BIOLOGY 30
REPRODUCTION & DEVELOPMENT
Chapter 16 in Textbook
Name:
Gonads Ovaries Testes
Hormones produced: Gametes produced:
• Fertilization: fusion of male and female sex cells, which produces a
zygote.
• Zygote: a fused cell that divides many times to form an embryo, then a
The Male Reproductive System (Chapter 16.1)
Penis
• Composed of 3 cylinders of spongy tissue.
• During sexual arousal, tissue fills with blood from the arteries
• The increasing pressure seals off the veins that drain the penis
• Result = penis engorges with blood = erection
• The tip (Glans) is covered by a fold of skin called the foreskin, which may be removed by circumcision
Scotum
• Sac which contains testes
• Regulates temperature of testes by contraction of cremaster muscle. o Cold = contracts
§ Brings testes close to body to warm up. o Warm = relaxes
• Goal = keep testes 3o below normal body temperature.
Testes
• Stored in scrotum
o Before birth, testes develop in the abdomen and then migrate down a canal into scrotum around the time of birth.
• Sperm-producing organ
o Made in tightly coiled tubes called seminiferous tubules inside testes
o Sperm produced is not fully mature when it leaves testis (not motile yet)
• Source of male hormone testosterone
o Made by interstitial cells scattered between the seminiferous tubules
Testes & Spermatogenesis:
• Sperm cell is stream lined with a small amount of cytoplasm and therefore a limited energy reserve
• Sertoli cell nourishes developing sperm cell
• Mitochondria located next to flagellum, which propels sperm cell
• Acrosome - caps head of sperm cell
o Filled with enzymes that dissolves outer coating surrounding the egg for sperm cell to penetrate egg
Epididymis
• Coiled tubes
• About 6 meters long!!
• Posterior to the testis
• Stores sperm
• Site of further sperm maturation o Gains motility
• Contracts during ejaculation, expelling sperm into the…
Vas deferens
• Sperm can be store here for months
o If not ejaculated, will eventually be phagocytized
• tube carries sperm from testes to urethra
• Vasectomy - a means of birth control o more on this later!
Sperm Route
Ejaculatory duct
• Connects seminal vesicle to urethra
• Passes through prostate gland
Seminal vesicle
• Lies below and behind bladder
• Secretes thick, clear fluid into ejaculatory duct
o 60% volume of semen (the fluid that is ejaculated)
o Fructose – used for energy by sperm
o Prostaglandins – chemical messengers which, once in female,
stimulate uterine peristalsis to help move semen up the uterus
Prostate Gland
• Doughnut shaped gland which surrounds urethra • Secretes thin milky fluid into urethra
o 20% of seminal volume
o Alkaline – continues to neutralize acid from residual urine in
Cowper's (bulbourethral) Gland
• Pair of small glands along urethra, below the prostate
• Secrete mucous before emission of sperm & semen o Neutralizes the urine in urethra (urine kills sperm) o Thought to lubricate penis and vagina
• Released before ejaculation
o Fluid may contain some sperm
o One factor in the high failure rate of the “withdrawal method”
of birth control.
Erection & Ejaculation
• Parasympathetic(erection) & sympathetic (ejaculation) nervous response, and somatic nervous system.
• Erection: erectile tissue (spongiosum) fills with blood (compressing
veins & urethra) - no blood leaving, no urine entering).
