Lecture 31 Reproductive

Question 1

Organs

Answer 1

gonads = testes + ovaries
ducts
accessory glands
external genitalia

Question 2

Meiosis

Answer 2

46 chromosomes (2n, diploid) → 23 chromosomes (n, haploid)

Question 3

46 Chromosomes

when does DNA replicate

Answer 3

22 homologous pairs of autosomes + 1 pair of sex chromosomes (XX = female, XY = male)
DNA replicates prior to meiosis; each chromosome is duplicated, consists of 2 sister chromatids

Question 4

Meiosis I

Answer 4

homologous pairs separate, 2n (duplicated) → n(duplicated)

Question 5

Meiosis II

Answer 5

sister chromatids separate, n (duplicated) → n (single chromosomes)

Question 6

male

Answer 6

1 primary spermatocyte (2n) → → 4 sperm cells (n)

Question 7

female

Answer 7

1 primary oocyte (2n) → 1 egg cell (n) … → 1 fertilized egg + polar bodies

Question 8

Spermatogenesis

Answer 8

occurs in seminiferous tubules of testes

spermatogonia → primary spermatocyte → secondary spermatocytes → spermatids → sperm

Question 9

Sertoli cells

Answer 9

support developing spermatocytes + endocrine function

Question 10

blood testis barrier

Answer 10

tight junctions between Sertoli cells form barrier to immune system

Question 11

hormonal control

general pattern

Answer 11

hypothalamus: GnRH → anterior pituitary: FSH & LH → gonads: steroid sex hormones + others

Question 12

FSH

Answer 12

stimulates gamete production in male and female

Question 13

LH

Answer 13

stimulates secretion of sex hormones by gonads and stimulates ovulation in females

Question 14

Steroid sex hormones

Answer 14

♂: testosterone, DHT; ♀: estrogen [estradiol], progesterone
- stimulate gamete production, overall reproductive function, development
of reproductive organs and secondary sexual characteristics

Question 15

Negative feedback

Answer 15

Negative feedback control regulates hormone levels in males and partly in females

Question 16

Positive feedback

Answer 16

Positive feedback control triggers ovulation in females

Question 17

Hormonal Control of Spermatogenesis

Answer 17

Sertoli cells
Leydig (interstitial) cells
Negative feedback control

Question 18

Sertoli cells

Answer 18

respond to FSH, support developing spermatocytes

- androgen binding protein (ABP) binds and concentrates testosterone

Question 19

Leydig (interstitial) cells

Answer 19

produce testosterone in response to LH

- testosterone binds to ABP in Sertoli cells → promotes spermatogenesis

Question 20

Negative feedback control

(Spermatogenesis)

Answer 20

inhibin - secreted by Sertoli cells, inhibits FSH secretion

testosterone inhibits GnRH and LH secretion

Question 21

Oogenesis

Answer 21

occurs in ovarian follicles in ovaries
follicular cells (granulosa cells and theca cells) surround a developing egg cell (oocyte)

Question 22

Follicle

Answer 22

primary follicle → secondary follicle → mature follicle → (Ovulation) corpus luteum

Question 23

Egg

Answer 23

oogonia → primary oocyte → (meiosis 1) secondary oocyte (egg) → (requires fertilization, meiosis 11)

Question 24

Ovarian Cycle

Answer 24

follicular phase (day 0-14)
ovulation (day 14)
luteal phase (day 14-28)

Question 25

follicular phase

Answer 25

growth and maturation of follicle, oocyte goes through meiosis I

Question 26

ovulation

Answer 26

egg bursts through wall of ovary, swept into uterine tube

Question 27

luteal phase

Answer 27

corpus luteum forms from remaining follicle cells;
- corpus luteum continues to secrete estrogen and progesterone;
degenerates at the end of the cycle unless fertilization occurs

Question 28

Uterine Cycle

Answer 28

menses (0) 
proliferative phase (14)
secretory phase (28)

Question 29

menses

Answer 29

• uterine lining (endometrium) is sloughed off and discharged

Question 30

proliferative phase

Answer 30

endometrium regrows, becomes thicker and vascularized

Question 31

secretory phase

Answer 31

endometrium continues to thicken and becomes secretory

Question 32

Hormonal Control of the Female Reproductive System

Answer 32

Early follicular phase
Late follicular phase
Luteal phase

Question 33

Early follicular phase

Answer 33

• FSH and LH secretion begins to increase
• follicular cells stimulated to produce steroid sex hormones:
  theca cells: produce androgens → granulosa cells: convert androgens to estrogens
• estrogen levels rise → stimulates proliferative phase
• at low to moderate levels, estrogen inhibits FSH and LH secretion (negative feedback)

Question 34

Late follicular phase

Answer 34

• estrogen secretion peaks
• at high levels, estrogen exerts positive feedback → stimulates FSH and LH secretion
• LH surge triggers ovulation
• high estrogen level prepares reproductive tract for ovulation and sperm entry

Question 35

Luteal phase

Answer 35

• after ovulation, corpus luteum secretes estrogen and progesterone
• progesterone levels rise → stimulates secretory phase, prepares uterus for pregnancy
• estrogen, progesterone and inhibin exert negative feedback, inhibit FSH and LH secretion

Question 36

if fertilization occurs

Answer 36

zygote undergoes cell divisions to form a blastocyst (~100 cells)
- blastocyst implants in the uterus about 7 days after fertilization
- implanted embryo secretes human chorionic gonadotropin (hCG)
hCG “rescues” the corpus luteum → continues secretion of estrogen and progesterone,
keeps endometrium intact for the developing embryo
- placenta takes over production of progesterone and estrogen by the 7
th week

Question 37

if fertilization does not occur

Answer 37

corpus luteum degenerates (→ corpus albicans)

→ estrogen and progesterone levels decrease → menstruation