Reproduction Flashcards
Differences between Sexual and Asexual Reproduction
Fusion of genetic material from two parents
Singler parent produces offspring
Genetically different offspring
Genetically identical to parent offspring
Increased variation and faster evolution
Rapid reproduction and no need to search for mates
Requires two individuals and few organisms are produced
Less variation and slower evolution
Signifcance of Meiosis for Reproduction
Breaks up parental combinations of alleles, with homologous chromosomes undergoing crossing over and independent assortment creating new combinations (recombinants)
Produces four genetically unique gametes with each gamete receiving a unique combination of alleles
Significance of Gamete Fusion (Fertilization) for Reproduction
Creates a zygote, combines genetic material from both parents and introduces new combinations of alleles with the zygote having a unique genetic makeup different from parents.
Differencces between Male and Female in Reproduction
Sperm
Egg
Small
Large
Motile
Sessile
Millions per ejaculation
One or two eggs per month
Minimal cytoplasm and reserves
Significant cytoplasm and reserves
The large number of sperm maximize fertilization chances
Invest resources in fewer eggs for offspring development
Anatomy of the Female Reproductive System
Ovary: Site of production where the egg matures, along with site that produces estrogen and progesterone
Oviduct: Site of fertilization, provides a pathway for the egg to travel to the uterus by sweeping it by cilia on its walls
Uterus: Site of implantation of the fertilized egg
Cervix: Muscular tissue that separates the vagina from the uterus, secretes mucus to help sperm swim
Vagina: Organ used in intercourse, folded to allow expansion during birth, and secretes mucus to allow movement of male organ during intercourse and as a primary line of defense
Anatomy of Male Reproductive System
Testes: Produces sperm and testosterone
Scrotum: Sac which contains testicles (nutsack)
Sperm Ducts: Two muscular tubes each connected to a testes. Carry sperm rom testes to urethra during ejaculation
Prostate Gland: Secretes alkaline fluid to neutralize the acidic conditions of the urethra and vagina
Seminal vesicle: Secretes mucus to help swimming and fructose to provide energy for sperm
Urethra: Tube inside the penis which is the pathway of semen and urine out of the body
Penis: Male sex organ which ejaculates semen into vagina during intercourse
Epididymis: Coiled tubes where sperm is stored and matures
Hormones involved in Menstrual Cycle
Anterior Pituitary: FSH and LH
Ovaries: Estrogen and Progesterone
Estrogen gets produced by the follicle cells
Progesterone gets produced by corpus luteum / yellow cells
The Main Hormonal Changes in a Menstrual Cycle
A menstrual cycle is usually 28 days, and the first day is day 1
FSH is secreted by the pituitary gland causing its levels to rise, which simulates the follicles to develop. This allows for the egg inside the follicle to mature and allow the follicle cells to secrete estrogen
Estrogen causes the follicle cells to make more FSH receptors so that they can respond more strongly to the FSH. This increases secretion of FSH which is a positive feedback loop and causes estrogen levels to rise which simulates the thickening of the endometrium
When estrogen levels reach its peak it simulates secretion of LH from the pituitary gland, and when LH reaches its peak it causes ovulation
Once ovulation occurred, LH stimulates the follicle cells to develop into corpus luteum, which starts to reduce estrogen secretion and secrete high amounts of progesterone to prepare for endometrium implantation
The high levels of estrogen and progesterone inhibit FSH and LH making it a negative feedback loop which prevents further follicle development or ovulation
If no fertilization takes place, the corpus luteum degenerates and causes a fall in levels of estrogen and progesterone which stimulates menstruation.
