LECTURE 23 + 24 - REPRODUCTIVE PHYSIOLOGY

how do the gametes differ from somatic cells?

• are they haploid or diploid?

• what process are the gametes formed through?

-all gametes are haploid

• produced via meiosis

  • spermatogenesis: formation of sperm

  • oogenesis: ovum

• somatic cells in the body are all diploid

  • formed by the function of the gametes

how do the “products” of meiosis and mitosis differ?

both meiosis and mitosis require DNA replication prior to cell division

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-mitosis produces 2 identical copies to the parent cell

• product: 2 identical diploid cells

• one division

• responsible for growth, repair, and regeneration of tissues

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-meiosis

• 1st division produces 2 diploid cells

  • crossing over occurs during prophase 1 —→ 2 daughter cells are not identical

• 2nd division produces 2 haploid cells per daughter cell

  • results is a total of 4 haploid cells

  • cells are not identical

what does spermatogenesis form?

spermatogenesis: formation of sperm cells

know the general process of spermatogenesis.

• what cells are a part of each division?

-begins with the spermatogonia are the stem/germ cells that are involved in sperm production

• undergo mitosis producing primary spermatocytes

• primary spermatocytes are produced from the onset of puberty until death

-primary spermatocytes undergo meiosis 1

• forms 2 secondary spermatocytes

• due to crossing over the 2 secondary spermatocytes are not identical

-secondary spermatocytes undergo meiosis 2

• forms immature sperm cells called spermatids

• each secondary spermatocyte produces 2 spermatids (haploid)

-spermatids mature into spermatozoa

*look at lecture 23 slide 12 for better visualization

what are immature sperm cells called?

spermatids

what features do sperm gain following maturation?

• know the general structure of a sperm cell

• what does the acrosome do?

• where is the DNA stored

spermatozoa: mature sperm

• spermatids mature into spermatozoa

• maturation includes the development of the flagella and overall sperm structure

3 main regions:

• head

  • contains the:

  • nucleus

    • stores DNA

  • acrosome

    • contains enzymes that break down the protective coat of the ovum

      • allows for delivery of the nucleus (the genetic information)

• midpiece

• contains remaining organelles

  • includes many mitochondria

    • provides ATP for movement via the flagella

• midpiece is discarded following fertilization of the ovum

  • mitochondria and its DNA only comes from the ovum

• flagellum

where does spermatogenesis take place? where are the spermatogonia found in this structure?

-sperm development occurs within the seminiferous tubules of the testes

-spermatogonia are attached to the basement membrane of the seminiferous tubules

what are sertoli cells? what two hormones active Sertoli cells? what effect is seen if these hormones bind to Sertoli cells? what hormone is produced by the sertoli cells?

-sertoli cells contain receptors for the hormones testosterone and for follicle stimulating hormone

-binding of hormones results in the release of factors that stimulate spermatogenesis and sperm maturation

-produce the hormone inhibin

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HORMONES INVOLVED IN SPERMATOGENESIS

-sperm production is regulated by follicle stimulating hormone and luteinizing hormone

• both are produced and released by the anterior pituitary gland

-follicle stimulating hormone binds to sertoli cells resulting in the initiation of spermatogenesis

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FOLLICLE STIMULATING HORMONE

-activates the sertoli cells found in the seminiferous tubules

• spermatogonia begin spermatogenesis

  • meiosis 1 and 2 occur

• results is 4 immature spermatids

what are leydig cells? what hormone actives leydig cells? what effect is seen if this hormone binds to Leydig cells? what hormone is produced by the Leydig cells?

-AKA interstitial cells

-found between the seminiferous tubules

-contain receptors for luteinizing hormone (this activates leydig cells)

-produce and release the hormone testosterone

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LUTEINIZING HORMONE

-binds to leydig cells resulting in the release of testosterone

• testosterone binds to receptors in the sertoli cells —→ maturing and production of sperm

how are the release of luteinizing hormone and follicle stimulating hormone inhibibted?

INHIBITION OF LH AND FSH

-sertoli cells produce and release the hormone inhibin —→ inhibits the release of FSH from anterior pituitary

-excess testosterone levels inhibit the release of luteinizing hormone from the anterior pituitary

-keeps testosterone levels at normal levels

know the other effects of testosterone on the body.

