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REPRODUCTION & DEVELOPMENT (EMBRYONIC DEVELOPEMENT (The embryo now has…
REPRODUCTION & DEVELOPMENT
MALE REPRODUCTIVE STRUCTURES
The
testes
are the primary male reproductive organs and are enclosed in the
scrotum
, which help regulate temperature.
The
epididymis
serves as a storage facility for sperm until sexual intercourse, which is moved into the
vas defrens
Seminiferous tubules
produce sperm cells and are found within the many lobules of the testes.
As the vas defrens passes above the ureter and it receives products from the
seminal vesicle
before becoming an
ejaculatory duct
in the
prostate
.
In the prostate, the
ejaculatory duct
empties into the urethra, which receives products of the
bulbourethral glands
before exiting through the
penis
.
FEMALE REPRODUCTIVE STRUCTURES
The Uterus
The uterus is designed to protect and nourish the developing baby.
The uterine wall:
Endometrium --- The innermost, vascular layer which implantation occurs.
Myometrium --- the muscular layer
Perimetrium --- the outermost tunic
The cervix connects to the vagina, which opens to the outside of the body.
The vagina serves as an receptacle for the penis during sexual intercourse and as the birth canal.
Fallopian tube
The fallopian tube is the uterine tube associated with each
ovary
, which produce the oocytes. This is usually the site of fertilization.
Infundibulum
is located adjacent to the ovary and they move any oocyte released by the ovary and into the tube.
External Genitalia
The Uvula
Mons Pubis --- Mound of hair-covered skin overlying a fat pad and the pubis symphysis.
Labia Minora --- The fine, inner labia that serves as a protective function and is usually hair free. Contains sebaceous glands and numerous melanocytes.
Labia Majora --- protective, course, outer labia that is usually covered with hair. Contains numerous sweat and sebaceous glands.
Clitoris --- small erectile body, located at the anterior regions of the labia minora. It contains many specialized sensory nerve receptors that stimulate orgasms.
MEIOSIS
(Make gametes)
MEIOSIS I
ANAPHASE I
--- Chromosomes are pulled apart to opposite poles.
Sister chromatids remain attached
TELOPHASE I
--- Two new haploid nuclei (each containing 23 chromosomes).
Cytokinesis occurs here (pinching of the cell)
METAPHASE I
--- Homologous chromosomes line up at equator.
Spindle fibers attach to centromeres.
PROPHASE
--- Nuclear membrane goes away.
Chromosomes pair up (tetrad)
Crossing over occurs
MEIOSIS II
ANAPHASE II
--- Chromatids are pulled apart.
Each chromatid becomes a chromosome (92 in total)
TELOPHASE II
--- Reverse prophase.
Creates 4 unique haploid gametes
METAPHASE II
--- Spindle fibers line up chromosomes in the middle
Centrioles are now at opposite poles
PROPHASE II
--- Nuclear membrane breaks down.
Chromatin becomes chromosomes
INTERPHASE
--- DNA replication occurs
HORMONES
Influence on Ovarian and Uterine cycles
FSH
(Anterior pituitary)
Stimulates dev. and maturation of ovarian follicles
LH
(Anterior pituitary)
Stimulates ovulation (at peak)
GnRH
(hypothalamus)
Stimulate anterior pituitary to produce and secrete FSH and LH
Estrogen
( ovarian follicles before ovulation; corpus luteum after ovulation); placenta )
Initiates and maintains growth of the functional layer of the endometrium
Progesterone
(Corpus luteum or placenta)
Primary hormone responsible for functional layer of growth after ovulation; cause an increase in blood vessel distribution, uterine gland size, and nutrient production.
Inhibin
(Ovarian follicles)
Inhibits FSH secretion to prevent excess follicular development
Influence on spermatogenesis
FSH
Stimulates sustentacular cells to secrete ABP
ABP
Keeps testosterone levels high in the testis
LH
Stimulates interstitial cells to release testosterone
Testosterone
stimulates spermatogenesis
Inhibits GnRH
stimulates libidio and development of secondary sex characteristics
GnRH
Stimulates pituitary to release FSH and LH
Inhibin
Inhibits FSH secretion with rising sperm counts.
SPERMATOGENESIS
4.
Spermiogenesis begins with spermatids that become motile sperm.
2.
Meiosis I begins for the primary spermatocyte (diploid). Haploid cells produced during meiosis I are now secondary spermatocytes.
3.
Meiosis II originates with the secondary spermatocytes and produces spermatids.
1.
Germ cells that are diploid are known as spermatogonia. These cells further divide and produce a new germ cella and a committed cell (primary spermatocyte).
OOGENESIS
Before Birth
Primary oocytes begin meiosis, but are arrested in Prophase I until puberty.
