By 6th week: fingers and toes and some brain activity;
embryo begins to move
b.
c.
d.
e.
xii. From 8 weeks to birth: the embryo is called a fetus
xiii. By End of first trimester, it is only 2 inches long, but organ
systems have begun to form
Second Trimester
i. Mother’s abdomen begins to swell as uterus enlarges
ii. Fetuses heartbeat can be heard and skeleton begins to form
iii. Layer of soft hair grows over skin
iv. Fetus begins to wake and sleep
v. Can feel fetus moving around: swallows, hiccups, sucks its
thumb and makes a fist; kicks feet and curls toes
vi. By end of second trimester, it is about 32 cm long and eyes
are open
Third trimester
i. Fetus grows quickly and undergoes changes so it can
survive outside the mother
ii. Can see light and darkness through abdominal wall, and can
react to music and loud sounds
iii. During last half of the trimester, the fetus develops fat under
its skin to insulate the body for a steady temperature.
Miscarriage:
i. Spontaneous abortion occurs in more than 20% of all
conceptions (1st trimester usually)
ii. Usually because there is a genetic abnormality that prevents
normal fetal development
Birth
i. Birth occurs 270 days after fertilization
ii. Three stages:
1. Contractions dilate the cervix to about 10 centimeters;
5 fingers
a. Hormones initiate childbirth causing smooth
muscles lining uterus to contract
b. Amniotic sac breaks and fluid falls through
vagina (breaking water)
c. Muscles in cervix and vagina relax allowing
them to enlarge for fetus to pass through.
d. Muscular contractions are called labor
2. Birth of the fetus
a. Usually less than 2 hours
b. Pushing
3. Afterbirth:
a. fluid, blood, placenta are pushed out of the
body with contractions; umbilical cord is
severed
b. Afterbirth (placenta, amnion and uterine lining)
come out of the body about 10 minutes after
the baby is born.
iii. Baby’s lungs expand as the baby cries for the first time and
breathes on its own.
iv. Umbilical cord is cut and tied; baby’s circulatory system
closes off and is now independent of the mother.
v. Soon the respiratory and excretory systems become fully
functional.
2. Vulnerability of Early Growth and Trauma of Birth
a. So much growing and developing in embryonic stage, makes it a
vulnerable time for the infant.
b. Spontaneous abortions
i. Trauma
ii. Inherited defects (select against defective genotypes –
natural selection and evolution)
iii. Usually so early that mother is not aware that she was even
pregnant – less costly, mother can become pregnant again
c. Right after birth, fetus must make many physiological adjustments
in a short amount of time:
i. Lungs fill with air
ii. Umbilical veins and arteries are lost
iii. More work on heart
3. Maternal Health
a. Nutrition
i. Need good nutrition (carbs, proteins, fats)
ii. Need more calories (not eating for two!)
iii. Need to get folic acid or neural tube defects
iv. Gain 20 – 35 pounds
v. If poor nutrition right before birth  brain function suffers
b. Infections
i. Antibodies help prevent all but the most serious infections
ii. Teratogens (agents that cause birth defects)
iii. Measles during the 1st six weeks can cause 50% chance of
organs not forming properly or deafness
c. Prescription Drugs
i. In the 1960s tranquilizer thalidomine  missing or deformed
arms and legs
ii. Anti-acne drugs can cause facial and cranial deformities
iii. NO IBUPROFEN
d. Alcohol
i. Fetal alcohol syndrome
ii. Common cause of mental retardation
iii. Smaller than normal brain and head, facial deformations,
poor motor coordination, heart defects
iv. 60 – 70 % of alcoholic women have babies with FAS
e. Cocaine
i. Prevents nervous system from developing normally
ii. Chronically irritable and abnormally small
f. Cigarette Smoke
i. Smoking reduces vitamin C in the blood and fetus
ii. May disrupt other nutrients
iii. Harms the growth and development (underweight newborn)
iv. Risk is higher for stillbirth, miscarriage and premature
delivery
4. First Four Weeks – Neonatal Life
a. Reflexes:
i. newborn is helpless but has some helping reflexes
ii. sucking, rooting: breastfeeding
iii. Moro reflex (arms embrace when lost support of head)
iv. Babinski reflex: big toe curls down when foot is stroked
v. Grasping
vi. Blink, smile, sneeze, cough and gag
b. Human Newborns are helpless compared to other animals
i. Main way of helping self is to cry
