Chapter 2: Transport of Gametes and Fertillization

Question 1

at what stage in meiosis do the first and second meotic blocks occur?

Answer 1

first block: prophase I

second block: metaphase II

Question 2

stigma

Answer 2

the apex of the protrusion that is formed when the follicle bulges from the surface of the ovary

Question 3

stimulus for ovulation

Answer 3

LH surge from anterior pituitary that occurs at the midpoint of the menstrual cycle

Question 4

results of LH surge

Answer 4

follicle reorganizes program of gene expression from one directed toward development of follicle to one producing molecules that set into motion the processes of follicular rupture and ovulation

local blood flow increases resulting in local edema; plasma proteins leak into tissues

cumulus cells secrete hyaluronic acid that loosens cells surrounding egg

Question 5

matrix metalloproteinases

Answer 5

a family of lytic enzymes that degrade components of extracellular matrix; local production occurs as result of release of certain pharmacologically active substances produces an inflammatory reaction that ultimately results in rupture of outer follicular wall about 28 to 36 hours after LH surge

Question 6

result of follicular rupture

Answer 6

cumulus oophorus detaches from granulosa and egg released from ovary expulsion of both antral fluid and ovum from ovary;

Question 7

what is expelled from ovary at ovulation?

Answer 7

ovum

zona pellucida

two-three-cell thick corona radiate

sticky matrix containing surrounding cells of cumulus oophorus

Question 8

corona radiata

Answer 8

adhering cumulus cells after ovulation has occurred

Question 9

mittelschmerz

Answer 9

pain some women feel at the time of ovulation possibly due to slight bleeding from ruptured follicle

Question 10

changes in uterine tubes prior to ovulation

Answer 10

more high ciliated and smooth muscle activity in the tube and its suspensory ligament increases as the result of hormonal influences

Question 11

capture of the egg by uterine tube

Answer 11

fimbriae move closer to ovary, sweep rhythmically over its surface; adhesive interactions between egg complex and ciliary surface of the tube

Question 12

transport of egg in uterine tube

Answer 12

egg is transported toward the uterus mainly as result of contractions of smooth musculature of the tubal wall

takes 3 to 4 days whether or not fertilization occurs

Question 13

immotile cilia syndrome

Answer 13

women whose tubal cilia do not function; many of these women are still fertile, so cilia action not obligatory to move egg

Question 14

tubal fluid

Answer 14

combination of secretions by the tubal epithelial cells and transudate from capillaries just below the epithelium

egg is in this during tubal transport

Question 15

slow transport and fast transport of egg

Answer 15

slow transport occurs in ampulla and more rapid transport through isthmus and into uterus

egg is temporarily prevented from entering isthmic portion of tube, under influence of progesterone the egg is allowed to pass

Question 16

sperm transport in male reproductive tract

Answer 16

transport closely connected with structural and functional maturation

after spermiogenesis in seminiferous tubules, sperm are morphologically mature but nonmotile and incapable of fertilizing egg;

transported via testicular fluid to the caput (head) of epididymis through rete testis and efferent ductules (propelled by seminiferous tubules and assisted by smooth muscle contraction and ciliary currents in ductules)

in epididymis, changes in glycoproteins in the plasma membrane of the sperm head

Question 17

sperm transport in male reproductive tract: ejaculation

Answer 17

spermatozoa rapidly pass through ductus deferens, become mixed with fluid secretions from seminal vesicle and prostate gland

Question 18

seminal vesicles

Answer 18

provide fructose to the semen (main energy source)

Question 19

prostate gland

Answer 19

provides citric acid, acid phosphatase, zinc, magnesium ions

Question 20

semen

Answer 20

contains 40-250 million sperm, mixed with seminal vesicle fluid (60%) and prostate secretion (30%) pH: 7.2-7.8

Question 21

sperm transport in female reproductive tract

Answer 21

begins in upper vagina and ends in ampulla region of uterine tube

when in upper vagina, confronted with harsh acidic environment that normally is bactericidal

prostate provides a buffering effect, briefly raising pH from 4.3-7.2

cervical canal and cervical mucus block the sperms path

Question 22

cervical mucus

Answer 22

composition and viscosity vary considerable throughout the month; not readily penetrable

Question 23

cervical mucin

Answer 23

makes up cervical mucus; a glycoprotein with a high carbohydrate composition

Question 24

E mucus

Answer 24

during days 9-16 of cycle, water content of cervical mucus increases, facilitates the passage of sperm through cervix at the time of ovulation

Question 25

G mucus

Answer 25

after ovulation, under the influence of progesterone, watery cervical mucus production ceases, a new type of sticky mucus, which has much decreased water content, is produced; almost completely resistant to sperm penetration

