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Essentials of Biology Sylvia S. Mader Chapter 29 Lecture Outline Prepared by: Dr. Stephen Essentials of Biology Sylvia S. Mader Chapter 29 Lecture Outline Prepared by: Dr. Stephen Ebbs Southern Illinois University Carbondale Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

29. 1 How Animals Reproduce • Animals generally reproduce sexually (two parents), but some 29. 1 How Animals Reproduce • Animals generally reproduce sexually (two parents), but some can also reproduce asexually (one parent). – Fragmentation is a mechanism whereby a new organism can regrow from a fragment of the original organism. – Parthenogenesis is a modified form of sexual reproduction where an unfertilized egg becomes a whole individual.

Asexual Versus Sexual Reproduction • Sexual reproduction involves the gameteproducing gonads of animals. – Asexual Versus Sexual Reproduction • Sexual reproduction involves the gameteproducing gonads of animals. – The male sperm-producing testes – The female egg-producing ovaries • Copulation brings these haploid gametes together, allowing fertilization to produce a diploid zygote. • Some animals are hermaphroditic, having the reproductive organs of both male and female.

Reproduction in Water Versus on Land • In most aquatic organisms, external fertilization occurs Reproduction in Water Versus on Land • In most aquatic organisms, external fertilization occurs and the resulting organism is free-living. • On land, evolutionary modifications arose to provide the embryo and nutrients and to prevent dehydration. – Extraembryonic membranes are present in the eggs of birds and reptiles. – The mammalian placenta, comprised of shared tissues between the mother and fetus, provides nutrients, removes wastes, and prevent dehydration.

29. 2 Human Reproduction • The human reproductive tract consists of two components. – 29. 2 Human Reproduction • The human reproductive tract consists of two components. – The gonads. – The accessory organs that assist reproduction or, in females, house the embryo.

Male Reproductive System • There are several components to the male reproductive system. – Male Reproductive System • There are several components to the male reproductive system. – The testes produce the sperm. – The epididymis is a coiled tubule that receives sperm produced by the testes. – The vas deferens stores sperm and conducts the sperm to the urethra in the penis. – The penis is a muscular accessory organ that facilitates transfer of sperm to the female.

Male Reproductive System (cont. ) Male Reproductive System (cont. )

Male Reproductive System (cont. ) • The sperm is carried in a fluid (semen) Male Reproductive System (cont. ) • The sperm is carried in a fluid (semen) comprised of products from three glands. – The seminal vesicles produces a fluid that nourishes the sperm. – The prostate gland produces a fluid that is believed to enhance sperm motility. – The bulbourethral gland produces a lubricating secretion to facilitate copulation.

Male Reproductive System (cont. ) Male Reproductive System (cont. )

Male Reproductive System (cont. ) • The release of sperm during copulation occurs in Male Reproductive System (cont. ) • The release of sperm during copulation occurs in two phases. – During emission, the secretions of the three glands are released as sperm enter the ejaculatory ducts. – During expulsion, rhythmic contractions of muscle expel the semen from the penis.

The Testes • The testes are comprised of coiled seminiferous tubules. • Sperm production The Testes • The testes are comprised of coiled seminiferous tubules. • Sperm production (spermatogenesis) occurs continually within the seminiferous tubules.

The Testes (cont. ) • The sperm produced have three distinct parts. – The The Testes (cont. ) • The sperm produced have three distinct parts. – The head, carrying the genetic material (acrosome) – The tail, which provides movement – The body, which houses mitochondria to provide energy for movement

Hormonal Regulation in Males • Several glands and hormones regulate sexual function in males. Hormonal Regulation in Males • Several glands and hormones regulate sexual function in males. – The hypothalamus controls the secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) by the anterior pituitary. – The anterior pituitary also produces FSH to enhance spermatogenesis. – The anterior pituitary produces LH to promote testosterone production. – Testosterone, produced by interstitial cells, is essential for normal sexual function.

Female Reproductive System • There are several components to the female reproductive system. – Female Reproductive System • There are several components to the female reproductive system. – The egg-producing ovaries – The oviducts (fallopian tubes), which conduct the egg to the uterus – The uterus, where development of the embryo occurs. – The cervix and vagina provide openings through which sperm enter during copulation.

