Chapter 18: Reproductive System
18.1 Human Reproductive Systems
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_________________________________ involves distinct parents; produces ______________
- The gametes are produced by _______________________; testes, which produces sperm, and ovaries, which produce egg cells
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A gamete is a general term for the reproductive cells that will form a new individual
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A ______________________________ means that the egg and sperm contain half the number of chromosomes of normal body cells
- In order to form gametes properly, the normally _______________________________________ must be cut in half, with the resulting gametes having exactly half the usual complement of allelles
- This way, when _________________________________________________, the original diploid number is restored
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A ______________________________ means that the egg and sperm contain half the number of chromosomes of normal body cells
- In the male, meiosis produces ____________________________
- In the female, meiosis produces only ________________________, investing almost all of the cytoplasm and organelles in one gamete
- Forming gametes is only one function of the reproductive system
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Other functions of the reproductive system include:
- Triggering _____________________________
- Maintaining ___________________________________________
- Stimulating _____________________________________________________________
- The male reproductive system consists of internal and external structures designed to produce and deliver sperm
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The male reproductive system is essentially one long tube, with sperm generated in the gonads at one end, matured along the route, and released from the body at the other
- Accessory glands add secretions to nourish and carry sperm before it is released
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The __________________ delivers sperm during sexual intercourse
- The penis becomes erect during sexual arousal because it contains spongy tissue that fills with blood
- The ___________________ transports sperm and urine, but not at the same time due to a valve system
- The head of the penis, the _____________________, consists of sensitive skin that is covered by the foreskin in uncircumcised males
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The ______________________ is a pouch that holds the __________________________
- Below the thin, nonfatty skin of the scrotum is the cremaster muscle that controls the position of the testes relative to the body
- Testes produce male sex hormones, ___________________________
- Sperm forms in the ___________________________________________ of the testis
- It takes 60 days for a mature sperm to develop
- From the seminiferous tubules, the sperm travels through the _________________ for 20 days where it becomes capable of moving and fertilizing the egg cell
- During ejaculation, the sperm move to the _________________________________, which is covered in smooth muscle and undergoes peristaltic contractions that move the sperm
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Several accessory glands add secretions to the sperm as they travel through the ducts of the male reproductive system
- The ________________________________ secrete a fructose and mucus fluid that is an energy source (60%)
- The ________________________________ secretes a thin milky fluid that contributes to the mobility and viability of sperm (25%)
- The ________________________________ secrete a clear mucus that helps neutralize any acidic urine in the male’s urethra (15%)
- These accessory gland secretion combine with the sperm to form _____________
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Semen production may be affected by spinal cord injuries as well as several diseases
- Repeated bouts of sexually transmitted infections can cause scarring of the sperm-carrying ducts
- Prostatitis, inflammation of the prostate, can alter sperm passage
- Organs of the female system are fewer than the male, represented mainly by the _______________________________, ovaries, ______________________________, and the external female genitalia
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The most obvious feature of the female’s external reproductive anatomy is the ________________________
- The vulva consists of the outer ___________________________ and the inner _______________________________
- The ______________________________ is located at the front of the vulva where the top edges of the labia minora meet
- The urethra opens between the labial folds
- The vaginal opening is just below the urethra
- The ______________________ are the female gonads, which produce gametes and sex hormones
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__________________________ extend from the top of the uterus toward the ovaries
- Don’t connect to the ovaries, instead they end in _____________________, finger-like projections that wave to create a suction to pull the egg into the oviduct
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Two separate cycles occur in the non-pregnant female reproductive cycle
- The ___________________________ cycle
- The ___________________________ cycle
- As well as associated cyclic changes in the breasts and cervix
- Together, they cause the cyclic menstrual flow of the post-pubertal female
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An embryo implants and grows in the ________________________, the muscular wall of which is 1/3 inch thick
- The wall contacts rhythmically during labor, childbirth, and orgasm
- Its inner surface, the ____________________________ changes in thickness during the menstrual cycle
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The lower third of the uterus is narrowed forming the _______________________, which dilates during childbirth
- The sperm must also travel through the cervix to reach the egg
- The __________________ is the passageway into and out of the uterus
