Lecture 36

Question 1

Is the “sex typical behavior” universal?

Answer 1

No, not all the time
- variation across animals (sex-role reversal)

Question 1

Is sex always for reproductive only?

Answer 1

no
- non-reproductive courtship/pairbonding/ sexual behaviors occur in many taxa within and between sexes

Question 2

Describe the function of the anterior pituitary

Answer 2

Anterior pituitary contains non-neural endocrine cells under the control of hypothalamic hormones

Question 3

Describe the HPG axis and how it regulates sex steroid secretion from the gonads in both sexes

Answer 3

1.) Hypothalamus secretes GnRH
2.) GnPH moves through hypothalamic- pituitary portal vessels
3.) GnPH acts on anterior pituitary
4.) Anterior pituitary secretes TWO hormones- FSH and LH
5.) FSH and LH acts on the gonads
6.) Gonads will release sex steroids

Question 4

Male reproductive physiology

Answer 4

• Generation of mature gametes (sperm) at a steady rate after puberty
• External genitalia to deliver gametes to the female reproductive tract
  -They are reproductive from puberty to their time they die

Question 5

Female reproductive physiology

Answer 5

-Generation of mature gametes (eggs) on ca monthly cycle (menstrual cycle)
- internal genitalia and uterus to recieve male gametes for fertilization and support a developing offspring
- Parturition
- Lactation

Question 6

Why are the fallopian tubes close to the ovaries?

Answer 6

So when ovulation happens, the egg can be brushed in to the opening of the fallopian tube (it can meet a sperm there and fertilization can occur)

Question 7

What happens if fertilization implantation does not happen?

Answer 7

Uterine lining is shed (menstruation)
-not common in mammals

Question 8

What does FSH in both sexes have affects on?

Answer 8

Gametogenesis (generation of gametes)
Females: oogenesis
Males: spermatogenesis

Question 9

What does LH usually affect?

Answer 9

LH is associated with the secretion of the steroids

Question 10

What are follicles?

Answer 10

Fluid filled aggregations of ovarian cells that have important endocrine functions.

1.) Eggs (oocytes) are encased in follicles
2.) They grow during the menstrual cycle (only a small number of them are activated during each menstrual cycle)

Question 11

What is the important endocrine function of follicles?

Answer 11

• secretes hormones
  -supports the egg

Question 12

What is the follicular phase of the menstrual cycle?

Answer 12

• multiple follicles begin to develop (triggered to do that because of changes in endocrine signaling in HPG axis)
• One dominant follicle becomes dominant
• The dominant follicle matures and suppresses the other follicles from developing.
• Dominant follicle releases its egg into the fallopian tube (ovulation occurs)

-possible for more than one follicle to be dominant and more than one egg to be released during ovulation (twins)

Question 13

Is the egg a mature gamete in the follicle?

Answer 13

No, egg has been arrested in meiosis one (not finished yet).
- Completes meiosis one right before ovulation happens
- Egg has to finishes meiosis two when it meets the sperm

Question 14

What happens during ovulation?

Answer 14

Follicle opens up, releasing the egg out of the ovary and can be swept up by the fallopian tube

Question 15

What happens to the remaining follicular tissues after the egg is released?

Answer 15

• different into the corpus luteum
• releases tons of sex steroids (estrogen and progesterone)

Question 16

Luteal phase

Answer 16

The second phase of the menstrual cycle
- The corpus luteum functions (releasing sex steroids- one of the things the hormone is doing is causing the lining of the uterus to thicken and vascularize in preparation for implantation if fertilization were to happen)
- The corpus luteum degenerates
At the end of the luteal phase if no implantation or fertilization of an embryo, luteal function declines)
-sex steroids drops and then the uterine lining sheds

Question 17

What happens in the luteal phase if fertilization happens?

Answer 17

Fertilization happens ovulation
- embryo implants in uterus
- corpus luteum will persist and not degenerate
- sex steroids continue to be pumped
- development of fetus
- parturition

Question 18

What happens in the luteal phase if fertilization does not happen?

Answer 18

Corpus luteum degenerates and menstruation (uterine bleeding)

Question 19

What happens to the anterior pituitary hormones (FSH and LH) levels in beginning of follicular phase?

Answer 19

FSH levels are increasing
- activates follicles and causes them to start maturing

Question 20

What happens to the sex steroids (estrogen and progesterone) levels in beginning of follicular phase?

Answer 20

sex steroids lvls are low (negative feedback)
- not that much estrogen secretion= anterior pituitary releases more FSH

Question 21

What happens when the dominant follicle do?

Answer 21

releases a lot of estrogen
- negative feedback still
causes decline of FSH levels
as estrogen levels rise, FSH levels decline.

Question 22

What happens at late follicular phase and beginning luteal phase?

Answer 22

-high FSH and LH secretion
- LH surge corresponds with ovulation (causes ovulation)
- LH triggers dominant follicle to rupture and release the egg
- High estrogen levels as well (POSITIVE FEEDBACK)

Question 23

Describe the negative and positive feedback of the the menstrual cycle

Answer 23

Negative feedback occurs throughout the cycle, but positive feedback occurs during few days causes the LH surge
- then it switches back to negative feedback

Question 24

What are possible causes of the switch in estrogen functioning?

Answer 24

• Changes in estrogen receptor expression during which cycle (maybe they only express a certain receptor type for a few days)
  Most likely: there are different populations of the hypothalamic cells that respond to estrogen
  (they are always there, but during the LH surge, one population becomes more responsive to estrogen)

Question 25

What happens during the early luteal phase?

Answer 25

Progesterone levels rise
(high levels of progesterone and estrogen)
- dropping LH and FSH levels (negative feedback)
- LH and FSH will start to rise again after the corpus luteum degenerates

Question 26

If implantation happens, what happens to corpus luteum?

Answer 26

Corpus luteum does not degenerate
- estrogen and progesterone levels have an affect on uterine lining (endometrium)
- endometrial wall thickens at end of follicular phase (lots of capillaries grow)
- luteal phase maintains the thickened uterine lining to get them ready for implantation
- more and more progesterone and estrogen gets pumped out until delivery. (negative feedback to prevent GnRH secretion, FHS + LH secretion so another follicle does not generate)

Question 27

If implantation does not happen? What happens to the uterine lining?

Answer 27

• corpus luteum degenerates, estrogen and progesterone levels drop
• The endometrium degenerates and sheds (menstruation)

Question 28

How does the corpus luteum know that implantation happens and that it should degenerate?

Answer 28

once embryo gets going, it secretes hCG

hCG gets into parental circulation and acts on gonads to let them know there is a developing embryo.