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Unit 2 – Reproduction and Development Unit Outcomes Examine the principal features of the human reproductive system Identify the male and female reproductive structures and describe their functions Identify the risks that STIs present to individuals and to human reproduction Explain how STIs can interfere with the passage of eggs and sperm Unit Outcomes Research the effects of STIs Identify the main reproductive hormones and describe how they interact Explain the role of sex hormones in the development and regulation of primary and secondary sex characteristics Analyze blood hormone data and associated physiological events Unit Outcomes Research and assess the medical use of reproductive hormones in humans Trace the processes and events that occur during embryonic development Describe the significance of the primary germ layers and identify the tissues and organs that come from them Compare embryonic changes and extraembryonic structures in humans and other animals Unit Outcomes Trace the processes and key events that occur during fetal development Describe and investigate the effect of teratogens and other environmental factors on the development of prenatal body structures and systems Trace the processes of parturition and lactation, and outline their control mechanisms Why is Reproduction Important It produces variation within a species It provides a basis for natural selection within a species 14.1 – The Male and Female Reproductive Systems Both male and female reproductive systems include a pair of gonads (which produce gametes) These gonads also produce sex hormones These hormones often control primary sex characteristics and secondary sex characteristics The Male Reproductive System Male & female reproductive organs do not differ greatly until the 3rd month of fetal development The purpose of this system is to produce sperm and allow them to leave the body The Male Reproductive System Structures: Scrotum: Testes: Epididymis: holds the testes away from the body to keep them cool. Sperm production only occurs at temperatures about 3 degrees below body temperature. are the organs responsible for spermatogenesis. They develop inside the abdominal cavity of a male fetus and descend only about 2 months before birth. The testes hold seminiferous tubule that produce sperm. holds spermatozoa for about 2-4 days while they mature Vas deferens: stores sperm, and conducts sperm during ejaculation. When a male has a vasectomy, the vas deferens if cut and tied off, to prevent conduction of sperm. Seminal Vesicle: Prostate Gland: Cowper’s Gland: Ejaculatory Duct: produces a rich nutrient fluid (fructose) that is an important component of semen. produces a white, milky, alkaline fluid component of semen. This fluid neutralizes the acidity of urethra and the vagina, allowing sperm to survive. (aka bulbourethral gland) produces a rich alkaline mucous that becomes part of the seminal fluid. This also neutralizes any acid sperm might be exposed to. is responsible for the movement of fluid from the seminal vesicle to the vas deferens. Urethra: Penis: Prepuce (foreskin): is responsible for conduction of urine and semen out of the penis. During ejaculation, a sphincter muscle closes off the bladder, preventing urine from exiting the urethra. is the male organ for copulation. Beneath the skin, lies the urethra surrounded by spongy protective tissue that expands to form the glans penis. is a loose sheath of skin covering the glans penis of uncircumcised males. The foreskin produces an oily secretion known as smegma. Erectile Tissue The erectile tissue of the penis (corpus cavernosum) fills with blood when a man is sexually excited (controlled by the parasympathetic nervous system through vasodilation) This causes the penis to swell and become rigid Erectile Dysfunction (ED) Increased blood flow to the penis is actually controlled by the parasympathetic nerves They cause a relaxation of muscle tissue that allows the arteries running into the penis to dilate and carry more blood Therefore, if the parasympathetic nerve is damaged, erections become difficult or impossible to sustain Other factors may also lead to erectile dysfunction, including an imbalance in hormones, particularly testosterone Stress can also lead to erectile dysfunction Viagra is a drug that relaxes the muscles constricting the blood vessels running into the penis (these muscles are similar to the smooth muscle in the digestive system). Therefore, it is much easier for the blood to enter the erectile