Human Reproduction | Embryology ppt

December 21, 2012 | By | Reply More

Human Reproduction | Embryology ppt

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Human Reproduction


}  Reproductive System

◦     Not needed for the survival of the individual

◦     Species survival

}  Sexual reproduction

◦     Genes from two individual

◦     Combine at random

◦     Creates new combinations

◦     Increases chances of species survival

}  Sexual Reproduction

}  Each individual produces gametes

◦     Formed in gonads by meiosis

–  Male: testes produce:

–  Sperm

–  Testosterone

–  Female: ovaries produce:

–  Ova

–  Estrogens, Progesterone

}  Gametes unite in process of fertilization

◦     Restores diploid number

◦     Forms zygote

}  Sexual Determination

}  Each zygote inherits

◦     23 chromosomes from mother

◦     23 chromosomes from father.

◦     23 pairs of homologous chromosomes.

–  alleles

}  Kinds of chromosomes

◦     1-22 pairs of chromosomes: autosomal

◦     23rd pair are sex chromosomes.

–  Male: XY

–  Female: XX

}  Chromosomal gender of zygote determined by fertilizing sperm.

}  Formation of Testes

}  First 40 days after conception the gonads of males and females are similar in appearance.

}  During this time:

◦     Spermatogonia and oogonia migrate from yolk sac to developing embryonic gonads

◦     Gonads could become either.

}  TDF (testis-determining factor):

◦     hypothetical

◦     promotes the conversion to testes:

–  gene located on short arm of Y, called SRY (sex determining region of Y chromosome)

–  Found in all mammals

}  Formation of Testes

}  Structures in the testes:

◦     Seminiferous tubules: 43 to 50 days post conception

–  Germinal cells: sperm.

–  Nongerminal cells: Sertoli cells (sustentacular cells).

◦     Leydig cells (interstitial cells):

–  Appear about day 65.

–  Endocrine function: secrete androgens

–  Main: Testosterone

}  Formation of Testes

}  Leydig cells secrete testosterone.

◦     Begins 8th week and peaks at 12-14th week.

◦      Masculinizes embryonic structures.

}  Testosterone then declines to very low levels until puberty.

◦     Decline occurs by end of second trimester

}  Testes descend into scrotum shortly before birth.

◦     Temp about 3 degrees below internal temp

◦     35 degrees C

}  Formation of Ovaries

}  Absence of Y chromosome and TDF, female develop ovaries.

}  Ovarian follicles do not appear until 2nd trimester.


Development of Accessory Sex Organs and Genitalia

}  Presence or absence of testes determines the accessory sex organs and external genitalia.

}  Male accessory organs derived from wolffian ducts.(mesonephric)

}  Sertoli cells secrete MIF(mullerian inhibition factor).

}  Female accessory organs derived from mullerian ducts. (paramesonephritic)

} Development of Accessory Sex Organs and Genitalia

}  Both duct systems in both sexes  between days 25 and 50

◦     Regression of mullarian ducts begins about day 60

}  Testosterone

◦     responsible for development of male accessory sex organs

◦     External genitalia identical first 6 weeks, then testosterone stimulates development of penis

◦     Not the active agent in all cells

–  converted to dihydrotestosterone (DHT) in some target cells

–  Needed for penis, spongy urethra, scrotum, prostrate

◦     Testosterone directly needed for wolfian derivatives:

–  Epididymis, ductus deferens, ejaculatory duct, SV


} Development of Accessory Sex Organs and Genitalia

} Endocrine Regulation of Reproduction

}  First trimester

◦     Embryonic testes are active endocrine glands

–  Secrete large amounts of testosterone

◦     Embryonic ovaries not mature until third trimester

}  Time of birth:

◦     Gonads in both sexes relatively inactive

}  Before puberty:

◦     Low levels of sex steroids in both

◦     Due to lack of stimulation

}  Puberty:

◦     Increased stimulation from gonadotropic hormones

◦     Induce increase in sex steroids

Endocrine Regulation of Reproduction

Hypothalamus releases LHRH (GnRH) into hypothalamo-hypophyseal portal vessels.

}  Anterior pituitary secretes:

◦     LH: luteinizing hormone.

–  In male: interstitial-cell stimulating hormone (ICSH)

◦     FSH: follicle-stimulating hormone.

}  Secreted in pulsatile fashion to prevent desensitization and down regulation of receptors.