Female Reproductive System (cont. ) Female Reproductive System (cont. )

The Ovaries • The ovaries are composed of millions of follicles that contain oocytes The Ovaries • The ovaries are composed of millions of follicles that contain oocytes for production of eggs. • When mature, the egg from a follicle erupts and is released (ovulation). • After ovulation, the follicle develops into the corpus luteum, which degenerates if fertilization does not occur.

The Ovaries (cont. ) The Ovaries (cont. )

The Ovaries (cont. ) • The ovarian cycle can be divided into two phases. The Ovaries (cont. ) • The ovarian cycle can be divided into two phases. – The follicular phase, stimulated by FSH from the anterior pituitary, results in maturation of the follicle and release of estrogens – The luteal phase, stimulated by LH from the anterior pituitary, results in development of the corpus luteum and release of progesterone.

The Ovaries (cont. ) The Ovaries (cont. )

The Ovaries (cont. ) • The interactive effects of estrogens and progesterone on the The Ovaries (cont. ) • The interactive effects of estrogens and progesterone on the uterus produce the menstrual cycle. • The follicular phase occurs during the first 14 days of the menstrual cycle. – From days 1 -5, hormone levels are low, causing the endometrium to be sloughed from the uterus (menstruation). – During days 6 -13, release of estrogen promotes development of the endometrium (proliferative phase).

The Ovaries (cont. ) • Ovulation occurs around day 14. • The luteal phase The Ovaries (cont. ) • Ovulation occurs around day 14. • The luteal phase occurs during the last 14 days of the menstrual cycle. – During days 15 -28, progesterone promotes development of the endometrium to prepare for a fertilized embryo (secretory phase). – If a fertilized embryo does not implant, endometrium degrades and menstruation occurs.

The Ovaries (cont. ) The Ovaries (cont. )

Control of Reproduction • There are several techniques available to prevent pregnancy. – Abstinence Control of Reproduction • There are several techniques available to prevent pregnancy. – Abstinence (avoid copulation) – Oral contraceptives (inhibition of FSH and LSH synthesis) – Contraceptive implants (disrupt ovarian cycle) – Intrauterine devices (alter uterine conditions) – Barrier methods (block sperm) – Spermicides (kill sperm)

Control of Reproduction (cont. ) Control of Reproduction (cont. )

Infertility • Infertility is a failure to achieve pregnancy. • In the US, about Infertility • Infertility is a failure to achieve pregnancy. • In the US, about 15% of couples experience infertility problems. – 40% of cases are attributed to the male. – 40% of cases are attributed to the female. – 20% of cases are attributed to both. • One means of overcoming infertility is through assisted reproductive technologies (ART).

Assisted Reproductive Technologies • Artificial insemination by donor involves insertion of harvested sperm into Assisted Reproductive Technologies • Artificial insemination by donor involves insertion of harvested sperm into the vagina. • For in vitro fertilization, an egg is fertilized outside the woman’s body and implanted later. • Gamete intrafallopian transfer is the same as in vitro fertilization except that the egg and sperm are placed into the fallopian tubes immediately. • A single sperm is injected directly into an egg in intracytoplasmic sperm injection.

Sexually Transmitted Diseases • There are several causes of sexually transmitted diseases (STDs). – Sexually Transmitted Diseases • There are several causes of sexually transmitted diseases (STDs). – Viruses are the cause of AIDS, genital warts, genital herpes, and a form of hepatitis. – Bacteria can cause chlamydia, pelvic inflammatory disease, gonorrhea, and syphilis. – Yeast and protozoa can cause infections.

29. 3 Human Development • Human development includes all of the events from fertilization 29. 3 Human Development • Human development includes all of the events from fertilization to the full formation of a child. • The stages of development in humans are similar to those in other land animals, including the presence of nourishing extraembryonic membranes.