tissues and cause an erection. Sperm Sperm are very small cells built for speed There is very little cytoplasm in a sperm cell, which increases the cell’s mobility http://img.tfd.com A single sperm cell has a large number of mitochondria It also has an acrosome, which contains special enzymes that allow it to penetrate the membrane of an egg cell Spermatogenesis Inside the testes are tiny tubes called seminiferous tubules They are lined with spermatogonia These spermatogonia divide and form spermatocytes In about 9 to 10 weeks, the spermatocytes develop into sperm cells Sertoli cells nourish the developing sperm When they are ready, sperm cells move to the epididymis to complete their maturation Spermatogenesis Animation http://faculty.sunydutchess.edu Seminal Fluid Seminal fluid consists of contributions from three different glands This fluid protects and nourishes the sperm as it travels out of the man’s body and into the woman’s reproductive tract Seminal Vesicles This gland produces one component of seminal fluid: – Fructose - provides energy sperm need to swim Prostate Gland The prostate produces: 1. an alkaline buffer that neutralizes the acidity of the vagina 2. Prostaglandins – stimulates contraction of vaginal walls to help move sperm along to uterus/oviduct Cowper’s (bulbourethral) Gland This gland produces mucus-rich fluids that provide lubrication and buffer the acidity in the vagina Sperm Survival Within the epididymis, the sperm can survive for extended periods (some die and are removed by the immune system) However, at body temperature sperm only live for 24-72 hours Sperm can be stored indefinitely at -100oC (which is how they are stored at sperm banks) The Female Reproductive System The female reproductive system involves more complicated cycles than the male reproductive system Female hormone levels fluctuate throughout their menstrual cycle (whereas males maintain a relatively constant level of testosterone) The Female Reproductive System http://www.uh.edu Structures Ovary - Corpus Luteum – Oviduct - Fimbriae - Produces ovum (eggs) – from approx. 400,000 follicles - and is the site of egg maturation before ovulation. As well, is the site of corpus luteum (important for pregnancy). cells remaining after a follicle has ruptured during ovulation, this scar-like tissue secretes estrogen and progesterone for about 3 months if fertilization and pregnancy occurs, or deteriorates after about 14 days if fertilization does not occur. aka the fallopian tube. Connects ovary to uterus. Fertilization occurs here. small fingerlike projections at the ends of the oviducts that sweep to draw the egg into the fallopian tube Uterus Organ where implantation of the zygote (fertilized egg) occurs. Made up of 2 layers: 1. Myometrium – muscular lining of the uterus that provides support for embryo and contracts during labor. 2. Endometrium – glandular lining of the uterus that provides nourishment to embryo (layer is shed during menstruation) Cervix Vagina Dense muscle band that plugs closed with mucous during pregnancy and prevents material from getting into the uterus. Separates the birth canal (vagina) from the uterus. This keeps the fetus in the uterus and must dilate during labor in order for the fetus to be born vaginally. aka the birth canal. Site of many nerve endings and is very acidic to protect the person from pathogens or microbes that enter the vagina. External Structures (Vulva) Labia majora – large, fatty, hair covered folds that protect the genitals Labia minora – smaller folds of skin inside the labia that are kept moist with special secretory cells Clitoris – small shaft of erectile tissue with a large number of nerve endings (very sensitive) Oogenesis and Ovulation The ovary contains many small groups of cells known as follicles Within the follicle, an oocyte undergoes meiosis and becomes an ovum and 3 polar bodies The ovum created contains 23 chromosomes and most of the cellular material from the oocyte Granulosa Cell - nourish the developing ovum and becomes the corpus luteum after ovulation. When it is ready, the follicle ruptures the outer ovary wall and releases the ovum Oogenesis & Ovulation http://faculty.sunydutchess.edu Differences Between Sperm & Eggs Sperm Egg Size 50 μm long (5 μm head, 5 μm middle piece, 40 μm tail) 100 μm diameter Energy Reserves Mitochondria Fat before ejaculation, fructose in Fertilized eggs rely on the seminal fluid after ejaculation endometrium as an energy source Middle piece of sperm has 50 to 100 mitochondria Cytoplasm contains about 140 000 mitochondria