Limited Time Offer: Get 2 Months of ABCmouse.com for only $5!

Chapter 18

 

Chapter 18: Reproductive System

 

18.1 Human Reproductive Systems

  • _________________________________ involves distinct parents; produces ______________
    • The gametes are produced by _______________________; testes, which produces sperm, and ovaries, which produce egg cells

 

  • A gamete is a general term for the reproductive cells that will form a new individual
    • 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

 

  • 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
  • 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

 

  • 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

 

  • 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

 

  • 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

 

  • 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 _____________

 

  • 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

 

  • 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
  • __________________________ 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

 

  • 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

 

  • 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
  • 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
  • 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
  • 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

 

  • 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

 

  • 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

 

  • Most cases (90%) of male infertility are due to sperm production and formation problems
    • Irregularly shaped sperm and those with motility defects
  • 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
  • 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

 

  • _______________________, 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
  • Just prior to ovulation, meiosis continues
    • Until menopause (cessation of uterine and ovarian cycles)

 

  • 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
  • A group of supportive cells, ___________________________, surround the oocyte
    • After ovulation, the corpus luteum (follicle cells) remains in the ovary and slowly degenerates

 

  • 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
  • _______________________ 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

 

  • 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

  • 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
    • 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)

 

  • 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

 

  • 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!

 

  • ______________________________ 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
  • 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

 

  • 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
    • Signaling the next ovarian cycle to begin
      • Signaling the next uterine cycle to begin
  • If fertilization has occurred, implantation results
    • The corpus luteum secretes progesterone maintaining the endometrial lining

 

  • The embryo produces _____________________________________________, which extends the life of the corpus luteum
    • Tested for in pregnancy tests
  • 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

 

  • ______________________________ 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

  • ____________________________________ located in the pectoralis muscle
    • Supported by ligaments and protected by adipose tissue
  • ___________________________________ 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
  • There are many options:
    • Blocking sperm transport
    • Inhibiting ovulation
    • Removal of fertilized egg or embryo

 

  • _________________________________ 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

 

  • The ________________________________, a popular barrier method, covers the penis and traps the sperm
    • Effective in protecting against sexually transmitted infections
  • The _______________________________ is a vaginal liner
    • Also effective in protecting against sexually transmitted infections
    • Expensive and difficult to use effectively

 

  • ________________________ 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

 

  • __________________________ 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
  • __________________________ (nonoynol-9) inactivates sperm by damaging the cell membrane
    • A cream, jelly or foam is inserted into the vagina prior to intercourse

 

  • The _________________________________ is a disk infused with spermicide that covers the cervix
    • Can be inserted several hours prior to intercourse

 

  • __________________________________________________ (pill, patch, ring) are popular
    • Taken daily and very effective
      • As few as two missed pills in a row increase the chance of pregnancy
    • 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

 

  • 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

 

  • 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
  • The hormone-free time triggers menstruation
    • There is little evidence that foregoing menstrual periods is dangerous
      • Three-month dose packets available

 

  • ________________________________ 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

 

  • 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
    • It isn’t known exactly how it works
      • It may prevent ovulation or fertilization depending on when it is taken or may prevent implantation

 

  • ________________________________ (IUDs) are placed inside the uterus
    • ParaGard and Mirena
  • IUDs must be inserted by a clinician
  • Prevent pregnancy by contacting the uterus

 

  • ___________________________________ involve a woman being aware of her cycle and observing the signs of fertility
    • 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

 

  • Many women use the calendar as a guide in addition to physical changes surrounding ovulation
    • 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

 

  • 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

 

  • ________________________________ is a popular method of birth control in the U.S.
    • 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

 

  • 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

 

  • _____________________________________ 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

 

  • A large number of pregnancies in the U.S. are unplanned
    • 2 million (~47%)
  • Some terminated by an ________________________________
    • A hotly debated and divisive issue
  • 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
  • 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
Get 2 Months for $5!