• Sphinter at base of bladder closes
• Semen (seminal/ejaculatory fluid) enters urethra, pushed out by smooth muscle contractions
The Male Reproductive System Summary:
• System is composed of testes, seminiferous tubules, interstitial cells, Sertoli cells, epididymis, vasa deferens, Cowper's glands, seminal vesicles, prostate gland, ejaculatory duct, urethra, and penis
• Testes produce sperm cells and testosterone
The Female Reproductive System - Chapter 16.2
The basics:
• Ovaries: Hold and release eggs (ovum)
• Oviduct (fallopian tube): Passageway for the ovum to move from the
ovary to the uterus
• Uterus (womb): Site of implantation of a fertilized ovum, and where
embryo, then fetus develops
• Vagina (birth canal): The muscular canal extending from the uterus to
the exterior of the body. Strongly acidic (to kill invaders)
Consists of:
• External genitalia
o Two sets of labia that surround the clitoris and vaginal opening
• Internal Reproductive Organs o A pair of gonads (ovaries)
o A system of ducts and chambers to conduct the gametes to the uterus
Ovaries
• Lie in abdomen, below most of the digestive system
• Enclosed in a tough protective capsule
• Produces eggs (follicles)
o egg cell = ova (singular = ovum)
• Produces female sex hormones o Estrogen
o Progesterone
Follicles
• Consists of one egg cell surrounded by layers of follicle cells. o Nourish and protect the developing egg cell
• All of the 400,000 follicles a woman will ever have are present at birth. o Only a few hundred will be released during a woman’s
reproductive years
o One (very rarely 2 or more) follicle matures and releases its
egg during each menstrual cycle
• Follicle cells release the primary female sex hormone… estrogen. o Secondary sex characteristics, wider hips, more body fat,
necessary for breast development
• At ovulation, the egg “explodes” out of the follicles leaving behind the follicular tissue
o This grows into a solid mass called a Corpus Luteum o Secretes progesterone (necessary for pregnancy)
• If fertilization does not occur, the corpus luteum disintegrates and a
Oviduct a.k.a. Fallopian tube • Conducts eggs to the uterus
• Fertilization occurs here
o If embryo grows here = ectopic pregnancy
• The ovary and oviduct don’t actually touch.
• The egg is released into the abdominal cavity and is “sucked” into the oviduct.
o Oviduct has fingers called “fimbrae” and hairs called “cilia” that
vibrate and sweep the egg into the tube by swishing body fluids
towards itself]
o These cilia also help move the egg towards the uterus
Uterus (womb)
• Houses and nurtures the developing fetus
• Oviducts enter at the top; cervix (opening) at the bottom
• The lining is called the endometrium o Richly supplied with blood vessels
o Varies in thickness depending on the stage of the menstrual cycle
o Controlled by hormones o 2 Layers
§ Basal layer = stable, does not change thickness
§ Functional layer = changes thickness with menstruation
Vagina
• Birth canal
• Average = 7.5 cm in length
• pH = 4-5
• Upper end closes at cervix
• Receives penis during sexual intercourse
Cervix
• muscular band that separates vagina from uterus
• Holds fetus in place
• Dilation of cervix during birth permits fetus to enter birth canal
• What is a Pap test?
The Female Reproductive System: Summary
Gamete Formation:Linking reproduction to meiosis
• A human body cell contains 46 chromosomes that are paired together o 23 pairs
o Called diploid cells
• If 2 diploid cells fuse the result would be … o 92 chromosomes (46 pairs)
o Chromosome number would increase exponentially
• Sperm and egg must contain only 23 chromosomes each in order to maintain appropriate chromosome count
o Haploid = half the normal number of chromosomes o 23 chromosome sperm +23 chromosome egg = 23 pairs
Terms:
• Mitosis
o Cell division in which normal body cells (somatic cells) are produce
o Used only for growth or repair o The identical replication of a cell
o If Parent = 46 chromosomes, then Daughter cells = 46 chromosomes
• Meiosis
o Cell division in which sex cells are produced o Occurs only in gonads
o Daughter cells contain half the number of chromosomes as the original parent
o If parent = 46 chromosomes, then Daughter cells = 23 chromosomes.
Spermatogenesis
• Each ejaculation = 400 million sperm
• Males can ejaculate daily without loss of fertility
Oogenesis
• Ovary contains fibrous connective tissue and small groups of cells called follicles
• Follicles are composed of 2 types of cells: primary oocyte and
granulosa cells
o Oocyte contains 46 chromosomes
o Undergoes meiosis
o Transforms into a mature oocyte, or ovum
o Granulosa cells provide nutrients for oocyte
• female ovary undergoes continual decline after onset of puberty
• Ovary contains about 400 000 follicles at puberty
• Between the ages of 12 and 50 in a woman's life about 400 eggs will mature
• Female sex hormones are produced within ovary
• Menopause marks end of a female reproductive life
Hormonal Control of Male Reproduction
Testosterone
• Primary Function: Stimulate spermatogenesis
• Secondary Function
o Maturation of testes and penis o Sex drive
o Facial hair o Body hair o Deeper voice
o Increased muscle strength o Body oil secretion -- acne
Hormonal Control of the Testes
Hypothalamus releases:
• Gonadotropin-Releasing Hormone (GnRH) o Stimulates pituitary to release LH & FSH
Pituitary releases:
• Follicle-Stimulating Hormone (FSH)
o Stimulates spermatogenesis by seminiferous tubules • Luteinizing hormone (LH)
o Stimulates testosterone production by interstitial cells
o Indirectly stimulates spermatogenesis because testosterone is required for sperm production.