OTHER EFFECTS OF TESTOSTERONE ON THE BODY

-secondary male sex characteristics:

• thickening of the thyroid cartilage

• facial hair growth

• increased body hair growth

-increased muscle mass and bone density

-increased libido

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other effects of estrogen

• increases prolactin levels

• development of breast tissue

• increases libido

• increases adipose deposition

know what the seminal vesicles, bulbourethral glands, and prostate gland contribute the ejaculate.

SEMINAL VESICLES

-secretes products into the ejaculatory duct

• sperm move from the ampulla into the ejaculatory duct

-contributions to ejaculate:

• alkaline substance to neutralize the urethra (and female reproductive tract)

• mucus

• fructose

• coagulating enzymes

PROSTATE GLAND

-secretes products into the prostatic urethra and ejaculatory duct

-contributions to ejaculate:

• enzymes

• citrate

BULBOURETHRAL GLANDS

-secretes products into the membrane urethra

-contributions to ejaculate

• lubricant and basic substance to neutralize the urethra

know the general process of oogenesis.

• what cells are a part of each division?

• what is produced following each meiotic division?

• how does this process differ from spermatogenesis

• when does meiosis 1 take place? what must happen for meiosis 2 take place?

oogenesis: formation of ova

-begin with oogonia are the stem/germ cells that are involved in ovum production

• undergo mitosis producing primary oocytes

• primary oocytes are produced while in utero and remain dormant until puberty

-primary oocyte undergoes meiosis 1

• forms 1 secondary oocyte and one polar body

• completed prior to ovulation

• secondary oocyte is ovulated

-secondary oocyte undergoes meiosis 2

• completed following fertilization

  • if fertilization does not occur —→ secondary oocyte is lost during menses

• forms 1 ovum and 1 polar body

know the sperm pathway through the female reproductive tract

• where does fertilization take place be specific.

-sperm is ejaculated into the vagina —→ through the cervix —→ uterus —→ fallopian tube

-fertilization occurs in the infundibulum of the fallopian tube

• funnel shaped portion of the fallopian tube

• ~90% of fertilization occurs here

what cell type is released from the ovary during ovulation?

-ovaries: site for oogenesis

-ovulation: release of the secondary oocyte from the ovary

• secondary oocyte is released into the pelvic cavity

• fimbriae manipulate the oocyte into the fallopian tube

where does implantation of the zygote occur?

-zygote forms when sperm and ovum meet

• second meiotic division occurs prior to zygote formation

-zygote moves through the fallopian tube into the uterus

-implantation occurs in the endometrium of the uterus

know the general structure and features of the follicular cells below:

• primordial follicles

• primary follicles

• preantral follicles

• early antral follicles

• mature follicles

PRIMORDIAL FOLLICLES

• primary oocytes are in their dormant phase

• surrounded by a primordial follicle

  • comprised of granulosa cells

PRIMARY FOLLICLES

• at puberty primordial follicle begins to develop forming a primary follicle

• follicle begins to thicken (the granulosa cells thicken) —→ provides nutrients to primary oocyte and can secrete hormones

  • granulosa cells

• zona pellucida forms —→ protective coat that surrounds the primary oocyte

PRENATAL FOLLICLES

• AKA secondary follicles

• follicle continues to thicken and meiosis 1 occurs forming secondary oocyte

EARLY ANTRAL FOLLICLES

• formation of the antrum

  • filled with follicular fluid

  • contains water, hyaluronic acids, hormones, and other proteins

  • produced primarily by the granulosa cells

MATURE FOLLICLES

• antrum enlarges

• granulosa cells surrounds the oocyte which is now embedded within the antral fluid

• secondary oocyte is released

  • hormones prepare the reproductive tract for implantation

know the phase of follicular development in order (above)

primordial follicles —→

primary follicles —→

preantral follicles —→

early antral follicles —→

mature follicles

what is the corps luteum? what hormones does the corpus luteum secrete?

-remaining granulosa cells that formed the follicle

• act as an endocrine structure

  • secretes estrogen and progesterone

what are the phases of the ovarian cycle?