Question 26

two modes of sperm transport in cervix: rapid transport

Answer 26

initial rapid transport relies on muscular movement of female reproductive tract; hinges on female orgasm; early arriving sperm not as capable of fertilization

Question 27

two modes of sperm transport in cervix: slow transport

Answer 27

involves the swimming of spermatozoa through cervical mucus, their storage in cervical crypts and final passage through cervical canal

Question 28

sperm in uterine tubes

Answer 28

only several hundred sperm reach uterine tubes spermatozoa collect in isthmus and bind to epithelium for about 24 hours

Question 29

capacitation

Answer 29

when bound to isthmus, sperm undergo this reaction because of secretions of the tube; (1) removal of cholesterol from surface of sperm; (2) removal of many of the glycoproteins that were put on the surface while in epididymis required for sperm to be able to fertilize the egg

Question 30

hyperactivation of sperm

Answer 30

after capacitation, sperm undergo period of hyperactivation to break free of bonds that held them to the tubal epithelium; assists sperm in penetrating zona pellucida and corona radiata; only small number of sperm released at one time

Question 31

meeting of sperm and egg

Answer 31

sperm make their way up while egg moves down; peristaltic contractions divide the uterine tube into compartments within a given compartment, the gametes are caught up in a churning motion that brings them together

fertilization occurs in the ampullary portion of the uterine tube

Question 32

chemoattractive agent of egg?

Answer 32

possible that egg might be releasing certain chemicals that the sperm are able to pick up; mammalian sperm posses odorant receptors and respond behaviorally to certain chemically defined odorants

known to respond to certain temperature gradient

only capacitated sperm have ability to react to chemical or thermal stimuli

Question 33

changes in follicle following ovulation

Answer 33

after ovulation, basement membrane that separate the granulosa cells from the theca interna cells breaks down, allowing theca blood vessels to grow into cavity

Question 34

luteinization

Answer 34

granulosa cells undergo a series of major changes in form and function after ovulation

Question 35

granulosa lutein cells

Answer 35

granulosa cells 30-40 hours after LH surge begin secreting large amounts of progesterone and some estrogen

terminally differentiated

Question 36

corpus luteum

Answer 36

follicle continues to enlarge following rupture; because of yellow color, known as corpus luteum

granulosa lutein cells continue to secrete progesterone for ten days even though at this point they have stopped dividing

Question 37

luteolysis

Answer 37

in the absence of fertilization and hormonal stimulus from embryo, corpus luteum begins to deteriorate late into menstrual cycle

involves preprogramming luteal cells to apoptosis and uterine luteolytic factors such as prostaglandins F2

regression of corpus luteum and reduction of progesterone causes hormonal withdrawal that results in the degenerative changes in endometrial tissues during last days of menstrual cycle

Question 38

corpus albicans

Answer 38

granulosa lutein cells begin to deteriorate and are replaced with collagenous scar tissue; looks white now

Question 39

chorionic gonadotropin

Answer 39

if fertilization occurs, production of this hormone by placental tissue maintains the corpus luteum in a functional condition and causes increase in its size and hormone production

Question 40

corpus luteum of pregnancy

Answer 40

composed primarily of theca lutein cells

remains functional for the first few months of pregnancy

after second month, placenta produces enough estrogen and progesterone to maintain pregnancy on its own

Question 41

penetration of corona radiata

Answer 41

outer layer of egg complex encountered by the sperm is the corona radiata and some leftover cells from cumulus oophorus

corona radiata is highly cellular layer with an intercellular matrix consisting of proteins and a high concentration of carbohydrates especially hyaluronic acid

sperm accomplishes penetration through swimming motion and hyaluronidase that is emanating from the sperm head

Question 42

zona pellucida

Answer 42

consists of 4 glycoproteins, ZP1, ZP2, ZP3, ZP4

ZP2 and 3 combine to form basic units that polymerize into long filaments which are periodically cross linked by ZP1 and 4

after penetrating corona radiata, sperm bind to zona pellucida by binding to sialic acid molecule which is the terminal part of a sequence of four sugars at the end of O-linked oligosaccharides attached to the polypeptide core of ZP3