Number Produced 300 – 500 million per day 300 – 400 thousand follicles are present at the start of puberty – 1 egg is released per month Motility High motility due to flagellum No structures for propulsion Other Structures Sperm has an acrosome which contains enzymes that help the sperm to enter the egg Egg is covered by an outer membrane which can only be penetrated by a sperm of the same species 14.2 – The Effect of Sexually Transmitted Infections on the Reproductive System During sexual intercourse, body fluids are exchanged The fluids can contain STIs (Sexually Transmitted Infections) in the form of bacteria or viruses Viral vs. Bacterial STIs Bacterial STIs Viral STIs Chlamydia Gonorrhea Syphilis HIV HPV Hepatitis Genital Herpes HIV / AIDS AIDS is caused by the human immunodeficiency virus (HIV) This virus attacks and destroys helper T cells http://biology.kenyon.edu HIV Replication Animation Hepatitis B Hepatitis viral infections come in 3 subtypes: A, B and C Hepatitis B is transmitted in the same fashion as HIV The hepatitis B virus attacks the liver http://www.torontoliver.ca Hepatitis B Symptoms of hepatitis B include flu-like symptoms, jaundice, and liver failure Hepatitis viruses can cross the placenta and infect the unborn child Occasionally, a person who is infected with the hepatitis B virus may be asymptomatic, and can therefore pass on the virus to others without knowing it There are effective vaccines for both hepatitis A and B Genital Herpes It is estimated that 1 in 3 sexually active Canadians has genital herpes Herpes is caused by either HSV 1 or HSV 2 viruses The majority of genital herpes cases are caused by HSV 2 Genital Herpes Symptoms can vary from case to case Symptoms may include tingling, itching, and appearance of blisters Blisters can then rupture and become painful sores (these open sores increase the chance of HIV infection) Outbreaks may be accompanied with swollen glands, aching joints, and fatigue The herpes virus may infect babies during the birthing process, possibly leading to blindness, neurological disorders, or death Genital Herpes There is no cure for herpes Even if an infected person is not symptomatic, they can still pass on the virus during intercourse No vaccine is yet available for herpes HPV (Human Papilloma Virus) HPV is the name of a group of viruses It is transmitted during skin-to-skin contact Some people infected with HPV develop genital warts, while other people can show no symptoms at all http://upload.wikimedia.org Cervical Cancer Cervical cancer is one of the primary forms of cancer in women Pap tests done by physicians collect cells from the surface of the cervix These cells are then checked for any abnormal tissue growth New evidence indicates that cervical cancer may be caused by the Human Papillomavirus (HPV) Chlamydia Chlamydia is the most common bacterial STI in Canada Infection rates are twice as high in young women than in young men Chlamydia Symptoms are immediate and often include discharge from the penis or vagina, burning pain during urination, or fever 75% of infected people show no symptoms In women, the infection may lead to pelvic inflammatory disease (PID), which causes scar tissue in the oviducts Chlamydia can be treated with antibiotics Gonorrhea Often found together with chlamydia bacterial infections The rate of infections is higher in men than in women Symptoms are similar to those of chlamydia This can also cause PID and serious eye infections for babies born to mothers with gonorrhea http://www.faqs.org/health Syphilis Although much less common than other bacterial STIs, the rate of syphilis infection has increased sharply since 1997 http://www.wales.nhs.uk Syphilis Initially, infectious ulcerated sores appear (known as chancres) This is followed by a rash (often on palms of hands, soles of feet), and then the bacteria affects the cardiovascular and nervous system Infected persons may become mentally ill, blind, lame, or develop heart disease If bacteria infect a developing embryo, birth defects or stillbirth can result Syphilis can be treated effectively with antibiotics Preventing STI Transmission 1. 2. 3. 