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For pregnancy to occur, the sperm must be able to pass into the oviducts
- Infertility can result from physical blockage of oviducts from scarring due to infection, especially sexually transmitted infections
- Scarred or damaged oviducts may lead to an ectopic pregnancy (egg implants in the oviduct instead of the uterus), which must be terminated as they can be life-threatening
18.2 Gametogenesis: Development of Sex Cells
- Several hormones regulate gamete production
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The hypothalamus in both sexes secretes _________________________________________ (GnRH), which stimulates the pituitary gland to release ______________________________________ (FSH) and ________________________________ (LH)
- These hormones act on the testes in males and the ovaries in females beginning at puberty
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FSH and LH stimulates testosterone production by the testis
- _________________________________ causes spermatogonia to divide and regulates the growth and development of male reproductive structures
- _______________________________________, sperm production, begins at puberty in the walls of the seminiferous tubules
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Sperm production/maturation:
- First divide into spermatogonia
- Spermatogonia form into primary spermatocytes
- Spermatocytes become secondary spermatocytes and then spermatids
- Spermatids mature into the spermatogenic cell, the ________________
- A total of __________ sperm are produced
- Mature sperm consist of a small head that contains DNA, a midpiece with mitochondria to produce ATP, and a tail used for locomotion
- The tail forms at the end of spermatogenesis
- An enzyme-containing ___________________________, on the tip of the sperm head help the sperm to enter the egg
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Most cases (90%) of male infertility are due to sperm production and formation problems
- Irregularly shaped sperm and those with motility defects
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Low sperm counts lower the odds of conception
- Normal = 300 million sperm/ejaculate or 20 million sperm/ml of semen
- < 10 million sperm/ml = infertility
- At around age 35, sperm count begins to decline
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Exposure to pesticides, solvents and cigarette smoke also decrease sperm counts
- Many drugs (cocaine, marijuana) are associated with decreased fertility
- Anabolic steroids cause the testes to shrink, resulting in low sperm count
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_______________________, the formation of female gametes, occurs in the ___________
- Oogenesis begins in the female in utero (at 8 weeks) and pauses until puberty
- The oocytes (developing egg cells) stop during meiosis
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Just prior to ovulation, meiosis continues
- Until menopause (cessation of uterine and ovarian cycles)
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Egg production/maturation:
- First divide into oogonia
- Oogonia form into primary oocytes
- Primary oocytes become secondary oocytes
- The mature oocyte cell is referred to as the ______________ (egg) which is ovulated
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A group of supportive cells, ___________________________, surround the oocyte
- After ovulation, the corpus luteum (follicle cells) remains in the ovary and slowly degenerates
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The ______________________________________ is a programmed series of events that occur in the ovary as oocytes mature and ovulate, governed by hormones (FSH and LH)
- Hormones released from the ovary (estrogen and progesterone) act on the endometrium of the uterus
- Hence the ovarian and uterine cycles
- The ovaries are small, almond-shaped organs that lie in the pelvic cavity
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_______________________ occurs via meiosis like spermatogenesis, except:
- At birth, a finite number of oocytes are in each ovary (200,000 – 2 million)
- Oocytes ___________________________, so that by puberty only 150,000 – 200,000 remain in each ovary
- Only 400 will actually mature and ovulate during a woman’s reproductive lifetime
- Only __________________________ is produced via meiosis
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An ovulated egg undergoes an off-center meiosis that produces tiny cells (___________________________) that won’t be involved in fertilization
- The larger cell, the _________________, is ovulated and capable of being fertilized
- The egg will contain enough nutrients to nourish the _______________________ through its early development
- If the egg is not fertilized, it moves from the oviduct through the uterus and cervix and out the body via the vagina
- Estrogen and progesterone (from the ovary) regulate the ovarian cycle via feedback loops that involve the hypothalamus (Gonadotropin releasing hormone) and pituitary (FSH, LH)
- The first half of the ovarian cycle is the ________________________________ and the second half is the ______________________________
18.3 The Menstrual Cycle
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The term _____________________________________ refers to the periodic changes of the uterus
- The cycle depends on the hormonal relationships of the brain, ovaries, and the lining of the uterus
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During the menstrual cycle, the uterus prepares for potential implantation of a fertilized egg
- Remember that the egg is being matured at the same time in the ovary (the ovarian cycle)
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The endometrial lining thickens and sheds approximately every 28 days in response to hormone levels
- Most women do not adhere precisely to a 28-day menstrual cycle
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Fertilization must occur within 24 hours of ovulation
- The ovum takes 6-7 days to travel to the uterus, during which time it begins to degenerate unless fertilized
- Sperm can remain in the female reproductive tract for several days!