• LH, FSH, and GnRH concentrations in the blood are controlled by negative feedback systems
Male hormonal control: Summary
• The gonadotropic hormones FSH and LH are produced by the pituitary gland in response to GnRH from the hypothalamus
• Sperm production is stimulated by FSH and testosterone
• LH stimulates testosterone production in the testes
• FSH, LH, and testosterone levels are regulated by negative feedback
• High FSH levels stimulates production of FSH by the pituitary and GnRH by the hypothalamus
Female Reproductive System Control
• Hypothalamus - produces releasing GnRH
• Anterior Pituitary – secrete gonadotropic hormones. o FSH - follicle stimulating hormone.
o LH - luteinizing hormone.
• Ovaries - secrete the female sex hormones. o Estrogen –thickening of uterine lining
o Progesterone – matures/maintains uterine lining
• FSH is released from AP
o Start the ripening of ovum within follicle
• Estrogen is produced by follicle
o Development of endometrium for possible pregnancy o Feedback to hypothalamus to inhibit FSH and release LH
• LH surge on day 14
o Stimulates ovulation
o Conversion of follicle into corpus luteum
• Progesterone production
o Continued development of endometrium o Feedback to inhibit release of LH
If no fertilization:
1. Flow Phase (Menstrual Phase)
• Start of bleeding marks Day 1 of phase
• Shedding of the endometrium (uterine lining)
• Average = 4-5 days
• Sometimes up to 8 days
2. Follicular Phase
• Occurs during day 6-13
• Period of repair and thickening of endometrium.
• FSH from the pituitary promotes follicle development in the ovary.
• Occurs during day 6-13
• Period of repair and thickening of endometrium. WHY??
• FSH from the pituitary promotes follicle development in the ovary.
• As follicle develops it produces estrogen,
• thickening of the uterine lining
• LH production increase
• FSH production decrease
3. Ovulation Phase
• LH causes ovulation to occur on day 14.
• Secondary oocyte is released from the follicle/ovary.
4. Luteal Phase
• Final preparation of endometrium to receive the fertilized ovum
• LH stimulates development of the Corpus Luteum. o causes progesterone levels to increase.
• Estrogen and progesterone inhibit GnRH, thereby decreasing LH and FSH levels.
o This low level of hormones initiates the flow phase.
Menopause
• The end of a woman’s reproductive years • Between ages of 45 – 55
• Ovaries no longer respond to FSH & LH from AP o Ovaries do not produce estrogen or progesterone
• Marked by circulatory irregularities (hot flashes), dizziness, insomnia, sleepiness, depression
Female Hormonal Control: Summary
• Oogenesis is the process by which an ovum matures within a follicle. Oogenesis is stimulated by FSH (Follicle stimulating hormone)
• Ovulation involves the release of the egg from the follicle, and is stimulated by LH (leutenizing hormone)
• Menstruation is the shedding of the endometrium, and marks the beginning of the menstrual cycle.
• During the menstrual cycle, levels of estrogen and progesterone change. Estrogen stimulates thickening of the endometrium. Progesterone inhibits ovulation and uterine contractions, firms the cervix, and stimulates the endometrium.
Fertilization & Pregnancy (16.3 in textbook)
3 Steps of Fertilization
1. Capacitating
• Acidic environment of the female reproductive tract causes small pores to open in the acrosome (“enzyme-loaded” head) of the sperm
2. Acrosomal reaction
• Enzymes released from acrosome digest the outer membrane surrounding the egg cell
3. Fertilization
• A single sperm cell fuses with the plasma membrane of ovum
• Head passes into the cytoplasm
• Electrochemical reaction in egg
• Makes membrane impermeable to other sperm
• Fertilization must occur within a very short window of opportunity. o Egg is only fertile for 10 - 15 hours
o Sperm are only fertile for 48 hours
Pregnancy
• If pregnancy is established, menstruation does not occur.