ii. Humans are the slowest maturing primate
iii. Parents are in demand but more learning period
iv. Human newborns are helpless but ready to learn
5. Phases of Post Natal Growth
a. Infancy:
i. About 7.5 pounds and 20” long
ii. Head and neck are 30% of the body (adults 10%)
iii. Legs are only 15% of body (adults 50%) and weak
iv. Body made of a lot more water
v. Large brain early in life (cranial); doubles in size the first year
and is adult size by age 10
vi. Brain grows in cell size, not cell number; make more
connections, more fatty myelin sheaths
vii. Other organs grow in first years of life; thymus 40% in first
year; adult size by age 12; then shrinks; thymus is important
at educating T cells in immune system
viii. Length, chest circumference increase
b. Childhood
i. Rapid neurological development
ii. Gradual increases in organ sizes, height and weight
iii. Toddler, more neuromuscular control
iv. Learn to speak
v. Rate of neurological development varies a lot as does
physical growth
vi. Men do take longer for neurological development
vii. Increased height and length of legs (epiphyseal growth)
viii. By 10, skull is like that of an adult
c. Adolescence and Puberty
i. Childhood growth is slow and steady, then adolescent
growth spurt
ii. Hormones are secreted and secondary sex characteristics
are now evident
iii. Increase in weight and then height
iv. Growth spurt usually over 2 years
d. Menarche
i. Girls become sexually mature with first menstrual period
after height growth spurt declines
ii. Need some body fat and fatter girls have periods first
iii. Now seeing decline in age of first menarche
6. Reaction Norm
a. Now that we see the biological basis of human development, we
will see how the environment plays a role.
b. Environment can play a part in shaping the adult organism
c. Ie, the genotype may have potential to be 70 inches if environment
is ideal.
d. Sometimes growth is slowed and then there is catch up growth, but
sometimes it cannot get back on track.
e. Something may effect critical part of growth process (iodine
deficiency), length of time that growth delayed was too long
(malnutrition)
f. Chronic mild undernutrition: body size reduced, adolescence
delayed, sexual maturation delayed.
7. Factors that influence growth and nutrition
a. Genetics
i. Body shape and size, fat deposition, and growth patterns are
more related to genetics
ii. Body size is determined by many genes
iii. Ossification and dental development are also genetically
controlled
iv. Racial differences in height, skeletal maturation
v. Sex differences between males and femailes
b. Neural control
i. Growth center in the brain (hypothalamus) keeps growth on
track genetically so if there is a problem (illness, some
malnutrition) there can be catch up with growth.
ii. Peripheral nervous system also helps
c. Hormonal control
i. Endocrine glands influence growth
ii. Fetal hormones, and other hormones throughout the lifetime
d. Nutrition
i. Need food for essential growth
e.
f.
g.
h.
i.
j.
k.
ii. In post-war Germany, children lagged behind normal growth
curves
iii. Hard to test malnutrition (unethical); rats and mice
iv. Nutritional needs vary throughout the life cycle of the child
v. Need lots of nutrition, calcium, protein, vitamins, iron
Secular trends
i. People grow differently at different stages of history
ii. People today grow faster than before
Socioeconomic Class
i. Higher socioeconomic class are taller
ii. Size of family is also important
Season and Climate
i. Growth in height is faster in the spring
ii. Weight is faster in autumn
iii. Not necessarily weather, other conditions that go along with
weather
Exercise
i. Adults and children can grow muscle mass with exercise
ii. Reduce fat storages
Disease
i. Asthma can lead to delay in puberty
ii. Tuberculosis and cystic fibrosis can influence height
Antenatal insults
i. Before birth while mother is pregnant
ii. Alcoholic mothers can have children with fetal alcohol
syndrome, retarded growth and development
iii. Smoking leads to lower birth weight
iv. Undernutrition
Emotion
i. Emotional factors influence growth, post war Germany
ii. Stress can outweigh dietary supplement
8. Summary
a. The advantage of slow growth and maturation is ability to learn and
become enculturated
b. Growth is a long time, but can delayed to prevent environmental
damage.
c. Can lead to permanent reduction in size.