29. 3 Human Development (cont. ) • There are four extraembryonic membranes. – The 29. 3 Human Development (cont. ) • There are four extraembryonic membranes. – The chorion is part of the placenta and facilitates exchange of gases, nutrients, and wastes. – Blood cells form in the yolk sac. – The blood vessels of the allantois are part of the umbilical cord. – The amnion contains fluid that cushions and protects the embryo.

29. 3 Human Development (cont. ) 29. 3 Human Development (cont. )

Fertilization • Fertilization of an egg by sperm forms a diploid zygote. – The Fertilization • Fertilization of an egg by sperm forms a diploid zygote. – The acrosome of a sperm secretes enzymes that digest the zona pellucida of the egg. – The sperm then binds to the plasma membrane of the egg and enters the cell. – The genetic information of the sperm fuses with the egg nucleus to complete fertilization.

Early Embryonic Development • The embryonic development involves developmental events prior to implantation. – Early Embryonic Development • The embryonic development involves developmental events prior to implantation. – Ovulation releases a mature egg. – Fertilization occurs to form a zygote. – The zygote undergoes cleavage (cell division) to form a morula. – The morula develops into a fluid-filled ball of cells called a blastocyst. – The blastocyst implants in the uterus.

Early Embryonic Development (cont. ) Early Embryonic Development (cont. )

Later Embryonic Development • The next step in development is gastrulation. – Cells of Later Embryonic Development • The next step in development is gastrulation. – Cells of the embryo begin to invaginate. – The amnion begins to develop. – After the initial development of the outer ectoderm and inner endoderm, the mesoderm develops. – Gastrulation is complete when the three germ layers are present.

Later Embryonic Development (cont. ) Later Embryonic Development (cont. )

Later Embryonic Development (cont. ) Later Embryonic Development (cont. )

Neurulation • The nervous system forms during the neurulation by induction. – The mesoderm Neurulation • The nervous system forms during the neurulation by induction. – The mesoderm cells form a dorsal supporting rod called the notochord. – The neural plate forms dorsal to the notochord. – The neural tube forms as the neural plates begin to fold. – Other mesoderm cells consolidate into somites to give rise to vertebrae and muscles.

Neurulation (cont. ) Neurulation (cont. )

Organ Formation Continues • Human embryos at five weeks have flippers called limb buds Organ Formation Continues • Human embryos at five weeks have flippers called limb buds which give rise to arms and legs. • At the same time the head and sensory organs develop. • The umbilical cord has formed, connecting the embryo to the chorion. • The allantois forms and the connection to the placenta is completed.

Organ Formation Continues (cont. ) Organ Formation Continues (cont. )

Placenta • The placenta is comprised of the embryonic fetus and the uterine wall. Placenta • The placenta is comprised of the embryonic fetus and the uterine wall. • The chorionic villi of the chorion project into the uterine wall to facilitate exchange between fetus and mother. • The umbilical cord carries fetal blood to and from the placenta. • While fetal and maternal blood do not mix, a variety of chemicals can cross the placenta into the fetus.

Placenta (cont. ) Placenta (cont. )

Fetal Development and Birth • Human fetal development occurs during the last six months Fetal Development and Birth • Human fetal development occurs during the last six months of gestation. – The fetus increases in size and weight. – The genitalia develop during the third month. – Hair develops after the third month. – The heartbeat can be detected after 2. 5 months. – Fetal movement begins.

The Stages of Birth • Birth is triggered when the fetal hypothalamus triggers the The Stages of Birth • Birth is triggered when the fetal hypothalamus triggers the pituitary to stimulate the release of androgens into the bloodstream. • The placenta uses the androgens to form estrogens, which stimulate formation of oxytocin and prostaglandin. • The estrogens, oxytocin, and prostaglandin cause the uterus to contract.

The Stages of Birth (cont. ) • The movement of the fetus out of The Stages of Birth (cont. ) • The movement of the fetus out of the uterus is called parturition. – During the first stage of parturition, the cervix dilates and the amnion bursts. – The baby is born and the umbilical is severed during the second stage. – The placenta (afterbirth) is expelled from the uterus in the third stage.

The Stages of Birth (cont. ) The Stages of Birth (cont. )