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Reproductive System and Development (Male Reproductive Structures (Seminal…
Reproductive System and Development
Male Reproductive Structures
Testes
enclosed in scrotum
contains seminiferous tubules
produces sperm and androgens (male sex hormones), especiallly testosterone
Scrotum
pouch of skin designed to regulate temperature of testes
between thighs
homologous to labia majora in female
Seminiferous Tubules
produces sperm cells (spermatozoa)
contain interstitial cells between tubules that secrete testosterone
contain 2 types of cells
sustentacular cells; AKA Sertoli cells or nurse cells
provide protective environment for developing sperm, their cytoplasm helps nourish developing sperm
release hormone inhibin when sperm count is high (inhibits FSH secretion)
bound by tight junctions, which form blood-testis barrier- helps protect developing sperm from materials in the blood, protects sperm from leukocytes (which may perceive sperm as foreign because of different chromosome numbers and proteins
population of dividing germ cells that continuously produce sperm beginning at puberty
Epididymis
comma-shaped structure composed of internal duct and external covering of connective tissue
stores sperm until fully mature and capable of being motile
releases its sperm into vas deferens during sexual intercourse
Vas Deferens (AKA ductus deferens)
receives sperm from epididymis during sexual intercourse
transports sperm outward by means of rapid peristalsis
passes above a ureter behind bladder
Seminal Vesicle
lie posterior to and at base of urinary bladder
provides fructose for nourishment
medial portion merges with a ductus deferens to form ejaculatory duct
secrete a viscous, whitish-yellow, alkaline fluid containing fructose and prostaglandins
fructose nourishes sperm as they travel through female reproductive tract
prostaglandins are hormonelike substances that promote widening and slight dilation of external os of cervix, which facilitates sperm entry into uterus
Ejaculatory Duct
pseudostratified ciliated columnar epithelium
conducts sperm and a component of seminal fluid toward the urethra
each duct opens into the prostatic urethra
Prostate
donut-shaped organ located at base of bladder and encloses the proximal part of urethra
raises semen pH
includes submucosal glands that produce mucin
secretes a slightly milky fluid that is weakly acidic and rich in citric acid, seminalplasmin, and prostate-specific antigen (PSA)
citric acid is a nutrient for sperm health
seminalplasmin is an antibiotic that combats urinary tract infections in male
PSA acts as enzyme to help liquefy semen following ejaculation
alkaline and functions to neutralize acidity of vagina
Bulbourethral Glands (Cowper's glands)
mucus coats and lubricates urethra for passage of sperm during sexual intercourse
secretory product is a clear, viscous mucin that forms mucus
Urethra
transports semen from both ejaculatory ducts to the outside of the body
subdivided into prostatic urethra (extends from bladder through prostate gland), membranous urethra (continues through urogenital diaphragm), and a spongy urethra (extends through penis)
Corpus Cavernosa
terminates in shaft of the penis
keeps penis erected
Corpus Spongiosum
continues within the glans
keeps urethra open so sperm can exit
Female Reproductive Structures
Ovary
produces oocytes that carry maternal chromosomes
located in pelvic cavity lateral to uterus
Fallopian Tube
site of fertilization
AKA uterine tubes
extends laterally from both sides of uterus towards the ovaries
function to transport ovulated oocyte to uterus
composed of infundibulum (contain fimbriae), ampulla (fertilization of oocyte usually occurs here), and isthmus (extends from ampulla toward lateral wall of uterus), uterine part (extends from isthmus and penetrates wall of uterus)
Fimbrae
finger-like projections
generate a current that moves any oocyte released by ovary into fallopian tube
Uterus
protects and nourishes developing baby by forming a vascular connection that later develops into the placenta
implantation occurs in endometrium (innermost layer of uterus)
connects to vagina
during birth, oxytocin levels increase to initiate uterine contractions of labor
if no oocyte is fertilized, the muscular wall of uterus contracts and sheds its inner lining as menstruation
receives blood supply from the uterine arteries
Regions
Fundus: curved, superior region extending between the lateral attachments of the uterine tubes
Body: middle region, major part of organ, composed of thick wall of smooth muscle
Cervix: narrow, inferiormost portion of uterus that projects into vagina
