lecture 18 dr may

DR. MAIE AL-BADER - REPRODUCTION- 2012 1

Reproduction
Upto 6 wks after conception
Indifferent gonads

Testis determining factor
(sex determining region Y – SRY gene)
Loacted on short arm of Y chromosome

SRY gene present SRY gene absent
Testes Ovaries

Sertoli cells Leydig cells
In semineferous In interstitial Ovarian follicles
tubules tissue

Testosterone Dihydrotestosterone
Mullerian
inhibiting
Internal External genitalia
Factor/substance
genitalia


Development of Internal Genitalia - males
Before 6 wks gestation BOTH DUCTS exist in both sexes
Between 6 – 8 weeks: in male, testes develop

In males once the testes develop:
• SERTOLI CELLS: secrete Mullerian Inhibition Factor/substance (MIF or MIS) which
leads to regression of the mullerian duct
• LEYDIG CELLS: secrete testosterone which lead to the growth & development of the
Wolffian duct. This duct will give rise to the male internal genitalia (epididymis, vas
deferens, seminal vesicle, ejaculatory duct)


Development of Internal Genitalia - females

In females:
• The internal genitalia are: fallopian tubes, uterus and upper third of vagina. The
absence of testosterone and MIS will lead to female internal genitalia


Development of External Genitalia – males & females

In males:
• 5a-dihydrotestosterone (dependent on 5a-reductase)  external genitalia (penis,
prostate, scrotum and penile urethra)
In females:
• The external genitalia are: clitoris, labia majora and minora and lower two thirds of the
vagina


Male Reproductive System

• Paired testes suspended in the scrotal sacs of the scrotum
• Testes develop in abdominal cavity but descend into scrotal sac during development
(sterility!)
• Boys under 6 yrs of age: if testis didn’t descend, then surgical intervention


Organ Function
Testes Produce sperms and sex hormones
Epididymis Sites of maturation (ability to swim) and some storage of sperm
Vas deferens Conduct and store sperm
Urethra Conducts sperm (and urine)
Penis Organ of copulation (sexual intercourse)


Testes consist of 2 Parts:
1. Seminiferous tubules:
• Germinal cells: sperms
• Sertoli cells: possess FSH receptors
2. Interstitial tissue: Interstitial/Leydig cells (possess LH receptors)  testosterone


Spermatogenesis

• Spermatogenesis
• occurs in the seminiferous tubules upon LH & FSH stimulation (starting at ~13 yrs of age)
• Takes on average 70 days to complete
• 120 million sperm are produced/day (~ 60 - 150 million/day)
• Spermiogenesis: mediated by Sertoli cells that are responsible for eliminating most of the
spermatid cytoplasm to give spermatozoa


Mature sperm (spermatozoa) contain 3 parts:
1. Head: contains a nucleus covered by an acrosome (stores enzymes to penetrate egg)
2. Middle piece: contains mitochondria wrapped around microtubules of the flagellum
(mitochondria provide energy for movement)
3. Tail: contains microtubules as components of flagellum; its movements propels sperm


• Mature sperm gain motility in epididymis and become more resistant to changes in pH &
temperature (most sperms stored in the vas deferens)
• During ejaculation sperms and secretions from the seminal vesicle, prostate gland and
bulbourethral gland make up the semen which is carried by the ejaculatory duct to the
urethra


Control of Male Sex Hormone Secretion


Functions of Testosterone

• It is the main sex hormone in males
• Essential for development of male secondary sex characteristics
– Tallness, longer legs, broad shoulders
– Enlargement of larynx and vocal cords; deepening of voice
– Greater muscles strength (athletes, side effects)
– Sex drive and aggressiveness
– Oil and sweat glands secretion leading to acne and body odor
– Development of hair on face, chest and back
– Triggers baldness if appropriate genes are present
• Essential for the maturation of sperm


Female Reproductive System


Organ Function

Ovaries Produce egg each month; produce sex hormones
Oviducts (fallopian tubes) Conduct egg; location of fertilization

Uterus (womb) Houses developing embryo and fetus
Vagina Receives penis during copulation and serves as birth canal


Oogenesis

• Mitosis of primordial oogonia occurs in female fetus until midgestation (peak of 7 million
oocytes) and then ceases. Then there is progressive loss of oocytes & by puberty there are
approximately 400,000 oocytes (only ~400 follicles ovulate in women)
• Oocyte begins first meiotic division in utero: first division is arrested in prophase until the time
of ovulation


• At the time of ovulation, the primary oocyte completes the first meiotic division producing
the first polar body and a secondary oocyte
• Sperm cell penetration (fertilization) initiates the completion of the second meiotic division
and the expulsion of a second polar body


• The follicles (granulosa and thecal cells) produce female sex hormones
• Changes in the ovary are the result of changing levels of FSH and LH from the
anterior pituitary
• At menopause: oogenesis ceases


Control of Ovarian Steroidogenesis

Which receptors do the following cells have? Thecal cell, Granulosa cell, Luteal cell


Menstrual cycle

• Ovarian cycle
• Follicular phase
• Ovulation
• Luteal phase

• Endometrial cycle
• Proliferative phase
• Secretory phase
• Menstruation


Ovarian Cycle: Follicular Phase

• Lasts from day 1 to about day 13 of the cycle (assuming that the cycle is 28 days) during
which:
• 7-12 primary follicles stimulated  secondary follicle  graafian follicle (only ONE will
become mature graafian follicle)
• Granulosa and thecal cells secrete estradiol (peaks at ~ day 12; 2 days before ovulation)
• Granulosa cells are stimulated by FSH; thecal cells are stimulated by LH