When the levels of estrogen and progesterone are low enough FSH and LH start to be secreted again and a new menstrual cycle beings
Feedback Loops in Menstruation Cycle
Positive Feedback:
Rising estrogen levels from developing follicles stimulate the release of GnRH which leads to more FSH production, creating a positive feedback loop that promotes follicle growth
Negative Feedback:
As estrogen levels peak, they supress GnRH and FSH release which limits follicle growth and allows for LH to surge
If pregnancy doesn’t occur, the degenerating corpus luteum leads to a decline in progesterone levels which triggers menstruation and prepares for the cycle to repeat again
Function of Anterior Pituitary Hormones in Menstrual Cycle
FSH:
Stimulates development of follicles
Stimulates maturation of oocyte inside the follicle
Stimulates secretion of estrogen from the follicle
LH:
Causes ovulation
Stimulates the development of the corpus luteum after ovulation
Stimulates the follicle cells to secrete less estrogen
Function of Ovary Hormones in Menstrual Cycle
Estrogen:
Repairs the endometrium after menstruation
Stimulates LH secretion
Has positive feedback loop during the first half of the cycle to make more FSH receptors
Has negative feedback loop during the second half of the cycle to inhibit secretion of FSH and LH
Progesterone:
Maintains the lining of the endometrium to prepare it for implantation
Inhibits the secretion of FSH and LH
Fertilization Process
Sperm navigates through female reproductive system towards egg using tail
Specific molecules on the sperm’s surface bind to complementary receptors on the zona pellucida which ensures species-specific fertilization
Sperm’s acrosome releases enzymes that digest a path through the zona pellucida which allows the sperm to reach the egg’s plasma membrane
The sperm’s head which contains the genetic material enters the egg’s cytoplasm
The rest of the sperm is degraded and not incorporated into the embryo
The membrane surrounding the sperm and egg nucleus dissolves, which allows for both nucleuses to come fuse forming a zygote, containing combined genetic information from both parents
IVF Process
For three weeks, a woman takes a drug to stop her normal menstrual cycle
For 10-12 days, high does of FSH are injected once a day to have many follicles develop in the ovaries
LH and HCG are then injected to promote superovulation. HCG loosens the eggs in the follicles and matures them
A device is inserted through the vagina wall extracts the eggs from the follicles
Sperm is collected from the male individual and they get processed to find the healthiest ones
Many sperm and egg get mixed in a petri dish, and get incubated at 37 degrees
The next day, the dishes are observed to see if fertilization happened, and if it did then two or three of the embryos are chosen to be placed in the uterus through a long plastic tube
A pregnancy test is done a few weeks later to find out if any of the embryos have implanted, and a scan is done a few weeks later to find out if the pregnancy is progressing normally
Arguements for and Against IVF
Helps infertile couples to have children
Against God’s will
Embryos that are killed through IVF can not feel pain
Multiple embryos are produced than needed and get denied a chance of life
The cost is worth it
IVF is very expensive
Improving medical technology makes it safe
Risk to the mother of multiple pregnancies
Benefits of Superovulation
Having more eggs available for fertilization outside the body improves chances of obtaining viable embryos for implantation
With multiple eggs there’s a higher chance of obtaining a healthy embryo suitable for transfer to the uterus
Adaptations of Sperm
Divided into three sections
Head contains nucleus which has parental DNA, acrosome cap which releases enzymes that digest the zona pellucida, and centrioles needed to divide the zygote
Mid-piece contains mitochondria which provides ATP to move the tail
Tail has a microtubule to facilitate movement
Adaptations of Egg
Surrounded by two layers:
Zona pellucida which acts as a barrier to sperm entry
Corona radiata which is an external layer of follicular cells that provide support and nourishment to the egg
Additionally, cortical granules release their contents to harden zona pellucida upon fertilization to prevent polyspermy
Large cytoplasm to provide nutrients needed for mitosis of the developing zygote
FSH and LH in Puberty for Males and Females
FSH Stimulates follicle growth and maturation in ovaries
LH triggers ovulation from follicle
FSH supports sperm production
LH stimulates testosterone production
Estrogen is produced in the follicles
Testosterone is produced in the testes
Secondary Sexual Characteristics During Puberty
Growth of hair in pubic area and under the armpit, and change of behaviour associate with sex drive
Development and enlargement of the testes, scrotum and penis
Maturation of the ovaries and enlargement of vagina and uterus
Increased skeletal muscle development
Development of breasts
Deepening of voice
Widening of pelvis
Continuous production of sperm
Monthly ovulation and menstruation
Spermatogenesis
Formation of sperm in males, and takes place in seminiferous tubules
Germinal epithelial cells divide by mitosis to produce spermatogonia (diploid)
Spermatogonia undergo growth and become primary spermatocytes
FSH simulates primary spermatocytes to undergo Meiosis 1 and become secondary spermatocytes
Testosterone simulates secondary spermatocytes to undergo Meiosis 2 to become spermatids (4 spermatids total)
Spermatids move to the center of the seminiferous tubule where they associate with Sertoli cells through the help of testosterone to help them mature into spermatozoan
Sertoli cells provide nourishment to developing sperm and to aid with development, and Leydig cells secrete testosterone
Oogenesis
Production of the egg, and takes place in ovaries and begins before birth
Before birth, germinal epithelial cells undergo mitosis to form Oogonia
Oogonia undergo mitosis and develop into primary oocyte, which are surrounded by layers of cells forming a primordial follicle
Primary oocytes begin Meiosis 1 but stop in prophase 1 until puberty
During puberty, primordial follicles develop into primary follicles, growing larger in size
FSH simulates primary follicles to develop into secondary follicles which contains an extra layer of cells
Primary oocyte undergoes Meiosis 1, forming 2 haploid cells which are uneven in size. The larger one which receives most of the cytoplasm is called the secondary oocyte, whereas the smaller one is called the 1st polar body which eventually disintegrates
Just before ovulation, secondary follicle continues to develop which eventually forms the mature follicle which leads to the secondary oocyte beginning Meiosis 2 but stopping at prophase 2.