4. There are a number of ways to reduce the chance of passing on STIs: Abstinence Long-term monogamous relationships Condom use Personal responsibility 14.3 – Hormonal Regulation of the Reproductive System Hormones play an important role in the operation of the reproductive system The hormones involved in reproduction are produced in the hypothalamus, the pituitary, and the gonads Male Reproductive Hormones GnRH – gonadotropic releasing hormone, released in hypothalamus; stimulates the anterior pituitary to release LH and FSH LH – luteinizing hormone, stimulates the interstitial cells of the testes to produce testosterone FSH – follicle stimulating hormone, stimulates production of sperm in the seminiferous tubules Testosterone – responsible for male secondary sex characteristics (including hair growth, muscle growth, deeper voice), required for sperm production Hormones (con’t) Inhibin – hormone that inhibits GnRH, LH, and FSH production (negative feedback) Interstitial Cells – surround the seminiferous tubules, produce testosterone when stimulated by LH Sertoli Cells – provide nutrients and support for developing sperm Feedback of Gonadotropins Aging and the Male Reproductive System Most men experience a gradual decrease in testosterone levels starting at about 40 years of age This is known as andropause As well, hormonal changes in males over age 40 can also result in gradual growth of the prostate gland Older males also have a higher chance of prostate cancer as well Female Reproductive Hormones The pituitary and hypothalamus control the production of estrogen and progesterone FSH (Follicle-stimulating hormone) and LH (luteinizing hormone) regulate the production of estrogen and progesterone Estrogen is also responsible for female secondary sex characteristics: – Breast development – Hair growth Hormones GnRH – (released from the hypothalamus) stimulates the anterior pituitary to produce FSH and LH LH – responsible for the development of the corpus luteum, promotes secretion of progesterone, surges of LH cause ovulation FSH – stimulates development of the follicle and the production of estrogen Estrogen – secreted by the follicles in the ovaries, causes maturation of the egg and stimulates growth of the endometrium Progesterone – secreted by the corpus luteum, causes the endometrium to become secretory and inhibits both FSH and LH to prevent ovulation The Menstrual Cycle This cycle is divided into 4 phases (28 days): 1. Flow Phase – shedding of the endometrium (lasts ~ 5 days) 2. Follicular Phase – development of follicles within the ovary. During this phase, estrogen concentration in the blood increases (thickens endometrium); (lasts ~ 8 days) 3. Ovulation – oocyte bursts from ovary (lasts ~ 1 day) 4. Luteal Phase – follicle cells differentiate into the corpus luteum following ovulation. Progesterone (inhibits further ovulation, stimulates endometrium, and prepares the uterus for the embryo) and estrogen are secreted. Without fertilization, secretions decrease and the endometrium is then shed during the next flow phase; (lasts ~ 14 days) Birth Control Pills Along with its effect of maintaining the uterine lining, progesterone also prevents further ovulations Women can prevent ovulation by ingesting progesterone in a pill form, or through implanted capsules containing similar hormones The pill increases a woman’s progesterone levels, preventing the release of an ovum Aging and the Menstrual Cycle Women have a limited number of menstrual cycles due to their limited number of follicles As the number of follicles decreases, the amount of estrogen and progesterone in the woman’s body decreases The woman’s menstrual cycles become irregular and eventually stop completely Menopause 1. 2. 3. 4. 5. Menopause (the cessation of menstrual cycles) often occurs around age 50 During menopause, a number of different effects are experienced: ‘Hot flashes’ Variable changes in mood Increasing cholesterol levels Diminished bone mass Increased risk of breast and uterine cancer Treatment for Menopause Many women consider hormone replacement therapy during or following menopause However, there are some risks to the hormone replacement therapy (increased risk of blood clots, stroke, breast & colorectal cancer, and dementia) Endocrine Disruptors A number of man-made chemicals can interrupt the function of hormones If these disrupt the function of sex hormones, then the reproductive cycles of men and women can be effected as well As well, testosterone-blocking chemicals can lead to feminization in males 15.1 – Fertilization and Embryonic Development 150 to 300 million sperm cells travel through the cervix upon ejaculation during intercourse Ultimately, only a single sperm cell fuses with the ovum http://content.answers.com Embryonic Development The fertilized egg (the zygote) undergoes a number of cellular divisions on its way to the uterus By the time it reaches the uterus, the single fertilized egg has become a cell mass known as a