Cell Bio Gametogenesis (11)

weeks 0-8; type of prenatal (before birth) development period

weeks 9-38; type of prenatal (before birth) developmental period

specialized germ cells from the male and the female; haploid as a result of meiosis

• formation of fully-developed gametes
• in males this starts in puberty
• in females it starts before birth and ENDS at fertilization

the first two weeks of pregnancy

all of the somatic cells (all cells in the body EXCEPT for the gametes)

• primary oocytes are arrested in prophase of meosis I from before birth until puberty
• - they don't proceed to meiosis II until ovulation

• In females there are unequal meiotic divisions that produce a primary oocyte and a small polar body --> then another unequal meiotoc division that produces a secondary oocytes and a second small polar body
• In males, meiotic divisions are all equal and all meiotic derivatives produce spermatids

• 1) Acrosome: specialized golgi derived structure; found in the head; enzyme filled
• 2) Mid-piece: houses mitochondria to provide energy for flagellum (tail)
• 3) flagellum tail

(4N; 92; tetraploid) formed from spermatogonial stem cells dividing by mitosis; are initially diploid and are undergo meiosis

(2N; 46; diploid) primary spermatocytes that have undergone meosis I; they undergo a meiosis II which results it HAPLOID spermatids

four spermatids

• the process by which spermatids are remodeled to form mature sperm (spermatozoa)
• elongation, tail development, cytoplasm shed

line the periphery of seminiferous tubules; support and nurture the germ cells and regulate spermatogenesis (analogous to zona pellucida)

make testosterone (analogous to theca cells)

After the zona pellucida and the single layer of follicle cells form

when the primary oocyte enlarges during puberty; follicular epithelial cells become cuboidal and then columnar, forming the primary follicle

• Hypothalamus-Pituitary-Ovary Axis refers to the effects of the hypothalamus, pituitary gland, & gonads as a whole because they often behave in cooperation

• • the hypothalamus produces GnRH
• • the anterior pituitary produces LH & FSH
• •the gonads produce estrogen and testosterone

released from the hypothalamus and targeted for the anterior pituitary; causes the synthesis and secretion of LH and FSH

released from the anterior pituitary and targeted for the ovary; stimulates ovarian follicle growth, differentiation, and steroidogenesis

stimulates 4-12 ovarian (primordial) follicles to grow, differentiate, and secrete estrogen (as well as other steroid hormones)

released from the anterior pituitary and targeted for the ovary; stimulates ovulation, corpus luteum formation and steroidogenesis

stimulates ovulation, corpus luteum formation, and steroid hormone production, like progesterone

released from the follicle cells in the ovary and targeted for the uterus, vagina, oviduct, & mammary glands; controls growth & differentiation of targets

released from the follicle cells in the ovary and targeted for the uterus, vagina, oviduct, & mammary glands; controls growth & differentiation of targets

a highly vascular tissue that consists of spindle-shaped stromal cells similar to fibroblasts and arranged in a characteristic whorled texture

develops from ovarian follicle during luteal phase of the menstrual cycle after a secondary oocyte from the follicle is released during ovulation; involved in the production of progesterone

regressed form of the corpus luteum; may persist as a scar on the surface of the ovary

epithelial cells that have lots of cytoplasmic ridges directly connecting them to the oocyte; they're an important source of nutrients for the oocyte

GnRH (gonadotropin releasing hormone)

• the number of FSH receptors on it's membrane surface; the more receptors, the faster and larger the follicle will get
• a dominant follicle continues to mature and is ultimately ovulated (takes 2-3 menstrual cycles to complete)
• remaining developing follicles degenerate via apoptosis

• pituitary makes FSH
• stimulates estrogen synthesis from ovarian follicle
• once a threshold is reached, it signals the PITUITARY to rapidly synthesize & secrete LH
• FSH --> threshold estrogen --> LH surge

the trigger for ovulation and release of the primary oocyte from prophase of Meiosis I

• It releases the first polar body and then enters Meiosis II where it is arrested at METAPHASE (II)
• arrested at metaphase II it's called a mature, secondary oocyte

• prostaglandins - lipid paracrine hormone
• the smooth muscle-like THECA cells contract and expel the secondary follicle

the zona pellucida & one or more layers of follicle cells called the corona radiata

within 12-24 hours

caused by non-disjunction or translocation of chromosome 21

process of oocyte death; over 99% of oocytes are apoptosed, with under .01% actually ovulated

• Thalidomide birth defects
• Rubella (German Measles) birth defects
• Down's Syndrome (Trisomy 21)
• Angelman Syndrome (Chromosome 15 deletion) Prader-Willi syndrome (Chromosome 15 deletion) Premature menopause (accelerated oocyte atresia) Egg donation
• Infertility
• Effect of maternal age on birth defects

the abdominal pain associated with ovulation in some women caused by slight bleeding into the peritoneal cavity (abdomen)

• mittelschmerz (abdominal pain)
• a better indicator is a slight drop in basal body temperature followed by a gradual rise after ovulation

• a menstrual cycle where the ovaries don't release an oocyte therefore ovulation doesn't happen
• often caused by inadequate release of FSH and LH from the anterior pituitary

