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Physiology (MPP 3202) > Ch. 20 Reproduction (Day 1) > Flashcards

Ch. 20 Reproduction (Day 1) Flashcards

1
Q

What are the 2 types of cells in the human life cycle?

A
  1. Germ cells
    - -ova, sperm
  2. Somatic cells
    - -everything else in the body
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2
Q

Gametogenesis: Males vs. Females

A

Males: large numbers of gametes produced continuously from stem cells, beginning at puberty and extending until senescence (age-dependent decrease in testosterone production)

Females: release only ONE gamete at a time from limited pool of preformed gametes in a process that is repeated at regular monthly intervals

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3
Q

Where does gametogenesis begin?

A

In utero - mitotic divisions to increase germ cell numbers; PAUSES at birth and RESUMES at puberty

Timing varies between males and females

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4
Q

Spermatogenesis

A
  1. Spermatogonium DNA replicates but no division to form primary spermatocyte (46 chromosomes to 92) at PUBERTY

–MEOISIS 1 OCCURS–

  1. Primary spermatocyte splits into 2 secondary spermatocytes (46 chromosomes each)

–MEIOSIS 2 OCCURS–

  1. The 2 secondary spermatocytes split into 4 spermatids (23 chromosomes each), which mature into sperm via spermiogensis
  2. Sperm have 23 chromosomes each, released from tests during “spermiation”
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5
Q

Oogensis

A
  1. Oogonium (46 chromosomes) DNA replicates but no division into Primary Oocyte (92 chromosomes)

–MEIOSIS 1 OCCURS (puberty)–

  1. primary oocyte splits into 1 secondary oocyte (46 chromosomes) and 1 polar body (dies)
  2. secondary oocyte begins Meiosis 2 and is released during ovulation
  3. secondary oocyte splits into 1 Ootid (23 chromosomes) and 1 polar body (23 chromosomes, dies)
    5a. Meiosis 2 is completed ONLY IF FERTILIZATION OCCURS
    5b. If fertilization doesn’t occur, Ootid dies (?)
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6
Q

Oocyte production

A
  1. Primary oocyte
    - a) toward end of gestation, female’s oogonia begin meiosis to produce PRIMARY OOCYTES
    - b) ovaries of newborn girl have 2 million primary oocytes
    - c) by puberty, this number is cut to ~400,000
    - d) only about 400 of these will be ovulated in her lifetime
  2. Primary oocytes contained w/in primary follicles - have one layer of cells
    - a) in response to FSH, some of primary follicles grow to produce many layers of granulosa cells (granulose cells support developing oocyte in middle of that follicle)
    - b) some develop fluid-filled vesicles called secondary follicles
  3. Continued growth results in fused vesicles to form single atrium; this is a mature Graafian follicle
  4. As Graafian follicle grows, primary oocyte finishes meiosis 1 to become secondary oocyte (plus a polar body, which soon degenerates)
  5. Secondary oocyte begins meiosis 2, but stops at metaphase 2
  6. Meiosis 2 will complete, ONLY if there is fertilization of ovum
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7
Q

Is it the sperm or egg that determines genetic sex of zygote?

A

Sperm

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8
Q

Sex determination in embryo

A

If zygote contains Y chromosome: male (even if multiple X’s)

If zygote gets only Y but no X –> lethal b/c X chromosome is essential for survival

X-inacitvation in females: early in development, after ovaries develop, one X in each body inactivates (becomes Barr body) - inactivation is random - some may be sperm-derived, others ovum-derived

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9
Q

Are polar bodies and Barr bodies the same?

A

No, they’re 2 different bodies

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10
Q

Why does X-inactivation occur in females (Barr body)?

A

So that only one X is viable in gamete (for reproduction later on in life)

random inactivation of one of X chromosomes

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11
Q

Chromosomal sex and development of embryonic gonads

A

Genetic sex is determined by which sex chromosome is carried by the sperm (X or Y)

Key gene carried on Y chromosome: “Testis Determining Factor” (TDF), aka “Sex Determining Factor” (SRY)

If sperm contributes Y: SRY expression stimulates testis differentiation

If sperm contributes X: lack of SRY allows ovary differentiation

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12
Q

The presence/absence of what gene on the sperm determines genetic sex?

