The reproductive system

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The reproductive system

• Overview
• Male reproductive system
• Female reproductive system
• Fertilization, implantation and pregnancy
• Parturition and lactation

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The reproductive system

• Overview
• Male reproductive system
• Female reproductive system
• Fertilization, implantation and pregnancy
• Parturition and lactation

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Overview

• Role of the reproductive system
• Gamete production
• Fertilization
• Zygote (offspring) development

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The reproductive system

• Overview
• Male reproductive system
• Female reproductive system
• Fertilization, implantation and pregnancy
• Parturition and lactation

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Male reproductive system

• Testes main organs
• - produce gametes (spermatocytes)
• - secrete male hormone, testosterone (Leydig
  cells interstitial cells)

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• Spermatogonia multiply at the base of the
  seminiferous tubules. Their growth, development
  and maturation are supported by the Sertolis
  cells. They migrate toward the lumen while
  undergoing meiosis ? spermatocytes

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Control of spermatogenesis and hormone production
in males

• At puberty, the hypothalamus secretes GnRH ?
  Follicle-stimulating hormone (FSH) and
  Luteinizing hormone (LH)
• LH stimulates secretion of testosterone by the
  Leydig cell
• FSH promotes sperm production by the Sertolis
  cell. Testosterone must also be present for the
  Sertolis cells to work adequately
• Testosterone produces a negative feed-back on LH
• Inhibin, secreted by the Sertolis cell have a
  negative feedback on FSH

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Testosterone

• 1- to help spermatogenesis
• 2- promote the development of secondary sexual
  characters and behavior
• - stimulate the development of the reproductive
  organs
• - stimulate the male pattern growth of hair
  (chest, legs...)
• - the skin become thicker, coarser and darker
• - cause hypertrophy of the larynx with a
  deepening of the
• voice
• - stimulate increase of bone and muscle mass
• - stimulate the activity of the sebaceous
  glands
• - increase the metabolic rate
• - promote also epiphyseal disc closure so
  growth in length will
• stop
• - promote male sexual behavior
• 3- has a negative feed-back effect on the
  hypothalamus

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Sexual response in males

• 1- Arousal Thoughts, visual impulses, massages
  of the penis ? sacral parasympathetic NS?
  dilatation of the arteries supplying blood to the
  penis ---gt erection.
• 2- Ejaculation sympathetic NS ? rhythmic
  peristaltic waves in the ducts and perineal
  muscles ? ejection of semen or ejaculation.
  ?climax or orgasm.
• The semen contains the secretion from the
  various glands along the reproductive ducts with
  20 to 100 millions sperm per ml. Sperm can
  survive up to 72 h in the female body.
• 3- Resolution Ejaculationt is followed by a
  relaxation period during which a man cannot
  achieve another orgasm (NE in synapse has been
  exhausted and needs to be resynthesized).

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The reproductive system

• Overview
• Male reproductive system
• Female reproductive system
• Fertilization, implantation and pregnancy
• Parturition and lactation

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Female reproductive system

• Role
• - form gametes (oocytes)
• - support zygote development
• Characteristics
• - cyclic changes in activity
• - restricted period of fertility
• - limited gamete production

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Gamete development

• Oocytes mature during fetal development ? at
  birth, arrest in meiosis I
• Development resumes during each menstrual cycle
  upon ovulation, egg is arrested in meiosis II
• Development will resume only upon fertilization
  by a spermatocyte

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The menstrual cycle

• Several cycles
• Hypothalamus-pituitary gland cycle
• Ovarian cycle
• - follicular cycle
• - hormonal cycle
• Uterine cycle

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Menstrual cycle Hypothalamus-pituitary gland

• At puberty, GnRH stimulates the release of FSH
• FSH promotes follicle (egg and its surrounding
  layers) development
• LH secretion peaks in mid-menstrual cycle
• Secretions of LH and FSH are controlled by
  negative feedback from progesterone and estrogen,
  respectively (see ovarian cycle)

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Ovarian cycle follicular phase

• Under the influence of FSH
• - Several follicles develop. Only one will
  mature to ovulation. Follicular cells multiply
• - Primordial follicle ?primary follicle ?
  secondary follicle ? Graafian follicle
• - Synthesis of estrogen by granulosa cells