• what event separates the 2 main phases?

• what is happening during each of these phases

-consists of two separate phases that are separated by ovulation

• follicular phase - follicles begin to mature

• luteal phase - phase where the corpus luteum acts as a an endocrine structure

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DAY 1 —→ beginning of uterine bleeding (BEGINNING OF FOLLICULAR PHASE)

• endometrial lining is being shed

• continues to day 7

follicular development begins in the ovaries

• primordial follicles begin the process of development

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DAY 7 —→ bleeding ends

one follicle becomes the dominant follicle

• this is the follicle that will continue to mature and the oocyte within will be released during ovulation

• maturation continues until day 14

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DAY 14 —→ ovulation

• secondary oocyte is released

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DAY 14-25 —> corpus luteum acts as an endocrine structure secreting estrogen + progesterone (BEGINNING OF LUTEAL PHASE)

• prepares uterus for implantation

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DAYS 25-28 —→ corpus luteum degenerates resulting in the formation of the corpus albicans

what hormone triggers the release of luteinizing hormone and the follicle stimulating hormone?

• when do LH and FSH peak

• what effects do LH and FSH have on the female reproductive tract?

Gonadotropic Releasing Hormone (GnRH) triggers the release of luteinizing hormone and follicle stimulating hormone from the anterior pituitary gland

• luteinizing hormone is secreted at higher levels than follicle stimulating hormone

luteinizing hormone and follicle stimulating hormone levels peak at ovulation

• luteinizing hormone triggers estrogen and progesterone release

  • produced by the follicle/granulosa cell

• follicle stimulating hormone promotes maturation of the dominant follicle

-estrogen, luteinizing hormones, and follicle stimulating hormone levels drop following ovulation

• corpus luteum develops during this time

what causes the second peak in estrogen and progesterone levels?

corpus luteum releases progesterone and estrogen

• produces second peak in hormone levels

• prepares uterus for implantation

what hormone is responsible for triggering the thickening of the endometrium? when is the endometrial lining the thickest?

-dominant follicle releases the hormone estrogen —→ endometrial thickness increases

-endometrial lining is at its thickest following ovulation

-endometrial lining is shed on day 1 of the ovarian cycle

how are FSH and LH release inhibited?

hypothalamus release GnRH —→

anterior pituitary gland releases follicle stimulating hormone and luteinizing hormone

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follicle stimulating hormone acts on granulosa cells stimulating follicular development —→

• maturation of oocytes

follicle stimulating hormone triggers release of inhibin from granulosa cells

• inhibits release of FSH from the anterior pituitary

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luteinizing hormone acts on theca cells

• release of androgens

granulosa cells converts androgens to estrogen

• stimulates further estrogen production

estrogen inhibits the release of:

• FSH and LH from anterior pituitary

• GnRH from the hypothalamus

what does the sperm contribute to the ovum?

-sperm contributes nucleus (DNA) ——> formation of zygote

-acrosome contains enzymes that allow the sperm to penetrate the zona pellucida

• 2nd fertilization cannot occur due to cortical reaction

how do estrogen, progesterone, and human chorionic gonadotropin hormones levels change following fertilization and implantation?

HORMONES FOLLOWING FERTILIZATION AND IMPLANTATION

progesterone and estrogen levels continue to increase until delivery

• produced by the placenta

human chorionic gonadotropin (hCG) is secreted by the placenta

• increases estrogen and progesterone secretion

• thickens endometrial lining

what two hormones are necessary for milk synthesis and secretion?

• which hormone stimulates alveolar development and milk synthesis?

• which hormone is responsible for milk ejection?

• what triggers the release of these two hormones?

prolactin —→ initiated alveolar development and milk synthesis

oxytocin —→ responsible for milk ejection

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suckling triggers the release of prolactin releasing factor (PRF) and dopamine from the hypothalamus —→

increased PRF —→ increased prolactin secretion from the anterior pituitary —→

increased milk synthesis

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suckling triggers the release of oxytocin from the posterior pituitary —→

increased oxytocin —→

contraction of myoepithelial cells —→ milk ejection