• Fertilized egg is called a zygote.
o Once cell division brings the total cell count to around 8, it is
called a blastocyst.
• Takes 3-5 days for blastocyst to travel through oviduct to uterus.
• Blastocyst must implant into endometrium o Occurs 2-4 days after reaching the uterus
• During implantation, the blastocyst produces a hormone called HCG
o Human chorionic gonadotropin
o Prevents degeneration of corpus luteum
o Stimulates corpus luteum to increase progesterone secretion o Maintains uterine lining
o Prevents contractions
o Pregnancy test detects HCG in the urine of women.
§ “Turns the stick blue”
§
• Tissue grows out from the embryo and mingles with endometrium to form placenta
o A disc-shaped organ o Size of dinner plate o Weighs less than 1 kg.
o Contains maternal & fetal blood vessels o NO mixing of maternal and fetal blood!! o Diffusion of gasses, nutrients, & wastes
o Continues production of HCG, estrogen, progesterone
§ Maintains endometrium]
§ Corpus luteum not needed – dissolves
o Progesterone & estrogen have a negative feedback effect on the hypothalamus
§ No secretion of FSH
§ No secretion of LH
§ No new follicles mature
o Embryo remains firmly attached to placenta by umbilical cord.
Umbilical cord contains: • 2 fetal arteries
o Fetus to placenta • One fetal vein
Childbirth
• Also called parturition
• 38 – 42 weeks from conception o Average = 40 weeks • Three stages of childbirth
1. Labour
• Involuntary
• Rhythmic contractions of the uterus • Causes cervix to open
• Diameter = 10 cm
2. Delivery
• Involuntary uterine contractions • Conscious abdominal contractions
• Mother forces baby out through cervix and vagina
3. Afterbirth
• Immediately after delivery
• Blood vessels in placenta contract • Placenta separates from uterine wall • Expelled by muscle contractions
• Nobody totally knows.
• Baby plays some role in the timing.
• Progesterone decreases
o Allows uterus to contract
• Oxytocin from posterior pituitary
o Stimulates stronger uterine contractions
• Relaxin
o produced by placenta
o Causes ligaments of pelvis to loosen o Larger passageway for baby
Lactation
• During pregnancy, high levels of estrogen and progesterone prepare the breasts for milk production
o Each breast has about 20 milk glands o Connect to the nipple by ducts
o Breast enlarges during pregnancy in preparation for lactation
• Expulsion of the placenta causes the mother's pituitary to secrete prolactin
o Initiates lactation
• Prolactin inhibits the release of LH
o menstrual cycle is suppressed in nursing mothers
• The high estrogen and progesterone levels during pregnancy are thought to inhibit release of prolactin
• The first fluid formed by the mammary glands is colostrum o Thick
o contains lactose and milk proteins o lacks fat
o has antibodies
o after a few days, milk is produced
• Oxytocin is released from hypothalamus when infant suckles
Fetal Development
A blastocyst
• embeds in the uterine wall
• Consists of cells of the future embryo
• Surrounded by a sphere of cells
o Embryonic membrane (extra-embryonic membrane) o Support the developing embryo
Amnion
• Innermost embryonic membrane o Next to baby
• Fluid-filled sac that cushions the baby o "amniotic fluid"
• Protects embryo from trauma and temp fluctuations
Chorion
• Outermost membrane o Part of the placenta o Secretes HCG
Umbilical cord
• Connection between mother and baby o Belly-button to placenta
• Carries baby’s blood to and from placenta
Embryonic Development
• A blastocyst undergoes gastrulation
o Series of cell movements and shape changes o Produces an embryo with 3 cellular layers
1. Ectoderm
• Outer layer of cells
• Will become skin and nervous system
2. Mesoderm
• Middle layer of cells
3. Endoderm
• Inner layer of cells
• Liver, pancreas, lungs, lining of digestive tract
L – Lungs and linings M – Muscles & heart
N - Nervous system & Skin
HUMAN GESTATION: The 40 week journey
Divided into 3 trimesters: • 1st- weeks 1 to 12 • 2nd- weeks 13-24 • 3rd- weeks 25-38
1st Trimester
• From fertilization to end of 3rd month (0 – 12 weeks) • Zygote begins cell division as it moves down oviduct • Becomes blastocyst and implants in uterus
