Sex, Reproduction, & Development

Smoking and Pregnancy In The News

Types of Reproduction Sexual reproduction –Union of male & female gametes (sex cells) –Each parent supplies half genetic material Asexual reproduction –No union of gametes –Cloning, unless there is mutation

Asexual Reproduction Occurs in all 3 domains of life Disadvantage –Genetic sameness means less survival with changing environments –Variability only due to mutation Advantage –Individuals can reproduce

Asexual Reproduction

Binary Fission Dividing of individual into two Common in: –Archaea –Bacteria –Many protists

Asexual Reproduction by Spores Common in fungi –Life cycle with sexual & asexual stage

Asexual Reproduction by Budding Occurs in sponges, jellyfish & anemones

Asexual Reproduction by Fragmentation Occurs in flatworms & sea stars Fragments regenerate new parts

Parthenogenesis Eggs develop without fertilization Some species engage in behaviors simulating mating

Sexual Reproduction Prevalent among most vertebrates Common in many invertebrates Zygote –Fusion of haploid egg & sperm cells –Produces diploid cell

Hermaphrodite Both male & female in same body Some can reproduce by self-fertilization Forms of hermaphrodite –Simultaneous –Sequential

Modes of Fertilization External Fertilization –Female sheds eggs –Male fertilizes eggs after they leave her body

Modes of Fertilization Internal Fertilization –Male deposits sperm in or near the female reproductive tract –Eggs are fertilized in female’s body

Human Reproduction Sexual with internal fertilization Gonads = reproductive organs –Male – testes –Female –ovaries Other organs transport & receive sex cells Accessory glands facilitate reproduction

Production of Sperm Testes –Housed in scrotum –Placement allows for development –Temperature must be lower than body

Testes Structure Composed of seminiferous tubules –Site of sperm production (spermatogenesis) –Sperm production triggered by follicle stimulating hormone Spermatogonia give rise to sperm cells

Spermatogenesis Spermatogonia undergo mitosis Some daughter cells undergo meiosis

Epididymis Site of sperm cell storage –18 hours to 10 days Unused sperm cells are reabsorbed

Vas Defrens Long tube from epididymis thru pelvic cavity Loops over urinary bladder Delivers sperm to urethra

Accessory Glands Seminal vesicle –Adds fructose to nourish sperm cells –Bicarbonate buffers acidity of urethra & vagina Prostate –Alkaline fluid Bulbourethral glands –Mucus-like alkaline substance –Lubricant for sexual intercourse

Penis Cylinders of erectile tissue

Female Reproductive System Vagina –Accepts penis & receives sperm External genitals –Vulva –Mons pubis –Labia majora –Labia minora –Clitoris Erectile tissue

Ovaries Female gonad Contain primary oocytes –Can develop into eggs

Oogenesis One primary oocyte yields in one ovum & three polar bodies

Oviducts Ovulation – mature oocyte is released Oocyte enters oviduct Oviducts lead to uterus Oviduct is site of fertilization

Uterus Cervix – lower portion opens to vagina Uterus is site of prenatal development Endometrium – inner lining –Nourishing layer for embryo –Shed monthly if no pregnancy occurs

Reproductive Cycle

Birth Control Methods

Sexually Transmitted Diseases

Stages of Human Development Zygote – fusion of egg & sperm Embryo –Morula –Blastocyst –Implantation –Gastrulation –Neurulation Fetus

Morula 1 cell zygote begins to divide rapidly Mitosis without growth

Blastocyst Ball of cells Portion of interior destined to differentiate Cells begin to migrate (morphogenesis)

Implantation Approximately 1 week after fertilization Blastocyst secretes enzymes –Digests portion of endometrial wall Nourished by digested uterine cells

Implantation Embryo completes implantation Germ layers begin development (first 2) –Ectoderm –Endoderm

From Ovulation to Implantation

Gastrulation Primary germ layers fully formed Organs & tissues begin development

Neurulation Development of hollow nerve cord Neural groove forms

Embryo at Four Weeks

Fetus All organ systems are formed Growth & development continues

Fetus at Five Months

Human Fetus Near Full Term

Birth is Initiated by Hormones

Newborn Physiological Changes Obtains oxygen from environment Placenta no longer the source of nutrients Blood circulation is increased to lungs

Placental-Fetal circulation