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Reproductive & Development System (Events of the Menstrual Cycle (The…
Reproductive & Development System
Male Reproductive Structures
Seminiferous tubules of the testis
Location of spermatogenesis
sustentacular cells (Sertoli Cells)
stimulated by FSH
nourish and protects developing sperm, secrete androgen-binding protein
interstitial cells (Leydig Cells)
produce testosterone, stimulated by LH
male organs
testis
produces gametes and sex hormones
glans of penis
contains ereticle tissue that stimulates sexual arousal and climax
body of penis
contains erectile tissue that stimulates sexual arousal and climax
scrotum
protect and cove testicular structures
accessory glands
bulbourethral gland (Cowper's gland)
secretes mucin for lubrication of penile urethra
prostate gland
secretes slightly milky fluid
citric acid: nutrient for sperm health
seminalplasmin: combats UTI in males
PSA: enzyme to help liquify semen
seminal vesicles
secrete fructose and prostaglandins
fructose nourishes sperm in the female reproductive tract
prostaglandins promote the widening and slight dilation of cervix
Hormones
Males
LH stimulates interstitial cells to produce testosterone
testosterone facilitates the production sperm
FSH stimulates sustentacular cells to produce androgen-binding protein
Females
estrogen
if low, can inhibit GnRh, FSH, and LH secretion
follicle maturation
promotes oogenesis. at puberty they stimulate the growth of the reproductive organs and the growth spurt
promote appearance of the secondary sex characteristics
progesterone
cooperates with estrogen in breast maturation and regulation of the uterine cycle
FSH and LH
FSH promotes the maturation of follicles
LH induces the formation of corpus luteum
Human chorionic gonadotropin
secreted by the hypothalamus to initiate the ovarian cylcle
inhibin
secreted by follicular cells to inhibit further FSH production
preventing excessive ovarian follicle development, allowing current primary follicles to mature.
Female Reproductive Structures
provide the means for sexual maturation
produce special cells for procreation
ovum derived from primordial follicles
female organs
ovary
produces gametes and sex hormones
germinal epithelium
simple cuboidal epithelial layer surrounding ovar
tunica albuginea
deep to germinal epithelium
dense CT capsule
consists of oocyte surrounded by follicle cells
by puberty 400,000 follicles remain in ovaries
ovarian cycle: follicular, ovulation, and luteal phases
clitoris
stimulates sexual arousal and climax
labia minora
contains erectile tissue
labia majora
protect and cover some reproductive structures
greater vestibular gland
secretes mucin for lubrication
Spermatogenesis and Oogenesis
Spermatogenesis
Production of male gametes in seminiferous tubules, begins at puberty
Spermatogonia divide by mitosis to maintain germ cell line. some of their progeny become primary spermatocytes which undergo meisos i to produce secondary spermatocytes
Secondary spermatocytes undergo meiosis II, each producing two haploid (n) spermatids
Meiosis, basis of gamete production, consists of two consecutive nuclear divisions without DNA replication in between. Meiosis reduces the chromosomal number by half and introduces genetic variability. Synapsis and cross of homologous chromosomes.
Spermiogenesis converts spermatids to functional sperm, stripping away superfluous cytoplasm and producing an acrosome and a flagellum (tail).
Sustentocytes form the blood testis barrier, nourish spermatogenic cells, move them toward the lumen of the tubules and secrete fluid for sperm transport
Oogenesis
Oogonia are diploid cells that are the origin of oocytes. Mitotic divisions of oogonia produce primary oocytes.
Primary oocytes start the process of meiosis but are arrested in prophase I.
Childhood
Ovaries are inactive. They house primordial follicles. Some primordial follicles break down.
Monthly, from puberty to menopause
Up to twenty primordial follicles mature into primary follicles every month. Some of the primary follicles will mature into secondary follicles. Those that don't, disintegrate.
Typically only one secondary follicle matures into a mature follicle, where the primary oocyte completes the first meiotic division to produce a polar body and a secondary oocyte.
The secondary oocyte is a haploid cell that is arrested in the second meiotic phase.
If the secondary oocyte is fertilized, it completes the second meiotic division and becomes an ovum.
If the secondary oocyte is not fertilized, it degenerates.
