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 reproduction A single individual reproduces Many offspring are produced rapidly Disadvantage of asexual reproduction Little or no genetic variation

Sexual Reproduction Advantages of sexual reproduction Increases genetic variation Enhances reproductive success in changing environments Disadvantage 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. Oviduct Ovary Uterus Bladder (excretory system Urethra (excretory system Vagina 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 Ovaries Oviduct Follicles Corpus luteum Uterus Endometrium (lining of uterus Cervix (“neck” of uterus) Vagina

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. Seminal vesicle (behind bladder) Bladder (excretory system) Prostate gland Vas deferens Urethra Scrotum Epididymis penis Testis

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 Spermatogenesis Produces sperm in the male Oogenesis Produces ova in the female

Spermatogenesis Increases genetic variation Primary spermatocytes (diploid) are produced throughout a male’s reproductive years Diploid cells undergo meiosis to form four haploid sperm

Spermatogenesis sperm seminiferous tubule spermatocytes

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 OVULATION Diploid cell PRIMARY OOCYTE Start: within follicle Degenerating corpus luteum PRIMARY OOCYTE CORPUS LUTEUM Growing follicles SECONDARY OOCYTE, Mature follicle SECONDARY OOCYTE Ruptured follicle OVULATION OVUM

Puberty 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 voice Females: Hormone~ estrogen. Characteristics~ breasts, broadened pelvis, distribution of body fat

Reproductive hormones Testosterone from testes sperm production & secondary sexual characteristics Estrogen from ovaries egg production, preparing uterus for fertilized egg & secondary sexual characteristics

Hormonal control of the testes Stimuli from other areas in the brain 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) Hypothalamus Releasing hormone Anterior pituitary Negative feedback FSH LH Androgen production Testis Sperm production

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 releases progesterone maintains uterus lining produces estrogen

Hormones synchronize cyclical changes in the ovary and uterus

Menstrual cycle Controlled by interaction of 4 hormones FSH & LH estrogen progesterone FSH ovulation = egg release egg development corpus luteum estrogen progesterone lining of uterus days 7 14 21 28

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

Female reproductive cycle Feedback egg matures & is released (ovulation) builds up uterus lining estrogen ovary corpus luteum progesterone FSH & LH fertilized egg (zygote) maintains uterus lining HCG yes pituitary gland corpus luteum pregnancy GnRH no progesterone corpus luteum breaks down progesterone drops menstruation maintains uterus lining 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