Transcript Animal Reproduction and Development

Animal Reproduction and
Development
Chapter 38
Modes of Reproduction
• Sexual reproduction
– Meiosis, gamete formation, and
fertilization
– Offspring show genetic variation
• Asexual reproduction
– Single parent produces offspring
– Offspring are genetically identical
Stages of Development
Gamete formation
Fertilization
Cleavage
Gastrulation
Organ formation
Growth, tissue specialization
Development Overview
Eggs form and mature in female
reproductive organs, and sperm
form and mature in male
reproductive organs.
Gamete formation
A sperm and an egg fuse at their
plasma membrane, then the nucleus
of one fuses with the nucleus of the
other to form the zygote.
Fertilization
By a series of mitotic cell divisions,
different daughter cells receive
different regions of the egg
cytoplasm.
Cleavage
Cell divisions, migrations, and
rearrangements produce two or
three primary tissues, the
forerunners of specialized tissues
and organs.
frog egg
frog sperm
Gastrulation
midsectional views
Subpopulations of cells are
sculpted into specialized organs
and tissues in prescribed spatial
patterns at prescribed times.
Organ formation
top view
Organs increase in size and
gradually assume specialized
functions.
Growth, tissue
specialization
side view
Male
Reproductive
System
bladder
seminal vesicle
vas
deferens
prostate gland
bulbourethral gland
urethra
epididymis
scrotum
testis
penis
Spermatogenesis
• Spermatogonium (2n) divides by
mitosis to form primary spermatocyte
(2n)
• Meiosis produces haploid spermatids
• Spermatids mature to become sperm
Testicular Cells
• Sertoli cells
– Line the seminiferous tubules
– Nourish the developing sperm
• Leydig cells
– Lie between the seminiferous
tubules
– Secrete testosterone
Female Reproductive Organs
oviduct
ovary
ovary
uterus
uterus
oviduct
vagina
cervix
vagina
Menstrual Cycle
• The fertile period for a human
female occurs on a cyclic
basis
• Menstrual cycle lasts about 28
days
Fertilization
• Sperm penetrates to egg cytoplasm
• Egg nucleus and sperm nucleus
fuse to form diploid zygote
Pregnancy
• Averages 38 weeks from fertilization
• Takes two weeks for blastocyst to
form
• Weeks 3 to 8 are embryonic period
• Weeks 9 to birth are fetal period
Early Divisions
• Cleavage begins within 24 hours of
fertilization
Day 1
Day 2
Day 3
Day 4
(morula)
Day 5 - Blastocyst Forms
• Cell secretions produce a fluid-filled
cavity in center of ball of cells
• Layers of blastocyst
inner cell mass
– Inner cell mass
– Trophoblast
– Blastocoel
Trophoblast- The outer layer of cells of the
mammalian blastocyst that gives rise to the
placenta.
Implantation Begins
• Blastocyst
attaches to
endometrium
(UTERUS) ;
begins to burrow
into maternal
tissues
Uterine cavity
blastocoel
inner cell
mass
trophoblast
Extraembryonic Membranes
• The amniotic
membrane will
enclose embryo
• Yolk sac forms
• Chorion begins
to form fingerlike
villi
chorionic
villi
chorion
amniotic
cavity
connecting
stalk
yolk sac
DAY 14
chorionic
cavity
Human Chorionic
Gonadotropin (HCG)
• Hormone secreted by the blastocyst
• Stimulates corpus luteum to keep
making progesterone and estrogens
• This maintains endometrium, prevents
menstruation
• Can be detected by week 3 with a home
pregnancy test
Gastrulation - Day 15
• Primitive streak
forms along one
axis of the inner
cell mass
• Cells migrate
inward here to form
endoderm and
mesoderm
Gastrulation
• Sphere of cells is a
blastula
• During
gastrulation, some
cells move inward
• Produces a threelayer embryo
Vertebrate Body Plan Emerges
paired
neural folds
pharyngeal
arches
somites
4 weeks
The Placenta
Placenta at full term
• Interlocking fetal and maternal
tissues
• Performs digestive, respiratory,
and urinary functions for the
fetus
8 weeks
• Materials exchanged across
membrane that separates
bloodstreams
12 weeks
Embryonic Period
Week 4
• Weeks 3 to 8
• By the close of embryo
period
– Appears human
Weeks 5-6
Week 8
Fetal Period
• Weeks 9 to birth
• Fetus is initially about 1 inch long
• Fetus born before 22 weeks cannot
survive
• Survival is poor before 28 weeks
because lungs are not fully formed
• By 36 weeks, survival is 95 percent
Fetal Nutrition
• All nutrients for fetal growth and
development must be delivered via
the placenta
• Mother’s diet affects fetal health
• Smoking may affect ability to absorb
nutrients and to pass them to fetus
Birth (Labor)
• Cervical canal dilates
• Amniotic sac ruptures
• Uterine contractions
drive fetus from uterus
• Placenta is expelled as
afterbirth
Lactation
• During pregnancy, progesterone
and estrogen stimulate gland
development
• After birth, prolactin induces
synthesis of enzymes for milk
production
• Oxytocin triggers contractions
Stages of Human
Development - Prenatal
• Zygote - Single cell
• Morula - Solid ball of cells
• Blastocyst - Ball with fluid-filled cavity
• Embryo - 2 weeks to 8 weeks
• Fetus - 9 weeks to birth
• Newborn - First 2
Stages of
weeks after birth
• Infant - 2 weeks to 15
Human
months
Development
• Child - 10-12 years
Postnatal
• Pubescent - At
puberty
• Adolescent - Puberty
to maturation
• Adult
• Old age
-
Birth Control Options
Prevent fertilization
Prevent ovulation
Block implantation
Sexually Transmitted
Diseases (STDs)
• Worldwide epidemic of STDs
• Women are most affected
• Can cause infertility, pain,
and even death
Causative Agents of STDs
• Viruses
– AIDS (HIV)
– Genital herpes
(Herpes simplex)
– Genital warts
(HPV)
• Bacteria
– Gonorrhea
(Neisseria
gonorrhoeae)
– Syphilis
(Trepnema
pallidum)
– Chlamydial
infections
In Vitro Fertilization
• Conception outside the body
• Woman receives hormone injections to
stimulate ovulation
• Oocyte is removed and combined with
sperm in petri dish
• After fertilization and a few divisions,
ball of cells is implanted in uterus
Abortion
• Removal of blastocyst, embryo, or
fetus
• First trimester abortions are painless,
and relatively complication free
• Later abortions are more difficult and
more controversial