BIOL 66- Chapter 20: Reproduction

General terminology- Gonads

testis and ovary

General terminology- Gametes

sperm and egg

General terminology- Gametogenesis

spermatogenesis, production of sperm; oogenesis, production of egg

General terminology- Gonadotropic hormones

FSH, follicle-stimulating hormones; LH, luteinizing hormone

General terminology- Gonadal steroids

testosterone, estradiol, and progesterone

General terminology- Meiosis

chromosomes replicate and recombine, followed by two successive cell divisions resulting in 4 daughter cells, each with half the number of chromosomes (haploid) of the parent cell. Occurs in gonads and creates gametes only.

General terminology- Mitosis

Chromosomes replicate, followed by cell division that results in 2 daughter cells with the same number of chromosomes (diploid) of the parent cell. Daughter cells are genetically identical. Creates all body cells besides gametes.

Sexual Reproduction

in sexual reproduction, genes from two individuals are combined in random and novel ways with each new generation; with fertilization of ovum

Sexual Reproduction- Number of chromosomes per cell

in each cell, there are 23 pairs of chromosomes, with one chromosome from each parent in each pair (46 total in each cell)

Sexual Reproduction- Where is DNA located in cell

individuals DNA is contained within the 46 chromosomes

Sexual Reproduction- All chromosomes, except sex chromosomes

each pair contains two homologous chromosomes, meaning they look like each other and contain similar genes; similar appearance and similar instruction

Sexual Reproduction- Diploid

cells that contains 46 chromosomes (23 pairs)

Sexual Reproduction- Haploid

Cells that contains 23 chromosomes

Sexual Reproduction- Puberty and Meiosis

at puberty, meiosis in the gonads results in gametes (sperm, egg); each gamete is unique and has 23 chromosomes (haploid)

Sexual Reproduction- During Fertilization

during fertilization, sperm cell and egg cell fuse to produce a fertilized egg (zygote), which is diploid

Sexual Reproduction- Mitotic in Zygote

Mitotic cell division underlie the growth of the zygote into an adult. In mitosis, two genetically identical diploid “daughter” cells are produced

Sexual Reproduction- summary path of offspring

Adult Male (testes) and Adult Female (ovaries) → Meiosis, Sperm (23) and Ovum (23) → Fertilization, Zygote (46) → Growth by Mitosis (offspring)

Sex Determination- pairs 1-22

autosomal (numbered) chromosomes; they’re homologous

Sex Determination- Pair 23

sex chromosomes; not homologous

Sex Determination- Sex Chromosomes determination

X from mother, X or Y from father; Female= XX, Male= XY

Reproductive Endocrinology

During puberty, gonads secrete more sex steroid hormones, due to stimulation by gonadotropic hormones (FSH, LH) from anterior pituitary gland

Reproductive Endocrinology- Hormones

testosterone, estrogen, and progesterone

Reproductive Endocrinology- Three-hormone-sequence

GnRH → FSH and LH → gonads secrete sex hormones and undergo gametogenesis

Reproductive Endocrinology- Secretion in Females

secretion of gonadotropins and sex hormones in female is cyclical (menstrual cycle)

Male Reproductive System- Semen

Semen is composed of sperm and fluids from the testes, the epididymus, the seminal vesicles, and the bulbourethral and prostate glands; fluid with lots of sperm

Male Reproductive System- Testes: Seminiferous tubules

Sertoli cells: spermatogenesis and secretion of inhibin (inhibits secretion of FSH)

Male Reproductive System- Testes: Leydig or interstitial cells

between tubules; secretion of testosterone

Male Reproductive System- movement of sperm in testes

sperm move from the tubules into the rete testis, then into the efferent ductules, epididymis, and then into the vas deferens

Male Reproductive System- Accessory Organs: Duct System

epididymis, vas deferens, ejaculatory ducts, urethra; allows semen to leave the body and reach ovum

Male Reproductive System- Accessory Organs: Glands

Seminal vesicles, prostate gland, bulbourethral gland; secrete fluid component of semen, in which sperm is suspended

Male Reproductive System- Accessory Organs: Secondary Sexual Structures

penis, scrotum

Hormonal Control of Male Reproductive Function

FSH stimulates spermatogenesis and secretion of inhibin by sertoli cells in seminiferous tubules, while LH stimulates Leydig cells to secrete testosterone

Testosterone

spermatogenesis; stimulates anabolism → growth of muscles and other structures; increased testosterone secretion during puberty → growth of accessory organs, larynx

Spermatogenesis

64 days; appx 300 million sperm cells produced each day in seminiferous tubules; spermatogonia are in outermost region of seminiferous tubules