Endocrine Interactions

}  Primary effects of LH and FSH on gonads:

◦   Stimulation of spermatogenesis and oogenesis.

◦   Stimulation of gonadal hormone secretion.

◦   Maintenance of gonadal structure.

Endocrine Regulation

}  Negative Feedback:

◦     Inhibit GnRH from hypothalamus.

◦     Inhibit anterior pituitary response to GnRH.

◦     Inhibin secretion  inhibit anterior pituitary release of FSH.

–  By sertoli cells

}  Female: estrogen and progesterone.

}  Male: testosterone.

}  Onset of Puberty

FSH and LH high in newborn, falls to low levels in few weeks.

}  Puberty: driven by increased secretion of FSH and LH

}  Onset of Puberty

FSH and LH

◦     Brain maturation increases GnRH secretion.

◦     Decreased sensitivity of GnRH to negative feedback.

}  LH:

◦     Increased secretion triggers puberty

◦     Late puberty, pulsatile secretion of LH and FSH increase during sleep.

}  Stimulate a rise in sex steroid secretion.

}  Onset of Puberty

}  Stimulate rise in testosterone and estradiol-17b.

◦     Produce secondary sexual characteristics.

}  Age of onset related to the amount of body fat and physical activity in the female

}  Leptin secretion from adipocytes may be required for puberty.

}  Pineal Gland

}  Secretes melatonin.

}  Secretion influenced by light-dark cycles.

}  Inhibit gonadotropin secretion.

}  Role in humans not established.

}  4 Phases of Human Sexual Response

Excitation phase (arousal):

◦     Myotonia and vasocongestion.

◦     Engorgement of a sexual organ with blood.

◦     Erection of the nipples.

}  Plateau phase:

◦     Clitoris becomes partially hidden.

◦     Erected nipples become partially hidden by swelling of areolae.

}  Orgasm:

◦     Uterus and orgasmic platform of vagina contract.

◦     Contractions accompanying ejaculation.

}  Resolution phase:

◦     Body return to preexcitation conditions.

}  Refractory period

◦     In males

◦     Erection possible, but not ejaculation

}  Male Reproduction System

}  Testes:

◦     Seminiferous tubules:

–  Where spermatogenesis occurs.

–  Contain receptor proteins for FSH in Sertoli cells.

◦     Leydig cells:

–  Secrete testosterone.

–  Contain receptor proteins for LH.

}  Control of LH and FSH Secretion

}  Negative feedback:

◦     Testosterone inhibits LH and GnRH production.

◦     Inhibin inhibits FSH secretion.

◦     Aromatization reaction producing estadiol in the brain is required for the negative feedback effects of testosterone on LH.

◦     Brain is a target organ for testosterone

–  Converted to derivatives

}  Testosterone Secretion

}  Responsible for initiation and maintenance of body changes in puberty.

}  Stimulate growth of muscles, larynx, and bone growth until sealing of the epiphyseal discs.

}  Promote hemoglobin synthesis.

}  Acts in paracrine fashion and is responsible for spermatogenesis.

}  Testosterone Secretion

}  Negative feedback of testosterone and inhibin

◦     Keep relatively constant levels of gonadotropins

◦     Results in relatively constant levels

◦     Different in female

–  At menopause: no more sex steroids

◦     In males, gradual decrease

Endocrine function: testes

}  Testosterone: main androgen

}  Sertoli and Leydig cells secrete small amounts of estradiol.

◦     Have receptors for estradiol (as do other male structures)

◦     May be needed for spermatogenesis

}  Estradiol may be responsible for:

◦     Negative feedback in brain.

◦     Sealing of epiphyseal plates.

◦     Regulatory function in fertility.

}  Spermatogenesis

}  Spermatogonia:

◦     Replicate initially by mitosis.

◦     Produce two cells

}  One becomes a primary spermatocytes undergoes meiosis:

◦     2 nuclear divisions.

◦     2nd meiotic division produce 4 spermatids.

}  Spermiogenesis

}  Maturation of spermatozoa.

}  Cytoplasm is pinched off and ingested by the Sertoli cell cytoplasm.

}  Sertoli Cells

}  Blood-testes barrier:

◦     Prevents autoimmune destruction of sperm.

◦     Produce FAS ligand which binds to the FAS receptor on surface to T lymphocytes, triggering apoptosis.

}  Secretes inhibin.

}  Phagocytize residual bodies:

◦     Transmit information molecules from germ cells to Sertoli cells.

