Male reproductive system
fig 17-6
1
Testis & seminiferous tubules
fig 17-5
2
Spermatogenesis
fig 17-7
3
Structure of seminiferous tubules
fig 17-4
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Spermatogenesis
fig 17-9
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Spermatogenesis (notes)
Spermatogenesis begins at puberty
Spermatogonia  primary spermatocytes
mitotic division, occurring in basal compartment
primary spermatocytes cross tight junction to adluminal compartment
Primary spermatocyte  secondary spermatocytes
first meiotic division, occurring in adluminal compartment
Secondary spermatocyte  spermatids
second meiotic division, adluminal compartment
Spermatids  spermatozoa
no division, maturation process
6
Sertoli cell (functions)
1. form barrier between plasma & mature sperm
2. nourish developing sperm
3. secrete luminal fluid & androgen binding protein
4. respond to FSH & testosterone to stimulate spermatogenesis
5. secrete inhibin which inhibits release of FSH
6. absorb & destroy defective sperm
7
Structure of spermatozoon
fig 17-8
Acrosome: contains enzymes involved in fertilization process
8
Erection & ejaculation
fig 17-10
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Erection, emission & ejaculation (notes)
Erection:
stimuli from CNS systems, penile mechanoreceptors
parasympathetic nerves (nonadrenergic noncholinergic) release NO
NO stimulates soluble guanylate cyclase in penile arteriole smooth muscle
cyclic GMP relaxes smooth muscle & increases blood flow
increased blood flow into 2 corpora cavernosa & corpus spongiosum
erection compresses venous outflow & maintains erection
Emission: (movement of seminal fluid into prostatic urethra)
sympathetic NS  peristaltic contractions of vas deferens
Ejaculation:
semen entering prostatic urethra  spinal reflex involving somatic NS &
skeletal muscle of perineal floor
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Male hormonal control
fig 17-11
11
GnRH, LH, FSH (notes)
Gonadotropin releasing hormone (GnRH)
secreted by hypothalamus into hypothalamo-hypophyseal portal system
increases at puberty, ? less sensitivity to testosterone feedback
pulsatile release ~90 min  pulsatile LH & FSH release
Luteinizing hormone (LH)
from anterior pituitary, stimulated by GnRH, inhibited by testosterone
acts on Leydig cells of testis  testosterone release
Follicle stimulating hormone (FSH)
from anterior pituitary, stimulated by GnRH, inhibited by inhibin
acts with testosterone on Sertoli cells to promote spermatogenesis
Note: LH & FSH are produced by the same anterior pituitary cell
12
Testosterone (notes)
Source
synthesized & released by Leydig (interstitial) cells of testis
release stimulated by LH
Actions
inhibits release of GnRH & LH (not FSH)
stimulates spermatogenesis (in conjunction with FSH)
stimulates differentiation of male genitalia (in utero)
stimulates development of male 2 sexual characteristics at puberty
growth & development of internal/external genitalia
bone growth and epiphyseal plate closure, muscle development
axillary, pubic, body hair, male pattern baldness
fat distribution, laryngeal growth, sebaceous glands
behavioral effects, libido, aggression
Mechanism: steroid, androgen binding protein,  transcription,  translation
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Female reproductive system
fig 17-13a
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Female genitalia (internal)
fig 17-13b
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Female genitalia (external)
fig 17-14
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Oogenesis
Note: asymmetric meiotic divisions
timing of mitotic & meiotic divisions
fig 17-15
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Oogenesis (notes)
Timing of divisions
oogonium  primary oocyte (mitosis) in utero
1 oocytes begin 1st meiotic division, stop in prophase, still in utero
1 oocyte  2 oocyte + 1st polar body, (1st meiotic) before ovulation
2 oocyte  ovum + 2nd polar body (2nd meiotic) after fertilization
Note: one 1 spermatocyte  4 spermatozoa; one 1 oocyte  1 ovum
Follicular attrition
oocyte surrounded by layer of granulosa cells  primordial follicle
several million follicles form in utero, 2-4 x 106 remain at birth
~400,000 remain at puberty, ~400 ovulated during reproductive life
last ovulated may be 35 years older than first ovulated at puberty
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Follicular development
fig 17-16
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Follicular life cycle through menstrual cycle (notes)
In childhood & adult life
many primordial follicles develop to preantral follicles
day 1 – day 7
10-25 preantral follicles  antral follicles (larger oocyte, more layers
of granulosa cells, antrum appears, thecal cells differentiate)
around day 7
one antral follicle becomes dominant, rest degenerate
around day 14
mature follicle ~ 1.5 cm diameter, bulging through surface of ovary,
primary oocyte divides hours before ovulation occurs
day 14 – day 25
corpus luteum produces estrogens, progesterone & inhibin
day 25 – day 28
corpus luteum spontanteously degenerates, menstrual flow begins
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Follicular life cycle through menstrual cycle
fig 17-17
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Functions of granulosa & thecal cells
Granulosa cells
1. nourish the developing oocyte
2. secrete antral fluid
3. site of action of estrogens & FSH
4. contains aromatase, the enzyme which converts androgen to estrogens
5. secrete inhibin (inhibits FSH release by anterior pituitary)
Note the similarities between granulosa cells & Sertoli cells
Theca cells
1. secrete androgens which diffuse to granulosa cells
Note the similarity between theca cells & Leydig cells
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Estrogens synthesis by granulosa & thecal cells
Note: LH & FSH are shown as acting on the wrong cells in your text book
LH
FSH
Note: “estrogens” are a mixture of estradiol (most), estriol, & estrone
fig 17-19
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Hormonal control of the menstrual cycle
fig 17-18
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Sequential hormonal changes during menstrual cycle
1.
degeneration of corpus luteum  estrogen,  progesterone,
 inhibin  FSH & LH
2.
antral follicles develop  estrogen levels
3.
plasma estrogen levels increase
4.
