Transcript Human Development

Biology 212
Anatomy & Physiology
Human Development
Dr. Thompson
One of the best ways to understand the structure of the adult
human body is to understand how it developed.
Similarly: abnormalities during development produce
abnormalities in adult structure.
Assuming:
You paired up with an appropriate partner
You elicited normal sexual responses from each other
A few milliliters of semen,
containing 200- to 600-million
sperm, were deposited high
in the vagina, just below
the cervix of the uterus
Scenario I:
The woman is not within a few days before or after ovulation
• Her cervix will be
plugged with thick mucous,
so few if any sperm will
enter the uterus and
subsequently the Fallopian
tubes.
• The few sperm which might make it into the Fallopian tubes are
not pushed distally (toward the ampulla)
• The sperm do not meet an oocyte and die within 48 hours
• No fertilization occurs
Scenario 2:
The woman has just ovulated, or she will ovulate within 1 - 2 days.
• The mucous plug in her cervix will be thin and watery; sperm can
easily penetrate it
• Most sperm will die in
her vagina, but a few
million (1 - 2%) are pulled
through the cervix, into
the uterus, and into the
Fallopian tubes where
they are propelled toward
the ampulla (+100,000
make it this far)
• Sperm meet the oocyte, and fertilization can occur
At ovulation, oocyte is
surrounded by a thick
membrane called the
zona pellucida, and by
follicular cells called the
corona radiata
Fimbria surrounding
the opening of the
Fallopian tube sweep
this structure into the
infundibulum
Oocyte is viable for 12 – 24 hours, so fertilization
must occur within this time.
Fertilization occurs within ampulla of Fallopian tube
If fertilization does not
occur, oocyte will
degenerate and die
A few thousand sperm reach the ampulla of the
Fallopian tube within 30 to 60 minutes after
ejaculation
But
They are not capable of fertilizing oocyte
Must undergo processes called capacitation
and acrosome reaction
which will take 8 to 10 hours after ejaculation
Capacitation:
Prior to ejaculation,
membrane around head of sperm is strong
Semen contains chemicals to prevent weakening
Tail is moderately active
After ejaculation, Chemicals
in semen diluted / washed
away.
Secretions from uterus &
oviducts cause membrane
to weaken.
Movement of tail increases.
Acrosome Reaction:
Occurs as sperm make contact with
corona radiata and zona pellucida
Requires 15 to 60 minutes
Acrosome swells, becomes
leaky, releases digestive
enzymes
(Acrosome swells, becomes leaky,
releases digestive enzymes)
Enzymes digest path
through corona radiata
and zona pellucida
Hundreds of sperm
usually involved in this
digestion
Head of one sperm makes contact with outside of
oocyte, binds onto it, and is quickly taken into it.
Two systems prevent entry
of more than one sperm:
Fast block: Plasma
membrane of oocyte changes
its electrical charge, which
prevents other sperm from
binding onto it.
Slow block: Zona pellucida
swells, pushing other sperm
away from the oocyte.
Once head of sperm enters oocyte, its nucleus is
released into the cytoplasm.
Nucleus of sperm (23 chromosomes) and nucleus of
oocyte (23 chromosomes) meet and fuse together.
Cell now called zygote, with 46 chromosomes
Human Development: 3 Periods
Fertilization
2 weeks
2 weeks
8 weeks
8 weeks
38 weeks (birth)
Zygote undergoes repeated divisions (mitosis), called
cleavage, as it is transported through oviduct toward
uterus
Eventually forms solid mass of 20 – 30 cells called
, same size as the zygote. This reaches uterus
3 to 4 days after fertilization
Morula does not embed in uterus immediately.
Stays loosely attached for 4 to 5 days, nourished by
secretions of endometrium.
Continues dividing
into +100 cells,
forming hollow
sphere called
.
Fluid-filled cavity in
center =
Blastocyst develops mass of cells at one end, called
which will develop into
the embryo.
Cells surrounding cavity, called
develop into the placenta.
, will
Cells of trophoblast
secrete digestive
enzyme s, forming
finger-like projections
into of uterus.
Blastocyst
As trophoblast is causing implantation
and developing into placenta,
Embryoblast is enlarging and
developing into embryo
Fluid-filled
Embryoblast =
(12 – 14 days after fertilization)
Pre-embryonic period now over,
Embryonic period begins.
During next six weeks of embryonic period, cells of
embryoblast will differentiate into beginnings of all organs.
Fertilization – 2 wks = Pre-embryo
2 wks – 8 wks = Embryonic period
8 wks – birth = Fetal period
First: Cells of embryonic disk separate into two, and
then three germ layers:
Endoderm
- nearest the blastocyst cavity
(changes name to yolk sac)
Mesoderm
- in middle
Ectoderm
- nearest amniotic cavity
View From Top,
Showing Ectoderm
View From Edge (Cross-section)
Showing All Three Layers
As embryo develops:
Endoderm will form epithelial linings of digestive and
respiratory systems.
