Biology - Chapter 12: Reproduction and Developmental Biology Flashcards
Germ cells
- produce gametes via meiosis
- male spermatogonia, female oogonia
Spermatogenesis
- Spermatogonia undergo two meiotic divisions to become spermatids and differentiate into sperm
- Seminiferous tubules –> epididymis –> vas deferens –> ejaculatory duct –> urethra –> penis
Seminal Vesicle
- secrete fructose (nutrients for ATP)
- viscous mucus (cleans and lubricates urethra)
- prostaglandins (cause urethral contractions which propels sperm)
Prostate Gland
-alkaline secretions to counteract uterine acidity
Bulbourethral Gland
-viscous mucus (cleans and lubricates urethra)
FSH in Males
-stimulates sperm development in seminiferous tubules
LH in Males
-stimulates Leydig cells to produce testosterone
Testosterone
- Matures sperm
- gives rise to secondary sex characteristics
Ovary
-Produces eggs (ovum, ova) that travel through fallopian tube to uterus
Uterus
- Provides ideal environment for fertilized egg to implant and develop
- 3 layers: perimetrium, myometrium, endometrium (inner, lined with mucus)
Cervix
-Narrow opening of uterus leading to vagina
Oogenesis
1) Many oogonia produced, small fraction remains and differentiates into primary oocytes (begin meiosis but arrested in prophase I until puberty)
2) At puberty: one egg per month ovulates, completing meiosis I, producing a secondary oocyte (meiosis II) and polar body
3) If fertilization occurs: meiosis II is completed
4) At the end of meiosis II: 2-3 polar bodies and 1 oocyte
FSH in Females
-stimulates follicles in ovary to develop as well produce estrogen and progesterone
LH in Females
-stimulates ovulation of egg, corpus luteum formation, which produces estrogen and progesterone
Estrogen and Progesterone
- Menstrual cycle and reproduction
- Give rise to female secondary sex characteristics
Menstrual Cycle Phases
1) Follicular Phase
2) Ovulation
3) Luteal Phase
4) Implantation/No Implantation
Follicular Phase
- hypothalamus releases gonadotropin-releasing homrone (GnRH)
- -> anterior pituitary releases LH and FSH
- -> FSH binds to ovaries and induces follicles to develop
- -> developing follicles release estrogen
- -> endometrium thickens
- -> rapid LH spike –> ovulation
Ovulation Phase
- Egg is released from Graafian follicle
- -> fimbriae on oviduct catches egg, cilia sweep egg into oviduct –> egg travels down oviduct, awaiting sperm fertilization
Luteal Phase
- follicle develops into corpus luteum (maintained by FSH and LH)
- -> corpus luteum produces progesterone and estrogen
- -> uterine lining thickens (prepares for implantation)
If No Implantation occurs…
- LH and FSH levels drop
- -> corpus luteum can no longer be maintained
- -> progesterone and estrogen levels drop
- -> endometrium sloughs off (menstruation)
If Implantation occurs…
- outer layer of placenta produces human chorionic gonadotropin (HCG)
- -> maintains corpus luteum
- -> progesterone and estrogen levels maintained
- -> endometrium remains (no menstruation)
Positive Feedback Loops
- stimulate a pathway to increase production
- Lactation
- Childbirth
Negative Feedback Loops
- inhibit a pathway to decrease production
- GnRH release stimulates FSH and LH, stimulates testosterone, testosterone inhibits GnRH release, lowering FSH and LH
- same occurs with estrogen and progesterone in menstrual cycle
Fertilization
- Joining of a haploid sperm and a haploid egg to form a diploid zygote
1) Capacitation
2) Acrosomal reaction
3) Polyspermy Block
4) Completion of Meiosis II for the Secondary Oocyte
5) Zygote formation
Capacitation
- Final maturation step for sperm prior to fertilization
- Triggered by secretions in uterine wall
- Destabilizes sperm plasma membrane proteins and lipids which results in preparation of sperm tip and hyperactive state
Acrosomal reaction
- Recognition process between sperm and egg before fusion
- Ensures same-species fertilization
- Sperm eats away into egg
Polyspermy Block
- Prevents polyploidy by inhibiting polyspermy (multiple sperms penetrating egg)
- Fast block: occurs first, prevents sperm binding
- Slow block: zona pellucida impenetrable
Completion of Meiosis II for the Secondary Oocyte