mucus plug; suspected to be a barrier that prevents pathogens from invading the uterus from the vagina
3 tunics
perimetrium
outer layer
myometrium
thick, middle tunic of uterine wall
endometrium
innermost tunic
composed of simple columnar epithelium and an underlying lamina propria
lamina propria is filled with uterine glands, which enlarge during the uterine cycle
2 distinct layers
basal layer: deepest layer, permanent layer that undergoes few changes during each uterine cycle
functional layer: superficial layer, this layer grows from the basal layer under the influence of estrogen and progesterone secreted from ovarian follicles
if not fertilized and implanted, this layer sheds as menses
new functional layer grows from basal layer after the end of each menses
Vagina
serves as receptacle for penis during sexual intercourse
birth canal
serves as passageway for menstruation
3 tunics
inner mucosa
nonkeratinized stratified squamous epithelium, highly vascularized lamina propria
vaginal epithelial cells produce acidic secretion that helps prevent bacterial and other pathogenic infection
inferior region has folds (rugae); near external opening there is the hymen which is typically perforated during the first instance of sexual intercourse
middle muscularis
both outer and inner layers of smooth muscle
outer adventitia
contains some inner elastic fibers and an outer layer of areolar connective tissue
Follicle
consists of an oocyte surrounded by follicle cells which supports the oocyte
6 types of follicles
primordial follicle
earliest type of ovarian follicle
consists of a primary oocyte surrounded by a single layer of flattened follicle cells
primary oocyte is an oocyte that is arrested in the first meiotic prophase
primary follicle
consists of primary oocyte surrounded by one or more layers of cuboidal follicular cells (AKA granulosa cells)
secretes estrogen which stimulates changes in the uterine lining
secondary follicle
contains a primary oocyte, many layers of granulosa cells, and fluid-filled space called antrum
primary oocyte surrounded by two protective stuctures- zona pellucida and corona radiata
zona pellucida: allows passage of light, contains glycoproteins
corona radiata; external to zona pellucida, innermost layer of cumulus oophorus cells
oocyte forced toward one side of follicle, where it is surrounded by a cluster of follicle cells termed cumulus oophorus
mature follicle
AKA vesicular follicle or Graafian follicle
becomes large, contains a secondary oocyte, layers of granulosa cells, and a large, fluid-filled, crescent-shaped antrum
seondary oocyte has completed meiosis I and is arrested in second meiotic metaphase
only one mature follicle forms each month
corpus luteum
mature follicle ruptures and expels oocyte (ovulation) and remaining of follicle in ovary turns yellowish
secretes sex hormones progesterone and estrogen
stimulate and support the continuing buildup of uterine lining and prepare uterus for possible implantation of a fertilized oocyte
corpus albican
corpus luteum undergoes break down, turns into a white connective tissue scar
most are completely resorbed, only a few remain in ovary
Meiosis, Spermatogenesis, Oogenesis
Meiosis
sex cell division that starts off with a diploid parent cell in gonad (each containing 23 chromosomes) and produces haploid daughter cells called gametes
produces four daughter cells that are genetically different from parent cell
includes process of crossing over- genetic material is exchanged between homologous chromosomes
Meiosis I
homologous pairs of replicated chromosomes are separated when the cell divides
result is 2 cells, each containing 23 chromosomes (not pairs) that consists of replicated sister chromatids
AKA reduction division because it results in reduction of number of chromosomes in daughter cells
4 phases and cytokinesis
Prophase I
homologous replicated chromosomes in parent cell pair up to from a tetrad (synapsis)
crossing over occurs as chromosomes come together; ensures continued genetic diversity in new organisms
ends with breakdown of nuclear envelope
Metaphase I
pairs of each tetrad line up at midline, forming double line of chromosomes according to independent assortment (maternal and paternal chromosomes can be on either side of midline)
spindle fibers extend from centrioles at opposite ends of the cell and attach to centromere of each homologous replicated chromosome
Anaphase I
pairs of chromosomes are pulled to opposite ends of the cell (process of maternal and paternal pairs moving to opposite sides is called reduction division)
pairs of chromosomes are no longer together, but each replicated chromosome still consists of two sister chromatids
Telophase I