During ovulation, the secondary oocyte bursts out of the follicle, thus leaving the ovary and entering the oviducts. Only if fertilization takes place does the secondary oocyte complete Meiosis 2 producing an ovum.
Spermatogenesis VS Oogenesis
Both produce haploid cell
Both include meiosis and mitosis
Both have cell growth before meiosis
Occurs in testes
Occurs in ovaries
Starts during puberty
Starts during embryonic development
Continuous process and goes until death
Discontinuous process and stops at menopause
Cytokinesis splits cytoplasm equally
Cytokinesis splits cytoplasm unequally
Mechanisms to Prevent Polyspermy
Sperm’s head contains acrosome, releasing enzymes to digest zona pellucida. When the sperm interacts with the egg’s surface, the acrosome releases the enzymes. The enzymes create a path through the zona pellucida, allowing the sperm to penetrate. Once the sperm enters the egg, the zona pellucida undergoes structural changes to make itself impenetrable to other sperm
As soon as sperm’s membrane fuses with egg’s membrane, a change in egg’s membrane’s electrical potential occurs. This creates a positive charge which repels other positively charged sperm to block them from fusing with the egg. The egg’s cytoplasm undergoes cortical reaction, where calcium ions get released which trigger cortical granules to activate to harden the zona pellucida, forming an impenetrable barrier
Role of HCG and Pregnancy Tests
HCG stimulates corpus luteum to continue producing progesterone for maintaining the endometrium to keep pregnancy healthy
A pregnancy test uses monoclonal antibodies specialized to bind specifically to HCG. HCG is present in the mother’s urine, and the test strip is placed in urine. If HCG is present in the urine, it will bind to the monoclonal antibodies which results in a color change, causing a band to appear on the test strip indicating a positive pregnancy test
HCG Site of Production and Role
Site of production is embryo (blastocyst) or placenta
Prevents degeneration of corpus luteum
Stimulates corpus luteum to grow and secrete progesterone to maintain endometrium
Progesterone & Estrogen Site of Production and Role
Site of production is ovary during early pregnancy and placenta once it has formed (mid pregnancy)
Maintains endometrium in thickened conditions
Function of Placenta
Secretes estrogen and progesterone to maintain uterine lining
Facilitates exchange of materials between mother and fetus
Allows antibodies to pass to fetus
Prevents blood mixing
Umbilical Cord
Connects placenta to fetus
Umbilical arteries carry CO2 to placenta, while veins carry O2 and more glucose to the fetus
Amniotic Sac and Fluid
A bag that forms around the fetus which secretes amniotic fluid and prevents entry of pathogens
Supports and protects fetus from mechanical shock, allows it to move, and provides the fetus a sterile environment
Progesterone Production in Pregnancy
After ovulation, the empty follicle in the ovary transforms into corpus luteum, which produces progesterone to maintain healthy endometrium in preparation for blastocyst implantation
As the placenta develops, the placenta takes over progesterone production around the 8th week of pregnancy to ensure a continuous supply of progesterone throughout pregnancy
Role of Progesterone in Pregnancy
Maintains healthy endometrium
Keeps the uterus relaxed and prevents premature contractions, and suppresses production of oxytocin to prevent contractions
Suppresses the immune system to prevent mother’s body from rejecting the fetus
Transition to Childbirth and Contractions
At the end of pregnancy, progesterone levels drop while estrogen levels rise
The rise in estrogen levels initiates uterine contractions which causes baby’s head to move to the cervix
Contractions stimulate stretch receptors in cervix which then signal the brain to release oxytocin from the posterior pituitary gland
Oxytocin causes uterine contractions which stimulates stretch receptors to cause higher secretion of oxytocin thus creating positive feedback loop
Frequent uterine contractions cause the cervix to relax thus dilating it
Baby’s head gets pushed out of the cervix and vagina along with the rest of the body after that
Umbilical cord is cut and contractions continue to push out placenta