• Toward the end of the follicular phase: FSH and estradiol  stimulate the production of LH
receptors in graafian follicle preparing the follicle to the next half of the cycle

• The rapid increase in estradiol secretion  positive feedback effect  rapid LH secretion
 LH SURGE


Ovarian Cycle: Ovulation & Luteal Phase

Ovulation
• A woman usually ovulates only one ovum a month
• FSH  growth and maturation of graafian follicle & rapid estradiol secretion  makes a
thin walled blister on ovary surface  estradiol secretion triggers LH surge  rupture
graafian follicle wall (day 14)  OVULATION  expulsion of secondary oocyte (with the 1st
polar body) out of the ovaries into fallopian tube
• If ova is fertilized by a sperm entering its cytoplasm  ova completes the second meiotic
division  formation of 2nd polar body
Luteal Phase
• After ovulation  LH stimulates empty follicle (corpus luteum) to secrete estradiol &
progesterone (and inhibin which inhibits FSH only)  negative feedback inhibition of FSH
and LH  prevents the development of a new follicle  regression of corpus luteum 
decrease in estrogen and progesterone (starting at day 22 reaching very low levels by day
28)  MENSTRUATION


Endometrial Cycle: Proliferative, Secretory & Menstrual Phases

Proliferative Phase
• Occurs during ovarian follicular phase
• An increase in estradiol stimulates the growth (proliferation) of stratum functionale of the
endometrium

Secretory Phase
• Occurs during ovarian luteal phase
• An increase in progesterone  stimulates development of uterine glands
• Effects of increased estradiol and progesterone levels:
• endometrium becomes thick, vascular and spongy in appearance
• the uterine glands become engorged with glycogen, lipids & proteins
• endometrium ready to accept and nourish an embryo

Menstruation
• Resulting from:
• A decrease in estradiol and progesterone levels during late luteal phase
• Constriction of the spiral arteries leading to necrosis and sloughing of the stratum
functionale


Functions of Estrogens & Progesterone

• Estrogen is responsible for development and maintenance of female secondary sexual
characteristics.
• Less body and facial hair, more fat beneath the skin to give a rounded appearance.
• Enlargement of pelvic girdle and cavity to give wider hips.
• Both estrogen and progesterone
– are required for breast development
– help maintain endometrium during pregnancy
– help suppress gonadotropin secretion
– inhibit prolactin secretion


Fertilization, Pregnancy & Parturition

Fertilization
• During the act of sexual intercourse, the male ejaculates ~ 300 million sperms  into the
female vagina
• ONLY ~100-200 sperms survive to enter fallopian tube & stay for ~3 days
• Secondary oocyte in the fallopian tube lasts for ~ 24 hrs following ovulation
• So when does fertilization occur ?


Cleavage & Blastocyst Formation

• Cleavage occurs as the zygote goes down the fallopian tube giving a morula
• Blastocyst (early embryonic structure) consists of:
• An inner cell mass develops into fetus
• Surrounding chorion (trophoblast cells)  will become part of placenta
• Day 5th - 6th: blastocyst is attached to the uterine wall (trophoblast cells initiate
implantation)
• Day 7th - 10th: blastocyst is completely buried in the endometrium and the hormone
human chorionic gonadotrophin (hCG) is now secreted


Implantation & Formation of Placenta

• If fertilization does not take place  corpus luteum begins to regress (10 days after ovulation)
 decreased secretion of steroids  menstruation
• If fertilization takes place, above changes are prevented by secretion of hCG:
• This hormone is identical to LH: maintain corpus luteum  secretion of estradiol and
progesterone  maintain the endometrium  prevents menstruation
• it is required for the first 5-8 weeks of pregnancy until the placenta becomes active


The Structure & Function of the Placenta
• The placenta is a unique organ where exchange between fetal blood and mother's blood
takes place.
• By the 10th week it is fully formed and has begun to produce estrogen and progesterone
• Chorionic villi are treelike extensions of the chorion: they project into the surrounding
maternal tissues; maternal and fetal blood do not mix


Functions of Placenta
1. Exchange of molecules across placenta:
• The umbilical arteries deliver fetal blood chorionic villi blood circulates within the villi 
umbilical vein  back to the fetus
• Maternal blood is delivered to and drained from the cavities within decidua basalis (maternal
part; located between the chorionic villi)  maternal and fetal blood are brought close
together
• Serves as a site for the exchange of gases (O2 and CO2), nutrient molecules and waste
products


2. Endocrine function of placenta:
• Human chorionic gonadotropin (hCG)
• Fetal-placental unit
• After 5 ½ weeks of conception:
• Placenta starts secreting estrogens and progesterone
• Placenta is an incomplete gland because:
• It lacks precursors, cholesterol
• It lacks enzymes needed to convert progesterone into androgens (therefore in fetus
progesterone is converted into androgens  converted into estrogens in placenta)
• Fetal-placental unit: interaction between placenta and embryo to produce steroid
hormones


Labour & Parturition

• Powerful contractions of the uterus in LABOUR:
• are needed for childbirth (PARTURITION)
• are stimulated by oxytocin and prostaglandins


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