• Development of body organs (anterior brain, limb buds) • Heart starts beating by week 4
• Week 7, testosterone begins to be secreted if a Y-chromosome is present
o This testosterone causes development of testes. • Embryo is 7mm (500x larger than egg)
• Sucking reflex evident
• By week-8 all major structures of the adult are present (in basic form) o Embryo is now called a fetus
• Embryo is most sensitive during first trimester o Due to rapid development
2nd Trimester
• Fetus grows rapidly o To about 30 cm o Quite active
o Hair begins to develop
o Cartilage of skeleton is replaced by bone
3rd Trimester
• Rapid growth of fetus o To about 53 cm o 3-3.5 kg
• Fetal activity decreases o Less room to move
• Fully mature
o Ready for birth
Fertilization & Pregnancy: Summary
• In humans, fertilization and cleavage takes place in the Fallopian tubes. Cleavage is the division of cells in which the cell number increases but the embryo stays the same size.
• When the embryo reaches the uterus, it attaches to the wall of the endometrium
• The implanted embryo secretes hCG, which maintains the corpus luteum. The corpus luteum secretes progesterone and estrogen to prevent shedding of the endometrium (menstruation).
• Changes in hormone levels in a pregnant woman's body trigger the formation of structures that protect and nurture the developing embryo changes, including the amniotic cavity, the placenta, and the umbilical cord.
• Pregnancy is divided into three trimesters. Development of the embryo takes place in the first trimester. Development of the fetus takes place over the last two trimesters.
• Birth begins with parturition (labour). During labour, uterine contractions are triggered by the hormone oxytocin. The hormone relaxin loosens the pelvis and softens the cervix.
• Breast development is stimulated by estrogen and progesterone levels during pregnancy. Milk production is stimulated by prolactin. After birth, suckling triggers release of oxytocin, which stimulates release of milk.
• Reproductive technologies can help people with lower fertility to have children.
Birth Control
Sterilization:
• Most effective
• In males vas deferens is cut off and sealed
o Only effects sperm content of semen so minimal side effects
• In females tubal ligation or cutting of the oviducts
• Disadvantages of sterilization - hard to reverse
• Vasectomy
o Incision through scrotum o Cut and tie off vas deferens
o Sperm is still produced but can’t get out
§ Phagocytized
• Tubal Ligation
"The Pill"
• A combination of estrogen and progesterone given for 21 days of the 28 day cycle
• Effectively shuts down FSH and LH production so follicles do not develop.
• Many of the early problems have been sorted out but side effects possible
Barrier Methods: condoms, IUDs, diaphragms
Condom
• fits over the penis or in the vagina (female condom) and prevents semen from entering the female;
Diaphragm
• which fits over the cervix and prevents semen from entering the uterus • both of these methods are more reliable when used in conjunction with
a spermacidal foam or jelly
IUD
• Inter-Uterine Device
• placed in the uterus by a physician,
• prevent implantation of the blastocyst in the endometrium.
• Best for women who have had one pregnancy, middle to older and are at low risk for STD’
Natural Family Planning
• Requires knowledge of the day of ovulation
• If known, can avoid the 4 days either side of ovulation to account for unusually long -lived sperm or eggs.
• Women need exceptionally regular cycles to be effective
• "Basal" body temperature measurements (T rises at ovulation), vaginal pH measurements (more alkaline), mucus thickness can help determine time ovulation.
Reproductive Technologies
Amniocentesis
• a long needle is used to remove a sample of amniotic fluid from the amniotic sac surrounding the fetus
• fetal cells in the fluid are cultured for 2 to 4 weeks and then analyzed for chromosomal defects and other genetic disorders
Chorionic Villi Sampling (CVS)
• a small sample of tissue is removed from the chorion o the fetal part of the placenta.