~day 7, dominant follicle secretes high levels of estrogen
5.
plasma estrogen level increases sharply
6.
high estrogen levels suppress FSH levels causing degeneration
of non-dominant follicles
7/8.
 estrogen levels  LH surge (positive feedback)
9.
1st meiotic division of 1 oocyte
10.
~day 14, ovulation occurs
11.
the dominant follicle collapses, and reogranizes as the corpus
luteum
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Sequential hormonal changes during menstrual cycle
12.
corpus luteum secretes estrogen & progesterone
13.
plasma levels of estrogen & progesterone increase, suppressing
release of GnRH, LH, & FSH
14.
~day 25, corpus luteum spontaneously degenerates
15.
 secretion & plasma levels of estrogen & progesterone
16.
 estrogen & progesterone  FSH & LH levels which begin
follicular development of the next menstrual cycle
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Hormonal interactions in the female
fig 17-20
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Hormonal initiation of ovulation
fig 17-21
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Endometrial changes during menstrual cycle
fig 17-22
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Endometrial changes during menstrual cycle
Menstrual phase (first 3-5 days)
corpus luteum degenerates, estrogen & progesterone levels fall
endometrial blood vessels constrict  ischemia, then relax
endometrium degenerates resulting in menstrual flow
Proliferative phase (day 5-14)
increasing estrogen levels
 myometrial & endometrial growth
 progesterone receptors on endometrial cells
 cervix secretes abundant, clear, watery fluid
Secretory phase (day 15-28)
high progesterone levels
 blood vessels,  coiling of glands,  glycogen in cells
 cervix secretes thick sticky mucus (mucus plug)
 contraction of myometrium
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Estrogen actions
moderate increase inhibits release of GnRH & LH (negative feedback)
large increase stimulates LH release (positive feedback)
differentiation of female genitalia in utero is due to the absence of
testosterone, not any actions of estrogens
stimulates the changes seen at puberty
growth of external genitalia
growth of breasts (particularly fat deposition & duct growth)
bone growth & epiphyseal plate closure (pubertal spurt & female
configuration)
fat distribution, reduces LDL & raises HDL (anti-atherogenic)
during menstrual cycle
 Fallopian tube peristalsis & ciliary activity, growth of myometrium &
endometrium, cervical mucus abundant & clear
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Progesterone actions
high levels (in presence of estrogen) inhibit release of GnRH, hence LH
& FSH (negative feedback)
stimulates the changes seen at puberty
growth of breasts (particularly glandular tissue)
during menstrual cycle
 Fallopian tube peristalsis & myometrial contractions
 endometrial blood flow,  coiling of glands,  glycogen content
 thick sticky cervical secretion (mucus plug)
 body temperature by ~0.5 C
Note: adrenal androgens stimulate axillary & pubic hair growth, libido
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Female sexual response
Arousal phase
initiated by physical (e.g. clitoral stimulation) or psychological stimuli
mostly directed by parasympathetic nervous system
 blood flow to breasts, nipple erection
 blood flow to genitalia, swelling of labia, clitoral erection
 mucus secretion by vaginal epithelium
Orgasmic phase
mostly directed by sympathetic nervous system
rhythmic contractions of lower 1/3 of vaginal canal
associated physical responses ( heart rate,  respiratory rate,
intensely pleasurable sensations)
Note: achieval of orgasm is not necessary for fertilization to occur
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Fertilization 1
Viability of ovulated oocyte: ~24 hours
Viability of ejaculated sperm: ~4 days
Fertilization could occur from 4 days prior to, or 1 day after ovulation
Sperm transport & capacitation
each ejaculate contains ~3x106 spermatozoa
sperm transport into Fallopian tube part by peristalsis, part by sperm
flagellar action; only ~100 sperm make it
sperm capacitation: several hours in female tract, flagellar function
changes, membrane changes permit fusion with egg
Oocyte structure
ovulated as 2 oocyte, surrounded by zona pellucida (clear non-cellular
layer, and corona radiata (granulosa cells ovulated with oocyte)
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Fertilization 2
oocyte picked up by cilia on fimbriae, moves into ampulla of oviduct, and is
moved by ciliary action to uterus taking ~4 days
fertilization typically occurs in ampulla
sperm moves between corona cells, fuses with species-specific receptors
on zona pellucida
enzymes of acrosome dissolve path through zona pellucida
sperm head enters oocyte, tail remains outside
entry of first sperm causes oocyte membrane to become impermeable to
subsequent sperm
entry of sperm induces 2nd meiotic division & expulsion of 2nd polar body
sperm & ovum nuclei fuse  zygote
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Fertilization
fig 17-23
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Implantation
zygote takes 3-4 days to reach uterus, undergoing several cell divisions
en route
cell mass (morula) floats in uterus for additional 3 days & develops into
blastocyst
note: at this time corpus luteum is functioning and the cervix secretes
the mucus plug that prevents exit of blastocyst
blastocyst implants in endometrium and begins to organize placenta
placenta begins secretion of human chorionic gonadotropin (HCG) ~3
days after implantation
HCG maintains function of corpus luteum beyond normal life (~11 days)
HCG is what is detected by pregnancy tests
clinical labs can detect HCG before the next menstrual period is due
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Implantation of blastocyst
fig 17-24
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