Mesoderm will form skeletal, muscular, urinary,
reproductive, circulatory systems,
as well as muscle and connective
tissue layers of digestive and
respiratory systems .
Ectoderm will form skin and nervous system
The first system to begin developing is the nervous system.
This appears as a groove along the ectoderm, which closes
over to form a neural tube.
The neural tube
~ Day 22 – 23, sides of flat embryonic disk begin to fold
toward yolk sac.
By day 28: Embryo has “normal” body shape, amniotic
cavity pulled around to surround it.
Placenta continues to
develop from trophoblast;
many blood vessels develop
within it
Embryo floating in amniotic fluid; stays attached to
placenta
~ Day 28: Arm buds and leg buds begin developing.
Bones, muscles, and
blood vessels develop
from mesoderm as limbs
get bigger, nerves grow
out from spinal cord.
Other organs continue
developing internally.
Length ~ 4mm
(width of pencil)
Late embryonic period (4 – 8 weeks):
Nervous system continues to develop;
brain rapidly enlarges and folds
Eyes and ears begin to develop
Limbs continue developing, fingers and toes separate
Digestive system forms
Lungs bud off from digestive system and grow
Heart folds, divides into chambers, begins contractions
Kidneys, bladder, gonads develop
Face develops as two halves on side of head; move to
front and fuse
End of embryonic period
Beginning of fetal period (8 weeks):
• Body has human shape
• Almost all organs have begun developing
• Head growth still most pronounced
• Limbs complete
• Length ~ 3 centimeters
• Mass ~ 1 – 2 grams
Mass of quarter: 5.7 grams
Placenta well developed:
Fetal heart pumps blood from
embryo to placenta through
umbilical arteries:
Low in oxygen
High in carbon dioxide &
other wastes
In placenta:
Carbon dioxide & wastes
Oxygen & nutrients
Blood flows from placenta
back to embryo through
umbilical veins:
High in oxygen & nutrients
Low in carbon dioxide & other wastes
Ninth week:
(Organs and systems continue development)
Fetus = 5 cm long, 4 - 5 grams
External genitalia develop, but male and female still
very similar: penis / clitoris scrotum / labia
Tenth week:
(Organs and systems continue development)
Fetus = 7 cm long, 8 - 10 grams
External genitalia easily determined to be male or female
After tenth week:
(Organs and systems continue
to develop)
Fetus increases rapidly in size
After 17 weeks (four months)
Skin formed, but thin. Blood vessels easily
seen through it
Hair starting to develop. Fingernails and
toenails forming.
Eyelids still fused shut.
Ovaries form primordial follicles.
May suck thumb.
Moves arms, legs, head
Mother can feel movement.
After 26 weeks (six months):
Hair present over entire body. Will
become longer on scalp
Eyebrows and eyelashes forming
Eyelids almost open
Lungs producing surfactant
Testes begin descent through inguinal
canal
Swallowing amniotic fluid
Movement of hands, feet, face
After 34 weeks (eight months):
Skin pink, smooth
Longer hair on head
Eyes open, respond to light
Fingernails and toenails have
reached ends of fingers and toes
Testes have reached scrotum
Fingers can grasp objects, fine
movement of face and eyes
Nine months:
Ready for birth
Congratulations!
You have just given vaginal birth to a healthy baby.
She has been inspected: all parts are where they are
supposed to be.
Plus, she is hungry!
Your pituitary gland has been producing a
lot of the hormone prolactin, which has
caused your breasts to enlarge and
develop many glands to produce milk.
Your baby will naturally try to find your
breast and begin to suck on it.
This stimulates your pituitary
gland to secrete the hormone
oxytocin, which causes muscle
cells in the ducts of the milk
glands to force the milk toward
the nipple, where it is expressed
through 15-20 openings.
First few days: Milk is thick, high in fat, protein, minerals, antibodies.
Called colostrum
Later: ~90% water
~ 7% sugar
Also includes proteins, fats, vitamins, minerals
Your uterus continues to contract for a few days to expel functional layer of
endometrium. Assisted when nursing stimulates oxytocin.
These contractions also cause your uterus to begin returning to its normal,
nonpregnant shape and size; will take a few weeks
Joint between your pubic bones tightens up again; will take couple of weeks.
Baby, of course, started breathing as soon as she was born.
With each breath, more microscopic
air sacs (“alveoli”) in her lungs open
up;
Within few minutes: adequate to
support her need for oxygen.
Complete opening of all
alveoli: couple of days.
(Adjustments of the newborn)
Two openings in / near heart had
allowed blood to bypass lungs.
These two openings now close,
so blood flows through lungs to
pick up oxygen and get rid of
carbon dioxide.
Will take couple of days.