replicated chromosomes arrive at opposite ends of cell, then nuclear membrane may re-form around these chromosomes
Cytokinesis
cleavage furrow forms in cell, then cell cytoplasm divides to produce 2 new cells
each daughter cell contains 23 replicated chromosomes only, but each chromosome is composed of 2 sister chromatids bound together
cells formed then must undergo another round of cell division (meiosis II) to separate sister chromatids
Meiosis II
AKA second meiotic division
sister chromatids separate and become single chromosomes in haploid cells
Prophase II
resembles prophase stage of mitosis
in each of 2 new cells, nuclear envelope breaks down and chromosomes collect together
crossing over does not occur
Metaphase II
spindle fibers extend from centroles to centromere of each chromatid
replicated chromosomes (sister chromatids) align to from a single line along equator in middle of cell
Anaphase II
sister chromatids of each replicated chromosome are pulled apart at centromere and are now separated
sister chromatid is now called single chromosome and is pulled to opposite pole of cell
Telophase II
nuclear membranes re-form
Cytokinesis
cleavage furrow forms
cytoplasm in both cells divide
daughter cells mature into secondary oocytes in females; mature into sperm in males
Spermatogenesis
process of sperm development that occurs in seminiferous tubule of the testis
starts at puberty when significant levels of FSH and LH stimulate the testis to begin gamete development
Step 1
spermatogonia are diploid cells so they have 23 pairs of chromosomes; total of 46 chromosomes
sperm develop from primordial germ (stem) cells called spermatogonia
mitotic divisions of these cells produce a new germ cell and a committed cell (primary spermatocyte)
Step 2
haploid cells (containing 23 chromosomes) produced during meiosis I are called secondary spermatocytes
meiosis I begins in the diploid primary spermatocytes
Step 3
meiosis II originates with the secondary spermatocytes and produces spermatids
Step 4
process of spermiogenesis begins with spermatids and results in morphologic changes needed to form sperm
spermatid sheds excess cytoplasm and its nucleus elongates
acrosome cap forms over the nucleus; contains digestive enzymes that help penetrate the secondary oocyte for fertilization
sperm tail (AKA flagellum) forms
tail attached to midpiece, which contains mitochondria and a centriole (mitochondria used to provide energy to move tail)
Oogenesis
the maturation of a primary oocyte to a secondary oocyte
Before birth
embryonic and fetal period
oogonia are diploid cells (contain 23 pairs of chromosomes; total of 46) that are origin of oocytes
mitotic divisions of oogonia produce primary oocytes (diploid cells)
primary oocytes start process of meiosis but are arrested in prophase I
Childhood
ovary is inactive
houses primordial follicles
some deterioration of primordial follicles occur
meiosis I is arrested
Monthly, from puberty to menopause
about 20 primordial follicles mature into primary follicles every month
some primary follicles mature into secondary follicles
primary follicles that do not mature deteriorate
only one secondary follicle matures into a mature follicle
primary oocyte completes the first meiotic division to produce a polar body and a secondary oocyte
secondary oocyte is a haploid cell (23 chromosomes) that is arrested in the second meiotic metaphase
if second oocyte is fertilized, it completes the second meiotic division and becomes an ovum; if not fertilized, it degenerates
Hormones of Reproductive System
Male
inhibin
inhibits FSH secretion which regulates sperm production
testosterone
high levels facilitate spermatogenesis
acts on brain so there is increased desire for and sensitivity to sexual stimulation
stimulates development of secondary sex characteristics (hair in pubic and axillary regions, deeper voice, growth of facial hair)
Female
FSH and LH cause maturation of follicles
FSH and LH affect ovarian follicle's secretion of other hormones
Inhibin
helps inhibit FSH release by anterior pituitary to prevent excessive follicular development
estrogen
low levels inhibit production of GnRH, FSH, and LH
assists with development of mature ovarian follicle
high levels have a stimulatory effect on hypothalamus and anterior pituitary, which initiates positive feedback loop, which induces ovulation
initiates and maintains growth of functional layer of endometrium
LH
after ovulation, induces remaining follicular cells in ovary to develop into corpus luteum which secretes large amounts of progesterone, estrogen, and inhibin
human chorionic gonadotropin (hCG)
secreted when secondary oocyte is fertilized
enters mother's blood and acts on corpus luteum
mimics effects of LH so it continues to stimulate corpus luteum