}  Secrete ABP (androgen-binding protein):

◦     Binds to testosterone and concentrates testosterone in the tubules.

}  Hormonal Control of Spermatogenesis

}  Testosterone required for completion of meiosis and spermatid maturation.

}  Testes secrete paracrine regulators:

◦     IGF-1.

◦     Inhibin.

FSH necessary in the later stages of spermatid maturation.

}  Male Accessory Organs

}  Epididymis:

◦     Maturational changes.

◦     Resistance to pH changes and temperature.

◦     Storage.

}  Prostate secretes:

◦     Alkaline fluid.

◦     Citric acid.

◦     Ca++.

◦     Coagulation proteins.

}  Seminal vesicles secrete:

◦     Fructose.

}  Erection, Emission, and Ejaculation

}  Erection:

◦     Increased vasodilation of arterioles.

◦      NO is the NT.

◦     Blood flow into the erectile tissues of the penis.

◦     Parasympathetic

}  Emission:

◦     Movement of semen into the urethra.

◦     Sympathetic

}  Ejaculation:

◦     Forcible expulsion of semen from the urethra out of the penis.

◦     Sympathetic

}  Female Reproductive System

}  Ovaries:

◦   Contain large number of follicles which enclose ova.

◦   Extensions called fimbriae partially cover each ovary.

◦   At ovulation, secondary oocyte is extruded.


}  Female Reproductive System

}  Fallopian (uterine) tubes:

◦     Ova drawn into the tube by cilia.

}  Uterus:

◦     Womb.

◦     Endometrium shed during menstruation.

}  Vagina:

◦     Cervical mucus plug.

}  Ovarian Cycle

}  5 mo. gestation  ovaries contain 6-7 million oogonia.

}  Oogenesis arrested in prophase of 1st meiotic division (primary oocyte).

}  Apoptosis occurs:

◦      2 million primary oocytes at birth.

◦      400,000 primary oocytes at puberty.

}  400 oocytes ovulated during the reproductive years.

}  Ovarian Cycle

}  Primary oocytes contained in primary follicles.

◦     FSH stimulates cell growth.

}  Develop into secondary follicles.

}  Fusion of its vesicles into the antrum.

}  Mature graafian follicle:

}  1st meiotic division completed (secondary oocyte).

}  Ovarian Cycle

}  Secondary oocyte:

}  Under FSH stimulation:

◦   Theca cells secrete testosterone. Granulosa cells: contain the enzyme aromatase to convert testosterone into estrogen.

}  Ovulation

}  Graafian follicle forms bulge on surface of ovary.

}  Extrudes secondary oocyte into the uterine tube.

}  Empty follicle becomes corpus luteum and secretes:

◦     Progesterone.

◦     Estrogen.

◦     If not fertilized becomes corpus albicans.

}  Menstrual Cycle

}  3 phases: Ovarian

◦   Follicular Phase

◦   Ovulation

◦   Luteal Phase

}  Duration approximately 28 days.

}  Day 1 is the first day of menstruation.

}  Follicular Phase


}  Stimulates production of FSH receptors on granulosa cells.

◦     Follicles grow and become secondary follicle.

}  Granulosa cells secrete estradiol.

}  Increases sensitivity of FSH receptors.

FSH and estradiol stimulate production of LH receptors in graafian follicle.

}  Follicular Phase

}  Rapid rise in estradiol:

◦   Negative feedback on LH and FSH.

Hypothalamus increase frequency of GnRH pulses.

}  Augments the ability of anterior pituitary to respond to GnRH to increase LH secretion.

}  Follicular Phase

}  Positive feedback:

◦   LH surge begins 24 hours before ovulation.

◦   Triggers ovulation.

FSH increase stimulates development of new follicles.

}  Ovulation

}  Under FSH, graafian follicle grows large and thin-walled.

◦     Triggers LH surge.

}  Wall of graafian follicle ruptures.

}  Day 14.

}  Ist meiotic division is completed.


}  Luteal Phase

}  LH stimulates formation of the empty follicle into corpus luteum.

}  Corpus luteum secretes:

◦     Progesterone:

◦     Plasma concentration rapidly rises.

◦      Estradiol.

}  Negative feedback on LH and FSH.

}  Inhibin: suppress FSH.

}  Luteal Phase

}  Corpus luteum regresses unless fertilization occurs:

◦   Estradiol decreases.

◦   Progesterone decreases.

}  Withdrawal of estradiol and progesterone cause menstruation to occur.

