Unit 1C Flashcards
What is the goal of gametogenesis?
-to make hormones and gametes
-estrogen and progesterone for females
-testosterone for males
What is gametogenesis called for women?
oogenesis
What is gameotogenesis called for men?
spermatogenesis
How many eggs are produced from one cycle of oogenesis?
1 oogonia produced one viable secondary oocyte that only completes meiosis of fertilized
When does oogenesis start?
It is an intermittent process that starts before birth?
Why is oogenesis considered an intermittent process?
ovulation only happens once a month once puberty begins
How many eggs do women start with?
1.5 million primordial follicles at birth
What are the steps in oogenesis?
- 1 diploid oogonium (stem cell) undergoes mitosis and splits into 2 primary oocytes
- Mitosis begins in the diploid oocyte (makes it to prophase one)(this is where the 1.5 million follicles are)
- the two diploids enter a state of atresia (inactivity) until puberty begins
- When puberty begins the primary oocyte begins miosis 1 splitting it into a polar body and a secondary oocyte
- the polar body degenerates
- the second oocyte stays in metaphase 2 until fertilization
- secondary oocyte is released from the ovary into the ovarian tubes (this is where fertilization would happen)
- non-fertilized eggs are released during menstruation
- fertilized eggs complete miosis and turn into ovum
What is the difference between a polar body and secondary oocyte?
- the secondary oocyte has all of the genetic material and the polar body has everything else
- the secondary oocyte is what has everything useful so the polar body is discarded
How many eggs do women have when they begin puberty?
400,000
What is the primordial follicle?
-the most primitive type of ovarian follicle
-made of the primary oocyte in prophase one and a flattened layer of follicle cells
- up to 20 primordial follicles turn into primary follicles each month
-slowly grow as we grow
*image on slides
What is a primary follicle?
- made of the primary oocyte in prophase 1 with granulosa follicular cells
-the gfcs secrete estrogen and inhibin
-has thecal cells on the periphery of the follicle to secrete androgens and surround primary oocytes with estrogen - some primary follicles mature into secondary follicles, rest undergo atresia
*image on slides
What do androgens in the primary follicle do?
- are converted to estrogen by aromatase enzymes from GFCs
- supply more and more estrogen until cell division
What happens to secondary follicles
-primary oocytes in prophase one and associated follicular cells (cumulus oophorous) are forced to 1 side of the follicle by the antrum
- the oocyte is immediately surrounded by the zona pellucida and corona radiata
- typically one matures into vesicular follicles and the rest are reabsorbed
*image on slides
What happens in vesicular/mature follicles?
- secondary oocytes are arrested in metaphase 2
-first polar body from meiosis 1 degenerate
-antrum enlarges, and pushes towards ovarian surface until it ruptures at ovulation releasing a secondary oocyte, zona pellucida, and corona radiata
-granulosa cells keep secondary oocytes attached to oocyte
-zona pellucida is always with a secondary oocyte (sperm must penetrate to fertilize) - corona radiata kind of wears down over time
*image on slides
How do follicles mature?
primordial, primary, secondary, mature/vesicular
How does ovulation occur?
-happens in alternating ovaries
-corpus luteum forms from remnants of the follicle after ovulation (secretes large amounts of progesterone, some estrogen, and inhibin) to stimulate the buildup of the uterine lining
- uterus prepares for possible implantation of fertilized eggs
- corpus lutetium typically lasts 10-13 days unless fertilization occurs
-corpus luteum turns into corpus albicans if not used
What happens to the corpus luteum if fertilization occurs?
- the pre-embryo secretes human chorionic gonadotropin which mimics LH’s effects
- corpus luteum is maintained through the first trimester
-progesterone levels stay high
What happens to the corpus albicans?