A

SRY (aka TDF) gene

Presence of SRY = male

Absence of SRY = female

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13
Q

Sexual differentiation occurs early in development - internal organs

A

Regardless of genetic sex, embryo has potential to become phenotypically male or female - female pattern occurs unless humoral signals are released from fetal testis

Depends on presence of SRY gene on Y chromosome

If female: no SRY gene, biopotential gonads –> ovaries

If male: SRY expression elicits gonads –> testes

Testes produce masculinization factors (testosterone, anti-Müllerian hormone [AMH])

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14
Q

Wolffian Duct

A

Male

Degenerates if SRY isn’t present; develops if SRY is present

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15
Q

Müllerian Duct

A

Female

Degenerates if SRY is present; develops [ovaries, female reproductive organs] if SRY is NOT present

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16
Q

T/F: Testes secretion of testosterone is what determines if embryo is male or female.

A

FALSE

Testes secretion of testosterone is NOT what determines genetic sex - it’s the presence/absence of SRY gene expression that determines genetic sex

If SRY gene is present, testes develop and then testosterone is secreted

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17
Q

Leydig Cells

A

Males

Secrete testosterone

Controls development of Wolffian duct into accessory structures, development of external male genitalia (via DHT)

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18
Q

Sertoli Cells

A

Males

Secrete Anti-Müllerian hormone

Causes regression of Müllerian duct

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19
Q

T/F: Testosterone is NOT produced until testes differentiate

A

True

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20
Q

Sexual differentiation

A

Production of dihydrotestosterone (DHT) required for development of male external genitalia

21
Q

Masculinization

A

Due to testosterone

Converted to DHT (dihydrotestosterone)

Changes occur in brain development

22
Q

From birth to puberty - period of reproductive senescence

A

Testes stop producing testosterone by 3rd trimester; ovaries don’t produce embryonic sex hormones

Sex hormone secretion does NOT resume in either sex until gonads are stimulated at puberty

Onset of puberty: anterior pituitary begins releasing gonadotropic hormones

23
Q

Onset of puberty

A

Secretion of FSH and LH is elevated at birth and stays high for the first 6 months of postnatal life; declines to almost nothing until puberty

Puberty begins w/ release of LH (pulsatile)

  • a) results in increases in testosterone or estradiol-17beta secretion
  • b) these hormones produce secondary sex characteristics
  • -> females: growth spurt, breast development, menarche
  • -> males: growth spurt, muscle, penis and testis growth
  • -> both females and males: body hair - all stimulated by adrenal androgens
24
Q

What is menarche?