blastocyst The blastocyst then attaches to the endometrium wall (this is known as implantation) Maintenance of the Endometrium If the corpus luteum deteriorates, then the endometrium will be shed High levels of estrogen and progesterone must be maintained to prevent this from happening However, the level of the pituitary gonadotropin, LH, decreases as the estrogen and progesterone levels increase The outer layer of cells in the blastocyst produces a hormone called HCG (Human Chorionic Gonadotropin) HCG maintains the corpus luteum during the first three months of pregnancy, preventing the shedding of the endometrium The functioning corpus luteum keeps producing estrogen and progesterone Pregnancy tests identify HCG in the urine of a woman Once cells from the endometrium and embryo form the placenta, HCG is no longer produced Instead, the placenta itself produces estrogen and progesterone which maintain the endometrium until birth Prenatal Development – The Blastocyst The outer layer of the blastocyst produces two membranes - the chorion and the amnion Within the blastocyst’s inner layers, different germ layers form (gastrulation): Germ Layers Ectoderm – forms hair, nails, sweat glands, nervous system, eyes, ears, teeth, mouth lining Mesoderm – forms muscles, blood vessels & blood, kidneys & reproductive structures, connective tissue, cartilage & bone Endoderm – forms liver, pancreas, thyroid, bladder, lining of digestive system & respiratory tract The Germ Layers Neurulation and Organ Formation Between weeks 3 and 8, the organs form The germ layers separate and form organs During the 3rd week, a band of mesoderm cells forms along the back of the embryonic disk These cells forms a rod-like notochord, which will make up the skeleton The nervous system develops from the ectoderm located above the notochord Neurulation Organ Formation Neurulation marks the beginning of organ formation. First, the heart begins to form This is followed by blood vessels, lungs, kidneys, arms & legs, and structures of the head The brain continues its development, and the gonads begin to produce hormones that develop external genetalia (about the 6th week) Extra-Embryonic Membranes The Allantois & Placenta The placenta forms from cells from the endometrium and the fetus The placenta has numerous blood vessels Chorionic villi ensure that the placenta’s blood vessels come in close contact with the blood vessels of the mother The blood vessels that are found in the placenta come from the allantois, a third membrane in the blastocyst (forms part of the umbilical cord) The Amnion and Yolk Sac The amnion is a transparent sac that contains the amniotic fluid This fluid acts to cushion the fetus and prevents temperature fluctuations while allowing freedom of movement The yolk sac does not provide nutrients, but rather will become part of the digestive system later Uterine Structures 1. 2. 3. 4. 5. Cervix Umbilical Cord Placenta Oviduct Amniotic Fluid (Amniotic Sac) 15.2 – Fetal Development and Birth 1. 2. 3. Fetal development is typically broken into three (roughly equal) trimesters: 1st Trimester (Weeks 1 to 12) 2nd Trimester (Weeks 13 to 24) 3rd Trimester (Weeks 25 to 38) The number of weeks is counted from the last day of the mother’s last flow cycle, not the time from fertilization Fetal Development – First Trimester By week 2, germ layers form By the end of this trimester, the heart, brain, limb buds (with fingers & toes) have all developed Arms & legs move and there is a sucking reflex By end of the trimester, external reproductive organs distinguish male from female http://www.babyart.org Development of Male and Female Sex Organs: Sex of an individual - determined at conception. SRY gene - sex determining region of the Y chromosome (aka testis determining factor (TDF) gene) Anti-Mullerian hormone - prevents development of female sex organs (causes them to degenerate). Dihydrotestosterone (DHT) - promotes development of male sex organs. Testosterone - stimulates development of the epididymides, vas deferens, seminal vesicles, and ejaculatory duct. Second Trimester Fetus moves enough to be noticed All organs have formed Eyelids and eyelashes form Cartilage has been replaced with bone cells Soft hair covers the body http://static.flickr.com Third Trimester Rapid growth of baby (from 680 g to 3400 g), particularly layers of fat Organ systems are already established, but continue to develop http://health.state.ga.us Teratogens Whatever the mother inhales or ingests can end up in her circulating blood Many of these compounds can pass across the placental system into the fetal blood A number of substances and conditions can affect the normal development of the embryo and fetus Various Teratogens 1. 