-is formed from the shriveled corpus luteum
- is white connective scar tissue
-most structures are completely re-absorbed
Explain the negative feedback loop of ovulation
- the hypothalamus releases GNRH and starts puberty which stimulates the anterior pituitary to release FSH and LH
- FSH causes the follicles to mature and release estrogen
- if estrogen levels in the follicles get too high inhibin is released to pause LH and FSH
- When estrogen levels peak in the follicles it travels back to the anterior pituitary and stimulates it to raise LH levels which in turn stimulates ovulation
-when ovulation is started the corpus lutetium grown and releases progesterone to maintain uterine lining (stops after about 13 days if no implantation)
-if there is no fertilization the corpus albicans is made and if it is successful HCG is made
What are the phases of the ovarian cycle?
follicular phase, ovulation, luteal phase
Explain the follicular phase of the ovarian cycle
-around days 1-12
-primary, secondary, vesicular follicles are formed after primordial follicles are stimulated by gonadotropin
Explain the ovulation stage of the ovarian cycle
-around days 13-17
release of a secondary oocyte from the vesicular follicle
-meiosis stopped unless fertilization occurs
Explain the luteal phase of the ovarian cycle.
- Around days 18-27
- remaining follicular cells become corpus lutetium
-a normal span of 10-13 days but if fertilization occurs it will be extended
What are the layers of the uterus
- myometrium
-endometrium - basal layer
-functional layer
*image on slides
What is the myometrium?
Formed from three layers of smooth muscle
What is the endometrium?
-where implantation occurs
-contains highly vascularized uterine glands
-deeper basal layer adjacent to the myometrium containing basal cells
-more superficial functional layer beginning monthly growth at puberty
When does the function layer grow?
-begins monthly growth puberty
-under the influence of estrogen and progesterone
-sheds at menses
What are the stages of the uterine cycle?
-menstrual phase
-proliferative stage
-secretory stage
What is the menstrual phase of the uterine cycle?
- days 1-5
-sloughing of functional layer of endometrium
What is the proliferative stage of the uterine cycle?
Days 7-13
-development of functional layer of endometrium
What is the Secretory stage of the uterine cycle?
-days 15-17
- results in increased vascularization and uterine gland development in the endometrium
– ideal for impllantation
What happens before ovulation in the uterine and ovarian cycle?
- involves the primary, secondary, vesicular follicles
-days 1-14
-follicular and menstrual and proliferative cycles
-FSH and LH levels are low but changing
-follicular cells secrete estrogen and small amounts of androgens which are converted to estrogen by aromatase - gonadotropin levels increase in response to GnRH from the hypothalamus
-estrogen levels increase as follicles continue to develop
-estrogen stimulates the growth of the functional layer
-myometrium sheds the lining
What happens to hormones during ovulation?
-FSH and LH levels skyrocket and peak
-estrogen and progesterone levels vary greatly
What happens after ovulation in the ovarian and uterine cycle?
- progesterone levels are higher than estrogen levels (meaning functional layers remain) (functional layer will continue to remain if implantation occurs)
- secretory and luteal phases occur
- corpus luteum forms from remnants of the follicle, secreting large amounts of estrogen and progesterone
- LH peak causes ovulation pf secondary oocyte
- Corpus luteum secretes progesterone maintaining functional layer
- a sharp decrease in progesterone initiates menstruation
When does spermatogenesis begin?
puberty
How many sperm are made each day
100 million
How many sperm are produces from a spermatogonia
4 sperm per spermatogonia which mature in the epididymis
Where is the testis located?
in the scrotum
Where does spermatogenesis occur?
in the seminiferous tubules of the testis
What is required for spermatogenesis?
- testosterone to stimulate it and temperatures 2-3 degrees cooler than body temp
Where do the testis originally form?
In the pelvic region and descend around birth or up to three months later?
What is cryptorchidism?
-when the testis does not descend into the scrotum prior to birth
- orchiopexy surgery is required if testes do not descend
What happens if testes do not descend?
-orchiopexy surgery
- man will be sterile because sperm can only be made in the scrotum
- increased risk of testicular torsion, cancer, and developing a hernia near the groin
What is inside the seminiferous tubules?
-interstitial cells and sustentacular cells
What is inside the seminiferous tubules?
-interstitial cells and sustentacular cells
What do interstitial cells do?
produce androgens (testosterone) under LH stimulation
-produce a small amount of estrogen
What are sustentacular cells and what do sustentacular cells do?