}  Endometrial Changes

}  3 phases of endometrium changes:

◦   Proliferative phase.

◦   Secretory phase.

◦   Menstrual phase.

}  Proliferative Phase

Ovary is in follicular phase.

}  Estradiol stimulate growth of endometrium.

}  Spiral arteries develop.

}  Stimulate production of receptor proteins for progesterone.

}  Cornification of vaginal epithelium occurs.

}  Secretory Phase

Ovary is in luteal phase.

}  Progesterone stimulates development of uterine glands, which become engorged with glycogen.

}  Endometrium becomes thick, vascular and spongy.

}  Cervical mucus thickens and becomes sticky.

}  Menstrual Phase

}  Progesterone cause constriction of spiral arteries.

}  Necrosis and sloughing of endometrium occurs.

}  Lasts 1-5 days.

}  Menopause

}  Cessation of ovarian activity.

}  Age ~ 50 years.

}  Ovaries depleted of follicles.

}  Estradiol and inhibin withdrawl causes hot flashes, and atrophy of the vaginal wall.

}  LH and FSH increase.

}  Fertilization

}  Ejaculation 300 million sperm, 100 reach (uterine) fallopian tube.

}  Fertilization occurs in the uterine tubes

}  Acrosomal reaction:

◦     Acrosome of sperm contains hyaluronidase, an enzyme that digests a channel through zona pellucida.

}  Sperm fuses with ovum cell membrane.

}  Fertilization

}  As fertilization occurs, secondary oocyte completes 2nd meiotic division.

}  Sperm enters ovum cytoplasm.

}  Ovum nuclear membrane disappears, zygote formed.

}  Blastocyct Formation

}  Cleavage:

◦     30-36 hrs. after fertilization the zygote divides by mitosis.

}  Blastocyst develops:

◦     Inner cell mass: fetus.

◦     Surrounding chorion: trophoblasts form placenta.

}  Implantation

}  6th day after fertilization, blastocyst attaches to uterine wall.

}  Blastocyst secretes enzymes that allow blastocyst to burrow into endometrium.

}  Trophoblast cells secrete hCG.

}  hCG

}  Human chorionic gonadotropin.

}  Trophoblast cells secrete hCG.

}  Signals corpus luteum not to degenerate until placenta secretes adequate [hormone].

}  Effects similar to LH.

}  Basis of pregnancy test.


}  Placenta

}  Syncytiotrophoblast secretes enzymes that create blood filled cavities in the maternal tissue.

}  Cytotrophoblast then from projections (villi) that grow into the venous blood.

◦     Producing chorion frondosum on the side that faces the uterine wall.

}  Other side of chorion bulges into the uterine cavity.

}  Placental Changes

}  Decidual reaction:

◦     Endometrial growth.

◦     Accumulation of glycogen.

}  Decidua basalis: maternal tissue in contact with the chorion frondosum.

}  Maternal and fetal blood do not mix.

}  Amnion

}  Envelop the embryo.

}  Amnionic fluid contains sloughed cells of the fetus.

}  Placenta Function

}  Gas exchange:

◦     02 and C02.

}  Nutrient exchange.

}  Waste exchange.

}  Synthesis of proteins and enzymes.



}  Placental Hormones

}  hCS:

}  Chorionic somatomammotropin.

}  GH effects.

}  Diabetic-like effect:

◦   Glucose sparing effect.

◦   Polyuria.

◦   Lipolysis.

}  Placental Hormones

}  Fetal-placental unit:

◦     Placenta must cooperate with the adrenal cortex in the fetus to produce estrogen.

}  Estrogen stimulates:

◦     Endometrial growth.

◦     Inhibit prolactin secretion.

◦     Growth of mammary ducts.

◦     Enlargement of mother’s uterus.

}  Placental Hormones

}  Progesterone:

◦   Suppresses uterine contractions.

◦   Stimulates uterine growth .

◦   Suppresses LH and FSH.

◦   Stimulate development of alveolar tissue of the mammary gland.

}  Parturition

}  Estrogen in late pregnancy:

◦     Increases amount of oxytocin stored.

◦     Stimulate production of oxytocin receptors in myometrium.

◦     Stimulate prostaglandin production.

}  Uterine contractions:

◦     Oxytocin.

◦     Prostaglandins.

}  Lactation

Hypothalamus releases PRH.

}  Anterior pituitary releases prolactin:

◦     Stimulate milk production.

}  Oxytocin needed for “milk letdown”.


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