(Adjustments of the newborn)
Right after birth: Her temperature dropped by a couple of degrees.
Within few minutes: able to generate heat to regulate body temperature.
Few days: Stub of umbilical cord will dry
up and fall off, leaving the umbilicus
(“belly button”) as a scar.
First 12 to 15 months called Infancy.
Period of rapid growth – notably nervous, circulatory, skeletal, muscle systems
Learning gross motor coordination
Legs become strong enough to bear weight;
walking begins to develop
Visual acuity develops
Learns to recognize patterns of vison, hearing
Verbal expression and comprehension increase
rapidly; speech begins to develop
Lungs & heart strong enough to support active
movement
Childhood: end of infancy until puberty begins.
Less rapid growth
Continued improvement in function of most
systems, particularly nervous and muscular
Significant increase in cognitive function;
verbal expression and comprehension; fine
motor skills
Interestingly: very few other species have extended childhoods;
Evolved to allow for this cognitive development
Pubescent period lasts through puberty.
Caused when pituitary begins secretion of follicle stimulating hormone and
luteinizing hormone.
Rapid skeletal and muscular growth again.
Hips and shoulders widen proportionately more
Ovaries, uterus, oviducts, vagina, testicles,
prostate, seminal vesicles begin adult functions
Pubescent period lasts through puberty.
Caused when pituitary begins secretion of follicle stimulating hormone and
luteinizing hormone.
Rapid skeletal and muscular growth again.
Hips and shoulders widen proportionately more
Ovaries, uterus, oviducts, vagina, testicles,
prostate, seminal vesicles begin adult functions
Secondary sexual characteristics develop:
Enlargement of clitoris/penis, labia/scrotum
Growth of pubic, anal, and axillary (armpit) hair;
Specialized sweat glands begin functioning
Breasts develop in both girls and boys (gynecomastia)
Voice changes occur
Hair coursens over most of body
Cognitive function and verbal skills increase quickly
Emotional changes common.
“Typical” sequence of events in puberty
Age
Female
Male
10
Increase in height and fat deposition.
Breast development begins.
Spermatogenesis begins. Interstitial cells
appear & secrete testosterone
11
Breast development continues. Pelvis
widens. Pubic hair appears.
Growth spurt begins. Increased fat deposition.
Testes begin to enlarge
12
Ovaries, oviducts, uterus, vagina, clitorus,
& labia mature. Pubic hair more
apparent. Menstruation begins.
Epididymis, prostate, vas deferens, seminal
vesicles, penis, & scrotum mature. Pubic hair
appears.
13
Breasts fuller. Axillary hair appears.
Regular ovulation and menstruation.
Pubic hair more apparent. Frequent erections
and nocturnal emissions.
14
Skeletal growth slows. Breasts complete.
Sebaceous (oil) and sweat glands
increase. Acne common.
Growth of larynx deepens voice. Axillary and
facial hair appear. Shoulders begin to widen.
15
Voice deepens slightly. Regular
menstrual periods.
Ejaculations fully fertile. Moderate breast
development.
16
Adult stature reached.
Chest hair appears. Continued muscle &
skeletal growth. Sebaceous (oil) and sweat
glands increase. Acne common.
17
Adult stature reached.
Average age of puberty has decreased in past century
1900: 14.2 years in girls
1920: 13.8 years
1940: 13.4 years
1960: 12.8 years
1980: 12.6 years
2000: 11.6 years
2011: 10.8 years
Strangely: Few people seems to be following this type of information in
boys, but it also appears to be declining.
Factors influencing decreasing age of puberty:
a) Better general health and growth
b) Better nutrition: More fat and protein in diet
c) Increase periods of light
Interestingly: Body weight at beginning of puberty has remained
relatively constant in girls at about 47 kg (104 pounds), assuming body
fat of at least 18%.
No such correlation between weight and puberty appears to exist in boys.
Adolescent period lasts three to four years after puberty.
Bone and muscle mass continue to increase
in both sexes, but more pronounced in males.
Fat deposition continues to increase in both
sexes, but more pronounced in women.
Mental maturity increases;
Emotions typically stabilize.
Adult period:
Very little growth or neural
development occur.
Fat deposition continues in both sexes.
Reproduction and child-rearing typically
occur in this period.
Decreased function and diseases of many
organs (e.g. cancers, heart disease,
respiratory disease) common.
Gradual loss of verbal skills, visual and auditory acuity
Adult period:
Very little growth or neural
development occur.
Fat deposition continues in both sexes.
Reproduction and child-rearing typically
occur in this period.
Decreased function and diseases of many
organs (e.g. cancers, heart disease,
respiratory disease) common.
Gradual loss of verbal skills, visual and auditory acuity
Senescence (“old age”) involves deterioration and
loss of function of most organs. Bone and muscle
mass lost. Mental and verbal skills lost.