progesterone
primary hormone responsible for functional layer growth after ovulation
causes increase in blood vessel distribution, uterine gland size, and nutrition production
prolactin
produced in anterior pituitary
responsible for milk production
when amount increases, mammary gland grows
oxytocin
produced by hypothalamus
released from posterior pituitary
responsible for milk ejection
Male/ Female
Gonadotropin-Releasing Hormone (GnRH)
acts on specific endocrine cells in the anterior pituitary and stimulates them to release gonadotropins
Follicle-Simulating Hormone (FSH)
prior to puberty, virtually nonexistent in girls and boys
as levels increase, gonads produce significant levels of sex hormones and start of process of gamete and sexual maturation
Luteinizing Hormone (LH)
prior to puberty, virtually nonexistent in girls and boys
as levels increase, gonads produce significant levels of sex hormones and start of process of gamete and sexual maturation
Menstrual Cycle Events (AKA uterine cycle)
Menstrual Phase
Day 1-5 of cycle
phase marked by shedding of functional layer of endometrium and lasts through period of menstrual bleeding
FSH and LH stimulated to be secreted
some ovarian follicles develop and produce estrogen
estrogen level is higher than progesterone
follicle goes into secondary follicle stage
Proliferative Phase
Day 6-13
development of new functional layer of endometrium overlaps the time of follicle growth and estrogen secretion by ovary
estrogen and inhibin inhibit the hypothalamus and anterior pituitary which causes a drop in FSH
estrogen level increases, progesterone remains the same, FSH level is higher then decreases below LH
secondary follicle continues into mature follicle
Secretory Phase
Day 15-28
increased vascularization and development of uterine glands occurs primarily in response to progesterone secretion from corpus luteum
corpus luteum forms and secretes large amounts of estrogen, progesterone, and inhibin
progesterone stimulates uterine lining growth
if oocyte is not fertilized, the corpus luteum regresses and hormone levels drop
estrogen level starts off higher than progesterone, then progesterone increases and exceeds estrogen
without significant levels of progesterone, functional layer lining slacks off
Embryonic Development
3rd week
gastrulation occurs after implantation
forms 3 primary germ layers
mesoderm
middle layer of cells
forms the circulatory system, excretory system, most of reproductive system, skeletal system, and muscles
endoderm
inferior layer
made up of cells that line the archenteron
develops into digestive system
ectoderm
develops into nervous system, sense organs, skin, and skin derivatives
superior layer
ectodermal cells invaginate to form first neural groove which deepens into neural fold and then forms the neural tube (which forms brain and spinal cord)
cells from which body tissues develop
neurulation begins
somites
becomes bones and muscles
neural fold
becomes fold
neural tube
becomes spinal cord
measures about 2.5mm
heart formed late in third week
4th week
most of internal organs are formed
cartilage skeleton begins to develop
muscles appear
has an obvious tail
5th week
arm and leg buds appear along cartilaginous vertebral column
placenta and umbilical cord have become connected via blood vessels and are functioning in food, oxygen, and waste exchange between developing embryo and mother
blood cell production has begun in liver and spleen
heart starts beating
between 6th and 8th week
head and facial features become more refined
nose,eyes, and ears appear
upper and lower jaw formed, producing mouth
limb buds develop projections that will be fingers and toes
reproductive organs begin developing
surrounded by amnion fluid and amnion for protection
surrounded by chorion which will become placenta
Fetal Development
weeks 9-12
primary ossification centers appear in most bones
reproductive organs begin to develop
coordination between nerves and muscles for movement of limbs occurs
brain enlarges
body elongates
permanent kidneys develop
epidermis and dermis of skin become more fully developed
palate develops
weeks 13-16
body grows rapidly
ossification in skeleton continues
brain and skull continue to enlarge
limbs become more proportionate in length to body
weeks 17-20
muscle movements become stronger and more frequent
lanugo covers skin (fine, downy hair)
vernix caseosa covers skin; mixture of sebum from sebaceous glands and dead epidermal cells
limbs near final proportions
brain and skull continue to enlarge
weeks 21-38
body gains major amount of weight
eyebrows and eyelashes appear
eyelids open
blood cells from in marrow only
testes descend into scrotum (month 9)