IB Biology Reproduction
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Outline the role of hormones in the menstrual cycle, including FSH, LH, estrogen, and progesterone
- GnRH is produced in the hypothalamus when estrogen levels are high and progesterone is low. It travels to the anterior pituitary through a portal vessel. The Anterior pituitary produces FSH and LH in response to GnRH
- FSH, which stimulates follicle growth and maturation, is secreted and its levels begin to rise. This stimuates the follicle to develop and secrete estrogen.
- When estrogen peaks it causes an LH surge which leads to ovulation (release of egg from follicle) and causes the corpus luteum to develop.
- The corpus luteum produces estrogen and progesterone, which promotes growth and maintenance of the uterine lining (endometrium). When the corpus luteum deteriorates, due to a drop in LH, estrogen production decreases. This triggers menstruation.
List the three roles of testosterone in males
- prenatal development of male genitalia, development of secondary sexual characteristics
- maintenance of sex drive
Outline the process of in vitro fertilization
Fertility drugs (FSH and LH, or synthetic substitute) are given to female to increase ovulation. Many eggs are harvested. Eggs are then mixed with sperm in a culture dish, incubated, and embryos are grown to blastocyst stage. Blastocysts are then checked for abnormalities and some are then transferred to the uterus of the female. Extra embryos are frozen for use in second attempt if the first attempt is unsuccessful.
Outline the processes involved in spermatogenesis within the testis, including mitosis, cell growth, the two divisions of meiosis and cell differentiation
Spermatogenesis is the production of mature sperm cells. Diploid somatic cells are called spermatogonium, and are located in the outer layer of the seminiferous tubules. After Prophase of Meiosis I, the spermatogonium becomes a primary spermatocyte (still diploid). At the conclusion of meiosis I, the cell is divided into two haploid secondary spermatocytes. After meiosis II there are four spermatids. Spermatids are haploid, and mature into sperm cells and are nourished by the Sertoli Cells. Sperm cells spend about 21 days, or three weeks, in the epididymis before they become fulling functional. Spermatogenesis is a continuous process.
State the role of LH, testosterone, and FSH in spermatogenesis.
- LH stimulates testosterone production by the Leydig cells in the testes
- FSH acts on the Sertoli cells of the seminiferous tubules, promoting spermatogenesis
- Testosterone stimulates sperm production
Outline the processes involved in oogenesis within the ovary, including mitosis, cell growth, the two divisions of meiosis, the unequal division of cytoplasm, and the degeneration of polar body.
Oogenesis is the process by which mature ova are produced the ovaries. The process begins when oogonia multiply through mitosis. They grow larger and then begin meiosis, but stop at prophase I. This produces a primary oocyte. These primary oocytes remain in prophase I until puberty. At puberty the primary oocytes are activated by FSH and LH. During meiosis II, a secondary oocyte is produced along with a polar body that dies due to the unequal distribution of cytoplasm (ovulation). When prophase II is completed, a haploid secondary oocyte is produced. Fertilization triggers the completion of meiosis.
Outline the role of the epididymis, seminal vessicle and prostate gland in the production of semen.
The epididymis is the coil of tubes where sperm mature. The sperm are produced in the seminiferous tubules. The seminal vesicle secretes 60% of semen. It secretes alkaline fluid, mucus, sugar, a coagulant enzyme, ascorbic acid, and prostaglandins. The prostate gland secretes products directly in the urethra. It secretes thin, milky fluid containing citrate and an anticoagulant enzyme.
Compare the processes of spermatogenesis and oogenesis.
- Both eggs and sperm are haploid cells produced from a diploid somatic cell using meiosis. Eggs, usually one ovum, are released only when a female ovulate but the male's sperm are formed continuously and released at ejaculation.
- In spermatogenesis each diploid somatic cells produces 4 haploid gametes by meiosis. Sperm are produced continuously from puberty throughout life.
- At each division in oogenesis one of the two daughter cells is a polar body, which dies. The end result is therefore a single ovum (not four ova). When a girl is born all of her primary oocytes are already formed. A secondary oocyte is released at ovulation. The oocyte only completes meiosis when it is fertilized.
Describe the process of fertilization.
- The sperm binds to the receptor of the zona pellucida of the egg. This triggers the acrosomal reaction. Exocytosis from the acrosome releases hydrolytic enzymes which break down the zona pellucida. Membrane proteins of the sperm fuse to the membrane of the egg. This depolarizes the membrane, which makes the fast block to polyspermy. The nucleus and the basal body of the sperm enter the egg's cytoplasm. Calcium ions are released from the plasma membrane and release their contents into the perivitelline space. Water enters the perivitelline space through osmosis, and enzymes from the cortical granules clip off the sperm receptors . This is the slow permanent block to polyspermy.
- acrosomal, cortical
Outline the role of HCG in early pregnancy
HCG, or Human Chorionic Gonadotropin, can be detected in the urine by pregnancy tests. It is produced by the embryo. This hormone acts like LH to maintain corpus luteum to continue the production of estrogen and progesterone during pregnancy in order to maintain the uterine lining. This hormone causes morning sickness.
Outline the early embryo development up to implantation of the blastocyst.
Following fertilization, the zygote undergoes a rapid series of mitotic divisions, or cleavage, without increasing in size. Cleavage continues and the embryo turns into a morula. The morula is a ball of cells still surrounded by the fertilization envelope. As division continues, the embryo expands to make a hollow space called the blastocoel in the center of the embryo surrounded by a singer layer of cells. This is the blastocyst.
