Male Reproduction

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Male Reproduction
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Fig 24-9a
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Spermatogenesis

• Occurs in the seminiferous tubules
• 64 day developmental period

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Fig 24-9d
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Fig 24-9e
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Fig 24-10
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Hormones

• 1. Testosterone Secreted by the Leydig cells
  located in the interstitium of the testis is
  essential for growth and division of testicular
  germinal cells, the first stage in forming sperm
• 2. Lutenizing hormone secreted by the anterior
  pituitary stimulates Leydig cells to secrete
  testosterone

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Hormones

• 3. Follicle stimulating hormone secreted by
  the anterior pituitary stimulates Sertoli cells
• 4. Estrogens formed from testosterone by the
  Sertoli cells when they are stimulated by FSH
  required for spermiogenesis
• 5. Growth hormone Promotes early division of
  spermatogonia

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Mature Sperm

• 120 million/day
• Most stored in vas deferens, some in epididymis
• Activity of sperm is enhanced in neutral and
  slightly alkaline medium
• Live many weeks in the suppressed state of the
  genital ducts of the testes
• 1-2 days in female genital tract

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Function of the Seminal Vesicles

• Lined with secretory epithelium
• Secretes mucous containing fructose, citric acid,
  and other nutrients, as well as large quantities
  of prostaglandins and fibrinogen
• Prostaglandins
• React with female cervical mucus to make it mores
  receptive to sperm movement
• Possibly cause reverse peristaltic contraction in
  the uterus and fallopian tubes to move sperm
  towards ovaries

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Function of the Prostate Gland

• Secretes thin, milky fluid that contains calcium,
  citrate ion, phosphate ion, a clotting enzyme and
  a profibrinolysin
• During emission, the prostate gland contracts
  with the contractions of the vas deferens
• Slightly alkaline fluid is likely to neutralize
  the acidic vaginal secretions (pH 3.5-4)
• Sperm do not become optimally motile until pH
  6.0-6.5

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Semen

• Fluid and sperm from vas deferens (10), fluid
  from seminal vesicles (60), fluid from the
  prostate (30).
• pH 7.5

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Fertilization

• Sperm head binds to receptors on the zona
  pellucida
• Acrosome dissolves, releasing hyaluronidase and
  proteolytic enzymes that depolymerize the
  hyaluronic acid polymers in the intercellulear
  cement that hold the ovarian granulosa cells
  together, and digest proteins in the structural
  elements of tissue adhered to the ovum
• Only 1 sperm penetrates

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Neuronal Stimulus

• Erection is caused by parasympathetic impulses
  that pass from the sacral portion of the spinal
  cord through the pelvic nerves to the penis.
• These parasympathetic nerve fibers are believed
  to secrete nitric oxide and/or vasoactive
  intestinal peptide in addition to acetylcholine

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Neuronal Stimulus

• NO relaxes the arteries and the smooth muscle
  fibers in the corpora cavernosa
• When these large cavernous sinusoids become
  dilated when arterial blood flows rapidly into
  them under pressure, venous outflow is partially
  occluded.
• The corpora cavernosa are surrounded by strong
  fibrous coats therefore, high pressure within
  the sinusoids causes ballooning of the erectile
  tissue

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Fig 24-8
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VIAGRA

• Sexual stimulation leads to release of NO by
  parasympathetic neurons in the corpus cavernosum
• Guanylate cyclase is activated, stimulating the
  formation of cGMP
• Increased levels of cGMP promote corporal smooth
  muscle relaxation and increased blood flow,which
  lead to erection

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VIAGRA

• VIAGRA (sildenafil citrate) acts locally to
  improve the sexual response
• VIAGRA is a selective inhibitor of
  phosphodiesterase type 5 (PDE5) which is largely
  responsible for the breakdown of cGMP in the
  corpus cavernosum tissue
• By selectively inhibiting PDE5, VIAGRA encourages
  the cGMP connections necessary to achieve and
  maintain erections in response to sexual
  stimulation

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VIAGRA

• VIAGRA has no direct muscle relaxant effects on
  corpus cavernosum tissue in the absence of
  NO/cGMP pathway activation, therefore it helps
  produce erections only when sexual stimulation is
  present.

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VIAGRA? is a product of Pfizer Inc. www.viagra.com
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Female Reproduction
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Fig 24-12b
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Fig 24-12c
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Fig 24-12f
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Fig 24-12e
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Menstrual Cycle

• Cycles every 24-35 days
• Monthly production of gametes
• 3-7 day menses
• Described according to changes in
• 1.) Ovarian cycle
• 2.) Uterine cycle

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Ovarian Cycle

• Changes in ovarian structure and function
• Three phases
• Follicular phaseaverage of 14 days commences
  with the start of menstruation and up to
  ovulation
• Ovulation
• Luteal phase14 days

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Uterine Cycle

• Cyclic changes in uterine structure and function
• Three phases
• Menstrual phasebegins on day 1 and lasts 5-7
  days
• Proliferative phase which lasts for the duration
  of the follicular phase (end of menstruation to
  day 14
• Secretory phasecoincides with the luteal phase

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Hormonal Control of the Menstrual Cycle

• Ovarian and uterine cycles are under the primary
  control of
• Gonadotropin Releasing Hormone (GnRH) from the
  hypothalamus
• FSH and LH from the anterior pituitary
• Estrogen and progesterone and inhibin from the
  ovary

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Hormonal Control of the Menstrual Cycle

• First day of menstruation is day 1 of the cycle
• Just before the beginning of each cycle,
  gonadotropin secretion from the anterior
  pituitary increases
• FSH stimulates several follicles in the ovaries
  to begin to mature

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Hormonal Control of the Menstrual Cycle

• Granulosa cells (regulated by FSH) and thecal
  cells (regulated by LH) produce steroid hormones
• Thecal cells synthesize androgens that diffuse
  into the granulosa cells where aromatase converts
  them to estrogen

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Estrogen

• Increasing estrogen levels
• Negative feedback on pituitary FSH and LH
  secretion, preventing the maturation of more
  follicles in the same cycle
• Positive feedback Estrogen stimulates estrogen
  production by the granulosa cells

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Ovulation

• Immediately before ovulation, persistently high
  levels of estrogen aided by rising levels of
  progesterone enhance pituitary responsiveness to
  GnRH.
• LH surge
• 16-24 hours after LH peaks, ovulation occurs

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Fig 24-13
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Fig 24-18
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Pregnancy Hormones

• During the first three months of pregnancy, the
  corpus luteum is maintained by the actions of
  human chorionic gonadotropin (hCG) which is
  secreted by the chorionic portion of the placenta
• Secretion of hCG begins at implantation when
  trophoblast cells start to infiltrate the
  endometrial tissue

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Hormonal Contraception

• Administration of either estrogen or progesterone
  if given in appropriate quantity during the first
  half of the monthly female cycle can inhibit
  ovulation.
• Prevents pre-ovulatory LH surge
• Mechanism immediately before LH surge, there is
  a sudden depression in estrogen secretion by
  ovarian folliclesfeedback mechanism to provide
  the signal to anterior pituitary to release LH

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Hormonal Contraception

• Synthetic hormones are usedresist destruction by
  liver
• Synthetic estrogens
• Ethynyl estradiol
• Mestranol
• Synthetic progestins
• Norethindrone
• Norethynodrel,
• Ehynodial
• Norgestrel
• Norgestimate