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Role of estrogen

• promotes rapid growth in young girl, follow by
  closing of the epiphyseal disc
• induces development of the breasts
• stimulates fat deposit under the breast, in the
  hip areas
• promotes widening of the pelvis
• induces hair growth in the pubic, axillary areas
• Promote female behavior
• Promotes a negative feedback on FSH

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Ovarian cycle ovulation

• Under the influence of LH
• Burst of antrum fluid secretion by Graafian
  follicle rupture ? the oocyte and its corona
  radiata are ejected toward the Fallopian tube ?
  ovulation

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Ovarian cycle luteal phase 1

• Under the influence of LH mostly (and some FSH)
• Remaining granulosa cells form the corpus luteum
• The corpus luteum synthesizes progesterone under
  the influence of LH and estrogen under the
  influence of FSH.

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Ovarian cycle luteal phase 2

• High levels of progesterone and estrogen have a
  negative feedback on LH and FSH (respectively)
• LH and FSH levels drop
• Corpus luteum no longer active ? corpus albicans
• Progesterone and estrogen levels drop
• The negative feedback loop weakens
• FSH can increase against ? beginning of a new
  cycle

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Uterine cycle

• Proliferative phase- Estrogen promotes uterine
  endometrium development (multiplication of
  endometrial cells)
• Secretory phase- under the influence of
  progesterone ? promotes nutrient secretion from
  lining for egg implantation

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Figure 22.15
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Figure 22.16
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Figure 22.17
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The reproductive system

• Overview
• Male reproductive system
• Female reproductive system
• Fertilization, implantation and pregnancy
• Parturition and lactation

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Fertilization

• Maximum survival of sperm up to 5 days
• Maximum survival of oocyte 24 h
• If coitus during fertile period ? oocyte
  fertilization in Fallopian tube.
• The fertilized oocyte completes meiosis II, the
  nuclei fuse ? diploid zygote formed

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Twins

• What is the difference between identical twins
  and fraternal twins?

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Twins

• What is the difference between identical twins
  and fraternal twins?

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Implantation

• The fertilized egg undergoes several division as
  it is sliding toward the uterus where it implants
  after about 6 days (unfertilized eggs are
  destroyed and phagocytized by macrophages)
• Some cells of the eggs develop into the embryo,
  other cells form the membrane and placenta.
• The placental cells start (within 10 days)
  secreting human chorionic gonadotropin (hCG)
• hCG has a role similar to LH it sustains the
  activity of the corpus luteum (LH level decreases
  due to negative feedback from progesterone)

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Pregnancy

• At 3 months of pregnancy, the placenta secretes
  large enough amount of estrogen and progesterone
  to replace the corpus luteum (which then
  disappears)
• Estrogen promotes
• development of breast duct tissue, breast fatty
  deposit
• growth of uterine muscle
• Progesterone promotes
• - mammary gland development
• - suppress uterine contraction
• - maintain secretory glands in uterus
• - lactogen secretion (hormone involved in
  mammary gland development)

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Clinical applications

• A teratogen is a compound which can induce
  congenital malformations in developing babies
• Can you name some of these compounds?

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Clinical applications

• A teratogen is a compound which can induce
  congenital malformations in developing babies
• Can you name some of these compounds?
• Which stage of development is most susceptible?
• Prior to implantation
• First 3 months (embryonic stage)
• 3 months to birth (fetal stage)

thalidomide
dioxin
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Clinical applications

• Which stage of development is most susceptible?
• Prior to implantation
• First 3 months (embryonic stage)
• 3 months to birth (fetal stage)
• Embryonic stage, because all organs are being
  formed at this stage. Organs mature during the
  fetal stage and are not as susceptible to
  malformation.

thalidomide
dioxin
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The reproductive system

• Overview
• Male reproductive system
• Female reproductive system
• Fertilization, implantation and pregancy
• Parturition and lactation

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Parturition

• Pregnancy should
• last 9 months
• Stretch of the uterus triggers increased
  contraction and oxytocin release
• Oxytocin reinforces uterine contraction
• ? Babys birth

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Lactation

• First few days after birth, secretion of
  colostrum, a watery liquid rich in proteins.
• Then, milk is secreted by the mammary glands
  under the influence of prolactin
• Milk release is promoted by oxytocin
  (milk-let-down reflex)

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Clinical applications Birth control
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Clinical applications male circumcision
phimosis
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Female genital mutilation
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Clinical application female genital mutilation
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