Spermatogenesis process

mitosis, first meitotic division, second meitotic division, spermiogenesis

Spermatogenesis process- 1. Mitosis

spermatogonia duplicate via mitosis, one daughter cell becomes primary spermatocytes (2n)

Spermatogenesis process- 2. First meitotic division

primary spermatocytes divides into two identical secondary spermatocytes, each with 23 chromosomes (n) (with 2 identical chromatids per chromosome)

Spermatogenesis process- 3. Second Meitotic Division

results in spermatids (n)

Spermatogenesis process- 4. Spermiogenesis

spermatids transform into spermatozoa (sperm cells)(n)

Seminiferous tubule and Sertoli Cells

Sertoli cells in the tubule wall support spermatogenesis and protect developing sperm in the seminiferous tubules

Female Reproductive System- Spermatozoan and Ovulated egg

a spermatozoan ejaculated into the female reproductive tract must move through the cervix and uterus before it can fertilize an ovulated egg

Female Reproductive System- Ovaries

oogenesis; synthesize and secrete estrogen, progesterone, inhibin; Ovarian cycle

Female Reproductive System- Ovarian (monthly) Cycle

development sequence with ovulation of one ovum and some follicular cells per month

Female Reproductive System- Accessory organs: oviducts, fallopian tubes, uterine tubes;

transport released ovum plus some follicular cells via ciliary action and smooth muscle contractions; usual site of fertilization

Female Reproductive System- Accessory organs: Uterus

usual site of implantation and fetal development; narrows to form cervix, which opens to vagina

Uterine Wall Layer- Perimetrium

outermost layer, connective tissue; includes peritoneum lining the pelvic cavity

Uterine Wall Layer- Myometrium

a thick smooth layer; muscular

Uterine Wall Layer- Endometrium

includes epithelial layers that are sloughed off during menstruation

Female Reproductive System- Accessory organs: Vagina

Path for sperm to ovum

Uterus, Oviducts, and Ovaries

monthly, an ovary releases an ovum that moves from the ovaries into the oviducts, fertilized eggs are implanted in the uterus, where fetal development occurs

Oogenesis and Follicle growth- Primordial follicle

Oogonia (2n) are surrounded by granulosa cells, which secrete hormones; this hollow sphere is called a primordial follicle

Oogenesis and Follicle growth- Primary oocyte/primary follicles

most oogonia die and the rest begin the first meiotic division at 7 months gestation and are called primary oocytes (2n), contained in primary follicles; 2 million at birth, 400,000 at puberty; around 400 ovulate and the rest die

Oogenesis and Follicle growth- First Meiotic Division ends/ secondary oocyte

the first meiotic division finishes as the follicle develops, resulting in a secondary oocyte (n), which gets all of the cytoplasm, and a polar body

secondary oocyte location

this oocyte is in a mature or graafian follicle which contain a fluid-filled cavity called antrum

Oogenesis and Follicle growth- Second Meiotic division starts

second meiotic division starts and is arrested (paused) to be completed upon fertilization; dies if not fertilized

Oogenesis and Follicle growth- Graafian follicle/Ovulation

one graafian follicle develops and is ovulated each month

Follicles- Zona pellucida

the zona pellucida is a thin, gel-like layer around the secondary oocyte. it presents a barrier to fertilization of an ovulated oocyte by sperm.

Follicles- Corona radiata

the corona radiata is comprised of granulosa cells surrounding the zona pellucida

Menstrual cycle- types

28 day ovarian cycle and endometrial cycle

Menstrual cycle- Cyclical variation in hormones

cyclical variations in luteinizing hormone (LH), follicle-stimulating hormone (FSH), progresteron, and estradiol (an estrogen)

Menstrual cycle- Ovulation

occurs at around day 14 of cycle; middle of 28 day cycle; release of ovum into fallopian tube on the way to the uterus, fertilized=baby, not fertilized=menstruation

Menstrual cycle- Menstruation

shedding of epithelium of endometrium if ovulated egg is not fertilized; days 1-4 of cycle

Menstrual cycle- Ovarian Cycle: Follicular phase

day 1-13; development of follicles under influence of FSH; one follicle matured to graafian follicle; increased estradiol secretion from granulosa cells, leads to LH surge (spike) just prior to ovulation

Menstrual cycle- Ovarian Cycle: Ovulation

day 14; LH surge causes wall of graafian follicle to rupture at around day 14; Secondary oocyte is released from ovary and swept by cilia into oviduct, towards uterus

Menstrual cycle- Ovarian Cycle: Luteal Phase

days 15-28; transformation of follicle into corpus luteum (CL, yellow body) due to LH; CL secretes estradiol, progesterone (peaks during this phase)

