12-2: Regulation of Human Reproduction Flashcards
two modes of reproduction in animals
-asexual and sexual
sexual reproduction
-the fusion of haploid gametes forming a diploid zygote (embryo -> fetus)
• Female gamete = egg (aka oocyte) -> large, non-motile
• Male gamete = sperm -> small, motile
• Yields genetically-different organisms
asexual reproduction
-new individuals generated without fusion of gametes
• Yields genetically-identical organisms (aka clones)
-Parthenogenesis in bees
= the egg develops without being fertilized, rare in vertebrates and occurs as a response to low population density
Variation in patterns of sexual reproduction
-adaptation to a challenge in finding a mate in sessile, burrowing animals and some parasites = hermaphroditism
Hermaphroditism
-each individual has both male and female
reproductive systems
• A result of that => any two individuals can mate
bluehead wrasse
• Adaptation to a challenge of finding a mate in
bluehead wrasse
• Bluehead wrasses may reproduce in four
different ways throughout their lifetime:
• 1) as a female in a group spawning event;
• 2) as a female in a pair spawning event within the territory of a large male;
• 3) as a small male in a group spawning event; and
• 4) as a dominant, terminal male in a pair spawning event within its own territory.
oysters
• Adaptation to maximize gamete production in oysters • The individuals reproduce as males first, and then when their size is greatest - as females (they produce more gametes). • A result of that => releasing more gametes tends to result in more offspring
fertilization
• The union of sperm and egg: external or internal
• External: eggs released into environment -> male fertilizes them
-Requires: a moist habitat; proper timing; environmental cues; courtship behaviors
-Examples: many amphibians, some fishes, echinoderms
• Internal: sperm deposited in or near the female reproductive
tract -> fertilization within the female tract
-Requires: compatible reproductive systems; cooperative behavior
-Examples: mammals, reptiles, birds
Functions of Sex Hormones
-Direct regulation of gametogenesis: promote gamete formation
-Additional functions (indirect regulation)
• The appearance of the primary sex characteristics (internal and external anatomy; e.g. development of structures directly involved in reproduction)
• Formation of the secondary sex characteristics (physical and behavioral characteristics, e.g. male vocalization, facial and pubic hair, aggressiveness, etc.)
-Upon reaching sexual maturity, human males carry out
spermatogenesis continuously, whereas human females produce gametes in cycles
functions of reproductive cycle
- produce eggs
- allows successful fertilization
- maintain pregnancy
human females’ reproductive tract
- eggs produced in ovary
- eggs fertilized in oviduct
- sperm comes thru the vagina
- fertilized egg (zygote) implants in uterine wall
female reproductive cycles
- both controlled by hormones and synched:
1) Follicular phase of the ovarian cycleoverlaps with the menstrual flow and proliferative phase of the uterine cycle.
2) Luteal phase of the ovarian cycle overlaps with the secretory phase of `the uterine cycle
The ovarian cycle: the follicular phase
-It lasts from day 1 to day 14 of a 28-day long cycle, and includes follicle growth and ovulation of a (usually) single egg.
-Ovarian follicle is a microscopic
structure in the ovary that
contains the developing oocyte
and secretes estrogen.
Previous figure in words
• This is what happens inside the ovaries:
1. FSH stimulates follicle growth in the ovaries. Several follicles
begin to grow in each cycle, but usually only one follicle from just one ovary matures, and the others disintegrate.
2. The cells of the growing follicle start to make estradiol (estradiol is the main type of estrogen in humans) themselves, as they continue to mature.
3. The maturing follicle containing a fluid-filled cavity, enlarges, forming a bulge at the surface of the ovary.
4. The follicle and adjacent wall of the ovary rupture, releasing the oocyte. This is termed ovulation.
luteal phase
-It lasts from day 15 to day 28 of a 28-day long cycle
• This is what happens inside the ovaries:
1. LH stimulates the follicular tissue left behind in the ovary to
transform into a glandular tissue called corpus luteum.
2. The corpus luteum secretes progesterone and estradiol.
-The corpus luteum secretes progesterone, which is a steroid
hormone responsible for the development of the endometrium and maintenance if pregnancy occurred.
-If pregnancy didn’t occur, corpus luteum would have degenerate and become destroyed
follicle growth
• This cycle includes follicle growth and ovulation of a usually single egg.
• The follicular phase of the ovarian cycle lasts from day 1 to day 14, and considers the following stages:
1) Primary follicle: this is in fact the primary oocyte with special cells surrounding it for nourishment. Only one follicle will actually mature each
month, and the others that begin the process soon degenerate.
2) Growing follicle: the cells of the growing follicle start to make estradiol (main estrogen in humans), and the egg matures.
3) Mature follicle: it contains an internal fluid-filled cavity, and it grows very large, forming a bulge near the surface of the ovary.
-The follicular phase ends in ovulation on day 14.
luteal phase 2
• From the ovulation onward, which are days 15 to 28, the luteal
phase takes place, through the following stages:
• Empty follicle: once the follicle releases the egg, it becomes empty.
• Corpus luteum: follicle cells transform into a glandular structure called
corpus luteum (corpus=body, luteum=yellow). Corpus luteum secretes
progesterone and estradiol.
• Corpus luteum regression: if fertilization does not occur the corpus luteum
disintegrates. If pregnancy occurs, it continues to secrete progesterone,
which maintains the thick uterus lining for zygote to implant.
• If no pregnancy, the cycle resumes again.
menstrual cycle
- menstrual flow (day 0-5): lining of uterus (endometrium) is shed
- proliferative phase (day 6-14): endometrium builds up
- secretory phase (day 15-28): endometrium continues to thicken, if no pregnancy, it sheds
hypothalamus hormones
-GnRH stimulates anterior pituitary gland
anterior pituitary hormones
-stimulated by GnRH produces LH and FSH also referred as gonadotropins, target the Hormonal regulation in human females
ovaries hormones
-estrogen, progesterone
Hormonal regulation in human females
• Negative feedback => lower concentrations of estradiol and
progesterone inhibit GnRH and LH and FSH
• Positive feedback => higher concentrations of estradiol stimulate hypothalamus to increase its output of GnRH
• This positive feedback results in final maturation of the follicle.
hormone changes
Hypothalamus: continuously releases gonadotropin-releasing hormone (GnRH), 24/7, unless actively prevented from doing so by other hormones (most notably progesterone).
• FSH and LH are released into blood due to influence of GnRH from the hypothalamus. FSH and LH stimulate the follicle to grow.
• Estradiol is released due to positive influence of FSH and LH. Estradiol stimulates
the growth of the endometrium of the uterus. Throughout most of the cycle, estradiol inhibits the release of gonadotropin by the hypothalamus and LH/FSH
by the anterior pituitary.
• Day 12: Things change!
• On about this day, estradiol levels get so high that its influence radically changes.
This is unexpected, but it happens. On day 12, estradiol switches roles and positively stimulates the hypothalamus (and consequently anterior pituitary) resulting in a surge of LH and FSH at this time
day 0-7
• Uterus is shedding its lining; • A follicle is beginning to develop. It is producing estradiol at this time; • Estradiol level is still low => it suppresses LH and FSH secretion via negative feedback inhibition
day 8-14
• The follicle is larger. It produces more estradiol. It also produces progesterone; • Large amount of estradiol => positive feedback on LH and FSH secretion. This causes a spike in LH secretion; • The LH surge triggers ovulation.