-nondividing support cells sthat surround dividing germ cells which continuously produce sperm
- helps nourish sperm with fructose
- secretes androgen binding protein in responses to FSH
- releases inhibin when sperm count is high so FSH secretion is stopped
Give a spermatogenesis overview
- germ cells are diploid spermatogonium that produces four functional sperm
- mitotic decisions of cell produce a germ cell and primary spermatocyte
-primary spermatocyte continues to divide y meiosis in response to increased testosterone
-LH stimulates interstitial cells to secrete testosterone, fsh stimulates sustentacular cells to secrete abp which keeps testosterone levels high in the testes
Give a spermatogenesis overview
- germ cells are diploid spermatogonium that produces four functional sperm
- mitotic decisions of cell produce a germ cell and primary spermatocyte
-primary spermatocyte continues to divide y meiosis in response to increased testosterone
-LH stimulates interstitial cells to secrete testosterone, fsh stimulates sustentacular cells to secrete abp which keeps testosterone levels high in the testes
How do spermatogonium divide?
-meiosis one where diploid primary spermatocytes undergo meiosis 1 producing w haploid secondary spermatocytes
- meiosis 2 where each haploid secondary spermatocytes undergoes meiosis two producing 4 haploid spermatids
What is spermiogenesis?
-the final step of spermatogenesis
-makes sperm from spermatids
-physiological change to make them look like sperm
begins with spermatids that have finished nuclear division in results in morphological changes needed to form sperm
-sheds cytoplasm and nucleus elongates
- acrosome cap forms over nucleus
-tail formation from organized microtubules in nucleus
midpiece region contains mitochondria and centriole
What is an acrosome cap?
- cap over the nucleus on sperm containing digestive enzymes to help penetrate the secondary oocyte
What are the detailed steps of spermatogenesis?
- GnRH is secreted by hypothalamus to stimulate the anterior pituitary to secretes FSH and LH
- lh stimulates interstitial cells to secrete testosterone
- FSH stimulates sustentacular cells to secrete androgen binding protein which keeps testosterone levels high in the tesits
- Testosterone stimulates spermatogenesis but inibits FnRH secretion and reduces the anterior pituitary’s sensitivity to GnRH
- Rishing sperm count levels cause sustentacular cells to secrete inhinin which further inhibits FSH secretion
- Testosterone stimulates libido and development of secondary sex charecterisitces.
What is semen?
seminal fluid released during ejaculation
How much semen is released during ejaculation?
1.5-5 ml, sperm count is about 50-150 million
What is seminal fluid?
an alkaline secretion that is produced by accessory glands and neutralized vaginal acidity and provides nutrients to sperm traveling through the female reproductive tract
What do seminal vesicles do?
-make fructose that nourishes sperm
- prostaglandins that promote the widening of the external of cervix
What does the prostate gland secrete?
fluid rich in citric acid (nutrient) seminal plasma containing antibiotics, prostate-specific antigen(PSA) to liquefy semen after ejaculation
What do the boulbrethal glands do?
- pre-ejaculate that n and residual acidity in the urethra neutralizes
- produces clear, a viscous muffin that forms mucus and coats and lubricates urethra during sex
How is the zona pellicuda penetrated?
- capacitation: physiological conditioning undergone by sperm to become capable of fertilizing the secondary oocyte in the female reproductive tract
- acrosome reaction: release of digestive enzymes from acrosomes that allows sperm to penetrate zona pellicuda
after penetration the zona pellicuda immediately hardens to prevent other sperm from entering
What happens if multiple sperm enter the zona pellicuda?
polysperm immideatly fatal since there are 23 triplets of chromosomes
How are zygotes formed?
- upon contact of sperm and oocyte plasma membranes, only the sperm nucleus enters the oocyte (pronucleus)
- secondary oocyte completes second meiotic division forming an ovum
-nucleus of sperm and ovum pronuclei fuse to form diploid zygote
-zygote divides forming pro-fetus which is implanted in the uterus
