Human Reproduction and Development

How do organisms reproduce? Asexually Budding Binary fission (Splitting) Sexually External fertilization Internal fertilization

What does it mean to reproduce asexually?

Sexual reproduction Sex cells are called ________. The male gamete is a __________. The female gamete is an _____ or ____. In humans, each gamete has ___ chromosomes. Two gametes fuse to form a ______. A human zygote has ___ chromosomes from each gamete, giving a total of ____ chromosomes. gametes sperm cell ovum egg 23 zygote 23 46

Reproductive anatomy of the female 2 1 or Fallopian Tube 3 4 5

What do all of these things do? A woman’s eggs (ova) are made in the _______. An egg (ovum) matures in a _______. The egg is released during _________. When the egg is released, it travels to the uterus via one of the _______________. The thick, muscular wall of the uterus is lined by the ____________. ovaries follicle ovulation Fallopian tubes endometrium

What else? A fertilized egg is a ______. zygote After the zygote begins to divide, but before it develops body structures (9 weeks), it is called an _______. From 9 weeks until birth ( a time period called gestation) it is called a _____. If the zygote implants someplace other than the main part of the uterus, it is called an _________________ and is very dangerous. Most of these pregnancies are terminated. zygote embryo fetus ectopic pregnancy

How is all of this connected to the outside world?

External structures: protection and making the environment receptive The ______ is the narrow tube connecting the uterus to the body’s exterior. It is also the “repository for sperm during copulation.” The labia are folds of skin which protect the vaginal opening. The stimulation of the clitoris results in sexual arousal. This causes increased blood supply and lubrication production by the walls of the vagina and Bertholin’s gland. vagina

Male Reproductive Anatomy 3b 4 5 2 3a 1 (aka foreskin)

What do all of these things do? testes A man’s gametes (sperm) are made in the ______. The testes are kept a few degrees cooler than core body temperature (about 35 instead of 37ºC) due to their location in the scrotum -- this is key for proper sperm formation! Developing and mature sperm are stored in the __________. Sperm are released from here during ejaculation, when semen is expelled from the penis. When the sperm leave the epididymis, they travel to the _______ via the ____________ (and the short ejaculatory duct). The urethra also carries urine from the urinary bladder. true in male human only -- urethra is not a reproductive structure in female. epididymis urethra vas deferens

What else? The seminal vesicle, the prostate gland, and the bulbourethral gland, secrete fluids into the urethra that make up the fluid portion of semen (95%). The rest (5%) is made up of 200-500 million sperm (per ejaculation). The urethra passes through the penis, which consists mostly of erectile tissue that can fill with blood and cause an erection during sexual arousal.

Self test - Female System ovary 1. Where are eggs located before ovulation? ________ 2. What is the structure in which an egg matures before ovulation? ____________ 3. What happens in ovulation? __________________________________________ 4. When does a female begin to ovulate? ___________ 5. How often does she ovulate? ______________ 6. Where does fertilization of an egg occur? _________ 7. How many days after ovulation is an egg still viable? _____________ 8. How many days does it take for an egg to reach the uterus? ____________ A follicle A mature follicle bursts, releasing an egg into fallopian tube puberty Once a month (every 28 days) In fallopian tube About 1 day About 4 days

Self test - Male System testes epididymis Where are sperm first formed? _____________ Where are sperm stored within the male reproductive system? __________________ What are the last three tubes through which sperm pass in order to exit the body? ________________________________________ What are the components of semen? What is it made of? ___________________________________________ What is the role of the seminal vesicle, prostate gland, and bulbourethral gland? What do they contribute to the makeup of semen? ____________________________ About how many days after ejaculation can a sperm survive within the female fallopian tubes? ___________ epididymis vas deferens, ejaculatory duct, urethra Fluid (95%) and Sperm (5%) Fluid portion of semen 2 - 5 days

Yes. Sex can be fun (but not ‘til you’re much older) – and very, very dangerous, too, so ALWAYS USE A CONDOM!!

Life’s Greatest Miracle http://www.pbs.org/wgbh/nova/miracle/program.html

How does it all work? Hormones, hormones, hormones! Males and females are born with all their reproductive structures in place, but they don’t start making sex cells (gametes) until _______. During puberty, hormone levels increase in the body and the reproductive system _______ to become fully functional. Which hormones get things going during puberty? To start, a part of the brain, the hypothalamus, signals another part of the brain, the pituitary, to release two important hormones: • follicle-stimulating hormone (_____) • luteinizing hormone (___) This happens in both males and females. What happens next, however, is different in the two sexes. puberty matures FSH LH

Hormonal Control of the Testes What’s next? In males: LH from pituitary signals testes to produce ___________. FSH and testosterone both stimulate sperm production in testes. Starting during puberty, testes produce hundreds of millions of sperm a day. What else does testosterone do? Causes secondary sex characteristics: hypothalamus testosterone BRAIN pituitary http://www.medem.com/medlib/article/ZZZYUAM46JC LH FSH hypothalamus TESTIS pituitary testosterone Sperm Production! Voice deepens Growth of body hair Easier to increase muscle mass http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookNERV.html

