REPRODUCTION & DEVELOPMENT
REPRODUCTION & DEVELOPMENT
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:
and the endometrium become the placenta.
becomes the organ of exchange between the mother and developing fetus
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
(the surrounding membrane) is the
, which serves to cushion and protect the embryo from injury.
produces some early blood cells and sex cells.
At the end of the yolk sac is a pouch called the
, which serves as a base for developing the umbilical cord.
THE MENSTRUAL CYCLE
(ovarian cycle: 3)
Ruptured vesicular follicle becomes corpus luteum, which is a temporary endocrine gland that secretes
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.
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.
(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.
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.
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.
Occurs days 1-5 of Menstrual cycle
Marked as the sloughing off of the functional layer and last through the period of menstrual bleeding
MALE REPRODUCTIVE STRUCTURES
are the primary male reproductive organs and are enclosed in the
, which help regulate temperature.
serves as a storage facility for sperm until sexual intercourse, which is moved into the
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
before becoming an
In the prostate, the
empties into the urethra, which receives products of the
before exiting through the
Spermiogenesis begins with spermatids that become motile sperm.
Meiosis I begins for the primary spermatocyte (diploid). Haploid cells produced during meiosis I are now secondary spermatocytes.
Meiosis II originates with the secondary spermatocytes and produces spermatids.
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).
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.
Monthly (puberty to menopause)
When a female reaches puberty, the hypothalamus releases gonadotropin-releasing hormone.
follicle stimulating hormone
These hormones create a monthly sequence called the ovarian cycle. The ovarian cycle has three stages: follicular phase, ovulation, luteal phase.
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.
FEMALE REPRODUCTIVE STRUCTURES
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.
The fallopian tube is the uterine tube associated with each
, which produce the oocytes. This is usually the site of fertilization.
is located adjacent to the ovary and they move any oocyte released by the ovary and into the tube.
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.
--- Chromosomes are pulled apart to opposite poles.
Sister chromatids remain attached
--- Two new haploid nuclei (each containing 23 chromosomes).
Cytokinesis occurs here (pinching of the cell)
--- Homologous chromosomes line up at equator.
Spindle fibers attach to centromeres.
--- Nuclear membrane goes away.
Chromosomes pair up (tetrad)
Crossing over occurs
--- Chromatids are pulled apart.
Each chromatid becomes a chromosome (92 in total)
--- Reverse prophase.
Creates 4 unique haploid gametes
--- Spindle fibers line up chromosomes in the middle
Centrioles are now at opposite poles
--- Nuclear membrane breaks down.
Chromatin becomes chromosomes
--- DNA replication occurs
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
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.
Influence on Ovarian and Uterine cycles
Stimulates dev. and maturation of ovarian follicles
Stimulates ovulation (at peak)
Stimulate anterior pituitary to produce and secrete FSH and LH
( ovarian follicles before ovulation; corpus luteum after ovulation); placenta )
Initiates and maintains growth of the functional layer of the endometrium
(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.
Inhibits FSH secretion to prevent excess follicular development
Influence on spermatogenesis
Stimulates sustentacular cells to secrete ABP
Keeps testosterone levels high in the testis
Stimulates interstitial cells to release testosterone
stimulates libidio and development of secondary sex characteristics
Stimulates pituitary to release FSH and LH
Inhibits FSH secretion with rising sperm counts.