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Male reproductive system. fig 17-6. Testis & seminiferous tubules. fig 17-5. Spermatogenesis. fig 17-7. Structure of seminiferous tubules. fig 17-4. Spermatogenesis. fig 17-9. Spermatogenesis (notes). Spermatogenesis begins at puberty Spermatogonia  primary spermatocytes

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spermatogenesis notes
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

sertoli cell functions
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

structure of spermatozoon
Structure of spermatozoon

fig 17-8

Acrosome: contains enzymes involved in fertilization process

erection emission ejaculation notes
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

gnrh lh fsh notes
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

testosterone notes
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

oogenesis
Oogenesis

fig 17-15

Note: asymmetric meiotic divisions

timing of mitotic & meiotic divisions

oogenesis notes
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

follicular life cycle through menstrual cycle notes
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

functions of granulosa thecal cells
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

estrogens synthesis by granulosa thecal cells
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

sequential hormonal changes during menstrual cycle
Sequential hormonal changes during menstrual cycle
  • 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
sequential hormonal changes during menstrual cycle1
Sequential hormonal changes during menstrual cycle
  • 12. corpus luteum secretes estrogen & progesterone
  • 13. plasma levels of estrogen & progesterone increase, suppressingrelease of GnRH, LH, & FSH
  • 14. ~day 25, corpus luteum spontaneously degenerates
  •  secretion & plasma levels of estrogen & progesterone
  • 16.  estrogen & progesterone  FSH & LH levels which begin follicular development of the next menstrual cycle
endometrial changes during menstrual cycle1
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

estrogen actions
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

progesterone actions
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

female sexual response
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

fertilization 1
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)

fertilization 2
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

fertilization
Fertilization

fig 17-23

implantation
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