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

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the reproductive system
The reproductive system
  • Overview
  • Male reproductive system
  • Female reproductive system
  • Fertilization, implantation and pregnancy
  • Parturition and lactation
the reproductive system1
The reproductive system
  • Overview
  • Male reproductive system
  • Female reproductive system
  • Fertilization, implantation and pregnancy
  • Parturition and lactation
overview
Role of the reproductive system:

Gamete production

Fertilization

Zygote (offspring) development

Overview
the reproductive system2
The reproductive system
  • Overview
  • Male reproductive system
  • Female reproductive system
  • Fertilization, implantation and pregnancy
  • Parturition and lactation
male reproductive system
Testes: main organs:

- produce gametes (spermatocytes)

- secrete male hormone, testosterone (Leydig cells = interstitial cells)

Male reproductive system
slide7
Spermatogonia multiply at the base of the seminiferous tubules. Their growth, development and maturation are supported by the Sertoli’s cells. They migrate toward the lumen while undergoing meiosis  spermatocytes
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 Sertoli’s cell. Testosterone must also be present for the Sertoli’s cells to work adequately

Testosterone produces a negative feed-back on LH

Inhibin, secreted by the Sertoli’s cell have a negative feedback on FSH

Control of spermatogenesis and hormone production in males
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

Testosterone
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 ---> erection.

2- Ejaculation: sympathetic NS  rhythmic peristaltic waves in the ducts and perineal muscles  ejection of semen or ejaculation. climax or orgasm.

The semencontains 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).

Sexual response in males
the reproductive system3
The reproductive system
  • Overview
  • Male reproductive system
  • Female reproductive system
  • Fertilization, implantation and pregnancy
  • Parturition and lactation
female reproductive system
Role:

- form gametes (oocytes)

- support zygote development

Characteristics:

- cyclic changes in activity

- restricted period of fertility

- limited gamete production

Female reproductive system
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

Gamete development
the menstrual cycle
The menstrual cycle
  • Several cycles:
    • Hypothalamus-pituitary gland cycle
    • Ovarian cycle

- follicular cycle

- hormonal cycle

    • Uterine cycle
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)

Menstrual cycle: Hypothalamus-pituitary gland
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

Ovarian cycle: follicular phase
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

Role of estrogen
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

Ovarian cycle: ovulation
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.

Ovarian cycle: luteal phase 1
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

Ovarian cycle: luteal phase 2
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

Uterine cycle
the reproductive system4
The reproductive system
  • Overview
  • Male reproductive system
  • Female reproductive system
  • Fertilization, implantation and pregnancy
  • Parturition and lactation
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

Fertilization
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)

Implantation
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)

Pregnancy
clinical applications
A teratogen is a compound which can induce congenital malformations in developing babies

Can you name some of these compounds?

Clinical applications
clinical applications1
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)

Clinical applications

thalidomide

dioxin

clinical applications2
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.

Clinical applications

thalidomide

dioxin

the reproductive system5
The reproductive system
  • Overview
  • Male reproductive system
  • Female reproductive system
  • Fertilization, implantation and pregancy
  • Parturition and lactation
parturition
Pregnancy should

last 9 months

Stretch of the uterus triggers increased contraction and oxytocin release

Oxytocin reinforces uterine contraction

 Baby’s birth

Parturition
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)

Lactation