• Can be performed earlier in the pregnancy than amniocentesis • results can be obtained within a few days
• greater risk of spontaneous abortion from CVS than from amniocentesis
• ethical considerations: essentially all detectable fetal disorders remain untreatable in the uterus, and many cannot be corrected even after birth
In Vitro Fertilization
• ova can be surgically removed from a woman whose oviducts are blocked
• These are fertilized in a Petri dish in a laboratory
• The resulting embryos can then be inserted into the woman's uterus (or into a surrogate mother's uterus)
• Ethical considerations: post-menopausal woman can now have children; in surrogacy, who is the legal mother???
Sexually Transmitted Infections (STI's) • were once called venereal diseases • More than 20 STIs identified
• Most of the time, STIs have no symptoms, particularly in women • STIs tend to be more severe and more frequent for women than in men
o Some STIs can spread into the uterus and fallopian tubes to cause pelvic inflammatory disease (PID), which causes infertility and ectopic (tubal) pregnancy
o STIs in women have been associated with cervical cancer o STIs can be passed from mother to baby before, during, or
AIDS/HIV
• AIDS (acquired immunodeficiency syndrome) • First reported in the United States in 1981.
• It is caused by the human immunodeficiency virus (HIV)
o a virus that destroys the body's ability to fight off infection. • People who have AIDS are very susceptible to many life-threatening
diseases (called opportunistic infections) and to certain forms of cancer.
• Transmission of the virus primarily occurs during sexual activity and by sharing needles used to inject intravenous drugs.
Chlamydia
• many cases involve no symptoms and therefore infected persons may not seek medical treatment.
• This infection is now the most common of all bacterial STI's, with an estimated 4 to 8 million new cases occurring each year.
• In both men and women • abnormal genital discharge • burning with urination
• In women, untreated chlamydial infection may lead to pelvic inflammatory disease
o one of the most common causes of ectopic pregnancy and infertility in women.
• Many people with chlamydial infection, however, have few or no symptoms of infection.
• Once diagnosed with chlamydial infection, a person can be treated with antibiotics
Genital Herpes
• Affects an estimated 60 million Americans.
• Approximately 500,000 new cases of this incurable viral infection develop annually.
• Caused by herpes simplex virus (HSV).
• painful blisters or open sores in the genital area.
• These may be preceded by a tingling or burning sensation in the legs, buttocks, or genital region.
• The herpes sores usually disappear within two to three weeks, but the virus remains in the body for life and the lesions may recur from time to time.
• Severe or frequently recurrent genital herpes is treated with one of several antiviral drugs that are available by prescription.
• These drugs help control the symptoms but do not eliminate the herpes virus from the body.
• Women who acquire genital herpes during pregnancy can transmit the virus to their babies.
• Untreated HSV infection in newborns can result in mental retardation and death.
Gonorrhea
• discharge from the vagina or penis o “Ooooze”
• and painful or difficult urination.
• The most common and serious complications occur in women and, these complications include PID, ectopic pregnancy, and infertility. • Historically, penicillin has been used to treat gonorrhea, but in the last
decade, four types of antibiotic resistance have emerged.
• New antibiotics or combinations of drugs must be used to treat these penicillin resistant strains.
Syphilis
• caused by a spirochete bacterium.
• The first symptoms of syphilis may go undetected because they are very mild and disappear spontaneously.
• The initial symptom is a chancre;
o usually a painless open sore that usually appears on the penis or
around or in the vagina.
o can also occur near the mouth, anus, or on the hands. • may go on to more advanced stages, including a transient rash and,
eventually, serious involvement of the heart and central nervous system.
• The full course of the disease can take years.
• Penicillin remains the most effective drug to treat people with syphilis.
Genital Warts
• Caused by human papillomavirus,
o virus related to the virus that causes common skin warts. • Genital warts usually first appear as small, hard painless bumps in the
vaginal area, on the penis, or around the anus.
• If untreated, they may grow and develop a fleshy, cauliflower-like appearance.
• Genital warts infect an estimated 1 million Americans each year. • In addition to genital warts, certain high-risk types of HPV cause
cervical cancer and other genital cancers.