2. 3. 4. Cigarette Smoke – constricts fetus’s blood vessels, preventing the fetus from receiving enough oxygen Alcohol – affects the fetus’s brain, CNS, and physical development Prescription medications – antibiotics, acne medications, anti-thyroid drugs, and anticancer drugs Some nutrients – vitamin C in excess during pregnancy can lead to scurvy after birth (the drop in vitamin C supply after birth is responsible for this) Birth (Parturition) At the end of the third trimester, the fetus turns so that the front of the head faces the backbone The fetus also drops into the birth canal Stages of Labor Labor – Latent Phase Labor begins 38-40 weeks after conception Initially, the cervix begins to thin and the mucus plug that sealed the cervix falls out (usually one or two days prior to birth) Stage 1 (Active Phase) The cervix begins to dilate due to muscle contractions These contractions become more regular and intense as labor progresses Sometimes the amniotic sac will break because of uterine contractions, but often the attending physician will break the sac with a long needle This stage usually ends when the cervix has dilated to a diameter of 10 cm Stage 2 (Birth or Parturition) As the contractions continue, the fetus is moved down the birth canal A hormone known as relaxin (which is produced by the placenta prior to labor) causes a loosening of the ligaments in the pelvis Uterine contractions (along with active pushing of the mother) push the baby out of the birth canal Stage 3 (Afterbirth) Once the baby is born, the umbilical cord is clipped and cut A number of contractions expel the placenta and most of the umbilical cord http://en.wikipedia.org Lactation During pregnancy, high levels of estrogen and progesterone prepare the breasts for milk production Each breast has about 20 glands that produce milk Prolactin, whose levels rise dramatically after birth, stimulates milk production in these glands http://www.breastguide.info Feeding Immediately after birth, the breast produces colostrum It takes a few days for true breast milk to be produced When a baby feeds, the suckling action stimulates the nerve endings in the areola of the breast The stimulation of these nerve endings causes the release of oxytocin, which causes muscle contractions in both breast and uterine tissue At the height of lactation, some women can produce as much as 1.5 L of milk per day (containing 50 g of fat and 100 g of sugars) Medical Issues 1. Teratogens and the Fetus A teratogen is any agent that can cause a structural abnormality of the fetus during pregnancy Cigarette smoke, drugs, some prescription medications and alcohol are all teratogens 2. Fertility Treatments A number of treatments may be used to increase fertility About 15% of Canadian couples cannot conceive a child Drugs may be used to increase the number of eggs produced by the woman’s ovaries In vitro fertilization can be used to increase the chance of a sperm cell fertilizing an egg cell In some cases, a man cannot produce sperm TSE (testicular sperm extraction) may be used In this case, seminiferous tubule tissue is taken from the testicle and is cultured to produce sperm, which can then be used in in vitro fertilization or in ICSI (intracytoplasmic sperm injection) Artificial insemination can also be an option Ectopic Pregnancy On rare occasions, a fertilized embryo embeds itself in the wall of the fallopian tube (or other structure) instead of in the uterine lining As the fetus develops, it may rupture some of the blood vessels in the lining of the fallopian tubes About half of the ectopic pregnancies spontaneously abort, while the other half require medical intervention to remove the fetus 3. 4. Problems During Labor If the front of the baby’s head is facing forward instead of the spine, labor can be very painful and difficult for the mother In some cases, a baby might also be transverse (where the shoulders are turned 90 degrees to their normal position) In the case of a transverse birth, the attending physician can try to turn the baby with his or her hands while the mother rests between pushes In rare instances, a breech birth occurs During a breech birth, the baby enters the birth canal feet or buttocks first A breech baby who is delivered buttocks first can be delivered normally, but an episiotomy may be required If the baby arrives feet first, then a Caesarian section birth must be performed