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______________________________ of the embryo occurs in the _________________________, which is built up every month in anticipation of receiving an embryo
- If there is no successful fertilization (no pregnancy), the endometrial lining is shed resulting in the ________________________________
- The first day of the cycle is the first day of bleeding
- Estrogen increases during the ovarian cycle stimulating mitosis of endometrial cells and regrowth of blood vessels to prepare the uterus for a possible pregnancy
- After ovulation, progesterone (secreted by the corpus luteum) prepares the endometrium for pregnancy by maintaining blood flow to the uterine lining by inhibiting LH secretion (from the pituitary)
- If fertilization does not occur, the corpus luteum breaks down 14 days after ovulation, resulting in a drop in estrogen and progesterone
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The result is spasms in the arteries supplying the endometrium, which will be shed after losing its blood supply
- This is the cause of menstrual crams
- The menstrual flow includes blood and endometrial tissue which exits via the cervix and vagina
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The decrease in progesterone (as a result of the breakdown of the corpus luteum) signals the hypothalamus to release gonadotropin releasing hormone
- It then signals the pituitary to release FSH and LH
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Signaling the next ovarian cycle to begin
- Signaling the next uterine cycle to begin
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If fertilization has occurred, implantation results
- The corpus luteum secretes progesterone maintaining the endometrial lining
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The embryo produces _____________________________________________, which extends the life of the corpus luteum
- Tested for in pregnancy tests
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Corpus luteum secretes estrogen and progesterone which maintains the endometrium until the placenta forms (6-7 weeks)
- Corpus luteum disintegrates
- Placenta produces progesterone maintaining pregnancy
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______________________________ is a condition where the endometrial cells migrate through the oviducts and implant on other organs
- The endometrial cells respond to hormones thus grow, but are trapped in the body with no endpoint
- Associated with female infertility
Mammary Glands
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____________________________________ located in the pectoralis muscle
- Supported by ligaments and protected by adipose tissue
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___________________________________ are involved in milk production and secretion
- During the last two weeks of pregnancy, _____________________ stimulates breast swelling and milk production
- Milk is released in response to __________________________ production (from the pituitary gland)
18.5 Controlling Fertility
- Nearly 80% of sexually active women in the U.S. use some form of birth control (_________________________________) to prevent pregnancy
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There are many options:
- Blocking sperm transport
- Inhibiting ovulation
- Removal of fertilized egg or embryo
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_________________________________ of birth control prevent sperm from approaching the egg cell
- They are popular because they are easy to acquire and use
- They are prone to failure because they may be used improperly or not at all
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The ________________________________, a popular barrier method, covers the penis and traps the sperm
- Effective in protecting against sexually transmitted infections
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The _______________________________ is a vaginal liner
- Also effective in protecting against sexually transmitted infections
- Expensive and difficult to use effectively
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________________________ and __________________________ are latex domes that prevent sperm from entering the cervix, especially when filled with a spermicide
- Do not protect against sexually transmitted infections, but effective method of birth control
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__________________________ is when the penis is removed from the vagina before ejaculation
- Small amounts of semen may be released prior to orgasm making this method unreliable
- Does not protect against sexually transmitted infections
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__________________________ (nonoynol-9) inactivates sperm by damaging the cell membrane
- A cream, jelly or foam is inserted into the vagina prior to intercourse
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The _________________________________ is a disk infused with spermicide that covers the cervix
- Can be inserted several hours prior to intercourse
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__________________________________________________ (pill, patch, ring) are popular
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Taken daily and very effective
- As few as two missed pills in a row increase the chance of pregnancy
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Contain synthetic estrogen and progesterone, which work together to prevent ovulation and fertilization
- Estrogen prevents oocytes from developing and inhibits ovulation
- Progesterone affects the endometrium to prevent implantation