- During meiosis II, egg is arrested in metaphase
- After penetration, meiosis in the secondary oocytee continues, resulting in a haploid oocyte and polar body
Zygote formation
- Monozygotic twins: identical twins, one zygote splits. Two embryos with identical genetic materials
- Dizygotic twins: fraternal twins, two separate eggs fertilized by two separate sperm (different genetic material)
Cleavage
- rapid cell division without changing the total mass of the cell
- results in smaller cells called blastomeres
Axis of Cleavage
- Radial cleavage: cells alligned in vertical axis (deuterostomes)
- Spiral cleavage: misaligned cells, deviate from axis (protostomes)
Fate of Cells
- Determinate cleavage: blastomeres have decided fate
- Indeterminate cleavage: blastomeres do not have pre-set fate
Evenness of Embryo Division
- Holoblastic cleavage: throughout entire embryo, evenly divides embryo, in animals with little yolk (humans, sea urchins, except froggos)
- Meroblastic cleavage: partial cleavage, emrbyo not evenly divided, in animals with LOTS of juicy yolk (birds, fish, reptiles), exhibits polarity
Morula
- ball of blastomeres
- forms at 12 - 16 cell stage
Blastula stage
- hollow cavity
- forms at 128 ceell stage
- blastocoel is hollow, fluid filled cente
Blastocyst stages
- cells of blastula divide and differentiate to form
1) Trophoblast (outer ring of cells)
2) Inner Cell Mass (forms embryo)
Trophoblast
- outer ring of cells in blastocyst
- forms extraembroynic membranes (amnion, yolk sac, chorion, allantois): supports embryo
- implants embryo in uterus
- produces HCG (maintains corpus luteum and endometrium)
Inner Cell Mass
- forms embryo
- differentiates into two layers (bilaminar stage):
1) Hypoblast: partially contributes to yolk sac, degenerates via apoptosis
2) Epiblast: contributes to MAIN EMBRYO, allows for gastrulation to occur
Gastrulation
- formation of a trilaminar embryo
- Epiblasts invaginate inwards through primitive streak forming 3 germ layers: endoderm, mesoderm, ectoderm
Archenteron
- center cavity
- formed by blastopore
Ectoderm
- outer germ layer
- forms: CNS/PNS, ear, eye, nose, skin, enamel of teeth, adrenal medulla
Mesoderm
- middle germ layer
- forms: bone and skeleton, muscle, cardiovascular system, gonads, adrenal cortex, spleen, notochord
Endoderm
- inner germ layer
- epithelial lining of digestive respiratory, and excretory systems, PLTT( pancreas, liver, thyroid/para, thymus)
Organogenesis
-Formation of new organs
Neurulation
- nervous system development:
1) Neural plate development
2) neural fold/neural groove appears
3) neural tube formation
4) neural tube differentiates into CNS
Totipotent
-stem cell can become any cell
Pluripotent
-stem cell can become any of the 3 germ layers
Multipotent
-stem cell can only differentiate to specific tissue types
Amnion
- Innermost layer
- secretes amniotic fluid (water cushion, protects embryo)
Chorion
- Outermost layer
- Placental mammals: forms fetal half of the placenta
- Egg-laying animals: membrane for gas exchange underneath egg shell
Allantois
- sac that buds off of the archenteron
- stores waste for disposal
- Placental mammals: transports waste to placenta, becomes umbilical cord, forms urinary bladder
- Egg-laying animals: initially stores uric acid, later fuses with chorion
Yolk sac
- contains yolk (intraembryonic, provides nutrients)
- Placental mammals: transient function until placenta develops, first side of blood cell formation
- Egg-laying animals: provides nutrients
Factors Influencing Development
1) Embryonic Induction
2) Homeotic genes
3) Egg cytoplasm determinant
4) Apoptosis
Embryonic Induction
- organizers
- secrete chemicals that influence what neighboring cells become in the future
Homeotic genes
- Master controller
- turning different gene expressions on/off
- Homeobox is a common sequence of ~180 nucleotides that is crucial in animal development
Egg Cytoplasm Determminant
-If egg cytoplasm is unevenly distributed, an axis is created, influencing how embryo divides during cleavage
Apoptosis
- Programmed cell death important for normal development of fetus
- e.g. removing webbing between fingers and preventing cancers
