IB Biology Reproduction

• 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.

• prenatal development of male genitalia, development of secondary sexual characteristics
• maintenance of sex drive

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.

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.

• 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

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.

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.

• 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.

• 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

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.

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.

• 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

Amniotic sac, amniotic fluid

placenta

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.

amount of FSH increases

the follicle matures in the ovary

Days 22-25

About 13-14 days

Day 13

ovulation (egg released from follicle)

the corpus luteum matures

Days 21-25

It is beginning to disintegrate

estrogen increases

the uterine lining begins to thicken

Progesterone increases

The uterine lining is continuing to thicken

Day 26-Day 1

Menstruation

It influences the growth and development of a maturing follicle

It causes changes in the corpus luteum

Yes, both work to maintain the uterine lining

Estrogen secretion by the follicle increases, the follicle matures

LH stimulates the formation of a corpus luteum in the follicular tissue.

Mature sperm and egg cells are haploid, while other body cells are not (diploid)

Secretes estrogen and progesterone to maintain uterine lining for pregnancy

the tail allows the sperm to move

• Both produce gametes
• Each secrete the appropriate sex hormones

The mitochondria provide ATP for movement of the tail

Both eggs might be fertilized, resulting in a multiple pregnancy. (fraternal twins)

Leydig cells

seminiferous tubules

epididymis

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.

• Cons:
• 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
• Pros:
• 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