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