A

First menstruation

25
Puberty
Maturation of hypothalamic-pituitary axis - seems to be associated w/ childhood nutrition - age of menarche has decreased in Western societies as energy intake has increased Pulsatile secretion of GnRH increases --> increase in secretion of LH and FSH As energy intake increases --> increased storage of TG in adipose --> increased leptin secretion Leptin goes from adipose tissue to both hypothalamus and pituitary, which promotes release of GnRH and eventually secretion of LH and FSH which act on reproductive organs
26
Growth as a function of sex and age
Age of onset of puberty: - depends on activity levels and amount of body fat - leptin secreted by adipose cells required for onset - exercise may inhibit GnRH secretion - more active, slimmer girls begin puberty later - melatonin from pineal gland may play role, but this is not proven in humans
27
Interaction between hypothalamus, anterior pituitary, and gonads
Follicle-Stimulating hormone (FHS) and luteinizing hormone (LH) produced in anterior pituitary glands (males and females) - 3 effects: - 1) stimulation of spermatogenesis or oogenesis - 2) stimulation of gonadal hormone secretion - 3) maintenance of structures of gonads Release of FSH and LH controlled by release of gonadotropin-releaseing hormone (GnRH) from hypothalamus Regulated by negative-feedback loop where rising levels of gonadal hormone - 1) inhibit GnRH release - 2) inhibit pituitary response to GnRH
28
Hormonal Control of Reproduction
GnRH release is pulsatile in both males and females (more so in females; pulses every 1-3 hours) LH, FSH act via feedback inhibition on GnRh release Release of LH, FSH stimulated by low levels of gonadal steroids; when steroids increase, usually get feedback inhibition of LH, FSH BUT if estrogen greatly increases can get stimulation of gonadotropin (LH) release
29
Male Reproduction - Gross Anatomy
Accessory glands (seminal vesicles, prostate, bilbo-urethral glands) - secrete fluids which lubricate tubular system and nutrients (e.g. fructose) to support energy usage by sperm. Fluid from seminal vesicles constitutes to about 70% of sperm volume Placement of testis outside abdominal cavity maintains 2-3ºC
30
Duct of Epididymis
Site of maturation and storage of sperm; FSH receptors (on sertoli cells)
31
Seminiferous Tubule
Site of sperm production
32
During arousal and ejaculation, contractions of circular smooth muscle around epididymal duct advance sperm into ____ ____ and ultimately the ____.
Vas Deferences; urethra
33
Spermatogenesis in seminiferous tubules
Leydig cells - produce and secrete testosterone in response to LH; active in fetus, virtually disappear after first 6 months of postnatal life; reappear w/ onset of puberty Sertoli cells - regulation of sperm development - secrete proteins necessary for sperm development (e.g. androgen-binding protein) in response to FSH and testosterone
34
T/F: Sperm have receptors for testosterone.
FALSE Sertoli cells are the ones that have testosterone receptors
35
Hormonal control of spermatogenesis
negative feedback effects of testosterone and inhibin maintain relatively constant secretion of gonadotropin in males Androgen secretion decreases slowly in females to hypogonadal state by age 70 Other factors affecting testosterone secretion: physical inactivity, obesity, drugs
36
Fimbriae
female partially wrap around ovaries, "catch" oocytes after ovulation
37
Fallopian tube
female ciliary action moves egg from ovary toward uterus; dysfunction can result in infertility or ectopic pregnancy
38
Uterus
female normal site of implantation and development of fertilized egg
39
Cervix
female cervical canal lined w/ mucus-secreting cells - mucus forms protective barrier between vagina and uterus
40
Endometrium
female innermost tissue layer in uterus; epithelial thickness and character vary during menstrual cycle - cells progress through monthly cycles of proliferative, secretory, and menses phases coinciding w/ ovarian cycle
41
Myometrium
female middle muscle layer in uterus; contracts to expel baby at birth
42
Perimetrium
female outer CT layer in uterus
43
Follicular development - ovarian cycle
Preovulatory phase -follicle developing under influence of steadily rising levels of estrogen When estrogen levels peak, induces surge of LH which induces ovulation Postovulatory (luteal phase) -corpus luteum (remnants of ruptured follicle egg was released from in ovulation) secretes hormones which help prepare for pregnancy If no pregnancy, corpus luteum degenerates and cycle resumes
44
What happens when fertilization of the egg does NOT occur?
Corpus luteum survives for about 12 days If no pregnancy, C.L. undergoes apoptosis, becomes inactive (corpus albicans) As luteal cells die, secretion of estrogen and progesterone decreases As progesterone levels decrease blood supply to endometrium is compromised, surface epithelium begins to die 2 days after C.L. ceases fxn (14 days after ovulation), endometrium begins to slough its surface layer & menstruation begins—lasts from 3-7 days As steroids decrease negative feedback on hypox, pituitary, so GnRH --> FSH, LH increase Increasing FSH, LH induce start of the next ovulatory cycle (during menstrual cycle
45
Follicular phase - early
Follicular development begins under influence of FSH As follicle matures, FSH and LH stimulate granulose cells and thecal cells, respectively, to produce androgens Granulose cells also produce AMH which limits number of follicles development at a time by decreasing their sensitivity to FSH Thecal cells synthesize androgens --> diffuse to granulose cells --> covert androgens --> estrogens
46
Follicular Phase - mid-late
At the same time, estrogen stimulates its own production by granulose cells Menstruation ends during early follicular phase In response to rising estrogen, new endometrium begins to grow - increased cell number, enhanced blood supply As follicles enlarge, granulosa cells secrete fluid that collects in cavity in follicle (atrum). Fluid contains factors needed for ovulation
47
Ovulatory Phase
ovarian estrogen rises to a peak, its effect now changes to strong STIMULATORY effect on GnRH --> FSH, LH - get huge surge in LH increased estrogen levels also stimulates growth of endometrium to max thickness Mature follicle secretes enzymes which break down ECM holding follicular cells together; breakdown products induce inflammatory response - neutrophils secrete prostaglandins --> contraction of smooth muscle in outer thecal layer, rupturing follicle wall --> egg is extruded
48
Post-ovulatory (LUTEAL) phase
LH surge also causes remaining thecal and granulosa cells to migrate into antrum --> transform into luteal cells, remaining structure is corpus luteum (C.L.) C.L. secretes estrogen, highly increases progesterone and inhibin levels - negative feedback on hypothalamus and pituitary - gonadotropin secretion shut down Progesterone promotes further development of endometrium to support pregnancy, also promotes thickening of cervical mucus to protect uterus Progesterone elicits rise in basal body temp (~0.3ºC) which lasts until onset of menstruation

Physiology (MPP 3202) (32 decks)

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