Reproductive System Notes

Male and Female Reproductive Systems

• Gonads (primary sex organs) produce:

  • Sex hormones

  • Gametes

• Male gonads = testes; female gonads = ovaries

• Male hormones = testosterone; female hormones = estrogen & progesterone

• Male gametes = sperm; female gametes = ova (eggs)

Mitosis and Meiosis

• Mitosis

  • Diploid (2n): 2 sets of chromosomes (maternal + paternal)

  • Produces genetically identical daughter cells

  • Used for tissue regeneration and producing red blood cells (RBCs)

• Meiosis

  • Haploid (n): 1 set of chromosomes

  • Used to form gametes

  • Meiosis I and Meiosis II result in genetically different haploid cells

Male Reproductive Anatomy Basics

• Components:

  • Testes (gonads): produce sperm

  • Accessory organs: secrete non-sperm components of semen

  • Ducts: carry sperm from testes to the outside

  • Penis: delivery system for sperm

• Pathway: Sperm formed in testes, travel through ducts, joined by accessory secretions, exit through penis

The Testes

• Function:

  • Spermatogenesis: sperm production

  • Testosterone production

• Anatomy:

  • Seminiferous tubules: site of spermatogenesis

  • Ductus epididymis

  • Epididymis

  • Ductus deferens

Seminiferous Tubules

• Lumen: where sperm builds up

• Spermatogenic cells: developing sperm cells

• Sustentacular cells: support sperm production

• Myoid cells: muscle-like, contract to push sperm and hormones

• Interstitial cells: outside tubules in interstitial fluid (ISF), hormone production

Spermatogenesis and Spermiogenesis

• Spermatogenesis: Formation of immature sperm; involves meiosis

• Spermiogenesis: Maturation of sperm

• Spermatogenesis starts at the outside wall of the tubules, and daughter cells are pushed towards the lumen.

• Spermiogenesis starts in the lumen of the tubule.

Spermatogenesis Process

• Starts during puberty and continues (with gradual decline in 50s)

• Spermatogonia: stem cells that give rise to new cells to differentiate

  • Diploid cells that produce new daughter cells, genetically identical

  • Mitosis: One daughter cell replaces the spermatogonia that divided; the other commits to meiosis.

  • Meiosis I: Primary spermatocyte produces haploid cells called secondary spermatocytes.

  • Meiosis II: Produces 4 spermatids (immature sperm)

The Blood-Testis Barrier

• Formed by sustentacular cells connected by tight junctions.

• Goal:

  • To prevent immune cells from attacking spermatogenic cells after meiosis.

  • Spermatogenic cells are no longer genetically identical to other body cells after meiosis.

• Other functions of sustentacular cells:

  • Maintain a favorable local environment.

  • Provide nutrients.

  • Remove waste.

  • Produce regulatory signals.

Spermiogenesis

• Location: Occurs in the lumen and other parts of the duct system.

• Goal: To make sperm more motile (ability to move)

• Steps:

  1. Elongation (longer & thinner)

  2. Formation of flagella

  3. Shedding of extra cytoplasm (helps with motility)

  4. Mitochondria congregate near the head

  5. Formation of the acrosome (capsule) near the nucleus (helps with fertilization)

• After spermiogenesis, mature sperm go to the duct system to be released outside the body.

Hormonal Control of the HPG Axis (Male)

• The release of sex hormones from the gonads (testosterone) is regulated.

• HPG Axis: Hypothalamic-Pituitary-Gonadal Axis (3 tiers of control centers)

Three Tiers of Control (Male)

1. First-tier: Hypothalamus releases GnRH (Gonadotropin-Releasing Hormone).

2. Second-tier: Anterior pituitary releases FSH (Follicle-Stimulating Hormone) and LH (Luteinizing Hormone) in response to GnRH.

3. Third-tier: LH and FSH target cells in the testes

• GnRH travels from hypothalamus to the anterior pituitary, stimulating it to produce FSH and LH.

• FSH and LH travel to the testes, stimulating hormone production.

Effects of FSH and LH on the Testes

• LH targets interstitial cells → testosterone production

• FSH targets sustentacular cells → ABP (Androgen-Binding Protein) and inhibin production

Negative Feedback in the HPG (Male)

• After puberty: The hypothalamus is less sensitive to negative feedback.

  • Testosterone levels have to be higher to decrease tropic hormone production.

  • Testosterone levels can rise higher before there is a decrease in GnRH.

• Before puberty: The hypothalamus is very sensitive to negative feedback.

  • Even low levels of testosterone block any increases in testosterone and keep levels low.

  • Even low levels of testosterone are enough to provide negative feedback to the hypothalamus, preventing the release of GnRH and eventually FSH and LH.

• Testosterone, ABP, and inhibin provide negative feedback.

Female Reproductive Anatomy Basics

• Ovaries: gonads that produce ova and sex hormones

• Uterine tube: first duct that catches ova produced by the ovaries and moves them to the next duct system.

  • Typically the site where fertilization takes place (ova encounter sperm).