Fetal Development
9-12 weeks
liver prominent
sex readily detected
head dominant but body elongating, brain enlarging, lumbar enlargements apparent in spinal cord
skin epidermis and dermis obvious
blood cell formation
notochord degenerating
13-16 weeks
kidneys attain typical structure
cerebellum prominent
most bones are now distinct
most bones are now distinct
21-30 weeks
distal limb bones are beginning to ossify
Period of substantial increase
body is lean and well proportioned
testes reach scrotum in seventh month
skin is wrinkled and red
bone marrow becomes sole site of blood cell formation
myelination of spinal cord begins
17-20 weeks
fetal position
vernix caseosa
quickening occurs
30-40 weeks
approximate crown-to-rump length at end of interval 360 mm (14 inches)
fat laid down in subcataneous tissue (hypodermis)
skin whitish pink
embryonic development
The three week embryo is flattened, disc-shaped structure. Embryonic disc.
week 3
primitive streak
neural tube
somites forming
heart forming
amnion nearly covers embryo
chorion well developed
heart beating
week 4
internal organs forming
spinal cord and brain forming
somites present
embryo fully covered by amnion
cartilage skeleton and muscles develop
facial features and ears appear develop
week 5-8
All internal organs complete, some functioning
cartilage skeleton and muscles complete
extremities develop from limn buds
placenta and umbilical cord function
facial features and ears nearly complete
embryo assumes a human appearance
The shape transformation begins during the late third and fourth weeks of development.
Cephalocaudal folding occurs in the cephalic and caudal regions of the embryo.
Forms the head and buttocks region of the embryo.
Transverse folding occurs when the left and right sides of the embryo curve and migrate towards the midline.
Creates torso region of embryo.
Once the embryo has undergone cephalocaudal and transverse folding, organogenesis begins.
The upper and lower limbs attain their adult shapes, and the basic forms of most organs have developed by week 8.
During the embryonic period, the embryo is peculiarly sensitive to teratogens.
Teratogens are substances that can cause birth defects or the death of an embryo.
Alcohol, tobacco smoke, drugs, and some viruses.
Events of the Menstrual Cycle
The ovarian follows three phases
Follicular phase, ovulation, and luteal phase
The hypothalamus initiates the ovarian cycle by secreting GnRH, stimulating the secretion of FSH and LH.
FSH and LH target the ovaries and stimulate follicular development.
The maturing follicles secrete inhibin and estrogen. These hormones have a negative feedback on the hypothalamus.
Inhibin helps inhibit FSH release by the anterior pituitary and low levels of estrogen inhibit the secretion of GnRH, FSH, and LH.
Estrogen also assists with the development of the mature ovarian follicle. A secondary follicle matures under the influence of estrogen.
The developed mature follicle produces a higher amount of estrogen. Higher levels of estrogen have a positive feedback effect on the hypothalamus.
The positive feedback loop results on an LH surge, inducing ovulation. Ovulation is impossible without this surge.
LH influences the remaining follicular cells in the ovary to develop into the corpus luteum.
The corpus luteum acts as an endocrine gland, secreting copious amounts of progesterone, estrogen, and inhibin. This combination of hormones inhibit the hypothalamus and anterior pituitary. Helps build the uterine lining.
The corpus luteum degenerates in 10 to 13 days if no fertilization takes place. Decrease in hormones levels ensue.
The corpus luteum regresses and becomes a corpus albicans.
as the corpus luteum regresses, its levels of secreted progesterone and estrogen drop.
this causes the uterine lining to be shed, menstruation
the shed lining is called menses
this marks the end of the luteal phase
a female's first menstrual cycle is called menarche
Meiosis
Meiosis I
Prophase I
Homologous maternal and paternal replicated chromosomes pair up, and the pair forms a tetrad.
Crossing over occurs between homologous maternal and paternal chromosomes, increasing genetic diversity.
Metaphase I
Homologous replicated chromosomes line up above and below the equator of the cell, forming a double line of chromosomes.
Spindle fibers attach to the centromeres.
Anaphase I
Maternal and paternal pairs of replicated hormones are separated and pulled to the opposite ends of the cell; reduction division.
The sister chromatids remain attached in each replicated chromosome.
Telophase I
Nuclear division finishes and nuclear envelopes re-form. The cytoplasm divides and two new cells are produced, each containing 23 replicated chromosomes only.
The replicated chromosomes are still composed of sister chromatids.
Meiosis II
Prophase II
Nuclear envelope breaks down, and replicated chromosomes cluster together.
Metaphase II
Spindle fibers extend from the centrioles from the centrioles to each sister chromatid in each chromosome and align the replicated chromosomes along the equator line.
Anaphase II
Sister chromatids of each replicated chromosome are pulled apart at the centromere. They migrate to opposite ends of the cell
Telophase II
Nuclear division finishes, and the nuclear envelopes re-form. The four new daughter cells that are produced each contain 23 single chromosomes only.