At birth, female ovaries contain ~ 1.5 million primordial follicles within its cortex.
The ovary contains primordial germ cells (oogonia;diploid) that divide by mitosis, during the fetal period, to produce primary oocytes.
Childhood
Inactivity of ovaries in a child female is in atresia
By puberty only ~ 400,000 primordial follicles remain in the ovaries
The maturation of a primary oocyte to a secondary oocyte.
Monthly (puberty to menopause)
When a female reaches puberty, the hypothalamus releases gonadotropin-releasing hormone.
GnRH
releases
follicle stimulating hormone
(FSH) and
Lutenizing hormone
(LH).
These hormones create a monthly sequence called the ovarian cycle. The ovarian cycle has three stages: follicular phase, ovulation, luteal phase.
THE MENSTRUAL CYCLE
Ovulation
(ovarian cycle: 2)
Occurs on day 14 of the 28-day ovarian cycle
Release of secondary oocyte from vesicular follicle.
Only one ovary ovulates every month and is stimulated by a peak in LH secretion.
Fluid secretion of follicle cells cause the expulsion of the secondary oocyte from the edge of the follicle.
Luteal phase
(ovarian cycle: 3)
Ruptured vesicular follicle becomes corpus luteum, which is a temporary endocrine gland that secretes
progesterone
and
estrogen
that build up the uterine lining (ready for implantation)
The corpus luteum has a life span of about 10 -13 days if the secondary oocyte is not fertilized.
Occurs during days 15 -28 of ovarian cycle
Corpus luteum regresses and becomes the corpus albicans
Uterine lining sheds (menses) and this marks the end of the luteal phase.
Follicular phase
(ovarian cycle:1)
FSH and LH stimulate about 20 primordial follicles to mature into primary follicles.
Some primary follicles are stimulated to mature and release inhibin. These primary follicles soon become secondary follices
Occurs during days 1-13 of 28-day ovarian cycle
The primary oocyte, of the secondary follicle, finishes meiosis one and forms two cells: one polar body and one secondary oocyte.
The secondary oocyte reaches metaphase II before it is arrested again and does not complete meiosis unless fertilized by sperm.
Proliferate Phase
(2)
The initial dev. of the new functional layer of the endometrium overlaps the time of follicle growth and estrogen secretion by the ovary.
Occurs approx. days 6-14 of menstrual cycle.
Secretory Phase
(3)
Occurs days 15-28 of Menstrual cycle.
There is an increased progesterone secretion from the corpus luteum, which increases vascularization and development of uterine glands.
Menstrual Phase
(1)
Occurs days 1-5 of Menstrual cycle
Marked as the sloughing off of the functional layer and last through the period of menstrual bleeding
EMBRYONIC DEVELOPEMENT
Fertilization of an egg by a sperm. This results in a single cell called a zygote.
The zygote contains 46 chromosomes (23 from mom and 23 from dad).
Shortly after fertilization, the zygote becomes a blastomere through a sequence of mitotic events (cleavages)
When the 32-cell stage is reached the blastomere becomes a morula. Due to pressure exerted against interior cells:
The morula reaches uterus
Cells leave the blastocoele (central cavity), these cells become a blastocyst, with an outer layer called a trophoblast
The villi found on the outer rim (trophoblast) allow for implantation in the endometrium. After implantation the trophoblast becomes the chorion, which will become the placenta.
The inner cell mass (found within the blastocyst) develop the embryo
After the seventh day folowing inmplantation, the embryo implanys in the uterine lining.
The embryo now has a few accessory structures:
Chorion
and the endometrium become the placenta.
The
placenta
becomes the organ of exchange between the mother and developing fetus
The
umbilical cord
connects the developing off spring and the placenta (mother). It passes food and oxygen taken from the mothers bloodstream
The space between the embryo and
amnion
(the surrounding membrane) is the
amniotic fluid
, which serves to cushion and protect the embryo from injury.
The
yolk sac
produces some early blood cells and sex cells.
At the end of the yolk sac is a pouch called the
allantois
, which serves as a base for developing the umbilical cord.
FETAL DEVELOPMENT
MONTH TWO:
Cartilage skeleton and muscles complete
Placenta and umbilical cord function
Extremities develop from limb buds
Facial features and ears nearly complete
Embryo assumes a human appearance
MONTHS 3-9:
Sex readily detected (at 9-12 weeks)
Skin features, eyelashes, eyebrows, nails, and hair develop
Rapid growth, all organs functioning except the reproductive and the respiratory systems
Blood formation in bones begin
Bone tissue begins to replace cartilage
By the second month, all internal organs have developed. This is when the embryo becomes the fetus.