Explain how the structure and functions of the placenta maintain pregnancy
- The placenta is an organ used for exchange of gases, waste, and nutrients between the blood of the fetus and mother. Exchange is possible by surrounding capillaries of the fetus with pools of the mother's blood so exchange of gas and nutrients can occur without mixing of maternal and fetal blood. The Umbilical cord connects the fetus and placenta. The veins of the cord carry oxygenated, nutrient rich blood from placenta to fetus.
- The placenta makes prostogladins which help stimulate contractions, which eventually leads to parturition.
- High levels of estrogen from the placenta induce the formation of oxytocin receptors on the smooth muscle lining of the uterus.
- The chorion is the fetal portion of the placenta
The fetus is supported and protected by the __________ and _______.
Amniotic sac, amniotic fluid
Material are exchanged between maternal and fetal blood in the ________.
Outline the process of birth and its hormonal control, including the changes in progesterone and oxytocin levels and positive feedback.
Estrogen produced from ovaries and placenta induces oxytocin receptors to form on the smooth uterine muscle lining (myometrium). Oxytocin from fetus and mother's posterior pituitary stimulate uterine contractions, and also stimulate prostoglandin production from the placenta. Prostaglandins induce uterine contractions which stimulate more oxytocin production.
Between days 25 and 12 of the menstrual cycle, what happens to the amount of FSH produced by the body of an average human female?
amount of FSH increases
What happens to the follicle between days 25 and 12 of the menstrual cycle?
the follicle matures in the ovary
During which days of the menstrual cycle is the level of FSH at its lowest in the blood stream?
How long is the follicle phase of the menstrual cycle?
About 13-14 days
On which day of the menstrual cycle is the production of LH the greatest?
What event occurs immediately after this increased production of LH?
ovulation (egg released from follicle)
What happens to the corpus luteum during days 15-24 of the menstrual cycle?
the corpus luteum matures
During which days of the menstrual cycle is the production of LH the lowest?
What is happening to the corpus luteum between days 21-25?
It is beginning to disintegrate
What happens to the amount of estrogen produced by the body during days 6-12 of the menstrual cycle
What is occurring to the uterus during days 6-12?
the uterine lining begins to thicken
What happens to the amount of progesterone produced by the body during days 13-23 of the menstrual cycle.
What is occuring to the uterus during days 13 to 23?
The uterine lining is continuing to thicken
During which days of the menstrual cycle are the levels of both estrogen and progesterone at their lowest?
Day 26-Day 1
What is occuring when both progesterone and estrogen are at their lowest?
How is the name follicle stimulating hormone appropriate for its function?
It influences the growth and development of a maturing follicle
How is the name luteinizing hormone appropriate for its function?
It causes changes in the corpus luteum
Do estrogen and progesterone both cause similar changes in the uterus?
Yes, both work to maintain the uterine lining
What events occur during the follicle phase of menstruation?
Estrogen secretion by the follicle increases, the follicle matures
What events occur during the luteul phase of the menstual cycle?
LH stimulates the formation of a corpus luteum in the follicular tissue.
In what ways are mature sperm and egg cells different from all other types of body cells?
Mature sperm and egg cells are haploid, while other body cells are not (diploid)
What is the function of the corpus luteum in the ovary?
Secretes estrogen and progesterone to maintain uterine lining for pregnancy
What is the adaptive advantage of the tail on the sperm cell?
the tail allows the sperm to move
What are two functions that are common to both ovaries and testes?
- Both produce gametes
- Each secrete the appropriate sex hormones
What is the purpose of the mitochondria packed into the middle section of each sperm cell?
The mitochondria provide ATP for movement of the tail
What might happen if more than one egg were released at the same time from the ovaries?
Both eggs might be fertilized, resulting in a multiple pregnancy. (fraternal twins)
Draw and Label a diagram of the adult male reproductive system
Draw and label a diagram of the adult female reproductive system
Annotate a light micrograph of testis tissue to show the location and function of Leydig cells, germinal epithelium cells, developing spermatozoa and Sertoli Cells.
Label a diagram of a mature sperm
Label a diagram of a mature egg
Which cells produce testosterone?
Where are sperm produced?
Where are sperm stored?
How does an egg get from the ovary to the oviduct?
The oviduct has a funnel-like opening, and cilia on the epithelium lining the duct help collect the egg by drawing fluid from the body cavity into the duct.
Discuss the ethical issues associated with IVF
- creating life in a dish, some object to IVF on religious groups believing that God is lost in the process.
- People can check embryos for any abnormalities, like genetic or hereditary diseases. So they might choose to have an abortion if the child has undesirable defect
- -can dispose of excess embryos
- -Designer babies allow parents to choose traits such as hair and eye color, along with personality traits.
- -extra embryos are considered a life by some, so throwing away extras is killing life.
- multiple embryos end up frozen, storage is expensive and disposing of them is potentially problematic
- Procedures with thawed embryos are less successful
- Hard to decide whether or not to implant all of the embryos (very costly, favors wealthy)
- Health problems associated with multiple birhts
- There are many children that need to be adopted (IVF leaves children who could have been adopted without parents)
- Paternity/maternity issues with donated sperm/egg
- Extra embryos become available for research and can help find a cure. (stem cell research)
- Gives infertile couples a chance to have their won viable off spiring
- Don't have to wait for adoption to pull through
- Greater control over who you want your child to be
- Screen for genetic diseases and choose embryos that are free of the disease
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