Menstrual cycle- Ovarian Cycle: Luteal Phase- No Fertilization

if no fertilization, estradiol and progesterone decrease and CL turns into corpus albicans, causing menstruation

Hormonal Changes During Menstrual Cycle

Small increases in secretion of LH and FSH → follicular maturation in the follicular phase and an increase in the synthesis and secretion of ovarian steroid hormones

Hormonal Changes During Menstrual Cycle- LH surge

LH surge → ovulation and luteal phase; high progesterone concentration

Hormonal Changes During Menstrual Cycle- LH decrease

LH decreases → luteolysis

Menstrual Cycle- Endometrial Cycle: Menstrual Phase

days 1-4; as ovarian hormone secretion decreases, uterine blood vessels constrict rhythmically, depriving the tissue of blood; endometrium undergoes necrosis and is sloughed off, resulting in menstrual flow; myometrium contracts as well (cramps)

Menstrual Cycle- Endometrial Cycle: Proliferative Phase

days 5-14; growth and maturation of endometrium under influence of estradiol from the follicle

Menstrual Cycle- Endometrial Cycle: Secretory Phase

days 15-28; increased progesterone and estradiol from CL stimulate endometrial thickening, for implantation. if no implantation, estrogen and progesterone levels drop and shedding occurs

Fertilization

mature sperm stored in epididymus; appx 300 million sperm ejaculate during intercourse; fluid pressure of ejaculate propels sperm into uterus; only around 100 survive to enter each oviduct (acidic vaginal environment, energy requirement of travel) and about 10% can fertilized ovum, Capacitation

Capacitation

ability to fertilized egg; stimulated by high pH of female tract results in whip-like action of trail to propel sperm forward to oocyte; flagellum propels for survival

Fertilization- Where does it occur

fertilization occurs in oviduct, due to short viability and slow transport of egg

Fertilization- Time Window

5 day before and 1 day after ovulation due to sperms ability to fertilize for 4-6 days, and egg viability for 24-48 hours

Fertilization- Acrosome binds to zona pellucida

Acrosome in head of sperm binds with zona pellucida of egg, triggering acrosome reaction

Fertilization- acrosome reaction

alteration of head membrane and release of acrosomal enzymes, to digest through the zona pellucida to the oocyte

Early Development- Zygote

fertilized egg, complete its second meiotic division → diploid

Early Development- Cleavage

undergoes cleavage= mitotic cell division into 2 smaller cells (daughter cells)

Early Development- Morula

continued mitosis eventually results in morula (16 cells) at 50-60 hours after fertilization, which enters uterus 3 days after ovulation

Early Development- Blastocyst

by day 4, 32-64 cells converted to blastocyst = inner cell mass (to become fetus) + outer chorion (to become placenta)

Early Development- Implantation

on day 6, embryo attaches to uterine wall

Placenta- weeks 1-10

in weeks 1-10, blastocyst cells secrete human chorionic gonadotropin (hCG)- maintain CL and secretion of estradiol and progesterone, and to prevent menstruation

Placenta- week 5-6

CL regresses in week 5-6, and then placenta secretes progesterone and estrogen to maintain pregnancy

Placenta

organ of exchange of gases, nutrients, and waste between mother and fetus; develop in uterus; interlocking fetal and maternal tissue with extensive blood supply; umbilical arteries (2) and vein (1) are in umbilical cord

Placenta- Amniotic sac

the fetus is in the fluid-filled amniotic sac, “water breaks”

Labor

powerful uterine contraction to expel fetus; push baby out

Parturition

childbirth (delivery)

Labor and Parturition- Stimulation of uterine contractions

uterine contractions stimulated by oxytocin (uterus and hypothalamus/posterior pituitary) and prostaglandins (fatty acids, uterus)

Labor and Parturition- Progesterone

progresterone secetion decreases

Labor and Parturition- Estrogen

estrogen causes smooth muscle cells to form gap junction, so that the myometrium contracts as a single unit

Labor and Parturition- Cervix

cervix is made soft and flexible by estrogen, prostaglandins, and relaxin (ovary)

Lactation

production and secretion of milk after birth

Lactation- Mammary Glands

in breast produce and secrete milk; surrounded by myoepithelial cells (contractile cells for milk ejection) and adipose tissue; they become secretory in early pregnancy due to progesterone, estrogen, and prolactin

Lactation- Hormones: After Parturition

increased prolactin stimulate mammary glands to produce milk

Lactation- Hormones: Sucking

also causes secretion of prolactin and oxytocin, which result in secretion of milk into ducts, and ejection of milk, respectively