ZP3 are basically sperm receptors on zona pellucida

differences in sperm binding regions of ZP3 prevent interspecies fertilization

Question 43

acrosomal reaction

Answer 43

occurs upon binding to zona pellucida

fusion of parts of the outer acrosomal membrane with the overlying plasma membrane and the pinching off of fused parts as small vesicles;

results in liberation of multitude of enzymes stored in the acrosome stimulated by ZP3 molecules acting through G proteins in the plasma membrane on the sperm head;

a large segment of the polypeptide chain of ZP3 must be present to induce the acrosomal reaction

massive influx of calcium through plasma membrane of sperm head, followed by influx of sodium and efflux of hydrogen which increases intracellular pH

enzymes help sperm make it through the zona pellucida

Question 44

postacrosomal plasma membrane

Answer 44

after acrosomal reaction, inner acrosomal membrane forms the outer surface covering most of the sperm head; fuses with the remaining postacrosomal plasma membrane to maintain membrane continuity around sperm head

Question 45

penetration of zona pellucida

Answer 45

only possible after acrosomal reaction

accomplished through combination of mechanical propulsion by movements of the sperm’s tail and digestion of a pathway through the action of acrosomal enzymes

Question 46

acrosin

Answer 46

most important of the acrosomal enzymes; serine proteinase that is bound to the inner acrosomal membrane

Question 47

perivitelline space

Answer 47

space between the egg’s plasma membrane and the zona pellucida

now sperm can make contact with plasma membrane of egg

Question 48

binding and fusion of spermatozoon and egg

Answer 48

1. spermatozoon binds to and then fuses with the plasma membrane of egg; binding occurs when the equatorial region of the sperm head contacts the microvilli surrounding the egg; on sperm, FERTILINS and CYRITESTIN proteins bind to ALPHA-SIX INTERGRIN and CD9 PROTEIN molecules on the surface of the egg; integrin mediates the actual fusion and brings membranes into continuity
2. contents of the spermatozoon (head, midpiece and usually tail) sink into the egg, whereas the sperms plasma membrane, which is antigenically distinct from that of the egg, becomes incorporated into the egg’s plasma membrane; sperm contributes the centrosome, which is required for cell cleavage

Question 49

polyspermy

Answer 49

entrance of other spermatozoa into the egg after a spermatozoon has already fused with the egg

Question 50

fast block to polyspermy

Answer 50

rapid electrical depolarization of plasma membrane of eg from -70 to +10 mV within 2 to 3 seconds after fusion

prevents other spermatozoa from adhering to egg’s plasma membrane

lasts only several minutes, but it is sufficient for egg to mount permanent slow block

Question 51

slow block to polyspermy

Answer 51

successive waves of calcium ions pass through cytoplasm of the egg; first set of waves spreads from site of sperm-egg fusion is involved in completion of second meiotic division of the egg

later waves initiate the recruitment of maternal RNAs in the egg and act on cortical granules as they pass them by

cortical granules then fuse with plasma membranes and release their contents (hydrolytic enzymes and polysaccharides) into perivitelline space

polysaccharides causes the perivitelline space to swell, lifting zona pellucida from egg membrane

changes to sperm receptors on egg surface cause the egg itself to become refractory to penetration by other spermatozoa

Question 52

metabolic activation of the egg

Answer 52

sperm introduces into egg a soluble factor which stimulates a pathway leading to release of pulses of calcium ion within cytoplasm

calcium ion stimulates rapid intensification of egg’s respiration and metabolism through an exchange of extracellular sodium for intracellular hydrogen;

rise in intracellular pH and increase in oxidative metabolism

Question 53

decondensation of sperm nucleus

Answer 53

thanks to disulfide bonds formed among protamine molecules, sperm DNA is extremely tightly bound

after sperm comes into egg, it becomes permeable to egg cytoplasmic factors that reduce disulfide cross-links to sulfhydryl groups by reduced glutathione in ooplasm;

protamines are rapidly lost and as chromatin spreads out in sperm nucleus it becomes

pronucleus remodeling takes 6 to 8 hours; histones begin to associate with chromosomes

Question 54

completion of meiosis

Answer 54

after sperm penetrates egg, egg completes the last division and releases as second polar body into the perivitelline space

nucleus of egg moves toward the cortex as a result of the action of myosin molecules acting on a network of actin filaments that connect on pole of the mitotic spindle to the cortex

cytoplasmic factors control growth of male and female pronuclei

DNA replication occurs in the developing haploid pronuclei and each chromosome forms two chromatids;

when pronuclei come into contact, membranes break down and chromosomes intermingle; become organized around the mitotic spindle, derived from centrosome of sperm

Question 55

what is accomplished by fertilization?

Answer 55

1. stimulates the egg to complete the second mitotic division
2. restores the zygote to the normal diploid number of chromosomes
3. genetic sex of the future embryo is determined
4. through mingling of maternal and paternal chromosomes, zygote is a genetically unique product of chromosomal reassortment
5. metabolic activation of the egg, which is necessary for cleavage and subsequent embryonic development to occur