Sperm Formation in Testes In humans, Sperm Formation in Testes

And in the Female… Before puberty, the “pre-eggs” are in the ovary, stored within sacs called ________. What happens during & after puberty, when the pituitary begins to produce FSH and LH? In females, FSH and LH stimulate ovaries to eventually produce two other important hormones: ________ and ____________. Estrogen is primarily responsible for female secondary sex characteristics such as: Estrogen & progesterone also work with FSH and LH to produce mature ova (eggs) from the ovaries. This is a bit more complicated than sperm production, however… follicles estrogen progesterone Breast development Widening of hips Growth of body hair

Egg Formation in the Ovary Every month, one follicle in an ovary is activated by rising levels of FSH to develop and produce a mature egg or ovum. While the egg is maturing, the follicle produces the hormone estrogen. Once the egg reaches maturity, it is released from the follicle into one of the fallopian tubes. This release of the egg from the ovary is called _________. ovulation Pre-Egg After the egg is released, the empty follicle is known as the _____________. This structure plays an important role after ovulation by producing the hormones estrogen and progesterone. Let’s look at why… corpus luteum Mature Egg

What’s going on in the uterus while the egg is maturing in the ovary?? Monthly changes also occur within the uterus. The sequence of events that includes the development and release of an egg for fertilization and the preparation of the uterus to receive a fertilized egg is called the _____________. There are four parts to the menstrual cycle: Follicular Phase Ovulation Luteal Phase Menstruation menstrual cycle

The Menstrual Cycle Follicular Phase (about 10 days) Ovulation Begins when estrogen levels in blood are low Pituitary releases FSH and LH. FSH stimulates a follicle in the ovary to start maturing Follicle begins to produce estrogen Estrogen causes lining of uterus to thicken in preparation for receiving a fertilized egg Ovulation Shortest phase in cycle; Due to increasing levels of estrogen, pituitary suddenly produces extra large amount of FSH and LH especially LH especially causes mature follicle to rupture/burst, releasing the mature egg into the oviduct

More Menstrual Cycle Luteal Phase Begins after release of egg Follicle turns yellow and is known as Corpus Luteum Corpus Luteum releases estrogen and hormone progesterone also; these hormones inhibit production of FSH & LH and thus inhibit the development of another follicle Estrogen & progesterone also allow further development of lining of uterus, in preparation for fert. egg implantation Chance of fertilization of egg greatest the 2 days after ovulation (10-14 days after end of last menstrual cycle) If fertilization occurs, zygote implants in lining of uterus Uterus & embryo release hormones that keep corpus luteum functioning for several weeks, so lining nourishes developing embryo until placenta forms

Even More Menstrual Cycle Menstruation (from day 0-7) If no fertilization, egg passes through uterus without implanting Corpus luteum begins to disintergrate, less hormone produced When level of estrogen (& progesterone) in blood drops enough, lining of uterus detaches and is shed, along with unfertilized egg New cycle begins on first day of menstruation

Recap: Menstrual Cycle Hormones Hormones control everything! FSH & LH made by the Pituitary. Estrogen made by the Ovarian follicle and the Corpus Luteum. Progesterone made by the Corpus Luteum.

The ovary and the uterus, side by side

The Menstrual Cycle is controlled by Hormones: FSH, LH, Estrogen, Progesterone

Fertilization & Development

So what happens if sperm meets egg? An enzyme-filled sac called an acrosome lies just inside the tip of the sperm’s head. These enzymes can penetrate the jelly coat of the egg. When this happens, the sperm membrane fuses with the egg’s membrane and the sperm nucleus is released into the egg.

Now what? The fertilized egg (the zygote) is now a cell with 46 chromosomes. It will begin to divide (by mitosis) to eventually produce all of the cells of the body. Early, rapid cell divisions are called cleavage. The hollow ball of cells with a fluid-filled hollow center develops. This ball is called a blastula.

Implantation & Gastrulation 6 to 7 days after fertilization, the blastocyst attaches itself to the wall of the uterus (implantation). Now we go from a hollow ball of cells to a three-layered stage called the gastrula.

The three cell layers in the gastrula are embryonic tissues that will develop into all the parts of the adult animal Ectoderm  forms nervous system & skin Endoderm  forms innermost lining of our digestive, respiratory, & urogenital systems, liver, pancreas, thyroid, & thymus Mesoderm  forms all other organs and tissues (kidney, heart, muscles, dermis)

Next step: Embryo develops notochord and neural tube Notochord supports developing tissues and eventually helps form backbone. Neural tube forms brain and spinal cord (the nervous system).

Let’s follow the development of a human… From fertilization… To implantation…

Extra-embryonic membranes support the embryo during development the amnion: forms fluid-filled cavity which protects embryo • the “yolk” sac: no yolk in human but produces first blood and germ cells • the chorion: forms embryo’s part of placenta • the allantois: forms part of umbilical cord and part of embryo urinary bladder

Evolutionary note: These four membranes are found in all mammal, bird, & reptile embryos.

Hormonal induction of labor Parturition Hormonal induction of labor

http://www2.mbusd.org/staff/pware/images/baby.jpg