• FSH, LH (gonadotropins) or clomiphene citrate
• a side effect of gonadotropin ovulation induction is a 10-fold increase in the incidence of multiple pregnancies

• spontaneous end of a pregnancy before fetal viability
• almost 1/5 spontaneous abortions are caused by insufficient progesterone production
• some women who have had multiple miscarriages are given progesterone

prevents ovulation because increased estrogen levels (with or without increased progesterone levels) act to negatively feedback on the hypothalamus and/or the AP to inhibit GnRH, FSH, and/or LH

• sperm swim up the cervical canal and are drawn up through the uterus & fallopian tubes by muscular contractions/ciliary movements
• females do 2/3 of the work
• makes do 1/3 of the work

• when there's contact between the sperm and the secondary oocyte plasma membrane
• after this occurs the oocyte finishes meiosis II and becomes a mature oocyte

• the ampulla (out-pouching of fallopian tube)
• the fallopian tube is therefore what transfers the zygote to the body of the uterus

• almond shaped glands that produce estrogen and progesterone, hormones responsible for secondary female sex characteristics and pregnancy regulation
• they produce and maintain oocytes

• it becomes the corpus luteum of pregnancy, fortified by increased progesterone production
• this corpus luteum of pregnancy is functional for 20 weeks
• after this 20 weeks the placenta makes enough estrogen & progesterone to support the pregnancy

• human chorionic gonadotropin (hCG) prevents the corpus luteum from degrading
• hCG comes from the implanted blastocyst (embryo)

progesterone insufficiency

• approximately 200-600 million
• usually 100 million/mL
• ejaculate volume ~ 2-6 mL

• less than 10 million/mL
• motility levels below 20% (even if the count is normal) are also associated w/ infertility

prostaglandins from the SEMEN

• 1) capacitation
• 2) acrosome reaction
• 3) eureka moment - oozyte and sperm PMs fuse
• 4) block of polysperm (Corticol reaction)

• freshly ejaculated sperm are unable to fertilize until they undergo capacitation, a process where the glycoprotein coat and seminal proteins are removed from the acrosome surface (takes about 7 hours)
• in vivo this step typically occurs in the female reproductive tract after ejaculation

• begins with the sperm penetrating the zona pellucida of the oocyte
• ZP3 is the sperm receptor on the oocyte and when it detects sperm it initiates the reaction
• the acrosome membrane of the sperm perforates due to the action of angiotensin converting enzyme (ACE)
• the acrosome membrane fuses with the sperm membrane
• this fusion causes release of hyaluronidase and proteases from the sperm that break down and permit sperm penetration through the zona pellucida

• a glycoprotein receptor in the zona pellucida that binds sperm and initiates the acrosome reaction
• it's unique among species, thus it is the protein that determines specieality

• enzyme derived from the acrosome that perforates the sperm's acrosome membrane
• this perforation releases enzymes that break down the matrix and allow the sperm to penetrate through the follicle and zona pellucida

• oocyte cortical granule contents are released and they modify the zona pellucida through cross-linking and proteolysis, making it impenetrable to other sperm (mostly done by lysosomal enzymes from granules)
• called the block to polyspermy and it occurs within seconds to minutes of sperm penetration

a calcium pulse within seconds of penetration that gets repeated across the oocyte membrane

• oocyte chromosomes decondense and form a pronucleus and a second polar body
• the newly arrived sperm nucleus enlarges and forms the male pronucleus

all the chromosomes replicate

• the head and tail of sperm to enter the cytoplasm of the oocyte
• the sperm plasma membrane is left behind

• the centriole that used for building the zygote's mitotic spindles
• that and male DNA are the only contributions the sperm makes to the zygote, everything else is maternally derived

• when maternal and paternal chromosomes intermingle during metaphase of the FIRST zygotic division
• the pronuclear membranes break down, chromosomes condense, and line up for the first metaphase
• approximately 24 hours after fertilization began

• 1) the secondary oocyte is stimulated to complete meiosis II
• 2) a normal diploid number of chromosomes are restored
• 3) determines the SEX of the embyro

• 1) parthenogenesis
• 2) polyspermy
• the two p's

• embryonic development without sperm
• artificial induction of oocyte cleavage is possible in some animals, but not in humans
• parthenos "virgin" + genesis "beginning, birth"

• an egg that has been fertilized by more than one sperm
• several sperm usually begin to penetrate the zona pellucida, but only one enters normally
• although rare, cases of dispermy result in a TRIPLOID zygote, which account for 20% of chromosomally-abnormal spontaneous abortions (SABs)

• 1) Menstrual Phase: days 1-5
• 2) Proliferative Phase: days 5-14
• estrogen levels rise, stimulate re-growth of endometrium functional layer
• 3) Secretory Phase: days 14-27
• estrogen levels peak then fall
• progesterone levels are high
• if no fertilization occurs, corpus luteum degenerates, estrogen & progesterone levels fall, and the secretory endometrium enters the ischemic phase
• 4) Ischemic Phase: days 27-28
• progesterone & estrogen levels fall rapidly and the functional endometrium becomes ischemic