Ch. 27: Reproduction and Embryonic Development
Ch. 27: Reproduction and Embryonic Development
Asexual reproduction
Budding Fission Fragmentation,
accompanied by regeneration
Development of an unfertilized egg
Sexual reproduction
The fission of two haploid gametes from two parents to form a diploid zygote
Sexual and asexual reproduction are both common among animals
Rotifers can reproduce both asexually and sexually
Hermaphroditism A single individual
has both male and female reproductive systems
Asexual Reproduction
Advantages of asexual reproductionA single individual reproducesMany offspring are produced rapidly
Disadvantage of asexual reproductionLittle or no genetic variation
Sexual Reproduction
Advantages of sexual reproduction Increases genetic variationEnhances reproductive success in changing
environmentsDisadvantage of sexual reproduction
Locating a mate
Reproductive anatomy of the human female
main functions of the female reproductive system
1. to produce eggs, the (female sex cells),
2.to receive sperm,
3. to provide an environment in which a fertilized egg can develop.
Vagina
OviductOvary
Uterus
Bladder(excretory system
Urethra(excretory system
Vaginal opening
Reproductive anatomy of the human female
Ovaries Contain
follicles that nurture eggs (ova)
Produce sex hormones
Functional from puberty to menopause
Oviducts (Fallopian Tubes) Convey eggs
to the uterus Muscular contractions &cilia
draw ovum (egg) into oviduct Fertilization occurs
OvariesOviduct
Uterus
Vagina
Endometrium(lining of uterus
Corpus luteum
Follicles
Cervix(“neck” of uterus)
Reproductive anatomy of the human female
Uterus (womb) Development
of fertilized egg Opens into
the vagina Vagina
Receives penis during intercourse
Forms the birth canal
Reproductive anatomy of the human male
main functions
1. the production of sperm—the male sex cells
2. their delivery to the female.
Testis
Scrotum
Prostate gland
Bladder(excretorysystem)
penis
Vas deferens Urethra
Epididymis
Seminalvesicle(behindbladder)
Reproductive anatomy of the human male
Semen Sperm, which are expelled through the ducts during
ejaculation Glandular secretions that carry, nourish, and
protect the sperm Testes
Produce sperm Located outside abdominal cavity within the
scrotum (saclike pouch~ 1-3°C below normal body temperature- sperm can only form at this lower temp.)
How sperm leave the testes
1. Seminiferous tubules: carries/stores sperm in testes 2.Epididymis: a series of coiled ducts for maturation & temporary
storage organ for sperm 3. Vas deferens: tube which carries sperm past lubricating glands 4. ( a.)Seminal vesicles: secrete fluid that protects & nourishes sperm
(b.) Prostrate gland: produces an alkaline fluid that neutralizes urine in the urethra
(c.) Bulbourethral glands: secrete fluid that may help lubricate the urethra
5. Urethra: tube in the penis that transports sperm out of the male’s body, also transports urine from the urinary bladder.
