HUMAN REPRODUCTION AND DEVELOPMENT

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HUMAN REPRODUCTION AND DEVELOPMENT

• Chapter 40

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• A. Male Reproductive System
• Consists of testes, a network of tubules
  glandular secretions.

• Testes (? gonads)
• Located outside body cavity in scrotum.
• Testes contain seminiferous tubules (highly
  coiled tubules within which sperm are produced).

Testis
Scrotum
When does sperm production begin? end?
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Vas deferens

• Epididymis
• Highly coiled tube in which sperm mature are
  stored until ejaculation.

Urethra
Epididymis
Testis

• Vas deferens
• Tube that transports sperm from epididymis into
  body cavity.
• Each vas deferens loops over urinary bladder
  joins to the urethra.

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Vas deferens

• Urethra
• Tube extending from urinary bladder through penis.

Bladder
Urethra
Urethra transports urine sperm, but not at the
same time. Pathway of sperm testis ? epididymis
? vas deferens ? urethra
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• Three sets of glands contribute fluids

• Seminal vesicles
• Secrete fluid containing fuctose prostaglandins
  into vas deferens.

Seminal vesicle
Prostate gland

• Prostate gland
• Surrounds urethra at point where vasa deferentia
  enter secretes milky, alkaline fluid into
  urethra.

Bulbourethral gland

• Bulbourethral glands
• Secrete an alkaline mucus into urethra.

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• During sexual arousal, penis becomes erect and
  semen is ejaculated.
• Semen consists of
• Sperm (100-500 million)
• Fluid from seminal vesicles, prostate
  bulbourethral glands.

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• B. Female Reproductive System
• Consists of ovaries, fallopian tubes, uterus
  vagina.

Ovary
Fallopian tube

• Ovaries (? gonads)
• Each ovary contains 1 million follicles at
  birth.
• Follicle developing egg (oocyte) follicle
  cells.

Uterus
Vagina
When does ovulation/menstruation begin? end?
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Ovary

• Fallopian tubes (oviducts)
• Tubes that transport oocyte from ovaries to
  uterus.
• Site of fertilization.

Fallopian tube
Uterus
Vagina
Cervix

• Uterus (womb)
• Muscular sac that functions to receive, retain
  nourish a developing embryo.
• Lower end of uterus (cervix) opens into vagina.
• Vagina (birth canal)

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• Cyclic Changes in the Ovary Uterus
• Regulated by hormones.
• GnRH - produced by hypothalamus regulates
  release of FSH LH from anterior pituitary.
• FSH - produced by anterior pituitary stimulates
  development of follicles.
• LH - produced by anterior pituitary triggers
  ovulation formation of corpus luteum.

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• Estrogen - produced by follicle cells corpus
  luteum causes endometrium (uterine lining) to
  thicken.
• Progesterone - produced by corpus luteum of
  ovary increases thickness of endometrium.
• Ovarian menstrual cycles occur about every 28
  days (puberty ? menopause).

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Day 1 of cycle low levels of estrogen,
progesterone, FSH LH signal hypothalamus...
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• C. Prenatal Development (gestation)
• Typically divided into 3 stages
• Preembryonic stage (first 2 weeks)
• Includes fertilization, cleavage, implantation
  beginning of gastrulation.
• Embryonic stage (3rd - 8th weeks)
• Completion of gastrulation organogenesis.
• Fetal period (9th week - birth)
• Organs begin to function coordinate to form
  organ systems.

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• 1. Fertilization
• Union of a sperm and egg, forming a zygote.

Female ovulates a secondary oocyte (arrested in
metaphase II).
Oocyte begins journey down fallopian tube must
be fertilized within 12-24 hours.
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• Male deposits sperm in female vagina.
• Sperm are capacitated (develop fertilizing
  ability) as they swim toward oocyte.

Acrosomal enzymes of sperm digest outer coverings
of oocyte. Only 1 sperm enters!
Sperm entry signals secondary oocyte to complete
meiosis II.
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• 2. Cleavage
• Period of rapid cell division following
  fertilization.

• Blastomeres - daughter cells
• Morula - solid ball of 16 cells
• Blastocyst - fluid-filled sphere (100 cells)

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Blastocyst (5 days post- fertilization)
trophoblast
inner cell mass
blastocyst cavity

• 3. Implantation
• Nestling of blastocyst into endometrium.

Trophoblast forms chorion. Trophoblast/chorion
produces hCG (human chorionic gonadotropin)
hCG prevents degeneration of corpus luteum
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amniotic cavity
9-day implantedblastocyst
epiblast
embryonic disc
hypoblast
chorion
yolk sac

• 4. Gastrulation
• Process that forms the 3 primary germ layers
  (ectoderm, mesoderm endoderm) blastocyst is
  now a gastrula.

16-day embryo (gastrula)
cut edge of amnion
epiblast
Notochord forms beneath primitive streak.
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• Derivatives of the primary germ layers
• Ectoderm - nervous system, sense organs,
  epidermis of skin, hair, nails, sweat glands
  oil glands.
• Endoderm - organs lining of digestive
  respiratory systems.
• Mesoderm - notochord, dermis of skin, bones,
  muscles, circulatory system, urinary system
  reproductive system.

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• Roles of Extraembryonic Membranes
• Chorion - forms the fetal portion of the
  placenta.
• Placenta functions in exchange of materials, and
  produces estrogen progesterone.
• Amnion - protects developing embryo.
• Yolk sac - produces blood cells until 6th week
  develops into intestines germ cells.
• Allantois - forms as outpocketing of yolk sac
  forms umbilical cord becomes part of urinary
  bladder.

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• 5. Organogenesis
• Formation of body organs organ systems.
• First major event in organogenesis is neurulation
  (formation of the neural tube).

• Notochord induces overlying ectoderm to form
  neural groove.

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• Sex Determination
• Sex is determined at fertilization
• XY embryos develop into males (SRY gene is
  activated in week 7).
• XX embryos develop into females

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• Digestive respiratory systems are last to
  mature.
• 6. Labor and Birth
• Occurs 266 days post-fertilization (280 days
  from last menstrual period).
• Stage 1 dilation stage (6-12 hrs)
• Initiated by oxytocin, which stimulates
• uterus to contract
• placenta to produce prostaglandins
• Descent of fetus ruptures amniotic sac dilates
  cervix to 10 centimeters.

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• Stage 2 delivery of infant (2 hrs)
• Lasts from full dilation to birth.
• Usually delivered in head-first orientation.
• Cesarean section - surgical delivery.
• Stage 3 delivery of placenta (30 min)
• Uterine contractions expel placenta
  extraembryonic membranes.
• Of every 100 secondary oocytes exposed to sperm,
  only 31 will survive to be born.

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• D. Postnatal Development