• Uterus: the second duct system; if ovum is fertilized, it implants on the wall of the uterus, providing structure and nutrients.

• Vagina: the final part of the duct system.

  • A passageway for any unfertilized ova to the outside of the body.

  • The female copulatory organ (used in sex).

  • Used as a birth canal.

The Ovaries

• Female gonads produce gametes (ova) and sex hormones (estrogens and progesterone).

• Ovarian cortex (outer): site of gamete and hormone formation within follicles (structures that surround the developing gamete and help with hormone production).

• Ovarian medulla (inner): houses blood, lymphatic vessels, and nerves.

The Uterus

• Wall of uterus:

  • Endometrium

  • Myometrium

  • Perimetrium

Oogenesis and Follicle Development

• Ova develop in the follicles and tend to mature together.

• Occurs in the ovarian cortex.

Oogenesis Before Birth to Puberty

• Not continuous

• Oogenesis begins before birth; no activity in childhood to puberty

• Oogonium (diploid cell) undergoes mitosis before birth and undergoes meiosis I but gets arrested in prophase I, becoming a primary oocyte.

• Primary oocytes stay arrested in prophase I.

Oogenesis Puberty to Menopause

• During puberty, the primary oocyte is unarrested and continues with meiosis I (still diploid).

• Finishes meiosis I, resulting in 2 haploid cells: one cell continues on to meiosis II, and the other produces a polar body (non-viable gamete).

  • Polar body produced by unequal cytokinesis (to ensure the ovum can survive, one cell gets all the cellular contents)

  • Polar body eventually degenerates or produces other polar bodies.

• Oogenesis results in one viable gamete, unlike spermatogenesis.

• The cell with the cellular contents will go on with meiosis II but arrest in metaphase II (secondary oocyte).

• Both polar bodies and oocyte are haploid cells.

• The secondary oocyte gets ovulated (released from the ovary); if it does not get fertilized, it stays in metaphase 2 and moves out through the uterus to be lost.

• If fertilization occurs, it finishes meiosis II and becomes a diploid cell.

Stages of Follicle Development

• Primordial follicle: Most basic stage; present around primary oocytes; has a single layer of follicular cells.
  *During childhood, follicles are still forming.

• Follicular cells develop into two cell types: granulosa and thecal (form a ring outside the follicle).

  • Thecal cells produce androgens.

  • Granulosa cells convert the androgens to estrogens and also produce inhibin.

• Primary follicle (before puberty): Similar to primordial, but bigger; pockets of follicular fluid (secretions from granulosa cells building up).
  *Many primordial follicles do not mature into primary follicles and die from atresia (the primary oocyte dies first, and the follicle dies as well; same with secondary).

• Vesicular follicle (after puberty): Occurs each month; only one matures. Covers the secondary oocyte; pockets combine to form the antrum.

The Ovarian Cycle

• A month-long cycle that includes the maturation of follicles, ovulation, and conversion of empty follicles to endocrine organs.

  1. Follicular Phase: Maturation of follicle cells (into vesicular follicle)

  2. Ovulation: Follicle ruptures, and the secondary oocyte is released and moves to the uterine tubes.

  3. Luteal Phase: Follicles are converted to temporary endocrine organs.

• Fraternal twins: Multiple vesicular follicles that mature and rupture at the same time, releasing multiple secondary oocytes.

• Identical twins: Cell division after fertilization.

• During the luteal phase, ruptured follicles develop into the corpus luteum, which secretes large amounts of progesterone.

  • If pregnancy occurs, it's maintained for 3 months to help prevent the pregnancy from ending.

• Lasts around 10 days; if pregnancy does not occur, it develops into scar tissue (corpus albicans), which does not produce hormones and ends the ovarian cycle.

Stages of the Ovarian Cycle

• Follicular Phase:

  • Primordial follicle: Primary oocyte surrounded by a single layer of squamous follicle cells.

  • Primary follicle: Follicle cells become cuboidal granulosa cells; microvilli and thecal cells develop.

  • Secondary follicle: Primary oocyte surrounded by multiple layers of granulosa cells; follicular fluid found in small cavities around the oocyte.

  • Vesicular follicle: Primary oocyte finishes meiosis I to become secondary oocyte; surrounded by granulosa cells and a fluid-filled antrum.

  • Maturation of a primordial follicle to this stage takes around 350 days.

• Ovulation Phase:

  • Ruptured follicle. Secondary oocyte is released from the vesicular follicle.

• Luteal Phase:

  • Corpus luteum: Remnant of the ruptured follicle; secretes progesterone and some estrogen.

  • Corpus albicans: Remnant of the corpus luteum after it ceases hormone secretion.

Timing of Oogenesis and Follicle Development

• None of the secondary follicles will mature past this point before puberty
  Most development occurs during fetal period, then some development happens during childhood and then the cycle starts at puberty

• Vesicular follicle develops

• Follicle ruptures if fertilazation occurs/ last 10 days if not fertilized, 3 months if it does occur

• Ovum will be lost, and the ovarian cycle reoccurs if fertilization occurs

• During menopause, there are no follicles left, so the ovarian cycle will not occur.