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Taken daily and very effective
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The ___________________________________ and _____________________________ reduce the chance of a missed dose
- The patch is applied to the skin once a week
- The ring is placed in the vagina
- Estrogen and progesterone diffuse from the patch or the ring having the same effect as the pill
- Minor side effects of combination hormones may include: nausea, breast discomfort, weight gain, headaches, and acne
- Serious side effects include: increased risk of blood clots for women who smoke and a delayed return to fertility after use is discontinued
- Benefits includes: some protection against ovarian and endometrial cancer
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Birth control pills come in 28-day packets
- 21 of the pills contain hormones, 7 are placebos
- Patches and the vaginal ring are kept in place for 21 days, then removed for a week
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The hormone-free time triggers menstruation
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There is little evidence that foregoing menstrual periods is dangerous
- Three-month dose packets available
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There is little evidence that foregoing menstrual periods is dangerous
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________________________________ are used by breast-feeding women to prevent pregnancy
- Does not interfere with milk production
- Medroxxyprogesterone acetate (___________________________) is an injectable form of progesterone that is administered every 3 months
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High doses of birth control pills can be used as _______________________________ in the event of failure of other methods
- “Plan B” pills must be taken within 72 hours after unprotected sex
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It isn’t known exactly how it works
- It may prevent ovulation or fertilization depending on when it is taken or may prevent implantation
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________________________________ (IUDs) are placed inside the uterus
- ParaGard and Mirena
- IUDs must be inserted by a clinician
- Prevent pregnancy by contacting the uterus
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___________________________________ involve a woman being aware of her cycle and observing the signs of fertility
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The calendar method times ovulation and works best if a woman has regular periods
- Few women have a regular cycle, so this is a risky method of birth control
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The calendar method times ovulation and works best if a woman has regular periods
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Many women use the calendar as a guide in addition to physical changes surrounding ovulation
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For some women, a reliable indicator of ovulation is the appearance of thin, stringy cervical mucus caused by high estrogen levels
- The mucus helps to guide the sperm through the uterus
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For some women, a reliable indicator of ovulation is the appearance of thin, stringy cervical mucus caused by high estrogen levels
- The presence of this thin mucus is an indicator that the woman is fertile
- After ovulation, when progesterone levels are high, the mucus thickens making it difficult for the sperm to pass through
- A woman’s body temperature also changes throughout the menstrual cycle
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________________________________ is a popular method of birth control in the U.S.
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Very effective, but difficult to undo
- In males, the procedure involves prohibiting sperm from traveling between the testes and the penis
- In females, it involves prohibiting the passage of the egg from the ovaries to the oviducts
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Very effective, but difficult to undo
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A ______________________________ involves cutting and tying off each vas deferens
- The duct that carries sperm from the testes to the urethra
- Requires only a local anesthetic
- About 50% of cases can be reversed
- Sperm continues to be made and erections continue
- No change in semen volume or steroid levels
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_____________________________________ requires an operating room
- Incredibly difficult to reverse
- Another option for women is the insertion of spring-like tubes in the oviducts that block them
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A large number of pregnancies in the U.S. are unplanned
- 2 million (~47%)
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Some terminated by an ________________________________
- A hotly debated and divisive issue
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Mifepristone (RU486) blocks progesterone secretion which maintains the endometrium
- The endometrium and the embryo are lost
- This method is used during the first seven weeks of pregnancy
18.6 Health, Lifestyle, and Fertility
- When a couple decides to have children, they should eat a healthy diet and exercise
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They should avoid stress and males should avoid exposing the testes to too much heat
- Hot tub, laptop on the lap
- Tobacco, cocaine, and marijuana should also be avoided