Gameto./Fertilization Flashcards
Gametes are formed from…
germ cells that originate very early in the developing embryo and are developmentally different from testicular or ovarian cells
How many meiotic division does spermatogenesis have?
2
Spermatogenesis steps
- Male germ cell (2n)
- Spermatogonium (2n)
- Primary spermatocyte (2n)
First meiotic division - 2 Secondary spermatocytes (n)
Second meiotic division - 4 spermatids (n)
- 4 Sperm cells (n)
Through further development, spermatids become _______, ________, and _________
compact, streamlined, motile
Sperm motility is ___ under _____ conditions and is activated by _______ or slightly _____ pH.
low, acidic, neutral, basic
What is semen?
A mixture of sperm and fluids and molecules to support sperm and facilitate fertilization
Where is sperm produced?
Testes (located in the scrotum, outside body cavity)
Why are the testes outside the body cavity?
To ensure that the optimal temperature for spermatogenesis (slightly below body temp) is maintained
Where does spermatogenesis take place?
seminiferous tubules
What are the germ cells protected by from noxious substances in the blood?
Sertoli cells within seminiferous tubules
Where is testosterone produced?
In the clusters of Leydig cells in the seminiferous tubules
When do the four haploid spermatids form into sperm cells?
As they move toward the lumen of the seminiferous tubules
What happens to the nucleus and cytoplasm of spermatids?
The nucleus becomes the head of sperm cells, and the cytoplasm is lost
What also develops from spermatid to sperm cell?
A flagellum (tail) and the mitochondria becomes the midpiece (provides energy for motility)
What is an acrosome cap?
A cap that forms over the nucleus in the head of a sperm cell that contains digestive enzymes to penetrate the protective layers of the egg (also contains actin and bindin)
Where does sperm move to and are stored after being in the lumen of the seminiferous tubules?
to the epididymis
What are the components of semen?
-sperm cells
-mucus, protein, & fructose (2/3 of volume, produced by seminal vesicles)
-thin, milky fluid (produced by prostate gland, makes up rest of volume)
-bulbourethral glands produce a secretion that neutralizes acidity in the urethra
In males, the urethra is a common duct for what two systems?
urinary and reproductive
How do male hormones change during puberty?
Hypothalamus release more GnRH and stimulates the anterior pituitary to release more LH and FSH. LH stimulates Leydig cells to produce testosterone while FSH stimulates Sertoli cells to promote spermatogenesis and produce inhibin.
What do testosterone and inhibin do in terms of negative/positive feedback?
-Testosterone inhibits the hypothalamus and anterior pituitary
-Inhibin inhibits the anterior pituitary
-Testosterone stimulates the production of more testosterone and Sertoli cells > reproductive tract and other organs (sperm)
During embryogenesis, the primary oocytes enter _________ of the first meiotic division, and their development is ________ (until sometime between ___________ and _________).
prophase, arrested, puberty, menopause
When the primary oocytes resumes meiosis, it _________ the first division, resulting in _______ of ______ size
completes, two cells, unequal
Steps of Oogenesis
- Female germ cell (2n)
- Oogonium (2n)
- Primary oocyte (2n)
First meiotic division - Secondary oocyte and first polar body
Second meiotic division - Ootid and second polar body
- Ovum and polar bodies disappear
What do LH and FSH stimulate in oogenesis (humans)?
A follicle to grow and induce the primary oocyte to complete Meiosis I
What does LH also stimulate in oogenesis?
The ovulation of the oocyte. After completion of meiosis I, secondary oocyte arrests again at metaphase II
What stimulate the second meiotic division of an egg?
fertilization
After ovulation is induced, where is the oocyte taken?
to the Fallopian tube
Where does fertilization of an egg take place?
in the Fallopian tube or oviduct
How does the oocyte travel in the oviduct?
cilia lining the oviduct propels it toward the uterus
What is the uterus?
a muscular, thick-walled cavity
Where is sperm deposited during fertilization?
In the vagina and swim up to the cervix
What happens during fertilization?
Egg and sperm fuse to produce diploid zygote. The zygote then divides to become a blastocyst and continues down oviduct. Blastocyst attaches to endometrium. Estrogen stimulates the endometrium to develop new blood vessels to nourish the developing embryo.
What are the two linked cycles of the female reproductive cycle?
- The ovarian cycle (oocytes and hormones)
- The uterine cycle (prepares endometrium for arrival of blastocyst)
What happens during the uterine cycle?
- Starts 5 days into menstrual cycle and endometrium builds
- After 5 days of ovulation, the uterus is maximally prepared for a blastocyst and stays that way for ~9 days
- If no blastocyst appears, then the endometrium breaks down and sloughs off during menstruation (why females bleed)
What happens during the ovarian cycle?
*repeats every 28 days
Btwn puberty and menopause, 6-12 follicles mature each month and produce estrogen
1. Oocyte maturation
2. One of the follicles continues to grow while the others degrade and nourishes the growing egg w/ the nutrients and proteins it will use if fertilized (oocyte maturation)
3. Ovulation (after 2 weeks): follicle ruptures and egg releases
4. Follicle forms an endocrine mass > corpus luteum (produces estrogen and progesterone for 2 weeks)
5. Corpus luteum degenerates if a blastocyst does not implant in uterus
Female hormones and puberty
- Hypothalamus stimulates GnRH
- This stimulates anterior pituitary to release FSH and LH
- Ovarian tissue grows and produces estrogen
NEGATIVE AND POSITIVE FEEDBACK
What marks the start of each uterine and ovarian cycle?
Menstruation
When does estrogen exert negative feedback control on FSH/LH?
The first 12 days of the ovarian cycle
When does estrogen exert positive feedback on FSH/LH?
Day 12-14 of ovarian cycle
What triggers a follicle to rupture?
The surge of LH and some FSH during day 12-14 of the ovarian cycle
What happens in ovarian/uterine cycle if NO fertilization occurs?
Corpus luteum degenerates at day 26 and progesterone/estrogen levels plummet
-endometrium sloughs off and menstruation occurs
-starts negative feedback and cycle begins again
What happens in the ovarian/uterine cycle if fertilization DOES occur?
Egg and sperm fuse and zygote becomes blastocyst. Blastocyst begins to secrete human chorionic gonadotropin (hCG) after implantation, which keeps corpus luteum functional.
-Corpus luteum keeps producing progesterone and maintains endometrium
What is the basis for pregnancy testing?
Presence of hCG in blood or urine
What is RU-486?
An antagonist of progesterone and blocks progesterone from binding to its receptor; endometrial cells “think” no progesterone is present and menstruation is stimulated
What are the complex series of events in fertilization?
-recognition
-fusion of plasma membranes
-blocks to polyspermy
-pronuclear fusion
-activation of development
Why is polyspermy bad?
More chromosomes than needed and spindles get all screwed up in mitosis
Fertilization with sea urchins
-acrosomal process (coated with bindin) extends out of sperm head to make contact w/ female vitelline envelope and bindin receptors
-stimulates the egg plasma membrane to form fertilization cone, engulfing sperm head and brings it into contact w/ egg cytoplasm
Fast block to polyspermy: sea urchins
An influx of sodium ions occurs within seconds of the sperm entering the V.E. depolarizing the egg’s plasma membrane and discouraging further binding of sperm
Slow block to polyspermy: sea urchins
-happens after a minute
Calcium ion levels increase at sperm entry and spreads as a wave by CICR throughout cortical region of egg/oocyte, stimulating fusion of cortical granules to plasma membrane which causes V.E. to form fertilization envelope that prevents additional sperm from entering