6. Penis: copulatory organ, releases semen
7. Ejaculation: the release of semen
Reproductive anatomy of the human male
Gametogenesis: The formation of sperm and ova requires meiosis
SpermatogenesisProduces sperm in the male
Oogenesis Produces ova in the female
Spermatogenesis
Increases genetic variationPrimary spermatocytes (diploid) are
produced throughout a male’s reproductive years
Diploid cells undergo meiosis to form four haploid sperm
Spermatogenesis
seminiferoustubule
spermatocytes
sperm
Oogenesis
Most of the process occurs within the ovaries
Lifetime supply of primary oocytes is present at birth
One primary oocyte matures each month to form a secondary oocyte
If the secondary oocyte is fertilized, it completes meiosis and becomes a haploid ovum
Oogenesis
OVULATIONStart: PRIMARY
OOCYTEwithin follicle
Growingfollicles
Mature follicleRuptured follicle
OVULATION
SECONDARYOOCYTE
CORPUS LUTEUM
Degeneratingcorpus luteum
PRIMARY OOCYTE
SECONDARY OOCYTE,
OVUM
Diploid cell
Puberty: when secondary characteristics develop and the potential for sexual reproduction is reached(sperm production or ovulation)
Changes are controlled by hormones secondary sex characteristics: Males: hormone~ testosterone, characteristics~
body hair, muscle development, deep voiceFemales: Hormone~ estrogen. Characteristics~
breasts, broadened pelvis, distribution of body fat
Puberty
Testosterone from testes sperm production
& secondary sexual characteristics
Estrogen from ovaries egg production,
preparing uterus for fertilized egg & secondary sexual characteristics
Reproductive hormones
Hormonal control of the testes
Androgens (testosterone
most important) stimulate sperm production They also maintain
homeostasis by a negative feedback mechanism that inhibits the secretion of FSH (follicle-stimulating hormone) and LH (luteinizing hormone)
Stimuli from otherareas in the brain
Hypothalamus
Releasinghormone
Anteriorpituitary
LHFSH
Testis
Negative feedback
Androgenproduction
Spermproduction
The Reproductive Cycle of the Human Female I
A cyclic pattern of hormone secretion and reproductive events.
Humans and many other primates have menstrual cycles.
If pregnancy does not occur the endometrium is shed through the cervix and vagina: menstruation
The Reproductive Cycle of the Human Female. II
Menstrual cycle: changes that occur in the uterus. Day 1: the first day of menstruation. Menstrual flow phase.
Menstrual bleeding. Usually lasts for a few days
Proliferative phase. Regeneration and thickening of the endometrium. About 1 – 2 weeks in duration.
Secretory phase. Continued endometrial thickening about 2 weeks
The Reproductive Cycle of the Human Female. III
Ovarian cycle. Follicular phase.
Several ovarian follicles begin to grow.. Usually only one follicle continues to develop, the others disintegrate. The follicular phase ends with ovulation.
Follicle and adjacent wall of the ovary rupture Secondary oocyte is released. Luteal phase.
Follicular tissue remaining in the ovary develops into the corpus luteum. Secretes estrogens and progesterone.
Egg maturation in ovary
releasesprogesterone
maintainsuteruslining
produces estrogen
Hormones synchronize cyclical changes in the ovary and uterus
LH
FSH
estrogen
progesterone
lining of uterus
egg developmentovulation = egg release
corpus luteum
0 7 14 21 28days
Menstrual cycle Controlled by
interaction of 4 hormones FSH & LH estrogen progesterone
Hormonal coordination of the menstrual and ovarian cycles .
FSH (follicle stimulating hormone) produced by pituitary stimulates development of follicle
LH (luteinizing hormone) stimulates the development of the corpus luteum, stimulates ovulation
Estrogen: secreted by ovaries, stimulates development of uterine lining
Progesterone: secreted by corpus luteum, maintains uterine lining
corpusluteumovary
Female reproductive cycle
pregnancy
maintainsuterus lining
no
yes
Feedback
estrogenegg
matures &is released(ovulation)
builds up uterus lining
FSH & LH
progesterone
progesterone
fertilized egg(zygote)
HCG
corpus luteum breaks downprogesterone drops
menstruation
corpusluteum
maintainsuterus lining
GnRH
pituitarygland
hypothalamus
Fertilization results in a zygote and triggers embryonic development
Fertilization is the union of a sperm and an egg to form a diploid zygote
(PATH) Millions of sperm ->vagina -> cervix -> uterus -> oviduct (site of fertilization)
sperm + egg -> zygote
23(n) + 23(n) -> 46(2n)
Fertilization
Only one of these sperm will penetrate this human egg cell to initiate fertilization
The shape of a human sperm cell is adapted to its function
Fertilization
Implantation
Implantation: fertilized egg implants in thickened uterine lining