Spermatogenesis vs. Oogenesis

Hormonal Control of the HPG Axis (Female)

• First-tier:

  • Hypothalamus releases GnRH.

• Second-tier:

  • Anterior pituitary releases LH and FSH in response to GnRH.

  • Estrogens from the vesicular follicle trigger an LH surge from the anterior pituitary.

• Third-tier:

  • Ovaries secrete androgens in response to LH.

  • Ovaries convert androgens to estrogens and secrete estrogens and inhibin in response to FSH.

Effects

1. Estrogens stimulate a dominant follicle to mature to a vesicular follicle.

2. The new vesicular follicle produces large amounts of estrogens, triggering an LH surge.

3. The LH surge and FSH trigger ovulation.

Three Tiers of Control (Female)

1. First-tier: Hypothalamus releases GnRH

2. Second-tier: Anterior pituitary releases FSH + LH

3. Third-tier: LH and FSH target cells in the ovarian follicles

Effects of FSH and LH on the Ovarian Follicles

• LH acts on thecal cells and FSH acts on the granulosa cells

• estrogens stimulates oogenesis and the continued maturation of follicles in the ovarian cortex, or stimulating female secondary sex characteristics

Positive Feedback in the HPG – the LH Surge

*Estrogens provide positive feedback by ramping up the vesicular follicle and having more estrogen beign produced and sends positive feedbacks to the anterior pitutary and produces more LH and FSH (LH surge), big increase of LH causes ovulation
*After ovulation occurs it goes back to negative feesback
*Lutenizing hormone: refers to the conversion of the follicule into the corpus lumenen

Negative Feedback in the HPG

• After ovulation occurs, it goes back into the negative feedback.

• The estrogens and inhibin provide negative feedback.

• The estrogens inhibit the release of GHRH and LH, and inhibin inhibits the release of FSH.

• The levels of tropic hormones will all go down and will stay that way until the next ovarian cycle.

• HPG is not active before puberty because the hypothalamus is very sensitive to the negative feedback and keeps the follicles from maturing.

• After puberty, the hypothalamus is not as sensitive to inhibition and takes higher levels to inhibit the hypothalamus from stimulating GnRH.

• Once there are very few follicles left from maturation or atresia, the ovarian cycles will stop, and menopause will start.

The Role of the Corpus Luteum

• The corpus luteum produces progesterone, and the levels will rise.

• Progesterone from the corpus luteum also helps inhibit tropic hormones if the levels are rising.

• If fertilized, it will still release progesterone and not let other follicles mature.

• If not fertilized, the progesterone levels will drop, and a new ovarian cycle starts.

Changing Hormone Levels over the Course of the Ovarian Cycle

• LH surge: causes the LH surge, positive feedback triggers LH+FSH

• negative feedback if pregnancy does not occur

The Uterine Cycle

1. Menstrual Phase

2. Proliferative Phase

3. Secretory Phase

• The uterine cycle is happening with the ovarian cycle

• The uterine cycle occurs in the lining of the uterus (endometrium)

• Menstrual phase happens during the follicular phase

• Ovulation happens after the proliferative phase

• Secretory phase happens during the luteal phase

Endometrium Layers

• Stratum basalis: bottom and always present, doesn't change, and helps form the stratum functionalis

• Stratum functionalis: changes during the curse of the uterine cycle, has an extensive blood supply, endometrial glands are responsible for producing a subbtance that helps nurtioting and develpoing concepts

Uterine Cycle Phases

• Menstrual phase: the stratum functionalis breaks down and is shed from the uterus and lost through the vagina along with blood; first part of follicular phase

• Proliferative phase: the stratum functionalis is being built back up, more blood and endometrium glands; happening at the end of the follicular phase; oocyte is relased

• Secretory phase: the stratum functionalis really builds up and gets thicker, extensive blood supply, well-developed endometrial glands secretes uterine milk: nourish a developing conceptus if a fertilized ovum does implant

If pregnancy does occur, the secretory phase continues, and the straum functionalis develops more to sustain a conceptus

Phases of the Uterine Cycle

*Proliferative Phase: lead to increase estrogen production; estrogen rise and stimulates the formation of stratum functionalisand estrogen stimulates the endometrium to make progesterone receptors (preparing) positive feedback
*Tropic hormones go down and also change the ovary hoemone levels as well corpus luteum

*progesterone is responsible for stimulating continues development of the stratum functionalis to get thicker etc, progesterone levels at the end of the cycle depends on whether or not preganacy occurs, if it doesn't the corpusl luteum turns to the corpus albicans, no longer any progesterone, if it does occur the levels will stay high and the secretory phase continues and relase the uterine milk

human choriconic geanetotropinor (HCG) is sinthesis by the creptus and keeps the corpus luteum present and releasing progestorne, after the first 3 months the placenta is form and takes over and the corpus albicans is formed, HCG is what preganacy tests measuure